etf

1 1

tfrZL F53

FX^Sff

U.S. Department of Commerce

Volume 107 Number 3 July 2009

Fishery

Bulletin

U.S. Department of Commerce

Gary Locke

Secretary of Commerce

National Oceanic and Atmospheric Administration

Jane Lubchenco, Ph.D.

Administrator of NOAA

National Marine Fisheries Service

James W. Balsiger, Ph.D.

Acting Assistant Administrator for Fisheries

The Fishery Bulletin (ISSN 0090-0656) is published quarterly by the Scientific Publications Office, National Marine Fisheries Service, NOAA, 7600 Sand Point Way NE, BIN C15700, Seattle, WA 98115-0070. Periodicals postage is paid at Seattle, WA. POSTMASTER: Send address changes for subscriptions to Fish- ery Bulletin, Superintendent of Docu- ments, Attn.: Chief, Mail List Branch, Mail Stop SSOM, Washington, DC 20402- 9373.

Although the contents of this publica- tion have not been copyrighted and may be reprinted entirely, reference to source is appreciated.

The Secretary of Commerce has deter- mined that the publication of this peri- odical is necessary according to law for the transaction of public business of this Department. Use of funds for printing of this periodical has been approved by the Director of the Office of Management and Budget.

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402. Subscrip- tion price per year: $36.00 domestic and $50.40 foreign. Cost per single issue: $21.00 domestic and $29.40 foreign. See back for order form.

Scientific Editor

Richard D. Brodeur, Ph.D.

Associate Editor Julie Scheurer

National Marine Fisheries Service Northwest Fisheries Science Center 2030 S. Marine Science Dr. Newport, Oregon 97365-5296

Managing Editor

Sharyn Matriotti

National Marine Fisheries Service Scientific Publications Office 7600 Sand Point Way NE Seattle, Washington 98115-0070

Editorial Committee

John Carlson Kevin Craig Jeff Leis Rich McBride Rick Methot Adam Moles Frank Parrish Dave Somerton Ed Trippel Mary Yoklavich

National Marine Fisheries Service, Panama City, Florida

Florida State University, Tallahassee, Florida

Australian Museum, Sydney, New South Wales, Australia

National Marine Fisheries Sen/ice, Woods Hole, Massachusetts

National Marine Fisheries Service, Seattle, Washington

National Marine Fisheries Service, Auke Bay, Alaska

National Marine Fisheries Service, Honolulu, Hawaii

National Marine Fisheries Service, Seattle, Washington

Department of Fisheries and Oceans, St. Andrews, New Brunswick, Canada

National Marine Fisheries Service, Santa Cruz, California

Fishery Bulletin web site: www.fishbull.noaa.gov

The Fishery Bulletin carries original research reports and technical notes on investigations in fishery science, engineering, and economics. It began as the Bulletin of the United States Fish Commission in 1881; it became the Bulletin of the Bureau of Fisheries in 1904 and the Fishery Bulletin of the Fish and Wildlife Service in 1941. Separates were issued as documents through volume 46; the last document was No. 1103. Beginning with volume 47 in 1931 and continuing through volume 62 in 1963, each separate appeared as a numbered bulletin. A new system began in 1963 with volume 63 in which papers are bound together in a single issue of the bulletin. Beginning with volume 70, number 1, January 1972, the Fishery Bulletin became a periodical, issued quarterly. In this form, it is available by subscription from the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402. It is also available free in limited numbers to libraries, research institutions, State and Federal agencies, and in exchange for other scientific publications.

U.S. Department of Commerce

Seattle, Washington

Volume 107 Number 3 July 2009

Fishery

Bulletin

Contents

Articles

265-277 Chiang, Wei-Chuan, Chi-Lu Sun, Sheng-Ping Wang,

Su-Zan Yeh, Yong Chen, Wei-Cheng Su, Don-Chung Liu, and Wen-Yie Chen

Analysis of sex-specific spawning biomass per recruit of the sailfish Ustiophorus platypterus) in the waters off eastern Taiwan

278-285 Boldt, Jennifer L , and Christopher N. Rooper

Abundance, condition, and diet of juvenile Pacific ocean perch ( Sebastes alutus) in the Aleutian Islands

286-297 Broadhurst, Matt K., Russell B. Millar, Craig P. Brand, and Sebastan S. Uhlmann

Modified sorting technique to mitigate the collateral mortality of trawled school prawns (Metapenaeus macleayi)

The National Marine Fisheries Service (NMFS) does not approve, recommend, or endorse any proprie- tary product or proprietary material mentioned in this publication. No reference shall be made to NMFS, or to this publication furnished by NMFS, in any advertising or sales promotion which would indicate or imply that NMFS approves, recom- mends, or endorses any proprietary product or proprietary material mentioned herein, or which has as its purpose an intent to cause directly or indirectly the advertised product to be used or purchased because of this NMFS publication.

The NMFS Scientific Publications Office is not responsible for the con- tents of the articles or for the stan- dard of English used in them.

298-307 Brill, Richard, Peter Bushnell, Leonie Smith, Coley Speaks, Rumya Sundaram, Eric Stroud, and John Wang

The repulsive and feeding-deterrent effects of electropositive metals on juvenile sandbar sharks (Carcharhinus plumbeus)

308-317 Grizzle, Raymond E., Larry G. Ward, Larry A. Mayer,

Mashkoor A. Malik, Andrew B. Cooper, Holly A. Abeels, Jennifer K. Greene, Melissa A. Brodeur, and Andrew A. Rosenberg

Effects of a large fishing closure on benthic communities in the western Gulf of Maine: recovery from the effects of gillnets and otter trawls

318-328 Riley, Kenneth L., Charles R. Weirich, and David Cerino Development and growth of hatchery-reared larval Florida pompano ( Trachinotus carolinus)

Fishery Bulletin 107(3)

329-338	Mather, Martha E., John T. Finn, Kristen H. Ferry, Linda A. Deegan, and Gary A Nelson Use of non-natal estuaries by migratory striped bass (Morone saxatilis) in summer
339-342	Hoolihan, John P., Nerida F. Perez, Ronald M. Faugue, Andrea M. Bernard, Rebekah L. Horn, Derke Snodgrass, Duane R. Schultz Surface mucous as a source of genomic DNA from Atlantic billfishes (Istiophoridae) and swordfish (Xiphiidae)
343-358	Javier lopez-Rasgado, Francisco, and Sharon Z. Herzka Assessment of habitat quality for juvenile California halibut (Parolichthys californicus) in a seasonally arid estuary
359-372	Grigg, Emma K., A Peter Klimley, Sarah G. Allen, Deborah E. Green, Deborah L. Elliott-Fisk, and Hal Markowitz Spatial and seasonal relationships between Pacific harbor seals (Phoca vitulina richardii ) and their prey, at multiple scales
373-383	Graves, John E., Andrij Z. Horodysky, and Robert J. Latour Use of pop-up satellite archival tag technology to study postrelease survival of and habitat use by estuarine and coastal fishes: an application to striped bass (Morone saxatilis)
384-394	Craddock, James E., Pamela T. Polloni, Brett Hayward, and Frederick Wenzel Food habits of Atlantic white-sided dolphins (Lagenorhynchus acutus) off the coast of New England
395-402	Humborstad, Odd-Borre, Michael W. Davis, and Svein Lokkeborg Reflex impairment as a measure of vitality and survival potential of Atlantic cod (Gadus morhua)
403	Guidelines for authors

265

Abstract — Analyses of sex-specific yield per recruit and spawning stock biomass per recruit were conducted to evaluate the current status of the sail- fish ( Istiophorus platypterus) fishery in the waters off eastern Taiwan. Natural mortality rates estimated from Pauly’s empirical equation were 0.26/yr for females and 0.27/yr for males. The current fishing mortal- ity rates were estimated as 0.24/yr and 0.43/yr for females and males, respectively, which are much lower than the estimated F0 x (0.62/yr and 0.79/yr for females and males, respectively) and FSSB40 ( 0.46/yr for females) which are commonly used as target reference points in fisheries management. The effects of the fish- ing mortality, natural mortality, and age at first capture on the estimates of biological reference points were evaluated by using the Monte Carlo simulation. The results indicate that failure to consider the uncertainty in parameters such as natural mortality or age at first capture may lead to the improper estimation of biological reference points. This study indicates the possibility of current fishing mor- tality exceeding the target biological reference points may be negligible for sailfish in the waters off east- ern Taiwan. However, in view of the recent rapid increase in fishing effort, it is evident that the stock status and development of the fishery need to be closely monitored.

Manuscript submitted 17 July 2008. Manuscript accepted 28 January 2009. Fish. Bull. 107:265-277.

The views and opinions expressed or implied in this article are those of the author and do not necessarily reflect the position of the National Marine Fisheries Service, NOAA.

Analysis of sex-specific spawning biomass

per recruit of the sailfish ( Istiophorus platypterus)

in the waters off eastern Taiwan

Wei-Chuan Chiang '

Chi-Lu Sun (contact author) 2 Sheng-Ping Wang 3 Su-Zan Yeh 2

Yong Chen 4 Wei-Cheng Su 5 Don-Chung Liu 5 Wen-Yie Chen 1

Email address for contact author: chilu@ntu.edu. tw

1 Eastern Marine Biology Research Center of Fisheries Research Institute No. 22 Wuchuan Rd.

Chenkung, Taitung, Taiwan 961

2 Institute of Oceanography National Taiwan University No.1, Sec. 4, Roosevelt Rd Taipei, Taiwan 106

3 Department of Environmental Biology and Fisheries Science National Taiwan Ocean University No. 2, Beining Rd.

Keelung, Taiwan 202

School of Marine Science University of Maine 218 Libby Hall Orono, Maine 04469

Fisheries Research Institute No. 199, Ho-lh Rd. Keelung, Taiwan 202

Sailfish ( Istiophorus platypterus) is a circumtropically distributed spe- cies (Hoolihan, 2005). Sailfish is a member of the billfish family, Istio- phoridae, which also includes marlins and spearfishes, and is considered a bycatch species in commercial fisher- ies. Off the eastern coast of Taiwan, sailfish are economically important and seasonally abundant from April to October (abundance peaks from May to July). Sailfish are mainly caught by drift gill nets, although some are also caught by set nets, harpoons, and as incidental bycatch in inshore long- line fisheries (Chiang, 2004). There are virtually no discards of sailfish in Taiwan. For the past decade, the annual landings of sailfish off Taiwan waters have fluctuated between 500 and 1000 metric tons, of which over 50% have come from waters off Tai- tung (eastern Taiwan).

Globally, large predatory fish spe- cies, including billfish, are declining at alarming rates because of exces- sive exploitation (Myers and Worm, 2003). Recent increases in the ex- ploitation of billfish stocks by both commercial and recreational fisheries

clearly point to the need for accurate assessments, if the goal is to develop sustainable billfish fisheries (Uozumi, 2003). However, because few fisheries target sailfish, assessments have not been conducted, resulting in few or no effective management measures. For sailfish in the Pacific Ocean and Indian Ocean, no assessments have been conducted, and stock status re- mains unknown. Historical sailfish catch data from the Pacific Ocean are scant, as are data on the length and age composition of the catch. This lack of data precludes the use of most stock assessment tools such as production models and age-struc- tured models (Punt, 1997; Prager and Goodyear, 2001; Liu et al., 2006). However, recent biological studies on sailfish in the waters off eastern Taiwan (Chiang et al., 2004, 2006) have provided an opportunity to apply yield per recruit ( Y/R ) and spawning biomass per recruit ( SSB/R ) models (Govender, 1995; Griffiths, 1997) to estimate biological reference points including the fishing mortality rate corresponding to the point where the slope of the yield-per-recruit curve

266

Fishery Bulletin 107(3)

equals 10% of the slope at the origin (F0 Gulland and Boerema, 1973) and the fishing mortality rate cor- responding to a specific percentage ( x% ) of the spawn- ing biomass per recruit at the unfished level (FSSBx) for the eastern Taiwan sailfish stock. The status of the fishery for this stock could be examined by comparing the fishing mortality at the current level (FCUR) with the biological reference points.

A per-recruit analysis requires information on growth, mortalities, and selectivity of fishing gear. Catch curve analysis (Ricker, 1975) is the most common method employed for estimating total mortality when data on the age composition of catch are available. For a speci- fied natural mortality, FCUR could be computed simply by subtracting the natural mortality from the total mortality. However, in most cases large uncertainty is associated with the estimation of natural mortality and other life history parameters, which can lead to large uncertainty in the estimation of FCUR and biological reference points.

The objective of this study was to evaluate the cur- rent status of the sailfish fishery in waters off eastern Taiwan by comparing the current fishing mortality rate (estimated from analyzing length composition data collected from the fishery) with the biological reference points derived from the per-recruit analyses (Butter- worth et al., 1989; Sun et al., 2002, 2005). In addi- tion, a Monte Carlo simulation study was conducted for evaluating the influence of uncertainty associated with mortalities and the age at first catch ( tc ) on the estima- tion of biological reference points. This study provides an approach that can be used to assess the status of fisheries for which limited information does not allow us to conduct a full stock assessment.

Materials and methods

Length and age composition of the catch

Length composition data were obtained by measuring sailfish landed at the Shinkang fish market in eastern Taiwan (Fig. 1) during the period from July 1998 to July 2005. Specimens were randomly selected from the land- ings and measured for their lengths and weights. The sex of each specimen was identified from the appearance of its gonads. Samples of the first dorsal fin were taken from 1166 of the sampled individuals for which lengths were measured and used to age the sailfish (Chiang et al. 2004). These subsampled fish were used to construct sex- specific age-length keys, which in turn were used to con- vert the length-frequency data into age-composition data.

Estimating mortality rates

For each sex, the dynamics of a simulated year class can be projected forward from one year to another by using the exponential survival equation (Ricker, 1975):

Nt+1 = Nte~(M+FSt), (1)

Figure 1

The fishing grounds where sailfish ( Istiophorus platypterus) are caught as bycatch in the gill- net, harpoon, and longline fisheries based at the Shinkang fishing port of Taiwan. Crosshatched area is where the gillnet and harpoon fisheries take place and the longline fishery takes place in larger area indicated by oblique lines. Samples were collected during the period from July 1998 to July 2005 to estimate biological metrics for per- recruit analyses.

where Nt t\

M

F

St

the number of fish at the beginning of age

the instantaneous natural mortality rate; t the fishing mortality of fully-recruited fish; and

the fishing gear selectivity of fish at age t.

Selectivity is the relative vulnerability of different age or size classes to the fishing gear. In this study, we assumed that the selectivity follows a dome-shaped distribution because our length-frequency data were mostly col- lected from gill nets. This dome-shaped selectivity can be quantified with the following normal distribution density function:

St =

W

e 2ct2 ,

(2)

Chiang et al.: Analysis of sex-specific spawning biomass per recruit of Istiophorus platypterus in off eastern Taiwan

267

where p = the age at the mode of the dome-shaped selectivity; and

ct = the standard deviation of the dome-shaped selectivity.

The expected catch (Ct) of fish at age t can be estimated based on the catch equation (Ricker, 1975):

= ^-NAl-e-(M+FS‘\

M + FSt 1

(3)

The parameters of N0, F, p, and o can be estimated simultaneously by minimizing the following composite objective function:

^ (Ct -Ct)2 + (max(Sf)-l)2, (4)

t

where Ct = the observed numbers of catch at age t.

The F estimated above was considered as the current fishing mortality ( FCUR ) in this study. The approach outlined above for the catch-curve analysis is similar to the one described in Rudershausen et al. (2008).

A total of 1000 independent bootstrap samples of F were derived from 1000 sets of length-frequency data drawn randomly with replacement from the individuals of original length-frequency data.

Pauly’s (1980) empirical equation was used to esti- mate M for each sex, and the mean sea surface tem- perature around eastern Taiwan waters fitted to the equation was about 26°C.

Per-recruit analyses

Yield per recruit (Y/R) of sailfish in the waters off east- ern Taiwan was estimated from the following model:

Table 1

Biological parameters used in the per-recruit analysis for the sailfish ( Istiophorus platypterus ) in the waters off eastern Taiwan during the period from July 1998 to July 2005. VBGF is the von Bertalanffy growth function, L „ = the asymptotic length, K = the growth coefficient, t0 = the hypothetical age at length zero; Length-weight, rela- tionship is W = AxLB , where W = rought weight (in kg) and L = lower jaw fork length (in cm); Maturity fraction parameters rm = the slope of logistic equation fitted to the maturity data collected, and trn = the age at 50% sexual maturity.

Parameter Female Male

VBGF

L a 250.29 cm 240.539 cm

K 0.138/yr 0.145/yr

t0 -2.99 -2.781

Length-weight relationship

A 2.3234xl0-6 1. 1933xl0-5

B 3.1013 2.7828

Maturity fraction r m 1.525

The maximum lifespan ( tmax ) of sailfish in the waters off eastern Taiwan was unknown but was estimated by using the empirical relationship of Taylor (1958):

2.996 K '

(8)

The equation for spawning stock biomass per recruit (SSB/R) is

Y/

/r

(

W. x^x[\-e^M)

xe 1=0

, (5)

where Wt - the mean weight of fish at age t\ and tc = the age at first capture.

Mean weight at age was computed as a power function of midyear lower jaw fork length (. Lt ):

Wt =axLbt, ( 6 )

^max

X

' t- 1 \

frt xWtxe i=tr

t=t

m

V

(9)

where Wt = the mean weight at age t that was calcu- lated from the von Bertalanffy function and length-weight relationship for female sailfish; and

fr = the fraction of female sailfish that are mature.

and midyear lower jaw fork length was estimated from the von Bertalanffy growth function

Lt = L„[l-e-K{t+0-5-to)Y (7)

In this case fr is represented by a logistic equation fitted to maturity data collected from sailfish caught in the eastern waters off Taiwan (Chiang et al., 2004, 2006). The logistic equation can be written as

where K = the growth parameter;

= the average asymptotic length; and Co = hypothetic age at length of 0 (Ricker, 1975; see Table 1).

where rm

= the slope of the logistic curve; and = age at which 50% of fish are mature.

(10)

268

Fishery Bulletin 107(3)

Table 2

Scenarios designed to examine the effects of uncertainty ofF, M, and tc on the estimates of biological reference points of sailfish ( Istiophorus platypterus) in the waters off eastern Taiwan. Scenarios A-D were used to evaluate the effects of changes in a single parameter, scenarios E-H were used to evaluate the results of changes in combinations of two parameters, and scenarios I and J were used to evaluate the results when three parameters were subject to uncertainty. (aF=standard deviation from the boot- strapped estimation; M = natural mortality per year; tc = age at first catch)

Parameters

oF M

Scenario	Female	Male	Female	Male	tc
Base	0	0	0.26	0.27	5
A	0.046	0.045	0.26	0.27	5
B	0	0	0. 2-0.3	CO O 1 03 o	5
C	0	0	0.15-0.35	0.15-0.35	5
D	0	0	0.26	0.27	5-7
E	0.046	0.045	0.2-0. 3	0.2-0. 3	5
F	0.046	0.045	0.15-0.35	0.15-0.35	5
G	0	0	0.2-0. 3	0.2-0. 3	5-7
H	0	0	0.15-0.35	0.15-0.35	5-7
I	0.046	0.045	0.2-0. 3	CO o 1 03 o	5-7
J	0.046	0.045	0.15-0.35	0.15-0.35	5-7

Biological reference points

The following biological reference points were estimated in order to determine the current status of the sailfish fishery: Fov FSSB25, and ESSB40. FSSB2 5_ and ESSB40 are fishing mortality rates corresponding to the 25% and 40% of the spawning biomass per recruit at unfished level. The choice of 25% or 40% was relatively arbi- trary for the fishery, but these values have been used as different levels of reference points for other relatively long-lived marine fishes (e.g., Griffiths, 1997; Kirchner, 2001; Sun et al., 2002, 2005). The spawning potential ratio {SPR) is the SSB/R at a given fishing mortality divided by the SSB/R without fishing (Gabriel et al., 1989; Goodyear, 1993; Katsukawa et al., 1999; Wata- nabe et al., 2000; Sun et al., 2002, 2005) and can be calculated as

SPR =

SSB/R

SSB/R\f

(11)

Several authors have advocated designating F0 1 or F SSB40 as target reference points and FSSB25 as a threshold reference point in order to obtain near op- timal yields while minimizing the likelihood of stock collapse (Gulland and Boerema, 1973; Deriso, 1987; Hilden, 1993; Sun et al., 2002, 2005). We adopted these target and threshold reference points in this study.

quantify the uncertainty of F, F was assumed to follow a normal distribution with a mean and standard devia- tion (oF) — the latter estimated from the bootstrapped estimation of F. However, there was no information on the distribution of M and tc. We assumed a uniform distribution for M and tc by referring to the estimation of Pauly’s empirical equation and the age at full recruit- ment from the age composition of sailfish in the waters off eastern Taiwan. The values of M and tc were sampled randomly from the corresponding uniform distributions defined in Table 2. Ten scenarios were designed to exam- ine the effects of different combinations of the uncer- tain in parameters F, M, and tc on the estimation of biological reference points (Table 2). Scenarios A-D were used to evaluate the effects of changes in a single parameter, scenarios E-H were used to evaluate the results of changes in combinations of two parameters, and scenarios I and J were used to evaluate the results when three parameters were subject to uncertainty. For each scenario, 100 replicates of biological reference points were estimated by using the parameters of F, M, or tc randomly drawn from their assumed distributions. The median and the interquartile range were used to quantify the central tendency and variation for the dis- tributions of estimated biological reference points.

Results

Simulation study

The Monte Carlo simulation approach was applied to evaluate the sensitivity of estimating biological reference points with respect to parameters F, M, and tc. To

Age composition

Length data were obtained for 12,323 sailfish (3532 females and 8791 males), and age data for 1166 of these

Chiang et al.: Analysis of sex-specific spawning biomass per recruit of Istiophorus platypterus in off eastern Taiwan

269

1400

1200 -

1000 -

800 -

600 -

400

200 -

■ Female (n= 3532) Z Male (n=8791 )

80

i—TTr-if—i » IF1!1

95 110 125

140 155 170 185 200 215

260

Lower iaw fork length

Figure 2

The length-frequency distributions (5-cm intervals) of female (black bars) and male (white bars) sailfish ( Istiophorus platypterus) in the waters off eastern Taiwan during the period from July 1998 to July 2005. Most fish caught were 160-190 cm in lower jaw fork length.

0

1

8

10 11 12+

Age in years

Figure 3

The age-frequency distributions for female (black bars) and male (white bars) sailfish ( Istiophorus platypterus) in the waters off eastern Taiwan during the period from July 1998 to July 2005. Most fish caught were 4-7 years old.

fish (446 females and 720 males). The range of lower jaw fork length was 80-239 cm for females and 78-227 cm for males (Fig. 2). Age compositions of samples collected during the entire study period indicated that most sail- fish caught off eastern Taiwan are larger than the age at 50% matu- rity, and peak in length at 5 years (Fig. 3). Accordingly, the estimates of age at full recruitment (tc) and the sample size during studying periods are shown in Table 3. The estimates of t varied from 5 to 7 years for different time periods. Few sampled fishes were older than 11 years for both sexes and hence age 12 and higher were com- bined into the 12+ group (Fig. 3). The empirical estimates of maximum lifes- pan (tmax) were 13 years for males and 21 years for females.

Mortality rates

The estimates of F were 0.24/yr for females and 0.43/yr for males based on the samples collected during the entire study period. Based on boot- strap analysis, the standard deviation of F was 0.046/yr and 0.045/yr for females and males, respectively. In addition, 79% of bootstrap replicates of tc were 5 years old and few were 6 or 7 years old. The values of M estimated from the Pauly’s empirical equation were 0.26/yr for females and 0.27/yr for males. In this study, therefore, F of 0.24/yr for females and 0.43/yr for males, tc of 5 years and M of 0.26/yr for females and 0.27/yr for males were set as the base case values for the sub- sequent analyses. Sensitivity analyses were also conducted for examining the results of Y/R and SPR analyses by assuming values of 0.20, 0.30, and 0.35 for M.

Y/R and SPR models and biological reference points

In this study, selectivities for females and males were assumed to be dome-shaped, and the estimated selectiv- ity curves are shown in Figure 4. The estimates ofFCUR, F0 j, and Y/R under various values of M are summarized in Table 4. For the base case, FCUR (0.24/yr for females and 0.43/yr for males) were substantially lower than the corresponding biological reference points F0 1 (0.62 /yr for females and 0.79/yr for males). The estimates of Y/Rcvn were 3.37 kg for females and 3.72 kg for males and the estimates of Y/R0 x were 5.11 kg for females and 4.68 kg

for males (Fig. 5). Even in the most conservative case, when M was assumed to be 0.2, FCUR was still lower than F0 x for both females and males.

The effect of varying tc on Y/R is shown in Figures 6 and 7. At low levels of F, Y/R generally increased rapidly over the range of tc values tested. The values of tc that maximized the yield per recruit decreased with the magnitude of M and increased with the level of F but typically ranged between 2 and 5 years for females and males.

270

Fishery Bulletin 107(3)

Table 3 Sample sizes and estimates of age at full recruitment for female and male sailfish ( Istiophorus platypterus ) by year in the waters off eastern Taiwan during the period from July 1998 to July 2005.
	Sample size	Age at full recruitment		Sample size	Age at full recruitment
Female		Male
1998	131	6	1998	525	6
1999	702	5	1999	1943	5
2000	387	7	2000	578	7
2001	358	6	2001	730	5
2002	349	7	2002	576	5
2004	484	5	2004	1123	5
2005	1121	6	2005	3316	5
Overall	3532	5	Overall	8791	5

Table 4

Estimates of current fishing mortality (ECUR), current yield per recruit ( Y/Rcur ), and the reference points of F0 x and Y/R0 x at different levels of natural mortality (M) for female and male sailfish (Istiophorus platypterus ) in the waters off eastern Taiwan during the period from July 1998 to July 2005. F0 : = the fishing mortality rate corre- sponding to Y/Rq 1;Y/R01= the point of a yield-per-recruit curve where the slope equals 10% of the slope at the origin.

M (1/yr)	F CUR (1/yr)	K. i (1/yr)	Y!FCur (kg)	57*0.1 (kg)
Female
0.20	0.26	0.54	5.36	7.08
0.26	0.24	0.62	3.37	5.11
0.30	0.22	0.69	2.45	4.13
0.35	0.20	0.80	1.63	3.19
Male
0.20	0.46	0.70	5.79	6.66
0.27	0.43	0.79	3.72	4.68
0.30	0.41	0.83	3.06	4.04
0.35	0.38	0.91	2.21	3.17

Figure 4

The estimated selectivity curves for female (dashed line) and male (solid line) sailfish (Istiophorus platypterus ) in the waters off eastern Taiwan. Selectivity is the relative vulnerability of different age or size classes to the fishing gear. In this study, selectivity is assumed to be dome shaped because length-frequency data were mostly collected from gillnets.

The rapid growth and relatively late tc (5 years) of sailfish in the waters off eastern Taiwan produced low Y/R and high SPR at current fishing mortalities com- pared with reference points (Figs. 4 and 7). The esti- mates of FSSB25, FSSB40, SPR and Y/R under the various values of M are summarized in Table 5 and Figure 8. The base-case estimate of FCUR for females (0.24/ yr) was lower than the corresponding reference points FSSB4o (0.46/yr) and FgSB25 ( 0.94/yr); the current SPR was estimated to be about 57.20% of its unfished level. Under the low value of M (0.2/yr), the estimate of FCUR for females (0.26/yr) was lower than FggB40 (0.36/yr) and substantially lower than FggB25 (0.67/yr). Increas- ing tc to older than six years of age would ensure that the SPR was maintained at a value higher than the

threshold level (i.e., 25% of its unfished level) at almost any level of fishing mortality (Fig. 9) with relatively little effect on Y/R.

Simulation scenarios

The box plots of the estimates of F0 1 and FCUR/F0 1 are shown in Figure 10 for scenarios A-J with the assump- tion of uncertainty in F, M, and tc defined in Table 2. Although the medians of these two quantities were close to those of the base case for most scenarios, the variations of these quantities were diverse depending on the assumptions of uncertainty of the parameters. For scenarios A-D with only one parameter subject to uncertainty, the estimates of F0 4 were independent of

Chiang et al.: Analysis of sex-specific spawning biomass per recruit of Istiophorus platypterus in off eastern Taiwan

271

A

2 B

Figure 5

Yield per recruit ( Y/R ) against fishing mortality per year for female (A) and male (B) sailfish (Istiophorus platypterus) in the waters off eastern Taiwan. • = Fc UR and O = F01.

Table 5

Estimates of current fishing mortality (ECUR) and the reference points of SSB/RSSBx and SPR at different levels of natural mor- tality ( M ) for female sailfish (Istiophorus platypterus) in the waters off eastern Taiwan during the period from July 1998 to July 2005. FSSBx = the fishing mortality rate corresponding to SSB /RSSBx ; SSB/RSSBx = a specific percentage ( x% ) of the spawning biomass per recruit at the unfished level; SPR (spawning potential ratio) = the SSB/R at a given fishing mortality divided by the SSB/R without fishing.

M (1/yr)	^CUR (1/yr)	^SSB40 (1/yr)	^SSB25 (1/yr)	SSB/Rcur (kg)	SSB/RggB40 (kg)	SSB/RggB25 (kg)	SPRcur (%)
0.20	0.26	0.36	0.67	32.50	26.56	16.60	48.96
0.26	0.24	0.46	0.94	22.22	15.53	9.71	57.20
0.30	0.22	0.54	1.22	17.42	11.14	6.96	62.57
0.35	0.20	0.70	1.73	12.97	7.52	4.70	68.95

the changes in F but were very sensitive to the uncer- tainty in M. Adding the uncertainty in tc resulted in slightly higher estimates of F0 1 than that for the base

case. Higher estimates of F0 1 could have resulted from tc with values larger than 5 years (base case) selected in this scenario. In the case of this study, higher tc pro-

272

Fishery Bulletin 107(3)

Fishing mortality (1/year)

Figure 6

Yield-per-recruit isopleths against fishing mortality per year and age at first capture ( tQ ) at different levels of natural mortality (M) for female sailfish ( Istiophorus platypterus) in the waters off eastern Taiwan.

duced higher estimates ofF0 x for sailfish in the water of eastern Taiwan. For scenarios E-J that incorporated the combinations of uncertainties in F, M, and tc, large varia- tions were observed for estimates of F0 x when a higher level of uncertainty was assumed for M (scenarios F, H, and J). Even though combinations of parameters with higher uncertainties were considered, the upper bounds (the third quartile) of FCUR/F0 x were lower than 1 for all scenarios. This result implied that it was highly unlike that Fcur could exceed F0 v In contrast, the effects of adding uncertainties in F and tc were relatively minor.

Figure 11 shows the box plots of the estimates of

-^SSB40> -^SSB25’ -^CUR^0.1SSB40, and FCUR/F0 lggB25 ^or SCe'

narios A-J (with uncertainty). Similarly, higher levels of uncertainties in M resulted in higher variations for the estimates of FgSB40 and FggB25 (scenarios C, F, H, and J). Moreover, the estimates of FgSB40 and FggB25 were obviously higher than those of the base case when the uncertainty in tc was considered (scenarios D, G, H, I, and J), which might result from female fish younger than tc being less vulnerable to fishing gear. Therefore, higher values of SSB/R would be obtained when larger values of tc were selected and higher estimates of FgSB40 and FSSB25 were revealed for these scenarios. For all

scenarios, the medians of FCUR/FggB40 and FCUR/FggB25 were 0.71 and 0.37, respectively, which were similar to those of the base case (Table 5). The upper boundaries of FCUR/FSSB40 and FCUR/FSSB25 were substantially lower than 1 for all the scenarios and no simulation runs were observed to have the values higher than 1.

Discussion Mortality rates

The Y/R curve is so flat-topped that maximum Y/R cannot be well defined and may not be attained under any practical fishing mortality rate (Fig. 5). Reference points such as F0 1; FgSB25, and FggB40 have often been used to develop fishery management strategies. Previous studies have indicated that Y/R and SPR are sensitive to values of M (Griffiths, 1997; Kirchner, 2001; Sun et al., 2005). In this study, however, the estimates of FCUr were much lower than the target levels of F0 x or FsgB40 except for the scenario when M was assumed at the lower bound of 0.2. Moreover, the estimates of F CUR were never larger than the threshold level of FggB25 even

Chiang et al.: Analysis of sex-specific spawning biomass per recruit of Istiophorus platypterus in off eastern Taiwan

273

Figure 7

Yield-per-recruit isopleths against fishing mortality per year and age at first capture ( tc ) at different levels of natural mortality (M) for male sailfish ( Istiophorus platypterus) in the waters off eastern Taiwan.

when M was assumed to be 0.2. This result would indicate that the stock of sailfish in the waters off eastern Taiwan appears to be mod- erately exploited and has relative low risk of being overfishing.

Sex-specific per-recruit analyses and sensitivity analyses

Most assessment methods require historic infor- mation on catch, effort, and catch-at-age (or catch-at-length). The lack of long-term fishery statistics usually makes it difficult to evaluate the status of populations exploited by small- scale fisheries or taken incidentally (e.g., Gov- ender, 1995; Barbieri et al., 1997; Griffiths, 1997; Jones and Wells, 2001; Sun et al., 2002, 2005). Per-recruit analyses, which require only parameters related to life span and mortality, combined with an analysis of catch curves, can become an alternative method for evaluating the status of a fishery. Because per-recruit analyses can provide the estimates of biological reference points and the catch curve analysis can yield

10 ■

0 1 ■ — ■ — *

0 0.2 0.4 0.6 0.8 1

Fishing mortality (1/year)

Figure 8

Spawning potential ratio (expressed as a percentage) against fishing mortality for female sailfish (Istiophorus platypterus) in the waters off eastern Taiwan where age at first capture (tc) = 5 years (solid dots are SPRcvr levels; horizontal dashed lines are levels for the biological reference points of PgsB4o ar|d Fssb25’ and • = Fcur).

274

Fishery Bulletin 107(3)

Fishing mortality (1/year)

Figure 9

Spawning-potential ratio (SPR) isopleths against fishing mortality per year and age at first capture ( tc ) at different levels of natural mortality (M) for female sailfish ( Istiophorus platypterus) in waters off eastern Taiwan.

the estimate of current fishing mortality rate, the status of a fishery can be readily determined by comparing current fishing mortality with the biological reference points. Nevertheless, few results of previous studies have been discussed as to how the biological reference points based on per-recruit analyses were influenced by the uncertainties of biological parameters.

In this study, the effects of F, M, and tc on the es- timates of F0 v F SsB4o> and -^ssb25 were evaluated by using the Monte Carlo simulation method. Although other parameters (e.g., growth) are essential inputs for per-recruit analyses, we focused on the effects of F, M, and tc which are generally more difficult to esti- mate owing to a lack of enough auxiliary information (Chen et al., 2007). In addition, the assumption of selectivity of fishing gear could influence the results of per-recruit analyses. Generally, longline selectivity is assumed to be asymptotic and gillnet selectivity is assumed to be dome shaped. In this study, a dome- shaped selectivity was assumed for incorporating into the per-recruit analyses. Sailfish in the waters off eastern Taiwan were exploited by various fishing gears although large proportion of the catch was made by gillnet. However, insufficient length-frequency data

recorded by fishing gear lead to difficulty in estimat- ing the selectivity for different fishing gear. Therefore, collecting the information from fishing gear for length- frequency data is necessary to evaluate the influence of different selectivity assumptions on the results of assessment.

Implications of sex-specific assessment and management of the species

Uozumi (2003) indicated that the problems in the stock assessment of sailfish are the inability to obtain reliable biological parameters, standardization of catch per unit of effort, and a mechanism to develop reliable abundance indices. Sailfish are known to be sexually dimorphic (females grow faster and to a larger size than males (Chiang et al., 2004; Hoolihan, 2007), females become mature later than males, and sex ratio varies with length (Chiang, 2004). These attributes indicate that sex-specific assessments should be done to evaluate the status of sailfish. The sex-specific per-recruit analyses with the consideration of parameter uncertainty used in this study provide a method for evaluating manage- ment strategies.

Chiang et al.: Analysis of sex-specific spawning biomass per recruit of Istiophorus platypterus in off eastern Taiwan

275

B

ABODE FGH Scenario

ABODE FGH Scenario

ABODE FGH I J Scenario

D

0.7

- 0.6 o -L

§ 0.5

o

0.4

0.3

ABODE FGH I Scenario

FSgure 10

Box plots of the estimates of F0 1 and FCUR/F0 i f°r scenarios incorporating the uncertainty in total mortality (Z), natural mortality (M) and age at first capture (tc) for female (A, C) and male (B, B) sailfish (Istiophorus platypterus) in the waters off eastern Taiwan. The center line represents the median and the boxes represent the quartiles. The whiskers extend 1.5 times the interquartile range. Open circles are outliers. Horizontal dash lines indicate the levels of reference points at base case.

There is a possibility that the low F estimates may be an artifact of an influx of fish from outside the study area. Such a bias could occur if the probability that a fish will move from distant waters to within range of the eastern Taiwanese fleet is substantial and increases with the age of the fish (Sun et al., 2005). In principle, estimates for M could be obtained from research (such as tagging studies to determine M; Hampton, 2000). However, in the short to medium term, the values for M will have to be obtained from the results of studies for other stocks of sailfish. They have been similar to those obtained by Pauly’s (1980) method. This difference should be evaluated in relation to environmental factors. Although recent analyses of molecular markers do not support recognition of separate Atlantic and Indo-Pacific species of sailfish (Graves and McDowell, 2003), there is no evidence to indicate that sailfish become increasingly likely to migrate to Taiwan with increasing age. Although Prince et al. (2006) examined the tagging results in the eastern Pacific Ocean, they considered this spe- cies a single stock. It is unclear whether the sailfish population in the Pacific Ocean comprises a single or multiple stocks, and their regional or global abundance

is unknown (Ehrhardt and Fitchett, 2006). A tagging program in which electronic and conventional tags are used to examine the spatial movement patterns and stock structure of sailfish in this geographical region would prove beneficial for the sustainable management of the species.

There are no management measures for sailfish in the waters off eastern Taiwan at present. In the wa- ters off eastern Taiwan, sailfish are targeted by the gillnet fishery and caught incidentally in the longline, harpoon, and set net fisheries. This makes it difficult to effectively control the fishing effort of these fisheries for sailfish. In this case, the isopleths of SPR indicate that increasing tc to an age between six and seven years old would likely result in modest gains in terms of SPR (on the order of 40%) and also hedge against recruitment overfishing. For example, the target level of 40% SPR could be achieved at even double values of F 'cur if te for female sailfish was larger than five years (the age at sexual maturity). Of course the efficacy of increasing tc would be mitigated by any substantial release mortality. At present little is known about the mortality rates of fish released from gillnet and long- line vessels operating off eastern Taiwan, and further

276

Fishery Bulletin 107(3)

A

ABCDEFGH I J

Scenario

c

o

ABCDEFGH I J

Scenario

B

ABCDEFGH I J

Scenario

D

ABCDEFGH I J

Scenario

	0.8 -
o
3 co CO ll	0.6 -
:d o u.	0.4 -
	0.2 -

Figure 11

Box plots of the estimates of FSSB40( A), Fssb2s(®L ^cur/^o.issb4o(^') > anc^ -^'cur^o.issb25 for scenarios incorporating the uncertainty in total mortality (Z), natural mortality (M), and age at first capture itc) for female sailfish (Istiophorus platypterus ) in the waters off eastern Taiwan. The center line represents the median and the box represents the quartiles. The whiskers extend 1.5 times the interquartile range. Open circles are outliers. Horizontal dashed lines indicate the levels of reference points at base case.

study is needed before we can confidently recommend increasing tc as a measure to prevent overfishing.

In summary, sex-specific per-recruit modeling coupled with Monte Carlo simulation analyses are effective in evaluating the stock status of billfish because of the sexual dimorphism and uncertainty in key life history and fishery parameters of these species. This study reveals that sailfish in the waters off eastern Taiwan appear to be moderately exploited and have relative low risk of being overfished. However, in view of the recent rapid increase in fishing effort, it is evident that the stock status and development of the fishery need to be closely monitored.

Acknowledgments

We would like to thank two reviewers, Michael H. Prager, NMFS Southeast Fisheries Science Center, and Gerard DiNardo, NMFS Pacific Islands Fisheries Science Center, and one anonymous reviewer for their valuable and constructive comments. We thank Michael Prager for proposing the modified catch-curve method. This

study was partially financially supported by the Fisher- ies Agency, Council of Agriculture, Taiwan, through the grant 93AS-9.1.1-FA-F1(2) to Chi-Lu Sun.

Literature cited

Barbieri, L. R., M. E. Chittenden Jr., and C. M. Jones.

1997. Yield-per-recruit analysis and management strate- gies for Atlantic croaker, Micropogonias undulates, in the Middle Atlantic Bight. Fish. Bull. 95: 637-645. Butterworth, D. S., A. E. Punt, D. L. Borches, J. G.. Pugh, and G. S. Hughes.

1989. A manual of mathematical techniques for line- fish assessment (incorporating report of the SANCOR Marine Linefish Programme’s Workshop on Population Dynamics, February 4-6, 1987, Cape Town). S. Afr. Natl. Sci. Prog. Rep. 160, 89 p.

Chen, Y., L. Xu, X. Chen, and X. Dai.

2007. A simulation study of impacts of at-sea discarding and bycatch on the estimation of biological reference points F0 4 and Fmax. Fish. Res. 85:14-22.

Chiang, W. C.

2004. Population dynamics and stock assessment of the sailfish ( Istiophorus platypterus) in waters off eastern

Chiang et al.: Analysis of sex-specific spawning biomass per recruit of Istiophorus platypterus in off eastern Taiwan

277

Taiwan. Ph.D. diss., 171 p. National Taiwan Univer- sity, Taipei, Taiwan.

Chiang, W. C., C. L. Sun, S. Z. Yeh, and W. C. Su.

2004. Age and growth of sailfish ( Istiophorus platypterus) in waters off eastern Taiwan. Fish. Bull. 102:251— 263.

Chiang, W. C„ C. L. Sun, S. Z. Yeh, W. C. Su, D. C. Liu, and W. Y. Chen.

2006. Sex ratios, size at sexual maturity, and spawn- ing seasonality of sailfish Istiophorus platypterus from eastern Taiwan. Bull. Mar. Sci. 79:727-737.

Deriso, R. B.

1987. Optimal F0.1 criteria and their relationship to maximum sustainable yield. Can. J. Fish. Aquat. Sci. 44:339-348.

Ehrhardt, N. M., and M. D. Fitchett.

2006. On the seasonal dynamic characteristics of the sailfish, Istiophorous platypterus, in the eastern Pacific off central America. Bull. Mar. Sci. 79:589—606.

Gabriel, W. L., M. P. Sissenwine, and W. J. Overholtz.

1989. Analysis of spawning stock biomass per recruit: an example for Georges Bank Haddock. N. Am. J. Fish. Manag. 9:383-391.

Goodyear, C. P.

1993. Spawning stock biomass per recruit in fisheries management: foundation and current use. Can. Spec. Publ. Fish. Aquat. Sci. 120:67-81.

Govender, A.

1995. Mortality and biological reference points for the king mackerel ( Scomberomorus commerson ) fishery off Natal, South Africa (based on a per-recruit assessment). Fish. Res. 23:195-208.

Graves J. E., and J. R. McDowell.

2003. Stock structure of the world’s istiophorid bill- fishes: a genetic perspective. Mar. Freshw. Res. 54:287-298.

Griffiths, M. H.

1997. The application of per-recruit models to Argyro- somus inodorus, an important South African sciaenid fish. Fish. Res. 30:103-115.

Gulland, J. A., and L. K. Boerema.

1973. Scientific advice on catch levels. Fish. Bull. 71:325-335.

Hampton, J.

2000. Natural mortality in tropical tunas: size really does matter. Can. J. Aquat. Sci. 55:1002-1010.

Hilden, M.

1993. Reference points for fisheries management: the ICES experience. Can. Spec. Publ. Fish. Aquat. Sci. 120:59-66.

Hoolihan, J. P.

2005. Horizontal and vertical movements of sailfish (Istiophorus platypterus) in the Arabian Gulf, deter- mined by ultrasonic and pop-up satellite tagging. Mar. Biol. 146:1015-1029.

2006. Age and growth of Indo-Pacific sailfish, Istiopho- rus platypterus, from the Arabian Gulf. Fish. Res. 78:218-226.

Jones, C. M., and B. K. Wells.

2001. Yield-per-recruit analysis for black drum, Pogo- nias cromis, along the East Coast of the United States and management strategies for Chesapeake Bay. Fish. Bull. 99:328-337.

Katsukawa, T., Y. Lee, and Y. Matsumiya.

1999. Spawning per recruit analysis for female snow

crab Chionoecetes opilio in the Sea off Kyoto prefecture. Nippon Suisan Gakk. 65:288-293.

Kirchner, C. H.

2001. Fisheries regulations based on yield-per-recruit analysis for the linefish silver kob Argyrosomus inodorus in Namibian waters. Fish. Res. 52:155-167.

Leaman, B. M.

1993. Reference points for fisheries management: the western Canadian experience. Can. Spec. Publ. Fish. Aquat. Sci. 120:15-30.

Liu, K. M„ Y. T. Chang, I. H. Ni, and C. B. Jin.

2006. Spawning per recruit analysis of the pelagic thresher shark, Alopias pelagicus, in the eastern Taiwan waters. Fish. Res. 82:56-64.

Myers, R. A., and B. Worm.

2003. Rapid worldwide depletion of predatory fish communities. Nature 423:280-283.

Pauly, D.

1980. On the interrelationships between natural morality, growth parameters and mean environmental tempera- tures in 175 fish stocks. J. Cons. Int. Mer 39:175- 192.

Prager, M. H., and C. P. Goodyear.

2001. Effects of mixed-metric data on production model estimation: simulation study of a blue-marlin-like stock. T. Am. Fish. Soc. 130:927-939.

Prince, E. D., D. B. Holts, D. Snodgrass, E. C. Orbesen, J. Luo, M. Domeier and J. E. Serafy.

2006. Transboundary and movement of sailfish, Istiopho- rus platypterus, off the Pacific coast of Central America. Bull. Mar. Sci. 79:827-838.

Punt, A. E.

1997. The performance ofVPA-based management. Fish. Res. 29:217-243.

Ricker, W. E.

1975. Computation and interpretation of biological sta- tistics of fish population. Bull. Fish. Res. Board Can. 191, 382 p.

Rudershausen, P.J., E.H. Williams, J.A. Buckel, J.C. Potts, and C.S. Manooch III.

2008. Comparison of reef fish catch per unit effort and total mortality between the 1970s and 2005-2006 in Onslow Bay, North Carolina. Tran. Am. Fish. Soc. 137:1389-1405.

Sun, C.L., N.M. Ehrhardt, C.E. Porch, and S.Z. Yeh.

2002. Analyses of yield and spawning stock biomass per recruit for the South Atlantic albacore (Thunnus alalunga). Fish. Res. 56:193-204.

Sun, C. L„ S. P. Wang, C. E. Porch, and S. Z. Yeh.

2005. Sex-specific yield per recruit and spawning stock biomass per recruit for the swordfish, Xiphias gladius, in the waters around Taiwan. Fish. Res. 71:61-69.

Taylor, C. C.

1958. Cod growth and temperature. J. Cons. Int. Exp. Mer 23:360-370.

Uozumi, Y.

2003. Historical perspective of global billfish stock assessment. Mar. Freshw. Res. 54:555-565.

Watanabe, K., T. Hosho, K. Saiura, T. Okazake, and Y. Matumiya.

2000. Fisheries management by spawning per recruit analysis for the threeline grunt Parapristipoma tri- lineatum around Mugi-oshima Island on the coastal area of Tokushima prefecture. Nippon Suisan Gakk. 66:690-696.

278

Abstract — The relative value of pelagic habitat for three size classes of juvenile Pacific ocean perch (Sebastes alutus ) was investigated by compar- ing their abundance and condition in two areas of the Aleutian Islands. Diet, zooplankton biomass, and water column temperatures were examined as potential factors affecting observed differences. Juvenile Pacific ocean perch abundance and condition, and zooplankton biomass varied signifi- cantly between areas, whereas juve- nile Pacific ocean perch diet varied only by size class. Observed differ- ences in fish condition may have been due to the quantity or quality of pelagic prey items consumed. For the delineation of essential demersal fish habitat, important ecological features of the pelagic habitat must therefore be considered.

Abundance, condition, and diet of juvenile Pacific ocean perch ( Sebastes alutus ) in the Aleutian Islands

Jennifer L. Boldt (contact author)1 Christopher N. Rooper2

Email address for contact author: Jennifer.Boldt@noaa.gov

1 Joint Institute for the Study of the Atmosphere and Ocean School of Fishery and Aquatic Sciences

University of Washington Box 355020

Seattle, Washington 98195 Present address: Alaska Fisheries Science Center National Marine Fisheries Service 7600 Sand Point Way NE, Bldg. 4 Seattle Washington 98115-0070

2 Alaska Fisheries Science Center National Marine Fisheries Service 7600 Sand Point Way NE, Bldg. 4,

Seattle Washington 98115-0070

Manuscript submitted 12 August 2008. Manuscript accepted 4 February 2009. Fish. Bull. 107:278-285.

The views and opinions expressed or implied in this article are those of the author and do not necessarily reflect the position of the National Marine Fisheries Service, NOAA.

Studies defining essential fish habitat often focus on associations of marine fishes with seafloor characteristics (Neuman and Able, 1998; La Mesa et al., 2002). Although identifying these associations is necessary to define hab- itats used by fishes, it is also impor- tant to explore other factors that may affect fish survival. Pelagic production of food resources, such as zooplank- ton, may be a factor that affects the survival of demersal fish. Bottom-up control through variation in pelagic production, may in part explain the observations of large climate-change effects on demersal fishes, including rockfishes (Hollowed and Wooster, 1992; Hollowed et al., 2001).

Pacific ocean perch (Sebastes alu- tus', POP) are an important rock- fish species that migrate vertically off the seafloor and consume pelagic prey (Brodeur, 2001), thus providing a direct linkage between pelagic zoo- plankton and demersal fish produc- tion. In general, juvenile POP (defined as individuals <250 mm fork length [FL] based on their size at first ma- turity) are associated with high-re- lief structured habitats, such as rocky outcrops, boulder fields, deep-water sponges, and corals (Rooper and Boldt 2005; Rooper et al., 2007). Little is known of the costs and benefits to

juvenile POP of residing in different habitat types or the potential linkage between pelagic prey and demersal habitats.

One measure of the relative value of different habitat types to juvenile POP may be fish condition. Fish diet, habitat, and water temperature are integrated into overall fish condi- tion, which may affect fish growth and subsequent survival (Paul, 1997; Boldt and Haldorson, 2004). The goal of this study was to examine the relative abundance and condition of three size classes of juvenile POP in two different areas of the Aleutian Islands. Fish occupying suboptimal habitats were expected to be in poor condition compared to those living in optimal habitats. Additionally, we ex- plored potential causes for observed differences in fish condition by exam- ining POP diet, prey availability, and water temperature observed in the different habitats.

Methods and materials Study site

Fieldwork for this study was conducted from 28 May to 9 June 2004, and from 11 August to 23 August 2004, at two

Boldt and Rooper: Abundance, condition, and diet of Sebostes o/utus

279

168°0'CTW

170WW

ALASKA:

Gulf

of

Alaska

Umnak

Island

Samalga

Island

1 70°0'0“W

i69eo,onw

Islands of Four Mountains

Samalga

Pass

80

Kilometers

Figure 1

Map of the study area in the Aleutian Islands, Alaska. Study sites were located near the Islands of Four Mountains, north of Samalga Island (N), and south of Samalga Island (S). At both sites, juvenile Pacific ocean perch ( Sebostes alutus ) were collected with a bottom trawl, zooplankton were collected with a ring net, and water column temperature profiles were recorded with a conductivity, temperature, depth recorder.

sites near Samalga Pass in the Aleutian Islands (Fig. 1). One site was located on the south (S) side and one on the north (N) side of Samalga Island (Fig. 1). Two sta- tions were sampled at each of the two sites in August and two stations were sampled at the N site in June. All the stations were located at depths from 117 to 146 m in high relief habitat (boulder fields) inhabited by juvenile POP.

Juvenile POP abundance and size classes

Juvenile POP (<250 mm FL) were collected during day- light hours with a standard NMFS poly Nor’eastern bottom trawl. A net (with average net width of 16.5 m) was towed at a target speed of 3 knots over distances of 0. 4-1.0 km. The catch per unit of effort (CPUE in number of juvenile POP per hectare) at each site was calculated by using the area swept. Juvenile POP were measured for fork length and frozen for laboratory analy- ses. Temperature was measured twice daily at each site with a SeaBird CTD (conductivity, temperature, depth recorder, Sea-Bird Electronics, Inc., Bellevue, WA) to obtain temperature-depth profiles.

In the laboratory, juvenile POP were thawed, mea- sured, weighed, and dissected. Fish stomachs were

weighed full and empty, and stomach contents were preserved in 10% buffered formalin for later diet analy- ses. Length frequencies of juvenile POP were plotted and natural breakpoints were used to divide the fish into three size categories (<160 mm FL, 160-210 mm FL, and >210 mm FL). Diet and fish condition were analyzed by these size categories and by site.

Juvenile POP condition

Fish condition was assessed by using log-transformed length-wet-weight regression residuals (indicator of somatic growth and hereafter referred to as wet-weight residuals; n = 226) and log-transformed length-dry- weight regression residuals (indicator of energy stor- age and hereafter referred to as dry-weight residuals; n=226). Also, the energy content of dried fish (n=226) was determined with a Parr 1425 Semimicro bomb calorimeter (Parr Instrument Company, Moline, IL). If available, at least 10 fish of each size category per site were dried in a 60°F drying oven or in a freeze dryer until a stable weight was reached. To test for differences in dry weights between the drying methods, thirty ran- domly chosen fish were individually ground and divided in half; one half of each fish was dried in the drying oven

280

Fishery Bulletin 107(3)

and the other half in the freeze dryer. Also, twenty two randomly selected fish were homogenized and divided in half; one half was freeze-dried, the other half was oven-dried, and the energy content of both halves was determined with the carorimeter to determine if there were differences in energetic content attributable to the two drying methods.

Juvenile POP diet

Whole blotted wet weights of stomach contents were recorded. Prey items were identified to a general taxonomic level (large (>2.5 mm) cope- pods, small (<2.5mm) copepods, euphausiids, larvaceans, Limacina spp., chaetognaths, hype- riid amphipods, other), which were counted and weighed. Numerical and weight proportions of each prey group in an individual stomach were calculated and then averaged over all fish within each size category sampled at a site. The number of empty stomachs was recorded; however, empty stomachs were not included in average diet com- position calculations. When the average percent number of a prey item was less than 5%, it was grouped in the “other” category. A stomach con- tent index (SCI) was estimated as the stomach content weight as a proportion of the fish weight and averaged over all fish in each size category at each site.

Zooplankton

In August, two zooplankton samples were collected at each of the north and south sites with a 1-m ring net (505 -p mesh) hauled vertically from depths of 40-105 m. The volume filtered (m3) was estimated as the product of the area of the ring net opening and the maximum depth from which it was hauled (recorded by a tem- perature-depth recorder attached to the net bridle). The relative biomass of zooplankton in each study area was estimated as the settled volume of zooplankton per volume of water filtered. Zooplankton samples were pre- served in 5% buffered formalin for laboratory analysis. Taxonomic components of the zooplankton samples were examined in the same manner that prey were enumer- ated from juvenile POP stomach contents.

Statistical analyses

An analysis of variance (ANOVA) was used to test for differences in log-transformed juvenile POP CPUE in August between sites, with site, size class, and the interaction term as factors. An ANOVA was used to test for differences in the juvenile POP response variables: wet-weight residuals, dry-weight residuals, energy content, and percent number and weight of main prey items. Site was the factor tested for all size classes of fish sampled in August. In June, only the north site was sampled for juvenile POP; therefore comparisons with the south site were not possible for the month

70

60-

50-

40 -

30-

r-Tl

H

■ N, June

□ N, August

□ S, August

Fork length (mm)

Figure 2

Length frequency of juvenile Pacific ocean perch (POP, Sebastes alutus) collected with a bottom trawl at sites north (N) and south (S) of Samalga Island in August and at the N site in June. Juvenile POP were divided into three size classes based on this length frequency (<160 mm, <210 mm, and >210 mm fork length), which correspond to ages 1-2, 3, and 4-5 years, respectively.

of June. For large fish at the north site the factors tested were month, site, and a month-site interaction term. The nonparametric Wilcoxon rank-sum test was used to determine if the SCI was significantly differ- ent between sites for each size class of juvenile POP. ANOVAs were used to test for significant differences in the numerical proportions of major taxa found in the zooplankton samples between sites in August.

Results

Juvenile POP abundance and size classes

Juvenile POP were caught in the two trawl hauls con- ducted at each of the two sites in August and the two trawl hauls conducted at the north site in June. Overall catch per unit of effort (log [CPUE+ 1]) estimates indi- cated that the abundance of juvenile POP was signifi- cantly higher (P- 0.027) at the south site (mean=4.22, SE = 0.53) than at the north site in August (mean=1.82, SE = 0.63). There were no significant differences in CPUE among size classes, and the interaction between size class and site was also insignificant. The average CPUE at the north site in June (mean=2.22, SE=1.71) was slightly higher than that measured in August at the same site.

Juvenile POP fork lengths ranged from 83 to 249 mm. Three size classes of juvenile POP were apparent in a length-frequency plot (Fig. 2): small (<160 mm FL), me- dium (160-210 mm FL), and large (>210 mm FL). These size categories roughly correspond to five age classes of

Boldt and Rooper: Abundance, condition, and diet of Sebastes alutus

281

0.08 -i A 0.06 - 0.04 - 0.02 -

0

-0.02 - -0.04 - -0.06 - -0.08 - -0.1 -

-I—

B N, June

□ N, August

□ S, August

<160

1— -r r~^ '

<210

>210

6000 -| C

S

ct> 5000 "co

O 4000 > o> o

3000

<160 <210 >210 Size class (fork length in mm)

Figure 3

The average condition of three size classes (<160 mm, <210 mm, and >210 mm fork length) of juvenile Pacific ocean perch ( Sebastes alutus) collected with a bottom trawl at the north (N) and south (S) Samalga Island sites in August and at the N site in June. Condition is shown three ways: (A) log-transformed length-wet-weight residuals; (B) log-transformed length-dry- weight residuals; and (C) whole body energy content (calories per gram dry weight). Standard error bars are shown and asterisks indicate significant differences.

fish: age 1 and 2 (small), 3 (medium), and 4 and 5 years (large; D. H. Hanselman, Alaska Fisheries Science Center, personal communication). August sample sizes of small, medium, and large fish were 4, 4, and 43, respectively, at the north site, and 126, 93, and 67, respectively, at the south site. Only the large size class of juvenile POP was found in June at the north site (n = 34).

Juvenile POP condition

Generally, juvenile POP were in better condition at the north site than at the south site in August (Fig. 3). The linear regression of log wet weight as a function of log length was significant, as was the linear regression of log dry weight as a function of log length (P<0.001). There was no dif- ference in the dry weight expressed as a function of wet weight between the drying methods; there- fore, no correction factor was needed for drying technique. Both wet- and dry-weight residuals were higher at the north site for most size classes. Wet-weight residuals were significantly higher for both small and medium fish at the north site (P<0.05; Fig. 3). Dry-weight residuals were sig- nificantly higher for medium fish (P<0.001) and insignificantly higher for large fish (P= 0.686) at the north site (Fig. 3). Dry-weight residuals for small fish appeared to be lower for fish at the north site; however, the difference was not signifi- cant (P=0.156; Fig. 3). Because of small sample sizes of small and medium fish at the north site, variability in estimates were high and contributed to the opposing patterns of dry- and wet-weight residuals for small fish in the north. Large fish had similar wet- and dry-weight residuals at the two locations. Large fish sampled in June had significantly lower dry-weight residuals (P= 0.001) but similar wet-weight residuals (P=0.605) as those for large fish sampled in August at either site (Fig. 3).

Energy content as estimated with a calorimeter provided more precise estimates of fish condi- tion (with lower variability) than length-weight residuals. Oven-drying resulted in a slightly lower energetic content than freeze drying (2% difference in the means between the two meth- ods, SE = 0.002). A linear relationship (slope=1.31, intercept = -1363.86, r2 = 0.964) predicting the freeze-dried energetic content from the oven-dried energetic content was applied as a correction fac- tor to the energetic value of the remaining oven- dried fish. Energy content varied significantly between the sites for all size classes (P<0.006), but not between sampling times (June and Au- gust; P=0.178) at the north site. Energy content of all size classes of fish was significantly higher at the north site than at the south site in August (Fig. 3). Energy content of individual juvenile POP ranged from 3,463 to 5,569 cal/g dry weight. Small fish at the south

site had the lowest average energy content (4,618 cal/g dry weight), whereas, the small and medium fish at the north site had the highest average energy content (5,295 and 5,213 cal/g dry weight, respectively).

282

Fishery Bulletin 107(3)

Juvenile POP diet

Generally, the SCI was highest for small fish and lowest for large fish; large fish sampled in June at the north site had significantly fuller stomachs than large fish sampled in August at the north site (P<0.001; Fig. 4). The SCI was similar between sites for both small and medium fish (P=0.954 and 0.229, respectively). In August, large fish had significantly fuller stomachs at the south site than those at the north site (P=0.024; Fig. 4).

The proportion of POP with empty stomachs varied among sites and months (Fig. 4). In August, the pro- portion of empty stomachs was higher at the north site for both medium and large POP (0.33 and 0.32, respectively). Empty stomachs were not found in small

POP at the north site in August or in large POP at the north site in June (Fig. 4).

Large copepods (>2.5 mm) comprised the majority of juvenile POP diets for all size classes; however, larger prey items such as euphausiids were consumed by me- dium and large juveniles (Fig. 5). Small juvenile POP (sampled in August) consumed almost exclusively large copepods, as did the large POP sampled in June. Of the small and medium POP sampled at the north and south sites in August, there were no significant differences by numerical or weight proportions in the three main prey items consumed: large copepods, euphausiids, and larvaceans (P>0.05). The proportion (numerical and weight) of euphausiids consumed by large POP juve- niles was significantly higher at the south site (P<0.01).

Large POP juveniles at the north site consumed significantly more large copepods in June than in August (P<0.01).

Zooplankton

Zooplankton biomass, but not community com- position, was significantly different between the two sites in August (P=0.002). Average zooplankton biomass was three times higher at the north site than at the south site (Fig. 6). Zooplankton samples at both the north and south sites were numerically dominated by large copepods. Small copepods and hyperiid amphipods were also numerically important at both sites. There were no significant differ- ences in the proportions of large copepods, small copepods, or hyperiid amphipods between sites (P=0.109, 0.159, 0.365, respectively; Fig. 6). Other zooplankton components included euphau- siids, chaetognaths, Limacina pteropods, and larvaceans. Euphausiids were more numerous at the north site than at the south site, but this difference was not significant (P= 0.792).

Discussion

The comparison of juvenile POP in two areas of the Aleutian Islands revealed spatial differ- ences in the condition of fish of the same size class. Differences in fish condition have been attributed to food availability in past studies; for example, age-0 pollock with a relatively high index of condition and with high growth rates were found in areas of high prey abundance (Wilson et al., 2005). In the present study, the quantity of prey available, as indicated by the settled volume of zooplankton sampled in the water column, was very different between the sites. The ring net used in this study to sample zooplankton, however, did not sufficiently sample all juvenile POP prey; therefore, conclusions that can be based on these data are limited. In August, zooplankton biomass was high and

1 .6% -|

5 1 .4%

>

■O

O 1.2% -

° 1 .0% - 03 C/3

03 0.8% H

CO (/)

© 0.6% -

- 0.4% -

sz

o

« 0.2% -| o

' 0.0%

CO

Site: Month: Fork length:

A

N | S	N | S	N	N S
August	August	June	August
<160 mm	<210 mm		>210 mm

0.4 -|

0.3 -

0.2 -

0.1

0.0

Site:

Month

B

N S	N S	N	N | S
August	August	June	August
<160 mm	<210 mm		>210 mm

Figure 4

(A) Stomach content weight expressed as a percent of body weight (see SCI under heading “Juvenile POP diet” above), and (B) proportion of empty stomachs for three size classes of juvenile Pacific ocean perch (POP, Sebastes alutus) (<160 mm, <210 mm, and >210 mm fork length) at the north (N) and south (S) Samalga Island sites in August and at the N site in June, collected with a bottom trawl in the Aleutian Islands, Alaska. Standard error bars are shown for stomach fullness estimates. An asterisk indicates significant differences for that size class.

Boldt and Rooper: Abundance, condition, and diet of Sebastes alutus

283

A

Figure 5

Zooplankton prey consumed by three size classes of juvenile Pacific ocean perch ( Sebastes alutus) (<160 mm, <210 mm, and >210 mm fork length) collected with a bottom trawl at the north (N) and south (S) Samalga Island sites in August and at the north (N) site in June in the Aleutian Islands, Alaska. The average numerical (A) and weight (B) proportions of hyperiid amphipods, chaetognaths, Limacina ptero- pods, larvaceans, euphausiids, large copepods (>2.5 mm), and other prey (<5% of prey proportions) are shown. Other prey include small copepods (<2.5 mm), barnacle cyprids, crab zoeae, fish, fish eggs, insects, larval fish, invertebrate eggs, ostracods, polychaetes, shrimp, mysids, and jellyfish.

juvenile POP abundance was low in the north, where fish condition was highest. If the large zooplankton biomass at the north site indicates enhanced prey availability to juvenile POP, it may help explain the high POP condition observed at that site.

