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546 



jun i 4 wr 

DIVISION OF FISHES 
U. S. NATIONAL MUSEUM 



Longline Fishing for Deep-Swimming 
Tunas in the Marquesas Islands 
and Adjacent Areas 



By Howard O. Yoshida 




UNITED STATES DEPARTMENT OF THE INTERIOR 

Stewart L. Udall, Secretary 

Charles F. Luce, Under Secretary 

Stanley A. Cain, Assistant Secretary for Fish and Wildlife and Parks 

FISH AND WILDLIFE SERVICE, Clarence F. Pautzke, Commissioner 

Bureau of Commercial Fisheries, Harold E. Crowther, Acting Director 



Longline Fishing for Deep-Swimming 

Tunas in the Marquesas Islands 

and Adjacent Areas 



By 
HOWARD O. YOSHIDA 



United States Fish and Wildlife Service 
Special Scientific Report—Fisheries No. 546 



Washington. D. C. 
April 1967 



CONTENTS 

Page 

Introduction 1 

Methods^ 2 

Distribution and abundance of tunas 3 

Yellowfin tuna 3 

Bigeye tuna 5 

Other tunas 5 

Vertical distribution of tunas 6 

Size of tunas 7 

Summary 8 

Literature cited 10 



Longline Fishing for Deep-Swimming 

Tunas in the Marquesas Islands 

and Adjacent Areas 



By 



HOWARD O. YOSHIDA, Fishery Biologist 

Bureau of Commercial Fisheries Biological Laboratory 
Honolulu, Hawaii 96812 



ABSTRACT 



Six hundred forty-two tuna, including 438 yellowfin tuna ( Thunnus albacares ) , 
102 bigeye tuna (T. obesus ) , 51 albacore (T. alalunga ) , and 51 skipjack tuna 
( Katsuwonus pelamis ), were caught by longline fishing on three cruises across 
the Equator on long. 132° and 150° W. and around the Marquesas Islands (ca. 
long. 140° W.) between August 1956 and May 1958. These cruises were part of 
an investigation of fishery resources of the Marquesan area by the Bureau of 
Commercial Fisheries Biological Laboratory at Honolulu. 

The distribution and abundance of yellowfin tuna are considered in greatest 
detail in this report, because this species dominated the catches. Yellowfin tuna 
were more abundant during the Southern Hemisphere summer than winter and on 
long. 132° W. than on long. 150° W.; also, they were more numerous in the 
"inshore," <148 kilometers (80 nautical miles) from land, waters of the Mar- 
quesas than in the adjacent "oceanic" (> 148 kilometers from land) waters. 
Their abundance differed seasonally in the insular waters of the Marquesas. 

Although bigeye tuna were not as abundant nor as widely distributed, their 
distribution was somewhat similar to that of yellowfin tuna. 

No albacore were caught north of lat. 7° S. on long. 132° and 150° W. This 
distribution appeared to be associated with a discontinuity of the oceanic struc- 
ture extending east-west around lat. 10° S. 



INTRODUCTION 

Investigations of the high-seas fishery re- 
sources of the tropical and subtropical Pacific 
Ocean by the Bureau of Commercial Fisheries 
Biological Laboratory at Honolulu!' have in- 
cluded sampling of deep-swimming tunas taken 
by longline in equatorial waters. The early 
investigations were designed to cover a vast 
area of the equatorial Pacific to delimit the 
general distribution and abundance of the deep- 
swimming tunas. This exploratory fishing 
revealed a concentration of yellowfin tuna 
( Thunnus albacares ) along the Equator, with a 
zone of high abundance between long. 140° and 
160° W. (Murphy and Shomura, 1953a, 1953b, 

— Formerly known as the Pacific Oceanic Fishery 
Investigations (POFI) . 



1955; Shomura and Murphy, 1955). Later in- 
vestigations were centered on the distribution 
and abundance of yellowfin tuna around the Line 
Islands (Iversen and Yoshida, 1956, 1957), which 
are located within the general zone of high 
abundance. 

After the completion of the investigations in 
the central equatorial Pacific, exploratory fish- 
ing was extended to the Marquesas Islands and 
adjacent areas. The longline fishing in this 
region, however , was ancillary to a more inten- 
sive study of the surface tunas. In addition, a 
small part of the fishing was expended towards 
testing certain hypotheses that had developed 
from results of previous work in the central 
equatorial Pacific. 

There were three cruises to the Marquesas 
between August 1956 and May 1958 during which 
at least part of the time was spent in longline 



fishing (fig. 1). The seasons and areas of fish- 
ing are given in table 1. 

