LONGLINE FISHING FOR DEEP-SWIMMING TUNAS IN THE CENTRAL PACIFIC, JANUARY-JUNE 1952 Marine Biological Laboratory ,';' 4 - 1954 WOODS HOLE, MASS. SPECIAL SCIENTIFIC REPORT: FISHERIES No. 108 UNITED STATES DEPARTMENT OF THE INTERIOR FISH AND WILDLIFE SERVICE Explanatory Note The series embodies results of investigations, usually of re- stricted scope, intended to aid or direct management or utilization practices and as guides for administrative or legislative action. It is issued in limited quantities for the official use of Federal, State or cooperating agencies and in processed form for economy and to avoid delay in publication. Washington, D. C. August, 1953 47209 LONGLINE FISHING FOR DEEP-SWIMMING TUNAS IN THE CENTRAL PACIFIC, JANUARY-JUNE 1952 SPECIAL SCIENTIFIC REPORT: FISHERIES No. 108 UNITED STATES DEPARTMENT OF THE INTERIOR FISH AND WILDLIFE SERVICE Explanatory Note The series embodies results of investigations, usually of re- stricted scope, intended to aid or direct management or utilization practices and as guides for administrative or legislative action. It is issued in limited quantities for the official use of Federal, State or cooperating agencies and in processed form for economy and to avoid delay in publication. Washington, D. C. August, 1953 47209 United States Department of the Interior, Douglas McKay, Secretary Fish and Wildlife Service, John L. Farley, Director LONGLJJME FISHING FOR DEEP-SWIMMING TUNAS IN THE CENTRAL PACIFIC, JANUARY - JUNE 19 ?2 By Garth I„ Murphy and Richard S„ Shomura Fishery Research Biologists Pacific Oceanic Fishery Investigations Special Scientific Reports Fisheries No„ 108 WASHINGTON s AUGUST 1953 CONTENTS Page 111 XirOQUC LlOn B«a»««»e*0«oo**e*«eooeoonoco*oocooC'0*o*oooooo»oe -L Acknowledgements „ ........o 1 UD Gl SLl OPidl iJoLTjcL «*««»»«o««ooo«en«e«««o«oo9oo«ooosoooo*aoo«Ao il Horizontal distribution of yellowf in tuna ................... It AXUdCOi/C o«o«o«»ao*a«*«09oe*«»«00«*o*ooa*fi*i>oeoooooeooo*aor>oo -1- ,_' Sizes of yellowf in and bigeye . . ............................ . li; UCA X^CLuJ-vJO oo*ea*o*o o • • • * o • O(i«oa«o*«»i»«»so*O0««o«c>oocao»*oooi? I * | U 9.U cUTl C 36 X 1011X112, oot>»«oo»eo*»«>*ooooooa«c»oooooo*o««e>oo«>©ooooo X.iX Vertical distribution of the catches ........................ 19 Catches on experimental gear ..................... ........... 27 AilX'Sl^cl OUI^C* Cll/UU • a « oooecooeooeaa* o o o a o e « aooaaeeeao c « o e • o o • • o .5^ ILLUSTRATIONS Figure Page 1 Central Pacific Ocean, showing location of longline stations. ...... • •aeaeoooooaoaooeaaoceaoaaavO 2 The John R. Manning at the Equator on 180°. The crew has just finished setting the longline. ......... 3 3 Temperature sections corresponding to fishing on 155°, 169°, and 180° W. longitude. .................... h Temperature sections corresponding to fishing on 120° and 130° W. longitude. .......................... 10 5 Tuna catches on five longline -fishing sections across the Equator during the period February to June -i-y j£. • •«**a»oeoo0aeoeooooQO««0*«0«*o*ooooo*eoooo« I J CONTENTS Page ■i-ll uX^UULtO UJ-Cll IP • • • • o t, » e O C 0 I.. £> <> u .■ .> O O 0 • O (1 O O >■ 0 O D V B o X Ac Know x© Q^cnisn t»s e c *«.>»•• c <>•<>&• o ••»• * o ♦« u o <> x Operational Data „ ..................................... k Horizontal distribution of yellowfin tuna ................... h Sizes of yellowfin and bigeye ............. ............... Ik » , ., & „ „ ....,,-.»...,. D © « 0 • c c o © o © » o o ^ o JjX L>Ci a L/liX L. CX l/C U ••• oeo0O«o«»e*«**ooooeee •ov**o«o«ec * o o • o O • • o _5tC ILLUSTRATIONS Figure Page 1 Central Pacific Ocean, showing location of longline L> OOOOOOOO 2 The John R. Manning at the Equator on 180°. The crew has just finished setting the longline. ......... 3 3 Temperature sections corresponding to fishing on l55>°, 169°, and 180° ff. longitude. ... ...... ......... .. 9 h Temperature sections corresponding to fishing on 120° and 130° W. longitude. .......................... 10 5> Tuna catches on five longline -fishing sections across the Equator during the period February to June J-y J1— • *o*«**oeooeo0O«t>oooooe*o«c •••9*00000*0000 »e XX INTRODUCTION This is the second interim report on an investigation of the deep-swimming tuna resources of the central Pacific Ocean ''fig. l)„ This study is being conducted by the U„ S„ Fish and BITildlife Service through the Pacific Oceanic Fishery Investigations (POFl}„ The first report (Murphy and Shomura 1953) dealt with the results of fishing during the period from July 195>0 to September 19f>l. The fishing on which this report is based took place from January to June 1952, During Cruise 11 of the John R„ Manning (fig. 2), January to March 1952, section lines were fished across the Equator at 180°, 169% and 155° W. longitude. Cruise 1 of the Charles "h. Gilbert (May and June 1952) included sections at 130° and 120° W. longitude. In this paper the results of fishing are discussed together with a preliminary evaluation of the relation of the tuna to the environment . We use the vernacular names of the fishes throughout the report. These with their commonly accepted scientific names are as follows: White-tipped shark - Carcharinus longimanus (Poey) Silky shark - Carcharinus sp„±/ Great blue shark - Prion ace glauca (Linnaeus) Bonito shark - Isurus glaucus (Muller and Henle) Marlin - Makaira sp. Sailfish - Istiophorus orien talis (Schlegel) Wahoo - Ac ant hoc ybiun solandri (Cuvier and Valenciennes) Dolphin - Coryphaena hippurus (Linnaeus) Yellowf in tuna - Neothunnus macropterus ( Temminck and Schlegel) Bigeye tuna - Parathunnus sibi (Temminck and Schlegel) Skipjack - Katsuwonus pelamis (Linnaeus) Albacore - Germc alalunga (Bonnaterre) Lancet fish - Alepisaurus sp„ Barracuda - Sphyraena barracuda (V.albaum) ACKNOWLEDGEMENT TS Several persons contributed to the planning and organization of the two cruises, including 0. E. Sette, D. L. McKernan, and W. F„ Royce. Dr, Royce is also responsible for the provisional iden- tifications of the sharks o The successful completion of the cruises was due in no small part to the enthusiastic performance of the officers and fishermen of the John R„ Manning and the Charles H„ Gilbert, V A species closely resembling C. floridanus Bigelow, Schroeder, and Springer, anH C„ ahenea (Stead) . B 5 2 o i 8 < 0. b ^ tr I- Z 111 O in 10 S2 *v ■ &*-*«• »■• ^^^^^^ ■ ^^"^"2 t5*^ .-■til FIG 2 THE JOHN R MANNING AT THE EQUATOR ON 180° THE CREW HAS JUST FINISHED SETTING THE LONGLINE Wo Go Van Campen translated the Japanese fishing data included in the reports Miss Jean Hailing assisted in processing the catch records OPERATIONAL DATA Longline fishing on the banning and Gilbert was done in essentially the same manner as on the Hugh M, Smith (Murphy and Shomura 1953) with minor modifi cations-., Forty baskets of standard POFI long- line gear (Niska 1953) were used at each station during the cruises under consideration. Each of these baskets had a main line 1,260 feet long with six evenly spaced hook droppers. Each dropper was 88 feet in overall length. At certain stations on Cruise 11 of the Manning, 5 additional baskets of experimental gear were set.. These will be discussed in a later section., Fresh frozen sardines, approximately four to the pound, were used as bait Before use they were thawed and packed in rock salt for from 1 to 3 days. The baits were hooked through the eyes. Setting of the gear began about dawn and usually took an hour* Retrieving the gear usually started at noon and finished about U:00 P.M. Tables 1 and 2 give the exact working time for all stations. These tables indicate that the stations were in general comparable as regards the length of time the gear was fished and the daily scheduling of the fishingo HORIZONTAL DISTRIBUTION OF YELLOWFIN TUNA The results of the first longline cruises to the equatorial Pacific in the vicinity of 1$0°-160° HIT, longitude during the period from August to November indicated a marked concentration of deep- swimming yellowfin tuna in a zone north of the Equator (Murphy and Shomura 1953)= These surveys were made during a period of predominant southeast trades, which cause upwelling near the Equator and tend to displace the upwelled water northward (Cromwellii ) It was tenta- tively concluded that this enriched water, with its increased plankton and presumably increased tuna forage, was directly linked with the observed concentration of yellowfin,, Extrapolation of this theory to periods or areas charac- terized by winds other than southeast indicates that the location of the most productive zone should be somewhat different., Northeast winds should create a mirror image of the circulation created by southeast winds, with the zone of greatest productivity displaced to the south of the Equator, Easterly or variable winds should result in the zone of greatest productivity being symmetrically arranged about the Equator 2/ Cromwell, Townsend, MS, Circulation in a meridional plane in the central equatorial Pacific Table 1„ — Time taken for setting and hauling the lohgline, John R. Manning Cruise 11 „ Number Time Time taken Time Actual time Fish-handl breaki/ ing of started for setting started taken for Station baskets tc set (min. ) tc haul hauling (min.) (min. ) 1 ho 0615 hi 1213 237 65 2 ti 0613 62 1206 2U0 6k 3 ti 0620 55 1222 212 61 Ji ti 0613 $9 12' ! 211 62 5 11 0620 78 1220 179 S9 6 n 0615 69 1217 173 65 7 It 0600 78 12: 19k 63 0 1! 0612 61 1209 201 60 9 II 061] 62 ] 10 167 58 10 U5 0605 6). 