732 



Fishery Bulletin 94(4). 1996 



picture of gonadal activity, the similarity in trends 

 of monthly values of GSI's and oocyte diameters (Figs. 

 2 and 6) suggests that either method can be used to 

 determine spawning season for the samples as a group. 



The length frequencies of male and female samples 

 from New Caledonia and Tonga indicate sexually 

 dimorphic size differences. Such dimorphism had 

 previously been reported by Otsu and Sumida ( 1968). 

 In yellowfin tuna, sexually dimorphic growth has 

 been age verified, and males were found to repre- 

 sent the largest mode in fork lengths (Wild, 1986). 



Gonadal asymmetry has been recorded in several 

 fish species (Ovchinnikov, 1971; Sanwal and Khana, 

 1972) and was documented previously in albacore 

 by Otsu and Uchida (1959) and Ueyanagi ( 1955). The 

 former compared oocyte diameters from different 

 areas of one pair of ovaries and found that differ- 

 ences existed between anterior and posterior regions 

 of a single ovary but not between the sides. In con- 

 trast, Ratty et al. (1990) found that the smaller left 

 testis of males from the temperate troll fishery was 

 consistently more active than the larger right testis. 

 We found no significant difference in the diameters 

 of oocytes in left and right ovaries. 



The absence of advanced and fully ripe ovaries in 

 our samples is similar to the state of reproductive 

 development of ovaries in other studies of albacore 

 reproduction in the Pacific that have relied on long- 

 line fisheries as the main source of samples (Otsu 

 and Uchida, 1959; Otsu and Hansen, 1962). As these 

 authors have noted, albacore in, or close to, spawn- 

 ing condition are generally unavailable to the fish- 

 ery, either because they have stopped feeding and 

 will not take hooks or because they have moved be- 

 yond the range of gear. In order to capture the latter 

 category of fish, both the New Caledonia longliners 

 and the MV Lofa crew set and hauled their gear dur- 

 ing daylight hours; it is possible, however, that alba- 

 core, like some other tunas, spawn at night (Hunter 

 et al., 1986; Schaefer, 1996). In addition, albacore 

 may pass rapidly through the mature and spawned 

 stages of the cycle, as Hunter et al. ( 1986) found with 

 skipjack tuna, and McPherson with yellowfin tuna 

 (1991). Thus, there remain a number of key aspects 

 of the reproduction of South Pacific albacore, such 

 as spawning frequency, batch fecundity and length 

 at 509r maturity, that require further investigation. 



Acknowledgments 



We are grateful to the many South Pacific Commis- 

 sion TBAP and Fisheries Programme staff who as- 

 sisted in the collection of gonads and related data in 

 New Caledonia. Special thanks are due to the radio 



operators and crew of MV Lofa, who, in the course of 

 their normal duties, collected and weighed a consid- 

 erable number of gonads. We also thank Tevita Finau 

 Latu, Tongan Ministry of Fisheries, for coordinating 

 sampling on Lofa. This paper has benefitted from 

 discussions with colleagues at the Southwest Fish- 

 eries Science Center and South Pacific Commission, 

 notably John Hampton and Marc Labelle of the South 

 Pacific Commission and Norman Bartoo and David 

 Au of the Southwest Fisheries Science Center. 



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