Speces Synopss No. 2 FAO Fsheres Bology Synopss No, 45 (Dstrbuton restrcted) FIb/S45 SAST - Tuna SYNOPSIS OF BIOLOGICAL DATA ON BLACK SKLPJACK Euthynnus lneatus Kshnouye 1920 Exposé synoptque sur la bologe de la thonne Euthyrmus lneatus Kshnouye 1920 Snopss sobre la bologa del barrlete negro Euthynnus lneatus Kshnouye 1920 Preparéd by THOMAS P, CALKINS AND WITOLD L, KLAWE Inter-Amercan Tropcal Tuna Commsson La Jolla, Calforna, U, S, A, FISHERIES DIVISION, BIOLOGY BRANCH FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS Rome, 1963 130
FIb! S45 Tuna 1:1 IDENTITY 1. 1 Taxonomy 1. 1. 1 Defnton Order Percformes Suborder Scombrode Famly Scombrdae Subfamly Scombrnae Genus Euthynnus Jordan,t Glbert 1882 Speces Euthynnus lneatus Kshnouye 1920 The classfcaton of the speces of the genus Euthynnus s n dspute. In ths paper the organzaton of the genus suggested by Godsl (1954), and by Matsumoto (1959), wl be accepted. These authors devde the genus nto three speces; Euthynnus lneatus Eastern Pacfc Euthynnus yato Central Western Pacfc Euthynnus alletteratus Atlantc The black skpjack, Jthvnnu. tue, s a marne, pelagc fsh nhabtng the tropcal and subtropcal waters of the Eastern Pacfc. It occurs, roughly, from the area of the U. S. - Mexcan border to Peru, n farly close assocaton wth the manland and offshore slands. 1.1.2 Descrpton - Genus Euthynnus Jordan & Glbert 1882 The fshes of ths genus have the fusform, streamlned body and lunate caudal fn common to all tuna-lke fshes. The body s devod of scales except for the corselet. Euthynnus can be dstngushedfromkatsuwonusby the presence of a seres of oblque or longtudnal black markngs above the lateral lne (,uwonshas strpes on the belly). The dorsal fns are contguous or nearly so. Ths latter feature dstngushes Euthvnnus from ÀUXIS whose dorsal fns are wdely separated. The dstal margn of the frst dorsal s concave. Ths character dstngushes Euthynnus fromsarda, the bontos, whose frst dorsal has a margn that s nearly straght. There are usually eght dorsal and seven anal fnlets. The ntestne s straght, wjthout a fold. There are 37 or 39 vertebrae. Teeth are present on the palatnes n all speces and on the vomer n two of the three spece s, A detaled descrpton of the generc characters 'of the skeleton s gven bjr Godsl (1954). Speces Euthynnus lneatus Kshnouye 1920 The followng descrpton s taken from Godsl (1954). Ths speces can usually be separated from others of the genus by the dorsl markngs, "The general pattern conssts of a seres of three, four, or fve broad contnuous black strpes runnng horzontally on the back from the corselet to the caudal fn, The most ventral of these strpes nvarably starts anterorly below the lateral lne and generally crossesths n ts path to the caudal regon, Varatons consst manly of nterruptons n the contnuty of the strpes or branchngs of ndvdual strpes wth supplementary short r regular markng s between. However, varatons can be suffcently extreme to preclude a postve dentfcaton and such varatons wdely overlap the markngs of other descrbed speces." A specmen wth typcal markngs s shown n Fg, 1. The dorsal strpes of Euthynnus yato and E. alette ratus are typcally more broken, rregular and oblque. "These black dorsal strpes are supermposed upon a background of blue, deepenng nto black dorsally and shadng nto grey and slver below. The belly of the fsh s dusky or slvery wth an rregular number (usually from 2 to 6) of black spots between the pectoral and pelvc fns. Such spots are not dagnostc or nvarable for specmens are occasonally seen wth no apparent spots." Specmens occasonally are found whch have oblque strpes on the belly, Merstc counts are gven n the followng table. 131
1:2 F1b1545 Tuna Fg. 1 Black skpjack, Euthynnus lneatus. Fsh caught by D.C. Vann at Socorro Island; total length 512 mm, weght 4 lb.looz. (2.14 kg). Photograph by J.C. Brown. 132
