it vant ) i va Hub ony i i bi jackie ten Soiteruheina ye oye ein Vasa arte mae at iqesohuavsegeayston bane oe Seen ee Eh Roy Farah te i eet ohm, tu Pate AAs ha het haa ane sees iag kane mene te Tenis ae eed << ratneye yecemad ott WSs Ti Ase ig thas tat a ett RS ' JUN 3 2 Rips DLVISIGN OF FISHES U. Se 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 ~~~ —__~ FISH AND WILDLIFE SERVICE -~~~ SO AES Ge OE a ee a ee aa a a en et ee a ee Se ee eS on ne en ee eee ae ee ae a 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 il 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 vO iii 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 and around the Marquesas Islands (ca. the Equator on long. 132° and 150° W. 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 1955; Shomura and Murphy, 1955). Later in- Investigations of the high-seas fishery re- sources of the tropical and subtropical Pacific Ocean by the Bureau of Commercial Fisheries Biological Laboratory at Honolulul/ 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, 1/ — Formerly known as the Pacific Oceanic Fishery Investigations (POFI). 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 at 27.4-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 (19538a) 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. Ltt LONGLINE STATIONS eee: > / ep 9p gh og [Ze Hareeetee . 140° 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 H. Gilbert cruises 30 and 38 and John R, Manning cruise 34 Cruise Season Area fished Charles H. Gilbert cruise 30 Winter (August- September 1956) Summer (January- March 1957) John R. Manning cruise 34 Charles H. Gilbert Summer (February cruise 38 1958) ror Southern Hemisphere. Long. 132° W. from lat., 1°32 N.. topl2eO7mesre around Marquesas Islands and adjacent area. Long. 132° Wo from lat. 4°29. Ne vto: el 2 O2RaiSme around Marquesas Islands; long. 150° W. from Lat. 16°344/Se to ySsig0N IN Long. 150° W. from lat. 4°44' N. to 0°45' S. In the analysis of the results of fishing, the catch rates of yellowfin tuna and bigeye tuna (I. 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 (IT. 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 0 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 5 4 | OZ WINTER 1956 | 3 - 0 Sisleose NRE ES 5 T 7 Ae 12a | SUMMER 1957 | é 2 ise 1 T iy! auUo eS 5 Boa 150° W. I SUMMER 1957 & 3 oO om ob A 5 4 150° W. SUMMER 1958 15°S. 10° 5° 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 Long. 132° W. Between summer 1957 and winter 1956 Between long. 132° and 150° W. Summer 1957 Between summer 1957 and winter 1956 Marquesas Islands Between Marquesas Islands and long. 132° W. Winter 1956 Among Marquesas Islands long. 132° and 150° W. Summer 1957 CATCH PER 100 HOOKS Figure 3.--Catch rates for tuna (number of yellowfin 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 0 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 Comparison of catch rates Test Result Mann-Whitney U = 35.5, n, = ll, n =" 135) py <0 002 1 2. do UR= 7565 ny 13% ny = 15; p <0.002 do U = 4, n Seay ny = 9; p <0.002 do Lue sil n, = a5 ny = 25) 5D) 0.421 Reveral= X-.= 12.5078, d.f. = 2: pezonom Wallis 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 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- in winter 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). WINTER 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. 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. from lat, 4°44’ N. to 0°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 0 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, 3 ° W. | | WINTER 1956 tr o ida} <4 1 7 S | 2 0 ZA wEOENEO D A i] ee cS} a a 150° W. = 2 SUMMER 1957 & S 3 | 150° W. | 4 SUMMER 1958 1 0 Was 0 15%S? 10° Se o° 5°N. 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 Long. 132° W. Between summer 1957 and winter 1956 Summer 1957 Between long. 132° and 150° W. Test Result Mann-Whitney U = 60, ny iis ny = 13; p <0.002 do U=" 43); n, = 135 ny = 15; p <0.002 surface-schooling species (Shomura and Murphy, 1955), Around the Marquesas Islands, where they are abundant (Wilson, MS.2/), 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 0 to 2.2 albacore per 100 hooks, VERTICAL DISTRIBUTION OF TUNAS 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- eiisone 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. 2 B Zz = o & | 5 | = 200 eo al = | 2 40 150° W., 2 | 2 80}— 2 |JRM-34 : 2 120 \ : x = g | ie oe’ \\ 160 | “I | CHG-38 | | 2 200) 15° S: 10° 5¢ 0° 5°N. 