The 1982 assessment of the southern bluefin tuna (Thunnus maccoyii) population and the determination of catch levels which stabilize the parental biomass [Australia]
1984
Hampton, J. | Majkowski, J. | Murphy, G.I. (Commonwealth Scientific and Industrial Research Organization, Hobart (Australia). Div. Fisheries Research)
The southern bluefin tuna population is assessed using cohort analysis. Four combinations of natural mortality and terminal fishing mortality parameters provide quantitatively different results, but the overall conclusions, which confirm the previously recognized critical state of the population, are not affected by the choice of these parameters. Recruitment for 1950-76 was stable, but parental biomass underwent a significant decline (40 percent) from 1967 to 1975, then remained approximately constant until 1980. The 1980 parental biomass is estimated to be 21-30 percent of the virgin parental biomass. The global catch which would stabilize the parental biomass at its 1980 level is calculated as 30,000-32,000 t per year. This catch level can be increased by 50 percent by postponing age-at-first capture to 5 years. The relationship between catch and stable parental biomass is examined under different assumptions regarding recruitment.
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