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NOAA Technical Report NMFS SSRF-747 

Movement, Growth, and 
Mortality of American 
Lobsters, Homarus americanus, 
Tagged Along the 
Coast of Maine 



Jay S. Krouse 



September 1981 




U.S. DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric Administration 

National Marine Fisheries Service 



NOAA TECHNICAL REPORTS 

National Marine Fisheries Service, Special Scientific Report — Fisheries 

The major responsibilities of the National Marine Fisheries Service (NMFS) are to monitor and assess the abundance and geographic distribution of 
fishery resources, to understand and predict fluctuations in the quantity and distribution of these resources, and to establish levels for optimum use of the 
resources. NMFS is also charged with the development and implementation of policies for managing national fishing grounds, development and enforce- 
ment of domestic fisheries regulations, surveillance of foreign fishing off United States coastal waters, and the development and enforcement of interna- 
tional fishery agreements and policies. NMFS also assists the fishing industry through marketing service and economic analysis programs, and mortgage 
insurance and vessel construction subsidies. It collects, analyzes, and publishes statistics on various phases of the industry. 

The Special Scientific Report — Fisheries series was established in 1949. The series carries reports on scientific investigations that document long-term 
continuing programs of NMFS, or intensive scientific reports on studies of restricted scope. The reports may deal with applied fishery problems. The 
series is also used as a medium for the publication of bibliographies of a specialized scientific nature. 

NOAA Technical Reports NMFS SSRF are available free in limited numbers to governmental agencies, both Federal and State. They are also 
available in exchange for other scientific and technical publications in the marine sciences. Individual copies may be obtained (unless otherwise noted) 
from D822, User Services Branch, Environmental Science Information Center, NOAA, Rockville, MD 20852. Recent SSRF's are: 



722. Gulf menhaden, Brevoorlia paironus, purse seine fishery: Catch, fishing 
activity, and age and size composition, 1964-73. By William R. Nicholson. 
March 1978, iii + 8 p., 1 fig., 12 tables. 

723. Ichthyoplankton composition and plankton volumes from inland coastal 
waters of southeastern Alaska, April-November 1972. By Chester R. Mattson 
and Bruce L. Wing. April 1978, iii+ 11 p., 1 fig., 4 tables. 



Superintendent of Documents, U.S. Government Prinung Office, Washington, 
D.C. 20402, Stock No. 003-017-00452-0. 

732. Assessment of the Northwest Atlantic mackerel. Scomber scombrus, 
stock. By Emory D. Anderson. April 1979, iv-t- 13 p., 9 figs., 15 tables. For sale 
by the Superintendent of Documents, U.S. Government Printing Office, Wash- 
ington, D.C. 20402, Stock No. 003-017-00450-3. 



724. Estimated average daily instantaneous numbers of recreational and com- 
mercial fishermen and boaters in the St. Andrew Bay system, Florida, and adja- 
cent coastal waters, 1973. By Doyle F. Sutherland. May 1978, iv + 23 p., 31 figs.. 
11 tables. 

725. Seasonal bottom-water temperature trends in the Gulf of Maine and on 
Georges Bank, 1963-75. By Clarence W. Davis. May 1978, iv-t 17 p., 22 figs., 5 
tables. 



733. Possible management procedures for increasing production of sockeye 
salmon smolts in the Naknek River system, Bristol Bay, Alaska. By Robert J. 
Ellis and William J. McNeil. April 1979, iii + 9 p., 4 figs., 1 1 tables. For sale by 
the Superintendent of Documents, U.S. Government Printing Office, Washing- 
ton, D.C. 20402, Stock No. 003-017-00451-1. 

734. Escape of king crab, Paralithodes camtschalica, from derelict pots. By 
William L. High and Donald D. Worlund. May 1979, iii-i- 11 p., 5 figs., 6 tables. 



726. The Gulf of Maine temperature structure between Bar Harbor, Maine, 
and Yarmouth, Nova Scotia, June 1975-November 1976. By Robert J. 
Pawlowski. December 197S, iii + 10 p., 14 figs., 1 table. 

727. Expendable bathythermograph observations from the NMFS/MARAD 
Ship of Opportunity Program for 1975. By Steven K. Cook, Barclay P. Collins, 
and Christine S. Cany. January 1979, iv + 93 p., 2 figs., 13 tables, 54 
app. figs. 

728. Vertical sections of semimonthly mean temperature on the San Francisco- 
Honolulu route: From expendable bathythermograph observations, June 1966- 
December 1974. By J. F. T. Saur, L. E. Eber, D. R. McLain, and C. E. Dorman. 
January 1979, iii + 35 p., 4 figs., 1 table. For sale by the Superintendent of 
Documents, U.S. Government Prinung Office, Washington, D.C. 20402, Stock 
No. 003-0 17-0O438-4. 

729. References for the identification of marine invertebrates on the southern 
Atlantic coast of the United States. By Richard E. Dowds. April 1979, iv + 37 p. 
For sale by the Superintendent of Documents, U.S. Government Prinung 
Office, Washington, D.C. 20402, Slock No. 003-017-00454-6. 

730. Surface circulation in the northwestern Gulf of Mexico as deduced from 
drift bottles. By Robert F. Temple and John A. Martin. May 1979. iii- 13 p., 8 
figs., 4 tables. For sale by the Superintendent of Documents, U.S. Government 
Printing Office, Washington, D.C. 20402, Stock No. 003-017-00456-2. 

731. Annotated bibliography and subject index on the shortnose sturgeon, 
Acipenser brevirostrum. By James G. Hoff. April 1979, iii + 16 p. For sale by the 



735. History of the fishery and summary statistics of the sockeye salmon, 
Oncorhynehus nerka, runs to the Chignik Lakes, Alaska, 1888-1966. By Michael 
L. Dahlberg. August 1979, iv + 16 p., 15 figs., 11 tables. For sale by the 
Superintendent of Documents, U.S. Government Printing Office, Washington, 
D.C. 20402, Stock No. 003-017-00459-7. 

736. A historical and descriptive account of Pacific coast anadromous 
salmonid rearing facilities and a summary of their releases by region, 1960-76. 
By Roy J. Whale and Robert Z. Smith. September 1979, iv + 40 p., 15 figs., 25 
tables. For sale by the Superintendent of Documents, U.S. Government Printing 
Office, Washington, D.C. 20402, Stock No. 003-017-00460-1. 

737. Movements of pelagic dolphins (Stenella spp.) in the eastern tropical 
Pacific as indicated by results of tagging, with summary of lagging operations, 
1969-76. By W. F. Penin, W. E. Evans, and D. B. Holts. September 1979, 
iii + 14 p., 9 figs., 8 tables. For sale by the Superintendent of Documents, U.S. 
Government Printing Office, Washington, D.C. 20402, Stock No. 
003-OI7-00462-7. 

738. Environmental baselines in Long Island Sound, 1972-73. By R. N. Reid, 
A. B. Frame, and A. F. Draxler. December 1979, iv + 31 p., 40 figs., 6 tables. For 
sale by the Superintendent of Documents, U.S. Government Prinung Office, 
Washington, D.C. 20402, Stock No. 003-017-00466-0. 

739. Bottom-water temperature trends in the Middle Atlantic Bight during 
spring and autumn, 1964-76. By Clarence W. Davis. December 1979, iii + 13 p., 
10 figs., 9 tables. For sale by the Superintendent of Documents, U.S. Govern- 
ment Printing Office, Washington, D.C. 20402, Stock No. 003-017-00467-8. 