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 105-11I9WY OCEANIC DEPTH (M.) WML INSHORE 7 8 CATCH PER 100 HOOKS Figure 7.--Vertical distribution of longline catches of oceanic and inshore stations. of stations used 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 104m. Here again, it is difficult fo assess the relative influence of the areal distribution and the vertical distribution of the ftunas. As has been noted, no albacore were caught north of lat. 7° S, It could be argued that the tunas at Figures in parentheses are number in calculating the average catch rate (number of fish per 100 hooks). 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 between105 and169 m. with more fish taken in the 150- to 164-m. range. 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, 19538a). The length-frequency distributions of oceanic and inshore catches of yellowfin tuna (fig. 8) indicate essentially no difference. The length 0 aad Teal ele eee LONGLINE OCEANIC STATIONS 20 iy Q=—s== | + a 0 | Al | a SO eae ] =] oO LONGLINE INSHORE STATIONS | eral 20 | | N=228 | | cal | | | | | | io} +— | a ifn We We Ifa fea eo | | heel | dk | o 110 122 ig? 13.9 1259 185.9 i. lea Fe Pa Te] ey POLE-AND-LINE | | | | | MARQUESAS AREA | -- |aeleee| BS 50 | ae eae | N#126 WY | 5S eee 5 1Z leer eal | Baro i | 0 | zalenlera| leral eral ( L ; 98 no 122 53.9 5. 779 89.9 101.9 113.9 125.9 LENGTH (CM.) 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 LineIslands. 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 20 PERCENT ~) 6 0 110 122 146 158 170 113.9 1259 1499 1619 1139 LENGTH (CM) 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 21cm. 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. lalla nl ] Telhalhc)| lel Paral 1 i) | 1 Yi | | | | 35 KIPJACK Y - + eae loa foul ie ai | N=48 g | | 30 leet Y) +t ical 1 | ZY | | | 25/4 Yy a ad = | 20} VW sop esi Ly lial l | 15 i = i | YY | | | Wall 10 i Y / t E Af YZ 5 V _ a o& AEA! | | je [ie] 5 35 qr TIP i) | © 30\—ALBACORE Lapse a] N=46 [ imal lial 20} | q dette Y) | 15} ++ ! | | | 10;— | T | | AV | | | | | | ZA\ T ot AAA_|_| L BO SSP ] ] io ___BIGEYE | 3 N:97 7A A el jae VA g o | T ~ Y ] 7 y ou +! Z Z G as FA ler emai 50 62 74 86 98 110 122 134 146 158 170 192 194 539 659 +779 «2899 1019 1139 LENGTH (CM.) Figure 10.--Length-frequency distributions of 1259 1379 M499 1619 1739 1859 1979 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. 7° 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 between150 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. (ERRE WAT WINE Glee) 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 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. 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. in 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. WT (2) ee — 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. Fish, Bull. 58: 31-72. MURPHY, GARTHI., andRICHARD 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 Serv., U.S, Fish Wildl. 10 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., andGARTHI, 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 §.,, 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., and MURICE 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+105p. 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./ 1576 fica ment of Conservation--is concerned with the management, conservation, and development of the Nation's water, fish, Created in 1849 the Department of the Interior--a depart- wildlife, mineral, forest, and park and recreational re- | sources, It also has major responsibilities for Indian and Territorial affairs. As the Nation's principal conservation agency, the De-— } partment works to assure that nonrenewable resources are | developed and used wisely, that park and recreational re- sources are conserved for the future, and that renewable resources make their full contribution to the progress, pros- perity, and security of the United States--now and in the . future. | UNITED STATES POSTAGE AND FEES PAID DEPARTMENT OF THE INTERIOR EN eine aa FISH AND WILDLIFE SERVIOE BUREAU OF COMMERCIAL FISHERIES WASHINGTON, D.C. 20240 OFFICIAL BUSINESS Return this sheet to above address, if you do NOT wish to receive this material , or if change of address is needed (indicate change). Library Division of Fishes U. S. National Museum Washington, D. C. 20560 SSR 7