1218 190 59 11 II 0605 68 1205 207 65 12 II 0607 67 c 216 65 13 II 0600 65 1215 I81t 67 111 II 0606 Sk 1210 PLC 58 15 II 0600 70 1217 213 65 16 II 0605 60 1222 21.2 69 l? H 0602 6I4 120li 2k3 63 18 h0 0603 67 1207 161 67 19 U5 0616 70 1155 209 63 20 11 0615 63 1203 226 63 21 11 0607 7 2 1207 230 63 22 .. 0600 7k 1210 2U0 65 23 ti 061 C 7- 1206 225 71 2J4 11 0607 61* 1205 21k 63 25 n 060li 68 1205 215 65 26 i' 0600 73 1158 23k 66 27 ao 0608 70 1200 62 Average time fcr UO-basket sets Average tim° for U5"basket sets 61i.li min. 67.0 min. 202.3 min. 218.6 min. 63.6 min. (mean for all sets) — Fish-handling break came midway during hauling period. Table 2. — Time taken for setting and hauling the longlines Charles H„ Gilbert Cruise 1. Time Time taken Time Actual time Fish handling break?-/ started for setting started taken '"or Station^/ to set (min, ) to haul hauling (min.) (min,, ) 1 o6r 58 1235 225 25 2 0600 50 12U5 188 27 3 0600 55 1225 193 1x2 U 060r 50 1225 175 3D 5 0605 50 1300 135 25 6 0605 50 1255 165 3$ 7 061C 50 1300 230 30 8 0615 55 1255 1U0 Uo 9 05U5 60 12U7 133 Uo 10 ' 0555 55 1255 145 50 11 0550 55 1255 150 U5 12 0555 SS 1305 155 Uo 13 0605 60 1315 155 Uo lit 0600 55 1300 235 50 Average 5U.1 173,1 37a 1/ U0 baskets were used at each station, 2/ Fish-handling break came midway during the hauling period. section lines discussed in this - * were fished during the period January to June on 120°, 130°, 155°, 169°, ana 180° HIT. longitude. In general the period January to June is characterized by either northeast or variable trade win although southeast winds begin to predominate towards the ond of the period, particularly at the eastern end of the area (120°-13; lording to {'. S. Pilot Charts the period of fishing along 120° W. in late May 1952 was preceded by about a month o^ predominant but moderate southeast trades as was the 130° W. section fished in ear]; June of 1952. Fishing on the 155° •'<- and 169° W. sections in February and March receded by winds about equally divided between northeast and southeast, and. the 130° section fished in February of 1952 was preceded by predominantly northeast winds „ The actual winds experienced during the fishing 5f sse sections (table 3) are entirely compatible with the mean picture presented by the Pilot Charts, indicating that the winds during and possibly preceding this fishing closely resembled the normal or average picture „ Table 3. — Average wind direction and Beaufort force at the fishing stations, John R. Manning C LI, Charles H. Gilbert Cruise 1. Longitude Latitude 180° 169 "W 155 °w 130°W 12C 9°N _ _ _ — E -01 8°N - - NE-06 SE-Olj _ 7 °N - _ [E-06 - 6°ii - - - SE-02 - ^o,T - - NE- ' S -01 s -05 il*N - -05 E -05 - -c 3°>! NE-03 T-E-OU E - 5 -Oil SB-i 2°M - - - SE.:~ 1°N NE-03 NE- S ~ - - Equator .-02 E - / ■ • 1°S IE-03 E - -oh - SE- 2°S - - - - - 3°S ME-Oli E -0U - - k°s NE-05 f:£- „ - - 5°s v-05 E -0U - - - 6°s - - - - - 7 °Q NE-0ii E -05 - - - 8°S NE-0U " " TUrning to the temperature sections along each fishing line (figs. 3 and h) , it is apparent that, as might be expected from the wind observations, some upwelling was taking place in the vicinity of the Equator in each instance. Note especially the decreased surface temperature and the doming up of the isotherms near the Equator. The approximate location of the easterly flowing Countercurrent., included for orientation in figures 3 and U, was determined on the three western sections by a combination of ship's drifts, drifts of the longline while on station, and GEK^f fixes by the H ; M Smith while in close company with the fishing vessel. On the two eastern sections (120° and 130°) the location of the Countercurrent was taken from U. S, Pilot Charts for the appropriate months. Consideration of the results of the longline fishing (fig. 5) with the observations on the hydrographic structure (figs. 3 and U), the winds observed during the fishing (table 3), and the mean or average winds represented on the Pilot Charts indicates good agreement with what might have been expected a priori. Each of the five sections (fig. 5 and table Ii) shows a zone near the Equator in which yellowfin tuna were more abundant than to the north and south and which, in all likelihood, is associated with the upwelling suggested in the temperature sections. The more precise latitudinal location of the greatest concentration of yellowfin appears compatible with the average winds recorded on the Pilot Charts and the observed winds during the fishing. For instance the 120° and 130° sections which were associated with southeast winds, had their peaks of abundance north of the Equator, The 155° and 169° sections, which were associated with variable winds, had their peak abundance of yellowfin nearly centering on the Equator, and the ISO0 section, associated with northeast winds, had its peak of yellowfin abundance displaced to the south. Including the two sections previously reported on by Murphy and