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NOAA Technical Report NMFS SSRF-747 



a fe. Movement, Growth, and 

Mortality of American 
Lobsters, Homarus americanus, 
Tagged Along the 
Coast of Maine 

Jay S. Krouse 

September 1981 



U.S. DEPARTMENT OF COMMERCE 

Malcolm Baldrige, Secretary 

National Oceanic and Atmospheric Administration 
National Marine Fisheries Service 



The National Marine Fisheries Service (NMFS) does not approve, rec- 
ommend or endorse any proprietary 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 pro- 
motion which would indicate or imply that NMFS approves, recommends 
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. 



CONTENTS 

Introduction 1 

Methods 1 

Tagging areas 1 

Tagging 1 

Publicity 2 

Recovery 3 

Results and discussion 3 

Recaptures 3 

Growth 4 

Movement 5 

Mortality 10 

Summary 11 

Acknowledgments 12 

Literature cited 12 

Figures 

1 . Maine coast showing the three tagging areas and recovery points o f American lobsters 2 

2. Length-frequencies of American lobsters tagged and released at Kennebunkport, Boothbay Harbor, and Jones- 
port, Maine 3 

3. Size distributions of tagged American lobsters still at large after September 1977 at each tagging area 4 

4. Premolt-postmolt carapace length relations of recaptured tagged American lobsters that molted at each release site 5 

5. Kennebunkport, Maine, region showing dispersal of recaptured tagged American lobsters, May 1975-September 
1977 6 

6. Boothbay Harbor, Maine, region showing dispersal of recaptured tagged American lobsters, May 1975-September 
1977 7 

7. Jonesport, Maine, region showing dispersal of recaptured tagged American lobsters, May 1 975-September 1 977 . . 8 

8. Average distances traveled by tagged American lobsters during weekly time intervals prior to recapture 9 

9. Distances moved by recaptured American lobsters of various sizes tagged and released at Kennebunkport, 
Boothbay Harbor, and Jonesport, Maine 10 

10. Recaptures of tagged American lobsters as related to time at large at each tagging area 10 

Tables 

1 . Monthly tag recoveries of American lobsters by release area off Maine, 1 975-77 3 

2. Comparison of the proportions of American lobsters recaptured to those tagged by two biologists at each release 
area, 1975-77 4 

3. Mean sizes of tagged American lobsters recaptured along with those lobsters not recaptured, 1 975-77 4 

4. Comparison of the sex ratios of tagged American lobsters released with those recaptured at each release area, 
1975-77 4 

5. Average distances moved by recaptured American lobsters at each tagging area 9 

6. Summary of the distances traveled by recaptured tagged American lobsters at each tagging area, 1975-77 10 

7. Annual instantaneous rates of apparent total and fishing mortality on American lobsters estimated from returns 
grouped by different time intervals 11 

8. Estimated percentage of tag loss after various time intervals for American lobsters released at Kennebunkport, 
Boothbay Harbor, and Jonesport, Maine 11 



Movement, Growth, and Mortality of American Lobsters, Homarus 
americanus, Tagged Along the Coast of Maine 1 



JAY S. KROUSE 2 



ABSTRACT 

During the spring of 1975, 2,882 American lobsters, Homarus americanus, were tagged at three locations off 
Maine. Four months after release 65% of the lobsters had been returned and by the completion of the study in 
September 1977, 2,188 (75.9%) lobsters had been recaptured. Most returns (88%) occurred within a 5 n.mi. (9.3 
km) radius of the release site and only about 1% of the recaptured lobsters had moved more than 10 n.mi. (18.5 
km). Movement and catchability did not vary significantly by sex nor size. The majority of lobsters traveled 
shoreward or along the coast on a west to southwesterly course with minimal easterly movement. All long 
distance migrants O20 n.mi. or 37.0 km) followed a south to southwesterly course. Extremely high annual 
instantaneous fishing mortality rates (4.0-7.3) estimated for each release area confirm the overexploitation of the 
Maine inshore lobster fishery. 



INTRODUCTION 



METHODS 



During the past decade concern for the future well-being of 
the Maine American lobster fishery has intensified as levels of 
fishing effort have increased and catches have generally 
declined. In response to this interest in Maine's most valuable 
commercial fishery, the Lobster Research Project of the Maine 
Department of Marine Resources (DMR), initiated in 1966 
extensive studies of various facets of the fishery (Thomas 1973; 
Krouse and Thomas 1975; Krouse 1978) and biology of the 
lobster (Krouse 1973). Even though information from these 
studies has provided some basis for scientific management of the 
lobster fishery, additional research is required in many areas. 
One important area with a paucity of information is that of 
lobster movement along the Maine coast. To date there have 
been three tagging studies with Maine lobsters. Harriman 3 and 
Cooper (1970) tagged lobsters at Monhegan Island [about 10 
n.mi. (nautical miles), 18.5 km offshore] and determined that 
those lobsters were nonmigratory since most recaptures were 
recovered within a 2 n.mi. (3.7 km) radius of the island. In con- 
trast, Dow (1974) reported that 5 of 162 lobsters (23 returns in 
all) tagged by commercial fishermen off the Maine coast 
traveled 75-138 n.mi. (138.9-255.6 km) toward Cape Cod. Four 
of these migrant lobsters were larger than the Maine maximum 
legal size of 127 mm CL (carapace length) when tagged, 
indicating a positive relationship between a lobster's size and 
movement. 

In view of the limited size and scope of these lobster tagging 
studies conducted previously in Maine waters, we decided to 
undertake a coastwise tagging project. Objectives of this present 
study were to provide new information on growth, mortality, 
and movement or migration patterns of legal-sized lobsters 
(81-127 mm CL). 



'This study was conducted in cooperation with the Department of Commerce, 
National Marine Fisheries Service, under Public Law 88-309 as amended, Com- 
mercial Fisheries Research and Development Act, Project 3-228-R. 

2 Marine Resources Laboratory, Maine Department of Marine Resources, 
West Boothbay Harbor, ME 04575. 

'Harriman, D. M. 1952. Progress report on Monhegan tagging 
1951-52. Unpubl. manuscr., 8 p. Maine Dep. Mar. Resour., W. Boothbay 
Harbor, ME 04575. 



Tagging Areas 

Three tagging sites, Kennebunkport, Boothbay Harbor, and 
Jonesport, representing the western, central, and eastern 
sections of the Maine coast (Fig. 1), were selected on the basis of 
geographical location and local availability of lobsters. 

Well in advance of the scheduled dates for tagging, certain 
lobster dealers were contacted at each tagging area, and 
arrangements were made to purchase about 1 ,000 lobsters from 
each area. It was specified that these lobsters be locally caught 
and not sorted by size. These requirements would ensure that 
the tagged lobsters were characteristic of the area studied in 
terms of size, movement, and catchability. 

To determine whether the tagged lobsters were representative 
in size of those lobsters caught commercially, length- frequencies 
were plotted by 1 mm increments for lobsters tagged at each tag- 
ging site (Fig. 2). Because of the likeness between size composi- 
tion data of this present study and data obtained from Maine's 
Commercial Sampling Program (Thomas 1973), we are confi- 
dent that the lobsters tagged were typical of the legal size range 
of lobsters along the Maine coast. 