Juvenile POP stomachs sampled in June were more than twice as full as those sampled in August at the north site, indicating that POP are able to consume more than they appeared to consume in August. This

finding, along with differences in juvenile POP abun- dance and in zooplankton biomass between the two sample sites in August, may indicate that food limi- tation and competition contributed to the observed geographic differences in fish condition. In August, however, stomach fullness was similar at both sites for all size classes, indicating that fish were consum- ing similar amounts of food at both sites. Also, the proportion of empty stomachs tended to be higher at

284

Fishery Bulletin 107(3)

the north site where fish condition was highest. Zoo- plankton biomass and feeding conditions before our study likely contributed to the observed differences in fish condition.

In this study the types of prey consumed by juvenile POP were very similar between the two areas, and large calanoid copepods comprised the majority of ju- venile POP diets of all size classes examined. In fact, the types of prey consumed by juvenile POP varied more by size class of POP than by area. Medium and large juvenile POP consumed more larger prey, such as euphausiids, than the small juvenile POP. These findings are very similar to those found for juvenile POP in southeast Alaska (Carlson and Haight, 1976). We did not quantify juvenile POP prey to the species level; however, the type of large copepods (Euchaeta

B

Figure 6

(A) Average zooplankton biomass (mL/m3), and (B) numeri- cal proportion of main zooplankton taxa as sampled with a ring net at the north (N) and south (S) Samalga Island sites in August. Standard error bars are shown for zooplankton biomass and the asterisk indicates a significant difference. Main zooplankton taxa included hyperiid amphipods, small copepods (<2.5 mm) and large copepods (>2.5 mm). The “other” category comprises zooplankton taxa that individu- ally represented less than 5% of the numerical proportion of the zooplankton samples.

elongata, Calanus marshallae, Neocalanus cristatus, and Metridia sppj and euphausiids ( Thysanoessa ra- schii) in the zooplankton samples did not appear to differ between sites, indicating that the variety of prey species available to juvenile POP was similar between sites.

Water temperature and water column stratification are other factors that may affect fish condition. Bot- tom water temperatures were similar at both sites in August (5.4-5.6°C); however, the water column was more mixed at the north site and stratified at the south site. Water column stratification determines, in part, the amount of primary and, hence, secondary productivity by controlling nutrient flow from deeper waters. Previous studies have shown that the area north of Samalga Pass is an area of upwelling and high zooplankton biomass (Swift and Aagaard, 1976; Coyle 2005) and can be characterized as a more productive area than the south site. The higher production at the north site may lead to a higher zooplankton biomass, which we observed in this study, and higher zooplankton lipid stores and energy content, potentially benefitting predators such as juvenile POP.

In summary, we have shown that juvenile POP condition and abundance vary significantly be- tween areas, whereas juvenile POP diet varies by size class of this species. Juvenile POP condition was higher in the area with lower juvenile POP abundance. The differences in fish condition may be due to limitation in the quantity or quality of available prey. In order to delineate essential fish habitat for demersal marine fish species, therefore, one must consider not only the presence or absence of an organism and its benthic habitat, but also the important ecological features of the pelagic habitat.

Acknowledgments

We sincerely thank M. Auburn of Inverte Inc for examining zooplankton sample and stomach con- tents of juvenile POP. We also thank the following people for help in collection of samples: M. Zim- mermann, K. McKinney, K. Smith, and the captain and crew of FV Ocean Explorer. We also thank J. Hill, D. Beauchamp, and N. Overman for the calorimetry work, and M. Mazur for the helpful discussions. This manuscript was improved with reviews from M. Love, K. Aydin, L. Logerwell, M. Wilkins, A. Moles, and three anonymous reviewers. This project was funded jointly by the North Pacific Research Board (NPRB Publication no. 198) and the Essential Fish Habitat Program of the Alaska Fisheries Science Center. This publication was also partially funded by the Joint Institute for the Study of the Atmosphere and Ocean ( JISAO) under NOAA Cooperative Agreement No. NA17RJ1232, Contribu- tion no. 1628.

Boldt and Rooper: Abundance, condition, and diet of Sebastes alutus

285

Literature cited

Boldt, J. L, and L. J. Haldorson.

2004. Size and condition of wild and hatchery pink salmon juveniles in Prince William Sound, Alaska. Trans. Am. Fish. Soc. 133:173-184.

Brodeur, R. D.

2001. Habitat-specific distribution of Pacific ocean perch ( Sebastes alutus) in Pribilof Canyon, Bering Sea. Continent. Shelf Res. 21:207-224.

Carlson, H. R., and R. E. Haight.

1976. Juvenile life of Pacific ocean perch, Sebastes alutus, in coastal fjords of southeastern Alaska: their environ- ment, growth food habits, and schooling behavior. Trans. Am. Fish. Soc. 105:191-201.

Coyle, K. O.

2005. Zooplankton distribution, abundance and biomass relative to water masses in eastern and central Aleutian Island passes. Fish. Oceanogr. 14:77-92.

Hollowed, A. B., S. R. Hare, and W. S. Wooster.

2001. Pacific basin climate variability and patterns of northeast Pacific marine fish production. Progr. Oceanogr. 49:257-282.

Hollowed, A. B. and W. S. Wooster.

1992. Variability of winter ocean conditions and strong year classes of northeast Pacific groundfish. ICES Mar. Sci. Symp. 195:433-444.

La Mesa, G., P. Louisy, and M. Vacchi.

2002. Assessment of microhabitat preferences in juve- nile dusky grouper ( Epinephelus marginatus) by visual sampling. Mar. Biol. 140:175-185.

Neuman, M. J., and K. W. Able.

1998. Experimental evidence of sediment preference by early life history stages of windowpane ( Scophthalmus aquosus). J. Sea Res. 40:33-41.

Paul, A. J.

1997. The use of bioenergetic measurements to esti- mate prey consumption, nutritional status and ther- mal habitat requirements for marine organisms reared in the sea. Bull. Natl. Res. Inst. Aquaculture, suppl. 3:59-68.

Rooper, C. N. and J. L. Boldt.

2005. Distribution of juvenile Pacific ocean perch Sebastes alutus in the Aleutian Islands in relation to benthic habitat. Alaska Fishery Res. Bull. 11:102-112.

Rooper, C. N., J. L. Boldt and M. Zimmermann.

2007. An assessment of juvenile Pacific ocean perch (Sebastes alutus ) habitat use in a deepwater nursery. Estuar. Coast. Shelf Sci. 75:371-380.

Swift, J. H. and K. Aagaard.

1976. Upwelling near Samalga Pass. Limnol. Oceanogr. 21:399-408.

Wilson, M. T., A. L. Brown, and K. L. Mier.

2005. Geographic variation among age-0 walleye pollock (Theragra ehalcogramma ): evidence of mesoscale varia- tion in nursery quality? Fish. Bull. 103:207-218.

286

Modified sorting technique to mitigate

the collateral mortality of trawled school prawns

(Metapenaeus macleayi)

Matt K. Broadhurst (contact author)1 Russell B. Millar2 Craig P. Brand1 Sebastian S. Uhl matin'

Email address for contact author: mbroadhurst@nmsc.edu.au

1 NSW Department of Primary Industries Fisheries Conservation Technology Unit 2 Bay Drive

Coffs Harbour, New South Wales 2450, Australia

2 Department of Statistics The University of Auckland Princes St.

Auckland 1142, New Zealand

Abstract — The potential for changes to onboard handling practices in order to improve the fate of juvenile school prawns (Metapenaeus macleayi) dis- carded during trawling were inves- tigated in two Australian rivers (Clarence and Hunter) by comparing a purpose-built, water-filled sorting tray against a conventional dry tray across various conditions, including the range of typical delays before the start of sorting the catch (2 min vs. 15 min). Juvenile school prawns (n = 5760), caught during 32 and 16 deployments in each river, were caged and sacrificed at four times: immedi- ately (T0), and at 24 (T24), 72 (T72), and 120 (T120) hours after having been discarded. In both rivers, most mortalities occurred between T0 and T24 and, after adjusting for control deaths (<12%), were greatest for the 15-min conventional treatment (up to 41% at T120). Mixed-effects logistic models revealed that in addition to the sampling time, method of sorting, and delay in sorting, the weight of the catch, salinity, and percentage cloud cover were significant predic- tors of mortality. Although trawling caused some mortalities and compa- rable stress (measured as L-lactate) in all school prawns, use of the water tray lessened the negative impacts of some of the above factors across both the 2-min and 15-min delays in sorting so that the overall discard mortality was reduced by more than a third. When used in conjunction with selective trawls, widespread applica- tion of the water tray should help to improve the sustainability of trawling for school prawns.

Manuscript submitted 18 September 2008. Manuscript accepted 20 February 2009. Fish. Bull. 107:286-297 (2009).

The views and opinions expressed or implied in this article are those of the author and do not necessarily reflect the position of the National Marine Fisheries Service, NOAA.

Mitigating the collateral mortality from trawl fisheries is a complex issue that requires multifaceted strategies (Davis, 2002; Broadhurst et al., 2006). One option is to spatially and tempo- rally restrict fishing to avoid known large assemblages of nontarget organ- isms (termed “bycatch”) (Andrew and Pepperell, 1992). A broader approach involves physical modifications to gears to improve their selection of spe- cies and size of species. Such modi- fications are assumed to indirectly reduce mortality on the premise that the survival of escapees during fish- ing is generally much greater than those of organisms brought to the surface and discarded (Broadhurst et al., 2006). However, few (if any) modifications to trawls are 100% effec- tive and therefore, despite their use in many fisheries, there remains at least some unwanted bycatch (Andrew and Pepperell, 1992; Broadhurst, 2000). A remaining ancillary strategy that has been rarely applied, but which may help to address this problem, is to refine operational and postcapture handling techniques to improve the survival of discarded bycatch (e.g., Gamito and Cabral, 2003; Macbeth et al., 2006).

Similar to attempts in many of the world’s penaeid fisheries, attempts at resolving collateral mortality in the New South Wales river prawn-trawl

fishery have mostly focused on the first two strategies described above. From the early 1940s until 2003, this fishery comprised over 300 small (mostly <10-m) trawlers predominant- ly targeting either school ( Metapenae- us macleayi ) or eastern king (Penaeus plebejus ) prawns in five rivers and estuaries. In addition to the targeted catches, these trawlers have tradition- ally caught, and then discarded, large quantities of bycatch (estimated at up to 177 t/yr in some rivers and es- tuaries; Liggins and Kennelly, 1996; Liggins et al., 1996), often comprising juveniles of economically important species, including penaeids too small for sale (<approximately 15-17 mm carapace length [CL]). During the last 20 years, concerns over the mortality of these organisms have culminated in complete closures to fishing at some locations, and the development of, and legislation for, modifications to trawls, including bycatch reduction devices (BRDs) and square-mesh co- dends, for use throughout the remain- ing fleet (Broadhurst and Kennelly, 1996; Macbeth et al., 2007).

Effort in this fishery has now been reduced to 204 vessels distributed among three rivers; the Clarence (114 vessels), Hawkesbury (61) and Hunt- er (29). Although the modified gears used by the operators of these ves- sels are more selective than histori-

Broadhurst et at: Modified sorting technique to mitigate the collateral mortality of Metapenaeus macleayi

287

cal configurations, even under optimal conditions the relative reductions of many bycatch individuals are only between approximately 50% and 70% and therefore, at times, large numbers are still caught and discarded (Broadhurst and Kennelly, 1996). Recent work with trawlers in the Clarence River indicates that simply deploying trawls for shorter durations (30 rather than 60 min) and sorting catches in water can minimize the negative impacts to some of these discards (Uhlmann and Broadhurst, 2007; Broadhurst et al., 2008).

In particular, Broadhurst et al. (2008) described a purpose-built, onboard water-sorting system (termed a “water tray”) designed to facilitate the separation of prawns and fish, and then prawns into retained and discarded categories, while minimizing their ex- posure to air. This system was examined for its utility in reducing the mortality of fish after both immediate and delayed discarding from trawls deployed for the shortest commercially viable period (30 min). Although the mechanical interactions associated with trawling meant that the mortalities of many fish remained high, there were significant reductions in fatalities when the water tray was used during longer delays in starting sorting.

No work has been done to assess whether the water tray similarly reduces the mortality of discarded juve- nile prawns, although two relevant pilot studies support the application of this modification (Macbeth et al., 2006; Broadhurst and Uhlmann, 2007). Specifically, during four deployments at one location in the Clarence River, Macbeth et al. (2006) observed that the short- term (three days) mortality of juvenile school prawns was reduced from approximately 35% during conven- tional sorting to about 16%, simply by holding them in water-filled containers. However, irrespective of their handling, all surviving school prawns showed similar elevated stress responses (measured as L-lactate) over the monitoring period, which may have increased their susceptibility to other types of mortality (e.g., through infection or predation). By contrast, using comparable replication, Broadhurst and Uhlmann (2007) observed that regardless of their handling (including maximum and minimum gear deployments and subsequent air ex- posure), school prawns appeared resilient to both seine- and trawl-induced impacts, which manifested as total mortalities of <15%. The lack of impacts was further reflected by a return of elevated L-lactate concentrations immediately to baseline levels within 24 hours after the prawns had been discarded.

At least some of the observed discrepancies between the two studies above probably reflect their limited replication in space (one location) and time (one day of fishing). Other studies have demonstrated that a range of technical (e.g., gear design, deployment duration, and speed), biological (e.g., species, physiology, size, and catch volume and composition) and environmental (e.g., temperature, hypoxia, sea state, and light) factors can have complex interacting effects on the fate of dis- cards during trawling (Davis, 2002; Broadhurst et al., 2006). It seems appropriate, therefore, that during any

study that seeks to assess the utility of modifications to reduce collateral mortality, adequate information is collected on these factors across a range of commercial conditions. We sought to use this approach to assess the water tray for reducing the mortality of discarded school prawns in the Clarence and Hunter rivers.

Materials and methods

Trawlers and the water tray

Separate experiments were undertaken in the Clarence River (29°27'S, 153°09'E) between March and April 2007 and in the Hunter River (32°53'S, 151°45'E) between February and April 2008. A commercial prawn trawler (<14 m in length) rigged with standard twin trawls was used in the Clarence River and a commercial prawn trawler (<14 m) rigged with a single trawl was used in the Hunter River. All trawls were attached to square- mesh codends (27-mm mesh). The Hunter River trawler was equipped with a large horizontal canvas awning that covered most of the back deck (and catch sorting area). The Clarence River trawler had a much smaller, obliquely orientated, and less effective cover made from loose-weave polyvinyl chloride (PVC).

Before starting the experiments, the conventional sorting trays were removed from both vessels and re- placed with a modified design (comparable in price to conventional trays), termed the “water tray” which was scaled to fit, and measured 1800x1500x300 mm (Clar- ence River trawler) and 1200x1190x300 mm (Hunter River trawler) (Fig. 1 and Broadhurst et al., 2008). Irrespective of overall dimensions, the design of the water tray remained similar and included a V-shaped bottom, designed to concentrate the catch towards its center and below a vertically orientated, variable open- ing (Fig. 1). A pump provided flow-through water from the river at 30 L/min to the water tray through a 50- mm diameter inlet located in one side. For the Clarence River trawler, a metal screen (50-mm mesh size) was positioned horizontally above the bottom of the water tray to allow school prawns to filter through onto the V-shaped bottom, separating them from any larger fish (Fig. 1). This metal screen was removed from the water tray that was used on the Hunter River trawler. Dur- ing the sorting process in each water tray, nonpenaeid bycatch was either removed by hand, or directed out of the variable opening along with water and collected in a 35-L container. Once the bycatch was removed, school prawns were washed out with the remaining water and passed over a riddler (made from hexagonal mesh; Fig. 1), which separated unwanted and retained individuals into two 35-L containers (see also Macbeth et al., 2006 for details).

Monitoring sites

Two 3000-L polyethylene holding tanks were positioned at one location on the banks of each river. All tanks

288

Fishery Bulletin 107(3)

Mesh screen

4 4

1800 mm

Figure 1

Schematic diagram of the water tray and mechanism by which school prawns ( Metapenaeus macleayi) were riddled into discarded and retained categories in the Clarence and Hunter rivers during 2007 and 2008.

were supplied with local flow-through seawater (at a maximum rate of 63 L/min) and aerated by stone diffus- ers. At two sites (termed “monitoring sites”) within the limits of trawling in each river, several 10-mm diameter ropes (50 m in length) were attached horizontally at a level corresponding with the average low tide to 2.5 m stanchions or existing pylons (fixed to the river bed). The rope configurations were designed to secure up to 90 portable cylindrical cages (0.3-m diameter x 0.4-m depth), each made from a modified 35-L bucket and comprising one top and three lateral openings that were covered by 6-mm PVC mesh (each <230 cm2) and a solid base filled with locally collected sediment to a depth of about 6 cm (see also Broadhurst and Uhlmann, 2007 for details). Clips were attached to the tops of each cage so that they could be suspended along the 10-mm diameter rope. The cages were designed so that two could fit into in 75-L aerated water-filled PVC containers located on a dory, enabling them to be transported between the fishing and monitoring sites.

Experimental design

In both rivers, between seven and five days before start- ing each experiment, approximately 1000 school prawns

were collected in <5-min trawls rigged with a fine- meshed knotless polyamide, 10-mm mesh codend towed slowly in shallow water. At the end of each deployment, the codend was emptied into a water-filled container. Live and active juvenile school prawns were quickly removed, placed in tanks supplied with oxygen and transported to the two holding tanks on the river bank. The captive school prawns were fed chopped pilchard ( Sardinops neopilch ardus) at a rate of 5% biomass/24 hr and left to recover for at least five days, after which surviving, intact individuals were used as controls in the experiments described below.

Four treatment groups associated with trawling and discarding and one control group were examined in each river. The four treatments were chosen to repre- sent the temporal limits of the conventional (i.e., dry tray) and modified (i.e., water tray) onboard handling of catches. All treatments comprised a 30-min deploy- ment of the trawl, followed by the sorting of unwanted school prawns that was started after one of the follow- ing treatments: 1) a 2-min delay in a dry tray (termed the “2-min conventional-tray” treatment); 2) a 2-min delay in the water tray (“2-min water-tray” treatment); 3) a 15-min delay in the dry tray (“15-min conventional- tray” treatment); or 4) a 15-min delay in the water tray

Broadhurst et al.: Modified sorting technique to mitigate the collateral mortality of Metapenaeus madeayi

289

(“15-min water-tray” treatment). The conventional-tray treatments involved leaving the water tray empty of wa- ter and removing the mesh-separating screen. The 35-L container for the riddled, unwanted school prawns was filled with water during the water-tray treatments but was left dry for the conventional-tray treatments. Two replicates of each treatment were completed on each of four days of fishing in the Clarence River and two days of fishing in the Hunter River.

For each treatment, immediately after the unwanted school prawns were separated by the riddler into either a dry (conventional-tray treatments) or water-filled (water-tray treatments) 35-L container (Fig. 1), the transport dory was positioned alongside the trawler and 120 individuals were randomly selected and “dis- carded” into groups of 10 into 12 cages submerged in the water-filled 75-L PVC containers. Three of these cages were sampled immediately (termed T0 — see be- low), before the remaining nine were transported to the closest monitoring site and attached to the 10-mm rope within 20 min, and without exposing any of the school prawns to air. During transfer, all caged school prawns were held in aerated water and the water quality was checked with an Horiba U10 meter (Horiba, Irvine, CA) and maintained (via exchange) at the same levels as that recorded at the surface of the deployment site.

Within six hours of the first treatment deployment, 240 school prawns were removed from the holding tanks by scoop nets and placed in groups of 10 into 24 cages submerged in the water-filled 75-L PVC con- tainers onboard the dory (i.e., the same number of prawns as that for the two replicate deployments of each treatment). Six cages were sampled immediately (T0 — see below), while the remaining 18 cages were transferred to the same monitoring sites as those hous- ing the treatment school prawns and used as balanced controls in each experiment. For each replicate of the control and treatment groups on each day of fishing, school prawns in three of the cages were sacrificed and sampled at three times: 24 (T24), 72 (T72), and 120 ( T 1 20 1 hours after T0.

Data collected

The following data were collected during each deploy- ment in both experiments: towing speed (m/s); fishing depth (m); duration of air exposure of the catch (min); air temperature (°C); percent cloud cover; and the numbers and weights (kg) of retained and discarded catches. The Horiba U10 was used to record replicate measures of water temperature (°C), dissolved oxygen (mg/L), and salinity (psu) in the water tray. An EC 350 Greenspan Smart Sensor (Tyco Environmental Systems, Lakewood, NJ) was attached to the trawl to provide replicate mea- sures of the conductivity (pS/cm) and the temperature of the river once each minute during each deployment (except on the first day of fishing in the Clarence River). An algorithm was used to convert the normalized con- ductivity readings to salinities. Means of these read- ings were used to provide a datum for the salinity and

for the temperature at the surface and bottom for each deployment.

At each sampling time, the three cages from the two replicates of the control and each of the four treatment groups from each day of fishing were removed from the monitoring site. The sediments from the cages were emptied onto a tray. The numbers of alive and dead school prawns were recorded, and, if possible, they were measured to the nearest 1-mm CL. During the Hunter River experiment, the binary molt status (hard or soft) of school prawns was also noted by the rigidity of their carapace. This was not done during the Clarence River experiment because all school prawns were clearly in- termolts (i.e., hard). For one randomly selected fishing day during the Clarence River experiment, two live school prawns were immediately selected from two of the cages for each replicate of the treatment and con- trol groups at the T0, T72, and T120 sampling times and secured in aluminum satchels before being placed in liquid nitrogen. These frozen samples were later ana- lyzed for j -lactate (pmol/g) to provide an indication of the severity of anaerobic stress and subsequent recov- ery, by following the methods described by Broadhurst et al. (2002).

Statistical analyses

The data collected from each experiment were analyzed separately. Appropriate environmental, technical, and biological data collected from the gear deployments were treated as either fixed, categorical, or continuous variables. Where there was sufficient replication, these variables were considered with the fixed factors of pri- mary interest: “method of sorting” (conventional vs. water tray); delay in sorting” (2 min vs. 15 min); and sampling time (T0, T24, T72 or T120); and the random factors of fishing days, deployments, and cages in mixed- effects logistic models were fitted to the dichotomous status (dead vs. alive) of the trawled-and-discarded caged school prawns.

For each experiment, three separate models were used for trawled-and-discarded school prawns and com- prised data from 1) all deployments, 2) the water-tray deployments, and 3) the conventional-tray deployments only. A fourth model was fitted to control, caged school prawns, and was restricted to the above random factors and the fixed effect of sampling time. All models were fitted by using the lmer function in the R statistical software (The R Foundation for Statistical Computing, Vienna, Austria). A stepwise variable search algorithm was employed with the most parsimonious fit based on the lowest Akaike’s information criterion. The total mortalities of school prawns subjected to the four han- dling treatments of interest were eventually adjusted for deaths to the controls.

A balanced four-factor analysis of variance (ANOVA) was used to examine differences among treatment and control groups for the levels of L-lactate (pmol/g) in school prawns from one fishing day in the Clarence River experiment. The model used the following fac-

290

Fishery Bulletin 107(3)

Table 1

Summary of mean (±standard deviation) key technical, environmental, and biological variables collected during the deployments of trawls to assess the discard mortality of school prawns ( Metapenaeus macleayi) in the Clarence and Hunter rivers during 2007 and 2008. The number of replicate deployments is in parenthesis.

Variable	Clarence River	Hunter River
Technical
Deployment
Speed (m/s)	1.4 ±0.2 (32)	1.3 ±0.1 (16)
Depth (m)	7.3 ±1.8 (32)	6.3 ±1.7 (16)
Environmental
River temperature (°C)
Surface	23.9 ±1.1 (32)	22.5 ±0.8(16)
Bottom	23.8 ±1.1 (24)	22.8 ±0.3 (16)
River salinity (psu)
Surface	3.7 ±2.3 (32)	4.3 ±1.8 (16)
Bottom	5.4 ±1.9 (24)	10.2 ±5.8(16)
Cloud cover (%)	42.9 ±38.8 (32)	3.8 ±6.2 (16)
Air temperature (°C)	22.7 ±3.3 (32)	22.6 ±4.5(16)
Water tray
Dissolved oxygen (mg/L)	5.8 ±1.0 (16)	3.8 ±0.8 (8)
Temperature (°C)	24.4 ±1.6 (16)	22.0 ±1.6(8)
Salinity (psu)	2.5 ±1.5 (16)	4.6 ±2.3 (8)
Catch air exposure (min)
2-min conventional tray	13.8 ±5.1 (8)	6.3 ±1.9(4)
15-min conventional tray	23.5 ±6.0 (8)	20.0 ±2.7 (4)
2-min water tray	2.0 ±1.0 (8)	1.0 ±0.0 (4)
15-min water tray	1.6 ±0.7 (8)	1.3 ±0.5 (4)
Biological
Weight of catch (kg)
Total	11.8 ±7.4 (32)	19.4 ±16.1 (16)
School prawns	9.7 ±6.6 (32)	18.0 ±15.7 (16)
Carapace length (mm) of trawled-and-monitored school prawns:	15.3 ±2.6 (32)	15.1 ±3.8(16)

tors: treatment of prawns (four trawling and one control group); sample times (T0, T24, T120 and T120); deploy- ments (n = 2); and cages (n= 3). The factors “sampling time” and “treatment of prawns” were considered or- thogonal to each other and fixed. Deployments were random and nested in the treatment of prawns, whereas cages were nested in all factors. Data were transformed as required and tested for homogeneity of variances by using Cochran’s test. Any missing replicates were replaced with the cell mean and the residual degrees of freedom were adjusted accordingly. Significant .F-ratios of interest were examined with Student-Newman-Keuls multiple comparisons of means tests.

Results

School prawns represented more than 82% of the total catch from the Clarence River and 93% of the total catch from the Hunter River, and although their mean catches per 30-min deployment were quite variable,

were still within the ranges typically experienced in the fishery (Table 1). Bycatches were comparatively low in both experiments and, in addition to juvenile school prawns (approximately 9% of the total school prawn catch in each river), mostly comprised fish <200 mm total length, such as yellowfin bream (Acanthopagrus australis ), southern herring ( Herklotsichthys castel- naui), silver biddy (Gerres subfasciatus ), and narrow- banded sole ( Aseraggodes macleayanus).

Many of the technical and environmental variables were comparable between experiments and except for salinity and cloud cover, remained fairly consistent among replicate deployments (Table 1). In both rivers, there was evidence of a salinity gradient between the surface and bottom (Table 1). Catches were subjected to similar mean durations of air exposure during the 15-min conventional-tray (>20 min) and all water- tray (<2 min) treatments during both experiments. By contrast, and although highly variable, the mean duration of air exposure for catches handled during the 2-min conventional-tray treatment in the Clarence

Broadhurst et al.: Modified sorting technique to mitigate the collateral mortality of Metapenaeus macleayi

291

River (approximately 14 minutes) was greater than that in the Hunter River (approximately 6 minutes; Table 1).

The first mixed-effects model that was applied to all of the data for the trawled-and-discarded school prawns in both experiments included the fixed factors of sorting method (conventional vs. water tray), delay in sorting (2 min- utes vs. 15 minutes), and their inter- action, sample time, and the weight of total catch, and salinity at the bottom of the river during fishing. The sec- ond and third models were applied to the water-tray and conventional-tray deployments. Both models included sorting method (conventional vs. wa- ter tray), delay in sorting (2 minutes vs. 15 minutes), and their interaction, sampling time, and the weight of to- tal catch. Water tray salinity and dis- solved oxygen were also included in the second model, and air temperature and cloud cover were used in the third model. The fourth model was applied to the control data with sampling time as the only the fixed effect. The stage of molt was not included in any of the models for the Hunter River data because it was not possible to quan- tify the condition of all deceased in- dividuals. In any case, only 13.0% of all school prawns sampled at T0 had soft exoskeletons. Similarly, it was not possible to measure the CL of all dead school prawns at T24, T72, and T120, and therefore size could not be consid- ered in the analyses.

Clarence River experiment

A total of 4800 school prawns were caged during the experiment, of which 240 individuals were in each of the con- trol and four treatment groups at each of the four sam- pling times. Seventy school prawns escaped (as a result of faulty lids on their cages) before being sampled; they escaped from one cage for the 15-min conventional-tray treatment at each of T24 and T72, two cages for the 15- min conventional-tray treatment at T120, one cage for the 2-min water-tray treatment at T24, and two cages of controls at T72. Up to 12.0% of the control school prawns were dead at each sampling time (attributed to handling during transfer, being caged, or natural causes, Fig. 2A), providing adjusted temporal mortalities of up to 41.4% and 18.2% for the 15-min conventional and water-tray treatments, respectively (Table 2).

Irrespective of the four mixed-effects models fitted to the various data sets, or the treatment of school prawns, there was a strong significant impact of sampling time

on mortality that was largely attributable to the death of most individuals during their first 24 hours of cag- ing, after which the rate of attrition stabilized (Tables 2 and 3 , Fig. 2A , PcO.Ol). All three analyses of the trawled-and-discarded school prawns also showed a sig- nificant impact of the delay in the start of sorting, with an overall predicted (and unadjusted) mean ±standard error (SE) of 31.6 ±2.4% after 15 min, compared to only 21.2 ±1.9% after 2 min (Table 2, P<0.05).

In addition to the main effects of delay in sorting and sampling time, sorting method had a significant impact across all deployments, and there were consis- tently greater mortalities to those individuals discarded after sorting in the conventional tray (predicted unad- justed mean of 33.5 ±2.4%) than in the water tray (19.3 ±1.8%), and especially after a 15-min delay (predicted

292

Fishery Bulletin 107(3)

unadjusted mean ±SE of up to 53.4 ±6.5%; Tables 2 and 3, Fig. 2A, P<0.05). This clear trend in deaths precluded any interaction between sorting method and delay, although these means are presented in Fig. 2A for ease of interpretation (Table 3, P>0.1). The first model also detected a significant negative relationship between mortality and salinity at the bottom of the

Table 2

Percentage of total mortalities of trawled-and-discarded school prawns (Metapenaeus macleayi) adjusted for deaths to the controls for the sorting treatments of interest (2- min and 15-min delays in the conventional and water trays) at the four sampling times (immediately [T0], and after 24 hr [T24], 72 hr [T72], and 120 hr [T120]) in the Clarence and Hunter rivers during 2007 and 2008.

Conventional tray Water tray

2-min	15-min	2-min	15-min
delay	delay	delay	delay

Clarence River
T0	3.8	20.7	0.0	5.2
t24	21.4	37.0	15.7	16.6
T72	25.8	40.0	15.5	18.2
T120	22.8	41.4	6.3	17.8
Hunter River
T0	5.7	15.7	0.0	3.0
T'24	29.8	29.0	13.6	18.1
T72	26.4	35.7	20.2	21.5
Tl20	20.6	34.8	18.6	8.9

river (Table 3, P<0.01). The same significant negative relationship with mortality was observed for salinity in the water tray in the second model (Table 3, P<0.01). The third model identified total catch weight as having a significant positive relationship with the mortality of conventionally handled school prawns, whereas cloud cover had a negative relationship (Table 3, P<0.05).

ANOVA returned significant P-ratios for the treat- ment of prawns and sampling times for the levels of L-lactate in surviving school prawns from one randomly selected fishing day (Table 4 , PcO.Ol). There was no interaction between these factors (P>0.05), but the cor- responding means are presented for clarity (Table 4, Fig. 2B). Student-Newman-Keuls tests revealed that the overall mean ±SE concentration of L-lactate in control school prawns (4.63 ±0.76 pmol/g) was significantly low- er than all other treatments; which remained similar at between 6.77 ±1.28 and 8.40 ±1.21 pmol/g (P<0.05). Ir- respective of the treatment of school prawns, all prawns had significantly greater concentrations of L-lactate at T0 (13.49 ±0.81 pmol/g) than at T72 ( 3.48 ±0.28 pmol/g) and T120 ( 3.78 ±0.27 pmol/g) (Fig. 2B, P<0.05).

Hunter River experiment

A total of 2400 school prawns were caged across the con- trol and four treatment groups; of which 10 (in one cage from the 15-min conventional-tray treatment) escaped prior to their designated sampling time (T120). Similar to the Clarence River experiment, control deaths ranged between predicted means of 0.0% and 11.7%, providing adjusted total mortalities of up to 35.7% and 21.5% for the 15-min conventional- and water-tray treatments, respectively (Table 2, Fig. 3).

Table 3

Summary of variables tested in mixed-effects logistic models for their independence of the mortality of trawled-and-discarded school prawns ( Metapenaeus macleayi) in the Clarence and Hunter rivers during 2007 and 2008. Four separate models were applied: the first to all of the available data for trawled-and-discarded individuals (All); the second and third to only those dis- carded from the water tray (WT) and conventional tray (CT) treatments, respectively; and the fourth to the data for the controls (C). O P>0.1; • P<0.1; *P<0.05; **P<0.01; — , term not considered in the model.

		Clarence River			Hunter River
Variable	All	WT	CT	C	All	WT	CT	C
Sampling time	**	**	**	**	**	**	**	**
Sorting method (M)	**	-	-	-	**	-	-	-
Sorting delay (S)	**	*	**	-	O	O	**	-
MxS	O	-	-	-	O	-	-	-
Total weight of catch	«	O	**	-	**	**	0	-
Salinity bottom	**		O		O	O	O
surface (water tray)	-	**	-	-	-	O	-	-
Dissolved oxygen (water tray)	-	O	-	-	-	O	-	-
Air temperature	-	-	O	-	-	-	O	-
Cloud cover	-	-	*	-	—	"	O	—

Broadhurst et al.: Modified sorting technique to mitigate the collateral mortality of Metapenaeus macleayi

293

Figure 3

Differences in mean (± standard error) predicted percent mortality of school prawns ( Metapenaeus macleayi ) between the onboard sorting treat- ments and the controls for each of the sampling times in the Hunter River during 2008.

As with the Clarence River analyses, there was a significant effect of sam- pling time detected in all four mixed- effects models that was largely due to proportionally more deaths to school prawns during the first 24 hours, ir- respective of their treatment (Table 3,

Fig. 3, P<0.01). The method of sorting was also significant in the first model applied across all treatment deploy- ments, with relatively greater deaths after discarding from the conventional tray (overall unadjusted predicted mean ±SE of 29.3 ±2.0%), than from the wa- ter tray (17.6 ±1.6%) (Table 3, Fig. 3,

PcO.Ol). Sorting delay had no impact on the mortality of school prawns dis- carded across all deployments, or from the water tray, but was significant for those that were conventionally sorted (mortalities of 25.8 ±2.5% for the 2- min delay, and 32.9 ±2.8% for the 15- min delay; Table 3, P<0.01).

The only remaining significant main effect in any of the models was the to- tal weight of catch, identified as having a positive relationship with mortality across all deploy- ments, and those restricted to sorting in the water tray (Table 3, PcO.Ol). For the water-tray deployments, indi- viduals caught during the largest catch weights (47 kg) were more than 2.5 times as likely to be dead at each sampling time than those from the smallest catches (4 kg, Fig. 4). For both the T72 and T120 sampling times, the absolute probabilities of mortality during the larg- est and smallest catch weights were approximately 43% vs. 16% (Fig. 4).

Discussion

The mortalities of school prawns after being trawled, conventionally discarded, and adjusted for control fatali- ties were consistent between experiments and encom- passed the range of earlier estimates by Macbeth et al. (2006). Further, the unadjusted mortalities were comparable to those recorded for several other similarly treated decapods monitored without controls, including caridians (1-30%, Wassenberg and Hill, 1989; Cabral et al., 2002), brachyurans (0-50%, Hill and Wassenberg, 1990; Wassenberg and Hill, 1993; Kaiser and Spencer, 1995) and anomurans (0-19%, Kaiser and Spencer, 1995). These rates of death are considerably lower than those typically observed for many trawled-and-discarded fish and mollusks and further support the resilience of school prawns, and crustaceans in general, for with- standing a range of trawl-induced impacts (Broadhurst et al., 2006).

Irrespective of apparent broad phyla-specific differ- ences among collateral trawl mortalities, as is the case for several locally caught fish (Broadhurst et al., 2008),

Table 4 Summary of model terms, F-ratios, and degrees of free- dom (df) for ANOVA used to investigate L-lactate among trawled-and-discarded (2- and 15-min conventional- and water-tray treatments) and control school prawns (Metap- enaeus macleayi) in the Clarence River during one day of fishing in 2007. Data were ln(x+l) transformed. Three replicates were missing, and therefore the cell means were used and the df was adjusted accordingly. **P<0.01.
Variable	F- ratio	df
Treatment of prawns	14.09**	4, 5
Deployments (treatment of prawns)	0.58	5, 30
Sampling times	93.41**	2, 10
Treatment of prawns x sampling times	0.73	8, 10
Sampling times x deployment (treatment of prawns)	1.55	10, 30
Cages (treatment of prawns x sampling times x deployments)	0.95	30, 57

use of the water tray significantly reduced the short- term mortality of school prawns in both experiments. The extent of these reductions can be explained by at- tempting to partition mortality, along with the various significant predictors, into those fatalities caused 1) by the trawling process, and 2) after onboard handling.

294

Fishery Bulletin 107(3)

When they initially contact the anterior sections of a trawl, prawns and other crustaceans with extended abdomens (e.g., Norway lobster Nephrops norvegicus) typically respond by contracting their tail muscle ven- trally, effectively propelling themselves backwards into the top netting panels (Watson, 1976; Newland and Chapman, 1989). This behavior may be repeated several times, until an individual becomes fatigued, after which they often attempt to orientate towards the seabed using their swimmerets (Watson, 1989). Such activity is ineffective against the speed of the trawl, and therefore prawns are quickly forced against the meshes into the posterior trawl body and directed into the codend where they accumulate along with the rest of the catch.

The physiological responses supporting the above activity include anaerobic respiration and the rapid depletion of arginine phosphate in the tail muscle (On- nen and Zebe, 1983; Paterson et al., 1995). An end product of this exertion is lactic acid, which is removed during aerobic metabolism (Head and Balwin, 1986). In the present study, the concentrations of L-lactate in live school prawns immediately sampled (i.e., at T0) af- ter being discarded from the various treatments in the Clarence River were elevated to mean levels between 14.2 ±2.0 and 15.6 ±1.5 pmol/g, that were greater than those previously observed for this species after exercise (typically <12 pmol/g), indicating that these individu- als had been heavily exercising. Although some of the observed lactate accumulation could be attributed to

onboard handling and associated anoxia (Hill et al., 1991), especially during the conventional procedures, the similar rate of accumulation across all treatments supports a strong, uniform, negative impact of the trawling process.

For some individuals, the physiological damage de- scribed above may have been sufficient to result in their immediate death, while for others the cumulative impacts of significant covariates, such as the weight of catch and salinity, would have contributed toward their more protracted (over 24 hours) trawl-related mortali- ties. In particular, as the catch accumulated, at least some school prawns probably sustained fatal injuries, including wounding and blood loss, due to pressure and abrasion. Also, the ongoing stimuli associated with repetitive contact among conspecifics and other organ- isms may have triggered additional bursts of anaerobic exercise, and further compromised their physiological condition. These density-dependant effects were more obvious in the Hunter than in the Clarence River, prob- ably reflecting the considerably greater mean size of catch (19.4 kg [Hunter River]; 11.8 kg [Clarence Riv- er]), but also perhaps the slightly smaller mean size of school prawns (Table 1) and the presence of some soft individuals (i.e., 13% at T0). Both of these latter fac- tors have previously been demonstrated to increase the vulnerability of organisms to the impacts associated with discarding (Broadhurst et al., 2006).

Salinity also appeared to contribute towards mor- tality during trawling in the Clarence River. As with

Broadhurst et al.: Modified sorting technique to mitigate the collateral mortality of Metapenaeus macleayi

295

other penaeids (e.g., western king prawns [ Penaeus lati- sulcatus\ [Sang and Fotedar, 2004] and fleshy prawns [P. chinensis ] [Chen et al., 1995]), Maguire and Allan (1985) observed that although juvenile school prawns tolerate a range of salinities (from 1 to 30 psu), the mortality of captive individuals (in grow-out ponds) was negatively associated with salinities between 10 and 30 psu. On average, the salinities observed in the Clarence River were much lower than those of the Hunter River (5.4 vs. 10.2 psu) and possibly below the optimal range for osmoregulation. Although not necessarily fatal in the absence of other stressors, low salinities would require school prawns to maintain a comparatively greater metabolic rate to achieve osmotic balance, thereby increasing their susceptibility to other trawl-related impacts. Further, an abrupt reduction to even lower salinities during the retrieval of the trawl to the surface (as a consequence of the observed halocline) would require some readjustment of osmotic concentration to regulate tissue water. A similar transi- tion through haloclines has been identified as a factor contributing towards mortality in other species, includ- ing Norway lobster (Harris and Ulmestrand, 2004), and probably had a cumulative impact on the stress, and ultimately mortality, of some school prawns.

It is difficult to accurately quantify the cumulative impact of all trawl-related stressors on total mortality, especially since the death of some control school prawns indicates the potential for natural mortality (which was assumed to be constant across all treatments). However, after monitoring the fate of individuals collected imme- diately after the codend was emptied (individuals that had minimal air exposure before being sorted), Macbeth et al. (2006) estimated a short-term (over three days) mortality of 16% directly attributable to 60-min trawls, which was only slightly greater than that determined for individuals escaping through codend meshes during trawling (11%, Broadhurst et al., 2002). The results from the present study support these estimates, with an adjusted, protracted mortality in the 2-min water tray (arguably the mildest treatment) of less than 21% for both rivers.

Assuming comparable trawl-induced mortalities across treatments, the remaining differences in fatali- ties can be attributed to the use of the water tray for minimizing some of the negative impacts associated with onboard handling, and especially with air expo- sure. Most likely, by facilitating aerobic respiration, the water tray would have allowed some school prawns to recover and restore argine phosphate levels and acid-base regulation (Taylor and Spicer, 1988), which probably helped to limit further physiological damage and mortality.

In addition to limiting air exposure, the water tray maintained temperature homeostasis. Although there was no significant effect of air temperature in the mod- els applied to the conventional-tray treatments in either experiment, there was a significant negative relation- ship between cloud cover and mortality in the Clarence River (P<0.05). This association probably reflects the

greater convection, heating, and subsequent desiccation of school prawns in direct sunlight on the dry tray. Gamito and Cabral (2003) observed similar effects of heating on the mortality of brown shrimp (Crangon crangon) and suggested that this could be reduced by using light-colored sorting containers and avoiding trawling during the hottest time of the day. Sorting in the water tray is probably a more effective alternative in New South Wales, although the lack of any impacts of cloud cover in the Hunter River, combined with the similar range of temperatures between the two rivers also illustrates the utility of shading the conventional sorting tray with an appropriate cover.

The only obvious limiting factor of the water tray was its size for the trawler working in the Hunter River. Vessels in the Hunter River typically catch fewer school prawns than those in the Clarence River, and therefore a smaller water tray was used in the Hunter River . It is possible that, in addition to the trawling- related impacts discussed above, large catches in the sorting tray on the Hunter River trawler contributed towards mortality as a consequence of their greater bio- logical load. Although there was no significant impact of dissolved oxygen on mortality in the water tray, the mean dissolved oxygen recorded during the Clarence River deployments was higher than that in the Hunter (5.8 mg/L vs. 3.8 mg/L). Further, during one catch of 47 kg in the Hunter River, the dissolved oxygen in the water tray after 15 minutes of sorting was 2.4 mg/L. The potential for any negative effects associated with low dissolved oxygen could be simply reduced by in- creasing the water exchange or volume of the water tray, or both.

Although the results from this study indicate a significant reduction in discard mortality associated with using the water tray, it is important to remember that the discarded school prawns were protected in cages and therefore other collateral mortalities were not quantified. The levels of L-lactate at T0 indicated that alive, discarded school prawns were fatigued and, during conventional fishing, these individuals could be more susceptible to predation during their descent to the bottom (Lancaster and Frid, 2002). Further, because of the temporal increase in mortality, some school prawns may have maintained their vulnerability, particularly during the first 24 hours after having been discarded. The potential for these effects could be miti- gated by subtle modifications to the water tray. In par- ticular, because low (e.g., <15°C) water temperatures have been demonstrated to reduce metabolic activity in penaeids (Paterson, 1993), cooling the water tray may reduce some of the ancillary stressors identified above and help school prawns to recover more quickly. The concomitant use of a covered guiding panel that directs the discarded school prawns into the water behind the trawler could reduce predation.

Notwithstanding the need for some refinements, it is clear that using the water tray would eliminate most of the short-term mortalities associated with onboard handling, which would translate to a total reduction

296

Fishery Bulletin 107(3)

in discard mortality of school prawns of more than a third. When combined with other selective mechanisms, such as square-mesh codends that reduce the catches of school prawns of nontarget sizes, the water tray should contribute towards the sustainability of trawling in New South Wales rivers.

Acknowledgments

This work was funded by the New South Wales Depart- ment of Primary Industries and the Australian Fish- eries Research and Development Corporation (Grant no. 2005/056) and performed according to New South Wales Department of Primary Industries animal care and ethics protocols. Thanks are extended to the Clarence and Hunter river commercial fishing crews for their ongoing support, and to P. Butcher, K. Hall, S. McGrath and especially B. Paterson for advice and assistance.

Literature cited

Andrew, N. L., and J. G. Pepperell.

1992. The by-catch of shrimp trawl fisheries. Oceanogr. Mar. Biol. Annu. Rev. 30:527-565.

Broadhurst, M. K.

2000. Modifications to reduce bycatch in prawn trawls: A review and framework for development. Rev. Fish Biol. Fish. 10:27-60.

Broadhurst, M. K., D. T. Barker, B. D. Paterson, and S. J.

Kennedy.

2002. Fate of juvenile school prawns, Metapenaeus macleayi after simulated capture and escape from trawls. Mar. Freshw. Res. 53:1189-1196.

Broadhurst, M. K., and S. J. Kennedy.

1996. Rigid and flexible separator-panels in trawls that reduce the by-catch of small fish in the Clarence River prawn-trawl fishery, Australia. Mar. Freshw. Res. 47:991-998.

Broadhurst, M. K., P. Suuronen, and A. Hulme.

2006. Estimating collateral mortality from towed fishing gear. Fish Fish. 7:180-218.

Broadhurst, M. K., and S. S. Uhlmann.

2007. Short-term stress and mortality of juvenile school prawns, Metapenaeus macleayi, discarded from seines and trawls. Fish. Manag. Ecol. 14:353-363.

Broadhurst, M. K., S. S. Uhlmann, and R. B. Millar.

2008. Reducing discard mortality in an estuarine trawl fishery. J. Exp. Mar. Biol. Ecol. 364: 54-61.

Cabral, H. N., C. M. Teixeira, R. Gamito, and M. J. Costa.

2002. Importance of discards of a beam trawl fishery as input of organic matter into nursery areas within the Tagus estuary. Hydrobiologia 475/476:449-455.

Chen, J-C., M-N. Lin, Y-Y. Ting, and J-N. Lin.

1995. Survival, haemolymph osmolality and tissue water of Penaeus chinensis juveniles acclimated to different salinity and temperature levels. Comp. Biochem. Physiol. 110A(3):253-258.

Davis, M. W.

2002. Key principles for understanding fish bycatch discard mortality. Can. J. Fish. Aquat. Sci. 59:1834- 1843.

Gamito, R., and H. Cabral.

2003. Mortality of brown-shrimp discards from the beam trawl fishery in the Tagus estuary, Portugal. Fish. Res. 63:423-427.

Harris, R. R., and M. Ulmestrand.

2004. Discarding Norway lobster (Nephrops norvegicus L.) through low salinity layers — mortality and damage seen in simulation experiments. ICES J. Mar. Sci. 61:127-139.

Head, G., and J. Baldwin.

1986. Energy metabolism and the fate of lactate during recovery from exercise in the Australian freshwater crayfish Cherax destructor. Aust. J. Mar. Freshw. Res. 37:641-646.

Hill, A. D., A. C. Taylor, and R. H. C. Strang.

1991. Physiological and metabolic responses of the shore crab Carcinus maenas (L.) during environmen- tal anoxia and subsequent recovery. J. Exp. Mar. Biol. Ecol. 150:31-50.

Hill, B. J., and T. J. Wassenberg.

1990. Fate of discards from prawn trawlers in Torres Strait. Aust. J. Mar. Freshw. Res. 41:53-64.

Kaiser, M. J., and B. E. Spencer.

1995. Survival of bycatch from a beam trawl. Mar. Ecol. Progr. 126:31-38.

Lancaster, J., and C. L. J. Frid.

2002. The fate of discarded juvenile brown shrimps (Cran- gon crangon) in the Solway Firth UK fishery. Fish. Res. 58:95-107.

Liggins, G. W., and S. J. Kennelly.

1996. By-catch from prawn trawling in the Clarence River estuary. New South Wales, Australia. Fish. Res. 25:347-367.

Liggins, G. W., S. J. Kennelly, and M. K. Broadhurst.

1996. Observer-based survey of by-catch from prawn trawling in Botany Bay and Port Jackson, New South Wales. Mar. Freshw. Res. 47:877-888.

Macbeth, W. G., M. K. Broadhurst, B. D. Paterson, and M. E. L. Wooden.

2006. Reducing the short-term mortality of juvenile school prawns ( Metapenaeus macleayi) discarded during trawling. ICES J. Mar. Sci. 63:831-839.

Macbeth, W. G., R. B. Millar, M. K. Broadhurst, C. W. Hewitt, and M. E. L. Wooden.

2007. Intra-fleet variability in the size selectivity of a square-mesh trawl codend for school prawns (Metap- enaeus macleayi). Fish. Res. 86:92-98.

Maguire, G. B., and G. Allan.

1985. Development of methods for growing juvenile school prawns, Metapenaeus macleayi in estuarine ponds. In Second Australian National Prawn Seminar (P. C. Rothlisberg, B. J. Hill, and D. J. Staples, eds.) p. 337- 351. Second National Prawn Seminar, Queensland, Australia.

Newland, P. L., and C. J. Chapman.

1989. The swimming and orientation behaviour of Norway lobster, Nephrops norvegicus (L.), in relation to trawling. Fish. Res. 8:63-80.

Onnen, T., and E. Zebe.

1983. Energy metabolism in the tail muscles of the shrimp Crangon crangon during work and subsequent recovery. Comp. Biochem. Physiol. 74A:833-838.

Paterson, B. D.

1993. Respiration rate of the kuruma prawn, Penaeus japonicus Bate, is not increased by handling at low temperature (12°C). Aquaculture 114:229-235.

Broadhurst et al.: Modified sorting technique to mitigate the collateral mortality of Metapenaeus macleayi

297

Paterson, B. D., G. B. Goodrick, and S. G. Grauf.

1995. Inosine monophosphate (IMP) concentration in shrimp flesh cannot be used as an index of “fresh- ness” when comparing shrimp that have been har- vested in different ways. J. Aquat. Food Prod. Tech. 4(3):59-74.

Sang, H. M., and R. Fotedar.

2004. Growth, survival, haemolymph osmolatity and organosomatic indices of the western king prawn ( Penaeus latisulcatus Kishinouye, 1896) reared at dif- ferent salinities. Aquaculture 234:601-614.

Taylor, A. C., and J. I. Spicer.

1988. Functional significance of a partial-emersion response in the intertidal prawn Palaemon elegans (Crustacea: Palaemonidae) during environmental hypoxia. Mar. Ecol. Progr. 44:141-147.

Uhlmann, S. S., and M. K. Broadhurst.

2007. Damage and partitioned mortality of teleosts dis-

carded from two Australian penaeid fishing gears. Dis. Aquat. Org. 76:173-186.

Wassenberg, T. J., and B. J. Hill.

1989. The effect of trawling and subsequent handling on the survival rates of the by-catch of prawn trawlers in Moreton Bay, Australia. Fish. Res. 7:99-110.

1993. Selection of the appropriate duration of experi- ments to measure the survival of animals discarded from trawlers. Fish. Res. 17:343-352.

Watson, J. W.

1976. Electrical shrimp trawl catch efficiency for Penaeus duorarum and Penaeus aztecus. Tran. Am. Fish. Soc. 105:135-148.

1989. Fish behaviour and trawl design: potential for selective trawl development. In Proceedings of the world symposium on fishing gear and fishing vessels (Campbell, C. M., ed.), p. 25-29. Marine Institute, St Johns, Newfoundland.

298

Abstract — Reducing shark bycatch and depredation (i.e. , damage caused by sharks to gear, bait, and desired fish species) in pelagic longline fisher- ies targeting tunas and swordfish is a priority. Electropositive metals (i.e., a mixture of the lanthanide elements lanthanum, cerium, neodymium, and praseodymium) have been shown to deter spiny dogfish ( Squalus acanth- ias, primarily a coastal species) from attacking bait, presumably because of interactions with the electroreceptive system of this shark. We undertook to determine the possible effectiveness of electropositive metals for reducing the interactions of pelagic sharks with longline gear, using sandbar sharks (Carcharhinus plumbeus, family Carcharhinidae) as a model species. The presence of electropositive metal deterred feeding in groups of juvenile sandbar sharks and altered the swim- ming patterns of individuals in the absence of food motivation (these indi- viduals generally avoided approaching electropositive metal closer than -100 cm). The former effect was relatively short-lived however; primarily (we assume) because competition with other individuals increased feeding motivation. In field trials with bottom longline gear, electropositive metal placed within -10 cm of the hooks reduced the catch of sandbar sharks by approximately two thirds, com- pared to the catch on hooks in the proximity of plastic pieces of similar dimensions. Electropositive metals therefore appear to have the poten- tial to reduce shark interactions in pelagic longline fisheries, although the optimal mass, shape, composition, and distance to baited hooks remain to be determined.

Manuscript submitted 31 October 2008. Manuscript accepted 2 March 2009. Fish. Bull. 107:298-307 (2009).

The views and opinions expressed or implied in this article are those of the author and do not necessarily reflect the position of the National Marine Fisheries Service, NOAA.

The repulsive and feeding-deterrent effects of electropositive metals on juvenile sandbar sharks ( Carcharhinus plumbeus)

Richard Brill (contact author)1

Peter Bushnell2 Rumya Sundaram2

Leonie Smith3 Eric Stroud5

Coley Speaks4 John Wang6

Email address for contact author: rbrill@vims.edu

1 Cooperative Marine Education

and Research Program Northeast Fisheries Science Center National Marine Fisheries Service, NOAA 166 Water Street

Woods Hole, Massachusetts, 02543 Present address: Virginia Institute of Marine Science PO Box 1346 (mail)

Route 1208 Greate Rd. Gloucester Point,

Virginia 23062

2 Department of Biological Sciences Indiana University South Bend 1700 Mishawaka Avenue

South Bend, Indiana, 46634

3 Department of Biological Science Bangor University

Bangor Gwynedd, LL57 2DG, UK

4 Department of Marine Science Hampton University Hampton, Virginia, 23668

5 Shark Defense Technologies, LLC PO. Box 2593

Oak Ridge, New Jersey 074 3 8

6 Joint Institute for Marine and Atmospheric Research University of Hawaii at Manoa 1000 Pope Road

Honolulu, Hawaii, 96822

The worldwide bycatch of sharks is estimated to be 260,000-300,000 metric tons annually (11.6 to 12.7 million individual sharks) (Bonfil, 1994; Camhi et al., 1998). In pelagic longline fisheries targeting tunas and swordfish, it is not uncommon for the number of sharks caught to exceed that of the desired fish species (Stevens, 1992; Bonfil, 1994; Gilman et al., 2008). Shark populations are especially vulnerable to high rates of fishing mortality because of their slow growth rates, low reproductive output, and late sexual maturity. Once depleted, they also generally have slow rates of recovery because of these characteristics (Smith and Snow, 1998; Chen and Yuan, 2006). Scalloped hammerhead ( Sphyrna lewini), oceanic whitetip (Carcha- rhinus longimanus), and tiger shark (Galeocerdo cuvier ) populations have already decreased within the range from 60% to 99% of their historical biomass (Baum et al., 2003; Baum

and Myers, 2004; Gilman et al., 2008), and these species are now included on the International Union for Con- servation of Nature (IUCN) Red List of Threatened Species (IUCN, 2008). Such severe reductions in elasmo- branch populations have the poten- tial to detrimentally restructure marine ecosystems (Jackson et al., 2001; Myers and Worm, 2003; Worm et al., 2006; Myers et al., 2007). Sur- vival rates of pelagic sharks released from longline gear appear high for animals that are not moribund when the gear is retrieved (Moyes et al., 2006). Nonetheless, reduction of both shark bycatch and depredation (i.e., shark damage to longline gear, bait, and desired fish species) is considered a priority (Gilman et al., 2008, Man- delman et al., 2008).

Sharks (but not the large pelagic teleosts targeted by longline fisher- ies) possess a unique sensory system based on the ampullae of Lorenzini that can detect electric field gradi-

Brill et a I.: The repulsive and feeding-deterrent effects of electropositive metals on Carcharhinus plumbeus

299

ents as small as 5 nV/cm (Haine et al., 2001). These ampullary receptors are most sensitive to frequencies from 1 to 8 Hz (Montgomery, 1988), are capable of detecting weak electric fields generated by neuromus- cular activity, and can guide sharks to prey in the absence of other sensory stimuli (Kajiura and Holland, 2002; Kajiura, 2003; Collin and Whitehead, 2004). It should be possible, therefore, to develop effective deterrent procedures that could take advantage of the sharks’ electroreceptive sense. The procedures could then decrease the bycatch and incidental mortality of sharks and increase fishing efficiency and yield of the desired fish species. Strong electric fields have been shown to deter approaching sharks, presumably by overloading their electrosensory modality (Smith, 1974, 1991; Cliff and Dudley, 1992). However, cur- rently available electronic devices for achieving this behavioral response are designed to protect humans and aquaculture structures from shark attack and are large, expensive, and not practical for deployment on longline fishing gear. There are no data on the mini- mum field strength needed to achieve electrosensory repulsion.

Electropositive metals (generally mixtures of the lan- thanide elements praseodymium, neodymium, cerium, lanthanum, samarium, and yttrium) rouse juvenile lemon sharks (Negaprion brevirostris), nurse sharks ( Ginglymostoma cirratum), and spiny dogfish sharks ( Squalus acanthias) from tonic immobility when brought close to the head (Stoner and Kaimmer, 2008). Elec- tropositive metals have also been shown to deter spiny dogfish sharks from attacking baits in a tank study (Stoner and Kaimmer, 2008), and to reduce the catch of this species by 19% on bottom longline gear (Kaimmer and Stoner, 2008). Electropositive metals are assumed to stimulate the electroreceptive system by giving up cations to the more electronegative skin of the elas- mobranchs (Rice, 2008; Stoner and Kaimmer, 2008), although the exact mechanisms responsible for repul- sion are not known.

Our studies are designed to determine if electroposi- tive metals affect the behaviors of juvenile sandbar sharks (Carcharhinus plumbeus) under both laboratory and field conditions. Sandbar sharks are highly suit- able for this line of research because they do well and feed readily in captivity. They are also an obligatory ram-ventilating species and their constant forward mo- tion makes it easier to measure changes in swimming patterns caused by electropositive metals, compared to species that remain motionless on the bottom for extended periods. More importantly, although pri- marily a coastal species (Conrath, 2005; Conrath and Musick, 2008), the sandbar shark is a member of the family Carcharhinidae (requiem sharks), which in- cludes many of the other shark species that frequently interact with pelagic longline gear (Mandelman et al., 2008). Results with sandbar sharks should, therefore, provide a good indication of the efficacy of electro- positive metals for reducing shark bycatch in pelagic longline fisheries.

Our experiments with captive sandbar sharks include tests of the ability of electropositive metals to influence the swimming patterns of individual animals in the absence of food motivation and to repel sharks from pieces of cut bait. The former is intended to quantify repulsive distances, and both are intended to provide data directly comparable with those obtained previously with spiny dogfish sharks (Stoner and Kaimmer, 2008; Tallack and Mandelman, in press). Our deployment of longline fishing gear in a tidal lagoon system used as a nursery area by juvenile sandbar sharks (Conrath, 2005; Conrath and Musick, 2007) tested the ability of electropositive metal to deter sharks under field condi- tions and provided data comparable to data from recent studies where spiny dogfish sharks were targeted by a similar method (Kaimmer and Stoner, 2008; Tallack and Mandelman, in press).

Materials and methods

Experiments with captive animals were conducted during the summer months (June through August 2007) at the Virginia Institute of Marine Science, Eastern Shore Laboratory, in Wachapreague, Virginia. Juvenile sandbar sharks weighting up to ~5 kg (i.e., neonates to approximately 5 years old; Casey and Natanson, 1992) were captured with standard recreational hook-and-line fishing gear in the surrounding tidal lagoon system and transported to an outdoor circular fiberglass tank (7 m diameter, 1.8 m deep) as described previously (Brill et. al., 2008). The tank was supplied with sea water pumped from the adjacent tidal lagoon which was passed through sand filters to remove suspended particles, as well as phytoplankton and fouling organisms. Water from the holding tank was also continuously circulated through a separate set of sand filters, ultraviolet sterilizer, biofilter, and protein skimmer. Tank temperature and salinity over the course of the study (22-29°C and 30-33 %c, respectively) reflected that of the adjacent tidal lagoon. When not part of an active experiment, the sharks were fed pieces of cut menhaden ( Brevoortia tyrannus) every other day. All sharks were actively feeding before use in any trials.

Repulsion experiments with individual sharks

Experiments were performed on 10 sharks, and individu- als were not used more than once. For each replicate, an individual shark was transferred from the main holding tank to a smaller vinyl circular indoor test tank (3.6 m diameter, 0.67 m water depth) and allowed to acclimate for 24 hours. The test tank was supplied with seawater pumped from the adjacent tidal lagoon which was passed through sand filters. Temperature and salinity ranged from 22° to 29°C and from 30 %c to 33%e over the course of the study.

An experiment consisted of three one-hr periods. At the start of the first hour, a string of three lead fishing weights was suspended in the tank to allow the shark

300

Fishery Bulletin 107(3)

to acclimate to the presence of a new visual stimu- lus. At the start of the second hour the string of lead fishing weights was quietly removed and immediately replaced with either a string of three electropositive metal bars, or the string of lead fishing weights was placed back into the tank. This choice was randomized. At the start of the third hour, the string of electroposi- tive metal bars or lead fishing weights was removed and replaced with the other. Only the video records from the second and third hours (i.e., one hour in the presence of electropositive metal bars and one hour in the presence of lead fishing weights) were subsequently analyzed.

The three electropositive metal bars (~2 cmx2 cmxlO cm) comprised neodymium (76%), praseodymium (23%),

Figure II

Positions of a juvenile sandbar shark ( Carcharhinus plumbeus) at 1-sec intervals obtained with Lolitrack automated video analysis software (Loligo Systems, Tjele, Denmark). Three lead fishing weights (A) or three electropositive metal bars (B) were suspended in the tank using monofilament fishing line at the position indicated by the triangles. The video record was acquired with a digital video camera mounted directly above the center of a vinyl circular tank (3.6 m diameter, 0.67 m water depth). Small portions of the tank at the 12 o’clock and 6 o’clock positions were out of frame because of the maximum available height of the laboratory ceil- ing where the video camera was positioned.

and minor amounts (<0.04%) of cerium, lanthanum, samarium, and yttrium (Hefa Rare Earth, Vancouver, Canada). The three lead fishing weights had similar dimensions to those of the electropositive metal bars. The strings electropositive metal bars and lead fish- ing weights were constructed by using single pieces of nylon monofilament fishing line and were suspended in the tank at a position approximately 35 cm from the tank sidewall (Fig. 1). This lateral position was chosen because preliminary observations had shown that juve- nile sandbar sharks swam predominately in a circular pattern near the tank wall. There was sufficient space, however, for the fish to pass easily between the nylon line (holding the electropositive metal bars or lead fish- ing weights) and the tank wall. Individual electroposi- tive metal bars and lead fishing weights were attached to the nylon fishing line so as to be at approximately 16, 32, and 48 cm below the surface when suspended in the tank.

A digital monochrome video camera (IDS Imaging Development Systems Inc., Cambridge, MA) equipped with a wide angle lens was used to acquire a continu- ous record (on a laptop computer) of the swimming patterns of each shark. The camera was mounted on the laboratory ceiling, over the center of the tank, approximately 1.5 m above the water surface. This al- lowed an almost complete view of the tank, although small areas at the 12 and 6 o’clock positions remained out of frame because of the maximum height of the digital video camera imposed by the laboratory ceiling. The locations of the sharks were subsequently digitized (x, y coordinate system) at one-second intervals from the video record by using Lolitrack automated video analysis software (Loligo Systems, Tjele, Denmark). The software generally digitized the broadest area of the shark from the dorsal view (i.e., the area between the pectoral fins and first dorsal fin).

Shark positions were translated into quantifiable behaviors by calculating the distances between the sharks and the electropositive metal or lead weights from the one-second interval location records. These data were summarized by compiling frequency dis- tributions with 5-cm bins. Fractional values for each distance bin were calculated from the total number of position estimates for each animal when the electro- positive metal bars or lead fishing weights were present in the tank. The fractional bins were averaged across all fish. A two-way (treatmentxdistance bin) repeated measures analysis of variance (ANOVA) procedure was used to test for differences in the frequency distribu- tions (with the use of arcsine transformed percentage data), with post hoc tests for significant differences between individual bins (Sigma Stat, vera. 3.0.1, Systat Software, Inc., San Jose, CA). The significance level for all tests was P < 0.05.

