SPAWNING OF ALBACORE IN THE SOUTH PACIFIC OCEAN 



157 



The seasonal shift in fishing grounds, as indi- 

 cated by the areas fished by Samoa-based vessels, 

 may therefore reflect movements of the fish related 

 to their spawning in the more northern waters 

 during the southern summer months. 



Minimum size of spawning fish 



It was fu-st reported by Ueyanagi (1955) and 

 later supported by the findings of Otsu and Uchida 

 (1959b) that female albacore attain sexual matu- 

 rity and thus may first spawni at about 90 cm. in 

 length. Because of the larger sample now available 

 a further examination was made of this point. 



Figure 7 shows the developmental stage of each 

 ovarj' plotted by fish length and by ovary weight. 

 The data show that some fish are already mature 

 at 86 cm. This is not far different from pre- 

 vious results. The smallest fish found to be ma- 

 ture in the central equatorial Pacific measured 

 89.1 cm. (Otsu and Uchida, 1959b), and the 

 smallest from the western Pacific (Ueyanagi, 1957) 

 was 87 cm. long. Some albacore may therefore 

 become sexually mature and spawn for the first 

 time at a size of about 86 cm. 



As for the males, Ueyanagi (1957) judged from 

 their general appearance and oozing of milt that 

 testes weighing more than 150 grams were proba- 

 bly ripe. By plotting testis weight against fish 

 length, he showed that the smallest fish having 

 testes weighing more than 150 grams measured 

 97 cm., and he postulated that length to be the 

 minimum size of sexual maturity in males as 



FORK LENGTH IN CENTIMETERS 



FicDBE 7. — Ovary weight plotted by fish size. 



FORK LENGTH IN CENTIMETERS 



Figure 8. — Te.stis weight plotted by fish size. Dashed 

 line is at 150 grams, the weight used by Ueyanagi (1957) 

 as a criterion of ripeness. 



contrasted with 87 cm. for females. Following 

 Ueyanagi 's lead, we have plotted testis weight 

 agamst fish length (fig. 8). It can be surmised 

 from this figure that some male albacore are 

 probably sexually mature when they attain a 

 length of about 90 cm., since testes weighing more 

 than 150 grams already appear at this size. How- 

 ever, lacking more objective means of determining 

 maturity of the males, it cannot be said with 

 certainty that this is the size at which male 

 albacore are first capable of spawning. 

 Size of the albacore 



As shown in figure 3, the sampled fish ranged 

 between 72 and 110 cm. (15 and 64 lbs.). It is 

 interesting to compare the sizes of these fish 

 with those taken in Hawaiian waters, which are 

 believed to be part of the reproductive segment 

 of the North Pacific population. Although very 

 few albacore are landed in the Hawaiian fisherj-, 

 they are generally very large (see fig. 9, which is 

 based on fig. 7 in Otsu and Uchida, 1959b). 

 Albacore landed in Hawaii in 1955 and 1956 

 ranged in size between 93 and 128 cm. (33 and 

 93 lbs.), but females appeared to reach their 

 maximum size at 112 cm. In the South Pacific 

 samples, the largest fennile measured 106 cm. 

 (fig. 3). 



Perhaps most significant is that while the female 

 fish in the two areas were thus of comparable 

 sizes, there was a virtual absence of males larger 



