302 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



DISCUSSION 



Our samples did not include any ovaries that 

 were fully ripe. Three ovaries were classified as 

 "advanced" on the basis of the appearance of 

 the eggs. Although they were advanced in ma- 

 turity, and presumably close to spawning, it has 

 not been possible to determine the time required 

 for these ovaries to attain a fully ripe stage. 

 Because these advanced ovaries were collected 

 during the summer months, and since a large 

 percentage of ovaries collected in the fall were 

 in the early developing stage (fig. 8), it was pos- 

 tulated that some spawning occurs during the 

 summer in the vicinity of the Hawaiian Islands. 



Fully ripe fish apparently are not available to 

 the fishery. June (1953), working with Hawaiian 

 yellowfin, concluded that this species spawns in 

 Hawaiian waters. He found only one fully ripe 

 ovary among his samples, however, and stated 

 that "fish that are actually spawning either do 

 not take the hook or migrate into deeper water 

 outside the longlining grounds." Similarly, Schae- 

 fer and Orange (1956) stated that "apparently, 

 when the yellowfin tuna imminently approach 

 spawning, they become unavailable to the fish- 

 ery." This behavior was noted earlier by Schaefer 

 (1948) for yellowfin tuna and skipjack off Central 

 America. Brock (1954) also found that fully ripe 

 skipjack are not commonly available to the 

 Hawaiian skipjack fishery. Thus, the possibility 

 that fully ripe tunas are generally unavailable to 

 the fishery may be one reason for the small num- 

 ber of advanced ovaries and the complete absence 

 of ripe ovaries in our collections. 



Most of the ovaries examined from the central 

 equatorial Pacific were in the early developing 

 stage, but a few late developing ovaries were 

 present as well as those that contained relics of 

 past spawning. Absence of advanced stages may 

 mean that these fish do not spawn in this region. 

 Unfortunately, not much is known of the maturity 

 of the albacore taken in other regions of the 

 tropical Pacific. Some field observations on the 

 gonads of albacore landed by the Japanese tuna 

 mothership expeditions between April and Septem- 

 ber of 1951 are available for the western equatorial 

 Pacific between the Equator and 6° N. latitude 

 and between 144° E. and 174° E. longitude 

 (general vicinity of the Caroline and Marshall 

 Islands). Descriptions of these expeditions are 

 given by Shimada (1951), Ego and Otsu (1952), 



and Van Campen (1952). Of a total of 41 

 observations made by observers from POFI 

 during this period, 33 were recorded as immature, 

 6 as spent, and only 2 as mature. Judging from 

 these records, it may be assumed that the maturity 

 of the western Pacific albacore during this period 

 more nearly resembled that of the central equa- 

 torial Pacific albacore than that of the Hawaiian 

 fish. 



Ishii and Inoue (1956) postulated that the Coral 

 Sea and adjacent New Caledonia area were 

 spawning areas for the albacore. Their study was 

 based on only two ovaries which, according to 

 their descriptions, corresponded to our early 

 developing and late developing stages. On the 

 basis of these data, it is surmised that the maturity 

 of the fish in this area is much like that found 

 throughout the central and western equatorial 



2 4 68902 46 8 100 2 4 681 10 2 46 8 120 

 LENGTH (CM.) 



Figure 13. — Length composition of Indian Ocean albacore 

 (reproduced from Ueyanagi 1955, fig. 2). 



Pacific. It is interesting to note that Ueyanagi 

 (1955) reported on two well-advanced ovaries 

 obtained in February 1953 from the southern 

 waters of Sunda Islands (Indian Ocean) ; one of 

 the ovaries he referred to as "ripe" and the other 

 as "nearly ripe". 2 He has hypothesized that the 

 albacore which occur in the Indian Ocean spawn 

 in February, at least, in part. He believes that 

 the area from south of the Sunda Chain to north- 

 west of Australia may be the spawning grounds of 

 the Indian Ocean albacore, since the fish taken 

 there are generally large. Ueyanagi's size-fre- 

 quency data of the Indian Ocean albacore (fig. 13) 



' Ueyanagi very kindly sent us samples taken i from these two ovaries. 

 The sample lie referred to as "nearly ripe" corresponds in maturity to late 

 developing ovaries, and the "ripe" to one of the advanced ovaries in the 

 present study. 