The digital position records were also used to calcu- late swimming speeds, which were subsequently segre- gated into swimming speeds recorded when the fish was within 100 cm of the electropositive metal bars or lead fishing weights, and into swimming speeds recorded

Brill et al : The repulsive and feeding-deterrent effects of electropositive metals on Carcharhinus plumbeus

301

when the fish was further than 100 cm from the elec- tropositive metal bars or lead fishing weights.

Feeding deterrent experiments

Groups of sharks maintained in the outdoor circular fiberglass holding tank were used to determine the ability of electropositive metals to deter sharks from attacking bait. Individual pieces of cut menhaden were placed 30 cm below a single electropositive metal bar (-2 cm x 2 cmxlO cm and of the same composition described previously) by using a monofilament nylon fishing line. For control trials, pieces of cut menha- den were placed 30 cm below a stainless steel bolt of approximately the same dimensions as the electroposi- tive metal bar. Baits were attached to the monofila- ment line with light twine that allowed the bait to be removed by the sharks with moderate effort. Hooks were not used because of the risk of injuring the sharks and the likelihood that hooking would influence the willingness of the sharks to attack baits in subsequent trials. The line (with the bait and stainless steel bolt or electropositive metal bar) was suspended near the center of the tank and in approximately the middle of the water column. The order of presentation was randomized.

During each trial, the line was immediately removed from the water after the bait was attacked and the time from presentation to attack was recorded. The line was also removed from the water if the bait was not attacked within three minutes. In either case, five minutes were allowed before the next trial was begun. Because of the number of sharks in the tank, the ra- pidity of the attacks, and the frequent shark-shark interactions, it was not possible to identify which indi- vidual attacked the bait or to quantify specific changes in behavior as the bait was approached.

Two separate series of experiments were conducted. In the first, 14 actively feeding juvenile sandbar sharks were present in the holding tank and 14 trials (seven with the electropositive metal and seven with the stain- less steel bolt) were conducted every other day over a 14-d period. The sharks were fed to satiation at the end of each set of trials, but not on the days between experiments. Two additional sessions were run one week after the completion of the first 14 sessions. The original group of sharks was then released and re- placed with seven naive individuals. Eight trials (four with the electropositive metal bar and four with the stainless steel bolt) were conducted every other day, over a 12-day period. As in the previous experiments, the sharks were fed to satiation at the end of each set of trials, but not on the days between experiments. Feeding trials were run at approximately the same time everyday (late afternoon).

Longline experiments

Bottom longline fishing gear was used to test the ability of electropositive metal to influence shark catch rates

in the field. Longline trials were conducted during the summer months (July and August 2008). The gear was deployed a total of 26 times (two deployments per day) and all deployments except for one were in the tidal lagoon system adjacent to the eastern shore of Virginia (an area of tidal creeks and broad marshes separated from the Atlantic Ocean by a series of barrier islands to the east). One longline set was made in the ocean immediately offshore of the barrier islands. All longline sets were conducted during daylight hours and the gear retrieved after two hours when conditions permitted. Gear deployment schedules were primarily based on weather, as well as crew and vessel availability, rather than on time of day or tidal state. Experiments were generally not undertaken on consecutive days.

Approximately 40 hooks were deployed during each set. The monofilament dropper lines were two meters long and were terminated with steel circle hooks (10/0 or 11/0) baited with pieces of menhaden. Dropper lines were connected to the mainline at 10-m intervals to help ensure that each dropper fished independently. Small pieces (approximately 30-70 g initial weight) of electropositive metal comprising lanthanum (28%), cerium (53%), neodymium (15%), and praseodymium (4%) were attached to the dropper lines approximately 10 cm from the hook by using plastic zip ties. The elec- tropositive metal pieces, cut in cross section from the ingots supplied by the distributor (Hefa Rare Earth, Vancouver, Canada), were approximately 2-cm thick plates (-30-60 cm2 surface area per side). Plastic pieces, of approximately the same shape and surface area were attached at the same positions to control for any visual deterrent or mechanical effects. Lines with electropositive metal near the hook and with a plastic piece near the hook were attached to the mainline in an alternating pattern and in equal numbers during each gear deployment. This arrangement allowed the resultant catch data to be analyzed with a chi-square procedure based on the expectation that equal num- bers of sharks would be caught on hooks near a plastic piece or on hooks near electropositive metal, if the latter did not alter shark behaviors.

Captured sharks were brought into the boat, hooks were cut in two places to help ensure that they would be shed quickly, standard length was measured, and sex was noted. These sharks were then immediately re- leased. Clearnose skates ( Raja eglanteria ) were treated similarly. Large rays (orders: Rajiformes and Myliobati- formes) were released without removing them from the water to ensure crew safety, and were therefore usually not identified to species.

Results

Repulsion experiments with individual sharks

In the presence of the lead fishing weights, sharks swam predominately around the periphery of the tank, showed essentially no avoidance response, and fre-

302

Fishery Bulletin 107(3)

0-5 45-50 95-100 145-150 195-200 245-250

Distance bin (cm)

Figure 2

Frequency distributions (based on 5-cm bins) of the observed dis- tances in relation to lead fishing weights (filled circles) or electroposi- tive metal (open circles) calculated at 1-sec intervals from the video records of juvenile sandbar shai'ks ( Carcharhinus plumbeus, n = 10). When compared to the lead weights, significantly fewer (indicated by *, two-way repeated measures ANOVA, P <0.05) shark positions were recorded within 100 cm of electropositive meta, whereas more positions were recorded at distances more than approximately 200 cm from electropositive metal.

quently passed between the lead fishing weights and tank wall. In contrast, sharks generally avoided approaching electropositive metal bars, which precluded them from pass- ing between the electropositive metal bars and the tank wall. The locations of a single sandbar shark typifying these behaviors are shown in Figure 1.

The frequency distributions of positions in relation to the lead fishing weights or elec- tropositive metal bars demonstrate avoidance of the latter by the sharks (Fig. 2). Signifi- cantly fewer positions were recorded within approximately 100 cm of the electropositive metal bars, and significantly more positions at the maximum distances (further than ap- proximately 200 cm from the electroposi- tive metal bars). The frequency distributions under both circumstances increased with distance and truncated sharply at the great- est distances because of simple positional geometry and the limitations imposed by the dimensions of the circular test tank.

The swimming speed data were not nor- mally distributed and are therefore shown as box and whisker plots (Fig. 3). There appeared to be a tendency for swimming speeds to be greater in proximity to the electropositive metal bars than under the other circumstances. However, the small dif- ferences and extreme variability precluded statistically significant differences.

1.0 -

(/)

h

co

-a

CD

a)

a.

</)

cn

c

E

E

g

co

0.8

0.6

0.4

0.2

A B C D

Figure 3

Median swimming speeds in body lengths per second (BL/s) when juvenile sandbar sharks (Carcharhinus plumbeus) were within 100 cm of electropositive metal (A), more than 100 cm from electropositive metal (B), within 100 cm of lead fishing weights (C), and more than 100 cm from lead fishing weights (D). The high variability precluded statistically significant differences, but there appears to be a trend for fish to swim faster in proximity to electropositive metal than under the other circumstances. Limits of boxes show the 25th and 75th percentiles, the error bars the 90th and 10th percentiles, and the single points the 95th and 5th percentiles.

Feeding deterrent experiments

Bait pieces located approximately 30 cm from a stain- less steel bolt were generally attacked within 30 sec- onds of presentation (Figs. 4 and 5). In contrast, sharks did not attack baits located in proximity of an electropositive metal bar within three minutes, at least during the initial trials. When the repulsive effect was evident, sharks would rapidly approach the bait, flinch, turn sharply, and rapidly depart. Although we were not able to quantify these behaviors, they matched the responses of spiny dogfish sharks under simi- lar circumstances described by Stoner and Kaimmer (2008) and mirrored the apparent changes in swim- ming speeds of individual sharks near electropositive metal (Fig. 3).

When 14 sharks were present in the tank (Fig. 4), the repulsive effect extinguished fairly suddenly during day 2, but reappeared during the initial trials on day 4, and again during the initial trials on days 10 and 21. Because it was impossible to identify individuals, it is unknown if only one or a few sharks overcame the deterrent effect of electropositive metal. The repulsive effect did not reappear after a one-week period where trials were not run; indicating that once tolerance of electropositive metal is learned it is retained at least over the short term.

Brill et al.: The repulsive and feeding-deterrent effects of electropositive metals on Carcharhmus plumbeus

303

During the second set of experiments with fewer sharks in the tank (seven ani- mals versus 14), the deterrent effect of electropositive metal was apparent until day 8 and it did not completely disappear until day 12 (Fig. 5).

Longline trial experiments

Of the juvenile sandbar sharks captured, 39 were female, 26 were male, and there was one individual where sex was not recorded. Sharks ranged in size (standard length) from 47 to 130 cm, and had a median length of 72.5 cm. Only one cownose ray (Rhinoptera bonasus) was captured, the other rays were either Gymnura spp. or Dasyatis spp. Two Atlantic sharpnose sharks ( Rhizoprionodon terraenovae) and nine clearnose skates (Raja eglanteria) were captured during the one gear deploy- ment made outside the lagoon system.

The ratio of sharks caught on hooks near plastic to sharks caught on hooks near electropositive metal (2.6:1) was significantly different from the predicted ratio of 1:1 if the presence of the latter had no deterrent effect (chi square test P=0.001, df=l, x2=10.78). In other words, electropositive metal near the hooks re- duced the catch rates of sharks by 62% (Table 1). In contrast, the numbers of rays caught on hooks near plastic and on hooks near electropositive metal were not significantly different from the expected ratio of 1:1 (chi square test P- 0.67, df=l, X2=0.39), indicating that the presence of electropositive metal had no deterrent ef- fect. The low number of clearnose skates captured precluded any definitive con- clusions. However, the essentially equal numbers of skates caught on each hook type (Table 1) implies that the presence of electropositive metal does not deter this species.

Discussion

Repulsion experiments with individual sharks

Because juvenile sandbar sharks showed no reactions to lead fishing weights (other than to avoid running into them), we concluded that lead fishing weights exert no significant repulsive effect. In contrast, juvenile sand- bar sharks generally avoided approaching the electro- positive metal bars presumably because they produce mild irritation. Whether this irritation is chemical or electrical (i.e. , stimulation of the sharks electrorecep- tive system) is unknown. Given the apparent definitive

Trial number

Figure 4

Time taken for cut pieces of menhaden ( Brevoortia tyrannus) to be attacked when suspended 30 cm below a stainless steel bolt (filled circles) or an electropositive metal bar (open circles). The line was removed from the tank if the bait was not attacked within three minutes. Trials were conducted with 14 juvenile sandbar sharks ( Car - charliinus plumbeus) maintained in a circular fiberglass tank (7 m diameter, 1.8 m deep). Fourteen trials (seven with the electropositive metal bar and seven with the stainless steel bolt) were conducted every other day for the first 14 days, suspended for seven days, and then two additional trials were run to test whether the electropositive metal near the bait, as seen during the initial trails, would continue to deter the sharks.

Table 1

Catch of sharks (primarily juvenile sandbar sharks, Car- charhinus plumbeus ), rays (primarily Gymnura spp. and Dasyatis spp.) and clearnose skates ( Raja eglanteria) by bottom longline gear. Pieces of electropositive metal, or pieces of plastic of similar dimensions, were placed within 10 cm of the hooks. Hooks in proximity to electropositive metal or to plastic pieces were deployed in equal numbers and in an alternating pattern during each set.

Sharks

Rays

Skates

Hooks near electropositive metal

Hooks near plastic

16

42

10

13

304

Fishery Bulletin 107(3)

Figure 5

Time taken for cut pieces of menhaden to be attacked when suspended 30 cm below a stainless steel bolt (filled circles) or an electropositive metal bar (open circles). The line was removed from the tank if the bait was not attacked within three minutes. During these trials, seven juvenile sandbar sharks ( Carcharhinus plumbeus) were maintained in a circular fiberglass tank (7 m diameter, 1.8 m deep). Eight trials (four with the electropositive metal bar and four with the stainless steel bolt) were conducted every other day. The deterrent effect of electropositive metal was present over a greater number of days compared with the previous situation when 14 sharks were present in the tank. The difference is assumed to be due to increased competition for food which limited the repulsive effect of electropositive metal in the latter circumstance.

boundary of the area that is avoided (Fig. 1), we surmise the latter to be the case. Stoner and Kaimmer (2008) reach similar conclusions with respect the deterrent effect of electropositive metal on spiny dogfish sharks. The effective range of deterrence (-100 cm) for juvenile sandbar sharks is, however, considerably larger than that for spiny dogfish sharks (10-20 cm) (Stoner and Kaimmer, 2008). Whether this is due to differences in water temperatures (~10°C for spiny dogfish sharks versus 22-29°C for juvenile sandbar sharks), mass or shape of bars, specific composition of the electropositive metals, or species differences remains to be determined. The number of electrosensory pores present in sandbar sharks is approximately twice that in spiny dogfish sharks (2317 versus 1262, respectively; Cornett, 2006) which may explain the difference in the distances that these sharks were deterred.

Because of the limited range of deterrence, electro- positive metal would have to be placed near every hook in pelagic longline gear, although it appears that it could be placed at distances that are unlikely to inter- fere with capture of the targeted fishes. It is unknown if electropositive metal could protect hooked fishes from depredation by sharks, which is a significant problem (Gilman et al., 2008; Mandelman et al., 2008).

Feeding deterrent experiments

Stoner and Kaimmer (2008) theorize that the pres- ence of electropositive metal is irritating or possibly

interferes with the ability of sharks to locate a food item. We hypothesize that irritation is the more likely reason the bait was not attacked within three minutes during the initial trials with electropositive metal in our feeding experiments. The tank was brightly lit and the water was essentially free of suspended particles because of the extensive filtration. We therefore con- tend that the sandbar sharks located the bait primar- ily by vision (although olfaction may also be involved). Moreover, the pieces of cut menhaden would obviously not have the bio-electric signals emitted by living organisms (Haine et al., 2001). Further investigation into the exact mechanism(s) underlying the effect of electropositive metals as is clearly warranted.

Our specific experimental procedures were designed to ensure that feeding motivation remained high and thus to minimize the influence of feeding motiva- tion on our results. Any influence of competition on feeding motivation could not be controlled however, except by altering the number of sharks in the tank. Competition is well known to increase feeding mo- tivation (Ryer and Olla, 1991; Eklov, 1992) and we assume that it likewise lessens the deterrent effects of electropositive metal. Increased feeding motivation due to competition could, therefore, explain the short- lived deterrent effects of electropositive metal when 14 sharks are present in the tank. Our observation that the deterrent effect lasts longer during the tri- als when only seven sharks are present supports this contention.

Brill et al.: The repulsive and feeding-deterrent effects of electropositive metals on Carcharhinus plumbeus

305

Our data also imply that tolerance of electropositive metals can be learned, and that this learned behavior is retained for at least seven days. It is unknown how often individual sharks encounter pelagic longline gear, but it is unlikely to be anywhere near the frequency of our feeding trials with captive sandbar sharks. For this reason we propose that learned tolerance of electroposi- tive metals will unlikely diminish their deterrent effect when used with pelagic longline fishing gear.

Longline trial experiments

From our longline catch data (Table 1), it is clear that the presence of electropositive metal near hooks is a strong deterrent to juvenile sandbar sharks, but not to rays. In recent studies where similar methods were used resulted in either a smaller reduction in catch rates (20%) of spiny dogfish sharks (Kaimmer and Stoner, 2008) than we observed, or in no statistically significant reduction (Tallack and Mandelman, in press). Surpris- ingly, Kaimmer and Stoner (2008) also recorded a large reduction (46%) in the catch of longnose skates (Raja rhina) due the presence of electropositive metal near longline hooks, whereas we saw no indication of a repul- sive effect on clearnose skates.

The sensitivity of the electroreceptor system has been studied in a broad range of elasmobranchs (reviewed by Montgomery, 1988; Kalmijn, 2003) and there is no evidence of a lesser sensitivity in rays when compared to sharks. More specifically, the sensitivity of the elec- troreceptor system in the sandbar shark, the blacktip reef shark ( Carcharhinus melanopterus, family Car- charhinidae), and the mangrove whipray ( Himantura granulata, family Dasyatidae) are roughly equivalent (1 to 4 nV/cm; Haine et al., 2001; Kajiura and Holland, 2002). By implication, therefore, the catch rates of all the elasmobranch species interacting with the longline gear should be reduced equally, but clearly are not. The species-specific responses of sharks, skates, and rays to electropositive metal may reside at the receptor level (Tricas and New, 1998), the level of central processing, or simply reflect different behavioral tolerance related to feeding motivation. Kaimmer and Stoner (2008) and Tallack and Mandelman (in press) both speculate that the abundance of dogfish results in strong competition for food and increased aggressiveness, and that these limit the repulsive effect of electropositive metal. Our results showing a longer lasting repulsive effect of electropositive metal during feeding experiments when fewer sharks are present in the tank (Fig. 4 and 5) support this contention. Assessing the specific differ- ences between various species of sharks, skates, and rays could clearly be a fruitful area of investigation.

Health and environmental safety concerns with use of electropositive metals in fisheries

The electropositive metals used in our experiments are mixtures of lanthanide elements (e.g., lanthanum, cerium, neodymium, and praseodymium) that are collec-

tively known as the “rare earth” elements, although they are not particularly rare (Bulman, 1994). Lanthanide elements are generally considered nontoxic to mam- mals primarily because they are not easily absorbed if ingested (Haley, 1965; Bulman, 1994). Their accumula- tion in animal tissue is therefore generally very low to negligible even for animals in long-term feeding trials, and transfer to humans through foodstuffs is likewise very low (Redling, 2006). We therefore conclude that the use of electropositive metals as elasmobranch deter- rents would pose little if any toxicity to fishing crews handling the material, or to the food safety of targeted fish species. Lanthanide elements are also used as crop fertilizers and animal feed performance boosters for poultry, sheep, cattle, pigs, fish, and prawns; and in a variety of medical applications such as antimicrobial agents, MRI imaging, burn and cancer treatments, and for countering hyperphosphatemia in renal dialysis patients (Fricker, 2006).

Lanthanide elements injected intravenously can be toxic, however, because they cross cell membranes by passing through calcium channels, and because they have high affinity for calcium binding sites on biological molecules (Haley, 1965; Bulman, 1994). It is therefore at least possible that extensive distribution of lantha- nide elements in the marine environment could impact invertebrate species (e.g., mollusks and crustaceans) that routinely incorporate calcium into their shells and exoskeletons.

Conclusion and future directions

Improving gear selectivity (i.e., reducing shark bycatch and depredation) is considered a high priority in pelagic longline fisheries because of its ecological and economic benefits (Gilman et al., 2008, Mandelman et al., 2008). The use of electropositive metals appears promising in this regard. However, the specific composition, mass, and shape of the composite metal deterrent representing an optimal compromise between a high deterrent effect and a long useable durability in seawater remain to be ascertained. In conjunction with at-sea trials, behavioral assays with captive juvenile sandbar sharks would pro- vide an effective means for testing and optimizing the use of electropositive metals.

Acknowledgments

Funding for this project was provided by the Fishery Biology and Stock Assessment Division, Pacific Islands Fisheries Science Center, National Marine Fisheries Ser- vice, NOAA; the National Shark Research Consortium (NOAA/NMFS Grant no. NA17FL2813); and an Indiana University South Bend SMART grant to R. Sundaram. We also gratefully acknowledge the entire staff of the Virginia Institute of Marine Science Eastern Shore Lab- oratory for their continuing and genuine hospitality and technical support. All animal capture, maintenance, and handling procedures were approved by the College

306

Fishery Bulletin 107(3)

of William and Mary Institutional Animal Care and

Use Committee and comply with all current applicable

laws of the United States of America. This is contribu- tion 2991 from the Virginia Institute of Marine Science.

Literature cited

Baum, J. K., R. A. Myers, D. G. Kehler, B. Worm, S. J. Harley, and P. A. Doherty.

2003. Collapse and conservation of shark populations in the Northwest Atlantic. Science 299:389—392.

Baum, J. K., and R. A. Myers.

2004. Shifting baselines and the decline of pelagic sharks in the Gulf of Mexico. Ecol. Lett. 7:135-145.

Bonfil, R.

1994. Overview of world elasmobranch fisheries. FAO Fisheries Tech. Paper 341, 119 p. FAO, Rome.

Brill, R., P. Bushnell, S. Schroff, R. Seifert, and M. Galvin.

2008. Effects of anaerobic exercise accompanying catch- and-release fishing on blood-oxygen affinity of the sand- bar shark ( Carcliarhinus plumbeus, Nardo). J. Exp. Mar. Biol. Ecol. 34:132-143.

Bulman, R. A.

1994. Europium and other lanthanides. In Handbook on metals in clinical and analytical chemistry (H. G. Seiler, A. Sigel, and H. Sigel, eds.), p. 351-363. Marcel Dekker, Inc., New York, NY.

Camhi, M., S. Fowler, J. Musick, A. Brautigam, and S. Fordham.

1998. Sharks and their relatives — ecology and conser- vation. Occasional Paper of the IUCN Species Survival Commission no. 20, 39 p.

Casey, J. G., and L. J. Natanson.

1992. Revised estimates of age and growth of the sandbar shark ( Carcliarhinus plumbeus ) from the Western North Atlantic. Can. J. Fish. Aquat. Sci. 49:1474-1477.

Chen. P., and W. Yuan.

2006. Demographic analysis based on the growth param- eter of sharks. Fish. Res. 78:374—379.

Cliff, G„ and S. F. J. Dudley.

1992. Protection against shark attack in South Africa, 1952—90. Aust. J. Mar. Freshw. Res. 43:263-272.

Collin, S. P., and D. Whitehead.

2004. The functional roles of electroreception in non- electric fishes. Anim. Biol. 54:1-25.

Conrath, C.

2005. Nursery delineation, movement patterns, and migra- tion of the sandbar shark, Carcharhimus plumbeus , in the eastern shore of Virginia coastal bays and lagoons. Ph. D. diss., 184 p. Virginia Institute of Marine Science, Gloucester Point, VA.

Conrath, C. L., and J. A. Musick.

2007. The sandbar shark summer nursery within bays and lagoon of the eastern shore of Virginia. Trans. Am. Fish. Soc. 136:999-1007.

2008. Investigations into depth and temperature habitat utilization and overwintering grounds of juvenile sand- bar sharks, Carcliarhinus plumbeus : the importance of near shore North Carolina waters. Environ. Biol. Fish. 82:123-131.

Cornett, A. D.

2006. Ecomorphology of shark electroreceptors. M. S. thesis, 102 p. Florida Atlantic Univ., Boca Raton, FL.

Eklov, P.

1992. Group foraging versus solitary foraging efficiency in piscivorous predators: the perch, Perea fluviatilis, and pike, Esox lucius, patterns. Anim. Behav. 44:313- 326.

Fricker, S. P.

2006. The therapeutic application of lanthanides. Chem.

Soc. Rev. 35:524-533.

Gilman, E., S. Clarke, N. Brothers, J. Alfaro-Shigueto, J.

Mandelman, J. Mangel, S. Petersen, S. Piovano, N. Thomson,

P. Dalzell, M. Donoso, M. Goren, and T. Werner.

2008. Shark interactions in pelagic longline fisheries. Mar. Pol. 32:1-18.

Haine, O. S., P. V. Rid, and R. Rowe.

2001. Range of electrosensory detection of prey by Car- charhinus melanopterus and Himantura garnulata. Mar. Freshwat. Res. 52:291-296.

Haley, T.J.

1965. Pharmacology and toxicology of the rare earth elements. J. Pharm. Sci. 54:663-670.

IUCN (International Union for Conservation of Nature).

2008. IUCN Red List for Endangered Species, http:// i www.iucnredlist.org/ (accessed September, 2008).

Jackson J. B. C„ M. X. Kirby, W. H. Berger, K. A. Bjorndal,

L. W. Botsford, B. J. Bourque, R. H. Bradbury, R. Cooke, '

J. Erlandson, J. A. Estes, T. P. Hughes, S. Kidwell, C. B. Lange,

H. S. Lenihan, J. M. Pandolfi, C. H. Peterson, R. S. Steneck,

M. J. Tegner, and R. R. Warner.

2001. Historical overfishing and the recent collapse of coastal ecosystems. Science 293: 629-638.

Kaimmer, S., and A. W. Stoner.

2008. Field investigation of rare-earth metal as a deter- rent to spiny dogfish in the Pacific halibut fishery. Fish.

Res. 94:43-47.

Kajiura, S. M.

2003. Electroreception in neonatal bonnethead sharks, Sphyrna tiburo. Mar. Biol. 143:603-61.

Kajiura, S. M., and K. N. Holland.

2002. Electroreception in juvenile scalloped hammerhead and sandbar sharks. J. Exp. Biol. 205:3609-3621.

Kalmijn, A. J.

2003. Physical principles of electric, magnetic, and near-field acoustic orientation. In Sensory processes in aquatic environments (S. P. Collin and N. J. Marshall, eds.), p. 77-91. Springer-Verlag, New York, NY.

Mandelman, J. W., P. W. Cooper, T. B. Werner, and K. M.

Legueux.

2008. Shark bycatch and depredation in the U.S. Atlantic pelagic longline fishery. Rev. Fish Biol. Fish. 18:427- 442.

Montgomery, J. C.

1989. Sensory physiology. In Physiology of elasmobranch fishes (T. J. Shuttleworth, ed.), p. 79-98. Springer Verlag, New York, NY.

Moyes, C. D., N. Frugoso, M. K. Musyl, and R. W. Brill.

2006. Predicting postrelease survival in large pelagic fish. Trans. Am. Fish. Soc. 135:1389-1397.

Myers, R. A., J. K. Baum, T. D. Shepherd, S. P. Powers, and

C. H. Peterson.

2007. Cascading effects of the loss of apex predatory sharks from a coastal ocean. Science 315:1846- 1850.

Myers, R. A., and B. Worm.

2003. Rapid worldwide depletion of predatory fish communities. Nature 423:280-283.

Brill et al.: The repulsive and feeding-deterrent effects of electropositive metals on Carcharhinus plumbeus

307

Redling, K.

2006. Rare earth elements in agriculture: with empha- sis on animal husbandry. Ph.D. diss., 326 p. Univ. Munchen, Munchen, Germany.

Rice, P.

2008. A shocking discovery: How electropositive metals (EPMs) work and their effects on elasmobranchs. In Shark Deterrent and Incidental Capture Work- shop, April 10-11, 2008 (Y. Swimmer, J. H. Wang, and L. McNaughton, eds.). U.S. Dep. Commer., NOAA Tech. Memo., NOA A-TM-NMFS-PIFSC-16, 72 p.

Ryer, C. H., and B. L. Olla.

1991. Information transfer and the facilitation and inhi- bition of feeding and a schooling fish. Environ. Biol. Fish. 30:317-323.

Smith, E. D.

1974. Electro-physiology of the electrical shark- repellent. Trans. S. Afr. Inst, of Electr. Eng. 65:166- 185.

1991. Electric shark-barrier: Power-electronics. Power Eng. J. 5:167-176.

Smith, S. E., and D. W. Snow.

1998. Intrinsic rebound potentials of 26 species of Pa- cific sharks. Aust. J. Mar. Freshw. Res. 49:663-678.

Stevens, J. D.

1992. Blue and mako sharks bycatch in the Japa- nese south-east longline fishery off southeastern Australia. Aust. J. Mar. Freshw. Res. 43:227-236.

Stoner, A. W., and S. M. Kaimmer.

2008. Reducing elasmobranch bycatch: laboratory inves- tigation of rare earth metal and magnetic deterrents with spiny dogfish and Pacific halibut. Fish. Res. 92:162-168.

Tallack, S. M. L., and J. W. Mandelman.

In press. Do rare earth metals deter spiny dogfish? A feasibility study on the use of mischmetal to reduce the by catch of Squalus acanthias by hook gear in the Gulf of Maine (USA). ICES J. Mar. Sci.

Tricas, T. C., and J. C. New.

1998. Sensitivity and response dynamics of elasmobranch electrosensory primary afferent neurons to near thres- hold fields. J. Comp. Physiol. A Sens. Neural Behav. Physiol. 182:89-101.

Worm, B., E. B. Barbier, N. Beaumont, J. E. Duffy, C. Folke, B. S. Halpern, J. B. C. Jackson, H. K. Lotze, F. Micheli, S. R. Palumbi, E. Sala, K. A. Selkoe, J. J. Stachowicz, and R. Watson.

2006. Impacts of biodiversity loss on ocean ecosystem services. Science 314:787-790.

308

Effects of a large fishing closure on benthic communities in the western Gulf of Maine: recovery from the effects of gillnets and otter trawls

Raymond E. Grizzle (contact author)1

Larry G. Ward2

Larry A. Mayer3

Mashkoor A. Malik3

Andrew B. Cooper4

Email address for contact author: ray.grizzle@unh

1 Department of Biological Sciences and Jackson Estuarine Laboratory University of New Hampshire Durham, New Hampshire 03824

2 Department of Earth Sciences Center for Coastal and Ocean Mapping and Jackson Estuarine Laboratory University of New Hampshire Durham, New Hampshire 03824

3 Center for Coastal and Ocean Mapping University of New Hampshire Durham, New Hampshire 03824

4 Resource and Environmental Management Simon Fraser University

Vancouver, British Columbia V6B 5K3

Holly A. Abeels5 Jennifer K. Greene6 Melissa A. Brodeur7 Andrew A. Rosenberg8

edu

5 Coastal Watershed Institute Florida Gulf Coast University Fort Myers, Florida 33965

6 The Nature Conservancy Eastern Resource Office

1 1 Avenue De Lafayette, 5th Floor Boston, Massachusetts 02111

7 Consortium for Ocean Leadership

1201 New York Avenue, NW, Suites 400-420 Washington, D C. 20005

8 Department of Natural Resources and Ocean Process Analysis Laboratory University of New Hampshire Durham, New Hampshire 03824

Abstract — The recovery of benthic communities inside the western Gulf of Maine fishing closure area was evaluated by comparing invertebrate assemblages at sites inside and out- side of the closure four to six years after the closure was established. The major restriction imposed by the clo- sure was a year-round prohibition of bottom gillnets and otter trawls. A total of 163 seafloor sites (-half inside and half outside the closure) within a 515-km2 study area were sampled with some combination of Shipek grab, Wildco box corer, or underwater video. Bottom types ranged from mud (silt and clay) to boulders, and the effects of the closure on univariate measures (total density, biomass, taxonomic richness) of benthos varied widely among sediment types. For sites with predominantly mud sediments, there were mixed effects on inside and outside infauna and no effect on epifauna. For sites with mainly sand sediments, there were higher density, biomass, and taxonomic richness for infauna inside the closure, but no sig- nificant effects on epifauna. For sites dominated by gravel (which included boulders in some areas), there were no effects on infauna but strong effects on epifaunal density and taxonomic richness. For fishing gear, the data indicated that infauna recovered in sand from the impacts of otter trawls operated inside the closure but that they did not recover in mud, and that epifauna recovered on gravel bottoms from the impact of gillnets used inside the closure. The magni- tudes of impact and recovery, however, cannot be inferred directly from our data because of a confounding factor of different fishing intensities outside the closure for a direct comparison of preclosure and postclosure data. The overall negative impact of trawls is likely underestimated by our data, whereas the negative impact of gill- nets is likely overestimated.

Manuscript submitted 30 June 2008. Manuscript accepted 9 March 2009. Fish. Bull. 107:308-317 (2009).

The views and opinions expressed or implied in this article are those of the author and do not necessarily reflect the position of the National Marine Fisheries Service, NOAA.

The Western Gulf of Maine (WGOM) closure area was implemented by the National Marine Fisheries Service on 1 May 1998 as part of an over- all effort to rebuild overfished New England groundfish stocks such as cod (Gadus morhua), haddock ( Mela - nogrammus aeglefinus), other gadids, and flatfish. The WGOM closure is one of the largest year-round closures in the United States, designed to pro- tect habitat and help in the recov- ery of overfished species. The major restriction imposed by the closure was year-round prohibition of com- mercial fishing gear that is capable of capturing groundfish, principally otter trawls and gillnets. A variety of other fishing gears (e.g., lobster pots, recreational hook-and-line gear), how- ever, have been deployed in the area since its establishment. The WGOM closed area fits the definition of a marine protected area (MPA) because it provides some level of protection of

habitat and resources (NRC, 2002). In many areas, MPAs have been useful management tools but the causal mechanisms for their effec- tiveness in protecting habitat and meeting other management objectives differ widely, largely because MPAs vary widely in design and other char- acteristics (Fogarty and Murawski, 2005; Shipley, 2004). Hence, there is a need to assess individual MPAs in the context of environmental and other characteristics, as well as in regard to the particular combination of restrictions placed on each area. For assessing the data presented here, the closure was considered as an area that was potentially recover- ing from the impacts of gillnets and otter trawls.

There have been no published stud- ies on the effects of the WGOM clo- sure on seafloor habitats, and none designed specifically to address the effects of the closure on groundfish

Grizzle et al.: Effects of a large fishing closure on benthic communities in the western Gulf of Maine

309

stocks. Recent analyses of commercial trawl data (Murawski et al., 2004, 2005) have shown no appreciable effect of the closure on stock rebuilding in the region, although there has been substantial re- covery of some groundfish stocks since the closure was implemented. From studies of MPAs in other areas, for example, New England (e.g., Collie et al., 2005), it seems reasonable to expect that a closure of the magnitude of the WGOM area would have a measurable effect on habitat recovery and fish stock rebounds. Its role in these respects, however, remains to be demon- strated.

In this article, we present data from grab and box core samples of sediments and in- fauna, underwater video surveys of benthic fauna, and general seafloor conditions four to six years after the closure of WGOM, all of which indicate that the closure has resulted in substantial recovery of some bottom habitat types. We offer hypothetical causes for the recovery in the context of gear removal, and we discuss the implica- tions for ecosystem-level management of the closure.

Materials and methods

Study area

The study was restricted to a 515-km2 area that comprised a section of the central western WGOM closed area and a sec- tion outside the closed area (Fig. 1). The overall closure area, which covers much of Jeffreys Ledge, is about 30 km wide (east-west) and 110 km long (north-south) and is located off the southern Maine, New Hampshire, and northern Massachusetts coasts. The location of the study area was chosen mainly because it has similar environmental characteristics both inside the closure and outside the closure.

A 5-m pixel resolution bathymetric map covering about 85% of the area and produced from multibeam sonar data collected between December 2002 and Janu- ary 2003 (Malik and Mayer, 2007) was used as a gen- eral base map for the present study. It functioned as a guide for the final selection of sampling-site locations and for the interpretation of data related to potential gear impacts on bottom habitats.

An important feature of the study area for our re- search was the level of fishing activity, historically as well as after implementation of the closure. Data on date, location, and gear type (acquired by the National Marine Fisheries Service from federally permitted commercial fishing vessels) were acquired and plotted. For map production, the raw data (which were submit-

Figure 1

Location of the 515 km2 University of New Hampshire study area (UNH Study Area) in relation to the western Gulf of Maine closure area. The map has a resolution of 90-m to one pixel and indicates bathymetric contours with light gray (shallow water) and dark gray (deep water).

ted at 1-min intervals of longitude and latitude) were plotted. All locations with fewer than five trip records were deleted from our analysis to eliminate poten- tially spurious data arising from reporting mistakes or for other reasons. Vessel trip report data from 4.5- yr preclosure (1994-98) and postclosure (1998-2002) were obtained for all reported gear types. Bottom gillnets and otter trawls were represented in >95% of the data records, and therefore other gear types were not analyzed.

Study design

The study was a control-impact assessment (Osenberg et al., 1994) for which there was systematic sampling of the seafloor at approximately equal numbers of sites distributed inside and outside the closed area (Fig. 2). Sampling sites were located on a grid with sampling points at approximately 1.3-km intervals (0.75 min of

Massachusei

42°0'-

71 °0'

70°30'

-42°0'

70°0'

70°30’

70°0'

43°0'

42°30'-

Maine

Western Gulf of Maine Closure Area

Portsmouth

New

Hampshire

■ :

mj

'mWj

0 5 10 20 Kilometers

1 i i i I i i i I

43°30'

4 3° O'

42°30’

310

Fishery Bulletin 107(3)

70°20'

70”1 51

70*10’

70°20'

Figure 2

Locations of 163 seafloor sampling sites (white circles) within the 515 km2 University of New Hampshire study area that were sampled by some combination of Shipek grab, Wildco box corer, and towed video camera. Distribution of three major bottom sediment types: light gray=mud; medium gray=sand; dark gray=gravel (which includes all hard bottom types ranging from gravel to bouldershVertical dashed line is the western boundary of the WGOM closure.

latitude and 1 min of longitude), yielding a total of 216 target sampling sites (not all were sampled). A combina- tion of techniques was used at each site, including grab and box samples for infauna and sediments, and towed video for epifauna and general seafloor conditions, as described below.

Field and laboratory methods

All seafloor sampling occurred from June 2002 through September 2005. However, most sampling occurred during 2002 (~65% of the grab and box core sampling) and 2004 (-90% of the video sampling, and -30% of the grab and box core sampling). Hence, 90-95% of all seafloor sampling occurred during 2002 and 2004, and there was no temporal bias in sampling inside compared to outside of the closure. In other words, approximately equal numbers of sites inside and outside of the closure were sampled during each year of the study. All sam- pling gear was deployed from chartered commercial fishing vessels.

Bottom sediments were sampled with either a Shipek grab (Wildlife Supply Co., Buffalo, NY) with a design sampling area of 0.04 m2, or a Wildco box corer (Wildlife Supply Co.) with a design sampling area of 0.0625 m2. The depth of sediment penetration was measured to the nearest 0.5 cm for each sample, and a subsample of sediment was taken for grain size and organic content

analyses. Grab samples were rejected if they did not penetrate at least 2 cm into the sediment, and box core samples with less than 5 cm penetration were rejected. The contents of the box corer were subsampled with a 10.4-cm inside diameter (0.0085 m2 surface area) acrylic core tube. The entire grab contents and box core subsamples were washed through a 0.5-mm mesh sieve, fixed in 3% unbuffered formalin, and preserved in 70% isopropanol. In the laboratory, all invertebrates were removed under 3x magnification, sorted by major taxa, identified to family level in most cases, counted, and weighed (wet weight of preserved specimens).

Bottom sediments were analyzed for grain-size com- position (texture) by using standard sieve and pipette analytical techniques (Folk, 1980). Organic content was determined by loss-on-ignition (% LOI) after 4 hours at 450°C (Byers et al., 1978).

Epifaunal assemblages were determined from bottom videographs taken with a custom-made camera system composed of a video camera mounted on a frame with synchronized strobe lights and an integrated position- ing system. At each station the camera was suspended near the bottom (within 50 cm) and 6 to 10 minutes of downward looking video footage was recorded along a drift transect at least 50 m long. For quantitative anal- yses, the videotape from each transect was subsampled to isolate still images of sufficient quality to character- ize seafloor features so that a series of nonoverlapping

Grizzle et at: Effects of a large fishing closure on benthic communities in the western Gulf of Maine

311

images (n=13 to 94 per transect) along the length of each transect was produced. Each still image was ana- lyzed for bottom characteristics (predominant sediment type), visible burrow characteristics (size, density), and epifauna (taxa, density). A trio of laser beams fixed at known distances apart allowed the total area of each image to be determined.

Data analysis

The major focus of this study was to determine the effects of the WGOM closure by comparing samples taken inside the closure with samples taken outside the closure. Thus, potential confounding factors (e.g., sediment type, water depth, and sediment organic content) that might have affected comparisons between samples taken inside the closure with those taken outside (hereafter referred to as “in vs. out” comparisons) were assessed. Also, for the infauna analyses, data from the two sampling devices (grab and box corer) were analyzed separately to avoid complications with different sample sizes and selectivity of the gear.

Infauna (sampled by grab and box corer)

For both sampling devices, the role of sediment grain size (mud, sand, or gravel), water depth, sediment organic content (% LOI), and relative penetration of the sampling device were assessed, along with the factor of primary interest: whether the sample was taken from inside or outside the closure. Separate analyses were performed to examine each of the three dependent univariate infauna community variables: 1) density, 2) biomass, and 3) taxonomic richness.

All analyses were performed by using generalized linear models (GLM; McCullagh and Nelder, 1989) in S-PLUS 7.0 (Insightful Corporation, Seattle, WA). For normally distributed data or data that could be transformed to approximate normality, significance for main effects and interactions were examined by using a combination of forward and backward model selection based on the Cp statistic and sequential F-tests in an analysis of deviance with alpha levels of 0.05 and 0.10, respectively. For non-normally distributed data, signifi- cance for main effects and interactions were examined by using sequential chi-square tests in an analysis of deviance with alpha levels of 0.05 and 0.10, respectively. For each model, the inclusion of either Gaussian or exponential spatial correlation was examined with the extended generalized linear modeling capabilities in the S-PLUS correlated data library.

Epifauna (documented along video transects)

A generalized linear mixed-effects (GLME) model with Poisson error and log link was used to analyze the video count data of epifauna taxa and density (Breslow and Clayton, 1993). The mixed-effects portion of the model was necessary to account for multiple images within each transect and the images that may have been cor-

related. The use of GLME allowed individual transects to differ from one another for reasons unaccounted for by the data and directly accounted for the repeated- measures nature of the data. S-PLUS 7.0 and the GLME extension from the S+ Correlated Data library (vers. 1.0, release 1) were used for all analyses. The significance of each fixed-effect, both main effects and interactions, was tested in an ANOVA framework by using mar- ginal F-tests (Pinheiro and Bates, 2000) based on the (restricted) penalized quasi-likelihood with an alpha- level of 0.05 for main effects and 0.10 for interaction effects (Sokal and Rohlf, 1981). In addition to the main effect of inside or outside of the closure, water depth and sediment type were assessed as potential confounding factors. Offsets were included in each model to account for the fact that the total surface area observed varied from image to image because of the variations in the height of the camera. Separate analyses were performed on the two dependent variables: total density and taxo- nomic richness.

Results

Preclosure and postclosure plots of the report data from fishing vessel trips showed several relevant patterns (Fig. 3). First, both preclosure and postclosure trip data verified the general expected pattern that trawls are mainly used on soft sediments in deeper water (greater than 60 m), and gillnets are used mainly on rocky bottoms in shallower areas (less than 60 m). These patterns indicate that a major effect of the closure was the removal of trawl impacts from the deeper, mainly finer sediments, and the removal of gillnet impacts from rocky areas along the top and southeast flank of Jeffreys Ledge.

The report data indicated that total gillnet fishing intensity in the overall 515-km2 study area was simi- lar before closure (2056 trips) and after closure (1812 trips); however, gillnet intensity nearly doubled in the area outside of the closure after closure (761 trips be- fore closure compared to 1494 trips after closure). This pattern indicates that any data interpreted as showing recovery of benthic communities in rocky areas where gillnets were the major gear type needs to be tempered because of increased postclosure gillnet fishing intensity in the “control” area outside the closure.

In contrast, trawling intensity in the overall 515-km2 study area decreased from 1103 trips before closure to 581 after closure (Fig. 3). There was a 39% decrease for trawl intensity outside the closure, from 894 trips before closure to 544 trips after closure. Moreover, the only portion of the study area inside the closure that was likely strongly affected by trawls before the closure was the deeper area north of Jeffreys Ledge. This infor- mation indicates that any data interpreted as showing recovery of benthic communities in soft sediment areas needs to be tempered because of the decreased trawl- ing intensity after closure in the control area outside the closure.

312

Fishery Bulletin 107(3)

A total of 163 sites in the 515-km2 study area were sampled with some combination of grab, box corer, and videotape recording (Fig. 2). Bottom types ranged from organic-rich muds in deeper water (greater than 100 m) to hard bottom (gravel and boulders) in water less than 80 m deep. Hard bottom areas typically were composed mainly of gravel and in many cases sufficient amounts of sand to allow grab samples to be success- fully obtained for infauna analysis. Some hard bottom sites also had boulders present, as determined from the video imagery, and these sites were classified as gravel (Fig. 2). No plants were collected in the grab and core samples or observed in the video imagery. Infauna dom- inated the soft sediments in deeper waters (and were mainly sampled by box corer and video recorder), and epifauna dominated the shallower hard bottom areas (mainly sampled by grab and video recorder).

There were strong differences across the three sedi- ment types for both infauna and epifauna. For the in- fauna, there were three significant sediment interaction

effects for density, biomass, and taxonomic richness from grab data; all three measures were substantial- ly higher in sand sediments inside the closure than outside the closure (Fig. 4). For the epifauna, there were significant sediment interactions for density and taxonomic richness; both variables were substantially greater only in gravel sediments inside the closure. Although the interaction effects clouded interpretation of the main effects (i.e., all sediments combined), there was consistency in that all measures were higher in- side the closure compared to outside the closure. There were two significant main effects (Fig. 4, A-F): higher densities of infauna from grab (P=0.01) and box corer (P=0.02) data inside compared to outside the closure. There were two significant main effects comparisons for epifauna (Fig. 4, G-H): total community density (P=0.0001) and taxonomic richness (P=0.0004), which were both higher inside.

Overall, these data indicate the following trends by sediment type. For mud, there were no consistent trends

Grizzle et al.: Effects of a large fishing closure on benthic communities in the western Gulf of Maine

313

(aidiues/exet jo jsqtunu) sseuqou ojiuouoxex

(zlu j. '0/6) sseutojg

(siu L O/Jsqtunu) A)|SU9Q

(aidtues/exei jo J0qwnu) sseuqou oiwouoxej_

(zw/exei jo jeqiunu) sseuqou ojiuouoxei

> >> 5 o

£5o

•D >• SO

l/i T5 c

_ a> ,E

<. if 1 1 03 O

= o

W

(2tu l. 0/6) sseujoig

“| « >. 3 TO C I rn O

O

C c

CO ^

£ c § .2

P a3

P- >H

P

I

o

03

P

P

,p

T £

0) . .

5= — ,

3 fe W I

iZ 0

Jo

03

eg 3 <P O

•rH CO

^ 3

5h

P ^ 03 -m o X

P d) be cd

P

^ '•a

>> a?

'p -2

° 1 0) o a u

>> CO -4-3

4_J P

c 2

<D H

E 3

T3 CD

^ rn

>> «

42 II

to »

§ O >-1 CD

43 £ .2 a

(2lu (. o/Jsqcunu) A}|SU0q

(giu/jsqiunu) Aysueo

•£ a3

s s

o u C ai o s- X 3 03 to

-*-> o

■"CJ CD P CD P ^

.2 3

42 03

for significant in vs. out differences for infauna or epi- fauna. For sand, there were strong and consistently greater density, biomass, and taxonomic richness for infauna inside the closure, but no in vs. out differences for epifauna. For gravel, there were no in vs. out dif- ferences for infauna, but greater density and taxonomic richness for epifauna inside the closure. In the context of fishing gear use, these data indicate recovery inside

the closure from the negative impacts of otter trawls on infauna in sand, but not mud, and recovery inside the closure from the impacts of gillnets on epifauna on gravel bottoms. The magnitude of recovery, however, cannot be directly inferred from these data because of the confounding factor of different fishing intensities when the preclosure and postclosure data were com- pared (Fig. 3). The overall negative impact of trawls

314

Fishery Bulletin 107(3)

(on sand sediments) was likely underestimated by our data, and the negative impact of gillnets (on gravel) was likely over estimated.

Discussion

In control-impact studies like this one, spatial effects cannot typically unambiguously be distinguished from temporal effects of the activity of interest, because no data are available from before the activity was started (Osenberg et al., 1994). Hence, such studies (in con- trast to the more rigorous before-after, control-impact [BACI] designs) must be assessed with respect to how factors that may have changed over time in relation to the control and impact areas might have contributed to any observed differences. Thus, it is possible that there were differences in the benthic communities before the WGOM closure was implemented that could have affected our interpretation of the data. Although this possibility cannot be unequivocally discarded, several lines of evidence indicate it is reasonable to assume simi- lar conditions in both areas before the closure. First, the overall study area was chosen so that the control sites with continued fishing outside the closure were in close proximity to the treatment sites inside the closure where fishing impacts were removed; this proximity of the two areas minimized potential confounding differences related to distance. Second, the range of habitat types and relative coverage area by each type were similar inside and outside the closure. Finally, we know of no other events since establishment of the closure — other than fishing gear restrictions and subsequent intensity patterns — that may have differentially affected the study areas inside and those outside the closure. There- fore, although we feel it is reasonable to interpret the differences inside and outside the closure in our data mainly to be the result of the removal of gillnets and otter trawls from the closed area, details on the spatial distribution patterns for each type of gear use must be considered in order to fully assess these impacts.

The obvious intent behind the WGOM closure was to eliminate negative impacts from both gear types inside the closure. Implementation of the closure, however, also caused a shift in fishing intensity, particularly for gillnets. Although this shift did not affect the overall conclusion of significant impacts for both gear types and subsequent recovery inside the WGOM closure, it does indicate that the relative levels of impact of the two gear types may have been exaggerated by our data: the impacts of gillnets may have been over-estimated because of the substantially increased postclosure fish- ing intensity outside, and the trawl impacts may have been under-estimated. Displacement of fishing effort and intensity may be the general trend for fishing clo- sures, and there is no straightforward way to estimate the magnitude of this effect (Ward, 2004; Fogarty and Murawski, 2005).

The major conservation concerns regarding the use of gillnets have been bycatch and entanglement of non-

target species (He, 2006). Our data, however, strongly indicate that gillnets have been responsible for substan- tial reductions in epifauna on Jeffreys Ledge. Although Malik and Mayer (2007) reported seafloor marks on top of the ledge which may be evidence of the use of other bottom fishing gear in this area, available fishing activity data on preclosure and postclosure gear use in the study area indicate that gillnets are the major gear used on rocky bottoms in the area. Therefore, the substantial and significant differences between epifauna densities and taxonomic richness inside (compared to outside) the closure would indicate that macrofaunal communities on hard bottoms were damaged by gillnets and are recovering from these effects.

Our data from soft-sediment areas where otter trawls were the dominant gear type reflect the general trends observed in other studies (see reviews by Dorsey and Pederson, 1998; Watling and Norse, 1998; Johnson, 2002; and Kaiser et al., 2006): decreased density, bio- mass, and taxonomic richness in benthic communities. To our knowledge, only one previous study of bottom habitats inside the WGOM closure has been completed, an M.S thesis by Knight (2005). This research focused on areas north of our study area that were mainly af- fected by trawls, and it also had a similar study design of inside vs. outside a closure. The sampling occurred from 2002 through 2004, covering nearly the same time interval as our project, but also included areas in the easternmost portion of the WGOM closure that were not incorporated into the closure area until 1999 (two years after the initial closure area was implemented). These differences aside, Knight (2005) reported find- ings similar to ours: much higher abundances for some infaunal and epifaunal taxa inside the closure compared to outside. Knight (2005) also noted that a shift in taxo- nomic composition of infauna (e.g., increases in sabellid polychaetes inside the closure) and epifauna towards taxa less tolerant of physical disturbances had occurred at sites inside the closure.

As already noted, our data indicate substantial recov- ery but cannot be used to accurately infer the magni- tude of recovery because of concurrent and confounding changes in fishing intensity during the study period. Additionally, our understanding of the recovery process for seafloor habitats disturbed by fishing gears is in the early stages — in large measure because of the number of factors involved (e.g., gear type, frequency and intensity of gear disturbances, and seafloor sediment type). Re- cent meta-analyses of gear effects have revealed widely variable recovery times, and no consistent trends for many combinations of gear and bottom types (Collie et al., 2000; Kaiser et al., 2006). In two recent studies on nearby Georges Bank in the Gulf of Maine few mea- surable effects of two large fishing closures were found for epifauna and infauna. Link et al. (2005) reported no significant differences in a variety of measures of benthic communities from video recordings and grab samples when comparing sites fished mainly by scallop dredges outside the closed areas with those inside the closures 4.5 years after closure. They attributed their

Grizzle et al.: Effects of a large fishing closure on benthic communities in the western Gulf of Maine

315

findings to the naturally dynamic nature of the seafloor that is frequently affected by storms and strong tidal currents (also see Auster and Langton, 1999; DeAlteris et ah, 1999; Henry et al., 2006). Stokesbury and Har- ris (2006) reported similar findings for a video study of epifauna in the same general study areas. In contrast, Collie et al. (2005) showed substantial recovery of ben- thic epifauna (megafauna) on gravel bottoms inside one of the closed areas on Georges Bank, but differ- ences did not occur until 2.5 years after closure, and increases in biomass and abundance of some taxa were still occurring after five years. They suggested that re- covery times for faunal communities on gravel bottoms in their study area were on the order of ten years. In sum, these data further indicate that long-term studies will be needed to fully assess the effects of the WGOM closure on the recovery process for benthic communities on hard bottoms.

A similar conclusion can be drawn for recovery of ben- thic communities on muddy bottoms inside the closure: the recovery process is still ongoing. Previous studies that indicate otherwise, however, need to be considered. For example, two studies in the western Gulf of Maine indicated rapid recovery of mud bottom communities. Sparks-McConkey and Watling (2001) reported recovery to ambient levels for the infauna on muddy bottoms within 3.5 months after experimental trawling distur- bance. Simpson and Watling (2006) also found only short-term (less than three months) effects on mud-bot- tom infaunal communities regularly fished by shrimp trawls with rock hopper gear compared to an adjacent unfished area. In both studies, the dominant taxa were small, nearsurface-dwelling species (mostly polychaetes) with high reproductive rates and thus potentially able to recover quickly from disturbance. It should also be noted that both these studies involved much smaller spatial scales (two study areas, each <40 km2) than that of our study (515 km2) such that immigration over smaller distances may have resulted in faster recovery rates. In contrast to these findings of minimal effects and fast recovery, some studies have shown substantial effects of otter trawls on mud-bottom communities and long recovery times, and the differences can in part be explained by differences in dominant taxa. If mud bottom communities include long-lived species, many of which are also structure-forming, then trawls (and other mobile gear) can have substantial adverse ef- fects, as was found in the meta-analysis of Collie et al. (2000). Jennings et al. (2001) and Queiros et al. (2006) found significant decreases in infaunal biomass and production on muddy bottoms related to trawling intensity, as well as differential responses in relation to size spectra of the dominant taxa. Hixon and Tissot (2007) documented 600% higher densities of epibenthic invertebrates (and 23% more fish) based on video tran- sects in untrawled (compared to trawled) mud bottom areas. Long-lived, slow-growing sea pens (Stylatula spp.) dominated the invertebrate communities in un- trawled areas, but were rare in trawled areas. Tillin et al. (2006) reported similar sea-basin scale patterns

in benthic communities in the North Sea in relation to fishing intensity; large, suspension-feeding epiben- thic taxa dominated in lightly trawled areas, whereas mobile taxa and infaunal and scavenging species were dominant in areas that were more heavily trawled. Therefore, the level of effect and recovery times for benthic communities on mud bottoms affected by bot- tom trawls can be expected to vary widely, dependent in part on characteristics of the dominant species, and areas dominated by large or structure-forming taxa can be the most negatively affected. Further studies will be required to characterize the process over the long term, and such research should include more rigorous assessment of variations in fishing intensity than was possible in our study (Hiddink et al., 2006).

A final topic here concerns possible indirect effects on benthic communities caused by removal of fishing pressure on species that consume benthic invertebrates (Pinnegar et al., 2000). Unfortunately, little information is available on how fish populations have responded to the WGOM closure. However, available data indicate lit- tle or no increase in populations of fish such as gadids, skates, and flatfish that prey on benthic invertebrates (Murawski et al., 2004, 2005). However, recent exper- imental tethering studies showed greater predation rates on adult crabs ( Cancer spp.) in rocky areas inside the closure (Meyer, 2005). Meyer also found very slow colonization rates on experimental habitat plots inside and outside of the closure, and no significant effects of predator exclusion cages on these rates. In sum, these data suggest that any indirect effects caused by dif- ferential predation rates inside compared to outside of the closure would have been weak. Meyer’s (2005) colo- nization experiments (which were conducted over 4- to 12-month periods) also indicate that any recovery rates occurring inside the closure would be relatively slow.

The WGOM closure area is achieving a very impor- tant management goal: protection and enhancement of seafloor habitats. How are these changes related to ongoing recoveries of some fish populations and what are the management implications?

Closed area management measures are expected to have two separate effects on productivity and sustain- ability of fisheries (Stefansson and Rosenberg, 2005). First, if the closure is properly designed, it may reduce fishing mortality rates on some stocks by shifting lim- ited effort away from areas where catchability is high to areas where it is lower. Effort control is essential to ensure that effort increases don’t compensate for re- duced catchability. Reduced fishing mortality rates on overfished stocks should increase productivity through higher stock and recruitment levels.

Secondly, closed areas that protect habitat may in- crease productivity of stocks by increasing growth, re- production, and survival rates. This effect of closed areas is much harder to quantify or demonstrate with respect to recovery of the fish stocks. But, one impor- tant aspect of inferred habitat quality is the abundance of food resources for fishes, including both infauna and epifauna.

316

Fishery Bulletin 107(3)

The management implications from this study are also two-fold. The observed differences in infauna and epifauna indicate that the closed area has been an ef- fective measure for protecting habitat and potentially aiding stock recovery, although the latter has yet to be quantified. This conclusion is important regionally because closed area effects on reducing fishing mortal- ity in New England have been generally accepted, but habitat protection benefits are still controversial.

A second important implication from this study is in the design of closed areas. The results presented here indicate that the particular bottom types that benefit most from protection depend on the type and intensity of fishing gear use before the closure is es- tablished. For example, the rocky bottoms in our study area were heavily fished with gillnets before the closure was implemented, and they showed the most recovery for epifauna, but little difference for infauna. As man- agement of closed areas is modified in the future, these results will help clarify design criteria and refine the design of closures. Coupled with the improved ability to accurately monitor the position of vessels during fishing operations, these data may enable managers to more finely tailor spatial characteristics of closed areas thereby improving the effectiveness of management measures while potentially reducing the restrictions on fishing operations.

Acknowledgments

This research was funded by the Northeast Consortium and the Atlantic Marine Aquaculture Center (AM AC) at the University of New Hampshire. It was a collaborative effort between the scientific and fishing communities of New Hampshire. Fishing vessels were used on all research cruises, and included vessels captained by P. Kendall, C. Mavrikis, and J. Driscoll. We are very appreciative of the efforts of these fishermen in deploying sampling gear, solving a multitude of technical problems, and freely sharing their knowledge of the study areas. We thank J. Adams for participation in nearly all aspects of the study, particularly for many days at sea collecting core and grab samples. R. McDonnell, R. Cutter, and E. Merchant also assisted in field work. We thank K. Ward, K. Graiff, R. McDonnell, S. Mikulak, and M. Graffam for processing the benthic infauna samples. B. Clifford kindly provided the vessel trip report data. The manu- script was substantially improved by the comments of three anonymous reviewers. This is Contribution 472 in the Jackson Estuarine Laboratory Contribution Series.

Literature cited

Auster, P. J., and R. W. Langton.

1999. The effects of fishing on fish habitat. In Fish habitat: essential fish habitat and rehabilitation (L. R. Benaka, ed.), p. 150-187. Am. Fish. Society Symp. 22, Bethesda, MD.

Breslow, N. E., and D. G. Clayton.

1993. Approximate inference in generalized linear mixed models. J. Am. Stat. Assoc. 88:9-25.

Byers, S. C., E. L. Mills, and P. L. Stewart.

1978. A comparison of methods of determining organic carbon in marine sediments, with suggestions for a standard method. Hydrobiologia 58:43-47.

Collie, J. S., S. J. Hall, M. J. Kaiser, and I. R. Poiner.

2000. A quantitative analysis of fishing impacts on shelf- sea benthos. J. Animal Ecol. 69:785-798.

Collie, J. S., J. M. Hermsen, P. C. Valentine, and F. P. Almeida.

2005. Effects of fishing on gravel habitats: assessment and recovery of benthic megafauna on Georges Bank. In Benthic habitats and the effects of fishing (P. W. Barnes and J. P. Thomas, eds.), p. 325-343. Am. Fish. Soc. Symp. 41, Bethesda, MD

DeAlteris, J., L. Skrobe, and C. Lipsky.

1999. The significance of seabed disturbance by mobile fishing gear relative to natural processes: a case study in Narragansett Bay, Rhode Island. In Fish habitat: essential fish habitat and rehabilitation (L. R. Benaka, ed.), p. 224-237. Am. Fish. Soc. Symp. 22, Bethesda, MD

Dorsey, E. M., and J. Pederson.

1998. Effects of fishing gear on the sea floor of New England, 160 p. Conservation Law Foundation, Boston, MA.

Fogarty, M., and S. Murawski.

2005. Do marine protected areas really work? Oceanus 43(2): 1— 3 .

Folk, R. L.

1980. Petrology of sedimentary rocks, 182 p. Hemphill Publishing Company, Austin, TX.

He, P.

2006. Gillnets: Gear design, fishing performance and con- servation challenges. Mar. Tech. Soc. J. 40:11-18.

Henry, L.-A., E. L. R. Kenchington, T. J. Kenchington, K. G. Maclssac, C. Bourbonnais Boyce, and D. C. Gordon Jr.

2006. Impacts of otter trawling on colonial epifaunal assemblages on a cobble bottom ecosystem on West- ern Bank (northwest Atlantic). Mar. Ecol. Prog. Ser. 306:63-78.

Hiddink, J. G., S. Jennings, and M. J. Kaiser.

2006. Recovery status as an indicator of the large scale ecological impact of bottom trawling. Ecosystems 9:1190-1199.

Hixon, M. A., and B. N. Tissot.

2007. Comparison of trawled vs untrawled mud seafloor assemblages of fishes and macroinvertebrates at Coquille Bank, Oregon. J. Exp. Mar. Biol. Ecol. 344:23-34.

Jennings, S., T. A. Dinmore, D. E. Duplisea, K. J. Warr, and J. E. Lancaster.

2001. Trawling disturbance can modify benthic produc- tion processes. J. Anim. Ecol. 70:459-475.

Johnson, K. A.

2002. A review of national and international literature on the effects of fishing on benthic habitats. NOAA Tech. Memo. NMFS-F/SPO-57, 72 p.

Kaiser, M. J., K. R. Clarke, H. Hinz, M. C. V. Austen, P. J. Somer- field, and I. Karakassis.

2006. Global analysis of response and recovery of benthic biota to fishing. Mar. Ecol. Prog. 311:1-14.

Knight, E. P.

2005. The effects of trawling on benthic habitats: an anal- ysis of recovery in the Western Gulf of Maine closure. M. S. thesis, 94 p. Univ. Maine, Orono, ME.

Grizzle et at: Effects of a large fishing closure on benthic communities in the western Gulf of Maine

317

Link, J., F. Almeida, P. Valentine, P. Auster, R. Reid, and J. Vitaliano.

2005. The effects of area closures on Georges Bank. In Benthic habitats and the effects of fishing (P. W. Barnes and J. P. Thomas, eds.), p. 345-369. Am. Fish. Soc. Symp. 41, Bethesda, MD.

Malik, M., and L. A. Mayer.

2007. Investigation of bottom fishing impacts on benthic structure using multibeam sonar, sidescan sonar and video. ICES J. Mar. Sci. 64:1053-1065.

McCullagh, P., and J. A. Nelder.

1989. Generalized linear models, 500 p. Chapman Hall/ CRC, Boca Raton, FL.

Meyer, J. J.

2005. Top-down effects on the benthic invertebrate com- munity in the Western Gulf of Maine closure area: a measure of reserve effectiveness? M.S. thesis, 96 p. Univ. New Hampshire, Durham, NH.

Murawski, S., P. Rago, and M. Fogarty.

2004. Spillover effects from temperate marine protected areas. In Aquatic protected areas as fisheries manage- ment tools (J. B. Shipley, ed.) p. 167-184. Am. Fish. Soc. Symp. 42, Bethesda, MD.

Murawski, S., S. E. Wigley, M. J. Fogarty, P. J. Rago, and D.G. Mountain.

2005. Effort distrigution and catch patterns adjacent to temperate MPAs. ICES J. Mar. Sci. 62:1150-1167.

NRC (National Research Council).

2002. Effects of trawling and dredging on seafloor habi- tats, 126 p. National Academy Press, Washington, D.C.

Osenberg, C. W., R. J. Schmitt, S. J. Holbrook, K. E. Abu-Saba, and A. R. Flegal.

1994. Detection of environmental impacts. Ecol. Appl. 4:16-30.

Palumbi, S. A.

2002. Marine reserves: a tool for ecosystem manage- ment and conservation, 45 p. Pew Oceans Commission, Washington, D.C.

Pinheiro, J. C., and D. M. Bates.

2000. Mixed-Effects Models in S and S-PLUS, 528 p. Springer-Verlag, New York, NY.

Pinnegar, J. K., N. V. C. Polunin, P. Francour, F. Badalamenti, R. Chemello, M.-L. Harmelin-Vivien, B. Hereu, M. Milazzo, M. Zabala, G. D’Anna, and C. Pipitone.

2000. Trophic cascades in benthic marine ecosystems: les-

sons for fisheries and protected-area management. En- viron. Conserv. 27:179-200.

Queiros, A. M., J. G. Hiddink, M. J. Kaiser, and H. Hinz.

2006. Effects of chronic bottom trawling disturbance on benthic biomass, production and size spectra in different habitats. J. Exp. Mar. Biol. Ecol. 335:91-103.

Shipley, J. B.

2004. A summary and overview of the symposium. In Aquatic protected areas as fisheries management tools (J. B. Shipley, ed.) p. xv-xvii. Am. Fish. Soc. Symp. 42, Bethesda, MD.