METHODS 

Mann (1955) described in detail longline gear 
similar to that used for this study. The basic 
unit, the basket, was composed of a 384-m. 
mainline and eleven 5.5-m. hook droppers or 
branch lines attached to the mainline at27.4-m. 
intervals. Forty-four to sixty of these baskets 
were joined to make a set. The set was buoyed 
by a series of floats attached to basket junc- 
tures by 18.3-m. float lines. The bait was fro- 
zen Pacific herring ( Clupea harengus pallasi ). 
Murphy and Shomura (1953a) described in some 
detail the manner in which longlines are set and 
retrieved. As a rule, they are set at dawn and 
retrieved at noon. 

To estimate the depths fished by the longline, 
five or six sounding tubes were used regularly 
at each fishing station. They were attached to 
the sixth dropper, the middle dropper of the 
11-hook basket, and were distributed evenly, 
throughout the set. For each longline station 
the depths indicated by these sounding tubes 
were averaged and the mean depths were used 
to represent the mean maximum depth of the 
longline. At many stations additional sounding 
tubes were attached to the third, sixth, and ninth 
droppers of one basket to get an estimate of the 
configuration of the mainline. 

The total lengths of all the tuna caught on the 
cruises were obtained by the method described 
by Marr and Schaefer (1949). 

For some sections of this paper it was con- 
venient to classify the fishing stations as 
"oceanic" or "inshore.'' The division between 
oceanic and inshore fishing stations was made 
at a distance of 148 kilometers (80 nautical 



miles) from land (following Shomura and Murphy, 
1955). By this criterion, all of the stations 
fished on north-south transects on long. 132° 
and 150° W. were oceanic. The inshore stations 
were all near the Marquesas Islands. 




Figure 1. --Tracks of CHG ( Charles H. Gilbert ) 
cruises 30 and 38, and JRM ( John R. Manning ) 
cruise 34. 



Table 1. --Summary of fishing by season and area, Charles II. Gilbert cruises 30 and 38 and 

John R. Mann ing cruise 34 



Cruise 



Season- 



Area fished 



Charles H. Gilbert 
cruise 30 

John R_. Manning 
cruise 34 



W int er ( Augus t - 
September 1956) 

Summer (January- 
March 1957) 



Long. 132° W. from lat. 1°32' N. to 12°07' S.; 
around Marquesas Islands and adjacent area. 

Long. 132° W. from lat. 4°29' N. to 14°02 ' S.; 
around Marquesas Islands; long. 150° W. from 
lat. 16°34' S. to 3°01' N. 



Charles H. Gilbert 
cruise 38 



Summer (February 
1958) 



Long. 150° W. from lat. 4°44' N. to 0°45' S. 



— For Southern Hemisphere. 



In the analysis of the results of fishing, the 
catch rates of yellowfin tuna and bigeye tuna 
(T. obesus ) , by season and area, were subjected 
to simple statistical tests. Catch rates from 
two or more independent areas or seasons were 
tested to see whether they could have been 
drawn from the same population (Mann-Whitney 
U test or the Kruskal-Wallis one-way analysis 
of variance by ranks--Siegel, 1956). I concluded 
that fish were relatively more abundant in one 
area or season if differences in the catch rates 
were significant. 

Unless otherwise stated, all the seasonal 
designations in this paper refer to seasons in 
the Southern Hemisphere. 

DISTRIBUTION AND ABUNDANCE 
OF TUNAS 

The data on longline fishing from the three 
cruises already have been published (Austin, 
1957; Wilson and Rinkel, 1957; and Wilson, 
Nakamura, and Yoshida, 1958). The tuna catch 
of these cruises totaled 642 fish, comprising 
438 yellowfin tuna, 102 bigeye tuna, 51 albacore 
(T. alalunga ) , and 51 skipjack tuna ( Katsuwonus 
pelamis ). 

The distribution and abundance of yellowfin 
tuna are considered in greatest detail, since 
this species dominated the catches. 

Yellowfin Tuna 

Previous investigations in the equatorial 
Pacific Ocean disclosed the presence of con- 
centrations of yellowfin tuna within a band of 
latitude several degrees to the north and south 
of the Equator, and also indicated north-south 
and east-west shifts in these concentrations 
(Murphy and Shomura, 1953a, 1953b, 1955; 
Shomura and Murphy , 1955; Iversen and Yoshida, 
1956). 

In the winter of 1956, deep-swimming yellow- 
fin tuna were caught from lat. 1°32' N. to as far 
south as lat. 13°26' S. , the southernmost fishing 
station, on long. 132° W. (fig. 2). The catch 
rates were highest at the northernmost fishing 
station of the north-south transect and ranged 
from to less than 1 fish per 100 hooks for the 
remainder of the transect. A rather discontin- 
uous distribution is suggested. 

The latitudinal range fished during the sum- 
mer of 1957 on long. 132° W., was from lat. 
4°29' to 14°02' S. Yellowfin tuna were found 
throughout this range and were relatively more 
abundant than in the previous winter (fig. 2 and 



o 

o 
s 1 



132"W. . 