Tagging 

The sphyrion tag developed by Scarratt and Elson (1965) and 
later modified by Cooper (1970) was selected as the primary 1 
mark as it can be retained through a molt. The model we used in 
this study consisted of a supple yellow PVC (polyvinylchloride) 
tube (2 mm diameter x 55 mm long) attached by a thin 
polyethylene thread to a 7 mm long stainless steel anchor. Tags 
were attached according to the technique described by Cooper 
(1970). 

In order that the magnitude of tag loss could be evaluated a 
secondary tag was used. The tag selected was the Floy cinch-up 
which was secured to the pincer claw by either fastening it 
around the proximal end of the propodus or around the carpus 
of lobsters > 100 mm CL. Although this tag would be lost after 
ecdysis, we anticipated that a sufficient number of lobsters 
would be recaptured prior to molting, to enable estimation of 




NEW 
HAMPSHIRE 



P LIBERATION SUES 



O RECOVERY SUES 



Figure 1. — Maine coasl showing the three lagging areas and recovery points of American lobsters that moved i 20 n.mi. (37.0 km). Lobsters released at Boothbay Har- 
bor. Jonesport, and Kennebunkport, Maine, are denoted by B. J. and K in circles. 



the rate of sphyrion tag loss. Experimentation with the nylon 
cinch-up tag revealed that this material expands upon immersion 
in water and consequently might slip off the claw. To minimize 
stretching, the tags were soaked in tepid water prior to applica- 
tion. 

Publicity 

To ensure that fishermen and dealers would be informed of 
the tagging program, posters advertising rewards for the return 
of tagged lobsters were distributed to almost all lobster dealers 
along the Maine coast. Cash rewards were S2.00 for return of 
only the tag and $5.00 for lobster with tag(s) intact. Throughout 
the study we strived to maintain the fishing community's interest 
and cooperation through periodic press releases on the progress 
of the tagging program and frequent contact with those dealers 
most likely to receive tagged lobsters. 



Tagging commenced in late April 1975, which was the earliest 
that an adequate supply of lobsters could be guaranteed, yet 
early enough for sphyrion tags to become firmly encysted in 
advance of the peak molting period in August and September. 
Before each lobster was tagged, carapace length, weight, and sex 
were recorded along with the corresponding numbers of both 
tags. Immediately after the tags were attached, the lobster was 
placed in a partitioned fiber glass tray, where circulating 
seawater hastened blood coagulation. Following a short 
recovery period ('/i-lh) lobsters not displaying normal vigor 
were discarded while all others were transferred to individual 
sections of 10.2 cm diameter PVC pipe (23-28 cm long) con- 
tained in rectangular wire cages. These cages were hung over the 
side of the boat until all lobsters (about 1 ,000) for that area were 
tagged and could be released simultaneously. The holding 
period ranged from 1 to 5 d. This system of isolation eliminated 
the loss and mutilation of sphyrion tags which occurs when tag- 



12 




KENNEBUNKPORT 








10 






X ■ 


86.5 


8 






N ■ 


957 


6 






S » ■ 


0.12 


4 












2 
















I i 1 




1 


1 1 



100 
BOOTHBAY HARBOR 




CARAPACE LENGTH (mm) 

Figure 2. — Length-frequencies of American lobsters tagged and released at 
Kennebunkport (6 May 1975), Boothbay Harbor (17 May 197S), and Jonesport 
(30 May 1975), Maine. 

ged lobsters are crowded together. Other advantages were: 1) 
reduction of postrelease tag mortality (most deaths attributable 
to this cause would occur prior to release); 2) opportunity for 
the sphyrion tag to become firmly attached during the lobster's 



quiescence in "solitary confinement"; and 3) considerable 
savings in boat-running time by eliminating daily excursions to 
release lobsters. 

On 6 May, 957 tagged lobsters were released 2 n.mi. (3.7 km) 
seaward of the mouth of the Kennebunk River. Next on 17 May, 
942 lobsters were released 10 n.mi. (18.5 km) south of Boothbay 
Harbor. Finally on 30 May, 983 tagged lobsters were liberated 
about 12 n.mi. (22.2 km) southwest of Jonesport. Although 
immediate release points were virtually void of traps, substantial 
numbers of traps were within 1-5 n.mi (1.9-9.3 km). 

Recovery 

All recapture sites were identified and the latitude and 
longitude determined and plotted. The straight line distance be- 
tween release and recapture points was measured and the 
number of days at liberty were calculated for each lobster. All 
data were coded and key punched for subsequent tabulation 
(Krouse 1978). 4 

RESULTS AND DISCUSSION 

Recaptures 

Of 2,882 American lobsters tagged during the spring of 1975, 
75.9% were recaptured through September 1977 (Table 1). 
Returns by tagging area were 85.2% at Jonesport, 74.8% at 
Kennebunkport, and 67.4% at Boothbay Harbor. These different 
return rates may be explained, in part, by the proximity of 



'Krouse, J. S. 1978. Listing of data for lobsters tagged and recaptured off 
the Maine coast (1975-77). Research Reference Document 78/8, 37 p. Maine 
Dep. Mar. Resour., W. Boothbay Harbor, ME 04575. 



Table I.— Monthly tag recoveries of American lobsters by release area off Maine, 1975-77. Numbers in parentheses refer 

to lobsters that moiled. 





Kennebunkport 




Boothbay Harbor 




Jonesport 




Total 




Recaptured 




Recaptured 




Recaptured 




Cumu 
reti 


lative 




Number 


Cumu 
Nos. 


ative 


Number 


Cumulative 
Nos. % 


Number 


Cumulative 
Nos. % 


trn 


Month 


Nos. 


% 


1975 
























May 


136 


136 


14.2 


18 


18 


1.9 


— 


— 


— 


154 


5.3 


June 


244 


380 


39.7 


176 


194 


20.6 


315 


315 


32.0 


889 


30.9 


July 


119 


499 


52.1 


160 


354 


37.6 


285(1) 


600 


61.0 


1,453 


50.4 


Aug. 


132 


631 


65.9 


145(1) 


499 


53.0 


132(3) 


732 


74.5 


1,862 


64.6 


Sept. 


39(3) 


670 


70.0 


58(4) 


557 


59.1 


60(6) 


792 


80.6 


2,019 


70.1 


Oct. 


17 


687 


71.8 


33(1) 


590 


62.6 


29(7) 


821 


83.5 


2,098 


72.8 


Nov. 


11(3) 


698 


72.9 


9(2) 


599 


63.6 


9(5) 


830 


84.4 


2,127 


73.8 


Dec. 


5 


703 


73.5 


10(2) 


609 


64.7 









2,142 


74.3 


1976 
























Jan. 


3(1) 


706 


73.8 


5(1) 


614 


65.2 









2,150 


74.6 


Feb. 



























Mar. 
















KD 


831 


84.5 


2,151 


74.6 


Apr. 









3 


617 


65.5 


2(1) 


833 


84.7 


2,156 


74.8 


May 


KD 


707 


73.9 


2(1) 


619 


65.7 


2 


835 


84.9 


2,161 


75.0 


June 


2 


709 


74.1 


1 


620 


65.8 









2,164 


75.1 


July 


1(1) 


710 


74.2 


2(1) 


622 


66.0 


KD 


836 


85.1 


2,168 


75.2 


Aug. 