Simpson, A. W., and L. Watling.

2006. An investigation of the cumulative impacts of shrimp trawling on mud-bottom fishing grounds in the Gulf of Maine: effects on habitat and macrofaunal com- munity structure. ICES J. Mar. Sci. 63:1616-1630.

Sokal, R. R., and F. J. Rohlf.

1981. Biometry, the principles and practice of statistics in biological research, 859 p. W.H. Freeman and Co., New York, NY.

Sparks-McConkey, P. J., and L. Watling.

2001. Effects on the ecological integrity of a soft-bottom habitat from a trawling disturbance. Hydrobiologia 456:73-85.

Stefansson, G., and A. A. Rosenberg.

2005. Combining control measures for more effective management of fisheries under certainty: quotas, effort limitation and protected areas. Philos. Trans. R. Soc. Lond. B Biol. Sci. 360:133-146.

Stokesbury, K. D. E., and B. P. Harris.

2006. Impact of limited short-term sea scallop fish- ery on epibenthic community of Georges Bank closed areas. Mar. Ecol. Prog. Ser. 307:85-100.

Tillin, H. M., J. G. Hiddink, S. Jennings, and M. J. Kaiser.

2006. Chronic bottom trawling alters the functional composition of benthic invertebrate communities on a sea-basin scale. Mar. Ecol. Prog. Ser. 318:31-45.

Ward, T. J.

2004. Marine protected areas in fisheries: design and per- formance issues. In Aquatic protected areas as fisheries management tools (J. B. Shipley, ed.) p. 37-61. Am. Fish. Soc. Symp. 42, Bethesda, MD.

Watling, L., and E. A. Norse.

1998. Disturbance of the seabed by mobile fishing gear: a comparison with forest clear-cutting. Conserv. Biol. 12:1180-1197.

318

Abstract — Although the Florida pompano ( Trachinotus carolinus) is a prime candidate for aquaculture, the problematic production of juve- niles remains a major impediment to commercial culture of this species. In order to improve the understanding of larval development and to refine hatchery production techniques, this study was conducted to characterize development and growth of Florida pompano from hatching through metamorphosis by using digital pho- tography and image analysis. Newly hatched larvae were transparent and had a large, elongate yolk sac and single oil globule. The lower and upper jaws as well as the digestive tract were not fully developed at hatching. Rotifers were observed in the stomach of larvae at three days after hatch- ing (DAH), and Artemia spp. were observed in the stomach of larvae at 14 DAH. Growth rates calculated from total length measurements were 0.22 ±0.04, 0.23 ±0.12, and 0.35 ±0.09 mm/d for each of the larval rearing trials. The mouth gape of larvae was 0.266 ±0.075 mm at first feeding and increased with a growth rate of 0.13 ±0.04 mm/d. Predicted values for optimal prey sizes ranged from 80 to 130 pm at 3 DAH, 160 to 267 pm at 5 DAH, and 454 to 757 pm at 10 DAH. Based on the findings of this study, a refined feeding regime was developed to provide stage- and size- specific guidelines for feeding Florida pompano larvae reared under hatch- ery conditions.

Manuscript submitted 5 May 2008. Manuscript accepted 24 March 2009. Fish. Bull. 107:318-328 (2009).

The views and opinions expressed or implied in this article are those of the author and do not necessarily reflect the position of the National Marine Fisheries Service, NOAA.

Development and growth of hatchery-reared larval Florida pompano ( Trachinotus carolinus)

Kenneth L. Riley (contact author)1

Charles R. Weirich2 David Cerino2

Email address for contact author: klr1011@ecu.edu

1 Center for Aquaculture and Stock Enhancement Harbor Branch Oceanographic Institute at Florida Atlantic University 5600 U.S. Highway 1 North Fort Pierce, Florida 34946

Present address for contact author: Department of Biology

East Carolina University,

Greenville, North Carolina 27858-4353

2 United States Department of Agriculture, Agricultural Research Service 5600 U.S. Highway 1 North Fort Pierce, Florida 34946

Jacks and pompanos of the family Carangidae are represented by 33 genera and approximately 140 spe- cies found in tropical and subtropical oceans around the world (Helfman et al., 2003). Because carangids are highly regarded as food and game fishes, many species are exploited worldwide. Common to the south- eastern Atlantic and Gulf of Mexico coasts of the United States, the Flor- ida pompano (Trachinotus carolinus) is a prime candidate for aquaculture and stock enhancement programs because of its high value and limited availability from commercial harvests (Watanabe, 1995; Craig, 2000).

The larvae and early juveniles of 28 species of carangids of the South Atlantic and Gulf coasts have been described with some detail (Goode, 1882; Starks, 1911; Ginsburg, 1952; Aprieto, 1974; Laroche et al., 1984; Fahay, 2007). Fields (1962) described wild-caught Florida pompano rang- ing in size from 4.0 to 42.1 mm total length (TL), and more recently Fahay (2007) described fish ranging in size from 3.1 to 14.8 mm TL. Although these reports provide essential in- formation on the early life history of jacks and pompanos for fishery bi- ologists, additional knowledge on the morphological development, growth, and trophic requirements is essential to evaluate new species for culture

and to develop effective hatchery rear- ing techniques and feeding regimes.

Significant interest in the culture of Florida pompano developed in the United States during the 1960s and 1970s and, as a result, efforts were initiated to develop spawning and rearing techniques for this species (Moe et al., 1968; Hoff et al., 1972, 1978a; McMaster, 1988). Florida pom- pano exhibit a number of desirable characteristics for aquaculture (Wei- rich et al., 2006). The species exhibits a high rate of growth, readily accepts commercially prepared diets, adapts to low salinity environments, and has been successfully cultured in tanks, ponds, cages, and offshore netpens. Unfortunately, the production of a reliable supply of juveniles to stock grow-out operations has been a lim- iting factor with respect to commer- cial culture of this species. Hoff et al. (1972) reported producing an average of only 300 juveniles per spawning event, and until recently, researchers and commercial culturists alike were largely unsuccessful at producing the quantities of eggs and larvae needed for commercial production or stock en- hancement programs. Weirich and Ri- ley (2007) reported that in a series of nine spawning trials conducted over a two-year period, 3.2 million fertil- ized eggs were produced by 40 adult Florida pompano (1:1 sex ratio). These

Riley et al.: Development and growth of hatchery-reared larval Trachmotus carolmus

319

values approximate the necessary quantities needed for mass production. The advent of new broodstock man- agement techniques for domestication and controlled reproduction in captivity offer great promise for the culture of Florida pompano. However, there is a need to develop and refine hatchery technologies for this spe- cies because larvae undergo major functional and mor- phological changes throughout their early life history.

Florida pompano eggs are typical of marine fishes with pelagic eggs. In a single spawning event, one fe- male can produce 200,0000 to 400,000 small, buoy- ant eggs that range in size from 0.87 to 1.00 mm in diameter (Hoff et al., 1978a). Florida pompano eggs normally have a single oil globule, although eggs from some broodfish reportedly have several small oil glob- ules. The size and number of oil globules within eggs can serve as an indicator of egg quality and correlate with the amount of energy available for developing lar- vae (Barbaro et al., 1991). The yolk that is deposited during vitellogenesis must provide nutrition for the developing embryo and larvae. Newly hatched Florida pompano larvae are approximately 2.0 mm TL and are not well developed (Hoff et al., 1978b). Depending on water temperature and developmental rates, larvae use yolk reserves for two to three days after hatching (DAH), which coincides with pigmentation of the eyes, mouth formation, and first feeding. Florida pompano larvae have been cultured by using a variety of live zooplankton, including copepods, rotifers, and Artemia spp. Florida pompano undergo metamorphosis at 24 DAH at 15 mm TL and can easily transition to dry feeds (McMaster, 1988).

Previously published descriptions of Florida pom- pano larvae provide limited details on development and growth under hatchery conditions. To improve the understanding of larval development of this species, the present study was conducted to measure the growth of larvae from hatching through metamorphosis by using digital photography and image analysis. The specific objectives were 1) to compare morphological variation among larvae from three different spawning trials; 2) to document time of occurrence for critical periods including first feeding, yolk and oil globule exhaustion, gas bladder inflation, transition in diet, and onset of metamorphosis; and 3) to develop a model feeding re- gime for Florida pompano larvae.

Materials and methods

Spawning and egg incubation

This study presents data regarding developmental char- acteristics and growth of larvae obtained from captive reproduction of Florida pompano broodstock held at the U.S. Department of Agriculture, Agricultural Research Service (USDA-ARS) Center for Reproduction and Lar- viculture in Fort Pierce, Florida (Weirich and Riley, 2007). Broodstock (sex ratio, 1:1) were held in recirculat- ing tank systems under controlled photothermal condi-

tions and were sampled periodically to assess health and reproductive condition. To initiate spawning, ripe females (mean oocyte diameter >500 pm) and males were implanted with a 75 -pg slow-release pellet of gonadotro- pin-releasing hormone analogue (Syndel International, Inc., Vancouver, BC). Fish spawned volitionally approxi- mately 36 hours after hormone implantation, and eggs were collected and stocked into aerated 100-L incuba- tion tanks (24-26°C). Hatching occurred approximately 30-36 hours after fertilization.

Larval culture

In three independent larval rearing trials (initiated 15 June 2004, 17 June 2004, 17 August 2005), approxi- mately 50,000 larvae (0 DAH) were stocked into a 1.0-m3 round fiberglass tank. The tank was filled with 800 L of natural seawater that had been subjected to biologi- cal and mechanical filtration, in addition to ultraviolet sterilization, before use. Water quality was monitored daily with a multiparameter dissolved oxygen probe (YSI Incorporated, Model 85, Yellow Springs, OH). Water was not exchanged from zero DAH through five DAH. After five DAH, water quality was maintained by daily water changes ranging from 50% to 200% through 20 DAH.

Although similar production methods were used dur- ing each year of the study, trials were conducted within a greenhouse during the first year of the study and within an insulated, climate-controlled hatchery dur- ing the second year. After stocking, tanks were gently aerated and surface light levels were maintained at 300 lux (model LI-189, LI-COR, Lincoln, NE) for 16 hours daily. At two DAH, the aeration level was increased, tanks were inoculated with cultured microalgae ( Nan - nochloropsis oculata) (Instant Algae, Reed Mariculture, Campbell, CA) to maintain green water culture condi- tions, and surface light levels were increased to 2000 or 3000 lux. Larvae were fed enriched rotifers ( Brachionus plicatilis; 53-225 pm) from two DAH through 15 DAH. Rotifer strains and size distributions differed among years (Fig. 1). Larvae were fed Artemia spp. nauplii (-480 pm) from 12 DAH through 20 DAH (Embryon, INVE, Salt Lake City, UT). Live feed organisms were fed three times daily and were maintained at densi- ties of one to three individuals per mL. Artificial feed (400-800 pm diameter particles) was offered to larvae beginning at 10 DAH (INVE NRD Micro Pellet, Salt Lake City, UT).

Sample collection

Samples of 10 larvae were randomly collected daily from hatching through completion of metamorphosis at 20 DAH. Larvae were euthanized by brief immersion in cold seawater (4°C), placed on glass slides, and photographed by using a dissecting microscope at 4x magnification. A compound microscope at 100 x magnification was used to photograph the head and mouth of each larva from 0 DAH through 5 DAH; thereafter, the head and mouth of each larva was photographed by using the dissect-

320

Fishery Bulletin 107(3)

ing microscope. All larvae were photographed on their left sides in the sagittal plane, and a fine-point needle was used to position larvae as necessary. Microscopes were equipped with high-resolution digital cameras (Sony DSC-FS17, San Diego, CA), and photographs were recorded as uncompressed files in tagged image file format (TIFF) at 6 megapixels. For calibration, a 0.01-mm micrometer scale bar was photographed for each larval series and for both microscopes.

Image analysis

Larvae and selected anatomical features were mea- sured and analyzed by using SigmaScan Pro 5.0 image analysis software (SPSS Science, Chicago, IL). All mor- phometric measurements listed below were recorded to the nearest 0.001 mm and calibration errors were maintained at less than 1 pm (<0.1% of 1 mm). The total length (TL) and standard length (SL) of larvae was measured along lines parallel to the longitudinal axis of the fish (Snyder 1983).

Body depth — The distance, perpendicular to the lon- gitudinal axis of the body from the insertion of the first dorsal spine to the ventralmost point of the body. For yolksac larvae, the distance perpendicular to the longi- tudinal axis of the body from the dorsal crest through

CD

Figure 1

Size-frequency histograms of rotifer cultures used to feed larval Florida pompano (Tracliinotus carolinus). Stock cultures of rotifers (Brachionus plicatilis) were obtained from (A) Aquaculture Center of the Florida Keys (ACFLK, Marathon, FL) in 2004 and (B) Oceans Reefs and Aquariums (ORA, Fort Pierce, FL) in 2005.

the midpoint of the yolk to the ventralmost point of the body.

Head length — The distance, parallel to the longitu- dinal axis of the head, from tip of snout to the edge of the operculum.

Eye diameter — The distance, parallel to the longi- tudinal axis of the head, from anteriormost to posteri- ormost points of bony orbit.

Yolksac length — The distance, parallel to longitudi- nal axis of the body, from anteriormost to posteriormost points of the yolk sac.

Yolksac depth — The distance, perpendicular to the longitudinal axis of the body, from ventralmost to dor- salmost points of yolk sac.

Oil globule diameter — The distance, parallel to longitudinal axis of the body, from anteriormost to pos- teriormost points of oil globule.

Length of upper jaw — The length of the premaxil- lae and maxillae to the point of articulation with the dorsal process of the dentary.

Length of lower jaw — The length of the dentary to the point of articulation with the angular and maxillae.

At the time of measurement, observations of larval development state were recorded to identify the chrono- logical sequence of events. The following critical periods were noted when first observed: 1) hatching; 2) mouth formation; 3) body pigmentation; 4) eye formation and pigmentation; 5) stomach and digestive tract forma- tion; 6) first feeding; 7) yolk exhaustion; 8) oil globule exhaustion; 9) diet transition from rotifers to Artemia spp.; and 10) metamorphosis. Completion of the larval stage and metamorphosis was defined as the point when the axial skeleton is ossified and fish acquire the ana- tomical and morphological characteristics of juveniles.

The relationship between TL and age; SL and age; and mouth gape and age were plotted separately for each larval rearing trial. Total and standard length data of larvae were fitted to a simple curvilinear equa- tion (i.e., y=a+ b xx° 5). The comparison between these plots allowed assessment of somatic growth pattern through time. Repeated-measures analysis of variance was then used to statistically compare growth rates among rearing trials. To normalize observations and stabilize the variance, data were logarithmically trans- formed before statistical analysis. Tukey’s test was used to determine if significant differences existed among treatment means. Differences were considered signifi- cant at P<0.05. The general linear model function in SigmaStat 3.0 (SPSS Science, Chicago, IL) was used for all analyses.

Regression equations were calculated for total and standard length, yolk volume, and oil globule volume for larvae cultured from each spawn. Yolk volume was de- termined by using the equation for a prolate spheroid:

Yolk volume =

4/3 ji [ yolk-sac length ] [yolk-sac depth]2. (1)

Oil globule volume was determined by using the equa- tion for a sphere:

Riley et al.: Development and growth of hatchery-reared larval Trachinotus carolmus

321

Oil globule volume =

4/3 jt [ oil globule diameter /2]3. (2)

Length and volume data were then plotted against age. The curvilinear equation, y-a + by-x^1, was fitted to the yolk and oil globule volume data and plotted with 95% confidence limits.

The mouth gape was determined by using length measurements of the upper and lower jaws and the Law of Cosines equation for a triangle with two known sides and an angle between them:

a2 = b2 + c2 - 2 be cos a, (3)

where a = mouth gape; b = upper jaw; c - lower jaw; and

a = angle that forms the degree of mouth opening.

Calculations were based on the assumption that during active feeding the mouth of larvae opens to an angle ranging from 90° to 120° to capture prey (Shirota, 1970). Optimal prey sizes were estimated at 30% and 50% of mouth gape for larvae (Yasuda,

1960; Shirota, 1970; Hunter and Lasker, 1981; Cunha and Planas, 1999).

Results

During each 20-day trial, production of postmeta- morphic juvenile Florida pompano ranged from 1.5 to 5.0 fish/liter. Although water temperature is an important factor governing growth, there was no significant difference among any of the water quality parameters measured among rear- ing trials (P=0.67). In the first rearing trial, dis- solved oxygen was 5.7 ±0.2 mg/L (mean ± SE), temperature was 25.5 ±0.2°C, and salinity was 34.9 ± 0.6 g/L. In the second rearing trial, dis- solved oxygen was 5.6 ±0.2 mg/L, temperature was 25.5 ± 0.2°C, and salinity was 34.8 ±0.5 g/L.

In the third rearing trial, dissolved oxygen was 5.7 ±0.1 mg/L, temperature was 25.0 ±0.6°C, and salinity was 34.5 ±0.6 g/L.

Eggs collected from each spawning event were uniform in shape and appearance. Fertilized eggs were 0.99 ±0.04 mm in diameter and contained a single oil globule (Fig. 2A). Newly hatched larvae were transparent, small (TL = 2.6 ±0.4 mm), and not well developed (Fig. 2B). As typical of carangids, lar- vae hatched with large, elongate yolk sacs extending beyond the head and along the ventral region of the head and gut. A single oil globule was situated at the posterior end of the yolk sac. At hatching, the lower and upper jaws, as well as the digestive tract, were not fully developed. Pigmented eyes and functional mouth parts had formed by the end of two DAH when the larval swimming pattern became stronger and feed-

ing behavior was first observed. Melanophores were observed forming along the head and dorsal surface of the body at two DAH. The stomach and a primitive intestine were observed forming at two DAH, and the intestine had connected with the anus at three DAH. Rotifers and algae were first observed in the stomachs of larvae at three DAH. Larvae had exhausted yolk reserves at three to four DAH and the remaining oil globule at four to five DAH and were completely tran- sitioned to exogenous feeding at five DAH (Fig. 3; Fig. 4A). Larvae at seven DAH exhibited a fully formed

322

Fishery Bulletin 107(3)

and well developed digestive system (Fig. 4B). Artemia spp., which were first offered 12 DAH, were observed in the stomach of larvae along with rotifers at 14 DAH. Artificial feeds, which were offered beginning 10 DAH, could not be detected through observation with a dis- secting microscope. Although Florida pompano lack a gas bladder, approximately 10% of larvae consumed small air bubbles (129-235 pm) that were trapped in the peritoneal cavity from 5 to 10 DAH.

Swimming ability improved and larvae were notice- ably stronger with pectoral fin development at four to five DAH. The dorsal, pelvic, and anal fins began de- veloping at nine DAH and the formation of the caudal fin and fin rays was observed at 12 DAH. Morphologi- cal and osteological development at six and seven DAH was noticeably more advanced in the third rearing trial than in specimens collected in the previous trials. As evidenced by the formation of hypural elements, no- tochord flexion was first observed at 10 to 12 DAH in the first two rearing trials. In the third rearing trial, notochord flexion was observed 8 to 11 DAH. Larvae completed flexion at 12 to 16 DAH in the first two rear- ing trials, and at 11 to 12 DAH in the third rearing trial. Postflexion and the onset of transformation were apparent at 15 to 18 DAH in the first two rearing tri- als (Fig. 5A), and at 13 to 14 DAH in the third rearing trial. Larvae in the first two rearing trials completed transformation and had a full complement of fins and scales by 20 DAH (Fig. 5B), whereas fish in the third rearing trial completed transformation by 17 DAH.

Differences in growth were observed among trials. Mean growth rates calculated from TL measurements were 0.22 ±0.04, 0.23 ±0.12, and 0.35 ±0.09 mm/d for each of the larval rearing trials. Larvae in the third trial grew faster than fish in the first and second trial.

Measured growth parameters of Florida pompano larvae reared from one through 20 DAH are summarized in Table 1. Statistical analysis evaluating TL and age (Fig. 6) revealed no significant differences among growth rates from hatching through six DAH (P=0.84); howev- er, a significant difference in growth rate was detected for larvae reared in the third trial (P= 0.007) after seven DAH (Table 2). No significant differences were detected between the first two rearing trials (P=0.12).

Similar results were observed with a statistical anal- ysis of larvae, where SL and age (Fig. 7) were used to determine growth rates. Mean growth rates were 0.18 ±0.03, 0.18 ±0.10, and 0.31 ±0.08 mm/d for each of the larval rearing trials. No significant differences were observed among growth rates from hatch through eight DAH (P- 0.75); however, a significant difference in growth rate was detected for larvae reared in the third

Figure 4

Early stage Florida pompano ( Trachinotus carolinus ) reared in the laboratory and photographed with a dis- secting microscope and digital camera. (A) Larva at three days after hatching (DAH) near initiation of exog- enous feeding and with eye pigmentation. (B) Larva at 7 DAH with fully formed digestive system, distinctive pigmentation, and initial development of head spines. Scale represents 1 mm.

Riley et al.: Development and growth of hatchery-reared larval Trachmotus carolinus

323

Figure S

Late stage Florida pompano ( Trachinotus carolinus) reared in the laboratory and photographed with a dissecting microscope and digi- tal camera. (A) Postflexion larva at 18 days after hatching (DAH) undergoing transformation. Note presence of preopercular spines. (B) Juvenile at 20 DAH transitioning to artificial feeds. Scale rep- resents 1 mm.

trial (P<0.001) after nine DAH. Larvae in the third trial grew significantly faster than fish in the first and second trial (P<0.001). No significant differences were detected among the first two rearing trials (P=0.18).

No significant differences were observed in larval mouth size among rearing trials (P=0.16). The mean mouth gape of larvae was 0.266 ±0.075 mm at first feeding and increased with a growth rate of 0.13 ±0.04 mm/d (Table 3). The length of the upper and lower jaws and mouth gape increased linearly with age (Table 4). Predicted values for optimal prey sizes ranged from 80 to 130 pm at three DAH, 160 to 267 pm at five DAH, and 454 to 757 pm at 10 DAH. These values correspond closely with the sizes of rotifers and Artemia spp. nau- plii fed to larvae during each of the rearing trials.

Larvae that exhibited aggressive behavior progressed through metamorphosis earlier than their cohorts. Can- nibalism, defined by Smith and Reay (1991) as the act of killing and consuming the whole, or major part, of

an individual belonging to the same species regardless of its age or stage of development, was not observed in the rearing trials. The dominant, aggressive behavior observed was that of inflicting injury that resulted in mortality in small premetamorphic individuals.

Discussion

As a direct result of aquaculture research, the larval development of a number of valuable marine fish species has been described and characterized. The early life stages of species such as striped bass (Morone saxatilis ; Brown et al., 1998), red drum ( Scieanops ocellatus\ Lee et al., 1984), and red snapper (Lutjanus campechanus; Drass et al., 2000) were studied to support efforts for food production and stock enhancement in the United States, and global research on the early life history of a number of valuable species has led to the develop-

324

Fishery Bulletin 107(3)

Table 1 Morphometries of Florida pompano (Trachinotus carolinus) from one day after hatching (DAH) through 20 DAH cultured at 25°C. Metamorphosis was completed at 17-19 DAH. The relationship of head length to standard length ranged from 33% to 49%. Values are means ±standard error (SE) for larvae sampled from three rearing trials (n = 600).
Days after hatching	Total length (mm)	Standard length (mm)	Body depth (mm)	Head length (mm)	Eye diameter (mm)
1	2.27 ±0.50	2.14 ± 0.58	0.61 ±0.06	—	0.19 ±0.02
2	2.62 ±0.31	2.52 ±0.50	0.67 ±0.10	—	0.25 ±0.00
3	2.71 ±0.27	2.69 ±0.54	0.65 ±0.04	—	0.28 ±0.01
4	2.84 ±0.76	2.76 ±0.25	0.68 ±0.06	—	0.28 ±0.03
5	3.05 ±1.01	2.80 ±0.25	0.66 ±0.07	—	0.29 ±0.02
6	3.25 ±1.26	2.96 ±0.24	0.60 ±0.07	1.08 ±0.19	0.34 ±0.17
7	3.55 ±1.52	3.06 ±0.30	0.74 ±0.07	1.17 ±0.17	0.31 ±0.08
8	3.67 ±1.50	3.31 ±0.51	0.74 ±0.03	1.25 ± 0.27	0.35 ±0.12
9	3.95 ±1.36	3.67 ±0.47	0.87 ±0.07	1.42 ±0.24	0.39 ±0.17
10	4.20 ±1.64	3.80 ±0.53	0.91 ±0.04	1.42 ±0.27	0.42 ±0.26
11	4.37 ±1.78	4.10 ±0.88	0.95 ±0.01	1.53 ±0.45	0.45 ±0.26
12	4.49 ±1.67	4.46 ±1.24	0.95 ±0.02	1.68 ±0.59	0.47 ±0.37
13	4.87 ±1.96	4.79 ±1.39	0.98 ±0.09	1.77 ±0.68	0.47 ±0.32
14	4.95 ±1.35	4.95 ±2.06	1.20 ±0.23	1.89 ±0.62	0.53 ±0.39
15	5.18 ±1.48	5.15 ±2.20	1.15 ±0.03	1.90 ±0.74	0.52 ±0.43
16	5.51 ±1.44	5.54 ±2.13	1.31 ±0.32	1.99 ±0.78	0.55 ±0.61
17	5.71 ±1.46	5.42 ±0.20	1.39 ±0.22	2.15 ±0.69	0.61 ±0.49
18	5.99 ±1.46	5.48 ±0.17	1.51 ±0.05	2.22 ±0.74	0.59 ±0.40
19	6.72 ±1.44	5.92 ±0.11	1.61 ±0.10	2.23 ±0.94	0.60 ±0.47
20	8.55 ±1.80	6.92 ±1.88	2.53 ±0.85	2.59 ±0.86	0.79 ±0.50

ment of standardized hatchery practices to support the growth of commercial aquaculture. Examples of such species include barramundi ( Lates calcarifer ; Kohno et al., 1986), milkfish ( Chanos chanos; Kohno et al., 1996), mangrove red snapper (L. argentimaculatus; Doi et al., 1997), gilthead seabream (Sparus auratus ; Polo et al.,

Table 2

Growth equations based on total length (TL) and stan- dard length (SL) for Florida pompano ( Trachinotus caro- linus) reared at 25°C. Larval lengths were measured in mm and age was measured as number of days after hatch- ing. Separate growth equations were developed for each rearing trial because significant differences in growth were observed (P<0.001).

Trial	Equation	n	r2
1	TL = 2 .058e00533 Age	200	0.96
	SL = 1.967e0 0479Agc	200	0.98
2	TL = 2. 066e° 9438	200	0.94
	SL = 1.893e0 0508A^	200	0.93
3	TL= 2.381e0 0672A^	200	0.98
	SL= 2. 859e00697A^	200	0.96

1992) and European sea bass (Dicentrarchus labrax ; Kuzir et al., 2004).

In this study, image analysis proved to be a useful tool (with a high degree of accuracy) for document- ing the early development of larvae and for obtain- ing measurements of larval characters. The process of digitally photographing larvae and measuring growth was relatively quick and uncomplicated. Measurements were accomplished in real-time during rearing trials and therefore offered a broad spectrum of possible ap- plications for research or commercial hatcheries. With the exception of overall growth measured as TL and SL, no substantial amount of morphological variation was expressed among cohorts of larvae from an individual spawning event or multiple spawnings. Developmental characteristics of cultured larvae were not significant- ly different from previous descriptions of wild-caught Florida pompano larvae from 7.2 to 11.0 mm SL (Fields, 1962); however, it was determined that fish changed morphologically from larvae to juveniles with full fin- ray counts at 17 to 19 DAH, instead of at a previously observed time in which metamorphosis of cultured fish occurred at 24 DAH (McMaster, 1988).

Similar to the challenges in rearing any marine fish species with small eggs and larvae, the culture of Flor- ida pompano larvae is difficult and time consuming. It is unfortunate that larvae will not readily consume

Riley et al : Development and growth of hatchery-reared larval Trachinotus carolmus

325

Figure 6

Back-calculated total length at age for hatchery-reared Florida pompano ( Trachinotus carolinus) larvae collected from three spawn- ings. Each curve represents measurements collected from 200 fish. Larvae from the third trial were significantly larger after seven days (P=0.007).

a>

•p

(5

"D

c

.2

55

Figure 7

Back-calculated standard length at age for hatchery-reared Florida pompano (Trachinotus carolinus) larvae collected from three spawnings. Each curve represents data collected from 200 fish. Larvae from the third trial were significantly larger after nine days (P<0.001).

artificial feed or Artemia spp. at first feeding.

In nature, larval Florida pompano prey upon a wide variety of different types and sizes of zooplankton. Larvae have small mouths with limited yolk reserves and undeveloped diges- tive systems at first feeding. As a consequence, larvae require small, slow-moving prey that are recognizable as potential food items. Given that the optimal prey size for marine fish larvae is 25% of mouth gape at first feeding and increases to 50% within a few days (Hunter and Lasker,

1981), the production of appropriate size live feeds must be considered an essential component of larviculture protocols.

The marine rotifer, B. plicatilis (so-called large or small morphotypes), is the most commonly cultured and mass produced species of zooplank- ton worldwide (Yoshimura et al., 1996; Lubzens et al., 2001). Recent studies have shown that the strain and morphotypes of rotifer stocks within a hatchery can vary greatly, and rotifer stocks from commercial hatcheries often represent a mixture of species, strains, and morphotypes (Papkostas, 2006). Commercial hatcheries fre- quently buy or trade rotifer cultures with other hatcheries to meet production quotas, which can exceed one billion rotifers per day (Lubzens,

2001). In this study, we used image analysis to docu- ment the size distribution of rotifers obtained from local hatcheries. Image analysis coupled with routine sampling allowed us to monitor growth, reproduction, and size-frequency distribution of rotifer stocks. De- termination of rotifer size-frequency distributions was

useful for ensuring that a sufficient number of small individuals were available for first feeding larvae. Al- though rotifer strains and size distributions differed among years, there is little evidence that larval growth and survival was affected. Although production meth- ods for marine rotifers and Artemia spp. are currently

326

Fishery Bulletin 107(3)

Table 3 Mouth size of Florida pompano ( Trachinotus carolinus) at the onset of opening (three days after hatching, DAH) through 20 DAH. Values represent measurements (means ±standard error [SE] ) for larvae sampled from three rearing trials. Mouth gape estimates were based upon calculations assuming the mouth opens 90° (min) to 120° (max) during feeding and prey capture.
Days after hatching	Upper jaw length (mm)	Lower jaw length (mm)	Min mouthgape (mm)	Max mouthgape (mm)
3	0.28 ±0.02	0.24 ±0.00	0.213	0.319
4	0.29 ±0.02	0.27 ±0.05	0.250	0.372
5	0.30 ±0.01	0.28 ±0.05	0.427	0.640
6	0.36 ±0.09	0.38 ±0.09	0.525	0.784
7	0.37 ±0.12	0.39 ±0.19	0.618	0.924
8	0.39 ±0.04	0.43 ±0.12	0.763	1.132
9	0.47 ±0.11	0.52 ±0.16	1.065	1.550
10	0.53 ±0.17	0.59 ±0.26	1.221	1.805
11	0.55 ±0.02	0.62 ±0.22	1.912	2.838
12	0.61 ±0.03	0.68 ±0.29	2.265	3.392
13	0.70 ±0.03	0.69 ±0.35	3.250	4.863
14	0.77 ±0.09	0.73 ±0.45	3.472	5.197
15	0.79 ±0.03	0.75 ±0.39	4.002	5.979
16	0.88 ±0.13	0.85 ±0.39	4.383	6.575
17	0.89 ±0.07	0.86 ±0.50	5.216	7.757
18	0.94 ±0.06	0.89 ±0.50	5.306	7.958
19	1.01 ±0.18	0.89 ±0.62	5.501	8.252
20	1.06 ±0.19	1.03 ±0.55	5.878	8.802

the standard for commercial hatcheries, a variety of small copepods, protozoans, cladocerans, and molluscan larvae offer great promise as feed, provided they offer adequate nutrition.

As a result of the findings of this study a refined feeding regime for Florida pompano was developed (Fig. 8). The regime directly addresses the importance of feeding small prey items (80-130 pm) to larvae at first feeding (three DAH), and it pro- vides a stage- and size-specific guide- line for feeding larvae reared under laboratory conditions at 25°C. Future work should address the bioenergetics and nutritional requirements specific for Florida pompano larvae and deter- mine the effect of increased tempera- ture on larval growth and development. Although research conducted in this study was performed within a small- scale marine hatchery, the techniques could be used to formulate commer- cial hatchery production protocols for other subtropical and tropical marine species with similar early life-history patterns.

|< »| Artificial feeds (400-800 |jm)

|«e s»| Artemia Instar II (600-900 |jm)

|« *| Artemia Instar I (400-600 pm)

|* *) Brachionus plicatilis (125-250 pm)

»| Copepods and size-sorted rotifers (50-150 pm)

|< *) Nannochloropsis oculata (300,000 cells/mL)

[«-») Stock yolk-sac larvae (50 fish/L)

i 1 — —i 1 1 1

0 5 10 15 20 25

Day of culture

Figure 8

Recommended hatchery feeding regimen for rearing Florida pompano ( Trachinotus carolinus) from hatching through transformation. Chrono- logical stages of development are noted by the upper bar: A-preflexion; B-flexion; C-postflexion; D-metamorphosis, and E-juvenile.

Acknowledgments

This research was supported by the USDA Agricultural Research Service as part of the Engineering and Produc- tion Strategies for Sustainable Marine

Riley et al.: Development and growth of hatchery-reared larval Trachinotus carolmus

111

Table 4

Growth equations for upper jaw, lower jaw, and mouth gape of Florida pompano ( Trachinotus carolinus) reared from hatching through metamorphosis. Jaw length and mouth gape were measured in mm and age was measured as days after hatching.

Equation n r2

Upper jaw = 0.0492 Age+0.0562 510 0.98

Lower jaw = 0.0447 Age+0.1452 510 0.96

Mouth gape = 0.0367 Age-2.0308 510 0.92

Aquaculture Project (no. 6225-63000-007-00). We thank F. Hoff, J. Mountain, and K. Main for sharing their expertise and experiences rearing Florida pompano. We also thank R. Rulifson and A. Overton for providing comments that greatly improved this manuscript. This is Harbor Branch Oceanographic Institute contribution no. 1642.

Literature cited

Aprieto, V. L.

1974. Early development of five carangid fishes of the Gulf of Mexico and the South Atlantic Coast of the United States. Fish. Bull. 72:415-443.

Barbaro, A., L. Colombo, A. Francescon, P. Benedetti, G. Bozato, P. Belvedere, P. Lavens, P. Sorgeloos, E. Jaspers, and F. Ollevier.

1991. Developmental abnormalities in eggs of gilthead seabream ( Sparus aurata) following spawning induced with LHRH analogues. Special Publ. European Aqua- cult. Soc. 15:235-236.

Brown, J. J., A. Ehtisham, and D. O. Conover.

1998. Variation in larval growth rate among striped bass stocks from different latitudes. Trans. Am. Fish. Soc. 127:598-610.

Craig, S. R.

2000. Pompano culture. In Encyclopedia of aquacul- ture (R. R. Stickney, ed.), p. 660-663. John Wiley and Sons, New York.

Cunha, I., and M. Planas.

1999. Optimal prey size for early turbot larvae ( Scop - thalmus maximus L.) based on mouth and ingested prey size. Aquaculture 175:103-110.

Doi, M., A. Ohno, H. Kohno, Y. Taki, and T. Singhagraiwan.

1997. Development of feeding ability in red snapper Lutjanus argentimaculatus early larvae. Fish. Sci. 63:845-853.

Drass, D. M., K. L. Bootes, J. Lyczkowski-Shultz, B. H. Comyns, G. J. Holt, C. M. Riley, and R. P. Phelps.

2000. Larval development of red snapper, Lutjanus campechanus, and comparisons with co-occurring snap- per species. Fish. Bull. 98:507-527.

Fahay, M.

2007. Perciformes: fishes of the family Carangidae. In Early stages of fishes in the western North Atlantic Ocean (Davis Strait, Southern Greenland and Flemish Cap to Cape Hatteras), vol. 2, p. 1038-1081. NAFO

(Northwestern Atlantic Fisheries Organization), Dart- mouth, Nova Scotia.

Fields, H. M.

1962. Pompanos (Trachinotus spp.) of the South Atlantic Coast of the United States. Fish. Bull. 61:189-222.

Ginsburg, I.

1952. Fishes of the Family Carangidae of the Northern Gulf of Mexico and three related species. Publ. Inst. Mar. Sci. 2(2):47-117.

Goode, G. B.

1882. The Carangoid fishes of the United States — pompa- nos, crevalles, and amber-fish. Fish. Bull. 1:30-43.

Helfman, G. S., B. B. Collette, and D. E. Facey.

2003. Teleosts at last II: Spiny-rayed fishes. In The diver- sity of fishes, p. 244-270. Blackwell Science Publ., Oxford, U.K.

Hoff, F. H., J. Mountain, T. Frakes, and K. Halscott.

1978b. Spawning, oocyte development and larval rearing of the Florida pompano, Trachinotus carolinus. Proc. World Maricult. Soc. 9:279-297.

Hoff, F. H., T. Pulver, and J. Mountain.

1978a. Conditioning Florida pompano Trachinotus caro- linus for continuous spawning. Proc. World Maricult. Soc. 9:299-320.

Hoff, F. H., C. Rowell, and T. Pulver.

1972. Artificially induced spawning of the Florida pom- pano under controlled conditions. Proc. World Maricult. Soc. 3:53-64.

Hunter, J. R. and R. Lasker.

1981. Feeding ecology and predation of marine fish larvae. In Marine fish larvae: Morphology, ecology, and relations to fisheries (R. Lasker, ed.), p. 33-77. Wash- ington Sea Grant Program, Seattle, WA.

Kohno, H., S. Hara, and Y. Taki.

1986. Early larval development of the seabass Lates calcarifer with emphasis on the transition of energy sources. Nippon Suisan Gakkaishi 52:1719-1725.

Kohno, H., R. Ordonio-Aguilar, A. Ohno, and Y. Taki.

1996. Morphological aspects of feeding and improvement in feeding ability in early stage larvae of the milkfish, Chanos chanos. Ichthyol. Res. 43(2):133-140.

Kuzir, S., Z. Kozaric, and S. Nejedli.

2004. Development of mandibular arch in European sea bass Dicentrarchus labrax from the “Cenmar” hatchery, Croatia. Veterinary Archives 74(5):321-300.

Laroche, W. A., W. F. Smith-Vaniz, and S. L. Richardson.

1984. Carangidae: development. In Ontogeny and System- atics of Fishes (H. G. Moser, W. J. Richards, D. M. Cohen, M. P. Fahay, A. W. Kendall Jr., and S. L. Richardson, eds.), p. 510-522. ASIH/Allen Press, Lawrence, KS.

Lee, W. Y., G. J. Holt, and C. R. Arnold.

1984. Growth of red drum larvae in the laboratory. Trans Am Fish Soc 113(2):243-246.

Lubzens, E., O. Zmora, and Y. Barr.

2001. Biotechnology and aquaculture of rotifers. Hy- drobiologia 446:337-353.

McM aster, M. F.

1988. Pompano culture: past success and present opportunities. Aquacult. Mag. 14(3):28-34.

Moe, M. A., Jr., R. H. Lewis, and R. M. Ingle.

1968. Pompano mariculture: preliminary data and basic considerations. State of Florida Board of Conservation Technical Series No. 55. Florida Board of Conserva- tion, Tallahassee, FL.

328

Fishery Bulletin 107(3)

Papakostas, S., S. Dooms, A. Triantafyllidis, D. Deloof, I. Kappas, K. Dierckens, T. De Wolf, P. Bossier, O. Vadstein, S. Kui, P. Sorgeloos, T. J. Abatzopoulos.

2006. Evaluation of DNA methodologies in identifying Brachionus species used in European hatcheries. Aqua- culture 255 (l-4):557-564.

Polo, A., M. Yufera, and E. Pascual.

1992. Feeding and growth of gilthead seabream ( Spams aurata) larvae in relation to the size of the rotifer strain used as food. Aquaculture 103(l):45-54.

Shirota, A.

1970. Studies on the mouth size of fish larvae. Bull. Jpn. Soc. Sci. Fish. 36:353-368.

Smith, C., and P. Reay.

1991. Cannibalism in teleost fish. Rev. Fish Biol. Fish. 1( 1 ):41— 64.

Snyder, D. E.

1983. Fish eggs and larvae. In Fisheries techniques (L. Nielsen and D. L. Johnson, eds.), p. 165-197. Am. Fish. Soc., Bethesda, MD.

Starks, K.

1911. The osteology and relationship of fishes belonging to the family Carangidae. Stanford Univ. Publ. Univ. Ser. 5:27-49.

Watanabe, W. O.

1995. Aquaculture of the Florida pompano and other jacks (Family Carangidae) in the Western Atlantic, Gulf of Mexico, and Caribbean basin: status and potential. In Culture of high-value marine fishes (K. L. Main, and C. Rosenfeld, eds.), p. 185-205. Oceanic Institute, Honolulu, HI.

Weirich, C. R., D. R. Groat, R. C. Reigh, E. J. Chesney, and R. F. Malone.

2006. Effect of feeding strategies on production char- acteristics and body composition of Florida pompano reared in marine recirculating systems. N. Am. J. Aquacult.68 (4): 330-338.

Weirich, C. R., and K. L. Riley.

2007. Volitional spawning of Florida pompano, Trachi- notus carolinus, induced via administration of gonado- tropin releasing hormone analogue (GnRHa). J. Appl. Aquaculture 19(3):47-60.

Yoshimura, A., A. Hagiwara, T. Yoshimatsu, and C. Kitajima.

1996. Culture technology of marine rotifers and implica- tion for intensive culture of marine fish in Japan. Mar. Freshw. Res. 47:217-222.

Yasuda, F.

1960. The feeding mechanisms in some carnivorous fish. Rec. Oceanogr. Works Jpn. 5:153-160.

329

Abstract — For most migratory fish, little is known about the location and size of foraging areas or how long individuals remain in foraging areas, even though these attributes may affect their growth, survival, and impact on local prey. We tested whether striped bass ( Morone saxatilis Walbaum), found in Massachusetts in summer, were migratory, how long they stayed in non-natal estuaries, whether observed spatial patterns differed from random model predic- tions, whether fish returned to the same area across multiple years, and whether fishing effort could explain recapture patterns. Anchor tags were attached to striped bass that were caught and released in Massachu- setts in 1999 and 2000, and recap- tured between 1999 and 2007. In fall, tagged striped bass were caught south of where they were released in summer, confirming that fish were coastal migrants. In the first summer, 77% and 100% of the recaptured fish in the Great Marsh and along the Massachusetts coast, respectively, were caught in the same place where they were released. About two thirds of all fish recaptured near where they were released were caught 2-7 years after tagging. Our study shows that smaller (400-500 mm total length) striped bass migrate hundreds of kilometers along the Atlantic Ocean coast, cease their mobile lifestyle in summer when they use a relatively localized area for foraging (<20 km2), and return to these same foraging areas in subsequent years.

Manuscript submitted 27 August 2008. Manuscript accepted 26 March 2009. Fish. Bull. 107:329-338 (2009).

The views and opinions expressed or implied in this article are those of the author and do not necessarily reflect the position of the National Marine Fisheries Service, NOAA.

Use of non-natal estuaries by migratory striped bass ( Morone saxatilis) in summer

Martha E. Mather (contact author)1 2- 3

John T. Finn2

Kristen H. Ferry3- 5

Linda A. Deegan4

Gary A. Nelson5

Email address for contact author: mather@nrc.umass.edu

1 U. S. Geological Survey

2 Department of Natural Resources Conservation

3 Massachusetts Cooperative Fish and Wildlife Research Unit University of Massachusetts

160 Holdsworth Way, Room 226 Amherst, Massachusetts 01003

4 The Ecosystems Center Marine Biological Laboratory 7 MBL Street

Woods Hole, Massachusetts 02543

5 Massachusetts Division of Marine Fisheries 30 Emerson Ave

Gloucester, Massachusetts 01930

For most migratory fish species, little is known about the size of their feed- ing areas, the duration of time that individuals spend there, and whether fish return to the same feeding area year after year. Migration is an essen- tial part of the life history and ecologi- cal niche of many taxa and has been observed in marine, freshwater, and diadromous fish (Thorrold et ah, 2001; Dingle and Drake, 2007). Many fish migrate between some combination of spawning area, feeding area, and overwintering area (Harden Jones, 1968; Robichaud and Rose, 2001). Many anadromous fish return to natal systems for spawning (Klemetsen et al., 2003; Quinn and Myers, 2004), but a return to feeding areas has been shown for only a few fish species (Buzby and Deegan, 2000; Solmunds- son et ah, 2005). Consequently, an important but unresolved issue is the extent to which individuals migrate to the same specific, non-natal, feed- ing area.

Populations of striped bass ( Morone saxatilis Walbaum) exhibit a variety of movement patterns. Coastal popu-

lations at the northern and southern end of their range may move offshore from their natal estuaries in summer but do not migrate north and south along the coast (Collette and Klein- MacPhee, 2002). The U.S. Atlantic coast striped bass stocks spawn in the Chesapeake Bay, Delaware River, and the Hudson River. In the spring, some members of these stocks migrate northward along the coast to New England (Maine; New Hampshire; Massachusetts; Rhode Island; and Connecticut) and then return south in the fall (Berggren and Lieberman, 1978; Dorazio et al., 1994). Coastal migrants are caught seasonally in fisheries off all U.S. states between Chesapeake Bay and Canada (Bore- man and Lewis 1987, Rulifson et al. 2008). Many of these fish are caught by hook and line, a method that tar- gets feeding fish. These captures in- dicate that a wide range of possible foraging areas exist for coastal mi- grants. Although the spawning loca- tions of migratory striped bass, the basic directions of coastal movements, and some size and sex-specific char-

330

Fishery Bulletin 107(3)

Figure 1

(A) Spawning areas and northern range of U.S. Atlantic coast striped bass ( Morone saxatilis ), the latter of which represents the largest scale by which recaptures were grouped (Massachusetts, MA). The box delineates the Great Marsh (GM). Asterisks show major spawning areas. (B) The Great Marsh in northern Massachusetts consists of the Merrimack, Parker, Rowley, Ipswich, and Essex river estuaries and represents the smaller scale by which recaptures were grouped. The arrangement of estuaries in the Great Marsh served as the basis for random model 2 (RM-2).

acteristics of migrants are known, regional patterns of coastal migration related to the use of specific summer areas by individual fish have not been identified.

Migratory fish that are present in non-natal estuar- ies during the nonbreeding (summer, fall) and nonover- wintering seasons are most likely feeding. Although the migratory stock of striped bass is widely distributed throughout New England in summer, the specific feed- ing areas for individual fish are not known. Migratory striped bass can stay and forage in a specific estu- ary that they encounter during migration or they may continue to move along, feeding in multiple estuaries for short periods. They also may either return to the site where they spent the previous summer or choose a different site each year from the many estuaries they encounter. We tested whether striped bass found in Massachusetts estuaries in summer migrated, how long they stayed in the non-natal estuaries where they were tagged, whether observed spatial patterns differed from the predictions of random models, whether fish returned to the same area over multiple years, and whether fishing effort alone could explain the recapture pattern.

Materials and methods

From June 1999 through November 2000, 1939 striped bass (3-5 yr old, predominately the 1996 year class) were tagged with internal anchor tags. All fish (mean total length [TL] = 442 mm, standard error [SE]=7.0 mm; mean wet weight=0.91 kg, SE = 0.05 kg) were caught, tagged, and immediately released along the Massachu- setts coast, excluding Cape Cod (Fig. 1A). The specific estuary in which fish were tagged and released, date of tagging, total length, wet weight, and tag number of fish were recorded. Several tagging (Parker, Rowley, and Essex river estuaries) and recapture sites (Merrimack and Ipswich river estuaries; Fig. IB) are part of the Great Marsh barrier beach dune and salt marsh estuary that includes 10,117 ha of contiguous salt marsh on the North Shore of Massachusetts.

In 1999-2007, anglers voluntarily returned tags with recapture data to the U.S. Fish and Wildlife Service (USFWS) Cooperative Striped Bass Tagging Program. These recapture data included tag number, recapture date, recapture location (state, town), and approximate size of fish. Because the anchor tag was removed as

Mather et al.: Use of non-natal estuaries by migratory Morone saxat/lis in summer

331

part of the reporting procedure, for most individuals, only a single recapture record existed. An approximate location (latitude, longitude, ±4 km) was created by assigning the recapture to the center of the nearest water body. When more information was included (e.g., mouth of the Merrimack River estuary), that datum was assigned a more specific recapture location. Most recap- ture records referenced specific locations and therefore there was relatively little error in estimating recapture location this way. Because most fish were recaptured by recreational anglers, tag reporting rate was likely similar across recapture locations.

By comparing release and recapture locations, we examined whether striped bass tagged in Massachu- setts were part of the coastal migratory stock, whether they stayed in a localized area for a prolonged period in summer, and whether they returned to the same location after several years. To confirm the migratory status of striped bass tagged in Massachusetts, the location where tagged fish were recaptured in late fall, winter, or early spring was compared to the release location. To determine if striped bass remained in the same area throughout the summer, recapture loca- tions in summer were compared to the location where fish were released. For this, two nonexclusive, spatial recapture scales were used: the larger Massachusetts coast area (MA; Fig. 1A) and the smaller Great Marsh area (GM; Fig. IB). Two time periods were considered: the first season in which they were tagged (<104 days and before 21 September, i.e., summer), and all times combined. Without extensive movement records on in- dividual fish, the possibility that tagged fish moved out of the release estuary in the summer and then re- turned there in the fall cannot be discounted. However, to minimize this possibility, recapture records from the early (May 1 through 10 June) and late migration (22 September through 31 November) periods were excluded because these were times when migratory striped bass were hypothesized to be in transit. To determine if migratory striped bass returned to the same area in subsequent years, the number of fish that were recaptured in the area in which they were released was quantified for recaptures that occurred >12 months after release.

To examine whether the number of striped bass re- captured in their release location was different than expected by random movement models, simple, dis- crete time, stochastic Markov chain models were used (Agresti, 2002). These were parameterized by a series of model states (locations in the estuary or ocean where migratory striped bass could occur) connected by transi- tion probabilities (rates at which striped bass may move between these geographic locations). Although other models have been used for animal movement, especially when large amounts of telemetry data are available (Jonsen et al., 2003; 2006), Markov chains are simple, require the least amount of data, and have been used to model biological processes (Shull, 2001; Steel et al. 2001) including movement (Hestbeck et al., 1991; John- son et al., 2004). Furthermore, Markov chains require

few assumptions; for example, all that is needed to pre- dict the next location of an animal with this approach is knowledge of the animal’s present location.

Small-scale models were used to address how many recaptures would be expected at two scales of release (MA, GM) if striped bass movements were random. Although many movement models were plausible, the examples below provide insights into how to interpret observational recapture data for migratory striped bass. In random model 1 (RM-1), model states represented three localized, geographic locations in which a feeding, migratory striped bass could be found: 1) the target or release area (At at two scales, GM, MA); 2) the ocean; or 3) another adjacent area (Ao) (Fig. 2A). The prob- ability of staying in the release or target area was pe, the probability of leaving that area was 1 —pe. In the first random model (RM-1), a fish must move through the ocean to get to another location. In RM-1, the prob- ability of staying in the ocean ( p0 ) was 0.50, and the probabilities of staying in the two non-ocean estuaries were the same, although not necessarily 0.50 (RM-1; Fig. 2A). An assumption of RM-1 was that the fish did not prefer the release area over the adjacent area and that fish were equally likely to stay in the ocean or go to an estuary. A weekly time step was used. Transition probabilities for a striped bass in a model state always summed to 1.0.

In random model 2 (RM-2), eight states were used to simulate the complexity of the Great Marsh (Figs. IB and 2B). Four estuarine areas (AI-A4) had direct connections to Plum Island Sound and represented the Merrimack (A;), Parker (A2), Rowley (A3), and Ipswich (A4) estuaries. Three of these (A2-A4) were connected to the ocean through Plum Island Sound whereas the Merrimack River estuary (A;) was also connected di- rectly to the ocean. The Essex River (A5) was adjacent to Plum Island Sound, connected to the ocean, but not directly connected to Plum Island Sound. Neighboring estuaries that were not part of the Great Marsh were represented by (A0)

Both models began with the release of 100 striped bass (individuals or schools) from the target area (At for RM-1, or A3 for RM-2) and continued until the numbers of migratory striped bass in each model state stabilized (10 weeks). The outcome predicted what proportion of model fish would be recaptured in the release estuary if movements in all directions were equally likely, i.e., random. Pe, the proportion of fish still in the release area after 10 weeks, was adjusted to fit observed recap- ture proportion data for the first summer (<104 days and before 21 September). This weekly probability of fish remaining in the tagging estuary was matched against the observed recapture proportion. The ob- served recaptures for the Great Marsh were fitted to both models; the observed recaptures for Massachusetts were fitted only to the first, general model. Fitting to recaptures was possible because the model had only one parameter, pe. Density dependence and intraspecific interactions were not included in these simple models. Observed and expected were compared by using x2 ■

332

Fishery Bulletin 107(3)

Equal catchability and effort were assumed because anglers made most recaptures and angler effort per mile of coastline was similar. This assumption allowed us to use a simpler model than the complex model of Hilborn (1990), which assumed unequal capture prob- abilities.

To test whether the recapture rate in the first sum- mer after tagging was explained by patterns of fishing effort, data from the Marine Recreational Fisheries

A

(Pe)

B

Figure 2

Structure of two random models used to compare observed recaptures of striped bass ( Morone saxatilis) to what might be expected if movements into and out of the release areas were random. For all, pe was the weekly probability of a striped bass remaining in a patch and 1 —pe is the weekly probability of leaving. (A) In random model 1 (RM-1), the probability of leaving the ocean patch is 0.5 for each weekly time step. The probability of leaving the other two patches is the same but can differ from 0.5. In the comparison of the model output to recaptures, the target area may have represented either the Great Marsh or Massachusetts coast. (B) In random model 2 (RM-2), the complex structure repre- sented by the Great Marsh is diagrammed: A1=Merrimack; A2=Parker; A3=Rowley (target); A4=Ipswich; A5=Essex. In RM-2, the probability of remaining in all patches is pe. The probability of leaving A2 A3 A4 A5 and A0is l-pe. The probability of leaving A2 for Plum Island Sound (PIS) or the ocean is (l-pe)/2). The probability of leaving PIS for any other location is (l-pe)/5). The probability of leaving the ocean for one of the four neighboring patches is (0.5/4).

Statistics Survey were used.1 Effort data were obtained for five bimonthly periods (March- April, May- June, July-August, September-October, November-December) in 1999 and 2000, the two years that fish were tagged.

For the Coastal Household Telephone Survey (CHTS), fishing effort data were obtained from shore and pri- vate-boat anglers who live in coastal counties. Correc- tion factors, derived from an intercept survey, were used to account for trips taken by noncoastal residents, out- of-state anglers, and anglers who live in households without telephones. Data collection occurred during a two-week period at the end of each two-month sample period. For the CHTS, a computer-assisted, random digit dialing (RDD) approach was used to contact full-time residential households who were screened to determine if any household members participated in marine recreational fishing during the previous two months. Each active angler was asked to recall the number of saltwater fishing trips that were taken during the bimonthly period, as well as asked to provide details about each trip. Institutional hous- ing, businesses, wireless phones, and pay phones were excluded from the survey. Within each state, i samples were allocated among coastal counties in proportion to household populations. For each coastal county, data from the CHTS were used to estimate the average number of trips per household and then expanded by the county household population to esti- mate total trips. County estimates were summed and then expanded by intercept survey adjustment factors to produce state-level effort estimates. Private-boat and shore-angler modes for trips directed towards striped bass were combined for each New England state (Maine, New Hampshire, Massachusetts, Rhode Island, and Connecticut). To compare effort expended for striped bass across states, these effort estimates were divided by km of shoreline.2 To assess whether recaptures in Massachusetts mirrored general trends in fishing effort, the calendar dates when striped bass were recaptured in the Great Marsh and Mas- sachusetts were compared to the timing of fishing effort. To test whether striped bass were recaptured in Massachusetts in summer, because fishing effort did not exist elsewhere in New England, bimonthly patterns of recaptures were related to summer effort scaled by coastline for all five New England states by using a Spearman correlation.

Results

Striped bass recaptures were distributed along the Atlantic Ocean coast from Maine to the Chesapeake

1 Van Voorhees, David. Personal commun. 2000. National Marine Fisheries Service, Fisheries Statistics Division, Silver Spring, MD.

2 Millhouser, W. C., J. McDonough, J. P. Tolson. 1998. Per- sonal Commun. Report to National Oceanic and Atmospheric Administration, Managing Coastal Resources. 1315 East West Highway, Silver Spring, Maryland 20910.

Mather et al.: Use of non-natal estuaries by migratory Morone saxatilis in summer

333

70°0’0” W 70°p'0" W 70°0’0" W

0 75 150 300 450 600

Figure 3

Seasonal recapture locations for all striped bass (Morone saxatilis) tagged in 1999 and 2000 in Mas- sachusetts estuaries (n = 198). Recaptures for 1999-2007 were plotted for (A) November, (B) Decem- ber-February, (C) March-April. Because of symbol overlay, not all points are visible. ME = Maine, MA=Massachusetts, CT/RI = Connecticut and Rhode Island, HU=Hudson River (a spawning location), NJ = New Jersey, DE = Delaware River (a spawning location), CB = Chesapeake Bay (a spawning location). All years were combined. Numbers in all panels in Figure 3 and 4 sum to the total number of fish for which release and recapture locations (n = 198) were available. Months are grouped to illustrate seasonal distributional patterns of striped bass. Fish were recaptured by angling. The map projection is Albers Equal Area Conic, NAD (North American Datum), 1983.

Bay (Figs. 3 and 4; ?i = 198), indicating that striped bass tagged in Massachusetts were migratory fish. Without exception, striped bass recaptured in the late fall, winter, and early spring (November-April) were recaptured south of where they were initially tagged and released (Fig. 3, A-C). In November (end of migration), December-February (winter), and March-April (begin- ning of migration), with two exceptions, all recaptures occurred south of Massachusetts. For the two exceptions still in Massachusetts waters, the fish were recaptured south of where they were released. Most recaptures were made in the spring and summer when the sport fishery was most active (Fig. 4, A and B). In May and June, recaptures for all years were distributed throughout the migratory range of striped bass from New Jersey to Maine (Fig. 4A). During July, August, and September, most tagged fish, across all years, were recaptured in Massachusetts (Fig. 4B). In October, during the fall

migration, striped bass were captured both within and south of Massachusetts (Fig. 4C). Fish recaptured in Massachusetts in October were caught south of the location where they were released.

Of the fish that were recaptured in the summer of the year they were tagged (n- 41, tag to recapture <104 days), most stayed where they were tagged. For example, 77% (17 of 22) of the striped bass recaptured in the Great Marsh in the first summer were released there (Table 1). The Merrimack River, the northern- most river in the Great Marsh, appeared to attract striped bass with 9% of the recaptures made there even though this estuary was not a release site. All first summer recaptures were taken along the Mas- sachusetts coast (Table 1). No striped bass tagged in Massachusetts were recaptured in any other New England state (ME, NH, RI, CT) in the first summer after tagging (Table 1).

334

Fishery Bulletin 107(3)

70°Q’0” W 70°0'0” W 70°0'0” W

0 75 150 300 450 600

Figure 4

Seasonal recapture locations for all striped bass ( Morone saxatilis) tagged in 1999 and 2000 in Mas- sachusetts estuaries (n = 198). Recaptures for 1999-2007 were plotted for (A) May-June, (B) July, August, September, and (C) October. Because of symbol overlay, not all points are visible. ME=Maine, MA=Massachusetts, CT7RI = Connecticut and Rhode Island, HU = Hudson River (a spawning location), NJ = New Jersey, DE = Delaware River (a spawning location), CB = Chesapeake Bay (a spawning loca- tion). All years were combined. Numbers in all panels of Figures 3 and 4 sum to the total number of fish for which release and recapture locations (n = 198) were available. Months are grouped to illustrate seasonal distributional patterns of striped bass. Fish were recaptured by angling. The map projection is Albers Equal Area Conic, NAD (North American Datum), 1983.

The summer locations of striped bass along the Mas- sachusetts coast and in the Great Marsh were not the result of random movement. If fish were choosing either the ocean or the estuary randomly, the first model pre- dicted that only 0.25 of the tagged striped bass would be present in the release location during the first sum- mer. This is significantly less than the proportion ob- served in both the Great Marsh and along the Massa- chusetts coast (GM, 0.77, ;^=74.6, df=2, P=0.005; MA, 1.0, x2=151, df=2, P=0.005). The model can be used to back calculate the required probability that striped bass remained in the estuary by adjusting pe until the model output matches the observed proportion of observed re- captures. Based on RM-1, this approach indicated that to obtain the observed proportion of recaptures (0.77) for striped bass released and recaptured in the Great Marsh, the weekly probability that a striped bass re- mained in the Great Marsh was high (pe- 0.95; Table 2). Similarly, in order for all the observed recaptures (1.0)

to have occurred in Massachusetts during the first summer, the weekly probability of remaining in waters off the Massachusetts coast was very high, (pe- 1.0; Table 2). Using the more spatially complex and real- istic model (RM-2), to obtain the observed proportion of recaptures (0.77) in the Great Marsh, we found that the weekly probability of striped bass remaining in the Great Marsh was again high (pe= 0.75; RM-2, Table 2).

Many fish were caught where they had been released in subsequent years, and this finding would indicate that these fish return to non-natal estuaries. Across all years and times of year, 38% (41 of 108) of the recap- tured fish released in the Great Marsh and 61% (120 of 198) of the tagged fish released along the Massachu- setts coast were recaptured where they were released (Table 1). Across all times, of the fish recaptured where they were released (41 in GM; 120 in MA), 59% (24 of 41) were recaptured in the Great Marsh and 66% (79 of 120) were recaptured in Massachusetts 2-7 years after

Mather et al.: Use of non-natal estuaries by migratory Morone saxatilis in summer

335

Table 1

Recaptures of adult striped bass (Morone saxatilis) tagged and released in the Great Marsh region (GM), and for all Massachu- setts estuaries combined (MA). Data are shown for striped bass recaptured within the first summer of release (<104 days and before 21 September), after the first summer (2-7 years after tagging), and at all times. Detailed recapture locations are divided into two spatial scales; Great Marsh (GM) and Massachusetts (MA). For example, row 1 shows that 22 fish were recaptured in the Great Marsh in the first summer and of those 17 were released there. Recapture data are shown as numbers ( n ) and percentages (%). Numbers for recapture across scales are not exclusive and therefore columns do not sum to total recaptures. Also shown are fish tagged and released in MA in summer and recaptured in other New England states in the first summer. ME=Maine, NH = New Hampshire, RI = Rhode Island, CT= Connecticut.

Recaptures

Release location

Total GM MA

ME NH RI CT

(n) ( n ) (%) ( n ) (%) (n) ( n ) ( n ) in)

First year GM MA

2-7 years after tagging GM MA

Total recaptures GM MA

22 17 77

41

24

108 41 38

198

22 100 0

41 100 0

79

120 61

0 0 0 0 0 0

Table 2

Observed proportion of first summer recaptures of striped bass ( Morone saxatilis) in release location from field data and weekly probabilities of model fish remaining where tagged if striped bass movements were random. Observed proportions correspond to data in Table 1. For weekly probabilities of remaining, shown are two different model scenarios (RM-1 and RM-2). Data are shown for two regions of release and recapture: the Great Marsh (GM) and all Massachusetts estuaries combined (MA). P, is the proportion that would need to remain in the recapture location each week to obtain the observed proportion of recaptures over 10 weeks.

	Observed recaptures (Proportion)	GM-weekly probability of remaining where tagged	Observed recaptures (Proportion)	M A- weekly probability of remaining where tagged
Release location	RM-1 Pe	RM-2 Pe	RM-2 Pe
GM MA	0.77	0.95	0.75	1.00 1.00	1.00 1.00

tagging (Table 1). Thus, in subsequent migration cycles, many fish were recaptured in the location where they had been tagged.

Recapture patterns were not caused by effort alone. Striped bass recaptures in both Massachusetts and the Great Marsh in the first summer after tagging were highest in July and August in 1999 and 2000 (Fig. 5, white bars), the same months when recreational fishing effort was concentrated (Fig. 5, black bars). However, when scaled by kilometer of coastline, the fishing effort for striped bass in summer was as high in Connecticut and Rhode Island as in Massachusetts and higher in New Hampshire (Fig. 6). Nevertheless, in spite of heavy effort across the entire New England coast, no striped

bass tagged in Massachusetts during the summer was recaptured in any of the other four New England states in the first summer (Spearman correlation P= 0.55).