WINTER 1956 



132°W 



SUMMER 1957 









_, 150°W. . 

SUMMER 1957 



150° W 












5UMMER 1958 














































o L 




1 


FIRr- 





LATITUDE 

Figure 2. --Oceanic catch rates (number of fish 
per 100 hooks) for yellowfin tuna on long. 
132° W., winter 1956 and summer 1957, and on 
long. 150° W., summers 1957 and 1958. 

table 2). The catch rate was highest at lat. 
3°29' S. In the same season, but farther to the 
west, on long. 150° W., yellowfin tuna were less 
abundant and were irregularly distributed be- 
tween lat. 3°01' N. and 16°34' S. (fig. 2 and table 
2). The highest catch rate, 1.6 fish per 100 
hooks, was at lat. 0°06' N. Another transect 
was fished on this meridian the following sum- 
mer. On this 1958 transect, fishing was con- 
fined to a narrow band across the Equator, be- 
tween lat. 4°44' N. and 0°45' S. Catches of yel- 
lowfin tuna again were rather low and were 
concentrated within a few degrees of latitude 
north of the Equator. 

In summary it is evident that yellowfin tuna 
were relatively unavailable to longline fishing 
on long. 150° W. At long. 132° W., where a 
seasonal comparison can be made, yellowfin 
tuna were relatively more abundant in the sum- 
mer than in winter. They also were more 
abundant to the east, at long. 132° W., than at 
long. 150° W., at least during the summer of 
1957. In addition to these seasonal and longi- 
tudinal differences, relative abundance exhibited 
latitudinal shifts. 



Table 2. --Catch rates of yellowfin tuna by season and area 



Area or season Comparison of catch rates 



Test 



Result 



Long. 132° W. 



Summer 1957 



Marquesas Islands 



Winter 1956 



Summer 1957 



Between summer 1957 and 
winter 1956 

Between long. 132° 
and 150° W. 

Between summer 1957 
and winter 1956 

Between Marquesas Islands 
and long. 132° W. 

Among Marquesas Islands 
long. 132° and 150° W. 



Mann-Whitney U = 35.5, n = 11, n 2 = 13; p <0.002 



do 



do 



do 



Kruskal- 
Wallis 



U = 56, n = 13, n = 15; p <0.002 



U = 4, n = 5, n = 9; p <0.002 



U = 11, n = 5, n 2 = 5; p 0.421 



X = 12.5078, d.f. = 2; p <0.01 













" 




r-j 








































r-> 










- 


i 




1 — 1 







o 






n 


Hnnn 





30 31 1 2 3 4 

AUG. SEPT. 

1956 



FEB. 
1957 



Figure 3. --Catch rates for yellowfin tuna 
(number of fish per 100 hooks) at the in- 
shore stations. 



The daily catch rates (fish per 100 hooks) of 
yellowfin tuna at inshore stations near the Mar- 
quesas Islands are presented in figure 3. The 
catch rate varied considerably from day to day 
(0 to 8.4 fish per 100 hooks). Seasonally yel- 
lowfin tuna were relatively abundant during the 
summer (table 2). The catch rates during the 
winter ranged from to 2.2 fish per 100 hooks, 
but in the summer the range was 0.9 to 8.4. The 
Hawaiian longline fishery also shows a season- 
ality in abundance; greatest numbers are caught 
from May to September (Otsu. 1954). June 
(1953) suggested that the longline fishery in 
Hawaii is based on a spawning migration, for 
the months which have the highest catch rates 
for yellowfin tuna coincide with the period of 
greatest ovarian maturity. No comparable data 
on maturity are available from the Marquesas 
Islands. The occurrence of fish larvae, how- 
ever, has been taken to indicate spawning areas 



and seasons by many workers, e.g., Matsumoto 
(1958). The abundance of yellowfin tuna larvae 
was observed during the periods covered by our 
longline fishing. Strasburg (1960) gave data on 
larvae captured in 1/2-hour surface plankton 
tows in an area around the Marquesas Islands 
bounded by lat. 7°32' and 12°48' S., long. 134°46' 
and 143°55' W. The larvae were captured at 
the rate of 0.02 per 1,000 m.^ of water strained 
in winter and 1.65 per 1,000 m.^ of water 
strained in summer. Furthermore, as will be 
shown later, the higher catch rates on longlines 
in summer may have resulted from an influx of 
larger, and presumably more mature, yellowfin 
tuna into the Marquesas area. They well may 
converge on this area to spawn during summer. 