KD 


711 


74.3 


2(2) 


624 


66.2 









2,171 


75.3 


Sept. 


3(2) 


714 


74.6 


6(6) 


630 


66.9 


KD 


837 


85.2 


2,181 


75.7 


Oct. 









KD 


631 


67.0 









2,182 


75.7 


Nov. 









1(1) 


632 


67.1 









2,183 


75.8 


Dec. 









3(3) 


635 


67.4 









2,186 


75.9 


1977 
























Apr. 


1(1) 


715 


74.7 
















2,187 


75.9 


May. 


1(1) 


716 


74.8 
















2,188 


75.9 


Sept. 



























Totals 


(14) 


716 


74.8 


(26) 


635 


67.4 


(26) 


837 


85.2 


2,188 


75.9 



release sites to zones of moderate to high fishing intensity. For 
instance, at Boothbay Harbor tagged lobsters were released 
more seaward than at the other areas and were therefore more 
removed from immediate fishing pressure. Also, based on our 
sightings of boats towing their nets near the release area shortly 
after liberating tagged lobsters and rumors of trawlers catching 
tagged lobsters but not reporting them (unlawful for trawlermen 
to land lobsters in Maine), there is reason to believe that perhaps 
several of the Boothbay Harbor releases were removed from the 
fishery by trawlers. In Jonesport, where returns were the 
highest, even though releases were in an area with very few 
traps, substantial concentrations of traps were only about 1 
n.mi. (1.9 km) away in all directions; whereas, at 
Kennebunkport, where returns were intermediate to the other 
two areas, the proximity of the area's release site to the trap 
fields would be ranked between that of Jonesport and Boothbay 
Harbor. 

Because differences in tag recoveries by area might be par- 
tially due to any variations in the tagging adeptness of the two 
biologists who applied the tags in this study, we evaluated this 
possibility by comparing the proportions of the number of 
lobsters returned with those tagged by biologists at each release 
site (Table 2). As there were no significant differences (chi- 
square test, P>0.05) between these proportions, it appears that 
the biologists applied the sphyrion tags with nearly equal skill; 
thus any major variations in returns from different areas could 
not be related to differences in numbers of lobsters marked by 
any one tagger. 



Table 2. — Comparison of the proportions of American lobsters recaptured with 
those tagged by two biologists at each release area, 1975-77. Chi-square values 
indicating no significant difference (P>0.05) between proportions are denoted 
by NS. 



Table 3. — Mean sizes (carapace length) of tagged American lobsters recaptured 
along with those lobsters not recaptured, 1975-77. 



Kennebunkport 



Boothbay 
Harbor 



Jonesport 



Total 



Number la re- Number la re- Number °!a re- Number la re- 
Tagger tagged turned tagged turned tagged turned tagged turned 



A 


560 79 


514 70 


490 85 


1,564 78 


B 


394 69 


428 64 


493 84 


1,315 73 


*-' 


1.61 NS 


0.58 NS 


0.0001 NS 


1.03 NS 



Four months after release, 53-81 % (67% combined) of the tagged 
lobsters had been returned in each area, and after 1 yr 66-85% (75% 
combined) had been recaptured. These high rates of return, 
which corroborate the lobster fishery's high exploitation rate, 
have undoubtedly been reduced by tag loss, incomplete report- 
ing of recaptures, and natural and tag induced mortality. Based 
on our observations of lobsters following tagging until time of 
release and our close familiarity with the fishing community, it 
appears that only a negligible number of lobsters died as a result 
of tagging or were captured and not reported (exclusive of 
Boothbay Harbor). Thus, in this study, tag loss and natural 
mortality (< 10% annually, Thomas 1973) were probably the most 
important sources of error. 

The effect of size on catchability was examined by compar- 
ing the mean carapace length of lobsters recaptured at each 
release site with those tagged lobsters not recaptured before 
October 1977 (Table 3). The /-test (P>0.05) revealed no 
significant difference between the mean sizes of those lobsters 
caught with those still at large. Similarly, the chi-square test 
indicated no statistical differences (P>0.05) between sex 
ratios of lobsters returned to those liberated (Table 4). 





Kennebunkport Boothbay Harbor 
CL (mm) SE CL (mm) SE 


Jonesport 


Tagged 
lobsters 


CL (mm) SE 


Recaptured 
Not recaptured 


86.5 ±0.14 87.5 ±0.21 

86.6 ±0.24 87.0 ±0.29 


87.4 ±0.19 
87.8 ±0.40 



Table 4. — Comparison of the sex ratios of tagged American lobsters released 
with those recaptured at each release area, 1975-77. Chi-square values indicating 
no significant difference between sex ratios of lobsters released to those recap- 
tured are denoted by NS. 





Kennebunkport 
Ratio 
6 9 (6:9) 


Boothbay Harbor 

Ratio 

rf 9 (rf:9) 


Jonesport 


Tagged 
lobsters 


Ratio 
rf 9 (6:9) 


Recaptured 
Released 


316 400 0.79:1 

415 542 0.77:1 

0.07NS 


314 320 0.98:1 
456 486 0.94:1 

0.1 5NS 


359 478 0.75:1 

439 544 0.81:1 

0.05NS 



Although the above analysis indicates that there probably 
was no difference in the catchability of legal-sized lobsters by 
size and sex, plots of the percentages of lobsters not recaptured 
against carapace length show that 4-9% fewer 81 than 82 mm CL 
lobsters were returned (Fig. 3). This disparity might appear to 
be due to gear selectivity, but is in fact unlikely since previous 
studies (Krouse 1973; Krouse and Thomas 1975) show that 
lobsters become fully vulnerable to conventional lobster pots 
at about 75 mm CL. Actually this lower than expected catch of 
small legal lobsters is due to the Maine fishermen's method of 
measurement and interpretation of what lobsters are legal to 
keep. The minimum legal size is 81 mm (3-3/16 in) CL in 
Maine; but the minimum size retained in practice is closer to 
82-83 mm. This conclusion is further supported by length fre- 
quencies of Maine commercial lobster catches compiled by 
Thomas (1973) which showed marked deficiencies of the 81 
mm group; in fact, even the 82 through 84 mm sizes were less 
numerous than expected. 



A KENNEBUNKPORT 
O BOOTHBAY HARBOR 
D JONESPORT 




60 65 90 9S 100 

CARAPACE LENGTH (mm) 

Figure 3. — Size distributions of tagged American lobsters still at large after 
September 1977 (about 28 mo since release) at each tagging area. 



Growth 

From July 1975 through May 1977, only 66 (3.0%) lobsters of 
2,188 returns had molted prior to recapture. This extremely 



low number of recaptured new-shell lobsters may be attributed 
primarily to the high rate of return during the first 3 mo before 
the peak of the molting period. Accordingly, a decidedly 
higher proportion of those lobsters recovered after 4 mo had 
molted (Table 1). In fact, of 46 lobsters recaptured after the 
first season (1975) at all release areas, 28 (60.9%) had molted. 