FIb/S45 Tuna 1:3 'MERISTIC COUNTS OF Euthyrmus lneatus * Merstc Character Range Count 'TÑ4ost Common No. Specmens 1st dorsal spnes 13-15 14-15 2Q 2nd dorsal rays 11-12 II 10 Dorsal fnlets 8-9 8 20 Anal rays 11-13 11-12 18 Anal fnlets 7-8 7 20 Gll-rakers - 1st arch: Upper lmb 7-11 9-10 30 Angle 1 1 28 Lower lmb 23-29 26-27 30 Total: 32-41 35-38 30 Number of vertebrae 36-3 8 37 27 Precaudal vertebrae 19-20 20 24 1st complete haemal arch on Vert No. 15-17 15-16 23 * Taken from Godsl (1954) TTThe caecal mass and the lver are the domnant organs n the ventral vew of the vscerat. The lver has three lobes, the rght lobe beng about twce as long as the other two. It extends the full length of the body cavty. The most mportant skeletal features whch are dagnostc for ths speces are the vertebral count of 37 (36-38), as opposed to 39 n the other two speces, and the presencè of four protuberances whch occur on the 31st and 32nd vertebrae. 1. 2 Nomenclature 1. 2.1 Vald scentfc names Euthynnus lneatus Ksbnouye 1920 1, 2. 2 Synonyms Euthynnus affns lneatus Fraser Brunner 1949 133 1. 2. 3 Standard common names, vernacular names Negra, Bonto negro Barrlete negro Black skpjack; cross-bred mackerel Mexcan lttle tunny 1. 3 General varablty Ecuador Mexco, Peru Unted States; U.S. sportsfshermen Kshnouye 1.3.1 Subspecfc fragmentaton (races, varetes, hybrds) There are no recognzed subspeces of Euthynnus lneatus. Fraser-Brunner (1949> proposed that E. lneatus and E, yato are subspeces of. affns. Other authors have suggested thate. affns and E, yato are the same speces t that E, lneals s a separate speces. All seem to agree that E. alletteratus
1:4 FIb/S45 Tuna s a dstnct speces whch may or may not have subspeces. Races or subpopulatons of E. lneatus may exst but none have yet been defned. Godsl (1954) reported consderable varaton n the external markngs of E. lneatus. Some of the atypcal specmens whch he examned had dorsal markngs of the E. yato or E. alletteratus type. However, there was no varaton n nternal features n the specmens of atypcal appearance and all could be postvely dentfed as E. lneatus The varaton n external markngs was not confned to specfc geographcal areas, but seemed to be general throughout the range of the speces. Consderable varaton n dorsal markngs between two sdes of the same fsh sometmes occurs. The exstence of hybrds has never been observed or nvestgated. The blood (erythrocytes) of two E. lneatus was tested wth a seres of 540 bean extracts, by Dr. C. W. Cotterman and the junor author, as part of the prelmnary work on a program for typng fsh blood. On the bass of agglutnatons, the blood of the black skpjack can be dfferentated from that of sx other scombrods from the Eastern Tropcal Pacfc whch were tested wth the same seres of reagents 134
2:2 FIb/S45 Tuna I 350 300 I 250 200 I 5 loo 05 0 j05 mdl flhi& IUIRU1L u..uil UUUUI. uu uuau u..uuu. o uuuum R.U*HIU o o uuuuuu.u.. 000 l00r 200 I'REWLLAGIGEOO UNITED STATES o --'u..aavar pa ISLANDS. SN/NADA RANK - t- 20 I 10 loso TRES MARIAS /SL ANOS GIILFOF TEHUANTEPEC O ccfo -URUIãjà.Th o o o III uiuuu u.. tt!i u... u.uuuuuumu L uuuuuuu... e r P'OfJ I GULF OF 2oI'.uuuuuuuujUujuj PANAMA uuuuuusuumuuiuudl o. ui..iu...u.u...,......:::::::::::::::::::::::l o D o URUf L COCOS IS. o r-----'...c PARAMOUNT UI U..dUuluuuUuuuuUDr ouuuuuuop uauuuauuuauuuuuu BAN u GAL APA GOS - utuuuuuu ISLANDS UU1UUUUUUU$UUUIUUUL UUUUUUUUDr 1000 90... UUUUUUUUUL.. IUUUUUUUUL UUUUUUUUUI 900 U.U..'..'.,.u,.u.uI 150 " I..u,... u...,.,...,u. I.'.".'..'.'u,' uuuuuuuuuu UUUUUI uuuuuuui I «I Fg. 2 Records of adult black skpjack, Euthynnus lneatus, charted by one-degree squares. 136