Strasburg (1958: p. 348) noted several ways 
in which the proximity of land can influence the 
distribution of marine animals: "For certain 
oceanic species the presence of land acts only 
as a barrier to movements, whereas others 
congregate about islands and other land masses 
to feed or to reproduce. It occasionally happens 
that oceanic fish abound in insular environ- 
ments, either because of the islands' intrinsic 
nutritive richness or because they lie in the 
path of rich oceanic currents." 

My data, although rather meager, provide 
information on the abundance of yellowfin tuna 
close to the Marquesas Islands as contrasted 
with the adjacent oceanic areas. For this com- 
parison, the oceanic stations south of lat. 7° S. 
were selected. I believe that the effect of the 
equatorial enrichment system, in which yellow- 
fin tuna are known to be relatively abundant, is 
not discernible this far south. During summer, 
the average catch rates were higher in the in- 
shore waters of the Marquesas than in the ad- 



jacent oceanic areas; catch rates differed little 
during winter (fig. 4 and table 2). In the equa- 
torial Pacific Ocean, near the Line Islands, 
yellowfin tuna also tend to be more abundant 
near land than in the open ocean (Shomura and 
Murphy. 1955; Iversen and Yoshida. 1957). 



150' w.- 



MARQUESAS IS. 
132'W. 



150»W 



NO EFFOR1 
















| 




3 









WINTER 




SUMMER 



1 2 3 

CATCH PER 100 HOOKS 



Figure 4. --Catch rates (number of fish per 
100 hooks) for yellowfin tuna in the Mar- 
quesas Islands (inshore stations) and adja- 
cent oceanic areas south of lat. 7° S. 



from lat. 4°44' N. to C 45' S. the following sum- 
mer, the distributions of bigeye and yellowfin 
tunas were similar, except that the peak catch 
of bigeye tuna was at lat. 0°53' N. and the peak 
catch of yellowfin tuna was at lat. 2°57' N. 

Only small numbers of bigeye tuna were 
caught near the Marquesas Islands in both sum- 
mer and winter. The catch rates varied from 
to 0.8 fish per 100 hooks and, unlike the rates 
for yellowfin tuna, displayed no marked season- 
al difference. 

Other Tunas 

Small numbers of skipjack tuna and albacore 
were caught along with yellowfin and bigeye 
tunas. Deep-fishing longlines do not effectively 
sample the skipjack tuna, which is a small, 

3r 





132° W. 












WINTER 1956" 












o o H 


I 


m 






1 











Bigeye Tuna 

The distribution of bigeye tuna differed from 
that of yellowfin tuna on long. 132° W. in the 
winter of 1956 (fig. 5). Their distribution was 
relatively limited along this meridian (between 
lat. 4° and 11° S.). whereas yellowfin tuna were 
found from about lat. 2° N. to 13° S. In the 
summer of 1957, however, bigeye tuna were 
more abundant and more widely distributed (lat. 
4°29' N. to 14°02' S.) than they were in the win- 
ter of 1956 and their distribution closely paral- 
leled that of yellowfin tuna (figs. 2,5. and table 
3). 

Farther west, on long. 150° W., bigeye tuna 
were not as abundant nor as widely distributed 
as they were on long. 132° W. (fig. 5 and table 
3). They were taken in small numbers between 
lat. 5°51' S. and 3°01' N. on this transect but 
were distributed discontinuously within these 
latitudes. In contrast, yellowfin tuna were found 
from lat. 16°34' S. to 3°01' N. on this meridian 
during the same period. Along long. 150° W. 



z 
- 



a. 
u 
a. 





132° W. 






" 










SUMMER 1957 
















n o o 


1 ra 


■ 









m m m Ira 





= 

§ 





150° W. 

SUMMER 1957 


























o o m 


Y7i FT1 o 


) o n n 







150° W. 

SUMMER 1958 


























^\ 


1 


" 


nraoF 





15" S. 10° 5° 0° 5" J 

LATITUDE 

Figure 5. --Oceanic catch rates for bigeye 
tuna (number of fish per 100 hooks) on 
long. 132° W., winter 1956 and summer 1957, 
and on long. 150° W. , summers 1957 and 
1958. 



Table 3. --Catch rates of bigeye tuna by season and area 



Area or season 



Comparison of catch rates 



Test 



Result 



Long. 132° W. 



Between summer 1957 and 
winter 1956 



Mann-Whitney U = 60, n = 11, n = 13; p <0.002 



Summer 1957 



Between long. 132° and 
150° W. 



do 



U = 43, n x = 13, n 2 = 15; p <0.002 



surface-schooling species (Shomura and Murphy, 
1955). Around the Marquesas Islands, where 
they are abundant (Wilson, MSj'), longlines 
catch only small numbers. Catches of this fish 
on long. 132° and 150° W. also were small and 
sporadic. 