Shomura (1953), there are seven sections reconcilable with the theory that, through upwelling, southeast winds create a favorable environment north of the Equator, northeast winds tend to create a favorable environment south of the Equator, and van. ast winds create a favorable environment tending to center on the Equator. This is advanced with no implications as to the exact level of abundance that the yellowfin will attain in the "zone of greatest abundance " Predictions of the level of abundance would appear to involve many more complexities than simple prediction of the loca- tion of the greatest abundance on the basis of prevailing winds at and near the Equator „ zJ Geomagneticelectrokinetograph, an instrument for measurement of surface currents. E §0= inn 84" 83° 82° 0 100 P UJ UJ u_ 200 300 X p Q. UJ Q 400 500 600 700 13 UJ (.o tl Ll) EL UJ Q 1 1 1 1 1 1 1 1 r~ i i i i i 1 ' 1 ^ - I - -"---^^ — ■ _____^ - _ | - 1 1 1 1 1 1 1 i i i !r- 800 llltf- 83° 82" 35 81° 80° 0 100 200 H uj UJ 300 u. X 400 h- Q. UJ 500 Q 600 700 800 1 1 1 1 1 1 1 1 1 1 1 1 1 ' ' 1 1 a . - ~ 5 " 1 1 1 1 1 1 1 1 1 1 1 1 \- 1 1 , 1 COUNTERCURRENT i i I i 8° LATITUDE- FIG 3 TEMPERATURE SECTIONS CORRESPONDING TO FISHING ON 155°, 169°, AND 180° W LONGITUDE. o° 80° in i- 79° 78" 77° 0 P Ui iii u. 100 200 X 1- Q. UI 300 400 500 8- or 5 0- bJ Q 82° - 81° - 80° - 79° - 78° 77° 76° - 75° - 0 100 200 300 400 500 _ "> 1 1 1 1 T COUNTERCURRENT -80° i 1 r _l | L 1 1 1 THERMOCLINE ' 70°-'^ 1 1 \\ 120° \ SI 1 1 1 1 ^ COUNTERCURRENT Si i i i i > — 1 I I /'"~--80° / ^s^^ 60° I 1 I i i i ' 1 10° 1 1° 12° 13° LATITUDE FIG 4 TEMPERATURE SECTIONS CORRESPONDING TO FISHING ON 120° AND 130° W LONGITUDE. < 10 01 23456789 10 CATCH PER 100 HOOKS 120° 23456789 10 Q 3 I (/I MAY j_ _i i_ _i i i i i i_ 234567890 123456789 CATCH PER 100 HOOKS YELLOWFIN OTHER TUNA FIG 5 TUNA CATCHES ON FIVE LONGLINE FISHING SECTIONS ACROSS THE EQUATOR DURING THE PERIOD FEBRUARY TO JUNE 1952 Table a. — Summary of the tuna catching rates, John R.. Manning Cruise 11 and Charles H, Gilbert Cruise 1. Number caught per hundre d hooks Yellow- Big- Alba- Skip- Station Date Latitude L rig Ltude fin eye core jack Manning Cruise 11 1 1-29-52 08°02'N 15U05' - 0.1*1 - 2 1-30-52 06°i|0'N 155°05' H O0U1 0.1*1 - - 3 1-31-52 05°20 . i55°oo- N - 5.79 - - h 2-1-52 0U°0U'N 15U°56- a 9o92 - - 0.1*1 5 2-2-52 02°u6»N 155°11' w 5.37 1 21* - - 6 2-3-52 01°20»N 155C03« w h.96 0,83 - o.Ui 7 2-U-52 00°02»S 15U°57< t> 7,02 - - 0,83 8 2-5-52 01°20w 1.21* - - — 10 6-9-52 02°19'N 130°07 5,37 - - - 11 6-10-52 03°17'N 0Uo30'N 130°28 'W 5.37 0.1*1 1,65 - - 12 6-11-52 130°15 ■w 3.72 — — U 6-12-52 06°06'N 129 °55 •w 2,89 - - - 1 6-13-52 08°00'N 130o2U'W 1,65 2,89 " — 12 ALBACORE One of the more interesting results of the fishing on 180° %. longitude was the surprisingly high catch of albacore at 5°-6° S. latitude (table U). A relatively high catch was also made at 169 ° W. longitude, 7° S. latitude (table h) « These catches were made up of large individuals (table 5)? many of which appeared to be sexually mature „ It is possible that this area contains concen- trations of albacore capable of maintaining a sizeable commercial fishery. Table 5« — Length frequencies of albacore and skipjack, John R, Manning Cruise 11, Albacore 1 Skipjacl Approximate Approximate Length Number weight Length Number weight cm. pounds cm. pounds 83 1 25 62 _ _ 8U 1 26 63 - - 85 1 26 6ii - - 86 3 27 65 - - 87 1 28 66 1 Ill 88 1 29 67 1 15 89 k 30 68 - - 90 8 31 69 - - 91 9 32 70 - - 92 3 33 71 - - 93 1 35 72 - - 9U 2 36 73 - - 95 2 37 7li 1 u - - 96 3 38 75 - _ 97 1 39 76 3 2h 98 1 ho h 25 99 3 1x2 7 R 3 2? 100 2 1x3 79 JL 29 101 1 hlx 80 2 30 102 1 1x6 O -\ 01 1 31 103 1 hi 82 1 32 10U 1 U8 63 ■■ mm 13 SIZES OF YELLOWFIN AND BIGEYE Ihe sizes of the yellowfin tuna taken on the five section lines increase from west to east (table 6) with fish averaging abc 110 pounds at 180° and 1U0 pounds at 120° W, longitude, l/lfeat of 180° the trend to smaller tuna continues in an irregular manner to 135° E„ longitude, where Japanese commercial longline catches averaged 62 pounds (Murphy and OtsuT)- A parallel trend is evident in the bigeye tuna east of 180° (table 7)* and similarly west of 180° long- line catches of this species were roughly J4O pounds lighter in weigl I (Murphy and Otsu**' ) than between 180° and 120 .. _ongitude0 SEX RAH OS oh the exception of albacore the various species of tuna in the catches (table 8) have a preponderance of males, although the yellowfin tuna disproportion is the only one that is statistically significant. The excess of males in longline catches of bigeye and yellowfin has been previously noted in catches from H4O0 E longitude to 150° Wo longitude (Murphy and Otsu= , Murphy and Shomura 1953), In albacore the excess of females is not statistically signiiicanto