Molt increments in weight ranged from 21 .9 to 64.4% (40.9% 
mean) at Boothbay Harbor, 21.3 to 52.8% (39.8% mean) at 
Kennebunkport, and 27.3 to 67.5% (46.2% mean) at Jonesport 
(these values exclude lobsters with missing chelipeds). 
Increases in carapace length were 7.3-18.1% (12.7% mean) at 
Boothbay Harbor, 11.5-16.0% (13.1% mean) at Kennebunkport, 
and 10.6-18.5% (15.1% mean) at Jonesport. Variations between 
area molt increments are reflected by the analysis of 
covariance which indicated significant differences (P = 0.05) 
between the coefficients of the linear regressions of postmolt 
carapace length on premolt carapace length (Fig. 4). Despite 
these differences in growth increments by area, which might be 
resolved with additional data, the overall increase in carapace 
length (areas combined) approximates Dow's (1964) estimate 
of 14% for Maine lobsters. 

Estimates of von Bertalanffy growth parameters (Gulland 
1969) were not realistic (negative K and very low Z,„ values) 
due to the highly variable growth increments, small sample 
sizes, and the limited range of sizes and ages represented by the 
data. 



I20r 



no 



100- 



KENNEBUNKPORT 



+ \.o** 




N--I0 
r=0.93 



120 



< 100 

cr 

< 



90 - 



90 



BOOTHBAY HARBOR 



100 



.A* 



+ \2** 



N= 25 
r= 0.94 



85 



90 



95 



100 



I- 



\zo 




















JONESPORT 




no 


. 








•-----"" 


100 
90 


— u 


j_ 


' 


' 


N=23 
r = 0.94 

l 1 



Figure 4.- 



85 90 95 100 

PREMOLT CARAPACE LENGTH (mm) 



-Premolt-postmolt carapace length relations of recaptured tagged 
American lobsters that molted at each release site. 



Movement 

Before movement trends of recaptured tagged lobsters can 
be thoroughly analyzed, it is necessary to consider the inten- 
sity, distribution, and seasonality of fishing effort at each 
release site. Unfortunately, sufficient data were not available 
to quantify effort by area; however, in view of catch and effort 
information of the Maine commercial lobster fishery collected 
coastwise by DMR's Lobster Research Project personnel, it 
was apparent that fishing pressure was extremely intense at all 
tagging areas. Seasonal changes in fishing intensity and loca- 
tion of lobster trap fields are well-known occurrences along 
the Maine coast (Dow 1961; Thomas 1973; Cooper et al. 
1975). During the summer-fall period when the most intense 
fishing activity occurs, most traps are rather uniformly 
distributed along the shores of the mainland, around islands 
and ledge outcroppings where usually rough, rocky substrates 
provide ideal lobster habitat. In winter and spring when fishing 
effort is minimal, most traps are moved to deeper water (>30 
m) (Cooper et al. 1975) where 1) traps are less apt to be 
damaged or lost due to severe winter storms, 2) warmer water 
temperatures cause lobsters to be more active and subse- 
quently more catchable, and 3) lobsters are now more abun- 
dant due to the fact that most traps are fished in shoaler water 
(<30 m) during the warmer months. 

Another factor which should be considered when assessing 
movement trends of this study was the release of tagged 
lobsters at locations differing from those of original capture. 
Nevertheless, as mentioned previously, all lobsters tagged and 
released at a certain site were caught within that general area. 

Movement patterns were initially assessed by plotting the 
points of recapture at each release site (Figs. 5-7). Of the Ken- 
nebunkport releases (Fig. 5), most lobsters were recaptured in 
close proximity to shore within a 5 n.mi. (9.3 km) radius of the 
release site. Only 14 recaptures traveled >5 n.mi. and 10 of 
these lobsters moved in a southerly direction. The most 
notable movements were by a male (90 mm CL) which was at 
large 369 d and traveled 63 n.mi. (116.7 km) to Boston and a 
female (88 mm CL) which was allegedly caught near Tiverton, 
R.I. (185 n.mi., 342.6 km), 199 d after release. 

At Boothbay Harbor (Fig. 6), most lobsters were recovered 
between the mouths of the Kennebec and Damariscotta Rivers. 
Only one lobster was recaptured in the Damariscotta River, 
while none was reported from the Kennebec River. By con- 
trast, numerous tagged lobsters were returned from the 
Sheepscot River estuary. Twelve lobsters traveled ^.10 n.mi. 
(18.5 km) up this estuary. Significant easterly and southerly 
movement was limited to a female (87 mm CL), at large 23 d, 
that traveled 14 n.mi (25.9 km) to Monhegan Island; a male 
(107 mm CL), at large 88 d, which moved 42 n.mi. (77.8 km) 
to Cape Porpoise; and a female (99 mm CL) caught at Jeffreys 
Ledge (61 n.mi., 113.0 km) after 197 d at liberty. 

In comparison with other areas, directional movement of 
Jonesport recaptures appeared to be less restricted (Fig. 7). 
Although several lobsters were recaptured seaward of the 
release locations, most were taken inshore. The greatest 
movements (^.20 n.mi., 37.0 km) were by three lobsters that 
traveled southwesterly. The farthest distance moved was 134 
n.mi. (248.2 km) (to Kennebunkport) by an 89 mm CL male at 
large 405 d, followed by a 29 n.mi. (53.7 km) trek to Great 
Duck Island by a small male (81 mm CL) at large 49 d, and a 



70°40 



o 




70 20 



\o# — 



NAUTICAL MILES 



Figure 5. — Kennebunkport, Maine, region showing dispersal of recaptured tagged American lobsters. May 1975-September 1977. Number of recaptures given 
at each recover, point. Shaded area represents percentage of recaptured lobsters that traveled in a given direction (30° bearing intervals). 



20 n.mi. (37.0 km) movement to Schoodic Head by a 96 mm 
CL female at large 327 d. 

To evaluate directional movement more objectively, com- 
pass bearings were assigned to all recapture coordinates and 
grouped by 30° increments (Figs. 5-7). At Kennebunkport and 
Boothbay Harbor most lobsters were recovered at bearings 
1 °-30° and 270°-360° from the release areas while only 8.5<Vo of 
the returns from both areas traveled in other directions. At 



Jonesport there appears to have been more movement in an 
easterly direction (60°-90°); however, this is somewhat 
misleading because only 15 of the 184 lobsters that traveled 
toward the east exceeded 1 n.mi. (1.9 km), the remaining 169 
lobsters were caught about 1 n.mi. due east of the release site 
near Nashes Island (Fig. 7). 

In view of the information presented herein, it can be seen 
that the majority of recaptured lobsters moved inshore at all 



69°50' 



69°40' 



69°30' 




Figure 6. — Boothbay Harbor, Maine, region showing dispersal of recaptured tagged American lobsters, May 1975-September 1977. Number of recaptures given at 
each recovery point. Shaded area represents percentage of recaptured lobsters that traveled in a given direction (30° bearing intervals). 



release areas. Of course, it should be remembered that this 
shoreward movement may have been influenced by the reloca- 
tion of tagged animals from where they were originally caught. 
Limited movement toward the east, which was particularly evi- 
dent at Boothbay Harbor, might be the result of the 
counterclockwise current along the Maine coast. Accordingly, 
all long distance migrants (_^_20 n.mi., 37.0 km) of this study 



appeared to travel in the direction of the prevailing south to 
southwesterly coastal currents (Fig. 1). Likewise, the major 
migrants of Dow's (1974) tagging study followed a south by 
southwesterly course as they moved from Maine coastal waters 
toward New Hampshire and Massachusetts. Moreover, recent 
returns of several tagged Canadian lobsters (released off 
Grand Manan Island, N.B. (Fig. 1)) from various locations in 




Ofi 

a 

a 3 

a £ 

*■ -E 

O M 



n 






E S 



c 


c 








^ 


e 


_c 


< 


i 



E a 



•0C>* 



■ OZt-t? 



