MATURITY AND SPAWNING OF ALBACORE 



303 



closely resemble that of the central equatorial 

 Pacific albacore (fig. 9). 



The best indications of albacore spawning are 

 therefore available from two widely separated 

 localities, the Hawaiian Islands in the central 

 Pacific and Sunda Islands in the Indian Ocean, 

 the former during the northern summer and the 

 latter during the southern summer. 



It is not known whether the albacore appearing 

 in various parts of the Pacific Ocean belong to a 

 single intermingling population or whether there 

 are discrete populations in the various areas. 

 Suda (1956) is of the belief that the albacore occur- 

 ring in the North Pacific Current area are a 

 "feeding group" and that there is a corresponding 

 "spawning group" in the North Equatorial Current 

 area. Furthermore, he postulates that the alba- 

 core of the Indian Ocean as well as the tropical 

 South Pacific comprise the spawning group of 

 another feeding group located in South Pacific 

 temperate waters. If this is indeed the case, it 

 may be that the Hawaiian Islands represent a 

 portion of the spawning grounds of the northern 

 population, and that the Sunda Islands, that of 

 the southern population. 



Our data suggest that albacore attain sexual 

 maturity at about 90 centimeters in length 

 (weight, 33 lbs.). This signifies that the fish 

 exploited during the spring and summer by the 

 Japanese and the Americans in the temperate 

 waters of the North Pacific are largely sexually 

 immature fish (Suda 1955, Brock 1943). The 

 Japanese winter longline fishery in the North 

 Pacific, on the other hand, exploits both juvenile 

 and adult fish (Suda 1954). The gonads of these 

 adult fish do not show any development, however. 

 This situation is in contrast to that in the Ha- 

 waiian Islands where the catch is wholly of adult 

 fish (fig. 7). Many of these have gonads showing 

 considerable development. In the central equa- 

 torial Pacific, the fish are also generally large and 

 most are adults with gonad development inter- 

 mediate between North Pacific and Hawaiian 

 Islands fish. It appears possible that the Ha- 

 waiian and central equatorial Pacific albacore are 

 a segment of the population which, after attaining 

 a certain size in temperate waters of the North 

 Pacific, moves south into tropical and subtropical 

 waters to reproduce. 



SUMMARY 



1 . This study is based on examination of gonads 

 of albacore taken from three general areas: the 

 North Pacific (north of 30° N. latitude, between 

 180° longitude and the west coast of the United 

 States), the Hawaiian Islands, and the central 

 equatorial Pacific (Equator to 12° S. latitude, 

 between 180° and 150° W. longitude, with scat- 

 tered samples collected from as far east as 120° 

 W.). Although the three areas are treated sepa- 

 rately throughout this report, this does not infer 

 that the fish belonged to separate stocks, or pop- 

 ulations. 



2. Gonads of both sexes were used in the study 

 of the maturity of North Pacific albacore. Only 

 the ovaries were used for the other two areas and 

 the degree of maturity was determined largely 

 from egg diameter measurements. 



3. The several tests made to determine the 

 most efficient sampling procedure indicated that 

 mature eggs were randomly distributed throughout 

 the length of an ovary but there were some 

 differences in the transverse distribution. There 

 were no differences in the distribution between the 

 two ovaries of a pair. The adopted method of 

 sampling was to take a random sample from the 

 mid-section of an ovary. 



4. The ovaries were classified in three stages of 

 relative maturity: early developing, late develop- 

 ing, and advanced, on the basis of the most 

 advanced eggs present. The advanced ovaries 

 were not in a fully ripe condition. 



5. The North Pacific albacore were either 

 juveniles or sexually dormant adults with early 

 developing gonads. 



6. The Hawaiian albacore evinced varying 

 degrees of maturity from early developing to 

 advanced, with the bulk of the ovaries in the late 

 developing stage. Although the samples were 

 somewhat inadequate for a conclusive study, there 

 was indication that spawning may occur during 

 the summer months in the vicinity of the Ha- 

 waiian Islands. The data also indicated the 

 possibility of a somewhat protracted spawning 

 season. 



7. The ovaries from central equatorial Pacific 

 fish were in the early developing and late develop- 

 ing stages, with the early developing stage 

 predominating. 



