725 



AbStr3Ct.— The spawning seasonal- 

 ity of albacore, Thunnus alalunga, in 

 the South Pacific was studied by exam- 

 ining ovaries and testes collected from 

 longline vessels operating in the waters 

 off New Caledonia (21°-23°S, 164°- 

 166°E) and Tonga (16°-29°S, 171°- 

 177°W), January 1990 to February 

 1992. The monthly change in GSI val- 

 ues and mean oocyte diameters indi- 

 cated that albacore are annual spawn- 

 ers, with most spawning limited to the 

 austral summer months from Novem- 

 ber to February. Asymmetry in weight 

 of, but not in the reproductive develop- 

 ment of, the left and right gonad pairs 

 was apparent in samples from the two 

 collection sites; most right ovaries and 

 testes were heavier and larger than 

 those on the left side. 



Spawning seasonality of albacore, 

 Thunnus alalunga, in the 

 South Pacific Ocean 



Darlene Ramon 



Southwest Fisheries Science Center 

 National Marine Fisheries Service, NOAA 

 LaJolla, California 92038 

 e-mail address: darlene@pooh.ucsd.edu 



Kevin Bailey* 



South Pacific Commission 



Tuna and Billfish Assessment Programme 



B.P D5. Noumea Cedex. New Caledonia 



Manuscript accepted 1 July 1996. 

 Fishery Bulletin 94:725-733 (1996). 



Albacore, Thunnus alalunga, are 

 distributed throughout the Pacific 

 in temperate and tropical waters. 

 The North and South Pacific popu- 

 lations are considered to be sepa- 

 rate stocks because 1) catch rates 

 for these two populations are ex- 

 tremely low in the equatorial re- 

 gion, 2) the two populations have 

 nonoverlapping spawning areas 

 and different spawning seasons, 

 and 3) there is no evidence that al- 

 bacore tagged in the North Pacific 

 move to the South Pacific (Lewis 1 ). 

 In the South Pacific, albacore are 

 found from the Equator to 50°S lati- 

 tude and from the surface to depths 

 of 300 m (Yoneta and Saito, 1973). 

 South Pacific albacore generally are 

 considered to reach sexual maturity 

 in the size range of 85 to 90 cm fork 

 length [FL] (Ueyanagi, 1957; Otsu 

 and Hansen, 1962), when they are 

 usually between 6 and 8 years old 

 (Labelle et al., 1993). 



Two major fisheries target alba- 

 core in the South Pacific: a longline 

 fishery concentrating on adult fish 

 (80-110 cm) in tropical and sub- 

 tropical waters ( 10°-30°S) through- 

 out the year and a surface troll fish- 

 ery targeting subadults (50-80 cm) 

 in temperate waters (30°-40°S) dur- 

 ing the austral summer (Lewis 1 ; 

 Rensink 2 ). An area of research that 



was recognized by the second South 

 Pacific Albacore Research (SPAR) 

 workshop as needing further work 

 was delineation of the spawning 

 seasonality of albacore in the South 

 Pacific. A sampling and histological 

 project was organized by the Tuna 

 and Billfish Assessment Programme 

 (TBAP) of the South Pacific Commis- 

 sion (SPC) and the Southwest Fish- 

 eries Science Center (SWFSC) to 

 provide a better understanding of 

 albacore reproduction in the South 

 Pacific. Because adult albacore at 

 various stages of reproductive de- 

 velopment were needed, sampling 

 was limited to the longline fishery. 

 The purpose of our study is to re- 

 port on the spawning seasonality of 

 albacore in the South Pacific Ocean 

 by using oocyte development and 

 gonadosomatic indices as indicators 

 of spawning activity. 



* Deceased. 



1 Lewis, A. D. 1990. South Pacific alba- 

 core stock structure: a review of available 

 information. Third South Pacific albacore 

 research workshop; Noumea, New Cale- 

 donia, 9-12 October 1990, Working Paper 

 5, 13 p. South Pacific Commission, B.P. 

 D5, Noumea Cedex, New Caledonia. 



2 Rensink, G. 1991. Summary of the 

 1989-90 U.S. South Pacific albacore fish- 

 eries data. Southwest Fish. Sci. Center, 

 National Marine Fisheries Service, P.O. 

 Box 271, La Jolla, CA 92038. Admin. 

 Rep. 14: 1-21. 