Discussion

Our study provides the first evidence that smaller striped bass make repeated, seasonal, long distance movements between natal and non-natal estuaries. The striped bass we tagged in Massachusetts in the summer were caught in late fall, winter, or early spring, south of the location where they had been released. If striped bass that were tagged in Massachusetts in summer were spawning or

336

Fishery Bulletin 107(3)

2,500,000 - 2,000,000 -

500.000 H 0

1,000,000

800.000 H

600.000

400.000

200.000

0

B GM

1

' A MA _	i
i.J.fl.rl. 1	hi

□

Mar-Apr May-Jun Jul-Aug Sep-Oct Nov-Dec 99 99 99 99 99

Mar-Apr May-Jun Jul-Aug Sep-Oct Nov-Dec 00 00 00 00 00

Figure 5

Number of first summer recaptures (white bars) and fishing effort (black bars) by date in (A) Massachusetts (MA), and (B) the Great Marsh (GM) for striped bass (Morone saxatilis) released there. Numbers of recaptures correspond to those in Table 1. Effort is shown in number of fishing trips for striped bass (mean ±1 SD).

overwintering there, they would have no reason to go south towards the traditional overwintering or spawning grounds in the late fall. In addition, 33 of 46 striped bass implanted with acoustic tags in the Great Marsh, MA, in 2006 were detected by acoustic receivers in Delaware

Bay or Long Island Sound (474-939 km one-way migra- tion) in the winter, 2006-07 (Mather, unpubl. data). The U.S. Atlantic coast striped bass stocks that spawn in Chesapeake Bay, Delaware River, and the Hudson River have been observed previously off New England (Berg-

Mather et al.: Use of non-natal estuaries by migratory Morone saxatilis in summer

337

gren and Lieberman, 1978), but these coastal migrants were larger (>450 mm; Dorazio et al., 1994). We provide evidence that small adult striped bass, captured in Mas- sachusetts during the summer, were also part of the coastal migratory stocks.

These recaptures of migratory fish at the location where they were tagged were much higher than our model predicted if movements were random. In this study, during the first summer after tagging, many striped bass were recaptured in a relatively small, local area (<20 km2). Striped bass recaptured in the Great Marsh (77%) used only 0.73% of the New England coast- line available for feeding by migratory striped bass. Striped bass recaptured along the Massachusetts coast (100%) used only 25.1% of the New England coastline. Furthermore, no fish tagged and released in Massa- chusetts in summer was recaptured in other New Eng- land states in summer, in spite of high fishing effort.

These results indicate that some highly mobile striped bass that have traveled hundreds of kilometers to feed, cease their mobile lifestyle, and remain in relatively local areas (i.e., the Great Marsh or the Massachusetts coast) for a prolonged period in summer. Summer is an important period for food acquisition, and understand- ing why striped bass may choose one feeding area over another is critical to managing a fish that uses multiple habitats separated by hundreds of kilometers. Migra- tion patterns of striped bass may be linked to different conditions across habitats. High temperatures, low oxy- gen, and inadequate prey may deter striped bass from remaining in specific habitats (Coutant and Benson, 1990; Hartman and Brandt, 1995). In addition, growth can be higher in some locations than in others (Welsh et al., 2003). As such, migration may have evolved to move striped bass away from poor conditions (e.g., high temperature, low oxygen, or poor prey conditions) or towards better foraging conditions (e.g., seasonally abundant prey, moderate water temperatures). Prey resources may be available during a longer period of physiologically suitable conditions in northern estuaries than in southern estuaries. This feature could facilitate prolonged use of feeding habitats in northern estuaries in summer.

The degree of site fidelity observed was surprisingly high given that this highly mobile fish migrates hun- dreds of kilometers annually, encounters tens of estu- aries, and has the potential for multidirectional move- ment. Site fidelity has been documented in freshwater (Buzby and Deegan, 2000; McCairns and Fox, 2004), marine (Thorrold et al., 2001; Szedlmayer and Schro- epfer, 2005), and anadromous fish (Stewart et al., 2004; Minakawa and Kraft, 2005). However, many of these ex- amples of site fidelity are within physically constrained riverine systems. Some site fidelity has been observed for striped bass in freshwater (Jackson and Hightow- er, 2001), but it has only recently been examined for coastal migrants (Wingate and Secor, 2007; this study).

Home range, or the habitats used over a period of time (day, season, year), can be a useful way of think- ing about a species distribution and its relationship to

environmental conditions. The size of a home range can vary with sex, season, availability of resources, body size, feeding strategy, and group size (Baker, 1978). Although home range can be measured for any animal, the concept of home range may make little sense for animals that roam widely. For migratory fish that feed throughout their entire range or that use a large ocean feeding area, the concept of a feeding home range may have limited utility. However, a feeding home range pro- vides a useful conceptual framework for understanding movements of fish like striped bass that may migrate between discrete spawning and feeding areas. This discrete feeding home range of individual fish can also have implications for fisheries management. Migratory fish that stay in a specific area for a prolonged time may adopt different feeding strategies based on previ- ous experience in the estuary, and these feeding strate- gies may result in spatially explicit patterns of growth. In addition, local fishing pressure may influence feeding groups such that migratory fish that stay in a local area for a prolonged period may be caught and released more frequently, resulting in higher mortality. Consequently, knowing the movements of individual migratory fish in foraging areas is crucial for appropriate management.

Acknowledgments

This project was administered through the Massachu- setts Cooperative Fish and Wildlife Research Unit. The Massachusetts Cooperative Fish and Wildlife Research Unit is an association among the U.S. Geological Survey; University of Massachusetts Department of Natural Resources Conservation; Massachusetts Division of Marine Fisheries; Massachusetts Division of Fisheries and Wildlife, and the Wildlife Management Institute. J. Hightower and D. Parrish provided useful comments. We extend special thanks to the Plum Island Long Term Ecological Research Site (OCE 9726921) for generously providing lodging and the USFWS for compiling the tag database.

Literature cited

Agresti, A.

2002. Categorical data analysis. Wiley Series of Statistics Probability, Wiley, John & Sons, Inc., New York.

Baker, R. R.

1978. The evolutionary ecology of animal migration. Hol- mes & Meier Pubis., Teaneck, NJ.

Berggren, T. J., and J. T. Lieberman.

1978. Relative contribution of Hudson, Chesapeake, and Roanoke striped bass, Morone saxatilis, stocks to Atlantic coast fishery. Fish. Bull. 76:335—345.

Boreman, J., and R. R. Lewis.

1987. Atlantic coastal migration of striped bass. Am. Fish. Soc. Symp. 1:331-339.

Buzby, K. M., and L. A. Deegan.

2000. Inter-annual fidelity to summer feeding sites in Arctic grayling. Environ. Biol. Fish. 59:319-327.

338

Fishery Bulletin 107(3)

Collette, B. B., and G. Klein-MacPhee.

2002. Fishes of the Gulf of Maine, 3rd ed., 748 p. Smith- sonian Inst. Press, Washington, D.C.

Coutant, C. C., and D. L. Benson.

1990. Summer habitat suitability for striped bass in Ches- apeake Bay: reflections on a population decline. Trans. Am. Fish. Soc. 119:757-778.

Dingle, H., and V. A. Drake.

2007. What is migration? Bioscience 57:113-121.

Dorazio, R. M., K. A. Hattala, C. B. McCollough, and J. E. Skjeveland.

1994. Tag recovery estimates of migration of striped bass from spawning areas of the Chesapeake Bay. Trans. Am. Fish. Soc. 123:950-963.

Harden Jones, F. R.

1968. Fish migration. Edward Arnold Publisher, London.

Hartman, K. J., and S. B. Brandt.

1995. Predatory demand and impact of striped bass, bluefish, and weakfish in the Chesapeake Bay — Appli- cations of bioenergetics models. Can. J. Fish. Aquat. Sci. 52:1667-1687.

Hestbeck, J. B., J. D. Nichols, and R. D. Malecki.

1991. Estimates of movement and site fidelity using mark resight data of wintering Canada geese. Ecology 72:523-533.

Hilborn, R.

1990. Determination of fish movement patterns from tax recoveries using maximum likelihood estimators. Can. J. Fish. Aquat. Sci. 47:635-643.

Jackson, J. R., and J. E. Hightower.

2001. Reservoir striped bass movements and site fidelity in relation to seasonal patterns in habitat quality. N. Am. J. Fish. Manag. 21:34-45.

Johnson, G. E., J. B. Hedgepeth, J. R. Skalski, and A. E. Giorgi.

2004. A Markov chain analysis of fish movements to deter- mine entrainment zones. Fish. Res. 69:349-358.

Jonsen, I. D., R. A. Myers, and M. C. Flemming.

2003. Meta-analysis of animal movement using state- space models. Ecology 84:3055-3063.

2006. Robust hierarchical state-space models reveal diel variation in travel rates of migrating leatherback turtles. J. Anim. Ecol. 75:1046-1057.

Klemetsen, A. P., A. Amundsen, J. P. Dempson, B. Jonsson, N. Jonsson, M. F. O’Connell, and E. Mortensen.

2003. Atlantic salmon Salrno salar L., brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus. L.: a review of aspects of their life histories. Ecol. Freshw. Fish 12:1-59.

McCairns, R. J. S., and M. Fox.

2004. Habitat and home range fidelity in a trophically

dimorphic pumpkinseed sunfish, Lepomis gibbosus, population. Oecologia 140:271-279.

Minakawa, N., and G. F. Kraft.

2005. Homing behaviour of juvenile coho salmon. Oncorhyn- chus kisutch. within an off-channel habitat. Ecol. Freshw. Fish 14:197-201.

Quinn, T.P., and K. W. Myers.

2004. Anadromy and the marine migrations of Pacific salmon and trout: Rounsefell revisited. Rev. Fish Biol. Fish. 14:421-442.

Robichaud, D., and G. A. Rose.

2001. Multiyear homing of Atlantic cod to a spawning ground. Can. J. Fish. Aquat. Sci. 58:2325-2329.

Rulifson, R. A., S. A. McKenna, and M. J. Dadswell.

2008. Intertidal habitat use, population characteris- tics, movement, and exploitation of striped bass in the inner Bay of Fundy, Canada. Trans. Am. Fish. Soc. 137:23-32.

Shull, D. H.

2001. Transition-matrix model of bioturbation and radio- nuclide diagenesis. Limnol. Oceanogr. 46:905-916.

Solmundsson, J., J. J. Palsson, and H. Karlsson.

2005. Fidelity of mature plaice, Pleuronectes platessa, to spawning and feeding grounds. ICES J. Mar. Sci. 62:189-200.

Steel, E. A., P. Guttorp, J. J. Anderson, and J. C. Caccia.

2001. Modeling juvenile salmon migration using a simple Markov chain. J. Agric. Biol. Environ. Stat. 6:80-88.

Stewart, I. J., S. M. Carlson, C. P. Boatright, G. P. Buck, and T. P. Quinn.

2004. Site fidelity of spawning sockeye salmon, Oncorhyn- chus nerka W., in the presence and absence of olfactory cues. Ecol. Freshw. Fish 13:104-110.

Szedlmayer, S. T., and R. L. Schroepfer.

2005. Long-term residence of red snapper on artificial reefs in the northeastern Gulf of Mexico. Trans. Am. Fish. Soc. 134:315-325.

Thorrold, S. R., C. Latkoczy, P. K. Swart, and C. M. Jones.

2001. Natal homing in a marine fish metapopulation. Sci- ence 291:297-299.

Welsh, S. A., A. W. Kahnle, B. A. Versak, and R. J. LaTour.

2003. Use of tag data to compare growth rates of Atlantic coast striped bass stocks. Fish. Manag. Ecol. 10:289- 294.

Wingate, R. L., and D. H. Secor.

2007. Intercept telemetry of the Hudson River striped bass resident contingent: Migration and homing patterns. Trans. Am. Fish. Soc. 136:95-104

339

Surface mucous as a source of genomic DNA from Atlantic billfishes (Istiophoridae) and swordfish (Xiphiidae)

Abstract — Procedures for sampling genomic DNA from live billfishes involve manual restraint and tissue excision that can be difficult to carry out and may produce stresses that affect fish survival. We examined the collection of surface mucous as a less invasive alternative method for sourcing genomic DNA by comparing it to autologous muscle tissue samples from Atlantic blue marlin ( Makaira nigricans), white marlin ( Tetraptu - rus albidus), sailfish {Istiophorus platypterus), and swordfish ( Xiphias gladius). Purified DNA from mucous was comparable to muscle and was suitable for conventional polymerase chain reaction, random amplified poly- morphic DNA analysis, and mitochon- drial and nuclear locus sequencing. The nondestructive and less invasive characteristics of surface mucous col- lection may promote increased sur- vival of released specimens and may be advantageous for other marine fish genetic studies, particularly those involving large live specimens des- tined for release.

Manuscript submitted 26 November 2008. Manuscript accepted 26 March 2009.

Fish. Bull. 107:339-342 (2009).

The views and opinions expressed or implied in this article are those of the author and do not necessarily reflect the position of the National Marine Fisheries Service, NOAA.

John P. Hoolihan1 Nerida F. Perez2 Ronald M. Faugue2 Andrea M. Bernard3

Understanding genetic variation and identifying evolutionary lineages are important considerations for conser- vation management of large pelagic fishes (Palumbi, 1994; Ward, 2000). Some methods used for genetic sam- pling of billfishes (families Istiophori- dae and Xiphiidae) require excision of muscle, skin, or fin tissue, and excision requires manual restraint or killing of the animal. Some non- destructive sampling methods, such as fin and scale collection, exist that avoid the need to kill the fish (Yue and Orban, 2001; Wasko et ah, 2003; Hoolihan et al., 2004). Tissue exci- sion from very large live specimens is problematic because of personal safety concerns for handlers, and injuries to fish that may reduce survival. Most recreational billfish caught in the United States are released (Prince et al., 2007), whereas possession of billfish by U.S. pelagic longline ves- sels and sales of Atlantic billfishes have been prohibited since 1988. This regulation eliminates opportunities to obtain DNA samples from landed spec- imens, warranting a need for alterna- tive methods. To sample genomic DNA with nondestructive techniques and

Rebekah L. Horn3 Derke Snodgrass1

Duane R. Schultz (contact author)2

with minimal handling would promote the survival of released individuals and increase the opportunities to con- duct genetic studies.

One alternate potential source of genomic DNA is the epidermal cells found in billfish and swordfish sur- face mucous. Successful extractions of sufficient quantities of genomic DNA from surface mucous of freshwater fishes have been reported for Salmo trutta fario (brown trout), Esox lucius (northern pike) (Livia et al., 2006) and Scleropages formosus (Asian arowana) (Chansue, 2006), provid- ing an experimental model for large pelagic species.

The present study compares DNA extractions from surface mucous and autologous skeletal muscle tissue from billfishes and swordfish to determine the suitability of DNA extracted from surface mucous for random amplified polymorphic DNA (RAPD) and DNA sequencing analyses.

Materials and methods

Surface mucous and autologous skel- etal muscle samples were collected

Email address for contact author: dschultz@med.miami.edu

1 NOAA Fisheries

Southeast Fisheries Science Center 75 Virginia Beach Drive Miami, Florida 33149

2 Department of Medicine University of Miami Miller School of Medicine Miami, Florida 33136

3 Guy FHarvey Research Institute Nova Southeastern University Oceanographic Center 8000 North Ocean Drive Dania Beach, Florida 33004

340

Fishery Bulletin 107(3)

from three individuals from each of the following species: Makaira nigricans (blue marlin), Tetrapturus albidus (white marlin), Istiophorus platypterus (sailfish), and Xiphias gladius (swordfish). We compared purified DNA extracted from mucous and muscle using RAPD, mito- chondrial DNA (mtDNA) sequencing, and nuclear DNA sequencing analyses.

Sample preparation and DNA purification

Surface mucous samples were collected with a poly- urethane sponge as described by Schultz et al. (2006) and immediately processed, or stored at -80°C for later extraction. Each sponge was cut into small pieces, mixed with 1500 pL of phosphate buffered saline, and com- pressed repeatedly to remove mucous. All fluids were centrifuged through a single QIAamp® (Qiagen Inc., Valencia, CA) spin column. DNA purification was car- ried out by using Qiagen® buccal swab spin protocol with the following modifications: 1) a final concentration of 1 millimolar (mM) ethylenediaminetetraacetic acid (EDTA) was added to the phosphate-buffered saline extraction buffer; 2) the proteinase K treatment step was eliminated; and 3) an RNase mixture of A and T1 enzymes was used to degrade RNA after the final DNA purification step (Ambion Inc., Foster City, CA). The RNase cocktail enzyme mix was necessary because the Qiagen® spin columns copurify RNA and DNA in parallel when both are present in a sample. Cold ethanol precipitation and inclusion of EDTA in buffers were used to reduce nuclease degradation (Dessauer et al., 1996; Wasko et al., 2003).

For muscle tissue, 25 mg were macerated in 180 pL Buffer ATL (Qiagen Inc., Valencia, CA), and in- cubated overnight in a 56°C water bath in the pres- ence of 20 pL proteinase K. Purification followed the QIAamp® manufacturer’s protocol for tissue. Aque- ous samples of nucleic acid (1.5 p L) from mucous and muscle extractions were measured for purity with a NanoDrop 1000 Spectrophotometer (Thermo Fisher Scientific, Wilmington, DE) and showed a range of 1.7 to 2.0 for the DNA and RNA absorbance ratios (260 nm:280 nm).

RAPD analysis

Three different 10-mer oligonucleotide primers (Table 1) of arbitrary sequence (IDT Integrated DNA Technolo- gies, Coralville, IA) were tested against surface mucous DNA and autologous muscle DNA from three individuals of M. nigricans, T. albidus, I. platypterus, and X. gla- dius. PCR reactions for RAPD analysis were performed in a total volume of 25 pL containing 3 p L extracted genomic DNA, 2.5 pL of 10 mM 10-mer primer, 2.5 pL of 2.5 mM deoxynucleotide triphosphate (dNTPs), 0.75 pL of 25 mM MgCl2, 0.20 pL Taq DNA polymerase, 2.5 pL 10x buffer, 5 pL 5M betaine (N, N, N-trimethylgly- cine), 2 pL HotStart-IT® binding protein (USB Corp., Cleveland, OH), and 6.55 pL distilled water. Pre-PCR incubation with the HotStart-IT™ binding protein was

Table 1

Nucleotide composition of three 10-mer primers used for random amplified polymorphic DNA (RAPD) compari- son of DNA extracted from billfish surface mucous and muscle tissue, and percent content of guanine and cyto- sine (% GC).

Primer no.	Nucleotide composition	% GC
1	5'-GTTGCGGGCT-3'	70
2	5'-CAGCCCGGGT-3'	80
3	5'-AGGCCACCGC-3'	80

executed at 25°C for four hours to prevent mispriming and primer dimerization during amplification (Chou et al., 1992). RAPD PCR was performed in an Eppen- dorf Mastercycler (Westbury, NY) starting with initial heating for 5 minutes at 94°C, followed by 34 cycles at 94°C for 5 minutes, 42°C for 30 seconds, 72°C for 90 seconds, and a final extension of 72°C for 10 minutes. A negative control (no genomic DNA) was included in each PCR set to verify no reagent contamination. The PCR products were verified by electrophoresing 5 pL in 1.2% agarose gel (ISC BioExpress, Kayville, UT) and TAE buffer (pH 8.5) for 60 min at 100 V (60 mA), stained with ethidium bromide, and visualized through a UV transilluminator.

Sequencing analysis

Mitochondrial and single-copy nuclear loci were sequenced from three individuals from each of the fol- lowing species: M. nigricans, T. albidus, and I. platyp- terus. Insufficient samples of mucous and muscle were available for sequencing X. gladius. Mitochondrial NADH dehydrogenase subunit4 (ND4) was ampli- fied by PCR with the primer pair 61F and 1837R and cycling parameters outlined in Shivji et al. (2006). All amplifications of the anonymous single-copy nuclear locus WM13 were performed with the primer pair WM13-F and WM13-R developed by Buonaccorsi et al. (1999). Nuclear PCR reactions were performed in a total reaction volume of 50 p L containing 1 pL of extracted genomic DNA, 10 pmol/pL of each primer, 40 pM dNTPs, lOx PCR buffer, and 1 unit of HotStar Taq™ DNA Polymerase (Qiagen Inc., Valencia, CA). The PCR thermal profile consisted of an initial heating at 95°C for 15 minutes to activate the DNA polymerase, followed by 35-40 cycles at 94°C for 1 minute, 1 minute at 50°C, and 1 minute at 72°C, with a 5-minute final extension step at 72°C. Both nuclear and mitochondrial amplifications were performed in a MJ Research PTC- 200 thermal cycler (Waltham, MA). A negative control (no genomic DNA) was included in each PCR set to verify that there was no reagent contamination.

All amplified products were purified by using the QIAquick® PCR purification kit (Qiagen Inc., Valencia, CA) and sequenced with an Applied Biosystems 3130

Hoolihan et al.: Surface mucous as a source of genomic DNA from Istiophoridae and Xiphudae

341

A					B
		SM MT SM MT	SM MT	SM MT	SM MT	SM MT
				|			n
■ ■ ■	—	■***	mm mm		!*|S -
	1 2	3	4 5 6 7	8 9 10	i	2 3 4	5 6 7	8 9 10
c		SM MT SM MT	SM MT	D	SM MT	SM MT	SM MT
	mm
i	s ■Vn/'/A-. jjjjl	i	mm	M 1 (1	* «HK	1SH ft®	mm mm	Ik
	HNI
	1 2	3	4 5 6 7	8 9 10	1	2 3 4	5 6 7	8 9 10

Figure 1

Representative random amplified polymorphic DNA (RAPD) banding patterns from four species: A) Makaira nigricans (blue marlin), B) Tetrapturus albidus (white marlin), C) Istiophorus platypterus (sailfish), and D) Xiphias gladius (swordfish) for three 10-mer primers (Table 1) tested on each fish for the template DNA from surface mucus (SM), and autologous muscle tissue (MT). Lane contents are as fol- lows: 1, 100-bp ladder; 2, 5, and 8, negative controls (no DNA); 3 and 4, primer no. 1; 6 and 7, primer no. 2; and, 9 and 10, primer no. 3.

genetic analyzer (Foster City,

CA). Forward and reverse se- quences were assembled and edited with GeneDoc 2.6.002 (http://www.psc.edu/biomed/ genedoc, accessed 1 June 2008). To control for cross- contamination with other billfish or possible parasites or microbes, we compared the mitochondrial and nuclear se- quences derived from surface mucous to sequences obtained from autologous muscle tis- sue. Because autologous mus- cle tissue was not available for the T. albidus sequencing analyses, the mucous sample sequences were compared to homologous locus sequences obtained from reference T. albidus tissues available in our laboratory.

Results and conclusions RAPD analysis

Comparable RAPD amplicons were derived from surface mucous and autologous muscle tissue of M. nigricans, T. albidus, I. platypterus, and X. gladius for each of the three 10-mer primers tested. Representative RAPD banding patterns are illustrated in Figure 1. The nega- tive control reactions (minus template DNA) observed with each primer confirmed that the amplified genomic DNA from both sources was not an artifact of the primer concentration. Results indicated that sufficient quanti- ties of genomic DNA are available in surface mucous from all the species tested.

Sequencing analysis

For the three species screened, M. nigricans, T. albidus, and I. platypterus, the quality of nuclear and mitochon- drial PCR amplifications were comparable. For both the nuclear WM13 and the mt ND4 locus, sequences derived from a single individual from both sources of genomic DNA (mucous and autologous muscle tissue) were found to be identical when compared with respect to nucleotide base composition (5'-3' and 3'-5' directions), thereby demonstrating that the genomic DNA derived from sur- face mucous was not due to cross-contamination from other billfish or microbes, and in fact originated from the fish sampled. Nuclear and mitochondrial sequences derived from both sources of genomic DNA are avail- able from GenBank under the following accession num- bers: T. albidus : ND4 (997bp): FJ809995-FJ809997; WM13 (279bp): FJ809988; M. nigricans : ND4 (966bp):

FJ809991, FJ809992, and FJ809994; WM13 (279bp): FJ809986, FJ809987, and FJ809989; I. platypterus-. ND4 (1009bp): FJ809990 and FJ809993; WM13 (277bp): FJ809984 and FJ809985.

This study has shown that surface mucous contains sufficient quantities of genomic DNA to carry out RAPD analyses of istiophorid billfishes and swordfish, as well as sequencing applications of istiophorid billfishes. These extractions compare favorably to genomic DNA extractions from surface mucous reported for freshwater species S. formosus (Chansue, 2006), E. lucius, and S. trutta fario (Livia et al., 2006).

The slight differences between some of the mucous and muscle RAPD amplification profiles (Fig. 1) may be a result of contaminant DNA in the mucous (e.g., bacteria, microalgae), or other artifact variations known to occur in RAPD studies (Ellsworth et al., 1993). We found that the pre-PCR incubation of the template DNA master mix with HotStart-IT™ binding protein was crucial for preventing mispriming and primer dimer- ization that produced these artifact bands (Chou et al., 1992). In addition, the inclusion of betaine (N, N, N-tri- methylglycine) improved band visibility by eliminating the smearing attributed to the formation of secondary structure, which is caused by G-C rich regions (Henke et al., 1997). Importantly, for surface mucous RAPD analysis, the RNAase treatment of nucleic acid was a necessary step, whereas the inclusion of proteinase K was not.

342

Fishery Bulletin 107(3)

The nondestructive and less invasive procedures associated with sampling surface mucous offers many advantages when compared to fin clip and muscle tissue collection, particularly when very large fishes destined for live release are involved. Although the collection of surface mucous with sponges was ad- equate for the present study, commercially available products such as FTA® cards (Whatman Inc., Florham Park, NJ) may offer advantages. For example, Livia et al. (2006) reported that FTA® cards were a fast and reliable method of collecting, storing, and extracting genomic DNA from E. lucius and S. trutta fario. FTA® cards can be stored dry at room temperature, thus eliminating the need for laboratory freezers or special shipping considerations. We tested FTA® cards on a limited number of I. platypterus and T. albidus surface mucous samples (data not shown). Preliminary results were successful for PCR amplification, and further analyses are planned.

We report the first use of surface mucous from ma- rine fishes as an alternative method of DNA sampling. As such, the method offers advantages that warrant consideration when planning genetic studies on other marine species, particularly those where live-release is desirable.

Acknowledgments

This study was supported by National Oceanic and Atmospheric Administration grants to E. D. Prince and M. S. Shivji. Appreciation is extended to the captains and crew members who assisted in the field sampling.

Literature cited

Buonaccorsi, V. P., K. S. Reece, L. W. Morgan, and J. E. Graves.

1999. Geographic distribution of molecular variance within the blue marlin ( Makaira nigricans): a hierarchi- cal analysis of allozyme, single-copy nuclear DNA, and mitochondrial DNA markers. Evolution 53:568-579. Chansue, N.

2006. Rapid isolation of DNA from the mucus of Asian arowana (Scleropages formosus, Osteoglossidae). Thai J. Vet. Med. 36:55-59.

Chou, Q., M. Russell, D. E. Birch, J. Raymond, and W. Bloch.

1992. Prevention of pre-PCR mispriming and primer dimer- ization improves low-copy-number amplifications. Nu- cleic Acids Res. 20:1717-1723.

Dessauer, H. C., C. J. Cole, and M. S. Hafner.

1996. Collection and storage of tissues. In Molecular systematics, 2nd ed. (D. M. Hillis, C. Moritz, and B. K. Mable, eds.), p. 29-47. Sinauer, Sunderland, MA.

Ellsworth, D. L., K. D. Rittenhouse, and R. L. Honeycutt.

1993. Artifactual variation in randomly amplified polymorhic DNA banding patterns. Biotechniques 14:214-217.

Henke, W., K. Herdel, K. Jung, D. Schnorr, and S. A. Loening.

1997. Betaine improves the PCR amplification of GC-rich DNA sequences. Nucleic Acids Res. 25:3957-3958.

Hoolihan, J. R, J. Premanandh, M. A. D’Aloia-Palmieri, and J. A. H. Benzie.

2004. Intraspecific phylogeographic isolation of Arabian Gulf sailfish Istiophorus platypterus inferred from mito- chondrial DNA. Mar. Biol. 145:465-475.

Livia, L., P. Antonella, L. Hovirag, N. Mauro, and F. Panara.

2006. A nondestructive, rapid, reliable and inexpensive method to sample, store and extract high-quality DNA from fish body mucus and buccal cells. Mol. Ecol. Notes 6:257-260.

Palumbi, S. R.

1994. Genetic divergence, reproductive isolation, and marine speciation. Annu. Rev. Ecol. Systemat. 25:547- 572.

Prince, E. D., D. Snodgrass, E. S. Orbesen, J. P. Hoolihan, and J. E. Serafy.

2007. Circle hooks, “J” hooks, and “drop-back” time: a hook performance study of the south Florida recreational live bait fishery for sailfish, Istiophorus platypterus (Shaw). Fish. Manag. Ecol. 14:173-182.

Schultz, D. R., N. F. Perez, D. Snodgrass, J. E. Serafy, E. D. Prince, F. Arocha, T. R. Capo, and C. K. Tan.

2006. Enzyme-linked immunosorbent assays and billfish gender: testing muscle tissue and surface mucus in tag- ging studies. Bull. Mar. Sci. 79:859-864.

Shivji, M. S., J. E. Magnussen, L. R. Beerkircher, G. Hinteregger, D. W. Lee, J. E. Serafy, and E. D. Prince.

2006. Validity, identification, and distribution of the roundscale spearfish, Tetrapturus georgii (Teleostei: Istio- phoridae): Morphological and molecular evidence. Bull. Mar. Sci. 79:483-491.

Ward, R. D.

2000. Genetics in fisheries management. Hydrobiologia 420:191-201.

Wasko, A. P., C. Martins, C. Oliveira, and F. Foresti.

2003. Non-destructive genetic sampling in fish. An improved method for DNA extraction from fish fins and scales. Hereditas 138:161-165.

Yue, G. H., and L. Orban.

2001. Rapid isolation of DNA from fresh and preserved fish scales for polymerase chain reaction. Mar. Bio- technol. 3:199-204.

343

Abstract — We evaluated habitat quality for juvenile California halibut (. Paralichthys californicus) in a Pacific Coast estuary lacking in strong salin- ity gradients by examining density, recent otolith growth rates, and gut fullness levels of wild-caught and caged juveniles for one year. Juve- niles <200 mm standard length were caught consistently in the inner, cen- tral, and outer sections of the estuary. The density of juveniles was two times higher in the inner estuary during most of the year, consistent with active habitat selection by part of the population. A generalized linear model indicated temperature, sampling time, and the interaction between salinity and temperature were significantly related to density. However, the model explained only 21% of the variance. Gut fullness levels of wild-caught juveniles were highest during the summer, but recent otolith growth rates were not related to temperature. The proportion of individuals feeding successfully indicated that seasonal differences in food availability are more important than spatial varia- tion in prey abundance in driving feeding success. Feeding success of caged fishes was limited, precluding the use of growth rates as indicators of local habitat quality. However, mar- ginal increment widths were reliable indicators of somatic growth at low growth rates over two-week periods. The relatively high growth rates and abundance of small wild-caught juveniles found throughout the estu- ary indicates that the entire estuary system has the potential for serving as nursery habitat.

Manuscript submitted 9 July 2008. Manuscript accepted 20 April 2009. Fish. Bull. 107:343-358 (2009).

The views and opinions expressed or implied in this article are those of the author and do not necessarily reflect the position of the Nacional Marine Fisheries Service, NOAA.

Assessment of habitat quality for juvenile California halibut ( Paralichthys californicus ) in a seasonally arid estuary

Francisco Javier Lopez-Rasgado Sharon Z. Herzka (contact author)

E-mail address for contact author: sherzka@cicese.mx Department of Biological Oceanography

Center for Scientific Research and Higher Education of Ensenada (CICESE)

Km. 107 Carretera Tijuana-Ensenada Ensenada, Baia California, Mexico US Mailing address:

PO Box 434844

San Diego, California 92143

California halibut (Paralichthys cali- fornicus) is a species of commercial and recreational importance that is found in coastal waters from Wash- ington, U.S.A., to Baja California Sur, Mexico (Sweatnam et al., 2007). Spawning occurs along coastal areas and planktonic larvae inhabit the continental shelf for about a month before settling in shallow protected areas along the coast or in the outer reaches of protected embayments (Allen and Herbinson, 1990; Moser and Watson, 1990). Juveniles make facultative use of protected embay- ments such as coastal lagoons, bays, and estuaries (Horn and Allen, 1985; Allen, 1988; Kramer, 1990; Fodrie and Mendoza, 2006). Recent studies indi- cate that both protected embayments and coastal habitats contribute to the production of adults, but that juve- nile densities are substantially higher within embayments (Forrester and Swearer 2002; Fodrie and Mendoza, 2006; Fodrie and Levin, 2008). How- ever, there are no studies where juve- nile habitat quality has been assessed for California halibut on the intra- embayment level.

Juvenile flatfish occupying specific habitats or areas within embayments may exhibit considerable variability in abundance, growth, and mortal- ity rates (Allen and Baltz, 1997; Gil- liers et al., 2006). In addition, spe- cific regions within embayments may contribute disproportionaly to the

production of recruits to the adult population (Beck et al., 2001). Sogard (1992) reasoned that if rapid growth during the juvenile stage offers an advantage in terms of increased sur- vival, and if growth rates vary as a function of habitat quality, individu- als will select habitats that offer the maximum growth potential, although biological interactions such as pre- dation can influence habitat choice. Within this context, high-quality nursery habitats within embayments are those in which growth and sur- vival rates are higher than the cor- responding rates in coastal habitats (Gilliers et al., 2006).

In estuarine systems strongly influ- enced by freshwater inflow (“classical” estuaries), salinity exhibits strong spatial gradients from the mouth to the head of the estuary. Gradients in salinity have been related to the distribution of some species of flatfish (e.g., Allen and Baltz, 1997; Able et al., 2005). In contrast, estuaries in seasonally arid regions, such as the Pacific coast of Baja California and southern California, tend to receive freshwater inflow only during the rainy winter season or summer mon- soon. These “Mediterranean-type” es- tuary systems are increasingly hyper- saline with increasing distance from the river mouth during a large part of the year, and in the inner reaches of the estuaries the water exhibits high residence times, which influence nu-

344

Fishery Bulletin 107(3)

trient availability and production (Largier et al., 1997). Hence, spatial patterns of habitat use and quality for juvenile flatfish in classical and “Mediterranean-type” estuaries may differ substantially.

Use of habitat by juvenile flatfish has been re- lated mostly to temperature, salinity, dissolved oxy- gen, substrate type, and depth (Gibson, 1994; Able et al., 2005). The first three variables directly influ- ence metabolic processes, and hence abundance and growth (Gibson, 1997). Substrate type can be used as a proxy for food availability, and is related to success in predator avoidance (Gibson, 1994; Amezcua and Nash, 2001). Differences in distribution as a function of depth may be due to habitat partitioning among life stages (Kramer, 1990; Gibson, 1997). Because a direct assessment of juvenile habitat quality is diffi- cult, growth and density have served as proxies. These measures integrate the effect of biological factors and environmental conditions (Necaise et al., 2005; Gilliers et al., 2006). Specifically, estimates of recent otolith growth rates evaluated through the measurement of increment widths can be used as an integrative indi- cator of habitat quality and the suitability of environ- mental conditions over short time scales (Le Pape et al., 2003; Gilliers et al., 2006). The fine-scale temporal and spatial variation of growth rates can thus serve as indicators of habitat quality.

The use of otolith marginal increment widths as indi- cators of habitat quality relies on two premises. First, there must be a high correlation between somatic and otolith growth rates (Campana and Jones, 1992). This has been shown to be the case for juvenile California halibut (Kicklighter, 1990; Kramer, 1991). Secondly, differences in growth rates should reflect the quality of the habitat in which fish were captured (Sogard, 1992; Gilliers et al., 2006). The second premise can be rendered invalid if there is substantial movement to or from areas with different environmental condi- tions within the time interval used to evaluate growth. Haaker (1975) found little movement of tagged juvenile California halibut within Anaheim Bay in southern California. Tagging studies of age-0 winter flounder ( Pseudopleuronectes americanus) and plaice ( Pleuro - nectes platessa) have also indicated limited displace- ment on the scale of a few hundred meters (Saucerman and Deegan, 1991; Burrows et al., 2004). However, Fodrie and Herzka (2008) used otolith microchemistry to reconstruct movement patterns of juvenile California halibut within an arid estuary and found that 8 out of 14 (57%) individuals moved among sections of the estuary over a two-month period. Likewise, Herzka et al. (2009) examined length-frequency distributions and recapture locations of tagged individuals and found simultaneous evidence of estuarine emigration and residency. If juveniles move substantially within an estuary, the implicit assumption that an individual has remained in the vicinity of its capture location for the time period over which growth is evaluated may be violated. Caging experiments guarantee that an individual has remained at a given location under

measurable environmental conditions (Sogard, 1992). However, confinement has the potential to influence natural growth rates (Guindon and Miller, 1995). Cag- ing experiments and sampling of natural populations are thus complimentary approaches for using growth rates as proxies for habitat quality.

We evaluated nursery habitat quality for juvenile California halibut ( Paralichthys californicus) in a sea- sonally arid estuary, Punta Banda Estuary in Baja California, Mexico, based on recent otolith growth rates and an index of feeding success in relation to feeding levels. To determine if specific sections of the estuary serve as preferred juvenile habitat, we assessed spatial and temporal variability in density and evaluated re- cent otolith growth rates in relation to environmental conditions. In addition, we tested the hypothesis that juvenile density is higher in areas that favor higher growth rates. We simultaneously performed caging ex- periments and sampled natural populations to assess growth rates in relation to environmental conditions.

Materials and methods Study area

Punta Banda Estuary is a medium-size (11-km2 at high tide, 5-km2 at low tide) protected embayment located within the Southern California Bight. It is located 100 km south of the US-Mexico border on the Pacific side of Baja California, Mexico (Fig. 1). The estuary lies along the southeastern margin of Todos Santos Bay (31°42'- 31°47'N lat and 116°37 -116°39'W long), a semiprotected coastal system. The L-shaped estuary is connected to the bay at its northern end through a 125-m inlet (Ortiz et al., 2003). The fastest current velocities are found within the main channel at the mouth (~1 m/s), where depths are 10-12 m (Pritchard et al., 1978). A channel runs along the main axis of the estuary and is flanked by shallow submerged or exposed flats at low tide. The depth of the main channel in the central and inner sec- tions of the estuary is shallow (<3 m) compared to the outer section (approximately 8 m, see Ortiz et al., 2003 for a detailed bathymetry). Along the shorter axis, the main channel splits into different arms and the average depth is <1 m in relation to mean low water. Patches of eelgrass ( Zostera marina) are found in the central estuaries and there are tidal marshes along most of the banks. The bottom is sandy towards the outer reaches of the system and becomes increasingly silty toward the head (Ortiz et al., 2003).

Because the estuary is located in a seasonally arid region, the estuary behaves mostly as a negative estu- ary, in that temperature and salinity increase from the mouth to the head, particularly during the warmer months (Alvarez-Borrego and Alvarez-Borrego, 1982). Temperature and salinity also exhibit variations asso- ciated with the semidiurnal tidal cycle because of the exchange of water with Todos Santos Bay. Maximum tidal range during spring tides is about 1.7 m.

Lopez-Rasgado and Herzka: Assessment of habitat quality for juvenile Paralichthys cahfornicus

345

Experimental design

Density, recent growth rates, and environmental parameters (temperature, salinity, dissolved oxygen and gut fullness levels as a proxy for food availabil- ity) were measured approximately every other month between October 2004 and October 2005. To evaluate growth and abundance over a gradient of environmen- tal conditions, the inner, central and outer reaches of the estuary were chosen as sampling and caging locations (Fig. 1). Six 28-day caging experiments were performed throughout the year to evaluate recent oto- lith growth, somatic growth, and gut fullness levels (Table 1). Density of natural populations was evaluated at the beginning and end of each caging experiment. Juveniles collected at the beginning of each caging period were used for caging experiments, whereas those captured at the end were used for measuring otolith growth rates and evaluating gut fullness levels of natural populations. To minimize the range of sizes evaluated for growth and gut fullness levels and allow for direct comparison of otolith growth rates from natural populations and caged individuals, we limited the sizes of fish analyzed to between 50 and 160 mm standard length (SL).

Density and environmental variables

On each sampling date, five 10-minute tows were con- ducted in each section of the estuary with a 7.6-m wide otter trawl (headrope length 9.5 m, 2.0- and 0.5-cm mesh in the body and codend, respectively). The sam- pling gear was not efficient at catching fish <40 mm SL. For each section and sampling date, we sampled at a range of depths and areas to obtain a representa- tive index of density. Sampling was mostly limited to the mid-to-high tidal range of spring tides because we needed to gain access to the cages during low tides. All tows were performed with the prevailing current at a target tow speed of 3 km/hr. For each tow, initial and final coordinates, mean current speed and the distance covered by the trawl (approximately 500 m) were regis- tered by using a hand-held GPS. Temperature, salinity and dissolved oxygen (DO) were measured at the end of each tow with an YSI 85 dissolved oxygen and conduc- tivity meter (Yellow Springs Intruments, Concord, CA). Because previous studies have reported a relationship between depth and abundance of juvenile California halibut in shallow estuarine systems (Kramer, 1990; Fodrie and Mendoza, 2006), a consistent depth was maintained during each tow. The depth of each tow was monitored and recorded with an onboard fish finder. To obtain a density estimate representative of each sec- tion of the estuary, tows were performed at a variety of depths and locations.

After capture, California halibut were immediately measured for standard length. Length-frequency distri- butions were constructed for each sampling period and section of the estuary by 10-mm size classes. Density on an area basis was calculated by assuming a 7.6-m

Figure t

Map of Punta Banda Estuary, Baja California, Mexico where density and growth rates of California halibut ( Paralichthys californicus) were assessed between October 2004 and October 2005. Black asterisks indicate locations where experiments were performed. Sampling for natural abundance and growth estimates was conducted in the outer, central, and inner sec- tions of the estuary; the areas between these sections were not sampled. The gray solid line indicates the channel that runs along the main axis of the estuary.

trawl width and standardizing the tow to 1000 m2 (re- ported as fish/1000 m2). Estuarine emigration has been reported to occur during summer at lengths ranging from 140 to 200 mm (Haaker, 1975; Kramer, 1990; Hammann and Ramirez-Gonzalez, 1990). Hence, mean density (±standard error [ S E ] ) was calculated for fish <200 and >200 mm SL for each section of the estuary and sampling time.

Given that our primary interest was young juveniles, the densities of fish <200 mm SL were analyzed by two-way analysis of variance (ANOVA) with time and section of the estuary as fixed factors. Normality and homogeneity of variance were evaluated by using the Kolmogorov- Smirnov and Levene’s tests, respectively. The data were log (x+1) transformed before we conduct- ed the ANOVA to comply with the assumption of nor- mality. A Tukey HSD test for unequal sample sizes was used to identify homogenous groups. The size-frequency

346

Fishery Bulletin 107(3)

Table 1

Starting date, size range, and number of fish recovered in cages in the outer, central, and inner reaches of Punta Banda Estuary. Cages were recovered after 14 or 28 days; each row indicates a single cage (n = 6 juveniles). Asterisks indicate locations in which cages were not recovered. No data (n. d.); cages were not seeded because of low capture rates.

14-day caging period 28-day caging period

Starting date	Section	Size range mm SL	Number of fish recovered (% mortality)	Size range mm SL	Number of fish recovered (% mortality)
28 Oct 2004	Outer	89-158	*	72-130	*
	Outer	70-102	*	69-85	*
	Central	96-159	6(0)	55-103	6(0)
	Central	79-135	6(0)	67-146	4(33)
	Inner	78-146	6(0)	75-149	*
	Inner	75-150	4 (33)	67-148	*
12 Jan 2005	Outer	96-116	4(33)	80-145	*
	Outer	84-104	0(100)	82-143	*
	Central	88-115	5(17)	90-122	6(0)
	Central	90-113	6(0)	62-146	5(17)
	Inner	113-149	4(33)	120-140	4(33)
	Inner	95-112	4(33)	85-119	2 (67)
28 Mar 2005	Outer	61-125	1(83)	n.d.	—
	Outer	55-140	5(17)	n.d.	—
10 Mar 2005	Central	62-138	4(33)	54-150	4(33)
	Central	52-136	5(17)	n.d.	—
	Inner	80-150	6(0)	118-156	6(0)
	Inner	80-144	5(17)	102-160	6(0)
04 May 2005	Outer	114-140	4(33)	63-132	*
	Outer	65-140	2(67)	64-155	*
	Central	64-165	5(17)	69-157	5(17)
	Central	63-152	6(0)	n.d.	—
	Inner	68-150	4(33)	57-160	4(33)
	Inner	56-139	4(33)	56-146	4(33)
16 Jun 2005	Outer	88-146	3 (50)	89-159	*
	Outer	n.d.	—	106-133	*
	Central	91-157	6(0)	101-161	3(50)
	Central	72-99	3(50)	69-73	*
	Inner	65-170	4(33)	72-150	5(17)
	Inner	n.d.	—	63-172	4(33)
06 Sep 2005	Outer	75-122	4(33)	71-144	*
	Outer	73-141	6(0)	71-143	6(0)
	Central	53-146	4(33)	50-151	4(33)
	Central	n.d.	—	110-129	4(33)
	Inner	91-167	5(17)	147	1 (83)
	Inner	n.d.	—	n.d.	—

distributions of California halibut <200 mm SL caught in different sections of the estuary were compared by using the nonparametric Kruskall-Wallis H test.

The relationship between density of fish <200 mm SL, environmental conditions, section of the estuary and sampling time was evaluated by using a general lin- ear model (GLM). Densities were log(x+l) transformed to achieve normality. Temperature, salinity, DO, and depth were were included as continuous predictor vari-

ables. Section of the estuary and sampling time were included as categorical variables. Data corresponding to the beginning and end of each caging experiment were pooled for analysis and considered as a single point in time; the data from August 2005 were entered as a separate time point. Because there were significant cor- relations between salinity and tempreature (r= 0.487) and salinity and DO (r=-0.633), the model was run to include an interaction term for these variables. Model

i

!

!

Lopez-Rasgado and Herzka: Assessment of habitat quality for |uvenile Paralichthys califormcus

347

residuals were close to normally distributed (Shapiro Wilk’s statistic=0.984, P=0.031).

Otolith growth rates of natural populations

Using measurements of daily increment widths as a proxy for somatic growth rate, we relied on two assump- tions: 1) that growth increments in the form of ring formations in otoliths occurs daily, and 2) the increment widths of otoliths are proportional to somatic growth (i.e., there is a linear relationship between fish size and otolith size; Campana and Jones, 1992). Kramer (1991) and Kicklighter (1990) validated daily ring formation in larval and juvenile California halibut, respectively. Using caging experiments to evaluate otolith and somatic growth rates in juvenile California halibut, Kicklighter (1990) documented a strong linear relationship between SL and otolith length for juveniles ranging from 40 to 100 mm SL. Kicklighter (1990) also reported a linear relationship between mean recent otolith growth (14 days) and somatic growth (y=0.619x+0.093, r2 = 0.55). Hence, the measurement of recent increment widths as a proxy for somatic growth rates in juvenile California halibut is justified.

Wild-caught juveniles were placed over ice in indi- vidual bags and later frozen in the laboratory. We chose five individuals from each of the following size classes for otolith analysis: 50-80, 81-120 and 121-160 mm SL (n=15 per date and section of the estuary). Sagittal otoliths were extracted, cleaned in a sonicator with a 10% bleach solution to remove tissue, rinsed with dis- tilled water, dried, and mounted on slides sulcus-side- down with Krazy Glue (Industrias Kola Loka SA de CV, Mexico State, Mexico). The right or left sagittal otolith was chosen randomly. The percent difference in length between the sagittal otoliths dissected from the eyed or blind side of both right and left-eyed juveniles is small (mean ±standard deviation [SD] in relation to blind side=-1.7% ±3.0%, range -11.1% to 2.5%, n=20).

Polishing was necessary to reveal daily growth incre- ments in the otolith posterior margin. Polishing cloths of several sizes (34.3, 22.1, 14.5, and 6.5 pm) were used depending on otolith size and visibility of daily incre- ments. Otoliths were given a final polishing with a 0.3-pm aluminum powder and soaked in 5% EDTA to increase the visibility of daily growth increments.

We were interested in examining the relationship be- tween recent growth rate and environmental conditions over a relatively short time period to minimize the pos- sibility that individuals had moved substantially within the estuary. We measured the width of daily growth increments for the period corresponding to the 14 days before capture (corresponding to the second half of the caging experiment). Daily increments, consisting of an opaque and translucent ring, were viewed under 400 x magnification. The width of each increment was mea- sured parallel to the main growth axis of each otolith in the posterior margin (range of widths 3-15 pm; mean= 6 pm ±2 SD) by using an imagine analysis system con- sisting of a compound microscope and digital camera

connected to a computer loaded with Image J analysis software (National Institutes of Health, Bethesda, MD). We had difficulty distinguishing the interface between the opaque and translucent rings of the outermost in- crements with sufficient clarity to accurately measure the daily increment widths, although we could identify daily increments. We therefore counted the 14 incre- ments deposited before capture and measured the width of those in which the interface between the opaque and translucent rings was clear to obtain an accurate measurement. The number of increments measured in a given otolith ranged from 5 to 12 (mean = 9 ±3 SD). Otoliths for which we could not measure at least five increments were discarded (about 20%). In those cases, we prepared additional otoliths from fishes of the same size class. Each increment was measured three times and its average width was used in subsequent calcula- tions. Recent growth rates are reported in pm/day.

The width of daily increments can vary as a function of fish size. Analysis of covariance (ANCOVA) has been used in previous studies to remove size-related differ- ences in tests for differences in otolith growth rates among groups (e.g., Phelan et al., 2000). We evaluated whether recent otolith growth was correlated with SL within the 50-160 mm SL size range that we examined. Data from fishes collected in different sections of the estuary at a given time were pooled. Sampling periods were considered separately and six correlations were performed (n- 45 fish per sampling period). Only one correlation was positive and significant (October 2004; P<0.001) and a second was slightly negative and mar- ginally significant (January 2005; P=0.032). In both cases, the proportion of the variance in recent otolith growth rates explained by SL was very low (^=0.26 and r2 = 0.10, respectively). Hence, we did not find a strong dependence of recent otolith growth rates on size within our target size range. Recent otolith growth rates of natural populations were thus analyzed withg two-way ANOVA and by using time and section of the estuary as fixed factors. Data were log (x+1) transformed to comply with the assumption of normality. Tukey HSD tests were used to test for specific differences between means after ANOVA.

We used correlation analysis to test the hypothesis that higher growth rates coincide with higher density of juveniles <200 mm SL and to examine the relationship between recent otolith growth rates of natural popula- tions and temperature. Mean temperature during the 14 days before their capture was calculated by using data from thermographs deployed during caging experiments (see below). Correlation analysis was performed only for times and sections of the estuary for which both otolith and temperature data were available.

Somatic and otolith growth rates of caged fishes

Valle et al. (1999) examined the fine-scale distribution of juvenile California halibut in shallow (<1.1 m depth) waters of Alamitos Bay, CA, in relation to the presence or absence of eelgrass habitat. Juveniles were 2-6 times

348

Fishery Bulletin 107(3)

more abundant in unvegetated habitats. Eelgrass is not found in the outer and inner sections of Punta Banda Estuary and only sparse eelgrass beds are found in the central section. We placed cages solely in unvegetated areas because eelgrass is not the preferred habitat of juvenile halibut. Cages were constructed with a PVC frame (1 m widexl m long x 0.5 m high) wrapped in Vexar® low-density polyethylene netting of 0.5 x 0.5- cm mesh. Cages were closed on the bottom to prevent escapement. Similar designs have been used in other studies seeking to evaluate the growth of juvenile flatfish (Kicklighter, 1990; Sogard, 1992). Caging experiments began and ended during spring tides, allowing us access to subtidal habitat during lower low water. The day before starting each caging experiment, four cages were placed within a few meters of each other in the outer, central, and inner sections of the estuary (Fig. 1). Each cage was anchored by rebar fastened to the corners with cable ties. Temperature was measured continuously at each caging location by using thermographs placed in the vicinity of each caging location (HOBO Water Tem- perature Data Loggers model 856097, Onset Computer Corporation, Pocasset, MA). These thermographs were programmed to record every 30 minutes.

To supply the cages, individuals within the target size range (50-160 mm SL) were placed in ice chests filled with aerated seawater immediately after trawling. Seawater was exchanged frequently and mortality was minimal. Cages were seeded with juveniles caught in the same section of the estuary to avoid subjecting them to substantial changes in the environmental conditions to which they had been exposed.

The target number of fish to be placed within each cage was six. Other flatfish studies have used similar fish densities (Kicklighter, 1990). The number of fish introduced into each cage was held constant throughout the caging experiments. If we did not catch enough fish of the targeted size range in a given section of the estu- ary, fewer cages were seeded rather than altering fish density (Table 1). To evaluate somatic growth during the course of the experiment, each juvenile was marked by clipping the dorsal or anal fins, or both. Juveniles were then injected intramuscularly with tetracycline (0.05 mg/kg) to create an otolith mark indicative of the beginning of the caging period. To determine the cor- rect dose for each individual, wet weights were estimat- ed from SL measurements by using a relationship pre- viously obtained for juveniles captured in Punta Banda Estuary (wet weight (g) = 8.77-0.36SL + 0.0045SL2, r2 = 0.99).

We were concerned about cage loss. Hence, half the cages were retrieved after 14 days during lower low tide in- 2 cages per section of the estuary) and the re- mainder were recovered after 28 days. Otolith growth rates were thus measured after a 14- or 28-day caging period. Following retrieval from the cages, juveniles were identified by their pattern of fin clippings, SL was measured, and the number of survivors was recorded. Fish were placed on ice in the field and frozen in the laboratory for subsequent analysis of otolith growth

rates and gut fullness levels. Otoliths were removed and prepared as described above. It was more difficult to visualize daily growth increments in caged individuals that in those from natural populations (see also Fodrie and Herzka, 2008). Hence, we measured the width of the otolith anterior margin from the tetracycline mark to the edge. Tetracycline marks were viewed under 400 x magnification under ultraviolet light with a FlashUV2 flashlight (375 nm). Otolith growth rate was expressed as pm/day. Individual somatic growth rates of caged fishes were calculated as instantaneous growth coef- ficients (G, 1/d) with the folowing equation:

G = ( ln( SLt ) - ln( SL0 ))/ At ,

where SLt = standard lengths (mm) measured at the beginning of a caging period;

SL0 = standard lengths (mm) measured at end of a caging period;

4t = number of days fish remained within cages.

We used correlation analysis to examine the relationship between otolith and somatic growth rates (G) of caged juveniles retrieved after 14 days.

Gut fullness levels

Our main objectives were to evaluate whether food avail- ability was related to seasonal patterns in recent growth rates and to compare the amount of food ingested by wild-caught and caged California halibut. We assessed the gut fullness level of all juveniles captured in the field (n = 456) and those retrieved from cages (n= 214). The complete digestive tract (esophagus, stomach, and intestine) was dissected whole and preserved in 80% ethanol. An index was developed to classify fish by their relative gut fullness: 1) empty; 2) 1-25% full; 3) 26-50% full; 4) 51-75% full; and 5) 76-100% full. Gut fullness assessment was performed by a single person to maintain consistency. The frequency of occurrence of different gut fullness levels for each section of the estuary and sampling period was calculated as a per- centage of the total caged or wild-caught fish processed for a given date.

Results

Density and environmental variables

Mean density of juveniles <200 mm SL ranged from 0.36 ±0.36 to 9.68 ±2.71 fish/1000 m2 (overall mean=3.31 ±1.07 fish/1000 m2, Fig. 2A). It was roughly two times higher (—10 fish/1000 m2) in the innermost section of the estuary than in the central and outer sections ( — 4— 5 fish/1000 m2) during the winter and spring. Although during summer densities were lower than during winter and spring, they were still twice as high in the inner estuary than in the central and outer sec-

Lopez-Rasgado and Herzka: Assessment of habitat quality for juvenile Paralichthys californicus

349

tions (~3 vs. 1.5 fish/1000 m2). ANOVA results indi- cated that density varied significantly as a function of time (F12 154=3.97, P<0.005) and among sections of the estuary (F2 154 = 4.77, P=0.009). The interaction between factors was not significant (F2 4 154 = 1.33, P = 0.154). Post-hoc multiple comparison tests indicated that density was significantly higher in the inner estuary (4.55 ±1.02 fish/1000 m2) than in the central section (2.46 ±0.88 fish/1000 m2). In addition, density was significantly higher during winter (November and February) than during most summer months (June through October).

The size distribution of juveniles varied as a func- tion of time and section of the estuary. Recent re- cruits (<70 mm SL; Kramer, 1991) were relatively abundant throughout the estuary between October 2004 and February 2005, indicating that the peak in estuarine immigration occurred during winter. However, fish 60-80 mm SL were also captured be- tween May 2005 and July 2005. In the outer section, a large proportion (79% of total) of juveniles <100 mm SL were caught between October 2004 and April 2005; few individuals were >200 mm SL (Fig. 2B). Between May 2005 and October 2005, a greater per- centage of the fish caught were >200 mm SL (range 21 to 52%, Fig. 20. In the central and inner sec- tions, 87% and 85% of all fish caught were <200 mm SL. Throughout the estuary, juveniles <200 mm SL predominated between October 2004 and April 2005 (89% of total); fish >200 m SL were more frequent between June2005 and October 2005 (23% of total, Fig. 3).

The size-frequency distributions for the outer and central sections exhibited a single marked peak of 40-90 mm SL (51% of all fish caught) and 40-70 mm SL (32% of all fish caught), respectively (Fig. 4). In contrast, the size-frequency distribution of halibut caught in the inner section had a primary peak at 40-70 mm SL (21% of all fish caught) and a broad, secondary peak at 100-150 mm SL (28 % of the total catch). However, the size-frequency distributions of California halibut did not differ significantly among the outer, central, and inner sections of the estuary (Kruskall-Wallis H=1.35, P=0.51). The maximum SL found in the outer, central and internal sections of Punta Banda Estuary was 680, 788, and 784 mm, respectively.

Instantaneous measurements of temperature, sa- linity, DO, and depth taken during trawling varied throughout the year (range 15-24. 0°C, 32-38%c, 3-11 mg/L; Fig. 5). The GLM results indicated that density was signicantly and negatively related to temperature (f3= 0.59, F= 5.50, P=0.020), sampling time (F=2.264, P=0.039), and the interaction be- tween temperature and salinity ( /3 = 0 . 0 1 6 , F=4.906, P= 0.0208). All other predictor variables were not sig- nificantly related to density, although there was a weak negative relationship with salinity (/?=- 0.302, F=3.274, P=0.072). The GLM explained a low propor- tion of the variance (multiple r2 = 0.208).

co

E ST E E o o O o

CM O VI J-

o

14 12 10 - 8 - 6 - 4 -

Outer

Central

Inner

0

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct

28 i

26

24 -

22 -

20

18

16 -

14

12

Oct

Outer

Central

Inner

Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct

Figure 2

(A) Density of juveniles <200 mm standard length (SL) and (B) late juveniles >200 mm SL and adults of Cali- fornia halibut (Paralichthys californicus) captured in the outer, central, and inner sections of Punta Banda Estuary between October 2004 and October 2005. Values represent means ± standard error (SE). (C) Continuous temperature measurements made at locations in the outer, central and innermost sections of Punta Banda Estuary. Missing data reflect loss of thermographs.

Otolith growth rates of natural populations

Two-way ANOVA of log-transformed recent otolith growth rates indicated a significant interaction between time and section of the estuary (F10 249 = 8.30, P<0.001). In the outer section, the highest mean growth

350

Fishery Bulletin 107(3)

Oct-Nov 2004

n= 223

0 50 100 150 200 250 0 50 100 150 200 250 0 50 100 150 200 250

SL (mm)

Figure 3

Size-frequency distributions of California halibut ( Paralichthys californicus) cap- tured in the outer, central, and inner sections of Punta Banda Estuary between October 2004 and October 2005. Data corresponding to the beginning and end of each caging experiment were pooled. The 250 mm standard length (SL) size class includes fish >250 mm SL.

rates were found in January 2005 and May 2005 (8.13 ±0.40 and 6.75 ±0.45 ftm/d, respectively) and the lowest in September 2005 and March 2005 (4.52 ±0.16 and 5.47 ±0.35 pm/d, respectively; Fig. 6A). A similar pat- tern was observed for the central section. The highest growth rates in the inner section were found in Octo- ber 2004 and May 2005 (8.40 ±0.32 and 7.78 ±0.41

pm/d, respectively), and the lowest in September 2005 and January 2005 (4.11 ±0.15 and 4.89 ±0.40 pm/d, respectively). Correlation analysis indicated that the relationship between recent otolith growth rates and mean temperature during the 14 days before capture was not significant (r=0.31, F1 n=1.20, P=0.295), even though the mean temperature ranged between 15.8

Lopez-Rasgado and Herzka: Assessment of habitat quality for juvenile Paralichthys californicus

351

and 25.7°C (Fig. 2B). There was a positive relation- ship between density and recent growth rates, but the relationship was not statistically significant (r=0.43, P= 0.074).

Somatic and otolith growth rates of caged fishes

Throughout the caging experiments, two cages were lost in the outer section after the first two weeks. Another 12 cages were not recovered after 28 days (mostly from the outer section; Table 1). Excluding fish from cages that were not retrieved, 72.7% (131 juveniles) and 72.8% (83 juveniles) were recovered after 14 days and 28 days, respectively.

Recent otolith growth rates during the first 14 days were 5-6 times lower than those of wild-caught Cali- fornia halibut (1-2 pm/d, Fig. 6B). Minimum otolith growth was also detected during the second half of each caging period (Fig. 60. Somatic growth rates measured after 14 and 28 days were very low, indicating that conditions within the cages did not favor growth (Fig. 6, D and E). We therefore concluded that the growth rates of caged individuals did not reflect habitat value and did not test for growth differences between sections or caging periods.

Despite the low growth rates, there was a significant positive correlation between somatic and recent otolith growth of caged fishes during the first 14 d of the ex- periments (/•=(). 76, F1 12y=176.07, P<0.001, Fig. 7). This finding indicates that otolith and somatic growth are coupled in California halibut juveniles, even at very low growth rates. There was also a significant negative correlation between somatic growth rates and mean temperature (r= 0.56, Fin=5.15, P =0.044), although the correlation between otolith growth rates and tem- perature was not significant (F 1 u=1.21, P= 0.295; data not shown).

Gut fullness levels

Most juveniles captured in the wild had at least some food in their digestive tract (62%, 60%, and 64% of total in the outer, central and inner sections of estuary, respectively; Fig. 8A). The percentage of individuals with gut fullness levels >50% ranged roughly between 40 and 80%, varying as a function of time and section of the estuary. In general, fewer fish exhibited empty guts during the early spring and summer. In contrast, most of the fishes recovered from the cages after 14 days exhibited empty stomachs (Fig. 8B). Only occasionally did some caged individuals have noticeable amounts of food in the digestive tract.

Discussion

Density and environmental variables

California halibut <200 mm SL were consistently cap- tured throughout Punta Banda Estuary, indicating the

SL (mm)

Figure 4

Size-frequency distributions of California halibut (Paralichthys californicus) captured in the outer, central, and inner sections of Punta Banda Estuary between October 2004 and October 2005. Individuals smaller than 70 mm standard length (SL) are considered recent recruits. The 250 mm SL size class includes fish >250 mm SL.

entire system is used as juvenile habitat. Based on the relationship between daily otolith increment counts and SL reported by Rosales-Casian (2004) for juveniles caught in northern Baja California, and the age-length relationship reported by Hammann and Ramirez- Gonzales (1990) for halibut captured in Todos Santos Bay (TL (cm) = 8.98+9.51Age (yr)) fish <180 mm SL are young-of-the-year (see also Haaker, 1975; Kramer, 1991). Maturity occurs at approximately 20-23 cm total length (TL) for males and 38-47 cm TL for females (Haaker 1975; Love and Brooks 1990). Hence, most of our catch was comprised of juveniles, although some adults were also caught.

The distribution of juveniles relative to the mouth of medium-sized estuaries in Baja California and south- ern California appears to vary among systems. We

352

Fishery Bulletin 107(3)

found the highest abundance of juveniles in the inner reaches of Punta Banda Estuary throughout most of the year. Based on an annual survey, Hammann and Ramirez-Gonzalez (1990) reported higher abundance of juveniles in the central section of the same system between January and April. However, their sampling was limited to the main channel and did not include the inner reaches. Valle et al. (1999) reported that juvenile densities decreased from the mouth to the inner reaches of Alamitos Bay in southern California. In a fall survey, Fodrie and Mendoza (2006) found higher abundance of juveniles in the central and outer reaches of the sys- tems in southern California most similar in size, shape, and depth to Punta Banda Estuary (Batiquitos, Agua Hedionda Lagoon, Buena Vista, and Mission Bay). The density of juveniles captured in Punta Banda estuary is toward the lower range of those reported by Fodrie and

Mendoza (2006) for medium-size embayments (termed lagoons in their study, range 4-30 fish/1000m2 after taking into account their gear efficiency corrections).

Juveniles were caught throughout the range of instan- taneous temperatures measured in Punta Banda Estu- ary (15-24°C), although our GLM analysis indicated a weak but significant negative relationship between temperature and density. Likewise, other studies have also reported capturing juveniles at a broad range of temperatures (e.g., Allen 1988; Kramer 1990; Fodrie and Mendoza 2006). Madon (2002) conducted labora- tory studies on juveniles ranging from 118-172 mm SL and found them tolerant to a broad range of tempera- tures (14-28°C) and salinities (8-34%o). Within this size range, growth and osmoregulation were positive at various combinations of temperatures and salinities, except when both were low and outside the range of those measured in this study (14°C and 8 %o). Likewise, laboratory stud- ies on California halibut between 40-50 mm TL acclimated to 15°, 18°, 21°, and 24°C indicate preferred temperatures are similar to acclima- tion temperatures (Esquer-Mendez, 2006). Further, juveniles acclimated to 15-24°C only avoid temperatures substantially above and below those of the acclimation interval (<10.8°C and >29.1°C). The broad tempera- ture interval over which juveniles were captured in this and other studies is thus consistent with the high temperature tolerance of rela- tively small juveniles.

