Labelle et al. : Determination of age and growth of South Pacific albacore 



661 



year in the growth models presented in this paper. 

 Laurs et al. (1985) validated the daily increment for- 

 mation rates in sagittae of tagged north Pacific alba- 

 core that had been injected with oxytetracycline (OTC) 

 prior to release and concluded that the increment 

 counts, adjusted upwards by 5%, provided an accurate 

 estimate of absolute age. Preliminary estimates of ab- 

 solute age of south Pacific albacore were obtained from 

 counts of otolith increments, assuming similar incre- 

 ment deposition rates as for the north Pacific popula- 

 tion (Wetherall et al., 1989). These results indicated 

 that south Pacific albacore grew about twice as fast as 

 our estimates suggest. This would suggest that the 

 length-frequency modes and vertebral-rings analysed 

 here are more likely to be semestral than annual 

 features. 



The length increment data from 28 tag returns pre- 

 sented in this study clearly favor the hypothesis of 

 annual length-frequency modes and vertebral-rings 

 over a semestral formation rate. Given the assump- 

 tion that length-frequency modes represent cohorts of 

 albacore spawned during the same season, we would 

 expect the temporal spacing of length-frequency modes 

 to correspond to the frequency of spawning seasons. 

 Both gonadosomatic indices and microscopic examina- 

 tion of gonad tissue of south Pacific albacore clearly 

 indicate a single annual peak in spawning activity dur- 

 ing the austral summer (Ramon and Bailey, 1993). 



Most of the evidence therefore points towards an- 

 nual length-frequency modes and vertebral-rings, al- 

 though the conflicting results obtained from "daily" 

 growth increment counts on otoliths are deserving of 

 further study. It would be particularly useful to esti- 

 mate increment formation rates in vertebrae and 

 otoliths of tagged south Pacific albacore injected with 

 OTC before release, as was done for the north Pacific 

 population. During 1986-1989, 3,341 tagged south Pa- 

 cific albacore were injected with OTC, and to date, 

 three have been recaptured and the relevant hard parts 

 obtained. It is hoped that examination of this material 

 will, in due course, clarify increment deposition rates 

 in south Pacific albacore. 



A previous review of the available information on 

 stock structure lead Lewis ( 1990) to conclude that the 

 south Pacific population probably had very limited ex- 

 change with those of the North Pacific and the Indian 

 Ocean. Parasite studies (Jones, 1991), tagging pro- 

 grams, and ongoing electrophoretic surveys have not 

 yet revealed the existence of separate sub-stocks within 

 the south Pacific population. Thus, the growth rates 

 reported here could be considered as representative of 

 the growth patterns in the entire south Pacific alba- 

 core population. However, we cannot reject the hypoth- 

 esis that populations from other oceans have signifi- 

 cantly different growth patterns. It is also plausible 



that local phenomena, such as land mass effects and 

 upwelling zones that can affect the growth rates of 

 albacore within certain regions of the south Pacific. 



Acknowledgments 



Several persons and agencies have contributed signifi- 

 cantly to this research. Staff of the South Pacific Com- 

 mission (SPC), New Zealand Ministry of Agriculture 

 and Fisheries (MAF), and the United States National 

 Marine Fisheries Service have contributed to the tag- 

 ging, observer, and port sampling programs. Special 

 thanks go to Patrick Swanson of MAF for his assis- 

 tance in aging the vertebrae. We also thank all troll 

 fishermen who assisted with the observer program and 

 the release and recovery of tags. Financial assistance 

 for the observer and tagging programs and for the 

 data processing and analysis was provided by the Eu- 

 ropean Community Fifth European Development Fund 

 and the Canadian International Center for Ocean 

 Development. 



Literature cited 



Anonymous. 



1986. First South Pacific Albacore Research Workshop; 

 Auckland, New Zealand, 9-12 June 1986. South Pac. 

 Comm. Rep., Noumea, New Caledonia, 33 p. 



1991. Fourth South Pacific Albacore Research Work- 

 shop; Taipei, Republic of China-Taiwan. November 

 4-8, 1991. South Pac. Comm., Noumea, New Cale- 

 donia, 40 p. 

 Beardsley, G. L. 



1971. Contribution to the population dynamics of 

 Atlantic albacore with comments on potential 

 yields. Fish. Bull. 69(4):845-857. 

 Bell, R. R. 



1962. Age determination of the Pacific albacore of the 

 California coast. Calif. Fish Game. 48( 1 ):39-48. 

 Berry, F. H., D. W. Lee, and A. R. Bertolino. 



1977. Progress in Atlantic bluefin tuna ageing at- 

 tempts. Collective Volume of Scientific Papers. Int. 

 Comm. Conserv. Atlantic Tunas. 6(2):305-317. 



Berry, F. H. 



1978. Vertebrae related studies. /;; J. J. Hunt (ed.). 

 Proceedings of Atlantic bluefin tuna ageing workshop. 

 Collective Volume of Scientific Papers. Int. Comm. 

 Conserv. Atlantic Tunas. 7(2):337-339. 



Casselman, J. M. 



1983. Age and growth assessment of fish from their 

 calcified structures-techniques and tools. In E. D. 

 Prince and L. M. Pulos (eds.), Proceedings of the 

 international workshop on age determination of 

 oceanic pelagic fishes: tunas, billfishes, and 

 sharks. NOAA Tech. Rep. NMFS 8:1-17. 



