APPROXIMATE WEIGHT (POUNDS) 

 _6 11 18 



60 

 LENGTH I CM.] 



Figure 2. 



-Skipjack length-frequency distribution and 

 stage of development. 



It was noted earlier that one skipjack with 

 running ripe ovaries had been caught. Unfor- 

 tunately, the length of this specimen was not re- 

 corded. However, a sample from the school from 

 which this fish was taken showed their size to 

 range from 45.6 to 56.9 cm., and in all likelihood 

 this specimen fell within this length range. 



It seems from these observations that, although 

 some skipjack as large as 50.7 cm. were ap- 

 parently not ready to spawn, those in the Mar- 

 quesas-Tuamotu areas are capable of first spawn- 

 ing when they are about 43 cm. long. 



The size at first spawning has been determined 

 for skipjack in other areas of the Pacific. Brock 

 (1954, p. 102), discussing skipjack in Hawaii, 

 states, "The smallest fish that possessed maturing 

 ova during the spawning season were around 40 to 

 45 cm. long. Fish 35 to 40 cm. in length had 

 ovaries that, with a few exceptions, seemed im- 

 mature." In the southern waters of Japan, Yabe 

 (1954) noted that no definite information was 

 available because of the scarcity of data, but that 

 the smallest skipjack in his samples with mature 

 ova was 46.8 cm. long. In the eastern Pacific, 

 Orange (1961) found the minimum size at first 

 spawning for skipjack around the Revilla Gigedo 

 Islands to be about 55 cm., and around the Cocos 

 Island area about 40 cm. 



From the above discussion it appears that the 

 size at first spawning may vary with locality. 

 Skipjack in the Marquesas and Tuamotus, in 



482 



Hawaii, and in the southern waters of Japan all 

 seem to mature at about the same size, while in 

 certain areas in the eastern Pacific they attain a 

 larger size before reaching maturity. 



It is interesting that all samples from the 

 Marquesas and Tuamotus were composed pri- 

 marily of adult fish. The Hawaiian summer skip- 

 jack fishery also exploits mostly adult fish (Brock, 

 1954, fig. 1). In the eastern Pacific, if the size- 

 frequency samples presented by Hennemuth 

 (1957) are typical, the fishery depends on both 

 juvenile and adult fish. The Japanese skipjack 

 fishery probably exploits adult as well as juvenile 

 fish (Yabe, 1954; Yao, 1955). 



SPAWNING SEASON 



It would be relatively simple to determine the 

 spawning season of skipjack if all the ovaries 

 ripened at the same time and if ripe fish were 

 readily taken. Small numbers then could be 

 examined to follow the development of ova to the 

 time of spawning. My data show, however, the 

 presence of a diversity of developmental stages in 

 any one period; therefore, another method had to 

 be employed to define the spawning season. 



The temporal distribution of skipjack possessing 

 ripe or advanced ovaries should give some indi- 

 cation of the spawning season, the implication 

 being that these fish are actively spawning or very 

 close to spawning. The percentage distribution 

 of skipjack by month of capture and stage of 

 development is presented in figure 3. Only those 

 larger than the size at first spawning, and there- 

 fore, presumably only adult fish, were used in this 

 analysis. All but one specimen in my collection 



71 B 



85 g 



H 



101 S 



Bg 



44 

 10 

 10 20 30 40 10 20 30 40 50 60 70 80 90 10 20 30 40 50 

 PERCENT 



Figure li. — Seasonal distribution of early developing, 

 developing, and advanced skipjack. 



U.S. FISH AND WILDLIFE SERVICE 