Albacore first began to appear in the catches 
at about lat. 7° S. on long. 150° W. and at about 
lat. 11° S. on long. 132° W. The number caught 
at any one station was small. This distribution 
of albacore is interesting in light of the obser- 
vations by Yamanaka (1956) in the western 
South Pacific. Yamanaka noted a conspicuous 
discontinuity, characterized by sharp changes 
in water temperature, salinity, and sigma-t 
values, in the oceanic structure running in an 
east-west direction and centered on lat. 10° S. 
He suggested that this discontinuity probably 
limits distribution of albacore in the south- 
west Pacific. Our observations on the oceanic 
structure in this area indicate that this discon- 
tinuity extends as far east as long. 132° W. 

Only small numbers of albacore were taken 
around the Marquesas Islands in both winter and 
summer; the catch rates ranged from to 2.2 
albacore per 100 hooks. 

VERTICAL DISTRIBUTION OF TUXAS 

Iversen and Yoshida (1957) showed that the 
longlines tend not to fish as deep near the Equa- 
tor as they do several degrees to the north. 
They suggested that this difference was caused 
by the shear between the westerly South Equa- 
torial Current at the surface and the easterly 
Equatorial Undercurrent beneath. In general, 
results were similar on the north-south fishing 
transects across the Equator on long. 132° and 
150° W. (fig. 6). The mean maximum depths 
reached by the longlines within about 2° north 
and south of the Equator were not as great as 
those recorded farther north or south; this 
trend was not strongly evident during Charles 
H. Gilbert cruise 38. 

The Pacific Equatorial Undercurrent first 
was described by Cromwell, Montgomery, and 
Stroup (1954). Knauss and King (1958), who 
measured the velocities of the Undercurrent, 
found that it was symmetrical about the Equator 
and that the core of the current was flowing be- 

2/ 

— Wilson, Robert C. MS. The surface tuna re- 
sources of the Marquesas Islands. Division of 
Foreign Fisheries, Bureau of Commercial Fisher- 
ies, Washington, D.C. 20240. 



- 



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IBM -.Id 












^4 


/? ^- 






_ ^~ 




,< 1 

/ XHG-30 

























IJU yv - 














JRM-34 
\ 


*f 










\ . 
















CHG-38 





LATITUDE 

Figure 6 . --Latitudinal variation of the mean 
maximum depths of longline gear on long. 
132° and 150° W. CHG is Charles H. Gilbert 
and JRM is John R. Manning . 

tween 2 and 3.5 knots at 0°, long. 140° W. They 
also found that the Undercurrent was weaker on 
either side of the Equator; the velocity was 0.6 
knot at lat. 2° N. and 2° S. The depths reached 
by our gear demonstrate this configuration, be- 
cause the longlines usually were shallowest at 
the Equator, where the velocity of the Under- 
current is greatest, and became deeper on 
either side, where the Undercurrent is weaker. 

Longline catches have been used to evaluate 
the vertical distribution of tunas (Murphy and 
Shomura, 1953a, 1953b, 1955; Shomura and 
Murphy, 1955). Chemical sounding tubes at- 
tached to the gear have provided estimates of 
the absolute depths of the longlines, and ac- 
cordingly, the vertical distribution of tunas 
(Shomura and Otsu, 1956; Iversen and Yoshida, 
1957). Catches of tunas usually have been 
greatest on the deeper hooks of the longline. 
For example, Murphy and Shomura (1955: p. 27) 
stated that "...yellowfin are usually but not 
consistently more abundant at the deeper levels 
in the equatorial Pacific, the best bigeye catches 
are more regularly associated with the deeper 
fishing levels, and albacore are clearly caught 
in greatest abundance on the deepest fishing 
hooks." 

To determine the vertical distribution of 
tunas, the catch rates for all stations were 
combined and averaged by species according to 



YELLOWFIN 



BIGEYE ALBACORE 



60-74 
75-89 
90-104 
105-119 



Zlm 



120- 
135- 
150- 
165- 

105 
120 
135- 
150 
165 



134 
149 
164 
179 

-119 
-134 



1JI4) 



(4) 



(5) 



(61 



(16) 



(1) 



Ho 



(4) 



[4| 



(9) 



(2) 



—1(2) 



;-i49 

164 
179 



1 11) 



1(6) 



Do 



ID 



(3) 



(2) 



(4) 



(2) 



Jl'l 



01234567890101 
CATCH PER 100 HOOKS 

Figure 7. --Vertical distribution of longline catches of tunas at 
oceanic and inshore stations. Figures in parentheses are number 
of stations used in calculating the average catch rate (number 
of fish per 100 hooks) . 