In a review of juvenile flatfish dis- tribution in relation to environmen- tal conditions, Gibson (1994) noted that salinity generally has a limited effect on growth of juvenile flatfish, and that its primary effect is on dis- tribution and movement patterns, al- though others have noted that high salinities may imply a bioenergetic cost to juveniles (Wuenschel et al., 2005). Although the GLM analysis indicated a weak, non-significant relationship salinity and density, juveniles were captured in variable densities over a range of salinities (31.6-38.9%e). Further, we found higher densities of juvenile Califor- nia halibut in the inner reaches of Punta Banda Estuary, where salin- ity is usually highest. Hence, it does not appear that the higher salini- ties we measured during our study limited habitat availability. Given that salinity gradients in season- ally arid estuaries are much more limited than in “classical” systems,

20

15

10

o •

Ji * o J>

v J

20

15

10

B

12 14 16 18 20 22 24 26

Temperature (°C)

30 32 34 36 38

Salinity (ppm)

40

■55 20

15

10

2 3 4

Depth (m)

20

15

10

D

Q •

• *> » •

• \ *•

09, M * /p •

~ §. .c tg& -V

2 4 6 8 10 12

Dissolved oxygen (mg/L)

Figure 5

Scatterplots of standardized density of California halibut ( Paralichthys californicus) caught in the outer (n = 62), central (n = 65), and inner (n = 66) sections of Punta Banda Estuary in relation to (A) temperature, (B) salinity (in parts per million, ppm), (C) depth, and (D) dissolved oxygen (in mg/L) measurements taken during trawl sampling excursions between October 2004 and October 2005.

Lopez-Rasgado and Herzka: Assessment of habitat quality for juvenile Paralichthys cahfornicus

353

10

8

6

4

2

0

10

8

6

i Outer i Central i Inner

-o -o

B

ll S I a 1 1 1 1 I ■

i 1 1 i a

Oct Jan Mar May Jun Sep

Oct Jan Mar May Jun Sep

Figure 6

(A) Recent otolith growth rates of wild-caught juvenile California halibut ( Paralichthys californicus) sampled between October 2004 and October 2005. Different letters indicate significant differences. (B-E) Recent otolith and somatic growth rates of juveniles held in cages for either 14 (B, D) or 28 days (C, E). Values are means ±standard error (SE). Asterisks represent lost cages.

tolerant species such as juvenile California halibut may utilize the entire embayment as juvenile habitat.

Various studies have reported that small juvenile California halibut are found in higher densities in shallow habitats (~<2 m; Allen and Herbinson, 1990; Fodrie and Mendoza, 2006). This is consistent with our results; the highest densities of juveniles in Punta Banda Estuary occurred at depths between 1-2 m. To our knowledge there are no studies examining the causes of underlying the depth-related distribution pat- terns in juvenile California halibut, but size-specific depth preferences have been associated with resource partitioning, avoidance of predation by conspecifics, and feeding excursions into shallow areas (Kramer 1990; Gibson, 1994; Able et al., 2005). In addition, the use of shallower habitats subject to stronger variations in

temperature by smaller juveniles is consistent with the higher tolerance of smaller juveniles reported by Madon (2002).

The low proportion of the variance explained by the GLM analysis suggests other abiotic or biotic variables also influence juvenile density. The lack of a significant relationship between dissolved oxygen concentrations and density is probably due to the absence of low DO levels during our surveys; values <2 mg/L are typically associated with detrimental effects on growth and sur- vival of fishes (Stickney, 2000). Abundance of juvenile flatfish has been negatively related to sediment grain size, although the relationship varies among species and with size (e.g., Drawbridge, 1990; Amezcua and Nash, 2001). This may be due to the influence of sediment grain size on prey availability, or related to the burial

354

Fishery Bulletin 107(3)

behavior typically exhibit by flatfish in response to pre- dation pressure or as part of their ambush feeding be- havior (Haaker, 1975; Allen, 1990; Amezcua and Nash, 2001). We did not evaluate sediment grain size during our study. However, Ortiz et al., (2003) reported that in Punta Banda Estuary sediment grain size ranges from fine sand (0.19-0.93 mm) near the mouth of the to coarse silt (0.03 mm) near the head. We found that density was generally highest in the innermost reaches of the estuary, where sediments are finest. Hence, the higher abundance of juveniles in the inner estuary may be at least partially related to the characteristics of the substrate.

There is consistent evidence to suggest that the peak in estuarine immigration occurs primarily during win- ter and spring (Allen, 1988; Kramer, 1990; Hammann and Ramirez-Gonzalez, 1990; Valle et al., 1999), al- though settlement can also take place during the sum- mer months (Allen et al., 1990). Based on analysis of the long-term larval surveys preformed as part of the California Cooperative Oceanic Fisheries Investiga- tions Program (CalCOFI), Moser and Watson (1990) reported that off the coast of northern Baja California and in southern California, the peak in larval abun- dance occurs between February and April, with a sec- ondary peak during summer. We observed the highest abundance of recent recruits (40-50 mm SL) during winter and spring. There was secondary peak of small juveniles during the summer, which could reflect either estuarine recruitment (the recent ingress of juveniles into the system) or growth of previous recruits that entered the estuary at a very small size.

The marked decrease in the density of juveniles >150 mm SL that we observed during the summer is strongly suggestive of estuarine emigration. Although size-selec- tive mortality of larger juveniles (Sogard, 1997) could also lead to a decrease in density, the decrease occurred primarily in the inner and central estuary and was ac- companied by an increase the in abundance of larger juveniles in the outer section, which is consistent with movement toward the mouth of the estuary. Given that estuarine emigration coincided with the onset of higher temperatures within Punta Banda Estuary, tempera- ture gradients may provide the cue for emigration.

Lastly, late juveniles >200 mm SL and adults were captured throughout Punta Banda Estuary, albeit in low numbers. Spawning only occurs in coastal areas (Haaker, 1975). The presence of late juveniles and adults within the estuary suggests that these systems may serve as feeding grounds for larger halibut, despite their predominantly coastal habits (Haaker, 1975; Al- len, 1990).

Otolith growth rates of

natural populations and gut fullness

The daily otolith growth rates of the fastest (Octo- ber 2004; 7.32 pm/d) and slowest (September 2005; 4.54 pm/d) growing juveniles 50-160 mm SL varied approximately two-fold during the study. These values

are within the range of daily otolith growth rates reported for juvenile fishes (Sogard and Able, 2002; Gilliers et al., 2006). Recent otolith growth rates varied significantly as a function of time and section of the estuary, although juveniles grew throughout the year. This indicates spatial and temporal variability in the quality of juvenile habitat within the estuary (Sogard, 1992; Phelan et al., 2000; Necaise et al., 2005). Tem- perature, food availability and quality, size and preda- tion pressure are considered the most important factors influencing growth in juvenile flatfish (Gibson, 1994). We did not find a relationship between the average temperatures and recent otolith growth, although other studies on California halibut indicate that an increase in temperature from 20° to 23°C leads to higher somatic growth rates in the absence of food limitation (Haaker, 1975; Gadomski and Caddell, 1991). This could indi- cate that temperature does not substantially influence otolith growth rates (Campana and Jones, 1992). How- ever, Kicklighter (1990) reported a significant linear relationship (r=0.69, P<0.001) between temperature and otolith growth rates in caged juvenile California halibut held at a single site. We found a significant negative correlation between somatic growth rates and temperature in our caged fish, although the growth rates were very low. Hence, although there is evidence to suggest temperature does influence otolith growth in juvenile California halibut, for wild-caught juve- niles, other physical or biological factors play a more important role.

California halibut are primarily diurnal, visual feed- ers (Haaker, 1975). During our study, 40-85% of indi- viduals exhibited some degree of feeding (gut fullness levels >0%). Likewise, Plummer et al. (1983) found that 46% of juveniles and young adults (124-176 mm SL) captured in coastal waters using an otter trawl exhib- ited empty stomachs. Wertz and Domier (1997) reported that 69% of fish 156-1055 mm TL had empty stomachs.

Lopez-Rasgado and Herzka: Assessment of habitat quality for juvenile Para/ichthys cahfornicus

355

Figure 8

Percentage of (A) wild-caught and (B) caged juvenile California halibut (Para- lichthys californicus) with different levels of gut fullness. Sampling was performed in the outer, central, and inner sections of Punta Banda Estuary between October 2005 and October 2006. Asterisks represent lost cages.

Regurgitation of gut contents during trawling may par- tially explain the high incidence of empty stomachs in their studies and ours. However, Plummer et al. (1983) did not find significant diel and spatial differences in gut fullness levels. We have no way of correcting for the potential effect of regurgitation without a full study designed specifically for that purpose. Nevertheless, we find it likely that if regurgitation is frequent in juve- nile California halibut, our data are likely to be biased systematically.

Seasonal patterns in gut fullness levels were evi- dent: there was a high (up to 55%) percentage of empty stomachs in all sections of the estuary during the late fall and winter, when temperatures were low- est (~14-18°C). During the spring and summer, when temperatures were substantially higher (18-25°C), the incidence of empty stomachs was substantially

lower (10-40%, except for the outer estuary in March). Our qualitative observation that feeding levels are positively related to temperature is consistent with Madon’s (2002) laboratory results; he observed an increase in food consumption and metabolic rates at higher temperature. Further, somatic growth rates of juveniles in his experimental treatments (14°, 20°, 25° and 28°C) did not differ significantly, suggesting that higher food consumption is a response to higher metabolic demand.

In contrast, qualitative comparison of the months and sections of the estuary with the highest otolith growth (central and inner sections October 2004, outer section January 2005 and outer and inner sec- tions May 2005) with the proportion of individuals that exhibited evidence of feeding did not show a consistent relationship. Low growth rates (Septem-

356

Fishery Bulletin 107(3)

ber 2005) did not coincide with a high proportion of empty stomachs. However, our study was not designed to directly relate recent otolith growth with feeding. Gut fullness levels are only a crude point-estimate of feeding success. Our recent otolith growth estimates represent the average daily growth over a 14 day pe- riod, whereas the time required to process ingested food is substantially shorter (1-2 days). Detailed stud- ies of food availability and consumption rates (e.g., Sogard, 1992) are necessary to identify the factors underlying variation in otolith growth rates of juve- nile California halibut.

Density dependent processes, such as competition for food or space and predation pressure, can also influ- ence growth rates. We found a weak positive relation- ship between density and recent otolith growth rates of wild-caught juveniles, but the correlation was not significant (see also Fodrie and Levin, 2008). Hence, we did not find strong evidence to suggest limita- tion for food or space (negative density dependence) or the active selection of habitats supporting to higher growth rates (positive density dependence; Sogard, 1992). However, density-dependent growth regula- tion may occur at smaller spatial scales than those examined in this study, and cannot be conclusively ruled out.

Somatic and otolith growth rates of caged fishes

Due to the low growth rates of caged juveniles, we could not use our recent somatic and otolith growth measurements as proxies for habitat quality. Most caged juveniles had empty stomachs. This could be due to a variety of factors, including limited availability of prey within the cages, limited feeding success and foraging ability, competition for food resources due to high fish density, or as a result of a stress response in relation to handling (e.g., Guindon and Miller, 1995). A density of 6 fish/m2 is much higher than densities of juvenile California halibut found within embayments (Fodrie and Mendoza, 2006).

During the first 14 days of caging, somatic growth rates of caged juveniles were very low (G = 0.0003 to 0.0015 1/d). For fish 50 and 160 mm SL, this is equivalent to 0.01 to 0.12 mm/d, respectively, which is much lower than has been reported previously for wild-caught juveniles California halibut (0.13-1 mm/d, Haaker, 1975; Allen, 1988; Kramer, 1990; Kicklighter, 1990). Accordingly, recent otolith growth rates of caged juveniles were also three to six times lower than in wild-caught juveniles (equivalent to 0.89-1.63 pm/d, mean=1.32 pm/d). Kicklighter (1990) also found very low otolith growth rates during his caging experi- ments; daily increment widths along the main growth axis were 0.49 to 2.26 pm. Fodrie and Herzka (2008) also reported limited otolith growth in some juveniles held in cages in Punta Banda Estuary.

Somatic and otolith growth rates calculated over the 28 days caging period were substantially lower than over the first 14 days, implying little or no growth

during the second half of the experiment. The signifi- cant positive relationship between somatic and otolith growth during first 14 days indicates marginal incre- ment widths are reliable proxies for somatic growth at low growth rates, at least for a few days. However, uncoupling between otolith and somatic growth rates occurred during the second half of the experiment; there was virtually no difference in marginal incre- ment widths between fish retrieved after 14 and 28 days. As discussed by Paperno et al. (1997), uncoupling between otolith and somatic growth rates tends to oc- cur under extreme starvation conditions.

Conclusions

Our results indicate the entire Punta Banda Estuary serves as juvenile habitat for California halibut. This suggests that in arid or seasonally regions in which estuaries lack in strong environmental gradients, par- ticularly in salinity, entire systems may provide suit- able habitat for juvenile California halibut. Fodrie and Levin (2008) found evidence to suggest that juvenile abundance is an adequate proxy for recruitment to adult populations in this species. If so, the innermost section of Punta Banda Estuary, in which temperature and salinity is highest during most of the year, may con- tribute the most to the production of adults. In contrast, Fodrie and Herzka (2008) used otolith microchemistry to evaluate the nursery contribution of juveniles from different sections of Punta Banda Estuary to subadult production in the adjacent coastline, and found that the central and outer sections produced the majority of recruits. Considering that juveniles from the inner estuary must migrate through the central and outer sections of the estuary to emigrate from the system, it is possible that Fodrie and Herzka’s (2008) estimates of subadult production are biased. If the abundance of juveniles is indeed a good proxy for production of adults, then the inner section of Punta Banda Estu- ary is probably the most important area in terms of juvenile California halibut habitat. Put together, these studies highlight the need for assessing juvenile habi- tat utilization and production on various spatial and temporal scales.

Acknowledgments

The authors wish to B. Baron, J. P. Lazo and O. Sosa for their support and constructive feedback during the course of the study, as well as F. Valenzuela, A. Castillo, V. Francisco, N. Olivares, J. Sandoval, J. Mariscal, C. Rodriguez, and the Department of Research Vessels at CICESE for help in the field and laboratory. This proj- ect was funded through Basic Research Grant Number No. 39571 awarded to S. Z. Herzka by Mexico’s Consejo Nacional de Ciencia y Tecnologfa (CONACyT) and by a CONACyT Graduate Student Fellowship to F. Lopez- Rasgado.

Lopez-Rasgado and Herzka: Assessment of habitat quality for juvenile Paralichthys californicus

357

Literature cited

Able, K. W., M. J. Neuman, and H. Wennhage.

2005. Ecology of juvenile and adult stages of flatfishes: distribution and dynamics of habitat associations. In Flatfishes: biology and exploitation (R. N. Gibson, ed.), p. 164-184. Blackwell Publ., Oxford, UK.

Allen, L. G.

1988. Recruitment, distribution, and feeding habits of young-of-the-year California halibut (Paralichthys cali- fornicus) in the vicinity of Alamitos Bay-Long Beach Harbor, California, 1983-1985. Bull. South. Calif. Acad. Sci. 87:19-30.

Allen, L. G., R. E. Fensen, and J. R. Sears.

1990. Open coast settlement and distribution of young- of-the-year California halibut, Paralichthys californicus, along the southern California coast between Point Con- ception and San Mateo Point, June— October, 1988. In The California halibut, Paralichthys californicus, resource and fisheries (C. W. Haugen, ed.), p. 145-152. Calif. Fish Game Fish Bull. 174.

Allen, M. J.

1990. The biological environment of the California hali- but, Paralichthys californicus. In The California hali- but, Paralichthys califurnicus, resource and fisheries (C. W. Haugen, ed.), p. 7-29. Calif. Fish Game Fish Bull. 174.

Allen, M. J., and K. T. Herbinson.

1990. Settlement of juvenile California halibut, Para- lichthys californicus, along the coast of Los Angeles, Orange and San Diego Counties in 1989. CalCOFI Reports. 31:84-96.

Allen, R. A., and D. M. Baltz.

1997. Distribution and microhabitat use by flatfishes in a Louisiana estuary. Environ. Biol. Fish. 50:85-103.

Alvarez-Borrego J., and S. Alvarez-Borrego.

1982. Temporal and spatial variability of temperature in two coastal lagoons. CalCOFI Reports. 33:188-197.

Amezcua, F., and R. D. M. Nash.

2001. Distribution of the order Pleuronectiformes in rela- tion to the sediment type in the North Irish Sea. J. Sea. Res. 45:293-301.

Beck, M. W„ K. L. Heck Jr., K. W. Able, D. L. Childers, D. B.

Eggleston, B. M. Gillanders, B. Halpern, C. G. Hays, K.

Hoshino, T. J. Minello, R. J. Orth, P. F. Sheridan, and M. P.

Weinstein.

2001. The identification, conservation, and manage- ment of estuarine and marine nurseries for fish and invertebrates. BioScience. 51(8):633-641.

Burrows, M. T., R. N. Gibson, L. Robb, and A. Maclean.

2004. Alongshore dispersal and site fidelity of juvenile plaice from tagging and transplants. J. Fish Biol. 65:620-634.

Campana, S. E., and C. M. Jones.

1992. Analysis of otolith microstructure data. In Oto- lith microstructure examination and analysis. (D. K. Stevenson and S. E. Campana, eds.), p. 73-100. Can. Specail Publ. Fish. Aquat. Sci. no. 117.

Drawbridge, M. A.

1990. Feeding relationships, feeding activity and sub- strate preferences of juvenile California halibut, Parali- chthys californicus, in coastal and bay habitats. Master’s thesis, 214 p. San Diego State Univ., San Diego, CA.

Esquer-Mendez, J. L.

2006. Comportamiento termorregulador del lenguado de California Paralichthys californicus (Ayres, 1859). M.S.

thesis. 71 p. CICESE. Ensenada, Baja del Sur, Mexico. [In Spanish.!

Fodrie, F. J., and S. Z. Herzka.

2008. Tracking juvenile fish movement and nursery con- tribution within arid coastal embayments via otolith microchemistry. Mar. Ecol. Prog. Ser. 361:253-265.

Fodrie, F. J., and L. A. Levin.

2008. Linking juvenile habitat utilization to popula- tion dynamics of California halibut. Limnol. Oceanogr. 53:799-812.

Fodrie, F. J., and G. Mendoza.

2006. Availability, usage and expected contribution of potential nursery habitats for the California halibut. Es- tuar. Coastal Shelf. Sci. 68:149-164.

Forrester, G. E., and S. E. Swearer.

2002. Trace elements in otoliths indicate the use of open coast versus bay nursery habitats by juvenile California halibut. Mar. Ecol. Prog. Ser. 241:201-213.

Gadomski, D. M., and S. M. Caddell.

1991. Effects of temperature on early life history stages of California halibut Paralichthys californicus. Fish. Bull. 89:567-576.

Gibson, R. N.

1994. Impact of habitat quality and quantify on the recruitment of juvenile flatfishes. Neth. J. Sea. Res. 32(2):191-206.

1997. Behavior and the distribution of flatfishes. J. Sea. Res. 37(3-4):241-256.

Gilliers, C., O. Le-Pape, Y. Desaunay, J. Morin, D. Guerault, and R. Amara.

2006. Are growth and density quantitative indicators of essential fish habitat quality? An application to the common sole Solea solea nursery grounds. Estuar. Coastal Shelf. Sci. 69:96-106.

Guindon, K. Y., and J. M. Miller.

1995. Growth potential of juvenile southern flounder, Paralichthys lethostigma, in low salinity nursery areas of Pamlico Sound North Carolina, USA. Neth. J. Sea. Res. 34:89-100.

Haaker, P. L.

1975. The biology of the California halibut, Paralichthys californicus (Ayres) in Anaheim Bay. In The marine resources of Anaheim Bay (E. D. Lane and C. W. Hill, eds.), p. 137-151. Calif. Fish Game Fish Bull. 165.

Hammann, M. G., and A. A. Ramirez-Gonzalez.

1990. California halibut, Paralichthys californicus, in Todos Santos Bay, Baja, Mexico. In The California halibut, Paralichthys californicus, resource and fisher- ies (C. W. Haugen, ed.), p. 127-144. Calif. Fish Game Fish Bull. 174.

Herzka, S. Z., R. Griffiths, F. J. Fodrie, and I. D. McCarthy

2009. Short-term size-specific distribution and move- ment patterns of juvenile flatfish in a Pacific estuary derived through length-frequency and mark-recapture data. Ciencias Marinas. 35:41-57.

Horn, M. H., and L. G. Allen

1985. Fish community ecology in southern California bays and estuaries. In Fish community ecology in estuaries and coastal lagoons: Towards an ecosystem integration (A. Yanez-Arancibia, ed.), p 169-190. UNAM Press, Mexico City.

Kicklighter, W. T.

1990. The relationship between somatic growth and temperature in the formation of otoliths by juvenile California halibut (Paralichthys californicus). M.S. thesis, 77 p. San Diego State Univ., San Diego, CA.

358

Fishery Bulletin 107(3)

Kramer, S. H.

1990. Distribution and abundance of juvenile California Halibut, Paralichthys californicus, in shallow waters of San Diego County. In The California halibut, Paralichthys californicus, resource and fisheries. (C. W. Haugen, ed.), p. 99-126. Calif. Fish Game Fish Bull. 174.

1991. Growth, mortality and movements of juvenile California halibut, Paralichthys californicus in shal- low coastal and bay habitats of San Diego County, California. Fish. Bull. 89:195-207.

Largier, J. L., J. T. Hollibaugh, and S. V. Smith.

1997. Seasonally hypersaline estuaries in Mediter- ranean-climate regions. Estuar. Coastal Shelf Sci. 45:789-797.

Le Pape, O., J. Holley, D. Guerault, and Y. Desaunay.

2003. Quality of coastal and estuarine essential fish habitats: estimations based on the size of juvenile common sole (Solea solea L.). Estuar. Coastal Shelf Sci. 58:793-803.

Love, M. S., and A. Brooks.

1990. Size and age at first maturity of the California halibut, Paralichthys californicus, in the southern Cali- fornia bight. In The California halibut, Paralichthys californicus, resource and fisheries (C. W. Haugen, ed.), p. 167—174. Calif. Fish Game Fish Bull. 174.

Madon, P. S.

2002. Ecophysiology of juvenile California halibut Paralichthys californicus in relation to body size, water temperature and salinity. Mar. Ecol. Prog. Ser. 243:235-249.

Moser, H. G., and W. Watson.

1990. Distribution and abundance of the early life history stages of the California halibut, Paralichthys califor- nicus, and comparison with the fantail sole, Xysteteus liopepis. In The California halibut, Paralichthys cali- fornicus, resource and fisheries (C. W. Haugen, ed.), p. 31-84. Calif. Fish Game Fish Bull. 174.

Necaise, A. M. D. S., R. W. Ross, and J. M. Miller.

2005. Estuarine habitat evaluation measured by growth of juvenile summer flounder Paralichthys dentatus in a North Carolina estuary. Mar. Ecol. Prog. Ser. 285:157-168.

Ortiz, M., L. Huerta-Tamayo, and A. Hinojosa.

2003. Tidal sediment transport in Punta Banda Estuary, Baja California, Mexico. (Transporte de sedimento por traccion de marea en el Estero de Punta Banda, B. C., Mexico). GEOS, 23:283-294. [In Spanish.]

Paperno, R., T. E. Targett, and P. A. Grecay.

1997. Daily growth increments in otoliths of juvenile weakfish, Cynoscion regalis : experimental assessment of changes in increment width with changes in feeding rate, growth rate, and condition factor. Fish. Bull. 95:521-29.

Phelan, B. A., R. Goldberg, A. J. Bejda, J. Pereira. S. Hagan, P. Clark, A. L. Studholme, A. Calabrese, and K. W. Able.

2000. Estuarine and habitat-related differences in growth rates of young-of-the-year winter flounder (Peudopleuro- nectes americanus) and tautog (Tautoga onitis ) in three

northeastern US estuaries. J. Exp. Mar. Biol. Ecol. 247:1-28.

Plummer, K. M, E. E. DeMartini and D. A. Roberts.

1983. The feeding habits and distribution of juvenile- small adult California halibut ( Paralichthys californicus) in coastal waters off northern San Diego County. Cal- COFI Reports. 24:194-201

Pritchard, D. W., R. de la Paz-Vela, H. Cabrera-Muro, S. Farreras-Sanz, and E. Morales.

1978. Hydrography of Punta Banda Estuary. Part I: Data analysis (Hidrografia fisica del Estero de Punta Banda. Parte I: Analisis de datos). Ciencias. Marinas. 5:1-23. [In Spanish.]

Rosales-Casian, J. A.

2004. Age and growth of young-of-year (YOY) California halibut ( Paralichthys californicus), from Northwestern Baja California. Bull. Sourthen California Acad. Sci. 103(3):137-143.

Saucerman, S. E., and L. A. Deegan.

1991. Lateral and Cross-Channel Movement Young-of- the-Year Winter Flounder ( Pseudopleuronectes ameri- canus) Waquoit Bay, Massachusetts. Estuaries. 14:440-446.

Sogard, S. M.

1992. Variability in growth rates of juvenile fishes in different estuarine habitats. Mar. Ecol. Prog. Ser. 85:35-53.

1997. Size-selective mortality in the juvenile stage of tele- ost fishes: A Review. Bull. Mar. Sci. 60:1129-1157.

Sogard, S. M„ and K. W. Able.

1992. Growth variation of newly settled winter flounder [Pseudopleuronectes americanus) in New Jersey estuar- ies as determined by otolith microstructure. Neth. J. Sea. Res. 29:163-172.

Stickney R.

2000. Dissolved oxygen. In The encyclopedia of aqua- culture (R. R. Stickney, ed.) p. 229-232. John Wiley & Sons, New York.

Sweatnam, D., K. Barsky, M. Horezco, P. Kalvass, S. Lucas, B. Owens, K. Penttilla, D. Porzio, J. Price, R. Read, J. Simon, and S. Torres.

2007. Review of some California fisheries for 2006: Coastal pelagic finfish, market squid, dungeness crab, spot prawn, highly migratory species, ocean salmon, Califor- nia halibut, nearshore live-fishes, cabezon, surfperches, and leopard shark. CalCOFI Rep. 48:10-32.

Valle, C. F., J. W. O’Brien, and K. B. Wiese.

1999. Differential habitat use by California halibut, Paralichthys californicus , barred sand bass, Paralabrax nebulifer, and other juvenile fishes in Alamitos Bay, California. Fish. Bull. 97:646-660.

Wertz, S. P. and M. L. Domeier.

1997. Relative importance of prey items to California halibut. Cal. Fish Game. 83:21-29.

Wuenschel, M. J., A. R. Jugovich, and J. A. Hare.

2005. Metabolic response of juvenile gray snapper ( Lut - janus griseus ) to temperature and salinity: Physiologi- cal cost of different environments. J. Exp. Mar. Biol. Ecol. 321:145-154.

359

Abstract — Knowing where pinnipeds forage is vital to managing and pro- tecting their populations, and for assessing potential interactions with fisheries. We assessed the spatial relationship between the seasonal distribution of Pacific harbor seals ( Phoca vitulina richardii) outfitted with satellite transmitters and the seasonal distributions of potential harbor seal prey species in San Francisco Bay, California. Pearson’s correlation coefficients were calcu- lated between the number of harbor seal locations in an area of the San Francisco Bay and the abundance of specific prey species in the same area. The influence of scale on the analy- ses was assessed by varying the scale of analysis from 1 to 10 km. There was consistency in the prey species targeted by harbor seals year-round, although there were seasonal differ- ences between the most important prey species. The highest correlations between harbor seals and their prey were found for seasonally abundant benthic species, located within about 10 km of the primary haul-out site. Probable foraging habitat for harbor seals was identified, based on areas with high abundances of prey spe- cies that were strongly correlated with harbor seal distribution. With comparable local data inputs, this approach has potential application to pinniped management in other areas, and to decisions about the location of marine reserves designed to protect these species.

Manuscript submitted 30 May 2008. Manuscript accepted 21 April 2009. Fish. Bull. 107:359-372 (2009).

The views and opinions expressed or implied in this article are those of the author and do not necessarily reflect the position of the National Marine Fisheries Service, NOAA.

Spatial and seasonal relationships between Pacific harbor seals ( Phoca vitulina richardii) and their prey, at multiple scales

Emma K. Grigg (contact author)1

A. Peter Klimley1

Sarah G. Allen2

Deborah E. Green3

Deborah L. Elliott-Fisk1

Hal Markowitz4

Email address for contact author: ekgrigg@gmail.com

1 Department of Wildlife, Fish and Conservation Biology University of California, Davis 1 Shields Avenue

Davis, California 95616

* Present address: Division of Environmental Studies and Geology Alfred University 1 Saxon Drive Alfred, New York 14802

2 Point Reyes National Seashore 1 Bear Valley Road

Point Reyes, California 94956

3 San Francisco Public Utilities Commission Bureau of Environmental Management 1145 Market Street, Suite 500

San Francisco, California 94103

4 Department of Biology

San Francisco State University 1600 Holloway Avenue San Francisco, California 94132

Identification of foraging habitat is essential to understanding the ecology of marine predators. This information is vital to managing and protecting populations, as well as assessing the potential effects of commercial and recreational fisheries on both the marine predator and the fisheries. We determined the spatial overlap of one marine predator, the Pacific harbor seal (Phoca vitulina richardii) and its prey in the San Francisco Bay estuary (SFB), California, in order to identify foraging areas and sea- sonal patterns of resource use by this coastal pinniped.

The Pacific harbor seal (hereafter referred to as the harbor seal) is a small phocid seal common to wa- ters along the west coast of North America. Harbor seals are opportu- nistic predators, feeding primarily on benthic species and small, epi- benthic, schooling fishes, and occa- sionally foraging on pelagic species (Harkonen, 1987). A relatively small number of species tend to dominate the diet of harbor seals, but seasonal shifts in diet are seen in many ar-

eas, associated with seasonal fluc- tuations in prey availability (Brown and Mate, 1983; Tollit et al., 1998). Fecal samples collected in SFB in- dicate that harbor seals in this re- gion feed on Pacific herring (Clupea pallasii), northern anchovy (Engrau- lis mordax), plainfin midshipman ( Porichthys notatus), Pacific staghorn sculpin ( Leptocottus armatus), white croaker (Genyonemus lineatus ), yel- lowfin goby ( Acanthogobius flavima- nus), jacksmelt ( Atherinopsis californ- iensis ), and English sole (Pleuronectes vetulus) (Torok, 1994). Young harbor seals have a reduced diving capabil- ity, and eat benthic crustaceans — primarily shrimp (e.g., Crangon spp.) (Bigg, 1973). Based on VHF (very high frequency) radiotelemetry tracking, the foraging range of harbor seals in SFB is mainly within 1-5 km of a haul-out site (Torok, 1994; Nickel, 2003), indicating that harbor seals in SFB feed on local prey. Abun- dance of prey and distance from the primary haul-out site are the stron- gest predictors of harbor seal use of an area in SFB (Grigg, 2008).

360

Fishery Bulletin 107(3)

Given information on what harbor seals in the region were eating, our primary goal was to identify where these harbor seals were foraging within the study area. Identifying the preferred foraging habitat of pinnipeds can be difficult because of the logistical challenges as- sociated with locating and tracking these large, highly mobile animals while they are at sea. Harbor seals are considered “central place foragers” (Orians and Pear- son 1979) in that they return to a central place (the haul-out site) after foraging trips, they repeatedly visit specific foraging areas, and they tend to focus their for- aging effort in areas near the haul-out site (Thompson et ah, 1998). Radiotracking, both conventional VHF and satellite-linked (hereafter referred to as satellite tracking), is used to identify areas used by tagged animals, and to measure the frequency with which ani- mals return to these areas. For central-place foragers who feed primarily on a limited number of prey spe- cies and exhibit site fidelity to specific foraging areas, telemetry can be used in conjunction with information on prey distribution to identify foraging habitat (North and Reynolds, 1996; Robinson et al., 2007). The harbor seal was therefore an excellent subject with which to assess the usefulness of telemetry in identifying forag- ing habitat of pinnipeds.

A second goal of this study was to assess the influ- ence of spatial scale on our analysis. A number of in- vestigators have assessed the spatial overlap between distributions of marine predators and their prey (e.g., Rose and Leggett, 1990; Fauchald et al., 2000; Davo- ren et al., 2003). These investigators noted that the results of such analyses vary depending on scale (Rose and Leggett, 1990; Fauchald et al., 2000). As a result, studies encompassing multiple scales are recommended for addressing questions related to habitat selection (Olivier and Wotherspoon, 2005).

Although harbor seals in SFB appear to forage with- in the bay, harbor seals do periodically make trips to the outer coast (Grigg, 2008). A third goal of this study was to attempt to identify environmental factors asso- ciated with harbor seals leaving SFB to forage. Harbor seals could forage outside of SFB to exploit changes in availability of prey associated with coastal upwelling. Upwelling of cooler, nutrient-rich water is associated with increased productivity along the California coast and can influence the distribution of marine predators (Becker and Beissinger, 2003). Alternatively, harbor seals could forage outside of SFB when high numbers of harbor seals using haul-out sites within SFB re- sult in intraspecific competition for food resources in SFB.

We examined the associations between harbor seals and potential prey species, using satellite tracking to identify patterns of harbor seal distribution in SFB and a database available from the California Department of Fish and Game (CDFG) on abundance and distribution of potential prey species in the area. The objectives of this study were 1) to identify spatial and seasonal pat- terns of association between harbor seals and their prey in an urbanized estuary; 2) to examine the influence

of scale of analysis on the spatial relationship between predator and prey; 3) to relate shifts in prey abundance or environmental factors to seasonal differences in the use of waters inside and outside SFB; and 4) to assess the usefulness of satellite telemetry in identifying for- aging areas of harbor seals.

Materials and methods

Study area

San Francisco Bay is a turbid estuary with mean depths ranging from 3-11 m, and is the largest coastal embay- ment on the Pacific coast of the United States (Conomos et al., 1985) (Fig. 1). Harbor seals use SFB year-round for foraging, pupping, and resting on terrestrial haul-out sites (Allen et al., 1993; Grigg et al., 2004).

Harbor seal telemetry

Between January 2001 and January 2005, harbor seals were captured at a primary haul-out site in SFB (Castro Rocks; Fig. 1). At high tide, “tangle nets” 20-40 m long and 5 m deep were set, and harbor seals were caught as they approached the site. Harbor seals were fitted with dorsal- or head-mounted satellite-linked Platform Ter- minal Transmitters (PTTs; model ST-18, Telonics, Mesa, AZ; models SDR-T16 and SPOT3, Wildlife Computers, Redmond, WA; depending on model, tag power ranged from 0.4 to 0.5 watt, repetition rate ranged from 45 to 48 sec). Only harbor seals deemed large enough (>40 kg) to support the PTTs were tagged. The PTTs were glued to the harbor seal’s pelage with a quick-setting marine epoxy, and were shed by harbor seals before or during their annual molt.

Service Argos (CLS America, Inc., Largo, MD) was the processing center for the satellite telemetry da- ta and provided the geographical coordinates of the tagged harbor seals. When a harbor seal is at the sur- face, PTTs send periodic radio transmissions which are detected by polar-orbiting satellites. These satellites relay the signals to processing centers, where animal location estimates are calculated on the basis of the Doppler effect. Based on the number of received trans- missions and other factors, all locations are grouped into location accuracy “classes,” ranging from zero to three, and two additional classes (A and B) for loca- tions that could not be assigned an accuracy estimate (Table 1). Marine mammals are considered to be good study animals for satellite tracking because they sur- face to breathe and this allows sufficient time for a position to be determined by the satellites. In addition, the elevation of the tag does not change while the tag is on the animal; changes in tag elevation have been cited as a primary cause of spatial inaccuracy (Keating et al., 1991). Recent studies have assessed the useful- ness of PTTs for studying movements and habitat use of marine animals (e.g., Vincent et al., 2002; White and Sjoberg, 2002). Location classes with lesser accuracy

Grigg et al.: Spatial and seasonal relationships between Phoca vitulina richardii and their prey

361

are customarily removed from the data set, and filtering methods are used to remove improbable locations and improve the mean accuracy of the remaining loca- tions. Vincent et al. (2002) and Hays et al. (2001) found that locations in classes B and 0 were inaccurate, but class A lo- cations were more accurate and compa- rable to class 1 locations (Table 1). We therefore removed location estimates in classes B and 0 from the record of each harbor seal’s movements, but did not au- tomatically remove locations in class A.

All points that fell on land were removed, and then the remaining locations were filtered according to the speed neces- sary for a harbor seal to move between two successive locations, calculated in a geographic information system (GIS).

Any location that would have required a travel speed greater than 10 km/hr, or 2.78 m/s (Lowry et al., 2001), was flagged for inspection. These questionable har- bor seal locations were assessed by their spatial and temporal relationship to the prior or subsequent location with a great- er accuracy rating, and unlikely locations were removed. Points that would have re- quired an isolated movement away from and immediately returning to the same area, necessitating a narrow V-shaped movement track, were also eliminated (see Keating, 1994). Locations within 1 km of a haul-out site were removed in order to eliminate locations associ- ated with haul-out site use or under- water movements unrelated to foraging (Thompson and Miller, 1990). Finally, for these analyses, we analyzed spatial overlap between harbor seal locations and abundance of potential prey species around SFB, rather than analyzing sequential tracks of movement by in- dividual harbor seals. To improve independence of point location estimates for the correlation analyses, locations recorded within one hour of another location for the same harbor seal were removed from the data set.

Correlation analyses

Records of prey distribution and abundance during the study period were obtained from the Interagency Eco- logical Program for the San Francisco Estuary and from the San Francisco Bay Study, California Dep. Fish and Game. Monthly samples of fish, crab, and shrimp species were collected by CDFG at 39 sampling stations located around SFB (Fig. 1), using two sampling methods: an otter trawl (OT) and a midwater trawl (MWT). The OT was used to sample bottom-dwelling fish, shrimp, and crab, the MWT was used to sample mid-water fish, and

122<,30'0"W

122°20'0"W

122°10'0"W

122WW

The San Francisco Bay, CA, study area, showing Castro Rocks and other primary harbor seal ( Phoca vitulina richardii) haul-out sites, and 39 fish sampling stations around the bay sampled by the California Department of Fish and Game(CDFG). Catch-per-unit-of-effort data from the CDFG sampling stations were used to build seasonal harbor seal prey distribution maps for San Francisco Bay. Coastline data layer created by NOAA/NOS/ORR/CPRD (available online).

both trawls yielded quantitative data on fish abundance. For this study, we focused on eight species of fish known to be prey of harbor seals in SFB, combined crab species (primarily Dungeness crab, Cancer magister), and com- bined shrimp species (primarily Crangon spp.). Given concerns about harbor seals foraging on salmonids, CDFG data on the abundance and distribution of Chi- nook salmon (Oncorhynchus tshawytscha) in SFB were included in the analysis. Catch per unit of effort (CPUE) was calculated as follows for each station, month, and species, by using gear-specific formulas from CDFG:

OT CPUE =

(number caught/tow area) x 10,000,

(1)

362

Fishery Bulletin 107(3)

Table 1

Location-accuracy classes for marine mammal location estimates obtained with satellite telemetry and assigned by Service Argos, and reported in other studies. Also included are the proportions of the final, filtered harbor seal (Phoca vitulina richar- dii) location data set from the present study that fell into each location class. Vincent et al.(2002) calculated accuracy for tags deployed on captive grey seals (Halichoerus grypus) in France and calculated accuracy separately for the latitude and longitude of position estimates. Hays et al. (2001) calculated accuracy using tags located in fixed positions in Brazil and on Ascension Island, as mean deviation from true tag location.

Location accuracy class	Proportion of total locations used in this study	Service Argos accuracy estimate (m)	Vincent et al. 2002 (unfiltered; lat./long.) (m)	Hays et al. 2001 (mean deviation from true) (m)
3	0.20	<150	157/295	270
2	0.25	<350	259/485	540
1	0.21	<1000	494/1021	1330
0	0	>1000	2271/3308	10,100
A	0.34	None assigned	762/1244	990
B	0	None assigned	4596/7214	7000

where tow area = distance towed (in meters) x door spread of tow (3.42 m); and

MWT CPUE =

( number caught/tow volume) x 10,000, (2)

where tow volume = number of flowmeter revolutions x 0.0269 m/rev x net mouth area (10.7 m2 in this case).

Crab / shrimp CPUE =

number caught per 5 minute tow, (3)

CPUE from the 39 sampling stations was used to create maps of the relative abundance of harbor seal prey spe- cies in SFB, by using the inverse distance weighting interpolation method (Geostatistical Analyst extension to ArcGIS 9.2, ESRI, Redlands, CA). Inverse distance weighting is a deterministic interpolation method and makes no assumptions about the input data; this was important given the patchy nature of fish distributions in SFB. Given seasonal differences in prey species’ abundance and distribution, and in harbor seal behav- ior related to breeding and molting, we created four maps for each prey species, one for each harbor seal “season” (spring: March-May; summer: June-August; fall: September-November; winter: December-Febru- ary). In SFB, harbor seals pup during the spring and molt during the summer. Only records for those months and years when we had tagged harbor seals active in SFB waters were included in the analyses.

Using the Hawth’s analysis tools extension (avail- able online at http://www.spatialecology.com/htools) for ArcGIS 9.2 (ESRI, Redlands, CA), a 1-km grid was laid over a map of the entire study area, consisting of all waters from the mouth of SFB, to the eastern edge of Suisun Bay (Fig. 1). All harbor seal locations and environmental data sets in the GIS were reprojected to Universal Transverse Mercator (UTM) coordinates,

using the North American Datum of 1927 (NAD 27), zone ION, and resampled to an initial grid resolution of 1-km. For each season, an average CPUE of each prey species was assigned to each 1-km grid cell, by using the area-weighted mean of the values falling within that grid cell. In addition, we counted the number of harbor seal locations falling within each grid cell; be- cause the number of tagged animals was limited, data from individual harbor seals were pooled for this analy- sis (see Erickson et al., 2001). The minimum scale of analysis was 1 km2, well within the estimated average accuracy of the filtered harbor seal location data (Table 1; see also Bekkby et al., 2002).

To vary the scale of analysis, data from the 1-km grid cells were combined into progressively larger grid cell sizes, ranging from 2 to 10 km. Given the size of SFB (and the fact that the sample size decreased with each successively larger grouping), we did not consider scales larger than 10 km. Because of the irregular shoreline of SFB, some grid cells overlapped land; therefore, we removed grid cells that represented primarily land from the analyses. For all remaining grid cells, we calculated the number of harbor seal locations per km2.

For each spatial scale (1 to 10 km) and each season, we calculated the Pearson’s correlation coefficient be- tween the number of harbor seal locations per grid cell and the CPUE for each potential prey species in that cell. We plotted correlation coefficients versus scale for each season to assess the effects of scale on the strength of the spatial relationships between harbor seals and potential prey.

To estimate the availability of foraging habitat during each season, we used regression tree analyses (Breiman et al., 1984) to identify threshold values of prey CPUEs that would most strongly differentiate between grid cells with greater use by harbor seals and cells with lesser use by harbor seals, for each season. In other words, this threshold value indicated the minimum CPUE for prey in the grid cells representing areas that were fre-

Grigg et al.: Spatial and seasonal relationships between Phoca vitulma richardu and their prey

363

Table 2

Harbor seals ( Phoca vitulina richardu) captured in San Francisco Bay, CA (2001-05) and tagged with satellite telemetry tags, with sample size information. Ages are abbreviated as A (adult), SA (subadult), and Y (yearling). Dates and duration (in days) of telemetry tag attachment are shown. Numbers of both raw seal location estimates and filtered location estimates are shown. Accuracy filtering methods were based on location quality rankings provided by Service Argos, and a spatial filtering mechanism to reduce improbable locations. Location filtering consisted of the removal of points that fell within 1 km of a haul-out site, or outside of the study area.

Harbor seal ID	Age	Sex	Dates of tag attachment	Days tagged	Number of raw location estimates	Final sample size after accuracy and location filtering
15345	A	M	1/2001-6/2001	153	307	141, 21
15440	SA	F	7/2001-8/2001	34	106	65, 33
15436	SA	F	7/2001-8/2001	31	69	42, 24
19580	A	F	7/2001-3/2002	233	947	547, 365
19582	A	M	7/2001-8/2001	22	157	81, 3
15439	A	F	1/2001-9/2001	69	204	97, 27
15437	A	M	1/2002-5/2002	126	616	188, 26
10024	A	F	8/2002-1/2003	158	561	206, 87
10278	A	M	8/2002-11/2002	85	45	22, 8
10279	A	M	8/2002-11/2002	97	353	133, 63
10280	A	M	8/2002-3/2003	229	1013	451, 218
10297	SA	M	8/2002-3/2003	215	1156	480, 250
10863	SA	F	8/2002-2/2003	190	1269	588, 336
42526	SA	F	8/2003-1/2004	141	896	308, 111
42527	A	F	8/2003-3/2004	204	1369	485, 274
42529	Y	F	8/2003-12/2003	107	986	397, 270
42530	Y	F	8/2003-12/2003	123	1012	372, 202
21454	A	F	1/2005-6/2005	144	577	236, 53
42528	SA	M	1/2005-6/2005	135	524	179, 49

quently visited by harbor seals; lower abundances were found in cells repesenting areas less frequently visited by harbor seals. Grid cells with CPUE values above the threshold values identified in the regression tree were designated as potential harbor seal foraging habitat. Harbor seal habitat was mapped by using only the prey species with the highest correlations with harbor seal distribution (correlation coefficient >0.7) at the 10-km scale, because this coarser scale may be more appropri- ate for assessing behavior which influences lifetime fit- ness (Rettie and McLoughlin, 1999). The area (in km2) of potential foraging habitat was then calculated, both for SFB as a whole, and within 10 km of the primary haul-out site, Castro Rocks.

To examine potential reasons why some harbor seals were leaving the bay, correlation coefficients were cal- culated between the proportion of harbor seal loca- tions located outside of SFB, for each season, and the following three variables: 1) prey CPUE inside SFB; 2) number of harbor seals inside SFB and at Castro Rocks; and 3) indices of upwelling measured along the adjacent outer coast. The number of harbor seals in SFB fluctuates seasonally (Fancher, 1979; Grigg et al., 2004; Grigg, 2008), and we hypothesized that an increased number of excursions outside SFB would be positively correlated with the increased number of harbor seals in SFB. To ascertain the numbers of

harbor seals in SFB and at Castro Rocks, harbor seals were counted at the three largest haul-out sites in SFB and the numbers were averaged by season across years. For information on the strength of upwelling along the California coast, we used monthly upwelling indices compiled by the National Oceanographic and Atmospheric Administration Environmental Research Division. Statistical significance for all correlations was assessed with a=0.05.

Results

Harbor seal telemetry

Nineteen harbor seals were captured between January 2001 and January 2005 (Table 2). Data filtering for accu- racy reduced the number of location estimates for indi- vidual harbor seals by 39-69%, and additional location estimates were removed when within 1 km of a haul-out site, or outside of SFB. The mean number of locations per harbor seal after all filtering was 120 ±27 (standard error of the mean; SEM). The number of locations per season ranged from 134 during the spring season, to 1139 during the fall. Locations were evenly dispersed between day and night (47% during the day, 6 a.m. to 6 p.m., and 53% during the night, 6 p.m. to 6 a.m.).

364

Fishery Bulletin 107(3)

Scale (km)

-o- shrimp (mixed spp.) -*-crab (mixed spp.)

~x northern anchovy

Pacific herring

~s~ jacksmelt

plainfin midshipman + Chinook salmon -a- Pacific staghorn sculpin -a- English sole -o- white croaker yellowfin goby

Figure 2

The effects of scale on the analyses of spatial overlap between distribution of Pacific harbor seals ( Phoca vitulina richardii) and their prey species in San Francisco Bay, CA, 2001-05. Potential prey species included Pacific herring ( Clupea palla- sii), northern anchovy ( Engraulis mordax ), plainfin midshipman (Porichthys notatus). Pacific staghorn sculpin (Leptocot- tus armatus), white croaker ( Genyonemus lineatus), yellowfin goby (Acanthogobius flavimanus), jacksmelt ( Atherinopsis californiensis), English sole ( Pleuronectes vetulus ), Chinook salmon {Oncorhynchus tshawytscha), shrimp (mixed species, primarily Crangon spp.), and crab (mixed species, primarily Dungeness crab. Cancer magister). Graphs show the change in strength of Pearson’s correlations (r) between seal and prey locations with changes in analysis scale from 1 km to 10 km, for each season. Only statistically significant (P< 0.05) correlations are shown.

Correlation analyses

According to our analyses, three benthic species — plain- fin midshipman, English sole, and Pacific staghorn scul- pin— are important prey of harbor seals in SFB (Fig. 2). Spatial overlap between distribution of harbor seals and abundance of primary harbor seal prey species was greatest in central SFB, and in waters around Castro Rocks (Fig. 3). Although harbor seals used areas in the north and south SFB in all seasons, waters of central SFB and surrounding the primary haul-out site, Castro Rocks, were used most frequently. Correlations revealed both year-round consistency in the identity of harbor seal prey species and seasonal differences between primary prey species.

Spring (March-May): During the spring pupping season, harbor seal locations were most highly cor- related with English sole and crab (Figs. 2A and 3A). In all seasons, there were strong correlations between the distribution of crab and harbor seals (Fig. 4). In contrast to the fall and summer, there was no significant correlation between harbor seal locations and abundance of Pacific staghorn scul- pin during the spring.

Summer (June-August): During the summer molt- ing season, harbor seal locations were most highly cor-

related with English sole and Pacific staghorn sculpin (Figs. 2B and 3B). Harbor seals in SFB frequently visited areas where high numbers of Pacific staghorn sculpin were found in the 2001-05 CDFG trawls, most notably in the waters around the Castro Rocks haul- out site.

Fall (September-November): During the fall, harbor seal locations were most highly correlated with plain- fin midshipman, white croaker, and Pacific staghorn sculpin (Figs. 2C and 30. Across spatial scales, cor- relations with plainfin midshipman were particularly strong (often >0.8) during the fall.

Winter (December-February): During the winter, harbor seal locations were most highly correlated with plainfin midshipman, English sole, and Pacific herring (Figs. 2D and 3D). Harbor seals foraged in Pacific herring spawning areas, and correlations be- tween Pacific herring and harbor seals were greatest during this season. No significant correlation was found between the distribution of harbor seals and Chinook salmon. There was little correlation between the frequency of use of an area by harbor seals and the distribution of yellowfin goby, a non-native spe- cies that was found to be an important prey species in an earlier study of the diet of SFB harbor seals (Torok, 1994).

Grigg et al.: Spatial and seasonal relationships between Phoca vitulina richardii and their prey

365

122°30'0"W 122WW

Spatial overlap of Pacific harbor seals ( Phoca vitulina richardii) and important harbor seal prey species in San Francisco Bay, CA, for four seasons, 2001-05. Density of seal locations is indicated by shading of the 1-km grid, with darker shading indicating more frequent use by seals. Relative abundance of specific harbor seal prey species (as noted in the map legends) caught at each fish sampling station is indicated by size of the circle marking station location, and larger circles indicate greater catch per unit of effort of prey at that location, in number of individuals per hectare (1 hectare = 0.01 km2). Fish species shown are representative of harbor seal prey spe- cies found to have the greatest correlation with seal location for that season: A) Spring — English sole ( Pleuronectes vetulus ), B) Summer — Pacific staghorn sculpin ( Leptocottus armatus), C) Fall — plainfin midshipman ( Porichthys notatus ), and D) Winter — plainfin midshipman (P. notatus).

At the 1-km scale, most correlations were positive (i.e., greater co-occurrence of harbor seal locations with greater prey CPUE), but not strong (correlation coef- ficients <0.6). The correlation coefficients for plainfin midshipman were greatest among most spatial scales

during the fall and winter. The coefficients for English sole were greatest among most spatial scales during the spring and summer. The coefficients for Pacific staghorn sculpin were second greatest during summer and fall.

366

Fishery Bulletin 107(3)

In general, correlations increased with scale (Fig. 2). At the largest scale (10-km), correlations between distribu- tion of harbor seals and primary prey CPUEs were often >0.8. The prey species with high correlations (>0.7) at the 10- km scale included plainfin midshipman (fall and winter), Pacific staghorn scul- pin (summer and fall), English sole (all seasons), and Pacific herring (winter)

(Fig. 2). During spring, only English sole had a correlation of >0.7. For the forag- ing habitat map for spring, therefore, we included crab, which most closely ap- proached the 0.7 threshold value. Based on the threshold prey abundances identi- fied in the regression tree analysis, po- tential foraging habitat available in SFB ranged from 147 km2 in spring to 238 km2 in fall (Table 3, Fig. 5). Foraging habitat available within 10 km of Castro Rocks ranged from 101 km2 in spring to 144 km2 in fall.

When assessing seasonal differences in harbor seals’ use of waters inside vs. outside SFB, the proportion of harbor seal locations on the outer coast was greater during the summer (0.33) and spring (0.21) than during the fall (0.01) or winter (0.08). Use of areas outside of SFB was not correlated with prey CPUE in SFB, number of harbor seals in SFB or at Castro Rocks, or upwelling indi- ces. In general, the proportion of harbor seal locations recorded outside of SFB decreased with greater levels of prey availabil- ity in SFB, increased with greater numbers of harbor seals in SFB as a whole, and increased with greater upwelling indices. In contrast, when the proportion of locations on the outer coast was compared with the average maximum count at Castro Rocks, the proportion on the outer coast tended to be lesser when numbers of harbor seals at Castro Rocks were greater.

Discussion

We used a simple approach for identifying harbor seal foraging areas, using satellite tracking, available infor- mation on harbor seal diets from previous studies, and a data set on prey distribution obtained from a local management agency. In many cases, the abundance and distribution of prey is the most important factor influ- encing the spatial distribution of predators (Davoren et ah, 2003). The primary motivation for a predator to move is to locate prey patches which offer a sufficient energetic “reward” (Charnov, 1976), i.e., provide suf- ficient energy gained from ingestion of prey, once the energetic costs of capture have been deducted. Not sur-

122°30'0"W

122°20'0"W

122°10'0''W

122°0'0"W

Figure 4

Spatial overlap of Pacific harbor seal ( Phoca vitulina richardii ) distribution with abundance of crab species (mixed species; pri- marily Dungeness crab. Cancer magister) in San Francisco Bay, CA, during the spring seal pupping seasons, 2001-05.

prisingly, both terrestrial and marine mammals have been found to choose habitats that provide resources necessary for survival and reproduction, and for this reason, use of an area is often assumed to reflect quality or abundance of resources available in that area (Boyce and McDonald, 1999; Davoren et al., 2003).

Despite some controversy about possible biases in fecal analyses used to estimate diets (Harvey, 1989; Tollit et ah, 1998), analysis of fecal samples remains an important method of identifying prey species of pin- nipeds. However, it is often difficult to identify where harbor seals are foraging, even when fecal analyses are supplemented by VHF telemetry tracking (Torok, 1994). This problem has led some researchers to use techniques such as fatty acid signatures (Iverson et al., 1997) to identify harbor seal foraging areas. Our study presents an alternate approach to identifying these areas.

Grigg et al. : Spatial and seasonal relationships between Phoca vitulma richardii a nd their prey

367

Table 3

Area (km2) of Pacific harbor seal ( Phoca vitulina richardii) foraging habitat in San Francisco Bay, CA, based on areas where abundance of harbor seal prey species was above the threshold value calculated in the regression tree analyses. Area of foraging habitat throughout SFB is given, as well as area of foraging habitat within 10 km of Castro Rocks, the primary haul-out site used by harbor seals in this study.

Season	Prey species used in estimation of foraging habitat	Area of foraging habitat (km2)	Area of foraging habitat within 10 km of Castro Rocks (km2)
Spring	English sole ( Pleuronectes vetulus) Crab (mixed spp.; primarily Dungeness crab, Cancer magister )	146.8	100.7
Summer	Pacific staghorn sculpin ( Leptocottus armatus) English sole	222.9	140.2
Fall	Plainfin midshipman ( Porichthys notatus) Pacific staghorn sculpin English sole	238.4	144.1
Winter	Pacific herring (Clupea pallasii) Plainfin midshipman English sole	220.6	130.8

We assume that the spatial overlap between harbor seals and prey species reflects the tendency of harbor seals to frequent areas where the density of prey is greatest. Seasonal correlations between harbor seal loca- tions and prey density revealed the following patterns.

Spring prey species

The spatial correlation between harbor seals and Eng- lish sole during spring could reflect harbor seals’ use of shallower waters associated with breeding behavior because four of nine of the harbor seals tagged during this season were females of reproductive age, two of which were confirmed breeders (as determined from resightings with a pup). Harbor seal females wean their pups after four weeks and do not fast during the nursing period. Castro Rocks is submerged during high tides, requiring cows and pups to leave the site together. Pups have reduced diving capabilities (Bigg, 1973), which may predispose the females with pups to forage in shallower waters. English sole are abundant in the waters of central SFB and San Pablo Bay during spring, mostly in shoal waters of San Pablo Bay.

The consistent correlations between the distribution of harbor seal locations and crab may be due more to the foraging habits of harbor seal prey than to the harbor seals foraging directly on crab. Harbor seals consume crabs in California (Harvey et al., 1995), but whether crabs are important prey among harbor seals in SFB remains unclear. Pacific staghorn sculpin and English sole are major consumers of juvenile Dunge- ness crabs, and the vast majority of Dungeness crabs in SFB are juveniles (Reilly, 1983). In addition, crab numbers tend to be greatest in waters around Castro Rocks (particularly during spring), and therefore, the overlap of harbor seals and crab may also be related to proximity to Castro Rocks.

During spring, greatest concentrations of Pacific staghorn sculpin were found in the extreme south bay, indicating that the abundance of this prey spe- cies was greater near a large south SFB pupping site, Mowry Slough. These south SFB aggregations of Pa- cific staghorn sculpin were apparently not used by Castro Rocks harbor seals during spring, and the lack of correlation between harbor seals and sculpin dur- ing this season likely reflects the tendency of harbor seals to remain closer to their primary haul-out site during pupping.

Summer prey species

English sole appear to be an important food source for SFB harbor seals. English sole use the SFB as a nursery area and remain in the bay for 6-18 months (Budd, 1940). Although there was a significant cor- relation between harbor seal locations and English sole abundances in all seasons (see also spring prey species, above), abundance of age-l+ sole was less in the summer, when the correlation between harbor seals and English sole was greatest. Because harbor seals are opportunistic foragers, they may exploit the abundant young English sole found near their haul- out site during the molting season. Large mature English sole (> 250 mm) were rarely caught by CDFG surveys, and Torok (1994) suggested that any forag- ing on flatfish by south SFB harbor seals took place outside of SFB; however, harbor seals were occasion- ally observed feeding on large flatfish near the Castro Rocks site. In addition, harbor seals often visited areas where Pacific staghorn sculpin were numer- ous, particularly in waters around the Castro Rocks haul-out site. Harbor seals spend a greater proportion of their time hauled out during the molting season (Thompson et al., 1989), and harbor seals in this

368

Fishery Bulletin 107(3)

122°30'0"W 122°0'0"W

Figure 5

Pacific harbor seal ( Phoca vitulina richardii) foraging habitat in San Francisco Bay, CA, by season: A) Spring; B) Summer; C) Fall; D) Winter. Areas were designated harbor seal habitat if they contained abundances of primary seasonal prey species which met or exceeded the thresholds identified in the regression tree analyses. Primary seasonal prey species were identified based on strength of correlation in the GIS overlay analysis between harbor seal telemetry locations and abundance of individual prey species.

study were likely foraging on these species because of their close proximity to the harbor seals’ primary haul-out site during the annual molt. Longer-range foraging trips by harbor seals tend to occur outside of the molting and pupping seasons (Thompson et ah, 1989).

Fall prey species

Harbor seals in SFB frequently visit areas where ben- thic fish species common in SFB are found in greatest abundance. Adult plainfin midshipman tend to burrow into the sand during the day, emerging at night to

Grigg et al.: Spatial and seasonal relationships between Phoca vitulma richardii and their prey

369

feed (Fitch and Lavenberg, 1971). Harbor seals in SFB forage both during the night and day (Torok, 1994; Nickel, 2003), so harbor seals may be feeding on adult plainfin midshipman at night, in the same areas where greater numbers of juveniles were recorded during the day by CDFG trawls; spatial distribution of adult and juvenile plainfin midshipman is similar in SFB. Numbers of plainfin midshipman are greatest in cen- tral SFB during the fall. In addition, white croaker are abundant in SFB; age-l+ white croaker move into central SFB in the fall before migrating out of SFB in the late fall and winter. During fall, harbor seals occurred where there were greatest numbers of this species in central SFB and around Castro Rocks. The Pacific staghorn sculpin is one of the most abundant demersal fish in SFB, and is common in central SFB and San Pablo Bay. Numbers of adults are greatest during October through April. Harbor seals are more frequently located in areas with greatest abundance of this species, in both the fall and summer.

Winter prey species

The waters to the northeast of the Tiburon Peninsula and near the southeastern edge of Angel Island appear to represent important foraging areas for SFB harbor seals, particularly those using the Castro Rocks haul- out site. These areas were frequently visited by harbor seals year-round, and use of these areas has been noted in earlier studies of harbor seals in SFB (Torok, 1994, Nickel, 2003). During winter, abundance of plainfin midshipman was greatest in central SFB, most notably in waters to the northeast of the Tiburon Peninsula and the southeastern edge of Angel Island. Similarly, maxi- mum numbers of English sole were found in the central bay, around Tiburon Peninsula and Angel Island.

Pacific herring is believed to be a preferred prey of harbor seals in SFB, and seasonal distribution of harbor seals in SFB reflects seasonal increases in abundance of Pacific herring, which spawn in SFB dur- ing the winter (Grigg, 2008). Correlations between the distributions of Pacific herring and harbor seals were greatest during winter, and harbor seals often were seen in SFB covered with herring eggs. Well-known Pacific herring spawning areas, such as Richardson Bay, around the Tiburon Peninsula, and along the eastern shoreline of SFB from Castro Rocks south- ward, were visited frequently by harbor seals during this season.

Harbor seals do not appear to focus much foraging effort on Chinook salmon while they move through SFB. This part of the analysis may have been limited by the very small numbers of salmon caught by CDFG trawls. However, salmon were not reported in earlier studies of harbor seal diet in SFB based on fecal sample analyses (Torok, 1994).

Overall, our findings agree with previously reported harbor seal diets based on fecal sample analyses in SFB (Torok, 1994), with the notable exception of yellowfin goby. Torok (1994) found that yellowfin goby was the

most numerous species in harbor seal fecal samples, although his samples were primarily collected from harbor seals captured in the south SFB, whereas the tagged harbor seals used in this study were captured at a central SFB haul-out site. Yellowfin gobies are seasonally abundant in San Pablo Bay and Suisun Bay. Although both areas were visited by harbor seals in our study, these harbor seals may have foraged on gobies opportunistically, because they did not appear to fre- quently visit areas with abundant yellowfin goby. This may reflect partitioning of foraging habitat between harbor seals using primarily south SFB haul-out sites and using central and north SFB haul-out sites; separa- tion of harbor seals in northern and southern areas of SFB has been noted before (Allen et al., 1993; Grigg, 2008). Use of haul-out specific foraging areas has been noted in other harbor seal populations (Iverson et al., 1997; Thompson et al., 1998).

The accuracy of our methods for identifying foraging habitat for harbor seals in this region is supported by the fact that our findings agree with earlier stud- ies, which demonstrate the tendency of harbor seals to forage on seasonally abundant, primarily benthic prey found near their primary haul-out site (e.g., Har- konen, 1987; Thompson et al., 1998). Spatial overlap between harbor seals and the prey species surveyed in this study was greatest in waters within approxi- mately 10 km of Castro Rocks and declined in waters beyond this range. This is consistent with central place foraging theory, where site use is expected to de- cline with distance from the central place (e.g., haul- out site; Orians and Pearson, 1979). There may also be a tendency for harbor seals to feed in areas with more predictable prey, e.g., the waters of central SFB, where abundance of fish caught in CDFG trawls tends to be high year-round. Greater correlations between predator and prey can be expected in these areas where prey is predictably present, and lesser correla- tions in other less predictable, “ephemeral” prey areas (Davoren et al., 2003), e.g., other parts of SFB. Simi- larly, harbor seals may select a larger-scale region (e.g., central SFB) where prey are found in greater abundance, a trend that is reflected in the greater correlations at larger scales in our study and in other studies of marine predators and their prey (Rose and Leggett, 1990; Mehlum et al., 1999; Fauchald et al., 2000). Harbor seals’ tendency to return repeatedly to the same foraging areas indicates that they can track regions with predictably abundant prey over long time scales (e.g., seasonally), despite the likeli- hood that locations of individual prey patches may vary over much shorter time scales. In other systems and at smaller scales, prey patches are more variable in location, and correlations between predators and prey at smaller scales likely will be weaker (Mehlum et al., 1999). Harbor seals tend to choose haul-out sites located near abundant prey resources (Loughlin, 1978), and the selection of the Castro Rocks location as a haul-out site almost certainly reflects availability and abundance of prey resources nearby.