FIb/S45 Tuna 2:1 2 DISTRIBUTION 2.1 Delmtaton of the total area of dstrbuton and ecologcal characterzaton of ths area Black skpjack are known to occur along the Pacfc coast of the Amercas from southern Calforna to Peru. The present northern records for ths speces, off San Smeon, Calforna (35 20 'N by 121040 'W), was reported by Nowell (1961). There have been two other reports from Calforna waters (Roedel 1948, and Ftch 1952). Black skpjack have been taken off Baja Calforna (Godsl 1954), from the Tres Maras Islands, 2l 30 'N on the Mexcan coast (Fowler 1944) near Acapulco, Mexco (Mas and Jow, '1960), off Costa Rca (Schaefer and Marr, 1948), from Colomba Bank, 2 N by 79 W. and from Guayaqul Bank, 3 35'S by 80055tW (Godsl 1954, and Clemens, 1957). There are numerous reports of black skpjack from the Galapagos Islands (Fowler 1938 and 1944; Seale 1940; Schmtt and Schultz, 1940; Godsl 1954). They have been reported from northern Peru (Hldebrand 1946). The occurrence of black skpjack s sometmesreported n the logbooks of commercal tuna fshng vessels, although ths speces s not taken by these vessels. A search of the tuna boat logbook records of the Inter-Amercan Tropcal Tuna Commsson (IATTC) revealed that ths spces has been encountered, at varous tmes, nearly everywhere along the coast from the mddle of Baja Calforna to Guayaqul Bank, off northern Peru. They have frequently been reported from the Gulf of Calforna, the Revllaggedo Islands, all along the coast of Mexco and Central Amerca, and the Galapagos Islands. In addton, black skpjack have occasonally been reported from Clpperton and Cocos Islands and there s a sngle report from Shmada Bank (l6 52'N by 1l7 30'W), 1.80 mles southwest of Claron Island. Logbook reports of black skpjack from the waters south of Guayaqul Bank are rare. Ths may be due not to scarcty of the spece s n these waters but, rather, to reduced coverage by the tuna fleet. Locatons where black skpjack have been found as reported n the lterature, from tuna vessel logbooks and from scentfc logs of dceanographc cruses by the Scrpps Insttuton of Oceanography, the Bureau of Commercal Fsheres of the U.S. Fsh and Wldlfe Servce and the feld-books of Dr, C. L, Hubbs and Dr. D. P. De Sylva, are shown n Fg. 2. Locatons are shown to the nearest one-degree square of lattude and longtude. The major porton of the waters n whch black skpjack occur s tropcal, The Equatoral Pacfc Water mass extends approxmately from 23-24 N to northern Peru and the Galapagos Islands. To the north and south of ths tropcal water mass are transton regons whch are nfluenced by the cool Calforna Current n the north and by the cool Peru Current n the south. The prncpal warm currents are the North Equatoral, the Equatoral Countercurrent, and the South Equatoral. Near the coast, where black skpjack are most frequently found, these currents are usually weak and varable. The well-developed thermoclne, whch s a characterstc of most tropcal waters, tends to hnder the renewal of nutrents n the surface layer and thereby lmts bologcal productvty. However, n the area whch comprses the range of the black skpjack the thermoclne s relatvely shallow (10-50) meters. In general, the thermoclne shoals from west to east and there are areas near shore where the therrnoclne s suffcently shallow to permt the exchange of nutrents between the deep layer and the euphotc zone. There s a thermal dome located off Central Amerca (9 N by 90 W) where the thermoclne s frequently less than 10 m and sometmes reaches the surface. In the Gulf of Panama and n the Gulf of Tehuantepec seasonal hgh wnds brng about upwellng whch contrbutes to productvty. The Gulf of Guayaqul and the Galapagos are n the transton area between tropcal water and the cool rch water of the Peru Current. Upwellng enrches the nshore waters off Baja Calforna but the waters farther offshore n ths area are very poor n nutrents and standng crop. The waters of the Gulf of Calforna are warmer and more salne than adjacent waters. Upwellng alzo occurs n the Gulf of Calforna and the thermoclne s generally not deeper that 20 m. Ths descrpton wa compled from the followng references: Brandhorst 1958; Cromwell and Bennett, 1959; Cromwell 1958; Holmes, Schaefer and Shmada, 1957; Sund and Renner, 1959. 135