U 



U 

o 



o 

x 



the average maximum fishing depth of the long- 
lines by 15-m. depth intervals. No zero catch 
rates were used in calculating the averages. 
The vertical distribution of tunas at oceanic 
stations is shown in figure 7. Yellowfin tuna 
were caught at all fishing depths; the highest 
catch rate was at the 75- to 89-m. depth. Com- 
plicating factors were latitudinal differences in 
both the catch rates and the depths at which the 
longlines fished. For example the depth at 
which longlines fish is relatively shallow near 
the Equator and here the catch rate of yellowfin 
tuna was greatest. Therefore, the peak catch 
rate at the 75- to 89-m. depth may be merely a 
reflection of the greater abundance of yellowfin 
tuna close to the Equator, or on the other hand, 
it may indicate that the vertical distribution of 
yellowfin tuna is real and that more are caught 
here because the longlines fish the depths in 
which tuna are most abundant. 

Bigeye tuna, like yellowfin tuna, were caught 
at all depths fished. The highest catch rates 
were at 90 to 104 m. Here again, it is difficult 
to assess the relative influence of the areal 
distribution and the vertical distribution of the 
tunas. 

As has been noted, no albacore were caught 
north of lat. 7° S. It could be argued that the 



longlines did not fish deep enough north of lat. 
7° S. to catch them. This argument is apparent- 
ly not valid, however, for the longlines fished 
as deep between lat. 2° and 5°N. and 4° and 7° S., 
as they did south of 7° S. It can be seen (fig. 7) 
that albacore were distributed rather evenly 
between 105 and 164 m. 

The longlines fished relatively deep around 
the Marquesas--112 to 166 m., average maxi- 
mum depth. The vertical distribution of tunas 
in this area is shown in figure 7. Although 
yellowfin tuna were caught at all depths, greater 
catch rates were within the two deepest strata. 
Bigeye tuna were caught between 105 and 169 m. 
with more fish taken in the 150- to 164-m. 



SIZE OF TUNAS 

Longlines typically catch greater numbers 
of the larger tuna than does pole and line or 
troll fishing, either by inherent selectivity of 
larger fish by the longlines or because the 
deep-swimming populations are made up chiefly 
of large fish (Murphy and Shomura, 1953a). 
The length-frequency distributions of oceanic 
and inshore catches of yellowfin tuna (fig. 8) 
indicate essentially no difference. The length 



IS 

u 

p= 30 





LONGLINE 




























OCEANIC STATIONS 
































h 


J. 187 














































n 


"i(- 


































n 






n 






















.nnHn 




| 






On 

















1 

1 L 

INSH 


1 1 1 

DNGLINE 

ORE STATIO^ 
N=228 


S 
















































- 


pi 


" 


_ 


































n 












n 




























_'n 


1 












it 




n 















1135 



122 
1253 



134 
1375 



146 
1495 



158 
1615 



I7p 
1735 



18,2 
1855 



u 

2 
w 
- 





1 1 1 I 

POLE-AND-LIN 

MARQUESAS ARE 
1 N = 1?A 


E 

A . 


\ 






























n 






- 
































f— 1 


11 




n 


n 




1 


run 


n 




1 — 1 


r-i 


f—i 




rn 




p?a 





5,0 


V 


74 86 9,8 


110 


535 


655 


775 895 1015 
LENGTH (CM.) 


1135 



122 

1255 



Figure 8 . --Length-frequency distributions of 
yellowfin tuna caught by longlines at 
oceanic stations, inshore stations, and on 
pole and line in the Marquesas area (pole- 
and-line data from Wilson and Rinkel, 1957, 
and Wilson et al., 1958). 

ranges were about equal and the dominant 
sizes were similar. This situation is at vari- 
ance with that around the Line Islands. Although 
the catches there also are dominated by large 
yellowfin tuna, more small fish (50-110 cm.) 
are caught near the Line Islands than offshore 
(Shomura and Murphy, 1955; Iversen and 
Yoshida, 1957). No yellowfin tuna smaller than 
114 cm. were caught by longlining around the 
Marquesas, although their presence was shown 
by catches made by pole-and-line fishing (fig. 
8). Fish between 90 and 130 cm. were sparsely 
represented in catches of both longline and pole 
and line. This result may indicate that the 
smaller yellowfin tuna in that size range were 
not present in great numbers or that neither 
fishing method adequately samples them. 

The possibility has been mentioned that the 
seasonally greater abundance of yellowfin tuna 
around the Marquesas during the summer may 
have been caused by an influx of large fish. 



£ 30 





SUMMER 

N=214 










































n 


n 


n 


- 


























n 


■ 














n 













WINTER 

N-14 




1 


n 
































- 




n 


























r 














- 



















1]0 12,2 

1135 1255 



134 
1375 



146 
1495 



158 
1615 



170 
1735 



LENGTH (CM.I 



Figure 9 . --Length-frequency distribution of 
yellowfin tuna in the Marquesas Islands, 
arranged by season. 