370

Fishery Bulletin 107(3)

We did not attempt to identify average patch size of harbor seal prey in our study, choosing instead to dem- onstrate overlap with areas of abundant prey resources. As Dungan et al. (2002) noted, patches that are smaller than the size of the sampling unit cannot be detected. Average size of prey patches in SFB may be smaller than our minimum study scale of 1 km. Nickel (2003) suggested that the average maximum prey patch for harbor seals foraging in SFB was 200 m, based on frac- tal analyses of harbor seal positions obtained by VHF radiotracking. If true, our grid cells could potentially have contained no prey patches or more than one prey patch, and could illustrate relative quality of foraging areas rather than locations or sizes of individual prey patches. On the other hand, we would expect positive correlations between harbor seal locations and prey densities only at scales greater than the dimensions of aggregations of predator or prey. At scales less than the smallest aggregation of predator or prey, we would be more likely to see negative correlations, because of factors such as predator avoidance by prey (Rose and Leggett, 1990). The greater correlations seen at larger scales in our study may also reflect the tendency of large scales to reduce or average out the effects of stochastic processes affecting where prey patches are located (Corsi et al., 2001). Small but significant negative correlations were found only at smaller scales (1 to 4 km) in our study, primarily involving two species: jacksmelt (spring and summer) and yellowfin goby (spring). Jacksmelt are often found in large schools in SFB, and negative cor- relation of the jacksmelt and harbor seal distributions at smaller scales could be due to avoidance of foraging har- bor seals by jacksmelt schools. Catch per unit of effort of yellowfin goby is usually greatest in San Pablo Bay and Suisun Bay, and least in central SFB, which could explain the negative correlation with this species.

Based on observations of foraging locations of indi- vidual SFB harbor seals seen in past studies (Fancher, 1979; Torok, 1994), the amount of harbor seal habitat estimated by our methods may be conservative. Our estimates were based on only the species with the stron- gest correlations between harbor seal locations and prey abundance data during our study period. Had additional species’ distributions been included in the potential habitat maps, a greater proportion of SFB may have been designated as foraging habitat for harbor seals. In addition, our estimates were based on strong cor- relations between predator and prey for harbor seals captured at (and presumably using) a haul-out site in central SFB. Had harbor seals used in this study been captured at a site in the extreme southern or northern SFB, the relative strength of correlations between har- bor seals and individual prey species may have been different, if harbor seals that use these other sites focus on different prey species. However, both an earlier ra- diotracking study using harbor seals captured in south- ern SFB (Torok, 1994) and a 2000-2001 radiotracking study conducted using harbor seals captured at Castro Rocks (Nickel, 2003) identified large foraging areas in central SFB, a number of which fell within the same

areas indicated by our habitat maps. In addition, as harbor seals will shift prey species with seasonal and annual changes in local prey abundance (Tollit and Thompson, 1996), significant changes in the abundance or distribution of prey species in SFB could cause har- bor seals to switch to foraging areas not identified in our maps. With new information on prey distribution, locations of potential foraging habitat could easily be updated in the GIS.

Identifying factors that govern when harbor seals leave SFB to forage will require larger sample sizes, information on seasonal patterns of prey availability on the outer coast, and possibly more fine-grained data on individual harbor seal movements and behavior while at sea. In many areas, including SFB, harbor seals exhibit two foraging strategies (Thompson et al., 1998; Grigg, 2008). In one strategy, harbor seals make shorter, daily trips to and from foraging areas near the haul-out site; in the alternative strategy, harbor seals make longer foraging trips to more distant foraging areas, often lasting for a number of days and followed by extended haul-out periods. Harbor seals often move to protected estuarine haul-out sites to breed and molt, and num- bers of harbor seals at some haul-out sites in SFB are greatest during these seasons (Grigg et al., 2004). The proportion of harbor seal locations on the outer coast in our study was greater during the spring (pupping) and summer (molting) seasons and may reflect the need for some individual harbor seals to forage in coastal waters when the density of harbor seals was high in SFB, in order to minimize intraspecific competition for prey (and therefore, animals would forage in coastal waters but return to SFB haul-out sites to rest between trips). Alternatively, this behavior could reflect the movement by some harbor seals to pupping or molting haul-out sites located outside of SFB, and use of coastal forag- ing areas closer to these haul-out sites. Inspection of individual harbor seal movements (not shown) indicated that both patterns were probably occurring during our study period (Grigg, 2008).

Satellite telemetry enabled us to identify correlations between harbor seal distribution and the distribution of prey species known to be present in the diet of local harbor seals. Using the harbor seal locations and GIS overlay analyses, we identified species of fish likely to be important seasonal prey species of harbor seals in SFB, and areas likely to be important foraging areas (particularly for harbor seals using the Castro Rocks haul-out site). Use of Service Argos positions required substantial elimination of inaccurate positions, with resultant loss of sample size and resolution of harbor seal movements, and limited the scale at which the analyses could be conducted. Nonetheless, we feel that satellite telemetry provided a useful way to assess har- bor seal distribution in our coastal study area, allow- ing continual collection of information on harbor seal locations that would have been difficult using currently available VHF radiotelemetry tags, and eliminating the potential disturbance of an observer’s presence on foraging harbor seals.

Grigg et al.: Spatial and seasonal relationships between Phoca vitulma richardii and their prey

371

Finally, this spatially explicit approach to the identi- fication of foraging areas has applications to manage- ment of pinnipeds in other areas, and other marine predators that can be tracked with satellite telemetry. With local data inputs comparable to those used in this study, this approach could be applied to manage- ment of marine predators in other areas. Knowledge of the location of foraging areas is important to such management concerns as the potential effects of future shifts in the spatiotemporal distribution of prey (due to climate change, etc.), the link between local resource availability and local population trends, prediction of possible interactions of marine predators with fisher- ies, or identification of appropriate locations for marine protected areas.

Acknowledgments

We would like to thank the following individuals: C. Morton and his colleagues at the California Depart- ment of Transportation (Caltrans); J. Harvey and his students; F. Gulland; D. Greig; J. Neale; T. Garfield; R. Larson; K. Hieb; D. Kopec; S. Oates; and J. Grigg. We would particularly like to thank the students and staff at San Francisco State University (SFSU) who helped with this study. This project was supported by Caltrans, SFSU, and a University of California Grant to E.K.G. The research was conducted in accordance with Incidental Harassment Authorizations fr23de97-52 and frl4ja00-38 issued by the National Marine Fisheries Service (NMFS) to Caltrans, NMFS scientific research permit no. 373-1575, and SFSU Animal Care and Use Committee permit no. #99-534.

Literature Cited

Allen, S. G., M. Stephenson, R. W. Risebrough, L. E. Fancher, A.

Shi Her, and D. Smith.

1993. Red-pelaged harbor seals of the San Francisco Bay region. J. Mammal. 74:588-593.

Becker, B. H., and S. R. Beissinger.

2003. Scale-dependent habitat selection by a nearshore seabird, the marbled murrelet, in a highly dynamic upwelling system. Mar. Ecol. Progr. 256:243-255.

Bekkby, T, L. Erikstad, V. Bakkestuen, and A. Bjorge.

2002. A landscape ecological approach to coastal zone applications. Sarsia 87:396-408.

Bigg, M. A.

1973. Adaptations in the breeding of the harbour seal, Phoca vitulina. J. Reprod. Fertil. Suppl. 19:131-142.

Boyce, M. S., and L. L. McDonald.

1999. Relating populations to habitats using resource selection functions. Trends Ecol. Evol. 14:268-272.

Breiman, L, J. Friedman, R. A. Olshen, and C. J. Stone.

1984. Classification and regression trees. 368 p. Chap- man and Hall/CRC., Boca Raton, FL.

Brown, R. F., and B. Mate.

1983. Abundance, movements and feeding habits of harbor seals, Phoca vitulina, at Netarts and Tillamook Bays, Oregon. Fish. Bull. 81:291-301.

Budd, P.

1940. Development of eggs and early larvae of six Cali- fornia fishes. Calif. Dep. Fish Game Fish. Bull. 56, 53 p.

Charnov, E. L.

1976. Optimal foraging: the marginal value theorem. Theor. Popul. Biol. 9:129-136

Conomos, T. J., R. E. Smith, and J. W. Gartner.

1985. Environmental setting of the San Francisco Bay. Hydrobiologia 129:1-12

Corsi, F., J. de Leeuw, and A. Skidmore.

2001. Modeling species distribution with GIS. In Research techniques in animal ecology: controversies and con- sequences. (L. Biotani and T. K. Fuller, eds.), p. 389- 434. Columbia University Press, New York.

Davoren, G. K., W. A. Montevecchi, and J. T. Anderson.

2003. Distributional patterns of a marine bird and its prey: habitat selection based on prey and conspecific behavior. Mar. Ecol. Progr. 256:229-242.

Dungan J. L., J. N. Perry, M. R. T. Dale, P. Legendre, S. Citron- Pousty, M.-J. Fortin, A. Jakomulska, M. Miriti, and M. S. Rosenberg.

2002. A balanced view of scale in spatial statistical analy- sis. Ecography 25:626-640

Erickson W. P., T. L. McDonald, K. G. Gerow, S. Howlin, and J. W. Kern.

2001. Statistical issues in resource selection studies with radio-marked animals. In Radio tracking and animal populations (J. Millspaugh, and J. Marzluff, eds.), p. 211-245. Academic Press, San Diego, CA.

Fancher, L. E.

1979. The distribution, population dynamics, and behavior of the harbor seal ( Phoca vitulina richardsi ) in South San Francisco Bay, California. MS thesis, 109 p. California State Univ., Hayward, CA.

Fauchald, P., K. E. Erikstad, and H. Skarsfjord.

2000. Scale-dependent predator-prey interactions: The hierarchical spatial distribution of seabirds and prey. Ecology 81:773-783

Fitch, J., and R. Lavenberg.

1971. Marine food and game fishes of California. 179 p. Univ. California Press. Berkeley, CA.

Grigg, E. K.

2008. Environmental predictors of habitat use patterns of Pacific harbor seals (Phoca vitulina richardii ) in an urbanized estuary. Ph.D. diss., 113 p. Univ. Califor- nia, Davis, CA.

Grigg E. K., S. G. Allen, D. E. Green, and H. Markowitz.

2004. Harbor seal, Phoca vitulina richardii, popula- tion trends in the San Francisco Bay estuary, 1970- 2002. Calif. Dep. Fish Game 90:51-70.

Harkonen, T. J.

1987. Seasonal and regional variations in the feeding- habits of the harbor seal, Phoca-vitulina, in the Skager- rak and the Kattegat. J. Zool. 213:535-543.

Harvey, J. T.

1989. Assessment of errors associated with harbour seal ( Phoca vitulina) faecal sampling. J. Zool. 219:101— 111.

Harvey, J. T., R. C. Helm, and G. V. Morejohn.

1995. PYod habits of harbor seals inhabiting Elkhorn Slough, California. Calif. Dep. Fish Game. 81:1-9.

Hays, G. C., S. Akesson, B. J. Godley, P. Luschi, and P. Santidrian.

2001. The implications of location accuracy for the inter-

372

Fishery Bulletin 107(3)

pretation of satellite-tracking data. Anim. Behav. 61:1035-1040.

Iverson, S. J., K. J. Frost, and L. F. Lowry.

1997. Fatty acid signatures reveal fine scale structure of foraging distribution of harbor seals and their prey in Prince William Sound, AK. Mar. Ecol. Prog. Ser. 151:255-271.

Keating, K. A.

1994. An alternative index of satellite telemetry location error. J. Wildl. Manag. 58:414-421.

Keating K. A., W. G. Brewster, and C. H. Key.

1991. Satellite telemetry: performance of animal track- ing systems. J. Wildl. Manag. 55:160-171.

Loughlin, T.

1978. Harbor seals in and adjacent to Humboldt Bay, California. Calif. Depart. Fish Game 64:127-132.

Lowry, L. F., K. J. Frost, J. M. Ver Hoef, and R. A. DeLong.

2001. Movements of satellite-tagged subadult and adult harbor seals in Prince William Sound, AK. Mar. Mamm. Sci. 17:835-861.

Mehlum, F, G. L. Hunt Jr., Z. Klusek, and M. M. Decker.

1999. Scale-dependent correlations between the abun- dance of Brunnich’s guillemots and their prey. J. Anim. Ecol. 68:60-72.

Nickel, B. A.

2003. Movement and habitat use patterns of harbor seals in the San Francisco Estuary, California. MA thesis, 121 p. San Francisco State Univ., San Fran- cisco, CA.

North, M. P., and J. Reynolds.

1996. Microhabitat analysis using radiotelemetry loca- tions and polytomous logistic regression. J. Wildl. Manag. 60:639-653.

Olivier, F., and S. J. Wotherspoon.

2005. GIS-based application of resource selection func- tions to the prediction of snow petrel distribution and abundance in East Antarctica: comparing models at multiple scales. Ecol. Model. 189:105-129.

Orians, G. H., and N. E. Pearson.

1979. On the theory of central place foraging. In Analy- sis of ecological systems. (D. Horn, G. Stairs, and R. Mitchell, eds.). p. 155-177. Ohio State Univ. Press, Columbus, OH.

Reilly, P.

1983. Predation on Dungeness crabs, Cancer magister , in central California. In Life history, environment and mariculture studies of the Dungeness crab, Cancer magister , with an emphasis on the central California fisheries resource (P. W. Wild, and R. N. Tasto, eds.), p. 155-164. Calif. Dep. Fish Game Fish. Bull. 172.

Rettie, W. J., and P. D. McLoughlin.

1999. Overcoming radiotelemetry bias in habitat selec- tion studies. Can. J. Zool. 77:1175-1184.

Robinson, P. W., Y. Tremblay, D. E. Crocker, M. A. Kappes, C. E.

Kuhn, S. A. Shaffer, S. E. Simmons, and D. P. Costa.

2007. A comparison of indirect measures of feeding behavior based on ARGOS tracking data. Deep Sea Res. II 54:356-368.

Rose, G. A., and W. C. Leggett.

1990. The importance of scale to predator-prey spatial correlations: an example of Atlantic fishes. Ecology 71:33-43.

Thompson, P. M., M. A. Fedak, B. J. McConnell, and K. S.

Nicholas.

1989. Seasonal and sex-related variation in the activity patterns of common harbor seals ( Phoca vitulina). J. Appl. Ecol. 26:521-535.

Thompson, P. M., A. Mackay, D. J. Tollit, S. Enderby, and P. S.

Hammond.

1998. The influence of body size and sex on the charac- teristics of harbour seal foraging trips. Can. J. Zool. 76:1044-1053.

Thompson, P. M., and D. Miller.

1990. Summer foraging activity and movements of radio- tagged harbor seals ( Phoca vitulina) in the Moray Firth, Scotland. J. Appl. Ecol. 27:492-501.

Tollit, D. J., A. D. Black, P. M. Thompson, A. Mackay, H.

M. Corpe, B. Wilson, S. M. Van Parijs, K. Grellier, and S.

Parlane.

1998. Variations in harbour seal Phoca vitulina diet and dive-depths in relation to foraging habitat. J. Zool. 244:209-222.

Tollit, D. J., and P. M. Thompson.

1996. Seasonal and between-year variations in the diet of harbour seals in the Moray Firth, Scotland. Can. J. Zool. 74:1110-1121.

Tor ok, M.

1994. Movements, daily activity patterns, dive behavior, and food habits of harbor seals (Phoca vitulina rich- ardsi ) in San Francisco Bay, California. M.S. thesis, 88 p. California State Univ., Stanislaus, CA.

Vincent, C., B. J. McConnell, M. A. Fedak, and V. Ridoux.

2002. Assessment of Argos location accuracy from satel- lite tags deployed on captive grey seals. Mar. Mamm. Sci. 18:301-322.

White N. A., and M. Sjoberg.

2002. Accuracy of satellite positions from free-ranging grey seals using ARGOS. Polar Biol. 25:629-631

373

Abstract — Pop-up satellite archi- val tags (PSATs) have been used to study movements, habitat use, and postrelease survival of large pelagic vertebrates, but the size of these tags has historically precluded their use on smaller coastal species. To evaluate a new generation of smaller PSATs for the study of postrelease survival and habitat use of coastal species, we attached Microwave Telemetry, Inc., X-tags to ten striped bass ( Morone saxatilis) 94-112 cm total length (TL) caught on J hooks and circle hooks during the winter recreational fishery in Virginia. Tags collected tempera- ture and depth information every five minutes and detached from the fish after 30 days. Nine of the ten tags released on schedule and eight trans- mitted 30% to 96% (mean 78.6%) of the archived data. Three tags were physically recovered during or after the transmission period, allowing retrieval of all archived data. All eight striped bass whose tags trans- mitted data survived for 30 days after release, including two fish that were hooked deeply with J hooks. The eight fish spent more than 90% of their time at depths less than 10 m and in tem- peratures of 6-9°C, demonstrated no significant diel differences in depth or temperature utilization (P>0.05), and exhibited weak periodicities in vertical movements consistent with daily and tidal cycles.

Manuscript submitted 6 December 2008. Manuscript accepted 24 April 2009.

Fish. Bull. 107:373-383 (2009).

The views and opinions expressed or implied in this article are those of the author and do not necessarily reflect the position of the National Marine Fisheries Service, NOAA.

Use of pop-up satellite archival tag technology to study postrelease survival of and habitat use by estuarine and coastal fishes: an application to striped bass (Morone saxatilis )

John E. Graves (contact author)

Andrij Z. Horodysky Robert J. latour

E-mail address for contact author: graves@vims.edu

Virginia Institute of Marine Science College of William and Mary Route 1208 Greate Rd.

Gloucester Point, Virginia 23062

Developments in pop-up satellite archival tags (PSATs) have greatly improved scientific understanding of the postrelease survival, behav- ior, and movements of marine ver- tebrates— animals from which it is not always practical to physically recover tags to obtain data (Arnold and Dewar, 2001; Graves et. al. 2002). PSATs take measurements of physical conditions (e.g., temperature, pres- sure, light level) while attached to study animals, independently detach at predetermined times, float to the surface, and transmit data to orbiting satellites of the Argos system. Owing to the mass and size of older tags (~65 g), PSAT deployments have histori- cally been limited to large pelagic marine vertebrates such as billfishes, tunas, sharks, and sea turtles. Recent miniaturization of tag components has led to the development of a new gener- ation of PSATs that are 33% smaller, thus enabling the collection of high- resolution time-series data for infer- ences regarding short-term fate and habitat use by increasingly smaller species, including many estuarine and coastal fishes.

To evaluate the utility of the new generation of smaller PSATs for stud- ies of estuarine and coastal fishes, we deployed ten tags on large, coastal, migratory striped bass ( Morone saxa- tilis) caught on live baits rigged on two hook types in the winter recre- ational fishery off coastal Virginia and North Carolina. Although small-

er PSATs provide opportunities to investigate smaller species, coastal and estuarine fishes and the charac- teristics of their habitats present spe- cial challenges for PSAT deployments. First, many coastal species associate with physical habitat structures in which the tags could become entan- gled, possibly resulting in premature release of the tag. Secondly, many coastal species aggregate, providing opportunities for conspecifics or other species to interact with the tag, pos- sibly causing premature release or damage to the PSAT. Finally, because coastal species are found near shore, there is an increased probability that a released (transmitting) PSAT will wash ashore during the transmission period, potentially reducing the qual- ity and quantity of subsequent data transmissions. On the other hand, the increased probability of beaching dur- ing data transmission may provide researchers opportunities for directed tag recovery.

A second goal of this study was to gain insights into the postrelease survival of striped bass released from recreational fishing gear dur- ing the winter prespawning aggrega- tion near the mouth of Chesapeake Bay. Striped bass are a highly prized recreational gamefish, providing over $300 million to the U.S. economy and over $60 million to Virginia annu- ally (Kirkley and Kerstetter, 1997; Richards and Rago, 1999). Manage- ment regulations, such as seasonal

374

Fishery Bulletin 107(3)

Table 1

Summary of published postrelease survival experiments using J, treble, and circle hooks conducted on striped bass (Morone saxatilis ) released from the recreational fishery. F=freshwater, S=saltwater followed by the state abbreviation. Hook types are: J (straight-shank J hook), C (circle hook), and T (treble hook). For release mortality, estimates are for artificial lures (L), live bait (B), J hooks (J), or circle hooks (C).

Source	Water type and region	Season	Hook	Bait type or lure	Release mortality
Harell (1988)	F	Winter, summer	J	Live bait, lures	L: 15.6%, B: 30.7%
Hysmith et al. (1993)	F: TX	Winter, summer	J	Live bait, lures	38%
Diodati and Richards (1996)	S: MA	Summer	J	Live bait, lures	3-26%; mean 9%
Nelson (1998)	F: NC	Spring	J, T	Live baits, lures	6-27%: mean 6.3%
Bettoli and Osborne (1998)	F: TN	Winter, summer	J , T	Live baits, lures	14-67%
Lukacovic and Uphoff (2002)	S: MD	Summer	J	Natural baits	J: 9.1%
			C		C: 0.8%
Millard et al. (2003)	F: NY	Spring	J	Natural baits	8-18%

bag and size limits, have resulted in the release of over 90% of the striped bass caught by recreational anglers (Van Winkle et al., 1988). Current recreational postrelease mortality estimates for striped bass range between 3% and 67%, and a value of 9% is currently used in population assessments for the Chesapeake Bay stock (Diodati and Richards, 1996). However, previous studies have generally been conducted in fisheries and environmental conditions very different from those near the mouth of Chesapeake Bay during the winter months (Table 1).

A third goal of this study was to determine habitat use by coastal migrant striped bass during the winter prespawn aggregation in the coastal sea along Virginia. Habitat use by juvenile striped bass within estuarine and riverine waters has been fairly well studied (Tupper and Able, 2000; McGrath, 2005), as have the move- ments of adults during upriver spawning migrations (Carmichael et al., 1998). Little is known about the depth and temperature use or short-term movements of adult striped bass in winter prespawning aggrega- tions along the U.S. Mid-Atlantic coast, despite the importance of Chesapeake Bay to the coastal migrant population. The Chesapeake Bay stock is thought to be the most productive along the Atlantic coast, serving as a major source of coastal recruits and accounting for >90% of Atlantic coastwide landings in some years (Kohlenstein, 1981; Richards and Rago, 1999; Secor, 2000). Identifying habitat characteristics and patterns of habitat use by coastal migrant species in areas of ag- gregation are necessary for effective current and future management efforts (Carmichael et al., 1998; Conrath and Musick, 2008).

Materials and methods

The X-tag high rate archival tag (X-tag, Microwave Telemetry, Inc., Columbia, MD) used in this study is slightly buoyant, and weighs 40 g in air. The body of the tag contains a lithium composite battery, a micropro-

cessor, a pressure sensor, a temperature gauge, a light sensor, and a transmitter, all encased within a carbon fiber housing. Flotation is provided by a spherical resin bulb embedded with buoyant glass beads and the tag can withstand pressure equivalent to a depth of 2500 m. This tag model was programmed to record and archive a con- tinuous time series of temperature, light, and pressure (depth) measurements approximately every five minutes for 30 days. The tags can transmit depth measurements at intervals of approximately 1.3 m and temperature in increments of 0.17°C. Not having prior information on the time course or range of vertical movements of striped bass overwintering off the mouth of Chesapeake Bay, we chose not to activate an optional feature that provides for early tag release in the case of a mortality which is inferred if the tag remains at constant depth (±1.5 m) for four days. The X-tags were equipped with Satellite in View™ software that increases battery life and data recovery by restricting transmissions to times during which there is a high likelihood that the Argos satellite will pass above the horizon.

Striking a balance between availability and size of striped bass in the winter recreational fishery off the mouth of Chesapeake Bay, we arbitrarily set a mini- mum length threshold for tagging of 94 cm total length (TL). Striped bass in this size range are sexually ma- ture coastal migrants (Dorazio et al., 1994) that weigh 8 kg or more (Secor, 2000) and were considered to be of sufficient size to carry the X-tag.

Striped bass were caught by using live eels (Anguilla t'ostrata) as bait on 13.6-kg test sportfishing tackle with 1.2-m leaders of 36.3-kg test line. Five striped bass were caught on J hooks (Gamakatsu Octopus, size 7/0, no offset), and five on circle hooks (Gamakatsu Octopus Circle, size 7/0, no offset). Fish were netted and brought on deck where the hook location was noted, the hook removed, total length measured, and the PSAT attached before the fish was returned to the water (air exposure time less than two minutes).

PSATs were attached to striped bass by an assembly composed of 16 cm of 182-kg test monofilament fishing

Graves et al.: Use of archival tags to study postrelease survival of and habitat use by estuarine and coastal fishes

375

Figure 1

X-tag (Microwave Telemetry, Inc., Columbia, MD) attached to a striped bass ( Morone saxatilis). The nylon intramuscular tag anchor was inserted approximately 5 cm towards the dorsal midline, an area where the anchor had a high likelihood of securely interlocking with the pterygiophores supporting the dorsal fin spines.

line (Momoi Fishing Co., Ako City, Japan) attached to a large, hydroscopic, surgical-grade nylon intramuscular tag anchor according to the method of Graves et al. (2002). Attachment assemblies were implanted with a 5-cm stainless steel applicator attached to a 0.3-m tagging pole that was inserted behind a scale approxi- mately 5 cm deep into a target region approximately 6 cm posterior to the origin and 5 cm ventral to the base of the dorsal fin (Fig. 1). In this region, the nylon anchor can pass through and potentially interlock with pterygiophores supporting the dorsal fin well above the coelomic cavity containing visceral organs (Graves et al., 2002).

Data analyses

Net movement was calculated as a minimum straight line distance (MSLD) traveled between coordinates of initial tagging and coordinates of the first reliable sat- ellite transmission by using Argos location codes 1, 2, or 3 (Horodysky et al., 2007). Archived and transmitted point measurements of depth and temperature recorded by PSATs were summarized in 5-m and 1°C interval histograms. Data sets were truncated to remove records before tagging and after PSAT pop-up.

To assess potential diel differences in habitat utiliza- tion, mean depths and temperatures were generated for each diel period (day, night) of each tracking day (n = 30) for each of the eight striped bass. Diel period designa- tions were based on times of local sunrise and sunset;

crepuscular periods (30 minutes on either side of dawn and dusk) were eliminated from all diel analyses. Diel differences in the depth and temperature means were assessed separately with linear mixed effects models of the following form (Pinheiro and Bates, 2004):

Ypi=H + Tp + ai + £pi’ (1)

where p = the overall mean depth or temperature; x = the fixed effect of diel period p; at = the random effect due to individual fish; and e • = error terms.

Application of linear models requires satisfying three assumptions: independence and normality of the response within and among samples, and homogeneity of vari- ances among all levels of the fixed effects (Underwood, 2002). However, PSAT data constitute repeated noninde- pendent observations within individual fish and may fail to satisfy the assumptions of normality and homogeneity of variance. Accordingly, a repeated measures form of Equation 1, including a Box-Cox transformation of the depth and temperature data, rectified these problems in the striped bass data. To characterize the within- individual autocorrelation, several candidate covariance structures were fitted to the transformed depth and temperature data, and the appropriate structure was selected by using Akaike’s information criterion ( AIC ):

AIC = -21n(L) + 2p, (2)

376

Fishery Bulletin 107(3)

Table 2

Hook type, hooking location, release date, fish size, PSAT data recovery, and net movement data for striped bass (Morone saxati- lis) caught on live eels ( Anguilla rostrata) in the winter recreational fishery off the coast of Virginia and North Carolina. Starred (*) data recovery percentages indicate instances where PSATs were physically recovered, allowing a full download of all archived data. Minimum straight line displacements (MSLDs) were calculated in nautical miles (nmi) from the coordinates of tagging to the coordinates of first reliable satellite contact (Argos location code 1, 2, or 3).

Fish	Hook type	Hooking location	Date released	Total length (cm)	Data recovery (%)	MSLD (nmi)
1	J	Deep	26 Jan 08	94.0	90	29.9
2	J	Upper jaw	26 Jan 08	94.0	100*	56.3
3	C	Jaw corner	26 Jan 08	96.5	87	27.8
4	C	Upper jaw	27 Jan 08	111.8	100*	34.3
5	C	Jaw corner	27 Jan 08	94.0	90	58.6
6	J	Deep	2 Feb 08	96.5	96	12.5
7	C	Upper Jaw	2 Feb 08	104.1	30	27.1
8	J	Upper Jaw	2 Feb 08	101.6	100*	32.5
where L	= the estimated value of the likelihood function	externally, either	in the upper jaw or	the corner of the
	at its maximum; and		jaw. Two of five fish caught on J hooks were hooked
P	= the number of estimated parameters (Burn-	deeply and the other three were hooked externally.
	ham and Anderson, 2002).		Hooks were removed from all fish before they were
				tagged and released.
We performed fast Fourier transform (FFT) analy-	Eight of the ten PSATs popped up	on schedule and
ses to assess any periodicities inherent in the time	transmitted data that were received by satellites oi
series of the three recovered tags for which 100% of	the Argos system. A single, weak transmission was

the archived data were obtained. FFT approximates a function composed of sine and cosine terms from a time series (Chatfield, 1996) and is particularly well suited to analyzing high-resolution data sets resulting from archival tagging studies (Graham et al., 2006; Shepard et al., 2006). The influence of periodic components in a time series is indicated by the magnitude of the cor- responding spectral peak in a periodigram (Shepard et al., 2006). Spectral components of fractional periodici- ties (i.e., part of a tidal cycle, moon phase, etc.) occur- ring before and after the tag deployment duration can interfere with each other, generating frequency peaks that do not represent meaningful behavioral period- icities (Shepard et al., 2006). We therefore applied a Hamming window to the depth records of each of the three striped bass to reduce the effects of such adja- cent spectral components (Oppenheim and Schafer, 1989). All statistical analyses were performed with the software package R, vers. 2.7.1 (R Development Core Team, 2008).

Results

Ten striped bass, ranging in size from 94 to 112 cm TL (mean = 96.5 cm), were caught on live eels rigged with circle or J hooks in coastal waters (<20 m depth) of Virginia and North Carolina during late January and early February 2008 (Table 2). Fight times ranged from 1 min 10 sec to 5 min 30 sec (mean=2 min 16 sec). All five fish caught on circle hooks were hooked

received from one of the two remaining tags on the day it was scheduled to release, and no transmis- sions were received from the other PSAT. The tags had sufficient battery power to transmit data for ap- proximately 30 days, and during that time three of the eight reporting PSATs washed ashore. Two of these tags (from fish 2 and 4) were physically recov- ered while transmitting data. Transmissions from the third tag (fish 7) ceased when the PSAT washed ashore four days after surfacing; this tag was not recovered. A fourth tag (fish 8) remained adrift dur- ing its transmission period and subsequently washed ashore north of Cape Hatteras, NC, where it was recovered by a recreational angler.

Data recovery rates varied among the eight trans- mitting tags. All of the archived data were manually downloaded from the three tags that were recovered after having washed ashore. For the four tags that remained adrift during the transmission period and not subsequently recovered (fish 1, 3, 5 and 6), data recovery rates were high, ranging from 87 to 96%. The PSAT from fish 7 surfaced just off the seaside of the Eastern Shore of Virginia and washed ashore on Parramore Island after four days, at which time transmissions ceased to be received. During the four- day transmission period, 30% of the archived data were recovered from this tag.

From a visual inspection of depth and temperature data we inferred that all eight striped bass with re- porting tags, including the two fish that were deeply hooked with J hooks, survived for 30 days after re-

Graves et al.: Use of archival tags to study postrelease survival of and habitat use by estuarine and coastal fishes

377

1/28/2008 2/4/2008 2/11/2008 2/18/2008 2/25/2008 1/28/2008 2/4/2008 2/11/2008 2/18/2008 2/25/2008

-40 ■ ■ i i i i i ■

1/28/2008 2/4/2008 2/11/2008 2/18/2008 2/25/2008

-40 ■ ■ i i i i i •

1/28/2008 2/4/2008 2/11/2008 2/18/2008 2/25/2008

■ -i -i -i i 5

1/28/2008 2/4/2008 2/11/2008 2/18/2008 2/25/2008

20

— I (D

3

- 15 "S 5 c IB

5

2/4/2008 2/11/2008 2/18/2008 2/25/2008 3/3/2008

2/4/2008 2/11/2008 2/18/2008 2/25/2008 3/3/2008

Figure 2

Depth (left axis, open black symbols) and temperature (right axis, closed grey symbols) time series from Microwave Telemetry X-tags deployed on eight large coastal migrant striped bass ( Morone saxatilis) from January through March 2008. Tags for fish 2, 4, and 8 were recovered and represent the full 100% downloaded data streams.

lease. Each fish exhibited multiple vertical move- ments in the water column throughout the 30-day tagging period (Fig. 2). Inferences of survival based on depth and temperature data were also support- ed by calculations of net movement (Graves et al., 2002). Minimum straight line displacements for the eight striped bass ranged from 12.6 to 58.6 nautical miles (nmi; 23.3-108.5 km), with a mean of 34.9 nmi (64.6 km; Fig 3). During the 30-day tagging period, three individuals (fish 2, 4, and 5) left coastal waters and entered Chesapeake Bay, presumably initiating spawning migration.

Depth and temperature data archived by the eight transmitting X-tags demonstrated that coastal migrant striped bass spent >90% of their time in the upper 10 m of the water column in temperatures of 6-9°C (Fig 4). Two striped bass (fish 2 and 5) entered warm tem- peratures (~15°C) at approximately the same time on the same date. These individuals, tagged on different days in North Carolina waters, may have moved east- ward to a warm core eddy confirmed by satellite tem- perature imagery for 7 February 2008 (http://marine. rutgers.edu/cool/sat_data, accessed May 2008). It is also possible that these fish instead moved into shallow

378

Fishery Bulletin 107(3)

Figure 3

Minimum straight line displacements (MSLD) in nautical miles (nmi) of eight large coastal migrant striped bass (Morone saxatilis ) caught on recreational fishing gear and tagged with Microwave Telemetry X-tags from January through March 2008. Arrow bases (circles) indicate location of fish tagging and release, arrow tips denote the first point of contact with transmitting tag after release from the fish.

coastal or estuarine waters warmed by unseasonable temperatures (~18°C) on 7 February 2008.

Despite the daily variability in the tracks of indi- viduals, repeated-measures linear mixed-effects models yielded no significant diel differences in striped bass depth or temperature utilization (P>0.05). The best fitting model for both depth and temperature data was the autoregressive moving average (ARM A) covariance structure.

Fast Fourier transform periodigrams of the three recovered tags revealed weak periodicities in vertical movements consistent with one cycle per day (i.e., 24 hours), and weaker behaviors consistent with two and three cycles per day (i.e., 12 and 8 hours, respective- ly; Fig. 5). All three periodigrams had large spectral peaks near zero, a consequence of standardizing the depth data by the average depth; main spectral peaks follow this initial clustering (Shepard et al., 2006). The main spectral peaks were identified both with and without the Hamming window, and thus were not attributed to artifact. It is unclear if the periodicities of approximately 12 hours and 8 hours represent spe- cific behavioral cycles or harmonics that result from nonsinusoidal behavior (Chatfield, 1996).

Discussion

The primary goal of this study was to evaluate the per- formance of a new generation of smaller PSATs on estua- rine and coastal species in the nearshore environment. The larger, older models of PSATs have been deployed on coastal elasmobranchs (Grusha, 2005; Conrath and Musick, 2008). As comparatively smaller coastal and estuarine fishes become candidates for these smaller tags, researchers may wish to consider the minimum size at which drag and lift forces acting on the PSAT impact behavior and survival (Grusha and Patterson, 2005). From the movements of fish and the lack of observed mortalities, we conclude that striped bass of ~1 m TL length appear to be of sufficient size to carry the X-tag.

At the outset of this study we were concerned with the potential for premature release of PSATs because of entanglement in physical structure, fish-tag inter- actions that would result in premature release or tag damage, and the likelihood that tags would effectively transmit the archived data from nearshore waters. The lack of prematurely released tags in this study confirms that fouling or interactions with structure

Graves et al. : Use of archival tags to study postrelease survival of and habitat use by estuarine and coastal fishes

379

were not problematic for striped bass; however, the applicability of these results to other struc- ture-associated species is not known. Premature release of PSATs has been noted in many stud- ies and may become more prevalent with longer deployment times because of attachment methods and increased potential for fish-tag interactions (Domeier et al., 2003; Conrath and Musick, 2008; Graves and Horodysky, 2008). The selection of a specific attachment method and an appropriate release time will depend on the species studied and research objectives of the study (e.g., postrelease mortality, movement, or habitat use).

Fish-tag interactions present challenges for all PSAT studies and may occur as predation of a tag mistaken for a prey item or predation of an indi- vidual carrying a tag. Both outcomes are extremely difficult to quantify and compromise study objec- tives. In schooling piscivorous fishes, such as adult striped bass, predation of PSATs is more likely than predation of the study individuals. We cannot discount that our nonreporting and weakly trans- mitting tags may have been victims of tag preda- tion; it is often impossible to discern between tag predation and tag failure. However, it is unlikely that mortality of a tagged striped bass would result in a nonreporting tag because the PSAT should surface from a dead carcass after 30 days. The predation of live individuals by elasmobranchs, as well as the scavenging of dead fish carrying PSATs by elasmobranchs, was inferred in previ- ous studies (Kerstetter et al., 2004; Kerstetter and Graves, 2008). In these instances, the PSATs were not compromised during ingestion and success- fully transmitted after being regurgitated, but it is likely that damage during such events may be a cause of PSAT nonreportings.

The success of studies where PSAT technology is used depends upon on the quality and quantity of the archived data that are transmitted from the tag to the Argos satellite system. Reception of PSAT transmissions is maximized when the tag antenna is unobstructed and above the surface of the water in a vertical position. In our study, we obtained at least 87% of the data from tags that re- mained adrift for the entire data transmission period. There is an increased probability that tags attached to estuarine and coastal fishes will wash ashore during the transmission period that typically lasts about 30 days. Tags beach in a horizontal position which may result in decreased signal reception, especially if an- tennae are submerged in water or fouled with algae or other debris.1 Beached tags in this study transmitted 30-90% of their data. In the case of the tag attached to fish 7, which beached after only four days of trans- mission and ceased communicating with the satellite shortly thereafter, the transmission of over 3000 data points provided more than sufficient information to infer survival and investigate habitat use by that indi- vidual. The random transmission of data packets (nine

A

14 - 12

o >

g 10 I1

^ —

<3

<5 Q _

o. o E ,a>

4 -I T 1 1 ,

0 10 20 30 40 50

Percent time at temperature

Figure 4

Time-at-depth (A) and time-at-temperature (B) histograms from Microwave Telemetry X-tags deployed on eight large coastal migrant striped bass ( Morone saxatilis) from January through March 2008. Each fish was given equal contribu- tion. Error bars are ±1 standard error.

consecutive time points) by the X-tags during times when a satellite of the Argos system is likely above the horizon generally results in a rapid accumulation of data during the first week of the thirty-day trans- mission period (Fig. 6).

The two tags that were recovered while still trans- mitting (fish 2, 4) were carried by fish that moved from coastal waters into the mainstem of Chesapeake Bay. We timed the X-tags to release while striped bass were in coastal or estuarine waters before their annual spring spawning migration to freshwater. The release mechanism on the PSAT, which operates by electrolysis, requires a >5 ppt salinity to function,1 which necessi-

1 P. Howey. 2009. Personal commun. Microwave Tele- metry, Inc., 8835 Columbia 100 Parkway, Suites K & L, Columbia, MD 21045

380

Fishery Bulletin 107(3)

tates consideration when dealing with anadromous or catadromous fishes.

PSAT deployments in estuarine and coastal waters will likely have higher tag-to-human interaction rates than those deployed in oceanic waters, and will poten- tially lead to greater rates of tag recovery. However, to realize these potential benefits, which may be consider- able in highly populated regions, the incentive (finan- cial, material, or otherwise) for returning a recovered tag must be sufficient (Pollock et al., 2001). Historically, tag-recovery rates in PSAT studies have been very low. However, Kerstetter and Graves (2008) recently re- ported recoveries of 4 of 17 PSATs (23.5%) attached to sailfish released from pelagic longline operations in the Gulf of Mexico, south of Key West, FL, and all recover- ies came from the heavily used beaches of southeast Florida. Recovery of PSATs can further be aided by the

use of radio antennae if tags are transmitting1; tags in dense cover can also be located by a metal detector at close range (<0.5 m: A. Horodysky, personal obs.). Tag recovery is beneficial not only because it is possible to obtain 100% of the archived data from the PSAT, but recovered tags can be refurbished for approximately 20% of the cost of a new tag.

A second objective of this study was to assess po- tential differences in postrelease survival of striped bass caught on live eels rigged with J hooks and circle hooks in the winter recreational fishery. Although the limited sample size precluded statistical comparisons, tags from all eight fish returned data that indicated survival. Circle hooks reduce deep-hooking, hook-in- duced trauma, and mortality of many fishes (Cooke and Suski, 2004; Horodysky and Graves, 2005), including that of striped bass (Table 1). Previous research has demonstrated a high mortality of striped bass deep-hooked with J hooks and addi- tional and interactive stress-related mortal- ity of larger striped bass caught in warm, low-salinity waters (>20°C, <10 ppt) and handled in still higher air temperatures (>30°C) (Wilde et al., 2000; Lukacovic and Uphoff, 2002). Handling exhausted fish in warmer air can further raise basal meta- bolic rate, exacerbating oxygen demand and blood chemistry problems (Gingerich, et al., 2007) while simultaneously reducing the gill surface area because of the physical collapse of the gill lamellae and adhesion of the gill filaments (Cooke et al., 2002). We observed 100% survival of tagged fish, in- cluding two animals deeply hooked with J hooks, caught in cool, high salinity waters (<10°C, >25 ppt), and handled briefly (<2 minutes) in cool air temperatures (<18°C). Although further work is still needed, the results of these studies indicate that the winter recreational fishery in Virginia may not be a significant source of postrelease mortality for striped bass and that release mortality of this species likely varies tem- porally and spatially because of physiologi- cal stressors.

A third objective of this study was to gain insights into habitat use by striped bass overwintering near the mouth of Chesapeake Bay. Net displacements of the eight fish over the 30-day tagging period were limited, averaging less than 35 nmi (64.8 km). We did not use geolocation al- gorithms based on light and sea surface temperature data to infer horizontal move- ments of fish within the 30-day tagging period because the mean displacements over the 30 days were substantially less than the root mean square (RMS) errors associated with daily estimates of geolo- cation. Under optimal condition, such as

200

400

400

600

200

400

Fourier frequency

600

Figure 5

Fast Fourier transform periodigrams for depth data from three recov- ered Microwave Telemetry X-tags (fish 2, 4, and 8) deployed on eight large coastal migrant striped bass ( Morone saxatilis) from January through March 2008 and physically recovered. Periods of the main spectral peaks found with the raw data and the Hamming window are identified with open circles and labeled in hours.

Graves et al.: Use of archival tags to study postrelease survival of and habitat use by estuarine and coastal fishes

381

Figure 6

Cumulative percentage of archived data that are successfully received by the user as a function of the number of days of transmitted data during the 30-d transmission period for the X-tag high-rate archival tags (Microwave Telemetry, Inc.) pro- grammed with Satellite-In-View (SIV™) technology at Mid- Atlantic latitudes (available from R. P. Howey, 2009, University of Bath, Bath BA2 7AV, UK). Because of the frequency of Argos satellite passes, tags transmitting at higher latitudes will approach asymptotic data recovery more rapidly, and those transmitting at lower latitudes will approach asymptotic data recovery more slowly.

clear pelagic seas, RMS errors associated with geolocation estimates based on light and sea surface temperature data exceed 100 km (Teo et al., 2004; Nielsen and Sibert, 2007), and the hyperdynamic light conditions characteristic of turbid, tidal coastal waters such as those of Chesapeake Bay, which impede the accurate characterization of sunrise and sunset, would result in even greater RMS errors. Consequent- ly, light-based geolocation would seem to have limited applicability to short-term PSAT studies of estuarine and coastal fishes.

Habitat-use studies based on PSAT data may benefit from analytical frameworks that incor- porate repeated measures to account for the in- herent within-individual autocorrelation (James et al., 2006; McMahon et al., 2007). Diel differ- ences were not evident in depth or temperature use by coastal migrant striped bass during the January-March tag deployment period. Simi- larly, there were no significant differences in depth and temperature use among individuals or deployment days. During winter, the adult striped bass staging in coastal Virginia and North Carolina waters forage heavily on dense schools of Atlantic menhaden ( Brevoortia tyran- nus) before traveling into tributaries to spawn (Raney, 1952). The coastal waters of Virginia and North Carolina are fairly shallow and well- mixed, thus the movements of schooling striped bass during our tag deployment duration likely reflect pursuit of prey by a school of predators rather than the selection of preferred depth or temperature ranges by individual striped bass.

Behavioral rhythms in time-series resulting from ul- trasonic telemetry and, more recently, recovered PSATs, are ideally analyzed by fast Fourier methods if all da- ta are recovered (Hartill et al., 2003; Shepard, et al., 2006). Fast Fourier analysis of full depth time-series data streams from three recovered PSATs deployed on striped bass indicate subtle daily, 12-hour, and 8-hour periodicities. Daily periodicities may represent onshore- offshore movements of striped bass schools into shal- lower and deeper waters when they chase menhaden prey, 12-hour periodicities may correspond to ambient diel light regimes, and 8-hour periodicities may indicate subtle tidal or current effects in the use of depth by striped bass. Mid-Atlantic coastal waters and estuar- ies such as Chesapeake Bay feature semidiurnal tides; tidal stage had substantial impact on movements and habitat use of striped bass in Delaware Bay (Tupper and Able, 2000). Alternately, the 8-and 12-hour period- icities observed in the striped bass data may result from a combination of harmonics resulting from behaviors not strictly sinusoidal in character (Chatfield, 1996). Fourier methods should be applied only to full (100%) data streams to avoid inferring direct spectral relation- ships between two adjacent data packets that are in reality separated in time by sections of untransmitted archived data.

We investigated the applicability of a new generation of smaller PSATs for studies of estuarine and coastal fishes and have provided insights into postrelease sur- vival and habitat use of prespawn aggregating adult striped bass in the winter recreational fishery along the coast of Virginia. Results of this study indicate that tag fouling with physical structures, tag damage resulting from interaction with conspecifics, preda- tors, or scavengers, and reduced transmission efficiency due to beaching or entanglement are not major liabili- ties for striped bass. In fact, the potential for reduced transmission efficiency is more than offset by increased probability of tag recovery resulting in complete data retrieval and the opportunity to reuse the tag at a greatly reduced cost. Collectively, the results of this study on striped bass indicate that the new generation of smaller PSATs may prove to be an effective tool for studying the postrelease survival of and habitat use by other estuarine and coastal fishes.

Acknowledgments

The authors would like to thank K. Neill and the crew of the Healthy Grin for all of their efforts to deploy the tags. We thank P. Howey and R. Tolentino (Microwave Telemetry, Inc.) for technical assistance with tags and R. Howey (University of Bath) for developing the soft-

382

Fishery Bulletin 107(3)

ware for the tag transmission rarefaction curve. This research was funded by the Virginia Marine Resources Commission Saltwater License Fund, project RF08-06. VIMS contribution no. 3018.

Literature cited

Arnold, G., and H. Dewar.

2001. Electronic tags in marine fisheries research: a 30- year perspective. In Electronic tagging and tracking in marine fisheries (Reviews: methods and technolo- gies in fish biology and fisheries) (J. R. Sibert, and J. L. Nielsen, eds.) p. 7-64. Kluwer Academic Pubis., Dordrecht, The Netherlands.

Bettoli, P. W., and R. S. Osbourne.

1998. Hooking mortality of striped bass following catch and release angling. N. Am. J. Fish. Manag. 18:609- 615.

Burnham, K. P., and D. R. Anderson.

2002. Model selection and multimodel inference: a practi- cal information — theoretic approach, 488 p. Springer- Verlag, New York.

Carmichael, J. T., S. L. Haeseker, and J. E. Hightower.

1998. Spawning migration of telemetered striped bass in the Roanoke River, North Carolina. Trans. Am. Fish. Soc. 127:286-297.

Chatfield, C.

1996. The analysis of time series, 6th ed. Chapman and Hall, London.

Conrath, C. L., and J. A. Musick

2008. Investigations into depth and temperature habi- tat utilization and overwintering grounds of juvenile sandbar sharks, Carcharhinus plumbeus: the importance of near shore North Carolina waters. Environ. Biol. Fish. 82:123-131.

Cooke, S. J., and C. D.Suski.

2004. Are circle hooks an effective tool for conserving marine and freshwater recreational catch-and-release fisheries? Aquatic Conserv: Mar. Freshw. Ecosyst. 14: 299-326.

Cooke S. J., J. F. Schreer, D. H Wahl, and D. P. Philipp.

2002. Physiological impacts of catch-and-release angling practices on largemouth bass and smallmouth bass. Am. Fish. Soc. Symp. 31:489-512.

Diodati, P. J., and R. A. Richards.

1996. Mortality of striped bass hooked and released in salt water. Trans. Am. Fish. Soc. 125:300-307.

Domeier, M. L., H. Dewar, and N. Nasby-Lucas.

2003. Mortality rate of striped marlin ( Tetrapturus audax) caught with recreational tackle. Mar. Freshw. Res. 54(4):435-445.

Dorazio, R. M., K. A. Hattala, C. B. McColluch, and J. E.

Skjeveland.

1994. Tag recovery estimates of migration of striped bass from spawning areas of the Chesapeake Bay. Trans. Am. Fish. Soc. 123:950-963.

Gingerich, A. J., S. J. Cooke, K. C. Hansonb, M. R. D., C. T.

Hasler, C. D. Suski, and R. Arlinghaus.

2007. Evaluation of the interactive effects of air expo- sure duration and water temperature on the condition and survival of angled and released fish. Fish. Res. 86(2— 3): 169-178.

Graham, R. T., C. M. Roberts, and J. C. R. Smart.

2006. Diving behaviour of whale sharks in relation to

a predictable food pulse. J. R. Soc. Interface. 3:109- 116.

Graves, J. E., and A. Z. Horodysky.

2008. Does hook choice matter? The effects of three circle hook models on post-release survival of white marlin. N. Am. J. Fish. Manag. 28:471-480.

Graves, J. E., B. E. Luckhurst, and E. D. Prince.

2002. An evaluation of pop-up satellite tags for estimating postrelease survival of blue marlin ( Makaira nigricans) from a recreational fishery. Fish. Bull. 100:134-142.

Grusha, D. S.

2005. Investigation of the life history of the cownose ray, Rhinoptera bonasus (Mitchell 1815). M.S. thesis, 116 p. Virginia Inst. Marine Science, College of William and Mary, Gloucester Point, VA.

Grusha, D. S., and M. R. Patterson.

2005. Quantification of drag and lift imposed by pop-up satellite archival tags and estimation of the metabolic cost to cownose rays ( Rhinoptera bonasus). Fish. Bull. 103:63-70.

Harell, R. M.

1988. Catch and release mortality of striped bass caught with artificial lures and baits. Proc. Ann. Conf. South- east. Assoc. Fish. Wildl. Agencies. 41:70-75.

Hartill, B. W., M. A. Morrison, M. D. Smith, J. Boubee, and D.

M. Parsons.

2003. Diurnal and tidal movements of snapper (Pagrus auratus, Sparidae) in an estuarine environment. Mar. Freshw. Res. 54:931-940.

Horodysky, A. Z., and J. E. Graves.

2005. Application of pop-up satellite archival tag tech- nology to estimate postrelease survival of white marlin (Tetrapturus albidus) caught on circle and straight-shank (“J”) hooks in the western North Atlantic recreational fishery. Fish. Bull. 103:84-96.

Horodysky, A. Z., D. W. Kerstetter, R. J. Latour, and J. E.

Graves.

2007. Habitat utilization and vertical movements of white marlin ( Tetrapturus albidus) released from commercial and recreational fishing gears in the western North Atlantic Ocean: inferences from short duration pop-up archival satellite tags. Fish. Oceanogr. 16:240-256.

Hysmith, B. T., J. H. Moczygemba, and G. R. Wilde.

1993. Hooking mortality of striped bass in Lake Texoma, Texas-Oklahoma. Proc. Ann. Conf. Southeast. Assoc. Fish. Wildl. Agencies 46:413-420.

James, M. C., C. A. Ottensmeyer, S. A. Eckert, and R. A.

Myers.

2006. Changes in diel diving patterns accompanies shifts between northern foraging and southward migration in leatherback turtles. Can. J. Zool. 84:754-765.

Kerstetter, D. W., and J. E. Graves.

2008. Post-release survival of sailfish caught by com- mercial pelagic longline gear in the southern Gulf of Mexico. N. Am. J. Fish. Manag. 28: 1578-1586.

Kerstetter, D. W., J. J. Polovina, and J. E. Graves.

2004. Evidence of shark predation and scavenging of fishes equipped with pop-up satellite archival tags. Fish. Bull. 102:750-756.

Kirkley, J., and D. Kerstetter.

1997. Saltwater angling and its economic importance to Virginia. Univ. Virginia, Virginia Sea Grant Report VSG- 97-04, 71 p. Univ. Virginia, Charlottesville, VA.

Kohlenstein, L. C.

1981. On the proportion of the Chesapeake stock of striped

Graves et at: Use of archival tags to study postrelease survival of and habitat use by estuarine and coastal fishes

383

bass that migrates into the coastal fishery. Trans. Am. Fish. Soc. 110:168-179.

Lukacovic, R., and J. H. Uphoff.

2002. Hook location, fish size, and season as factors influencing catch-and-release mortality of striped bass caught with bait in Chesapeake Bay. In Catch and release in marine recreational fisheries (J. A. Lucy, and A. Studholme, eds.), p. 97-100. Am. Fish. Soc. Symp. 30, Bethesda, MD.

McGrath, P.E.

2005. Site fidelity, home range, and daily movements of white perch, Morone americana, and striped bass, Morone saxatilis, in two small tributaries of the York River, Virginia. M.S. thesis, 113 p. Virginia Inst. Mar. Sci., College William and Mary, Gloucester Point, VA.

McMahon, C. R., C. J. A. Bradshaw, and G. C. Hays.

2007. Satellite tracking reveals unusual diving character- istics for a marine reptile, the olive ridley turtle Lepido- chelys olivacea. Mar. Ecol. Prog. Ser. 329:239-252.

Millard, M. J., S. A. Welsh, J. W. Fletcher, J. Mohler, A. Kahnle, and K. Hattala.

2003. Mortality associated with catch and release of striped bass in the Hudson River. Fish. Manag. Ecol. 10:295-300.

Nelson, K. L.

1998. Catch-and-release mortality of striped bass in the Roanoke River, North Carolina. N. Am. J. Fish. Manag. 18:25-30.

Nielsen, A., and J. R. Sibert.

2007. State-space model for light-based tracking of marine animals. Can. J. Fish. Aquat. Sci. 64:1055-1068.

Oppenheim, A. V., and R. W. Schafer.

1989. Discrete-time signal processing. Prentice-Hall, Englewood Cliffs, NJ.

Pinheiro, J. C., and D. M. Bates.

2004. Mixed effects models in S and S-Plus (Statistics and computing). Springer-Verlag, New York.

Pollock, K. H., J. M. Hoenig, W. S. Hearn, and B. Calingaert.

2001. Tag reporting rate estimation: 1. an evaluation of the high-reward tagging method. N. Am. J. Fish. Manag. 21:521-532.

R Development Core Team.

2008. R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna.

Raney, E.C.

1952. The life history of the striped bass, Roccus saxa- tilis (Walbaum). Bull. Bingham Oceanogr. Collect., Yale Univ. 14:5—97.

Richards, R. A., and P. J. Rago.

1999. A case history of effective fishery management: Chesapeake Bay striped bass. N. Am. J. Fish. Manag. 19:356-375.

Secor, D. H.

2000. Spawning in the nick of time? Effect of adult demo- graphics on spawning behaviour and recruitment in Chesapeake Bay striped bass. ICES J. Mar. Sci. 57: 403-411.

Shepard, E. L. C„ M. Z. Ahmed, E. J. Southall, M. J. Witt, J. D. Metcalfe, D. W Sims.

2006. Diel and tidal rhythms in diving behavior of pelagic sharks identified by signal processing of archival tag- ging data. Mar. Ecol. Progr. Ser. 328:205-213.

Teo, S. L. H., A. Boustany, S. Blackwell, A. Walli, K, C. Weng, and B. A. Block

2004. Validation of geolocation estimates based on light level and sea surface temperature from electronic tags. Mar. Ecol. Prog. Ser. 283:81-98.

Tupper, M., and K. W. Able.

2000. Movements and food habits of striped bass ( Morone saxatilis ) in Delaware Bay (USA) salt marshes: com- parison of a restored and a reference marsh. Mar. Biol. 137:1049-1058.

Underwood, A. J.

2002. Experiments in ecology: their logical design and interpretation using analysis of variance, 504 p. Cam- bridge Univ., Press, NY.

Van Winkle, W., K. D. Kumar, and D. S. Vaughan.

1988. Relative contributions of the Hudson River and Chesapeake Bay striped bass stocks to the Atlantic coastal population. In Science, law, and Hudson River power plants: a case study in environmental impact assessment (L. W. Barnthouse, R. J. Klauda, D. S. Vaughan, and R. L. Kendall, eds.), p. 255-266. Am. Fish. Soc., Monograph 4, Bethesda, MD.

Wilde, G. R., M. I. Muoneke, P. W. Bettoli, K. L. Nelson, and B. T. Hysmith.

2000. Bait and temperature effects on striped bass hook- ing mortality in freshwater. N. Am. J. Fish. Manag. 20:810-815.

384

Abstract — Although the Atlantic white-sided dolphin ( Lagenorhynchus acutus) is one of the most common dolphins off New England, little has been documented about its diet in the western North Atlantic Ocean. Current federal protection of marine mammals limits the supply of animals for investigation to those incidentally caught in the nets of commercial fish- ermen with observers aboard. Stom- achs of 62 L. acutus were examined; of these 62 individuals, 28 of them were caught by net and 34 were animals stranded on Cape Cod. Most of the net-caught L. acutus were from the deeper waters of the Gulf of Maine. A single stomach was from the continen- tal slope south of Georges Bank. At least twenty-six fish species and three cephalopod species were eaten. The predominant prey were silver hake ( Merluccius bilinearis) , spoonarm octopus ( Bathypolypus bairdii), and haddock (Melanogrammus aeglefinus). The stomach from a net-caught L. acutus on the continental slope con- tained 7750 otoliths of the Madeira lanternfish ( Ceratoscopelus maderen- sis). Sand lances ( Ammodytes spp.) were the most abundant (541 otoliths) species in the stomachs of stranded L. acutus. Seasonal variation in diet was indicated; pelagic Atlantic her- ring ( Clupea harengus ) was the most important prey in summer, but was rare in winter. The average length of fish prey was approximately 200 mm, and the average mantle length of cephalopod prey was approximately 50 mm.

Manuscript submitted 18 September 2008. Manuscript accepted 5 May 2009.

Fish. Bull. 107:384-394(2009).

The views and opinions expressed or implied in this article are those of the author and do not necessarily reflect the position of the National Marine Fisheries Service, NOAA.

Food habits of Atlantic white-sided dolphins ( Lagenorhynchus acutus) off the coast of New England

James E. Craddock (contact author)1 Pamela T. Polloni1 Brett Hayward2 Frederick Wenzel3

Email address for contact author: jcraddock@whoi.edu

1 Biology Department

Woods Hole Oceanographic Institution Woods Hole, Massachusetts 02543

2 Integrated Statistics, Inc.

16 Sumner St.

Woods Hole, Massachusetts 02543

3 Protected Species Branch Northeast Fisheries Science Center National Marine Fisheries Service

166 Water Street, Woods Hole, Massachusetts 02543

The Atlantic white-sided dolphin (Lagenorhynchus acutus) is restricted to the temperate and subpolar North Atlantic Ocean, ranging from west Greenland (approximately 64°N) to North Carolina (about 35°N) in the western North Atlantic, and from Norway to the Bay of Biscay in the eastern North Atlantic (Leopold and Couperus, 1995). There are thought to be three populations in the western North Atlantic — the Gulf of Maine, Gulf of St. Lawrence, and Labrador Sea populations (Palka et al., 1997). Seasonal shifts in the Gulf of Maine population have been reported; high- est numbers are found in summer and fall and lowest numbers in winter (Northridge et al., 1997; Palka et al., 1997). Most of our animals, however, were obtained during the winter.

This study is the first detailed analysis of the food habits of the Atlantic white-sided dolphin in the western North Atlantic Ocean, here- after referred to as L. acutus rather than the more cumbersome Atlantic white-sided dolphin. Previously, only three live-caught specimens from off New England have been examined for stomach contents and reported in the literature. A single specimen col- lected in 1954 (Schevill, 1956) and a

second collected in 1976, likely a dis- carded incidental take from a gillnet set near Jeffreys Ledge (Katona et al., 1978), were taken in summer and contained the same species of fish and squid. These records indicated that Atlantic herring ( Clupea harengus), silver hake (Merluccius bilinearis), and northern shortfin squid (Illex il- lecebrosus) could be significant com- ponents of the diet. A single animal driven ashore in Trinity Bay, New- foundland, also contained Atlantic herring and northern shortfin squid (Sergeant and Fisher, 1957).

Other observations have reported a few more prey species for L. acu- tus. Stomachs of 14 of 40 stranded L. acutus examined from Cobscook Bay, Maine, contained one silver hake, nine shortfin squid, five rainbow smelt ( Osmerus mordax ), and fragments of unidentified decapod shrimp (St. Au- bin and Geraci, 1979; Sergeant et al., 1980). Katona et al. (1978) reported probable feeding on sand lances ( Am- modytes spp.) by L. acutus associated with feeding humpback (Megaptera novaeangliae ) and fin whales (Balae- noptera physalus). The only L. acutus feeding incident recorded was on De- cember 20, 1997, on Stellwagen Bank, southwestern Gulf of Maine, when a

Craddock et al.: Food habits of Lagenorhynchus acutus off the coast of New England

385

Georges Bank

Kilometers

71 °W

70° W

69° W

68° W

43° N

43° N

42° N

42° N

41°N

41°N

72° W

44° N

44° N

40° N

40° N

72° W

71°W

70° W

69° W

68° W

67° W

67° W

Maine

Gulf of Maine

T> m

New Hampshire

Massachusetts

50 m

100 m

200 m 1000 m

Figure 1

Occurrences from 1991 to 2006 of 62 Atlantic white-sided dolphins ( Lagenorhynchus acutus ) collected in the Gulf of Maine and south of Georges Bank and examined for stomach contents in this study. Circles are locations of net-caught dolphins; triangles are locations of stranded dolphins.

group was observed circling and feeding on a school of sand lance (Weinrich et al., 2001).

Materials and methods

This study records stomach contents from 28 inciden- tally caught and 34 stranded L. acutus from the Gulf of Maine population off the coast of New England (Fig. 1). The animals examined were collected between 1991 and 2006, most of them from 2004-5. The incidentally caught (hereafter referred to as net-caught) animals were taken either by otter trawl (22 stomachs) or by sink gillnet (six stomachs). Of these, 26 were from the Gulf of Maine, one was from deep water (500 m) on the continental slope south of Georges Bank near Munsen Canyon, and one was from the continental shelf south of Narragansett Bay. Thirty-four stomachs were from strandings: 33 from outer Cape Cod, Barnstable County,

MA, and one from Naushon, Elizabeth Islands, Dukes County, MA (Table 1).

We have examined every available stomach of net- caught L. acutus. All were taken in the U.S. commercial fishery and sampled aboard ship by fisheries observ- ers of the National Marine Fisheries Service (NMFS), Northeast Fisheries Science Center (NEFSC, Woods Hole, MA), Northeast Fisheries Observer Program (NE- FOP). NEFOP is the permitting and monitoring agency of the commercial fishing fleet in compliance with the Marine Mammal Protection Act (MMPA) and the U.S. Endangered Species Act (ESA).

Stranded animals were obtained by volunteers of the Cape Cod Stranding Network, currently known as International Fund for Animal Welfare (IFAW), Yar- mouth, MA. Most of the stomachs were initially frozen and curated by the NEFSC.

Contents from stomachs determined to be intact (reli- able) were examined for frequency, relative abundance,

386

Fishery Bulletin 107(3)

Table 1

Summary comparison of numbers, sex, and stomach contents of 34 stranded vs. 28 net-caught Atlantic white-sided dolphins (Lagenorhynchus acutus ) collected in the western North Atlantic Ocean off the coast of New England, between 1991 and 2006; and seasonality of the net-caught individuals. Total net-caught includes two calves with empty stomachs; seasonal net-caught excludes the two calves; S. of Georges = South of Georges Bank. Nontrace = whole prey.

Seasonal net-caught

	Strandings	Total net-caught	Winter	Summer	S. of Georges
Number of dolphins	34	28	22	3	1
Depth where captured (m), mean (range)	0	189.8(55-503)	186.9(71-265)	107.0 (55-187)	503
Number of males	22	9	9	0	0
Length of males (cm), mean (range)	227(156-280)	208 (173-260)	208 (173-260)	0	0
Adult males (>230cm)	10	2	2	0	0
Number of females	12	16	12	3	1
Length of females (cm), mean (range)	205(168-219)	199 (161-253)	203(171-253)	178(161-203)	252
Adult females (>200cm)	10	6	4	1	1
Number unsexed Number of stomachs containing food	0 22 (65%)	3 25 (89%)	1 20 (91%)	3 (100%)	1 ( 100%)
Number of empty stomachs	12 (35%)	3 (11%)	2 (9%)	0	0
Number of otoliths	856	10287	2157	287	7843
unidentified	231	54	51	2	1
Number of fish species	8	21	17	6	7
Number of cephalopod beaks	34	535	519	11	5
Number of cephalopod species	3	3	3	2	1
Number of identified prey Nontrace fishes	0	50	35	15	0
Near nontrace fishes (skulls)	7	56	38	4	14
Total fishes	332	5179	1120	135	3924
Nontrace cephalopods	0	2	0	2	0
Near nontrace cephalopods	0	1	0	1	0
Total cephalopods	20	282	274	4	4

and size (length, weight) of prey. Two net-caught dol- phins examined and subsequently eliminated from the analysis were one partly decomposed female with a mud-filled stomach and thoracic cavity and virtually no food in the stomach, and a partially decomposed male with an almost empty stomach taken on the continental shelf south of Narragansett Bay.