FIb/S45 Tuna 2:3 Z 2 Dfferental dstrbuton 2, 2,1 Areas occuped by eggs, larvae and othèrjunor stages: annual varatons n jhese patterns, and seasonal varaton for stages persstng over two or more seasons, Areas occuped by adult stages; seasonal and annual varatons of these, The eggs of black skpjack are pelagc but they have never been specfcally dentfed n plankton collectons. Mature and runnng rpe adults have occasonally been encountered and larvae and juvenles have been collected and dentfed. Larval and post-larval black skpjack have been collected from Pont Antono, Baja Calforna (29 45!N) to the vcnty of Malpelo Island (4 00'N by 81 351W), In the Gulf of Calforna they have been collected both from near the head and from the mouth, The stes of collecton form a contnuous band from the Tres Maras Islands, near the entrance of the Gulf of Calforna to the Gulf of Panama. Larvae and juvenles of black skpjack have, to date only been encountered wthn apprpxmately, 150 mles of the manland. The only excepton s one ndvdual captured near Malpelo laland (Klawe, n press). The locaton of capture of larval and juvenle black skpjack s shown n Fg. 3. Collectons have not been extensve enough to reveal annual varaton n the dstrbuton of larvae and juvenles. The areas occuped by adult stages have been dscussed n secton 2.1. Snce black skpjack are not sought by commercal fshng vessels, t s dffcult to detect seasonal and annual varatons n the dstrbuton of adult stages. However, when the logboòk reports of occurrence and those from other sources are analyzed by quarters of the year, there are some notceable dfferences n dstrbuton. In the frst quarter of the year, black skpjack have been encountered most often off the coast of Central Amerca and near the southern tp of Baja Calforna. In the second quarter there have been fewer reports from Central Amercan waters and a great ncrease of reports from tue lower Gulf of Calforna and from the Revllaggedo Islands. In thrd quarters the majorty of reports has been from the banks off the west coast of Baja Calforna. The reports of black skpjack from Calforna waters have all come n thrd quarters. In fourth quarters the reports have been scattered from Baja Calforna to central Peru wth not much concentraton n any area. There, have been more reports from the Galapagos Islands durng fourth quarters than at other tmes of the year. It should be noted that these apparent changes n seasonal dstrbuton may not be due to actual shfts n the populaton but may have resulted from seasonal changes n the concentraton of the commercal tuna fleet whch s largely governed by the regonal avalablty of yellowfn and oceanc skpjack. The reports of black skpjack from logbooks and from the lterature ndcate only the presence of black skpjack n a partcular area and furnsh no accurate nformaton as to quantty. It s a certanty that only a part of black skpjack sghtngs are reported n the logbooks, snce these fsh are, at the present tme, of no commercal value and there has been no program for collectng nformaton on ths speces. 2.3 Behavorstc and ecologcal determnants of the general lmts of dstrlmts and of dfferental buton and of the varatons of these dstrbuton Temperature, as for related speces, s probably an mportant determnng factor for the lmts of dstrbuton of black skpjack. Black skpjack have been reported from waters rangng from 60 F to 87 F (IATTC logbook records). They have been reported most frequently from waters wth surface temperatures between 75 F and 85 F. There have not been any experments performed to determne the absolute range of temperature whch can be tolerated by ths speces. 137
2:4 Fb/S45 Tuna cocos s. Fg. 3 Localtes of capture of larvae and juvenles of black skpjack, Euthynnus lneatus. 138