Maine and as far south as Cape Cod (Groom 1978, pers. com- 
mun. 5 ) further substantiate this southwesterly movement 
undertaken by some lobsters (usually the larger mature 
individuals). 

Another factor likely to be related to movement, particu- 
larly in view of this study's high return rate, is the time lobsters 
were at large prior to being recaptured. Mean times (days) at 
large varied markedly from long (86. 1 ± 3 .4) ( ± 1 SE) at Boothbay 
Harbor, to medium (70.5 ±2.6) at Kennebunkport, and short 
(51.8 ± 1.4) at Jonesport. Considering that recaptured lobsters 
tagged and released at Boothbay Harbor were at large the 
longest and also traveled the farthest (mean = 4.6 n.mi., 8.5 
km) (Table 5), the degree of movement seems to be dependent 

Table 5. — Average distances moved by recaptured American lobsters at each 
tagging area. Sexes were combined since there were no statistical differences 
between the distances moved by males and females (r = 0.594, 0.301, and 0.677 
for Kennebunkport, Boothbay Harbor, and Jonesport, respectively; />>0.05). 









A 


«rage 








Number 


nautical miles 




Area 


Sex 


recaptured 


moved (km) 


SE 


Kennebunkport 


Male 


314 


2.33 


(4.32) 


±0.21 




Female 


398 


2.63 


(4.87) 


±0.47 




Combined 


712 


2.50 


(4.63) 


±0.28 


Boothbay Harbor 


Male 


307 


4.62 


(8.56) 


±0.17 




Female 


317 


4.54 


(8.41) 


±0.21 




Combined 


624 


4.60 


(8.52) 


±0.14 


Jonesport 


Male 


351 


3.07 


(5.69) 


±0.39 




Female 


468 


2.80 


(5.19) 


±0.10 




Combined 


819 


2.92 


(5.41) 


±0.18 



upon time at large. However, an examination of the plots of 
average distances traveled (nautical miles) against time at large 
(weeks) indicates that after an 8-10 wk postrelease period, dur- 
ing which time lobsters apparently dispersed from the point of 
release, there was little if any association between the time 
lobsters were at large and the extent of movement (Fig. 8). For 
example, tagged lobsters recaptured near Boothbay Harbor 
that had been free 6 mo to 1 yr had moved no farther than 
those lobsters caught after only 2 mo of liberty. Furthermore, 
8 of 30 (27%) lobsters recaptured after being at large at least 1 yr 
were caught within 1 n.mi. (1.9 km) of the three release areas. 
Similarly, Fogarty et al. (1981) reported that lobsters tagged 
and recaptured along the coast of Rhode Island moved greater 
distances as the time at large increased to 90 d, after which 
movement appeared to level off. 

Average distances traveled by recaptured lobsters were 
calculated for each tagging area (Table 5). Lobsters at 
Boothbay Harbor moved the farthest (mean = 4.6 n.mi., SE = 
±0.14), followed by Jonesport (mean = 2.9 n.mi., SE = ±0.18), 
and then by Kennebunkport (mean = 2.5 n.mi., SE = ±0.28). 
These variations in distances moved at each tagging area 
appear to be associated with the proximity of the release site to 
neighboring trap fields, the configuration of the immediate 
coastline, and, possibly, to where the lobsters were originally 
caught. For instance, at Boothbay Harbor where lobster 
movement was the most extensive, the liberation area was not 
only farther from shore relative to the other areas, but also 
more removed from zones of moderate to intense fishing 
pressure. Of course these factors, particularly the latter, also 



KENNEBUNKPORT 



20 30 tO 50 60 70 



90 OO 



« 7 












BOOTHBAY HARBOR 




















































































*~ 5 




» 


•vV^ 






o o OO 




u 4 












o o O 




















en 3 








O°o 










... z 











o 




OO 


<9 












































o OO o 


o o 



































50 GO 

JONESPORT 



TIME AT LARGE < *••*■) 



5 W. Groom, Fishery Biologist, New Brunswick Department of Fisheries, 
Fredericton, New Brunswick, Canada, pers. commun. March 1980. 



Figure 8. — Average distances (nautical miles, 1.9 km) traveled by tagged 
American lobsters during weekly time intervals prior to recapture. Mean 
distances were calculated by dividing total miles moved by tagged lobsters recap- 
tured during a given week by the number of recaptures that week. 



explain why Boothbay Harbor recaptures were at large the 
longest. 

Most tagged lobsters remained in the vicinity of the release 
areas as indicated by the fact that 74, 92, and 98°/o of the returns 
at Boothbay Harbor, Jonesport, and Kennebunkport, respec- 
tively, were caught within a 5 n.mi. (9.3 km) radius of the 
release site and only about 1 % of the recaptures wandered > 10 
n.mi. (18.5 km) (Table 6). Even more restricted movement pat- 
terns were observed by Harriman (see footnote 3) and Cooper 
(1970) who reported that most lobsters tagged near Monhegan 
Island were recaptured within 2 n.mi. (3.7 km) of the island. 
Similarly, based on observations made by scuba divers and 
from research submersibles on lobsters near Boothbay Har- 
bor, Cooper et al. (1975) concluded that large-scale seasonal 
movements on and off the shallow (<24 m) inshore fishing 
grounds (notion of many fishermen) do not occur. More 
recently, Fogarty et al. (1981) noted that the majority of tag- 
ged lobsters released along the Rhode Island coast were 
recovered within 3.2 n.mi. (6 km) of the release site. 

The association of lobster size with movement was evaluated 
by averaging the miles moved by lobsters in 5 mm CL 
increments and then plotting these values against carapace 
length (Fig. 9). Although there appears to be no relationship 
between size and movement, it should be noted that only 2.2% 
of the lobsters tagged in this study were > 100 mm CL, and 
according to the studies of Dow (1974) and Groom (see foot- 
note 5) the majority of major migrants along the Maine coast 
exceeded 100 mm CL. Aside from the fact that relatively few 
large lobsters (>100 mm CL) were tagged in this study, it 
should also be mentioned that only 19(34.5%) of 55 recaptures 
> 100 mm CL were at large more than 3 mo and only 4 (7.3%) 



Table 6. — Summary of the distances traveled by recaptured tagged American lobsters at 
each tagging area, 1975-77. 





Kennebunkport 


Boothbay Harbor 

Cumulative 


Jonesport 


Nautical 




Cumulative 




Cumulative 


miles 


Number 


% 


Number 


% 


Number 


% 


traveled 


returned 


returned 


returned 


returned 


returned 


returned 


0-1 


219 


30.8 


56 


10.0 


311 


38.0 


2-3 


368 


82.4 


112 


26.9 


264 


70.2 


4-5 


111 


98.0 


291 


73.6 


174 


91.5 


6-7 


8 


99.2 


140 


96.0 


58 


98.5 


8-9 


1 


99.3 


12 


97.9 


3 


98.9 


10-11 


3 


99.7 


7 


99.0 


1 


99.0 


12-13 







2 


99.4 


4 


99.5 


14-15 







2 


99.7 







>15 


2 


100.0 


2 


100.0 


4 


100.0 


Total' 


712 




624 




819 





'These values are less than total number of recaptures reported in Table 1 because location 
of recapture was not known for all returns. 