The length-frequency distribution of fish caught 
in this area, arranged by season (fig. 9) shows 
that no fish longer than 150 cm. were caught 
during winter and that their modal size was be- 
tween 130 and 138 cm. In the summer about 
36 percent of the catch was composed of fish 
longer than 150 cm., and the mode was at 146- 
150 cm. These data should be viewed with 
caution, however, for the winter sample con- 
sisted of only 14 yellowfin tuna. 

Length-frequency distributions of skipjack 
tuna, albacore, and bigeye tuna are presented 
in figure 10. These tunas were not caught in 
sufficient numbers to warrant detailed com- 
ments. The modes in the length-frequency dis- 
tributions of bigeye tuna are indefinite; however , 
85 percent of the bigeye tuna were between 126 
and 178 cm. long. The size distribution of alba- 
core was relatively compact: All of the speci- 
mens measured between 90.6 and 111.6 cm., a 
length range of only 21 cm. Skipjack tuna ranged 
from 46.6 to 83.1 cm., and had a mode at 74- 
78 cm. 

SUMMARY 

1. This report is based on the tuna catches 
made by longline fishing on three cruises 
around the Marquesas Islands and across the 
Equator on long. 132° and 150° W. Six hundred 
forty-two tuna were caught, of which 438 were 
yellowfin, 102 bigeye, 51 albacore, and 51 
skipjack. 











































































N=48 








































































i 








































































% 
















































































































































- 








































































































































n 


n 


nn 


n 


i 











































































































































A 


N = 46 


vL 




















































































1 
















































































n 








































































^ 


r- 








































































vk 






_ 














































































n 





















































___ - 

BIGEYE 




















































N- 


97 
































M | M 


fin 


n 










































rur 




i II 


nn 















5,0 


e ? 


74 


86 


98 


110 122 134 


146 


158 


170 


18,2 


194 


533 


653 


773 


893 


101.9 


1133 1253 1373 
LENGTH (CM.) 


1493 


1613 


173.9 


1853 


197.9 



Figure 10. --Length-frequency distributions of skipjack tuna, 
albacore, and bigeye tuna. 



2. Yellowfin tuna were the most abundant and 
widely distributed species of deep-swimming 
tunas in the oceanic areas. Where areal and 
seasonal comparisons could be made, they were 
more abundant on long. 132° W. than on 150° W., 
and during the Southern Hemisphere summer 
than during winter. The concentrations also 
showed apparent north-south shifts. Yellowfin 
tuna also were more abundant in the inshore 
waters of the Marquesas than in oceanic waters 
south of lat. 7° S. 

3. The abundance of yellowfin tuna around 
the Marquesas varied seasonally. The presence 
of greater numbers of larger, and presumably 
more mature, fish and the occurrence of greater 
numbers of the larvae during the summer, sug- 
gest that they gather in this area to spawn. 

4. Although bigeye tuna were not as abundant 
or widely distributed, their distribution, in gen- 
eral, was somewhat similar to that of yellowfin 
tuna. The greatest relative abundance of bigeye 
tuna was to the east (long. 132° W.) and during 
the Southern Hemisphere summer; they also 
showed north-south shifts in centers of concen- 
tration. Only small numbers of this species 
were taken near the Marquesas. 

5. No albacore were caught north of lat. 
l' J S. on long. 132° and 150° W. There are indi- 



cations that an east-west discontinuity of the 
oceanic structure around lat. 10° S. somehow 
may restrict the distribution. Like bigeye tuna, 
albacore were not very abundant at the inshore 
stations around the Marquesas. 

6. Longlines did not fish as deep between 
lat. 2° N. and 2° S. as they did farther to the 
north and south. This fact was ascribed to 
shearing between the westerly flowing South 
Equatorial Current at the surface and the east- 
erly flowing Equatorial Undercurrent beneath. 

7. No conclusive statement could be made of 
the depths at which oceanic yellowfin and bigeye 
tunas were most abundant. Both species, how- 
ever, were caught at all depths fished by the 
longlines. Oceanic albacore south of lat. 7° S. 
were evenly distributed between 105 and 164 m. 
Near the Marquesas Islands catches of yellowfin 
tuna were often greater when the longlines 
fished deeper. Catches of bigeye tuna were 
greatest between 150 and 164 m. Albacore were 
deeper than yellowfin or bigeye tunas. 

8. The length.-frequency distributions of 
yellowfin tuna caught at oceanic stations and at 
stations near the Marquesas Islands were sim- 
ilar; yellowfin tuna from 90 to 130 cm. long 
were sparsely represented in catches near the 
Marquesas. Fish in this size range possibly 



are not present in any great numbers in this 
area. 

LITERATURE CITED 

AUSTIN, THOMAS S. 