FIb/S45 Tuna 3:1 BIONOMICS AND LIFE HISTORY 3. 1 Reproducton 3.1. 1 Sexualty (hermaphrodtsm, heterosexualty, ntersexualty) Black skpjack are heterosexual. Males and females do mot dffer n external appearance. 3. 1. 2 Maturty (age and sze) The number of mature black skpjack that have been examned and reported on s very small. Mead (1951) examned two females, taken off Gen - tral Amerca, whose ovares were swollen and turgd. The lengths were 54. 4 and 55. 0 cm (fork length). It seems probable that some ndvduals would reach maturty at a smaller sze. De Sylva and Rathjen (1961), n ther study of E. alletteratus, the Atlantc speces, gve the sual length at frst spawnng as 350 mm, The age of black skpjack (E. lneatus) at maturty s unknown. 3.1. 3 Matng (monogamous, polygamous, promscuous) The spawnng of black skpjack has never been observed. However, from examnaton of the eggs and from what s known of ts lfe hstory and that of closely related speces, t s certan that spawnng s pelagc. 3. 1.4 Fertlzaton (Internal, external) Fertlzaton s exterra1. 3.1.5 Fecundty The fecundty of black skpjack has never been nvestgated. It seems logcal that the number of eggs produced and the relaton of ths to sze of fsh s n the same order of magntude as that of related speces. For example, Vldoso (1960) estmated that the fecundty of the bonto Sarda chlenss s 288. 2 thousand for 500 mm fork length; 413. 3 for 550 mm; 754, 2 for 600 mm; 771. 1 for 650 mm. In mature oceanc skpjack, Katsuwonus pelams, between 61Ú and 700 mm, the number of ova n the maturng group has been found to range between 330.0 thousand and 1, 000.0 thousand (J. Joseph, unpublshed data). 3.1. 6 Spawnng - Spawnng seasons (begnnng, end, peak) In the waters off Central Amerca there s consderable evdence that spawnng takes place n wnter and sprng. Schaefer and Marr (1948) reported taldng two adults n an advanced stage of maturty n the Gulf of Ncoya, Costa Rca, In February 1947. Rpe adults were taken n Aprl of the same year from the nshore waters of Costa Rca. Juvenles were collected further offshore n March. Clemens (1956) collected 'post larvae" black skpjack from Central Amerca n January 1955. Mead (1951) reported takng larvae and rpenng adults off Central Amerca n May 1949. Although these collec - tons were all made n the wnter and sprng t s probable that black skpjack spawn all year n ths area wth the peak In early sprng. Kawe (n press) compled the followng table of the average number of larvae caught off Cape Blanco, Costa Rca, per hoùr of surface tow durng dfferent months: Month No. of larvae Month Spawnng n the Gulf of Panama may extend over a consderable part of the year. Matsumoto\ (1959) dentfed black skpjack larvae and juvenles n materal from the "Dana Expedtons", collected n the gulf n January 1922 and n September 1928. The specmens ranged n sze down to 5. 0 mm, ndcatng that spawnng could not have been far removed n tme and locaton. Larvae collected durng Scrpps Insttuton of Oceanography and Calforna Cooperatve Oceanc Fsheres Investgatons cruses ndcate that spawnng also takes place all year of the southern Mexcan coast wth a peak n the early sprng but n more northern waters, off Baja Calforna, spawnng s lmted to summer months (Kawe, n press). No. of larv I 1.5 vi 0. 1 II 0.1 vt 0. 2 m 3. 2 IX 1. 4 Iv 14. 9 X o. o V 0. 6 XI 0. 2 VI 0.0 x-ï' 0. 7 139
3:2 FIb/S45 Tuna - Number of spawnngs per year, frequency It ìs not known whether ndvdual black skpjack spawn more than once a year0 Most lkely the black skpjack, lke other tropcal tunas have an extended spawnng season n warmer waters, and ndvdual fsh do not spawn all ova at once0 - Spawnng tme of day. The tme of day n whch spawnng takes place s unknown - Inducton of spawnng, artfcal fertlzaton The factors whch nduce spawnng are unknown, The junor author collected rrmng rpe black skpjack of both sexes off Central Amerca n Aprl 1957 and attempted to fertlze the eggs0 No development resulted, however. 3,1. 7 Spawnng grounds Snce black skpjack eggs are pelagc and the adults are encountered near the surface t seems lkely that spawnng takes place n open water near the surface. The spawnng grounds appear to be n the open ocean but n close proxmty to land mas se For the locaton of probable spawnng areas see secton 2.2.1, 3.10 8 Egg: structure, szé, hatchng type, parastes and predators The egg of black skpjack s sphercal and contans a sngle ol globule. In appearance and structure t s smlar to those of other tunas The junor author measured a small sample of preserved eggs taken from a runnng rpe female, and found that the egg dameter was between 0. 