KENNEBUNKPORT 
BOOTHBAY HARBOR 
JONESPORT 



91-95 96- 100 IOI-I05 

CARAPACE LENGTH (mm) 



Figure 9. — Distances moved by recaptured American lobsters of various sizes 
tagged and released at Kennebunkport, Boothbay Harbor, and Jonesport, 
Maine. 



lobsters were free longer than 1 yr prior to being caught. 
Perhaps, at least for the larger lobsters, reductions in times at 
large may have curtailed movement. 

Mortality 

Mortality rates were estimated from a linear regression of 
the number of tagged lobsters recaptured on the time at large. 
Regression coefficients were substituted into Gulland's (1969) 
equation (6.3): 



log e n r = -(F+M)rT + log £ 

where the 
intercept (a) = log 



FN n 



T+W 



FN n 



( 1 _ e-V+Afl, 

slope (b) = -(F+M) r T 

n f = number of recaptures during interval r, 



where r = 0, 1, 2, 3 ... weekly, biweekly, or monthly 
period following release 
T = length of interval of time (r) 
N = number of tagged lobsters released. 

Because an estimate of total mortality, derived with tagging data 
along, is the sum of fishing mortality (/) plus not only natural 
mortality (M), but also all other causes of reductions in the 
number of tagged animals, the value ' 'A" ' (all sources of tag loss 
plus natural mortality) should replace M in the equations. 



The number of recaptures plotted over time indicated that 
return rates increased during the first 4-8 wk, then leveled off 
for a brief period and eventually began to decrease (Fig. 10). 



KENNEBUNKPORT 



a * 



10 12 14 16 18 20 22 24 26 28 30 32 34 36 



6 

I 5 

S 4 

E 
- 3 

-2 











8 


W E E K LY 


r 




BOOTHBAY HARBOR 




& 


BI-WEEKLY 


O 








a 


MONTHLY 


a ° • o 


e 




















o 












- 




c 

© 




uJ 




A 








& 


A 








e 




A 



2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 



_i i l i i ' ' 



_| — i l_l i i i i i 



2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 
TIME AT LARGE (Wtekl) 



Figure 10. — Recaptures (logg scale) of tagged American lobsters as related to 
time at large at each lagging area. 



Increases in the number of recaptures during the first few suc- 
cessive weeks following release may be attributed to slow mix- 
ing of tagged animals with the fishable population in associa- 
tion with spatial variations in fishing intensity. Accordingly, 
mortality estimates were calculated from return data exclusive 
of those initial recovery intervals (2-4 wk) when mixing of tag- 
ged and untagged individuals was considered to be incomplete. 



10 



Annual instantaneous rates of fishing mortality (F) and 
apparent total mortality (Z') which ranged from 4.14 to 7.31 
and 5.89 to 8.73 (Table 7), respectively, were extremely high as 

Table I. — Annual instanlaneous rales of nppfent total (Z') and 
f ish!ng (/") mortality on American lobsters estimated from returns 
grouped by different time intervals. Annual mortality rates expressed as 
- j s are in parentheses. 





Kennebunkpc t 
Z' F 


Boothbay Harbor 
Z' F 


Jot 


lesport 


T .e 
interval 


Z' 


F 


Weekly 


7.10 


4.14 


6.36 


4.13 


8.73 


7.22 




(99.9) 


(98.4) 


(99.8) 


(98.4) 


(99.9) 


(99.9) 


Biweekly 


7.08 


4.89 


6.16 


4.11 


8.39 


7.31 




(99.9) 


(99.2) 


(99.8) 


(98.4) 


(99.9) 


(99.9) 


Monthlv 


7.12 


4.93 


5.89 


3.98 


8.72 


7.27 




(99.9) 


(99.3) 


(99.7) 


(98.1) 


(99.9) 


(99.9) 



the result of the actual return rates which were, I believe, not 
fully representative of general conditions; the fact that annual 
mortality rates were calculated from tag return data collected 
when the catches of the seasonal lobster fishery were highest, 
and systematic errors inherent in most tagging studies. Gulland 
(1969) has classified these errors according to their effects on 
the various estimates. Types A and B errors result from tag 
loss and systematically bias mortality rates causing an 
underestimate of fishing mortality and an overestimate of the 
true total mortality (Z), respectively. Type A error, which is 
caused by death of fish shortly after tagging and incomplete 
reporting of recaptures, affects F but not Z. Type A errors 
appeared minimal except at Boothbay Harbor where trawlers 
were suspected of unreported catches of tagged lobsters. In 
fact, the relatively lower estimates of F at Boothbay Harbor 
may be attributable, in part, to this error. Of the Type B 
errors, which include natural mortality, emigration, and tag 
detachment, only the latter was of significant magnitude in 
this study to warrant consideration. 

Quantitative estimates of tag loss were obtained by follow- 
ing Gulland's (1963) methodology for estimating tag retention 
rates with data from double tagging experiments. Due to 
problems that we encountered initially with this procedure, 
Russell (1980) analyzed this method and corrected some of 
Gulland's basic equations. 

In all cases, estimated losses of the sphyrion tag were higher 
than those of the cinch tag (Table 8). Considering differences 
in modes of attachment, higher losses of sphyrion tags were 
expected; however, cinch tag losses were greater than antici- 
pated. Evidently some of the cinch tags became loose and 
subsequently slipped off the chela (claw). In retrospect, this 
type of loss would have been minimized had the tag been 
secured around the carpus (section proximal to the propodus) 
of the pincer claw. 



A comparison of the relatively high annual loss rates of indi- 
vidual tags (range of 39.4-51.5%) with those of both tags (range 
of 15.0-24.0%) clearly indicates how tag returns would have been 
reduced if only one tag rather than two had been used. Never- 
theless, in view of these estimates, we feel that tag loss was of 
sufficient magnitude to bias mortality estimates. This error, 
termed Type B, is an additional cause of mortality ("X") and 
results in an overestimate of Z but has no effect on F. Unfor- 
tunately, if we convert the highest annual tag loss rates 
(39.4-51.5%) (Table 8) to instantaneous rates (0.50-0.72) and 
then subtract these values from estimates of Z' (5.89-8.73) 
(Table 7), this only results in an insignificant reduction in Z'. 
Thus it is apparent that other factors besides tag loss have 
caused overestimates of Z. When these errors are operative 
only F is estimated from tagging data; thus Z is derived from 
some independent estimate and M is the difference between F 
and Z. 

Undoubtedly, the most meaningful mortality estimates 
derived from data of this study are those of F and even these 
values as well as estimates of Z are inflated as the result of 
incomplete mixing of tagged lobsters with the untagged popu- 
lation [Gulland's (1969) Type C error] along with other factors 
previously stated. Despite this bias, estimates of F do indeed 
reflect the Maine lobster fishery's extremely high rate of 
exploitation. 

SUMMARY 

1 . Of 2,882 lobsters tagged in the spring of 1975, 2,188 (75.9%) 
were recaptured through September 1977. Lobsters 
released at Jonesport had the highest return (85.2%) follow- 
ed by Kennebunkport (74.8%) and Boothbay Harbor 
(67.4%). 