JAPANESE FISHING Japanese longline fishermen began operating in the central Pacific in May of 1952 0 A summary of the most pertinent data from these operations in May and June of 1952 is given in table 9« This fishing along 170° Iff. to 180° shows very clearly that there was a concentration of yellowfin from the Equator north to about 5° N„ latitude, and that yellowfin were relatively scarce north of this zone during both May and June of 1952, It also furnishes a good indication that bigeye tuna were considerably more abundant north of 5° N„ latitude than south of that parallel* Because of the relative scarcity of bigeye and because of the necessarily limited extent of our fishing, it has not been possible to make any such definitive statement from our datas although there have been similar indications in nearly every fishing section, Ihe catches of the other species included in table 9 do not show such pronounced differences in abundance with latitude „ The general h of abundance (catch per hundred hooks) of both yellowfin and bigeye tuna are in close agreement with results obtained by the Manning' 3 fishing (compare tables h and 9), even though the Japanese fishing took place 3 months later in the year This is an indication that our catch rates made with 2l|0-hook sets are com- i th catch rates from the 1,500- to 2,000-hook sets used by commercial fishermen. In addition the sizes of the tunas were very similar (compare tables 6 and 7 with table 10), for the exploratory fishing and the full-scale commercial operations. V Murphy, Garth I., and T„ 0tsu„ MS Analysis of the catches of nine Japanese tuna longline expeditions to the western Pacific Ocean, 111 Table 6, — Length frequencies of yellowfin tuna, John R. Manning Cruise li, Charles H„ Gilbert Cruise 1. Lon *itude Wes Aooroximate T Length 180" 169C 155° 130° 120" weight cm., pounds 92 - - - 1 - 33 91 - - - - _ 39 102 - - i - - U6 107 - - - - S3 - : - - 60 117 ■ - ii - - 69 ] 2 3 S 0 - - 78 127 7 8 6 1 38 ] 3 ' 9 5 3 100 137 11 5 2 1 J. 110 UU 23 5 6 123 1U7 9 10 ii 3 137 152 1 h U e 3 150 157 - 1 2 2 - 166 162 - - - c 18 c 167 - - - 2 1 200 Total 55 59 75 31 19 Mean length 136.7 139.5 13606 LU8.3 1U7.J0 15 Table 7. — Length frequencies of bigeye tunas John R, Manning Cruise lls Charle Gilbert Cruise 10 Lor West Approximate length i8o'-' l69u 155 " 130" . weight cm,, p .' : 107 - - T - _ 58 112 - - - - 1 66 117 - - - - 75 122 - - - l 85 127 - - 2 - 1 95 132 - - 0 1 h 107 137 1 - 2 - - 119 1)42 1 - 2 1 132 LU7 1 1 1 - - lu6 152 - - 1 161 157 - 1 3 - 1* 177 162 - - - 1 3 195 167 - - - 3 198 172 - - - i 1 232 177 - - - 1 2 252 182 - - - - 1 273 187 - - - 1 1 296 192 - - - 1 - 320 197 "■ — "" "* 1 3U$ Total 3 2 19 10 26 Mean length 11*2.0 152,0 131*. 5 163,5 155.5 Table 8„ — Sex ratios, John R< Manning Cruise 11 and Charles H, Gilbert Cruise 1 Yellowfin Bi geye Alb acore Ski >jac ' Cruise Male Female Male Female Male Female Male Female Manning 11 120 73 17 10 25 33 9 7 Gilbert 1 33 23 19 > - - - - Total 153 96 36 19 25 33 9 7 Percent 61 39 65 35 U3 57 56 1*1* lo Table 9, — Summary of Japanese commercial fishing in the central Pacific durin and June 1952. Adapted from ; iwa Prefecture Fisheries Experiment Station bhly Report No. 2, July 1952., May Maj June June Item 00 - 05 "N 176° ff 07 - 11. 5 "N 178° - l6i4°W 00 - 01i"N 179 - 166°W 09 - 11.5"N 180 - 16U°W Number of boats 1 7 h Ho ok- days 21,000 187,020 106,800 180,590 Catch per hundred hook-days s Yellowfin tuna 3,33 0,06 6,U1 0,09 i ;eye tuna 1,67 2,61 0,37 2,71 ■Ubacore - 0,01 0,02 - Skipjack 0ol3 0,11 0,21 0,30 Black nurlin 0,52 0,58 0,29 0,71; VITnite marlin - 0,03 0,01 - Striped marlin - 0,02 - - Proadbill 0,01 0,03 0,01 0,02 Sail fish 0,03 0,10 0,15 0.10 Miscellaneous o.o5 O.Ui 0,20 0,21 0,67 1. 0,63 All s secies 6, LI li.{ 8.15 U,85 17 Table 10, — Length frequencies of tunas taken by Japanese commercial fishermen in the central Pacific during "lay and June 1952. Adapted from Kanagawa Prefecture Fisheries Experiment Station Monthly Reports No 1, June 19523 and No, 2, July 1952, Bi geye tuna Yellowfin tu May June Approxiir.cV wei ght June Length 07-11. 