90 and 0. 95 mm. The dameter of the ol globule ranged from 0. 23 to 0.26 mm. There s no nformaton on parastes and predators of black skpjack eggs. The eggs are undoubtedly eaten by a wde varety of organsms. 3. 2 Larval hstory 3 201 Account of embryonc and juvenle lfe (prelarva, larva, postlarva, juvenle> Young blaclç skpjack, lke other tunalke fshes, do not pass through a sharply defned metamorphoss markng transton from larva to postlarva to juvenle. The defnton of each stage, therefore, must be somewhat arbtrary0 Matsumoto (1959) defnes larvae as ndvduals wth less than a full fn-ray count, especally n the frst dorsal. These fsh are usually l mm or less n total length. The sze range of postlarvae s approxmately 12 to 18 mm0 In ths sze range the anal openng moves back from md-way between the pelvc and ama fns to the orgn of the anal fn0 Young tunas larger than 18 mm are classed by Matsumoto as juvenles. The larva of E. lneatus s smlar n appearance to that of other tunas (see Fg. 4). It would be dffcult to separate the larvae of ths speces from that of other related speces, unless a sze-seres s avalable0 Matsumoto (1959) descrbed a seres of young black skpjack rangng n sze from 5.0 to 27. 0 mm. The followng descrpton s based largely on hs work. At 5, 0 mm the head s large - about 37 percent of total length and the mouth s ais proportonately large, The anal openng s near the mddle of the body. There s no spne or ray development, Between 6 and 12 mm the body elongates.nd ncreases n sze n relaton to the head0 The dorsal spnes develop and pgment appears on the frst dorsal fn. When length has reached 10-12 mm all of the unpared fns are almost fully develoed. The fns and fnlets become more clearly defned, The number of rays n the pectoral, fns comes wthn the adult range. By length 22 mm the dorsal half of the body s dark as far back as the caudal peduncle (Mead, 1951). In the larger juvenles, vertcal bars appear fantly along the dorsal regon. - Schaefer and Marr (1948) state that juveles of black skpjack are less deep boded than yellowfn tuna of the same sze. Below 44 mm n lengtf, ll0
FIb/S45 Tuna 3:3 Fg. 4 7.1 mm larva of black skpjack, Euthynnus lneatus. From Matsumoto (1959). Fg. 5 45 mm juvenle black skpjack, Euthynnus lneatus. Drawng by Shela K. Hllsdon. 1L1
3:4 FIb/S45 Tuna the juvenles of black skpjack can be dstngushed from those of oceanc skpjack by the heaver pgmentaton of the dorsal fn n the former. At 86 mm the second dorsal s pgmented from the orgn of the rays to half-way to ther dstal end. The head and body are more darkly pgmented than yellowfn and oceanc skpjack of the same sze, A juvenle black skpjack s shown n Fg. 5. - Feedng Clemens (1956) held juvenle black skpjack n shp-board aquara and offered them varous food tems such as ground fsh flesh, planktonc fsh eggs and lvng zooplankton, The subjects dsplayed more nterest n the lve zooplankton than n the non-lvng materal, but dd not feed untl actvely swmmng larval blennes were offered. After feedng on larval blennes, the subjects were nduced to feed on planktonc fsh eggs and ground fsh flesh by gradually substtutng the non-lvng matter n the det. The juvenle black skpjack fed untl ther stomachs were greatly dstended. Feedng perods were adjusted so that the subjects were fed agan when ther stomachs had retúrned to normaln fve to sx hours. - Rates of: development and survval Clemens (1956) was able to hold some juvenle black skpjack (see above) for as long as ten days. In that perod ther weght ncreased eleven tmes and length ncreased approxmately 1,4 tmes over that at the begnnng of the holdng perod. The author felt that ths growth rate would have representeda mnmum n nature because of the unnatural condtons of confnement. Nothng s known as to the rates of development or survval of the larval or postlarval stages. None. - Parental care - Parastes and predators There s no ìnformaton on the parastes of black skpjack larvae, postlarvae or juvenles. There s no specfc nformaton on predators of these stages, however, t would be surprsng f, lke almost everythng n the sea, they were not preyed upon by almost every organsm whch s able to catch and aliow them. 3. 