SKIPJACK 



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I ■ I CHC'35 



SKIPJACK 



J_ j_X 



I 



SKIPJACK 



iiliL 



SKIPJACK 



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J_L 



CHG-35 

 I»X.l-2 

 19S7 



HMS.43 

 JAN. 23-24 

 I95t 



SKIPJACK 



Al 



CHG 36 

 MAR-f. 7 

 IMS 



CHG 38 

 API! 17 in 

 1958 



HMS'45 

 JUNE 8-9 

 l7Sa 



YEUOWFIN 



\\..iLl 



HMS-43 



JAN.23-2A 



1958 



1200 1500 1800 



lOil OlMW o:HKI ObOO 090<) 1200 



*!) ZO.NtTlMK 



Figure 2. — Diel variation in abundanci' of larval skipjack and 

 larval yellowfin. 



JAN. FER MAR APR. MAY JUNE 



OCT. NOV. DEC. 



FiGUUE 3. — Seasonal variation in the abundance of larval 

 skipjack. The slender bars represent averages for the diel 

 variability station, the thick bars averages for the offshore 

 surveys. 



The averages for tlie offshore surveys represent 

 more samples an(J a greater areal and temporal cover- 

 age than those for the diel variability station. 



Based on the offshore data, skipjack spawning ap- 

 pears to be greater during the southern summer 

 (January to February) and early fall (March to 

 April), but paucity of data during the southern win- 

 ter and spring (June to October) makes this con- 

 clusion tenuous. 



VERTICAL AND HORIZONTAL 

 DISTRIBUTION 



Strasburg (19G0) oliserved tliat most larval tunas 

 were captured within the up])cr (iO m. of water, witli 

 20 to '25 percent of the catch witliin the 70- to 130-m. 

 depth, and practically none below 140 m. Since the 

 possibility of larval tunas in waters below 140 m. had 

 been indicated in the earlier cruises (fig. 2), special 

 plankton hauls were planned for the diel variability 

 station during HMS-45. A closing net of dimen- 

 sions similar to those of the open net was added to 

 the towing cable to permit sampling at depths be- 

 tween 140 and 280 m. Although simultaneous sam- 

 pling was planned for deptli ranges of to 140 and 

 140 to 280 m., the actual ma.ximum depth sampled 

 by the upper net ranged between 121 and 150 m., 

 while the depths sampled by the lower net ranged 

 between 70 and 262 m. (appendix table A-4). 



No larval tunas were caught by the lower net. 

 Larvae were caught only in 6 of the 12 hauls by the 

 upper net. Although the results did not conflict 

 with those of Strasburg, the meager catches and the 

 departures from the planned sampling ckptlis caused 

 the results to be inconclusive. 



A relation lietween larval skipjack distribution and 

 area was not evident. Xo significant aical associa- 

 tion (Kendall coefficient of concordance) was found 

 in the average abundance of larvae for the several 

 legs of the offshore survey track, nor was a relation 

 between larval distribution and proximity to land 

 found in a comparison (Kendall cooflicient of con- 

 cordance) of the average abundance by inner, mid- 

 dle, and outer 75-mile sections of the offshore survey 

 legs (tables 4 and 5). 



T.VBi.K 4. — Ai'cr(i(jr iiiiinlxr of liirnil akipjuck iindir 10 m.' of 

 ocean surf ace for the tiorlh, soidh, east, and trest tegs of the off- 

 shore suri'cys (fig. 1). 



[Numbers of samples on which the averages arc based are in parentheses] 