5 °N 16U-178°W 00-11, 5 °N 180-172°W 00-0, 5 °N 179-172°W cm. pounds pounds less than 100 l* - _ - - 101-110 21 7 55 50 111-120 17U 13 71 68 65 121-130 277 21 91 178 dh 131-1U0 UlU 38 11U 3U3 106 LUl-150 581 35 1U0 Ul3 131 151-160 55U Sh 171 85 160 161-170 u36 30 205 - 192 171-180 230 12 2hh - 230 31 75 3 - - - 18 SAL DISTRIBUTION CF The depth at which the deep-swim- mas are most abundant is of considerable interest biologically and of practical importance commercially. It has been previously noted ( ikamura 19h3s Cchi 19 52, and Murphy and Shomura 1953) that in gen ;eye tun in greater numbers on the lowermost hooks of the Ion Line, In the absence oJ -•mation or .ctual dep' apture, the catches can be examined for catch rates at three relative depth vels (shallow, intermediate, and deer 'amination of the catches of yellowfin and bigeye tuna by relative depth of capture for Manning Cruise 11 (tables 11 and 12) show that the deeper- fishing hooks usually jher c;. than the shallow hooks0 Eoth chi-square analyses, however, show si i :ant interaction chi-square which indicates that the p, on the deep hooks was not consistent, 'icantlj ■ vellowfin were taken on the shallow hooks at stations ?, ?3, and 2U (table 11) „ Trie bigeye data (table 12) show reversal in the relationship of the intermediate and deep hooks „ may well be ; tion of the line to critical isotherms or the thermocline is different from <'r to itation Tbj di I ition of the albacore catch- (table 13' >od evidence that this species occupies the deeper, cooler ' i of water in the tropics <> depth data fr ;e 1 ( tabl and 15) indi ■ * h n those se on 120° and 130° VT. longitude were hed, the yellowfin were not stratified with depth so far as the dep + ; • fished by our gear is concerned. Ihe bigeye, on the. other hand, gave evidence of being more abundant at the levels fished by the deep hooks „ The failure of the deep hooks to c? 3 yellowfin may be a function of the shall w 1 experienced d r this f j ' (fig« h)» These shallow thermoclines, with the possible attendant streaming of the line, m iced all of the hooks at more nearly the same level than e the yellowfin are the least markedly stratified w it might be ■ ed that if the differential between shs were small, difference would be no- hes at ': three relative depth levels„ In an attei ) ascertain the actual depth of the main line a depth indicator was attached to the base of one of the central or ans during Cruise 11 of ' .., gauge was designed to furnish an estimate of the deepest point reached by the portion of the line to which the instrument was attached. The correlation of the depths indicated by the ' ^pth of the top of the thermocline (table 16) is Co'' P <0„05, suggesting that under some cj "ances the the Lne limits the penet result n be expected at least part of the time the thermocline is the boundary between moving surface water and the relatively still deeper layers „ 19 Table 11. — Chi-square analysis of yellowfin catches by hook depth, John R. banning Cruise 11. Number of Total number of fish Station Shallow hooks Intermediate hooks Deep hooks X Li i < 11 2u 1.750 5-61/ 6 9 10 25 1.039 7 10 2 h 16 6.?oo* 8 3 5 8 16 2 376 ?-lll/ 5 6 7 18 0.33U 12-131/ 6 7 5 18 0.33k ih-nl/ - 3 12 15 15.600** 18-221/ 2 8 8 18 a. ooi 23-2lii/ 15 h 5 2U 9.250** 25-2 iU £ ^ 7 9 21 1.1U2 U2. 32 6** Total X2 (d.f.20) Total 59 57 79 195 U.55U PooledX2 (d.f.2) 37 0 7 72**Interac tion X2 (d.f.18) Hypothesis; The population of yellowfin tuna is homogeneously dis- tributed with respect to depth} therefore a Islsl ratio is expected from the three depth zones. Conclusions % The Leant interaction ^ of 37.772 (d.f. 18, P.<0.01) indicates the data are not consistent; therefore the pooled values cannot be accepted without reservation. -I c'^t,innE lumped to give minimum e3 I id numbers of about 5< * indicates d significant (P<0.05) chi-square value. ndicates a highly significant (P<0.01) chi-square value. 20 Table 12. — Chi-square analysis of bigeye tuna catches by hook depth, John R. ".fanning Cruise 11„ Station 1-3^ ?r of fish Shallow hooks 3 2 Intermec hooks Q hooks 9 3 Total number of fish 16 lit X 3,875 6.1U2* Total 13 12 30 10 „ 01 7* Total x2Cd.f.U) 3,800 Pooled X2Cd.f.2) 6„ 21 7""- Interaction X2 (d.f.2) Hypothesis; The population of bigeye tuna is homogeneously distributed with respect to depth; therefore a lrlsl ratio is expected from the three depth zones. Conclusions; The significant, interaction X2 of 6,217 (d.f. 2, P<0,05) indicates the data are not consistent; therefore the pooled values cannot be accepted without reservation,, i/ Stations lumped to give minimum expected numbers of about 5>< -"- indicates a significant (P<0.0£) chi-square value „ 21 Table 13. — Chi-square analysis of albacore catches by hook depths, John R„ Manning Cruise 11. Number of fish Total number of fish Station Shallow hooks Intermediate hooks Deep hcoks ye 8-l6i/ - 8 19 27 20,222** 17-251/ - 17 25 17.360** 37. 58 2** Total X2(d.f.U) Total 16 36 52 37,5UO**PooledX2(d.f.2) 0,01*2 Interaction X2 (d.f.2) Hypothesis; The population of albacore tuna is homogeneously distributed with respect to depth; therefore a lslsl ratio is expected from the three depth zones. Conclusions; There is a definite difference of catch with depth, with the lowermost hooks catching more,, This is indicated by the significant individual, total and pooled ?t2 ' s and by a very low non-significant interaction Xr° -> Stations lumped to give minimum expected numbers of aboi ** indicates a highly significant (P<0.01) chi-square value. 