2. Catchability of legal-sized lobsters did not vary by sex nor 
size. 

3. Twenty-four ovigerous females ranging from 82 to 109 
mm CL were recaptured. 

4. Sixty-six (3.0%) of the lobsters recaptured had molted while 
at large. Percentage of increases in carapace length varied 
from 7.3 to 18.1% (12.7% mean) at Boothbay Harbor, 1 1.5 to 
16.0% (13.1% mean) at Kennebunkport, and 10.6 to 18.5% 
(15.1% mean) at Jonesport. 

5. The majority of returns from Kennebunkport (98.0%), 
Boothbay Harbor (73.6%), and Jonesport (91.5%) were 
caught within a 5 n.mi. (9.3 km) radius of the release sites. 
Recaptured lobsters moved on the average more at 
Boothbay Harbor (4.45 n.mi., 8.2 km) and less at 
Kennebunkport (2. 16 n.mi., 4.0 km). Only about 1% of the 
returns wandered >10 n.mi. (18.5 km). 

6. Most movement was shoreward with a westerly drift from 
the point of release. Few lobsters traveled in an easterly 



Table 8. — Estimated percentage of tag loss after various time intervals for American lobsters 
released at Kennebunkport, Boothbay Harbor, and Jonesport, Maine. 





Kennebunkport 




Boothbay Harbo 


r 


Jonesport 










Both 






Both 






Both 


Week 


Sphyrion 


Cinch 


tags 


Sphyrion 


Cinch 


tags 


Sphyrion 


Cinch 


tags 


1 


2.0 


1.6 


0.03 


1.2 


1.2 


0.01 


1.8 


1.2 


0.02 


4 


7.6 


6.3 


0.5 


4.8 


4.5 


0.2 


6.7 


4.9 


0.3 


16 


24.7 


21.1 


5.2 


16.7 


16.0 


2.7 


22.3 


17.0 


3.8 


52 


51.5 


46.5 


24.0 


39.4 


38.2 


15.0 


48.3 


39.9 


19.3 



direction. All long distance migrants (_s_20 n.mi., 37.0 
km) followed a south to southwesterly course. 

7. Male and female lobsters exhibited no differences in 
movement. There was no apparent relationship between a 
lobster's size (98% of the tagged lobsters ranged from 81 to 
100 mm CL) and the distance moved. 

8. Except for an initial period of about 8 wk, which we con- 
sider unrepresentative, there was no association between 
the time lobsters were at large and the distance traveled. 
Therefore, even if the recovery rate had been lower there 
is no reason to believe that the movement patterns would 
have deviated from those observed. 

9. Annual instantaneous fishing mortality rates, which were 
calculated from return data grouped at weekly, biweekly, 
and monthly intervals, were 4. 14 (98.4%) to 4.93 (99.3%) at 
Kennebunkport, 3.98 (98.1%) to4.13 (98.4%) at Boothbay 
Harbor, and 7.22 (99.9%) to 7.31 (99.9%) at Jonesport. 
Although the accuracy of these values has been biased by 
errors associated with tagging, the magnitude of these F s 
still reveals the lobster fishery's precariously high level of 
exploitation. 

ACKNOWLEDGMENTS 

I thank David Libby for his assistance with all phases of this 
study; Paul DeRocher and Donald Card (crew of the RV 
Duchess) for their invaluable help during the entire tagging 
operation. Thanks are also extended to Clarence Burke, David 
Parkhurst, and Gary Robinson who provided assistance with 
tagging. I am appreciative for the guidance offered by James 
Thomas. I thank those lobster dealers and fishermen who, 
often at an inconvenience to themselves, supported our pro- 
gram by reporting returns and furnishing pertinent informa- 
tion. An anonymous reviewer critically reviewed the 
manuscript and offered many valuable suggestions. 

LITERATURE CITED 

COOPER, R. A. 

1970. Retention of marks and their effects on growth, behavior, and 



migrations of the American lobster, Homarus americanus. Trans. Am. 
Fish. Soc. 99:409-417. 
COOPER, R. A., R. A. CLIFFORD, and C. D. NEWELL. 

1975. Seasonal abundance of the American lobster, Homarus 
americanus, in the Boothbay region of Maine. Trans. Am. Fish. Soc. 
104:669-674. 
DOW, R. L. 

1961. Some factors influencing Maine lobster landings. Commer. 
Fish. Rev. 23(9):1-11. 

1964. Supply, sustained yield, and management of the Maine lobster 
resource. Commer. Fish. Rev. 26(Ua):19-26. 

1974. American lobsters tagged by Maine commercial fishermen, 
1957-59. Fish. Bull., U.S. 72:622-623. 

FOGARTY, M. J., D. V. D. BORDEN, and H. J. RUSSELL. 

1981. Movements of American lobster, Homarus americanus, off 
Rhode Island. Fish. Bull., U.S. 78:771-778. 
GROOM, W. 

1978. Interim investigation of lobster stock, size, and migration system 
of lobster population in the Grand Manan region. New Brunswick Dep. 
Fish., Fredericton, 69 p. 
GULLAND, J. A. 

1963. On the analysis of double-tagging experiments. Int. Comm. 

Northwest Atl. Fish. Spec. Publ. 4:228-229. 
1969. Manual of methods for fish stock assessment. Part I. Fish 
population analysis. FAO Man. Fish. Sci. 4, 154 p. 
KROUSE, J. S. 

1973. Maturity, sex ratio, and size composition of the natural popula- 
tion of American lobsters, Homarus americanus, along the Maine 
coast. Fish. Bull., U.S. 71:165-173. 
1978. Effectiveness of escape vent shape in traps for catching legal-sized 
lobster, Homarus americanus, and harvestable-sized crabs, Cancer 
borealis and Cancer irroratus. Fish. Bull., U.S. 76:425-432. 
KROUSE, J. S., and J. C. THOMAS. 

1975. Effects of trap selectivity and some population parameters on size 
composition of the American lobster, Homarus americanus, catch along 
the Maine coast. Fish. Bull.. U.S. 73:862-871. 

RUSSELL, H. J., Jr. 

1980. Analysis of double-tagging experiments: an update. Can. J. 
Fish. Aquat. Sci. 37:114-116. 
SCARRATT, D. J., and P. F. ELSON. 

1965. Preliminary trials of a tag for salmon and lobsters. J. Fish. Res. 
Board Can. 22:421-423. 

THOMAS, J. C. 

1973. An analysis of the commercial lobster (Homarus americanus) 
fishery along the coast of Maine, August 1966 through December 
1970. U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF-667, 57 p. 



12 



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NMFS Circular and Special Scientific Report— Fisheries 

Guidelines for Contributors 



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entry and page numbers should be omitted. 

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Text. See also Form of the Manuscript below. Follow the 
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Special Publication No. 12, A List of Common and Scientific 
Names of Fishes from the United States and Canada, fourth 
edition, 1980. Use short, brief, informative headings in place 
of "Materials and Methods." 

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unpublished or some processed material, give author, year, 
title of manuscript, number of pages, and where it is filed — 
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Literature cited. In text as: Smith and Jones (1977) or 
(Smith and Jones 1977); if more than one author, list accord- 
ing to years (e.g., Smith 1936; Jones et al. 1975; Doe 19 
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mat, see recent SSRF or Circular. 

Abbreviations and symbols. Common ones, such as mm, 
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Abbreviate units of measures only when used with numerals; 
periods are rarely used in these abbreviations. But periods 
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Personal communications. Cite name in text and footnote. 
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