Stomachs were weighed whole, divided into their three components (forestomach, main, and pyloric), emptied of contents, and weighed again to determine both the size of the stomach and the mass of its con- tents. Whole prey (termed “nontrace” prey because they were found relatively intact [not in traces]) were separated, identified, weighed, and measured directly (standard length for fishes and mantle length for cepha- lopods); well-digested prey (termed "trace prey" because they were found in traces as hard parts, e.g. skull bones, otoliths, jaws, prootic bones of clupeids, teeth and opercula of bony fishes, toothplates of hagfish, and cephalopod beaks and pens) were separated, identi- fied, weighed, and original length measurements were estimated indirectly (standard length for fishes and

mantle length for cephalopods). Otoliths were removed from skulls of both nontrace and trace fishes and then cleaned, dried, and measured. The remaining contents were soaked overnight in hot water, if necessary, or elutriated directly through a series of sieves to remove soft tissue and retain hard parts. All items found were identified to the lowest taxonomic level possible (usu- ally to species) by using our own reference collection and published guides (Campana, 2004; Clarke, 1962, 1986; Collette and Klein-MacPhee, 2002; Gregory, 1933; Harkonen, 1986; Smale et al., 1995; Vecchione, 2002). Forestomach contents were then counted and measured and used in all further analyses (Table 2). All fish hard parts, including bones and otoliths, and hagfish toothplates, were stored dried. Cephalopod beaks were removed from buccal masses, cleaned, and stored in 70% ethanol. Crustacean remains and all parasites were counted and also stored in 70% ethanol.

Prey lengths and weights were calculated from otolith lengths for fishes, from lower rostral lengths for squids, and from lower hood lengths for octopods (Tables 3 and 4). Calculations of prey size were used to construct the

Craddock et al.: Food habits of Lagenorhynchus acutus off the coast of New England

387

388

Fishery Bulletin 107(3)

Craddock et al. : Food habits of lagenorhynchus acutus off the coast of New England

389

390

Fishery Bulletin 107(3)

20						red hake
15 :						/i=134 (summer=23, winter=1 11)
10 -
5 : 0 -	|	lu*.	Ml _	1.1.-,	.. illil litiLii i,	1 J . . 1 . _

V # # tff <§f $r

Length (mm)

Figure 2

Length-frequency distributions for fishes eaten by Atlantic white-sided dolphins ( Lagenorhynchus acutus ) in the Gulf of Maine (1991-2006). (A) Red hake (Uro- phycis chuss) all seasons; (B) haddock (Melanogrammus aeglefinus ) all seasons; (C) silver hake ( Merluccius bilinearis ) winter; (D) silver hake summer; (E) Atlantic herring (Clupea harengus) all seasons.

frequency diagrams shown in Figure 2 for the most abundant species.

Results and discussion

Stomachs of immature and adult dolphins of both sexes were examined. The two calves were 119 cm and 139 cm in length and had milk but no solid prey in their stomachs. The smallest juvenile was 161 cm and contained solid prey but no milk in its stomach. Females longer than 200 cm and males longer than 230 cm were considered mature (Sergeant et al., 1980) (Table 1).

Altogether, the 62 L. acutus stomachs contained 5561 fishes of at least 26 species, and 304 cephalopods of one octopus and two squid species (Table 2). Most of the stomach contents were trace remains. The most com- monly found prey species, in order of abundance, were;

1) Madeira lanternfish ( Ceratoscopelus maderensis), 3876 individuals, all but one from a single stomach;

2) silver hake (Merluccius bilinearis), 945 individuals from 22 stomachs; 3) sand lance ( Ammodytes spp.), 271 individuals from a single stranded dolphin; 4) spoonarm octopus ( Bathypolypus bairdii), 212 indi- viduals from 14 stomachs; 5) haddock (Melanogrammus aeglefinus ), 107 individuals from eight stomachs; 6) Atlantic hagfish (Myxine glutinosa ), 105 individuals

Craddock et at: Food habits of Lagenorhynchus acutus off the coast of New England

391

from 17 stomachs; and 7) red hake (Urophycis chuss), 103 individuals from 14 stomachs.

Gulf of Maine, winter

The 20 stomachs containing prey from L. acutus net- caught in winter in the Gulf of Maine provide our most complete data set for analysis (Table 3). These stomachs contained 1155 fishes of 17 species and 274 cephalopods of three species. Five species, three fishes and two ceph- alopods, silver hake (45.3%), spoonarm octopus (14.3%), haddock (15.3%), red hake (18.7%), and longfin inshore squid (1.1%) accounted for almost 95% of the mass of prey. We were unable to calculate the mass of hagfish; their toothplates (the only hard parts remaining in the stomachs) are not proportional to an individual’s size.

In order of frequency of occurrence and numerical abundance 1) the demersal silver hake was found in 90% of the stomachs and accounted for 71% of the fishes eaten; 2) the benthic spoonarm octopus were found in 65% of the stomachs and accounted for 77% of cephalopods; 3) the demersal haddock were found in 35% of the stomachs and made up 8.9% of the fishes; 4) the demersal red hake were found in 65% of the stomachs and accounted for 7.7% of the fishes; 5) the benthic scavenger hagfish were found in 50% of the stomachs and accounted for 7.5% of the fishes; and 6) the pelagic longfin squid were found in 60% of the stomachs and accounted for 23% of the cephalopods. The four fish species constituted 96% of the fish prey eaten, and the two cephalopods made up nearly all of the cephalopods consumed. Fishes made up 81% of all prey, and cephalopods, the remainder (19%). Notable were the scarcity or absence in winter of pelagic fish species (e.g., herring, alewives, smelt, mackerel, and sand lance).

Gulf of Maine, summer

Only three stomachs were available from animals net- caught in the Gulf of Maine in summer. These three contained 150 fishes of six species and six squids of two species (Table 4). The most abundant prey were silver hake, Atlantic herring, and red hake, which numeri- cally accounted for 63%, 19%, and 8% of total prey, respectively. These three species made up 29%, 64%, and less than 1% of total mass, respectively. Silver hake was numerically the most abundant species in both winter and summer stomachs. The pelagic Atlantic herring, which was almost absent in winter, was the most important species present in summer. The benthic spoonarm octopus, which was very abundant in the winter stomachs, was absent in summer.

Continental Slope south of Georges Bank

A single L. acutus was obtained south of Georges Bank near Munsen Canyon, in 500 m of water. This dolphin was a 252-cm lactating female. Its stomach contained over 3900 fishes of seven species (Table 4). Except for 37

silver hake and one white hake, this individual had been feeding on open-ocean pelagic fishes, of which 99% (3875) were Madeira lanternfish. Two other lanternfishes (the glacier lanternfish [Benthosema glaciate ] and the soft lanternfish [Diaphus mollis]), the white barracudina (Arctozenus risso), and the boa dragonfish (Stomias boa) were also present. This stomach contained 9.6 kg of prey, the largest amount of any L. acutus in this study; Madeira lanternfish made up 58% of the prey mass, and silver hake 41%.

Strandings

Stomachs of the stranded dolphins contained little iden- tifiable material (Table 1). No nontrace fish or cepha- lopods were present in any of these stomachs. About one-quarter of the otoliths (27%) were too digested to be identified or measured and therefore could not be used for further analysis. Of the identifiable otoliths, 87% were those of sand lance, all from one stomach (Table 2). The presence of these fish in that stomach was the only evidence indicating recent feeding.

Twenty-nine of the 34 strandings occurred in the winter. Stomachs of these dolphins contained eight fish species and three cephalopod species. Sand lance constituted 79% of all prey (both fishes and cephalo- pods) and made up 60% of the total mass. Silver hake and longfin squid made up 18% and 16% of the total mass, respectively. Five fish species present in the stomachs of stranded animals — cunner ( Tautogolabrus adspersus ), radiated shanny ( Ulvaria subbifui'cata), rainbow smelt, sand lance, and yellowtail flounder (Li- manda ferruginea) — were not found in the stomachs of our net-caught dolphins. Of the five stomachs from nonwinter strandings, four were empty and the fifth (in September) contained only one identifiable fish, a silver hake.

Prey species

In the Gulf of Maine, silver hake was by far the most important prey species in the stomachs that we exam- ined. A schooling, demersal fish, silver hake is found only along the Atlantic coast of North America, from Florida to Newfoundland, at a wide range of depths, from shallow waters to 900 m (Collette and Klein- MacPhee 2002; Iwamoto 2002). Previously, reports indicated the presence of silver hake in L. acutus diets but not as an important prey. Among the few otoliths found in stranded L. acutus stomachs, silver hake was the second most abundant prey species (Table 4).

Silver hake is also an important prey for other ma- rine mammals in the Gulf of Maine. It was a primary prey for harbor porpoise (Phocoena phocoena) during summer in the Bay of Fundy (Recchia and Read, 1989) and in autumn near Jeffreys Ledge in the western Gulf of Maine (Gannon et al., 1998). It was also the predomi- nant prey for net-caught young of the year harbor seals ( Phoca vitulina) taken in shallow waters in the western Gulf of Maine (Williams, 1999).

392

Fishery Bulletin 107(3)

Atlantic herring was present in stomachs of both winter and summer net-caught dolphins. It was of minor importance in the winter (only five individu- als identified in 20 stomachs analyzed), but was of primary importance (the largest biomass of all prey) in the summer; 29 individuals were present in the three stomachs analyzed. Lagenorhynchus acutus feeds on Atlantic herring in the summer months when the lipid content of herring is highest (Yasui and Gaskin, 1986). Even though only three stomachs from the sum- mer were analyzed, our findings are similar to those reported in the literature.

Lagenorhynchus acutus is rarely observed in the deeper waters of the continental slope south and east of New England (Selzer and Payne, 1988; Waring et al., 2008). The stomach contents of our single L. acutus taken incidentally in water 500 m deep, south of Georg- es Bank, were unlike those from the Gulf of Maine. The primary prey of this dolphin was the Madeira lanternfish, a myctophid living between 330 and 600 m during the day in slope water and on the continen- tal slope (Backus et al., 1968). This indicates that L. acutus is not limited to feeding on shallow-water and epipelagic species.

We have found that other species of cetaceans, when on the continental slope off the east coast of the Unit- ed States and southeastern Canada, feed primarily on Madeira lanternfish. We found large numbers, often more than 1000 individuals, in common dolphin (Del- phinus delphis), Atlantic spotted dolphin ( Stenella frontalis ), and pantropical spotted dolphin ( Stenella attenuata ), which had maximum numbers of 3646, 568, and 870 Madeira lanternfish, respectively. A single harbor porpoise (Phocoena phocoena) taken incidentally off Cape Hatteras in winter had nearly 500 Madeira lanternfish in its stomach (Read et al., 1996).

In the eastern North Atlantic Ocean, L. acutus feeds for the most part on oceanic fishes, primarily silvery pout ( Gadiculus argenteus ), lanternfishes, and pearl- sides (Maurolicus muelleri) (Couperus, 1997). Coupe- rus found that, in certain years, southwest of Ireland, L. acutus follow the spawning migration of mackerel ( Scomber scombrus) inshore in the late winter and spring and are caught by net in the mackerel fishery. A comparison of trace and nontrace prey in their stomachs indicated that although mackerel represented 88% of the fresh prey, the dolphins’ prior meals had comprised 88% mid-water fishes. Lagenorhynchus acutus feeds on herring when in shallow water off Norway (Jonsgard and Nordlii, 1952).

In addition to the above mentioned species, stomachs of L. acutus stranded on the coast of northern Europe have contained otoliths of blue whiting ( Micromesistius poutassou), tacauds (Trisopterus spp.), horse mackerel ( Trachurus trachurus), pilchard ( Sardina pilchardus), sand lances, pollock (Pollachius virens), whiting (Mer- langius merlangus), haddock, gobies (Gobiidae), drag- onet (Callionymidae), and argentine ( Argentina sphy- raena), (Desportes, 1985; Rogan et al., 1997; Santos et

al., 19951, 19962). Santos et al. (1995) also identified four species of cephalopods in the stomachs of L. acutus stranded in Scotland.

Despite previous observations of L. acutus feeding on sand lance (Weinrich et al., 2001), in this study we found sand lance in only one stomach, that of a stranded dolphin. Although approximately 50% of the stranded animals in our study had virtually empty stomachs, this one stomach contained 549 sand lance otoliths. The relatively empty stomachs indicate a lack of feeding before stranding. Little information exists on the digestion and egestion rates for cephalopod and teleost prey in cetaceans; therefore, it is impossible to accurately estimate how long a period elapsed between the last feeding and the stranding event (Mintzer et al., 2008). It is also possible that L. acutus regurgi- tates food because of the stress of a stranding event, leaving its stomach virtually empty. The trace sand lance otoliths found in the one stomach could have been trapped in the stomach rugae, giving a false impression of a recent meal. Regardless of when the sand lances were eaten, their presence in the stomach corroborates historic observations of L. acutus feeding on sand lance (Katona et al., 1978; Weinrich et al., 2001).

Lagenorhyncus acutus appears to exhibit size-selective predation; the average fish prey length is approximately 200 mm and cephalopod prey mantle length is about 50 mm during the winter (Fig. 2). The total lengths of the cephalopods (tentacle length plus the mantle length) are little more than half the length of the fishes. One large 464-mm silver hake, whose size was determined from a 22.4-mm otolith and two 100 mm dentaries, was found in the stomach of a winter net-caught dolphin. We assume that the dolphin ate only the head of this fish, which would itself have been approximately 200 mm. It is possible that the head had been cut off and discarded by fishermen.

Some very small red hake (less than 90 mm) were found in the stomachs of two L. acutus (Fig. 2A). These were smaller than the smallest silver hake, haddock, and herring eaten, and are therefore evidence of second- ary consumption. There were no large red hake or had- dock in either of the two stomachs. Large silver hake, the only predatory fish in each of the two L. acutus stomachs, was therefore the likely primary consumer of the small red hake.

Two cephalopods, spoonarm octopus and longfin in- shore squid, were both important prey in our L. acu- tus. In winter stomachs, the benthic octopus was the second most abundant prey species, and the pelagic squid was the sixth most abundant (Table 3). Histori- cal publications document northern shortfin squid in L.

1 Santos, M. B., G. J. Pierce, G. Wijnsma, H. M. Ross, and R. J. Reid. 1995. Diets of small cetaceans stranded in Scotland 1993-1995. ICES Council Meeting (C.M.). 1995/N:6, 9 p.

2 Santos, M. B., G. J. Pierce, A. Lopez, A. Barreiro, and A. Guerra. 1996. Diets of small cetaceans stranded in NW Spain 1994-95. ICES Council Meeting (C.M.). 1996/N:11, 6 p.

Craddock et al.: Food habits of Lagenorhynchus acutus off the coast of New England

393

acutus diets, but give no record of spoonarm octopus or longfin inshore squid. Spoonarm octopus was rare (one individual in 95 stomachs) in harbor porpoise from the Gulf of Maine (Gannon et al., 1998).

Both Atlantic hagfish and spoonarm octopus are bot- tom-dwelling species associated with sandy to muddy substrates on the continental shelf and upper slope. Spoonarm octopus is restricted to the western North Atlantic, and is found from Greenland to Florida (Muus, 2002). Atlantic hagfish is found on both sides of the North Atlantic and is bipolar, inhabiting comparable latitudes in the southern hemisphere (Collette and Klein-MacPhee, 2002). Lagenorhyncus acutus probably does not dive to the bottom to forage. It probably con- sumes benthic octopus and hagfish in several ways, namely 1) it may feed on catch unwanted and discarded by fishermen and 2) it may feed on animals that have been forced off the bottom by otter trawls or that have come off the bottom on their own, as with hagfish, to feed on fishes disturbed by otter trawls. Most of our net-caught dolphins (79%) were taken in bottom otter trawls. Spoonarm octopus and Atlantic hagfish were only found in dolphins caught in bottom otter trawls, not from those in sink or drift gillnets. Lagenorhyncus acutus feed in the vicinity of nets (Leopold and Coupe- rus, 1995), as do bottlenose dolphin ( Tursiops truncatus) (Corkeron et al., 1990) and other cetaceans (Fertl and Leatherwood, 1997). This would explain both the cap- ture of L. acutus by otter trawls and the occurrence of benthic animals in their diet.

Acknowledgments

We thank M. Moore and D. Rana for assistance sort- ing stomach contents. We also acknowledge K. Touhey, K. Pugliares, S. Herzig, C. Harry, and the volunteers of the Cape Cod Stranding Network; K. Patchett and K. Matassa, Marine Science Education and Research Center, University of New England; D. Potter, B. Len- tell, S. Wetmore, N. Gilles, and the Observers of the NOAA Fisheries Northeast Fisheries Science Center, Northeast Fisheries Observer Program (NEFOP); C. Potter, and M. Vecchione, Smithsonian Institution; R. Backus, M. Moore, A. Bogomolni, and R. Harbison,Woods Hole Oceanographic Institution; G. Early, Mote Marine Laboratory; K. Hartel and A. Williston, Museum of Comparative Zoology; J. Galbraith, J. Burnett, W. Duffy, B. Josephson, R. Merrick, F. Serchuk, S. Sutherland, G. Thornton, J. Kircun, and T. Vidal, Northeast Fisher- ies Science Center; C. Lea, Sea Education Association; M. Weinrich, Whale Center of New England; and one anonymous reviewer.

Literature cited

Backus, R. H., J. E. Craddock, R.L. Haedrich, D. L. Shores, J. M. Teal, A. S. Wing, G. W. Mead, and W. D. Clarke.

1968. Ceratoscopelus maderensis : peculiar sound-scatter-

ing layer identified with this myctophid fish. Science 1960:991-993.

Campana, S. E.

2004. Photographic atlas of fish otoliths of the North- west Atlantic Ocean, 284 p. NRC Research Press, Ottawa.

Clarke, M. R.

1962. The identification of cephalopod ‘beaks’ and the rela- tionship between beak size and total body weight. Bull. Br. Mus. (Nat. Hist.) Zool. 8:419-480.

Clarke, M. R., ed.

1986. A handbook for the identification of cephalopod beaks, 273 p. Clarendon Press, Oxford, U.K.

Collette B. B., and G. Klein-MacPhee.

2002. Bigelow and Schroeder’s fishes of the Gulf of Maine, 3rd ed., 748 p. Smithsonian Institution Press, Washington, D.C.

Corkeron, P. J., M. M. Bryden, and K. E. Hedstrom.

1990. Feeding by bottlenose dolphins in association with trawling operations in Moreton Bay, Australia. In The bottlenose dolphin (S. Leatherwood and R. Reeves, eds.), p. 329-336. Academic Press. San Diego, CA.

Couperus, A. S.

1997. Interactions between Dutch midwater trawl and Atlantic white-sided dolphins ( Lagenorhynchus acutus) southwest of Ireland. J. Northwest Atl. Fish. Sci. 22:209-218.

Desportes, G.

1985. La nutrition des odontocetes en atlantique nord- est (cotes Franfaises”-iles Feroe). Ph.D. diss., 190 p. Univ. Poitiers, Poitiers, France. [In French.]

Fertl, D., and S. Leatherwood.

1997. Cetacean interactions with trawls: a preliminary review. J. Northwest Atl. Fish. Sci. 22:219-248.

Gannon, D. P, J. E. Craddock, and A. J. Read.

1998. Autumn food habits of harbor porpoises, Phocoena phocoena, in the Gulf of Maine. Fish. Bull. 96:428- 437.

Gregory, W.K.

1933. Fish skulls. Trans. Am. Philo. Soc. 23(2), 481 p. Reprinted by Krieger Publishing Co. Malabar, FL 2002.

Harkonen, T.

1986. Guide to the otoliths of the bony fishes of the Northeast Atlantic, 256 p. Danbiu ApS. Hellerup, Denmark.

Iwamoto, T.

2002. Merluccidae. In The living marine resources of the western Central Atlantic, vol. 2 (K. E. Carpenter, ed.), p. 1017-1020. FAO, Rome.

Jonsgard, A., and O. Nordli.

1952. Concerning a catch of white-sided dolphins ( Lageno- rhynchus acutus) on the west coast of Norway, Winter 1952. Norsk Hvalfangst-Tidende 5:229-232.

Katona, S. K., S. A. Testaverde, and B. Barr.

1978. Observations on a white-sided dolphin, Lageno- rhynchus acutus, probably killed in gill nets in the Gulf of Maine. Fish. Bull. 76:475-476.

Leopold, M. F., and A. S. Couperus.

1995. Sightings of Atlantic white-sided dolphins Lageno- rhynchus acutus near the south-eastern limit of the known range in the north-east Atlantic. Lutra 38:77- 80.

Mintzer, V. J., D. P. Gannon, N. B. Barros, and A. J. Read

2008. Stomach contents of mass-stranded short-finned

394

Fishery Bulletin 107(3)

pilot whales (Globicephala macrorhynchus) from North Carolina. Mar. Mamm. Sci. 24(2):290-302.

Muus, B.

2002. The Bathypolypus-Benthoctopus problem in the North Atlantic (Octopodidae, Cephalopoda). Malaco- logia 44:175-222.

Northridge, S., M. Tasker, A. Webb, K. Camphuysen, and M.

Leopold.

1997. White-beaked Lagenorhynchus albirostris and Atlan- tic white-sided dolphin L.acutus distributions in north- west European and U.S. North Atlantic waters. Int. Whaling Comm. Rep. Comm. 47:797-805.

Palka, D., A. Read, and C. Potter,

1997. Summary of knowledge of white-sided dolphins ( Lagenorhynchus acutus ) from US and Canadian Atlantic waters. Int. Whaling Comm. Rep. Comm. 47:729-734.

Read, A. J., J. R. Nicolas, and J. E. Craddock.

1996. Winter capture of a harbor porpoise in a pelagic drift net off North Carolina. Fish. Bull. 94:381-383.

Recchia, C. A., and A. J. Read.

1989. Stomach contents of harbour porpoises, Phocoena phocoena (L.), from the Bay of Fundy. Can. J. Zool. 67:2140-2146.

Rogan, E., J. Baker, P. Jepson, S. Berrow, and O. Kiely.

1997. A mass stranding of white-sided dolphins ( Lageno- rhynchus acutus ) in Ireland: biological and pathological studies. J. Zool. 242:217-227.

Schevill, W. E.

1956. Lagenorhynchus acutus off Cape Cod. J. Mammal. 37(1):128-129.

Selzer, L. A., and P. M. Payne.

1988. The distribution of white-sided (Lagenorhynchus acutus) and common dolphins ( Delphinus delpliis) vs. environmental features of the continental shelf of the northeastern United States. Mar. Mamm. Sci. 4(2): 141-153.

Sergeant, D. E., and H. D. Fisher.

1957. The smaller Cetacea of eastern Canadian waters. J. Fish. Res. Board Can. 14:83-115.

Sergeant, D. E., D. J. St. Aubin, and J. R. Geraci.

1980. Life history and northwest Atlantic status of the Atlantic white-sided dolphin, Lagenorhynchus acutus. Cetology 37:1-12.

Smale, M. J., G. Watson, and T. Hecht.

1995. Otolith atlas of southern African marine fishes. Ichthyological Monographs of the J.L.B. Smith Institute of Ichthyology no. 1, xiv, 253 p. J.L.B. Smith Instit. Ichthyology, Grahamstown, South Africa.

St. Aubin, D. J., and J. R. Geraci.

1979. Strandings: a rare look into the biology of the Atlantic white-sided dolphin, Lagenorhynchus acutus. In Biology of marine mammals: insights through strandings (J. Geraci, and D. St. Aubin, eds.), p. 190-206. Mar Mamm. Comm., Washington, D.C.

Vecchione, M.

2002. Cephalopods. In The living marine resources of the western Central Atlantic, vol. 1 (K. E. Carpenter, ed.), p. 149-244. FAO, Rome.

Waring, G. T., E. Josephson, C. P. Fairfield-Walsh, and K. Maze- Foley, eds.

2008. U.S. Atlantic and Gulf of Mexico marine mammal stock assessments — 2007. NOAA Tech. Memo. NMFS- NE -205: 120-128.

Weinrich, M. T., C. R. Belt, and D. Morin.

2001. Behavior and ecology of the Atlantic white-sided dolphin ( Lagenorhynchus acutus) in coastal New England waters. Mar. Mamm. Sci. 17(2):231-248.

Williams, A. S.

1999. Prey selection in harbor seals in relation to fish taken by the Gulf of Maine sink gillnet fishery. M.S. thesis, 62 p. Univ, Maine, Orono, ME.

Yasui, W. Y., and D. E. Gaskin.

1986. Energy budget of a small cetacean, the harbor por- poise, Phocoena phocoena (L.). Ophelia 25(3):183-197.

395

Abstract — Assuring the vitality and survival potential of live-caught Atlantic cod ( Gadus morhua) is important for improving the sorting of fish before net penning operations designed to hold fish for growth and later market. When Atlantic cod are captured by Danish seine, the most commonly used fishing gear for live- caught fish, they undergo stressors such as forced swimming, net abra- sion, and air exposure. Laboratory experiments (at an air temperature of 9°C and water temperature of 8°C) were conducted with the aim of constructing a RAMP (reflex action mortality predictor) curve for predic- tion of vitality and survival potential in Atlantic cod captured in Danish seines, by varying the levels of these stressors. Atlantic cod exposed to increased duration in air (5-20 min) showed increased reflex impairment and mortality, with 75% mortality at 10 minutes of air exposure. Forced swimming in combination with net abrasion and air exposure did not increase reflex impairment or mor- tality above that associated with air exposure alone. The Atlantic cod RAMP curves indicated that fish with reflex impairment less than 50% would not show mortality and would likely recover from capture stress.

Manuscript submitted 29 October 2008. Manuscript accepted 6 May 2009.

Fish. Bull. 107:395-402 (2009).

The views and opinions expressed or implied in this article are those of the author and do not necessarily reflect the position of the National Marine Fisheries Service, NOAA.

Reflex impairment as a measure of vitality and survival potential of Atlantic cod ( Gadus morhua)

Odd-Berre Humborstad (contact author)'

Michael W. Davis2 Svein Lokkeborg1

E-mail address for contact author: oddb@imr.no

1 Institute of Marine Research Nordnesgaten 50

PO. Box 1870

Nordnes, N-5817 Bergen, Norway

2 NOAA Fisheries, Alaska Fisheries Science Center Fisheries Behavioral Ecology Program

Hatfield Marine Science Center Newport, Oregon 97365

In capture-based aquaculture (CBA; Ottolenghi et al., 2004), fish are caught live and held in net pens to supply high-quality fresh fish throughout the year and thereby increase the value of the catch, given a fixed boat quota. Animal welfare issues in CBA arise when handling stress and adaptation costs to new environments are added to the capture stress. Also the dura- tion of stress will increase dramati- cally compared to that of traditional commercial fishing where the human impacts on fish end with slaughtering immediately after capture. Improv- ing fish welfare in CBA should be achieved by keeping and storing only vital specimens after a sorting pro- cess. Operational indicators of vitality and survival potential are therefore needed.

Current sorting criteria include re- moving specimens showing any visual sign of damage such as injuries from net abrasion and mechanical han- dling. Also specimens having clear signs of barotrauma such as gas filled eyes (exophthalmia) or overinflated abdomens due to punctured gas- bladders are poor candidates for live storage and should be removed. This practice combined with the use of spe- cialized transport tanks and net pens, and the implementation of careful handling routines and monitoring of water quality have greatly decreased instantaneous and postsorting mor- tality. Still some delayed mortality

occurs in seemingly unharmed speci- mens because the internal status of the animal is not readily evaluated by visual inspection. Thus there is the potential for improving the sort- ing process before the transfer of fish to tanks or net pens by developing operational indicators of vitality and survival potential.

To date there are several physi- ological and behavioral indicators of fish condition available; however, they share the unfavorable attributes of being expensive and labor intensive and are therefore not suited for rou- tine use in commercial fisheries. More importantly, although applicable for determining sublethal stress levels, they show a lack of concordance with mortality outcomes (Davis et al., 2001; Davis and Schreck, 2005). Recently, reflex impairment has been tested as an indicator of vitality and survival potential (Davis and Ottmar, 2006; Davis, 2007). Correlations between stressor intensity, reflex impairment, and increased mortality were found for several species of round fish and flat fish exposed to simulated capture stressors.

The main objective of this study was to test whether reflex impair- ment could be used as a rapid real- time operational indicator to predict vitality and survival outcomes in fishing operations designed to hold Atlantic cod ( Gadus morhua, hereaf- ter referred to as “cod”) in net pens

396

Fishery Bulletin 107(3)

Table t Reflex actions that were consistently present in 20 control (unstressed) Atlantic cod (Gadus morhua ) and used to measure reflex impairment in fish exposed to stressors (forced swimming, net abrasion, and air exposure) associated with capture by Danish seines.
Reflex	Description
1. Body flexion 1	Fish flexed body when placed on a flat surface (sorting table).
2. Body flexion 2	Fish flexed when restrained.
3. Head complex	Restrained fish presented alternating mouth gaping and operculum flaring, as if gasping for air.
4. Operculum	Restrained fish either flared operculum rigidly open or strongly clamped operculum shut when
	operculum was lifted with a probe.
5. Gag	Restrained fish gaged when back of throat was stimulated with a probe.
6. Vestibular-ocular	Restrained fish tracked observer when it was rotated around long axis.
response (VOR)
7. Tail flexion	Fish held under belly flexed when tail flanks were stroked by hand along long axis.

for additional growth and later marketing (CBA pur- poses). The Danish seine is the most commonly used fishing gear for CBA, and the stressors tested in this study, forced swimming, net abrasion, and air exposure, are typical in and inherent to this type of fishing gear. A series of experiments were conducted to construct a RAMP (Reflex Action Mortality Predictor) curve for cod exposed to these stressors and we broadly followed the three step procedures in Davis (in press) to validate reflex impairment as an indicator of vitality.

First we established appropriate procedures for test- ing fish reflexes by determining consistent reflexes for testing; we established the effect of repeated reflex test- ing in control fish to test whether cod were distressed by the testing procedure; we determined the recovery time after exposure to a stressor; and we determined the effect of disturbance from repeated netting of fish from a holding tank.

Second we established experimental methods for ex- posing fish to key stressors and conducted stress experi- ments to determine the effect of air exposure and the combined effect of forced swimming, net abrasion, and air exposure on reflexes and survival.

Third after observing immediate and delayed mortal- ity, we correlated reflex impairment and mortality by producing RAMP curves for the effect of air exposure and the combined effect of forced swimming, net abra- sion, and air exposure.

Materials and methods

Experimental fish

Cod were hatched and later reared in net pens at Auste- voll Research Station (60°05'17"N 5°15'50"E), Austevoll, Norway. Five months prior to the experiments, fish were moved (after six months in net pens) to indoor -1600-L green fiberglass tanks with rounded corners (145 cm x 145 cm x 100 cm depth, water depth 80 cm), supplied with aerated sea water (8.0 ±1.0°C), and fed

standard commercial diets (Skretting Ltd, Stavanger, Norway) to satiation by using 24-hr disc feeders (1% of total biomass per day) under a continuous daylight regime. A total of 169 fish (31-49 cm total length [TL]) were tested for reflex impairment and mortality experi- ments. In order to maintain independence of observation no fish was used more than once.

Step 1: Consistent reflexes and appropriate procedures for reflex testing

A number of reflex actions in cod for potential inclusion in this study were identified based on previous work (e.g., Davis, 2007) and preliminary trial and error screen- ing on fishing vessels and in the laboratory. In order to identify the reflexes for testing and to standardize methods and stimuli to elicit these reflex actions, twenty cod were initially tested. Seven reflexes were found to be consistently present in control fish (Table 1). For subse- quent reflex impairment tests, the reflexes were scored as 1 (present) if a vigorous response was evident, or 0 if the response was not present or of weak or questionable strength. Reflex scoring insured consistent, high quality response data (Davis, in press).

To test reflex actions, fish were initially placed on a flat surface, corresponding to a sorting table on a fishing vessel and observed for spontaneous body flex- ing. Then fish were placed and held in a restraining device (Fig. 1) consisting of two plastic pieces (60 cm length x 10 cm width), each lined with a sponge to con- tact and hold fish, and connected at one end to form a hinge, while the other end was secured with a Velcro strap. Fish were then observed for body flexion in re- sponse to restraint. The restrained fish were then tested for reflexive head movements (a spontaneous alternating head and operculum movement), operculum movement (either tight closure or flaring after having been lifted with a probe), gag in response to throat stimulation, and vestibular-ocular response (eye rotation while the fish was rotated around its long axis). Finally fish were released from restraint and tested for body flexion in

Humborstad et al.: Reflex impairment as a measure of survival potential for Gadus morhua

397

Figure 1

Fish restraining device used to test reflex actions in Atlantic cod ( Gadus morhua). In this photograph, the fish is being tested for operculum reflex action.

response to hand stroking of the tail flanks along the long axis while being held under the abdomen. The en- tire sequence for reflex testing in a replicate fish was conducted within 60 seconds.

Repeated reflex testing was conducted with a group of ten fish to determine if cod were stressed by the reflex testing procedure itself. These fish were netted, restrained, and their reflexes were tested at 0, 60, and 180 minutes after the initial netting and restraint. Between each sampling time, fish were placed back into a tank with sea water and recaptured for the next reflex test.

The effect of recovery time (0-15 min) on reflexes af- ter exposure of fish to stressors was tested to determine an appropriate time to sample cod reflexes. Replicate fish (n = 35) were exposed to standard stressors (see de- tailed description of stressor administrations below in step 2) of 5 minutes of swimming, 1 minute of net abra- sion, and 5 minutes in air (all at 9.0°C). Then fish were returned to the stock tank and reflex testing was begun at 0, 5, 7, 10, or 15 minutes after exposure to stressors and completed within 8 minutes from starting time of testing for each exposure group [n-1 per group).

It was possible that disturbance from repeated net- ting of fish from a stock tank before netting replicate fish for stressor treatment could have affected the level of reflex impairment resulting from exposure to stress- ors, because fish could have been repeatedly stressed

by being chased before capture. To test this possibility, fish were exposed to 5 minutes of swimming, 1 minute of net abrasion, and 10 minutes of air exposure (all at 9.0°C) after being either captured from a tank (n = 8) in which four fish had been previously captured or from a tank (n- 8) in which 16 fish had been previously cap- tured. Then fish were returned to the tanks and reflex testing began 5 minutes after exposure to stressors and was completed within 9 minutes from the start of testing for each exposure group. Fish were then held to determine mortality. Immediate and delayed mor- tality resulting from stressors was observed by holding fish in tanks for 60 days and removing and counting dead fish daily (mortality observed as common death signs, e.g., motionlessness, static flaring of operculum, nonresponsiveness to touch stimuli, rigor mortis). The rearing regime for the stressed fish was similar to stock tank fish.

Step 2: Stressors, exposure experiments, and stress induction

Stressors were selected to mimic the stressors cod expe- rience during capture during Danish seine operations and to create a gradient of stress from low to moderate to lethal. Exposure to air was chosen for its known importance as a stressor for fish sorted on deck. Forced swimming is a relevant capture stressor. Net abrasion

398

Fishery Bulletin 107(3)

is important during haulback operations and transfer of fish from the seine to the boat in CBA. Moderate intensity of abrasion was administered in the experi- ment because these injuries are likely to occur during sorting and may increase the risk for infection, disease, and delayed mortality. Fish exposed to these stressors (air exposure, forced swimming, moderate net abrasion) may not have obvious external injury and the effects of such stressors may be difficult to assess by visual inspection during sorting. Moreover fish experiencing different levels of such stressors may differ in internal status and survival potential.

Exposure to air was caused by placing fish in a tank without water to simulate conditions that would occur during sorting on deck (on the sorting table) after cap- ture, and the intensity of the stressor was controlled by altering exposure duration. The swimming stressor was created by forcing fish to swim against a current cre- ated by lowering the water level in a tank (145 cm x 145 cmx8 cm water depth) in which water was introduced along the tank wall to cause a circular current of ap- proximately 20 cm/s. This stressor intensity was varied by controlling the amount of time that the fish was forced to swim against the current. Net abrasion was caused by capturing the fish in a net and sloshing them up and down at the water surface in a tank for a fixed time of one minute. After administration of stressors the fish were placed into a stock tank, and one indi- vidual at a time was taken out for reflex testing.

The effect of exposure to air alone was tested in cod (n = 32) exposed to either 5, 7, 10, or 20 minutes of air (all at 9.0°C). After air exposure, fish were placed into a stock tank and then individuals were taken out for re- flex testing. Testing began 5 minutes after the exposure to air ended and was completed within 9 minutes from the start of testing for each exposure group (n = 8 per group). Fish were then held to determine mortality.

The effect of exposure to seven combinations of swim- ming, net abrasion, and air was determined to simu- late stressors associated with capture by Danish seine. Replicate fish (n = 56) were exposed to swimming for 5, 10, or 15 minutes, net abrasion for 1 minute, and air for 5, 10, or 15 minutes (all at 9.0°C). Then fish were returned to tanks and reflex testing began 5 minutes after exposure to stressors and was completed within 9 minutes from the start of testing for each exposure group (?? = 8 per group). Fish were then held to observe mortality.

Step 3: RAMP curves and statistics

The proportion of reflex impairment in each fish was calculated as follows: 1 - (the sum of individual reflex scores /the total possible score of 7), i.e,. the proportion of reflex impairment was 2/7 if five out of the seven reflex actions (see Table 1) were present. Mortality for indi- vidual fish was scored as 1 (present) or 0 (absent) and the mortality date was noted. Statistical significance of correlation between reflex impairment and mortality was tested by using Spearman rank correlation. Sigmoid

curves (RAMP curves) showing relationships between reflex impairment and mortality were fitted by using SigmaPlot vers. 10.0 (Systat Software, Inc., Chicago, IL). When control fish reflexes were sampled repeatedly, the effects on reflex impairment were tested with Friedman analysis of variance (ANOVA), whereas the effects of sampling time, air exposure time, forced swimming, net abrasion, and air exposure were tested with Kruskal- Wallis ANOVA. The effect of disturbance on reflexes was tested with a two sample /-test. Statistical significance was accepted at P<0.05.

Results

Step 1: Appropriate procedures for reflex testing

Reflexes in control (unstressed) cod were not impaired by repeated testing at 0, 60, and 180 minutes after initial capture from a stock tank (ANOVA, F2g=0.64, P= 0.728), indicating that cod were not stressed by the reflex-testing procedure itself. Mean reflex impairment (proportion) for each testing period ranged from 0.03 to 0.06 and no mortality occurred.

Reflex impairment occurred immediately after ex- posure to 5 minutes of swimming, 1 minute of net abrasion, and 5 minutes of air exposure and was not significantly changed (mean ±1 standard error) by the time of sampling when sampled at 0 (0.71 ±0.08), 5 (0.65 ±0.03), 7 (0.61 ±0.05), 10 (0.50 ±0.07), or 15 min- utes (0.51 ±0.07) after exposure to stressors (ANOVA, F34= 7.92, P=0.095). These results indicate that reflex actions are real-time indicators of stress, and recovery does not happen within the first 15 minutes after ex- posure to stressors.

Repeatedly disturbing fish (16 times) in a stock tank by chasing and netting fish out of the tank before net- ting fish for stressor treatment did not result in in- creased mean (±1 standard error) reflex impairment (0.86 ±0.08) or mortality (0.75 ±0.16) after the fish were subjected to 5 minutes of swimming, 1 minute of net abrasion, and 10 minutes of air exposure when compared to repeatedly disturbing fish (4 times) (reflex impairments. 82 ±0.08; mortality=0.50 ±0.19), after the fish were exposed to the same stressors (reflex im- pairment /-test, /14 = 0.32, P=0.751; mortality /-test, /14=1.00, P=0.334).

Step 2: Exposure experiments

Cod exposed to increased duration in air (5, 7, 10, and 20 minutes) showed increased reflex impairment (ANOVA, F31=17.11, P < 0.001; Fig. 2). Mortality also increased with increased air exposure (ANOVA, P31=17.87, P<0.001; Fig. 2). Air exposure was an important stressor and mor- tality increased rapidly as the duration of time that fish were exposed to air increased, and 75% mortality was observed at 10 minutes of air exposure. At 20 minutes of air exposure 100% mortality was observed. No imme- diate mortality was observed from any of the air expo-

Humborstad et al.: Reflex impairment as a measure of survival potential for Gadus morhua

399

sure experiments, whereas 94% mortality (delayed mortality) occurred within 1 day (16 fish) and one fish died after 6 days.

Forcing cod to swim for 5, 10, or 15 min- utes at 20 cm/s in combination with net abrasion and air exposure did not increase reflex impairment or mortality above that associated with air exposure alone. Reflex impairment increased with increased ex- posure to a combination of swimming, net abrasion, and air, and this effect appeared to be associated primarily with increased duration in air (ANOVA, F'55 = 28.82, P<0.001; Fig. 3). Likewise, mortality in- creased with increased exposure to these stressors, and mortality appeared to be primarily associated with air exposure (ANOVA, F55 = 25.15, PcO.OOl; Fig. 3). Cod injury from net abrasion was not obvious, other than the presence of sloughed scales on the net. No immediate mortality was observed from any of the combined stress- ors, whereas 94% of observed delayed mor- tality occurred within 1 day (15 fish) and one fish died after 14 days.

Step 3: RAMP curves

Reflex impairment and mortality were correlated for individual cod exposed to air (Spearman rank correlation = 0.85, PcO.OOl, n=32) and when exposed to swim- ming, net abrasion, and air (Spearman rank correlation =0.85, PcO.OOl, n = 64). The relationship between reflex impair- ment and mortality was sigmoid (RAMP curve), initially showing increasing reflex impairment with no mortality, followed by a sharp increase in mortality at reflex impairment values > 0.6 (Fig. 4A). The relationship between reflex impairment and mortality calculated for cod in groups defined by experimental treatments that combined swimming, net abrasion, and air exposure (Fig. 4B) showed a simi- lar pattern to that shown by the RAMP curve for individual fish, indicating that reflex impairment could predict mortality in populations of cod, as well as in indi- vidual fish.

Discussion

10,5 5,10 15,10

Swim time, air exposure time (min)

Figure 3

Atlantic cod ( Gadus morhua) mean proportion of reflex impairment (•) and mortality (A) for seven treatment groups (n = 8 fish per treatment group) increased with increased stressor intensity. Fish were exposed to combinations of swimming (5, 10, and 15 minutes), net abrasion (1 minute), and air (5, 10, and 15 minutes). There were two groups of mean (±1 standard error) values that were significantly different (indicated by a, b).

Capture-based aquaculture (CBA) is a combination of capture by commercial fisheries and rearing by aquaculture. In this article we address key stressors associated with the capture portion of CBA. Stress and mortality in fish from com- mercial fisheries often result from several classes of

interacting acute stressors. These classes include cap- ture stressors (net entrainment, mesh passage, crushing, wounding, sustained swimming until exhaustion, and pressure changes), fishing conditions (towing time, light

400

Fishery Bulletin 107(3)

conditions, water and air temperatures, hypoxia, sea conditions, time on deck, and handling procedures), and biological attributes (behavior, size, and species) (Davis, 2002). This study demonstrated that reflex impairment can be used to assess vitality and survival potential of cod exposed to capture related stressors such as forced swimming, net abrasion, and air exposure. Cod showed reflex impairment immediately after exposure to stress- ors, suggesting that reflex actions are sensitive real time indicators that integrate neurological, hormonal, and

behavioral states that can be related to changes in fish vitality and welfare (Davis, in press). Importantly, the testing of reflex actions did not cause reflex impairment, indicating that cod were not stressed by the procedure. Also, disturbances caused by repeated netting of fish from the holding tank did not affect the level of reflex impairment resulting from exposure to stressors.

The RAMP curves for individuals and groups indi- cated that cod with less than 50% reflex impairment would not die and would likely recover from capture stress to resume normal feeding and growth. Similar correlations between stressor intensi- ty, reflex impairment, and increased mortality were found for several species of roundfish and flatfish exposed to simulated capture stressors (Davis and Ottmar, 2006; Davis, 2007). Future measurements of reflex impairment and mor- tality in cod caught by Danish seine and held in net pens can be used to validate the labora- tory RAMP curves for use in CBA operations. Experiments could be designed to expose cod to gradients of capture-related stressors in the field, to test for reflex impairment, and then to hold fish in the field in order to determine delayed mortality. Reflex impairment and mor- tality results from field stressor experiments could be compared with mortality rates that were predicted with the laboratory RAMP curve for cod. Possible differences in prediction of mor- tality rates between laboratory- and field-de- rived RAMP curves may be evident as a shift in the relationship between reflex impairment and mortality. These difference would be likely caused by the addition of stressor types in Dan- ish seine operations that were not included in the laboratory experiments. In general the types of stressors and not the intensity of stressors control the shape of the RAMP curve (Davis, in press). The RAMP curves could also be applied to estimate survival of escapees and discarded fish (e.g., Davis and Ottmar, 2006; Ingolfsson et al., 2007; Enever et al., 2009) and to improve selection of cod with high survival potential in tagging studies (Fowler and Stobo, 1999; Brat- tey and Cadigan, 2004). Also our result for time of delayed mortality is of interest in relation to tagging studies; because 94% of delayed mortal- ity occurred within 24 hours, holding fish for one day before release should reduce tagging mortality to negligible levels.

Exposure to air should be avoided when pos- sible for cod, but if inevitable, it should be kept below safe levels. Air exposure was the most important stressor associated with mortality in cod with 40% mortality observed at 7 minutes, 75% at 10 minutes, and 100% at 20 minutes (Fig. 2). However, during the reflex testing pro- cedures, air exposure of one minute or less did not induce reflex impairment or mortality and thus represents a conservative, safe level of ex-

— i 1 1 r 1 1

0.0 0.2 0.4 0.6 0.8 1.0

Reflex impairment (proportion)

Figure 4

Reflex impairment (proportion) could predict (A) mortality (absent 0, present 1) in individual Atlantic cod ( Gadus morhua), or (B) mean mortality (proportion) in populations of cod exposed to combinations of forced swimming, net abrasion, and air (see Methods section). For individual (•) cod in (A), the sigmoid curve (y=l. 471/(1 + e -(x-o. 935/0. 104)) +95 % confidence intervals was significant (r2 = 0.84, P < 0.001, n = 6 4). Note that many points overlap. For populations (A) of cod (B), defined by calculat- ing mean proportions for reflex impairment and mortality in ten combination stressor treatment groups (including control and 100% mortality groups), the sigmoid curve (y = l. 130/(1 + e -u-o. 809/0. 113)) +95 % confidence intervals were significant (r2= 0.97, P<0.001, n = 10). Note that two points overlap.

Humborstad et at: Reflex impairment as a measure of survival potential for Gadus morhua

401

posure. Sensitivity to air exposure has been shown to vary among species, with mortality occurring at 7 to 45 minutes of exposure (Davis, 2002). Air exposure is often inevitable during sorting in live-capture operations, and duration in air can be reduced to safe levels, e.g., by the introduction of water-filled sorting tables.

Increased temperature is another stressor that has been associated with mortality in captured fish and may become important if cod are captured or sorted at temperatures above 12°C (Davis, 2002; Sartoris et al., 2003; Brattey and Cadigan, 2004; Suuronen et al., 2005). Increased temperature may also raise sensitiv- ity to air exposure (Davis and Parker, 2004; Davis and Schreck, 2005). Temperatures in deep (200 m) and shallow (surface) water peak in July and August (at ~3 and ~8°C, respectively) in coastal areas suitable for CBA in northern Norway (Loeng, 1991). During spring months when capture for CBA purposes occurs, mixing in these areas is high, and temperatures remain around ~3°C throughout the water column and air temperature only rarely raises above 12°C in May (data from The Norwegian Meteorological Institute, Blindern, Oslo). Temperature should thus not be a critical factor at the temporal and spatial scales of current CBA practices in Norway, and accordingly we did not include temperature as a variable in our study. However attempts to develop CBA outside this temporal and spatial window (e.g., North Sea during summer months), warrant a high vigilance of temperature effects.

A likely effect of adding a stressor is that it may cause an increase in the overall stress response. How- ever, forcing cod to swim for 5, 10, or 15 minutes at 20 cm/s in combination with net abrasion and air expo- sure did not increase reflex impairment or mortality above that associated with exposure to air alone. This result even indicated that swimming for 10 minutes may have enhanced resistance to air exposure, having a palliative effect on the induction of further stress. In a study of free swimming cod, oxygen consumption did not increase until fish were swimming at 30 cm/s or higher, indicating that at less than 30 cm/s cod would not be stressed (Claireaux et al., 1995). Although not directly relevant to this study, sustained slow swim- ming in rainbow trout ( Oncorhynchus mykiss) and coho salmon ( Oncorhynchus kisutch) has reduced the dura- tion of recovery from exhaustive exercise (Farrell et al., 2001; Lee-Jenkins et al., 2007). Little is known about the palliative effects of low-intensity exercise in fish, either before or after exposure to stressors. Studies of the swimming performance of cod have been focused on measurements of endurance and burst swimming (40- 130 cm/s) and have included an evaluation of changes in the scope for metabolic activity (Reidy et al., 2000). Further study of the interactive effects of low-intensity exercise, the perception of stressors by fish, and their management of stress may contribute to methods for the significant reduction of stress in captured, released, transported, and net-penned fish.

Injury to cod from net abrasion was not obvious, other than the presence of sloughed scales on the net, and did

not appear to contribute to delayed mortality or reflex impairment. Fish with obvious damage to the skin, fin erosion (split fins), cataracts or opaque eyes, resulting from severe abrasion from net material will not pass the sorting procedure in CBA. Therefore a moderate intensity of abrasion was administered in this experi- ment because these injuries are not likely to be detected during sorting and may increase the risk for infection, disease, and delayed mortality. Such effects of moder- ate net abrasion were, however, not demonstrated in our experiment. Mortality rarely occurred in cod that were injured by net abrasion when escaping from a demersal trawl (Soldal et al., 1993). Injury to cod from fishing gear can occur, however; Baltic cod have been observed with a high incidence (48%) of skin infection probably associated with escape from fishing gear, but associated mortality was not determined (Mellergaard and Bagge, 1998). In other studies of net abrasion and consequent mortality, some species (herring, [ Clupea harengus ], and walleye Pollock [ Theragra chalcogram- ma ] were sensitive to net abrasion and showed delayed mortality associated with skin infection (Suuronen et al., 1996; Davis and Ottmar, 2006), whereas other spe- cies (sablefish [Anoplopoma fimbria ] and Pacific hali- but [ Hippoglossus stenolepis ] were more resistant and mortality was not correlated with skin abrasion (Davis and Ottmar, 2006).

Capture, transport, and holding of fish are often asso- ciated with induction of stress and reduction of vitality. Reflex impairment could be used to evaluate the role of different stressors at each stage of the live-fish fishery and to identify fish with the highest probability for sur- vival. Successful live-fish capture, transport, and rear- ing operations should aim to minimize stress, optimize water quality, and minimize the increase of metabolic wastes (Huntingford et al., 2006; Ashley, 2007). Water quality and temperature must be controlled through in- puts, tank and pen configurations, and flow rates. Food (e.g., Olsen et al., 2008) and stocking density (Staurnes et al., 1994) may be important factors because they control physiological and behavioral states of fish. The adjustments of wild fish to confinement and unnatural densities and how these short-term adjustments affect future performance and welfare are also important considerations. Reflex testing may be performed also in free-swimming fish (Davis and Ottmar, 2006; Stien et al., 2007), and monitoring reflex impairment in captive fish can be a rapid real-time method for identifying op- timal transport and rearing conditions and for tracking recovery in cod after live capture.

Acknowledgments

The authors are grateful to Anders Mangor- Jensen for organizing and providing facilities and fish at the Austevoll Research Station in Norway, and for assis- tance during experiments. Shale Rosen is thanked for assistance carrying out experiments. Anne-Britt Skaar Tysseland is thanked for calculations of swimming speed

402

Fishery Bulletin 107(3)

and 0rjan Eknes is thanked for rearing our fish. The work was funded by the Norwegian Research Council (173193, Fish welfare in capture-based aquaculture and 173538, Physiological and behavioral indicators for fish welfare assessment in aquaculture and fish capture).

Literature cited

Ashley, P. J.

2007. Fish welfare: current issues in aquaculture. Appl. Anim. Behav. 104:199-235.

Brattey, J., and N. Cadigan.

2004. Estimation of short-term tagging mortality of adult Atlantic cod ( Gadus morhua). Fish. Res. 66:223- 233.

Claireaux, G., D. M. Webber, S. R. Kerr, and R. G. Boutilier.

1995. Physiology and behaviour of free-swimming Atlan- tic cod ( Gadus morhua) facing fluctuating temperature conditions. J. Exp. Biol. 198:49-60.

Davis, M. W.

2002. Key principles for understanding fish bycatch discard mortality. Can. J. Fish. Aquat. Sci. 59:1834- 1843.

2007. Simulated fishing experiments for predicting delayed mortality rates using reflex impairment in restrained fish. ICES J. Mar. Sci. 64:1535-1542.

In press. Fish stress and mortality can be predicted using reflex impairment. Fish and Fisheries.

Davis, M. W„ B. L. Olla, and C. B. Schreck.

2001. Stress induced by hooking, net towing, elevated sea water temperature and air in sablefish: lack of con- cordance between mortality and physiological measures of stress. J. Fish Biol. 58:1-15.

Davis, M. W., and M. L. Ottmar.

2006. Wounding and reflex impairment may be predic- tors for mortality in discarded or escaped fish. Fish. Res. 82:1-6.

Davis, M. W., and S. J. Parker.

2004. Fish size and exposure to air: potential effects on behavioral impairment and mortality rates in discarded sablefish. N. Amer. J. Fish. Manag. 24:518-524.

Davis, M. W., and C. B. Schreck.

2005. Responses by Pacific halibut to air exposure: lack of correspondence among plasma constituents and mortality. Trans. Am. Fish. Soc. 134:991-998.

Enever, R., A. S. Revill, and A. Grant.

2009. Discarding in the North Sea and on the historical efficacy of gear-based technical measures in reducing discards. Fish. Res. 95:40-46.

Farrell, A. P., P. E. Gallaugher, and R. Routledge.

2001. Rapid recovery of exhausted adult coho salmon after commercial capture by troll fishing. Can. J. Fish. Aquat. Sci. 58:2319-2324.

Fowler, G. M., and W. T. Stobo.

1999. Effects of release parameters on recovery rates of

tagged groundfish species. Can. J. Fish. Aquat. Sci. 56:1732-1751.

Huntingford, F. A., C. Adams, V. A. Braithwaite, S. Kadri, T. G.

Pottinger, P. Sandpe, and J. F. Turnbull.

2006. Current issues in fish welfare. J. Fish Biol. 68:332-372.

Ingolfsson, O. A., A. Soldal, I. Huse, and M. B. Breen.

2007. Escape mortality of cod, saithe, and haddock in a Barents Sea trawl fishery. ICES J. Mar. Sci. 64:836- 1844.

Lee- Jenkins, S. S. Y., T. R. Binder, A. P. Karch, and D. G. McDonald.

2007. The recovery of locomotory activity following exhaustive exercise in juvenile rainbow trout ( Oncorhyn - chus mykiss ). Physiol. Biochem. Zool. 80:88-98.

Loeng, H.

1991. Features of the physical oceanographic conditions of the Barents Sea. Pol. Res. 10 (1):5-18.

Mellergaard, S., and O. Bagge.

1998. Fishing gear-induced skin ulcerations in Baltic cod, Gadus morhua L. J. Fish Dis. 21:205-213.

Olsen, R.E., K. Sundell, E. Ringo, R. Myklebust, G. I. Hemre, T.

Hansen, and 0. Karlsen.

2008. The acute stress response in fed and food deprived Atlantic cod, Gadus morhua L. Aquacult. 280:232- 241.

Ottolenghi, F., C. Silvestri, P. Giordano, A. Lovatelli, and M. B.

New.

2004. Capture-based aquaculture. The fattening of eels, groupers, tunas and yellowtails, 308 p. FAO, Rome.

Reidy, S. P., S. R. Kerr, and J. A. Nelson.

2000. Aerobic and anaerobic swimming performance of individual Atlantic cod. J. Exp. Biol. 203:347-357.

Sartoris, F. J., C. Bock, I. Serendero, G. Lannig, and H. O.

Portner.

2003. Temperature-dependent changes in energy metabo- lism, intracellular pH and blood oxygen tension in the Atlantic cod. J. Fish Biol. 62:1239—1253.

Soldal, A. V., B. Isaksen, and A. Engas.

1993. Survival of gadoids that escape from a demersal trawl. ICES Mar. Sci, Symp.

196:122-127.

Staurnes, M., T. Sigholt, H. P. Pedersen, and T. Rustad.

1994. Physiological effects of simulated high-density transport of Atlantic cod ( Gadus morhua). Aquacult. 119:381-391.

Stien, L. H., S. Bratland, I. Austevoll, F. Oppedal, and T. S.

Kristiansen.

2007. A video analysis procedure for assessing vertical fish distribution in aquaculture tanks. Aquacult. Eng. 37:115-124.

Suuronen, P, D. L. Erickson, and A. Orrensalo.

1996. Mortality of herring escaping from pelagic trawl codends. Fish. Res. 25:305—321.

Suuronen, P., E. Lehtonen, and P. Jounela.

2005. Escape mortality of trawl caught Baltic cod ( Gadus morhua) — the effect of water temperature, fish size and codend catch. Fish. Res. 71:151-163.

403

Fishery Bulletin

Guidelines for authors

Manuscript Preparation

Contributions published in Fishery Bulletin describe original research in marine fishery science, fishery engineering and economics, as well as the areas of marine environmental and ecological sciences (including modeling). Preference will be given to manuscripts that examine processes and underlying patterns. Descriptive reports, surveys, and observational papers may occa- sionally be published but should appeal to an audience outside the locale in which the study was conducted. Although all contributions are subject to peer review, responsibility for the contents of papers rests upon the authors and not on the editor or publisher. Submission of an article implies that the article is original and is not being considered for publication elsewhere. Articles may range from relatively short contributions (10-15 typed, double-spaced pages, tables and figures not included) to extensive contributions (20-30 typed pages). Manu- scripts must be written in English; authors whose native language is not English are strongly advised to have their manuscripts checked by English-speaking col- leagues before submission.

Title page should include authors’ full names and mailing addresses and the senior author’s telephone, fax number, and e-mail address, and a list of key words to describe the contents of the manuscript. Abstract should be limited to 200 words (one-half typed page), state the main scope of the research, and emphasize the author’s conclusions and relevant findings. Do not review the methods of the study or list the contents of the paper. Because abstracts are circulated by abstract- ing agencies, it is important that they represent the research clearly and concisely. Text must be typed in 12 point Times New Roman font throughout. A brief introduction should convey the broad significance of the paper; the remainder of the paper should be divided into the following sections: Materials and methods, Results, Discussion (or Conclusions), and Acknowl- edgments. Headings within each section must be short, reflect a logical sequence, and follow the rules of multi- ple subdivision (i.e., there can be no subdivision without at least two items). The entire text should be intelligible to interdisciplinary readers; therefore, all acronyms, abbreviations, and technical terms should be written out in full the first time they are mentioned. Include FAO common names for species in the list of keywords and in the introduction. Regional common names may be used throughout the rest of the text if they are dif- ferent from FAO common names which can be found at http://www.fishbase.org/search.html. Follow the U.S. Government Printing Office Style Manual (1984 ed.) and the CBE Style Manual (6th ed.) for editorial style; for fish nomenclature follow the most current issue of

the American Fisheries Society’s Common and Scientific Names of Fishes from the United States and Canada. Dates should be written as follows: 11 November 2000. Measurements should be expressed in metric units, e.g., 58 metric tons (t); if other units of measurement are used, please make this fact explicit to the reader. Write out the numbers zero through nine unless they form part of measurement units (e.g., nine fish but 9 mm). Refrain from using the shorthand slash (/), an ambiguous symbol, in the general text

Literature cited comprises published works and those accepted for publication in peer-reviewed literature (in press). Follow the name and year system for citation format in the “Literature cited” section (that is say, citations should be listed alphabetically by the authors’ last names, and then by year if there is more than one citation with the same authorship). If there is a sequence of citations in the text, list chronologically: (Smith, 1932; Green, 1947; Smith and Jones, 1985). Abbrevia- tions of serials should conform to abbreviations given in the Serial Sources for the BIOSIS Previews Database. Authors are responsible for the accuracy and complete- ness of all citations. Literature citation format: Author (last name, followed by first-name initials). Year. Title of report or manuscript. Abbreviated title of the series to which it belongs. Always include number of pages. Cite all software and special equipment or chemical solutions used in the study, not in a footnote but within parentheses in the text (e.g., SAS, vers. 6.03, SAS Inst., Inc., Cary, NC).

Tables are often overused in scientific papers; it is seldom necessary or even desirable to present all the data associated with a study. Tables should not be excessive in size and must be cited in numerical order in the text. Headings should be short but ample enough to allow the table to be intelligible on its own. All unusual symbols must be explained in the table legend. Other incidental comments may be footnoted with italic numeral footnote markers. Use asterisks to indicate probability in statistical data. Do not type table legends on a separate page; place them above the table data. Do not submit tables in photo mode.

• Zeros should precede all decimal points for values less than one.

• Sample size, n, should be italicized.

• Capitalize the first letter of the first word in all labels within figures.

• Do not use overly large font sizes in maps and for units of measurements along axes in figures.

• Do not use bold fonts or bold lines in figures.

• Do not place outline rules around graphs.

• Do not use horizontal lines through graphs to indicate measurement units.

• Use a comma in numbers of five digits or more (e.g. 13,000 but 3000).

• Maps require a North arrow and degrees latitude- longitude (e.g., 170°E).

404

Fishery Bulletin 107(3)

Figures include line illustrations, photographs (or slides), and computer-generated graphs and must be cited in numerical order in the text. Graphics should aid in the comprehension of the text, but they should be limited to presenting patterns rather than raw data. Figures should not exceed one figure for every four pages of text. Figures must be labeled with author’s name and number of the figure. Avoid placing labels vertically (except of y axis). Figure legends should explain all symbols and abbreviations and should be double-spaced on a separate page at the end of the manuscript. Please note that we do not print graphs in color.

Failure to follow these guidelines and failure to correspond with editors in a timely manner will delay publication of a manuscript.

Copyright law does not apply to Fishery Bulletin, which falls within the public domain. However, if an author reproduces any part of an article from Fishery Bulletin in his or her work, reference to source is consid- ered correct form (e.g., Source: Fish. Bull 97:105).

Submission

The Scientific Editorial Office encourages authors to submit their manuscripts as a single PDF (pre- ferred) or Word (zipped) document by e-mail to Fishery. Bulletin@noaa.gov. Please use the subject heading, “Fishery Bulletin manuscript submission”. Do not send encrypted files. Commerce Department personnel

should submit papers under a completed NOAA Form 25-700. For further details on electronic submission, please contact the Scientific Editorial Office directly (see address below). Or you may send your manuscript on a compact disc in one of the above formats along with four printed copies (one original plus three copies [stapled]) to the Scientific Editor, at the address shown below.

Richard D. Brodeur, Ph.D.

Scientific Editor, Fishery Bulletin Northwest Fisheries Science Center

2030 S. Marine Science Dr.

Newport, Oregon 97365-5296

Once the manuscript has been accepted for publication, you will be asked to submit a final electronic copy of your manuscript. When requested, the text and tables should be submitted in Word or Word Rich Text Format. Figures should be sent as PDF files, Windows metafiles, tiff files, or EPS files. Send a copy of figures in the origi- nal software if conversion to any of these formats yields a degraded version.

Questions? If you have questions regarding these guidelines, please contact the Managing Editor, Sharyn Matriotti, at

Sharyn.Matriotti@noaa.gov

Questions regarding manuscripts under review should be addressed to Richard Brodeur, Scientific Editor, at Rick.Brodeur@noaa.gov.

Fishery Bulletin

Subscription form

Superintendent of Documents Publications Order Form *5178

I I YES, please send me the following publications:

Subscriptions to Fishery Bulletin

for $36.00 per year ($50.40 foreign)

The total cost of my order is $ . Prices include regular domestic

postage and handling and are subject to change.

(Company or Personal Name) (Please type or print)

(Additional address/attention line)

(Street address)

(City, State, ZIP Code)

( Daytime phone including area code)

(Purchase Order No.)

Charge

your

order.

IT’S

EASY!

Please Choose Method of Payment:

| | Check Payable to the Superintendent of Documents | | GPO Deposit Account ] VISA or MasterCard Account your orders

I | | | | - 1 | | | | | | | | | | | |7|"| (202) 512-2250

(Credit card expiration date)

(Authorizing Signature)

Mail To: Superintendent of Documents

P.O. Box 371954, Pittsburgh, PA 15250-7954

Thank you for your order!

Also available online at http://bookstore.gpo.gov/collections/fishery-bulletin