22 Table lit. — Chi-square analysis of yellow.fin tuna catches by hook depths, Charler Ibert Cruise 1. Numb* Total number of Station Shallo1",' hooks Intermediate hooks Deep hooks X 7-1 : 11-11 10 ■ 5 IB 19 19 33 3.r 36U X d.f.6 iX2 X' • _s: 'in tuna is her ore a 1;1;1 ra ied Lusions data available indicate i copula ' yellowfin There are no differences in the eh caught with respect to depth. 1/ n , 23 Table l5.~Chi-square analysis of bigeye tuna catches by hook depths, Charles H, Gilbert Cruise 10 "umber of sh Total nurabe r of fish Station Shallow hooks Intermediate hooks Deep hoc. ■ l-3i/ U-H4I/ k 5 5 6 12 11 21 22 2o8l8 Total 9 11 23 U3 r,2U6 Total X2 (d.f.li) 8,000--- Pooled X2 (d,f.2) 0„ 2U6 Interaction 7C (d.f, 2) Hypothesis; The population of bigeye tuna is homogeneously distributed with respect to depth; therefore a lslsl ratio is expected from the three depth zones. Conclusions? The presence of a difference in the number of bigeye tuna caught with depth is indicated by a significant pooled IC? of 8 a 000 (d„f„25 P<0„05) and a low nonsignificant interaction pC . -> Stations lumped to give minimum expected numbers of about J?« * indicates a significant (P<0„05) chi-square value. 2U Table 16. — Estimated main-line depths from gauge readings and thermocline depths, John R. Manning Cruise 11. Station Gauge dep th Depth to top of thermoclin feet Fe k 5io 396 19 Uio h&4 20 h97 560 21 1*80 516 22 1 r'n a 30 23 370 3U6 2U 285 236 25 300 3U0 26 U55 U12 27 520 360 25 These results, coupled with earlier findings (Murphy and Shoraura 1953), indicate that the actual depth reached by the line is a function of a complex of factors. Only one of these is readily ascertainable and that is the distance between buoys. Since this distance governs the maximum amount the main line can sag down between buoys it gives the maximum possible depth that the line can reach. During Cruise 11 of the Manning the deepest hooks could have been fishing at about 550 feet (table 17), with the other hooks at lesser depths, Even this figure is approximate as there is variation in buoy distance between baskets and there is probably variation within a basket while it is soaking. Table 17. — Average buoy distance as determined from setting speed and time and maximum possible depth to deep hooks, John R. Manning Cruise 111/. Average Depth to Station buoy distance deep hooks 1 630 628 2 830 558 3 7U0 588 h 790 578 5 10U0 UU8 6 920 518 7 10l|0 UU8 8 820 568 9 830 558 10 760 588 11 810 568 12 790 568 13 770 578 U* 6h0 618 15 830 558 16 710 598 17 760 588 18 900 528 19 830 558 20 810 563 21 850 iiU8 22 870 U38 23 8110 51i8 2U 760 588 25 810 568 26 ~.cc 5U8 27 930 508 i/ Depth estimated from buoy distances from curves in Murphy and Shomura (1953) 26 cat; e expekdjen £ar lysis of earlier longline cruises indicated that the catch of yellowfin and bigeye tuna was g] r on the deeper-fishing ho (Murphy 2nd Shomura 1953). If abundance "unction of depth, it should be oossible to increase the catches by fis) at deeper levels. Accordingly 5 baskets of special gear w .shed at each of 16 stations on L^an-'.i.ig Cruise 11. On stations 10-17 (1G0° longitude) the gear had ^O-fathort float lines ii il 10. -fathom float lines were I Ions 19-26 (l£ de). Operationally, the special gear wor1 The haulir. was a little greater because of the long float lines, and the rain on the line hauler, but there did not appear to be any reason why such gear could not be used in large-scale or The catches of the 19 3f egular gear that were hauled after the break and 1] lsed as a basis for comparison - *der iy pi b] f fact of unequal arisons, 18, indicate there was little if any difference in the -catching efficiency of the two types of gear. It is of interest ths ore, the species showing the greatest relative catch on the deep hooks of the standard baskets, shows -_ 60-perc ni 3 in catch ever the expected when f?0-fath< Float lines were used, even th 3 is not statistically significant,. In regard to relat - 1 depth distribution, the special sr yellowfin on the ooks and equal numbers of albacore at all t! •■ ■■■ 'oak levels in 1st to the usual distribution on the st ' of 6 the askets of trasted wii no albacore on the shallow hooks of 320 bask ! ;ear, ap - int. The ■ ] " Ja are too scant to car'- indica- tion ; float lines were allow ooks to sink deep ' t the deepest hoc. [the greate .'