3 Adult hstory 3, 3, 2 Hardness The hardness of black skpjack s smlar to that of other tuna-lke fshes. They are hardy enough to be successful n ther natural envronment, but they can only stand a mnmum of handlng. 3. 3. 3 Compettors Black skpjack are found n close assocaton wth yellowfn tuna, oceanc skpjack, and dolphn fsh, among others. All of these speces undoubtedly compete wth the black skpjack for food. Whether ths competton s n any way harmful to any of the speces concerned s unknown. 3,3.4 Predators The large bll-fshes undoubtedly prey on black skpjack, and they have been found n the stomach contents of yellowfn tuna (Alverson, n press), 3. 3. 5 Parastes and dseases The parastc copepods Calgus coryphaene (see Shno, l959a) and Calgus macarov (see Shno, l959b) are known external parastes of black skpjack. The trematode Hrudnella marna was found to be parastc n the stomachs of several black skpjack examned by the authors. There s no nformaton avalable on dseases df black skpjack, 3.3.6 Greatest sze The largest black skpjack collected by the junor author was a runnng rpe male of fork length 636 mm and weghng 10 lb. 8oz. (4. 75 kg). Snce only few ndvduals have been examned for length and weght (compared to other tuna-lke fshes), t s lkely that ndvduals larger than the above occur. L
FIb/S45 Tuna 3:5 3. 4 Nutrton and growth 3. 4. 1 Feedng (tme, place, manner, season) Black skpjack feed throughout ther lves and n all seasons of the year. Lke related speces, feedng s probably by sght and therefore confned to the daylght hours and to the surface layer. 3, 4, 2 Food (type, volume) Accordng to Walford (1937), the black skpjack s a feeder of "voracous habts and nsatable appette. " The stomach contents he examned conssted of small fsh and squd. One stomach contaned fourteen small fsh and thrty s qud. One of the speces of fsh consumed by black skpjack s the frgate mackerel (Auxs thazard). Sxteen Auxs three to fve. nches long were found by F. G. Alverson n the stomach of a black skpjack taken n the Gulf of Tehuantepec (Kawe, n press). The dsplacement volume was 127 ml. The pelagc crab (Pleuroncodes planpes) has been found n the stomachs of black skpjack from the banks off Baja Calfortha. A juvenle serra mackerel (Scomberomorus serra) was dentfed n the stomach contents of a black skpjack collected n the Gulf of Panama by IATTC personnel. 3.4. 3. Relatve and absolute growth patterns and rates. The growth rate of adult black skpjack has never been nvestgated. Some nformaton on the growth of juvenles s gven n secton 3. 2, 1. 3.5 Behavor 3. 5, 1 Mgraton and local movements There have been no taggng programs conducted wth ths speces and therefore there s no exact nformaton on mgratons. Possble seasonal movements have been dscussed n secton 2. 2, 1. 3.5.2 Schoolng Black skpjack, lke other tuna-lke fshes, tend to school by sze. Bn (1952) stated that, n Peruvan.waters, black skpjack are frequently found schooled wth yellowfn tuna and oceanc skpjack of the same sze. They were present n smaller quanttes than the commercally mportant spece s, however. Commercal tuna fshermen have observed that black skpjack wll frequently gather around drftng or anchored tuna boats. Yellowfn and oceanc skpjack also dsplay thís type of behavor, but t s beleved to be more pronounced wth black skpjack. 3.5.3 Reproductve habts Spawnng s pelagc; outsde of that nothng s known of the reproductve habts of ths speces. 1143
FIb/S'45 Tuna 41 4 POPULATION (STOCK) 4.1 Structure 4.1.1 Sex rato There s no nformaton on.the sex rato of E. lneatus, De Sylva and Rathjen (1961) found that the sex rato of E, alletteratus landed n Florda dd not dffer sgnfcantly from 1:1.