1957. Summary, oceanographic and fishery 
data, Marquesas Islands area, August- 
September, 1956 (EQUAPAC). U.S. Fish 
Wildl. Serv., Spec. Sci. Rep. Fish. 217, 
v + 186 p. 

CROMWELL, TOWNSEND, R. B. MONTGOMERY, 

and E. D. STROUP. 

1954. Equatorial Undercurrent in Pacific 
Ocean revealed by new methods. Science 
119(3097): 648-649. 

IVERSEN, EDWIN S., and HOWARD O. YOSHIDA. 

1956. Longline fishing for tuna in the central 
equatorial Pacific, 1954. U.S. Fish Wildl. 
Serv., Spec. Sci. Rep. Fish. 184, iv + 33 p. 

1957. Longline and troll fishing for tuna in 
the central equatorial Pacific, January 
1955 to February 1956. U.S. Fish Wildl. 
Serv., Spec. Sci. Rep. Fish. 203, v + 38 p. 

JUNE, FRED C. 

1953. Spawning of yellowfin tuna in Hawaiian 

waters. Fish Wildl. Serv., Fish. Bull. 

54: 47-64. 
KNAUSS, JOHN A., and JOSEPH E. KING. 

1958. Observations of the Pacific Equatorial 
Undercurrent. Nature, London 182: 601- 
602. 

MANN, HERBERT J. 

1955. Construction details of improved tuna 
longline gear used by Pacific Oceanic 
Fishery Investigations. Com. Fish. Rev. 
17(12): 1-10. 

MARR, JOHN C, and MILNER B. SCHAEFER. 
1949. Definitions of body dimensions used in 

describing tunas. Fish Wildl. Serv.. Fish. 

Bull. 51: 241-244. 
MATSUMOTO, WALTER M. 

1958. Description and distribution of larvae 

of four species of tuna in central Pacific 

waters. U.S. Fish Wildl. Serv., Fish. 

Bull. 58: 31-72. 
MURPHY, GARTH I., and RICHARD S. SHOMURA. 
1953a. Longline fishing for deep-swimming 

tunas in the central Pacific. 1950-51. 

U.S. Fish Wildl. Serv., Spec. Sci. Rep. 

Fish. 98, iii + 47 p. 
1953b. Longline fishing for deep-swimming 



tunas in the central Pacific, January- 
June 1952. U.S. Fish Wildl. Serv., Spec. 
Sci. Rep. Fish. 108, iii + 32 p. 
1955. Longline fishing for deep-swimming 
tunas in the central Pacific, August- 
November 1952. U.S. Fish Wildl. Serv., 
Spec. Sci. Rep. Fish. 137, iv + 42 p. 
OTSU, TAMIO. 

1954. Analysis of the Hawaiian longline fish- 
ery, 1948-52. Com. Fish. Rev. 16(9): 
1-17. 

SHOMURA, RICHARD S., and GARTH I. MURPHY. 

1955. Longline fishing for deep-swimming 
tunas in the central Pacific, 1953. U.S. 
Fish Wildl. Serv., Spec. Sci. Rep. Fish. 
157, v + 70 p. 

SHOMURA. RICHARD S., and TAMIO OTSU. 

1956. Central North Pacific albacore sur- 
veys, January 1954-February 1955. U.S. 
Fish Wildl. Serv., Spec. Sci. Rep. Fish. 
173. v + 29 p. 

SIEGEL, SIDNEY. 

1956. Nonparametric statistics for the be- 
havioral sciences. McGraw-Hill Book 
Company, Inc., New York, Toronto, 
London, 312 p. 

STRASBURG, DONALD W. 

1958. Distribution, abundance, and habits of 
pelagic sharks in the central Pacific 
Ocean. U.S. Fish Wildl. Serv., Fish. 
Bull. 58: 335-361. 
1960. Estimates of larval tuna abundance in 
the central Pacific. U.S. Fish Wildl. 
Serv., Fish. Bull. 60: 231-255. 
WILSON, ROBERT C.andMURICE O. RINKEL. 

1957. Marquesas area oceanographic and 
fishery data, January-March 1957. U.S. 
Fish Wildl. Serv., Spec. Sci. Rep. Fish. 
238, v + 136 p. 

WILSON, ROBERT C, EUGENE L.NAKAMURA, 
and HOWARD O. YOSHIDA. 

1958. Marquesas area fishery and environ- 
mental data, October 1957-June 1958. 
U.S. Fish Wildl. Serv., Spec. Sci. Rep. 
Fish. 283, vi + 105 p. 

YAMANAKA, HAJIME. 

1956. Vertical structure of the ocean in rel- 
evant to fishing conditions for albacore 
adjacent to 10° S. in the western South 
Pacific. Bull. Jap. Soc. Sci. Fish. 21(12): 
1187-1193. /in Japanese with English 
summary .J 



MS # 1576 



10 



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