• con- centration of yellowfin and all of the hoc - best albacor' I hs„ Table 18. — Analysis of catch of tuna with type of gear used. Station Species of tuns Regular gear Special, gear =/ X2 10-17 Yellowfin tuna 21 6 0.038 Albacore tuna 20 10 2.917 19-26 Yellowfin tuna 33 7 0,250 Albacore tuna 13 2 00^17 ±1 The special gear on stations 10 through 17 differed from the regular gear by having ^0- fa thorn float lines. On stations 19 through 26 the length of float lines of the special gear was 30 fathoms „ 27 SUMMARY 1. During January, February, and "arch, the John P. -occupied fishing stations on 155°, 169°, and 180° W. longitude. Fishing on 120° and 130° '.V. longitude was done with the Charles H. Gilbert during L!ay and June. 2. The catches made during these cruises gave farther proof of the presence of a "rich zone" of yellowfin tuna previously reported for the equatorial region. 3. The latitudinal variation of this zone generally coincided with differences in the prevailing winds. '.There southeasterly winds prevailed, the concentration of tuna was to the north of the Equator, and where the winds were northeasterly or variable the zone was displaced to the south. U. The high catches of albacore tuna made in southern latitudes on 169° and 180° W. longitude point to a possible area of commercial exploitation .^or this species. 5. Both the yellowfin and bigeye tuna increase in average size from west to east. 6. With the exception of the albacore, the tunas (yellowfin, bigeye, and skipjack) showed a greater catch of males than females. 7. Results of Japanese commercial fishing in the central Pacific agreed closely as to catching rate and sizes of tuna taken with those obtained by POFI vessels fishing in the same general area 3 months earlier. 8. Both yellovjfin and bigeye tuna were usually caught in greater numbers on the deeper hooks. Exceptions probably were due to streaming of the line when the thermocline was at shoal levels. albacore catches revealed a mors definite stratification, with deep hooks consistently showing the highest catch rate. ?. Experimental fishing with longer float lines indicated that the modified z°'sr :Yas fishing at a deeper level, and was more efficient in the capture of albacore. 28 Table 19. — Numbers of fish caught on John R. Manning Cruise 1] (llO baskets with 10-fathom float lines). Yellow- Big- Alba- Skip- Sharks White- Great Station, fin eye core jack Marlin tipped Silky blue Others 1 1 _ _ _ 1 2 1 1 - - - - - 5 ii/ 3 - lit - - 1 - - 5 s>y k 2k - - 1 1 1 - k iW 5 13 3 - - - _ - 1 - 6 12 2 - 1 2 2 - 2 7 17 - - 2 - li - - iV 8 17 2 2 5 - 3 - 1 is/ 9 11 3 l 1 1 - 1 10 3 - - - - li - 1 11 li 1 2 l - 8 - 5 - 12 8 1 2 - 2 7 - 2 - 13 10 - l - 9 - 1 _ lii 8 1 2 - 2 5 - 3 - 15 2 1 2 - 1 1 - 1 - 16 1 - ii» - - 1 - 2 *? / 17 u - 6 - - 2 - - 18 1 — 6 - 3 — — — 19 7 _ 5 - 2 1 - - # 20 1 2 - - 3 - 2 iV 21 5 1 k l - - - 5 - 22 1* 1 - - - - 1 l - 23 9 - 1 - - 2 2 l - 2k 15 - - - 5 1 - - 25 11 1 k - l 1 - - 26 7 _ - - - 3 23 l - 27 3 1 "■ 1 1 ■" 1 "■ =/ 3 lancet fish, 2 unidentified sharkc «/ 1 bonito shark0 2/ 2 lancet fish. W 1 unidentified shark. 2J 1 wahoo. §] 2 sailfish, 1 lancet fish. 2/ 1 barracuda. 29 Table 20. — Numbers of fish caught on the 5 special baskets , John R. Manning Cruise 11 (stations 10-17, 50- fa thorn float lines; stations 19-26, 30- fathom float lines) „ 1 Sharks White- Great Station Yellowfin Albacore Marlin tipped Silky blue 10 _ 1 _ _ _ — 11 - - - - - 1 12 2 - 1 1 - 1 13 - - - - - - Ik 2 2 - — - — 15 2 - - - - - 16 - 6 1 - - - 17 - 1 - - - - 19 1 1 - — — — 20 - - - - - - 21 2 1 - 1 - - 22 - - - 2 1 - 23 - - 1 1 1 - 2k 2 - 1 2 - 1 25 - - - - - 2 26 2 " 1 30 Table 21„ — Numbers of fish caught on Charles H„ Gilbert Cruise 1 (lj.0 baskets with 10- fathom float lines) „ \ Sharks White- Great Station Yellowfin Bigeye Marlin tipped | Silky blue Others 1 2 1 3 8 ii 2 3 k 2i/ 3 2 10 1 - 1 1 22/ k 8 5 - 3 5 1 — $ 3 1 - 2 1 ^ 6 $ - - 1 - - * 7 h 2 1 8 - - 8 - 2 - - - 1 „ 9 3 - - 2 l - - 10 13 - - 3 - - - 11 13 1 - 9 1 1 _ 12 9 h - 2 2 2 _ 13 7 ~ 1 _ 2 2 3/i lii ii 7 1 — 1 3 l£/ i/ 1 unidentified shark, 1 skipjack, 2/ 2 unidentified sharks, 1 wahoo „ 21 2 unidentified sharks „ V h lancet fish„ ■^ 1 wahoo o ^ 1 unidentified shark 0 U 2 dolphins, 1 wahoo <, 2/ 3 lancet fish, 1 unidentified shark, 31 LITERATURE CITED KING, JOSEPH E., and Jo DEMOND 1953 Zooplankton abundance in the central Pacific, U. S. Fish and Wildlife Service, Fish, Bull., No. 82, vol. $kt PP» 111-lW*. MURPHY, GARTH I., and R. S. SHOMURA 1953 Longline fishing for deep-swimming tunas in the central Pacific, 1950-51. U. S. Fish and Wildlife Service, Spec. Sci, Rept.; Fisheries No, 98. NAKAMURA, H, 19U3 Tunas and spearfishes. Science of the seas, No. 10, vol, 3, (Translation from the Japanese language by W. G. Van Campen, U.S. Fish and Wildlife Service, Spec. Sci, Rept. 8 Fisheries No. U8, 195l)o NISKA, EDWIN L, 1953 Construction details of tuna longline gear used by the Pacific Oceanic Fishery Investigations, IT, S„ Fish and Wildlife Service, Comm. Fish, Rev, Vol, 15, No. 6, pp. 1-6, OCHI, To 1952 The experience of South Seas tuna fleets using portable catcher boats. Suisan Jih5, February 1952, pp. 38-1j5» 32 MBL WHOI Library - Serials 5 WHSE 01193 i