FIb/S45 Tuna 5:1 EXPLOITATION 5.1 Fshng equpment 5.1.1 Fshng gear There s no fshng gear specfcally used for E. lneatus; however, ths speces s ncdentally taken by gear engaged n explotng other speces. Black skpjack have been taken by tuna pursesenes, lve-bat pole and lne gear, commercal. trollng gear, and sport fshng gear. In varous places n Latn Amerca black skpjack are taken by trolled hand lnes. Walford (1937) stated that "they wll strke any lure trolled at any speed up to eght or ten mles an hour. 5.1. 2 Fshng boats There are no boats specfcally desgned for fshng for black skpjack. Ths speces s occasonally taken by all lypes and szes of commercal tuna vessels from small albacore trollers to the largest lve-bat and purse-sene vessels. In Ecuador and Peru, black skpjack are taken by canoe and raft fshermen as well as by the other types of boats mentoned above. 5. 2 Fshng areas 5. 2.1 General geographcal dstrbuton Black skpjack are dstrbuted over a wde area n the Eastern Pacfc (see secton Z. 1).; however, they are not fshed commercally anywhere except for a few caught n Latn Amercan waters whch are sold fresh n the local markets. Vrtually all of the black skpjack landed are caught wthn a few mles of the coast. 5. 2. 2 Geographcal ranges (lattudes, dstances from coast, etc.) See sectons 2.1 and 5.2.1. 5. 2. 3 Depth ranges Black skpjack are taken n the surface layer. 5.3 Fshng seasons 5.3.1 General pattern of fshng season There s no fshng season as such for black skpjack. They are encountered more by chance ]_ '45 than by desgn. 5. 3. 2 Duraton of fshng season Black skpjack are caught all year throughout most of ther range. 5. 3.3 Dates of begnnng, peak and end of season The landed catch s probably very small and very lttle of what s landed s reported. Therefore, t s mpossble to desgnate a begnnng, peak or end of the fshng season except n very localzed areas. In 1954 the Republc of Ecuador made a census of fshermen n the course of whch, among other thngs, the fshermen were questoned on the seasonal abundance of the varous speces landed. The black skpjack was lsted as beng most abundant from May to September n the open coastal areas and from January to March n the Gulf of Guayaqul (Ecuador, n.d.). 5.3.4 Varaton n tme or duraton of fshng season The fshery s not suffcently developed for varatons n tme or duraton of fshng season to 'be apparent. 5.4 Fshng operatons and results Neglgble. 5.4.1 Effort and ntensty 5.4.2 Selectvty Black skpjack are taken by non-selectve gear. 5.4.3 Catches Catch statstcs for black skpjack are spa rs'e. Most of the landngs are probably made by small boats n Latn Amerca and go unrecorded. Landngs have occasonally been recorded at Mancora, Peru, but t s unknown what proporton they are of the total landngs even n that mmedate area. Tuna purse-seners sometmes set on black skpjack by mstake. These catches are dumped overboard but estmates of the tonnage have' been
5:2 FIb/S45 Tuna recorded n the logbooks. These references show that some farly large schools of black skpjack are occasonally encountered and accdental catches from - loo tons have been recorded. 5.44 Past and present factors of effect on operatons and results The prncpal factor, past and present, affectng fshng operatons and results s the lack of a market for black skpjack. 5. 5 Fsheres management and regulatons None. 5. 6 Fsh farmng, transplantng and other nterventon. None L6