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Computer Simulations of Future Southern Bluefin Tuna Parental Biomass, Recruitment, and Catches under the 1982 Fishing Regime
Author(s) -
Hampton J.,
Majkowski J.
Publication year - 1986
Publication title -
north american journal of fisheries management
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.587
H-Index - 72
eISSN - 1548-8675
pISSN - 0275-5947
DOI - 10.1577/1548-8659(1986)6<77:csofsb>2.0.co;2
Subject(s) - tuna , fishing , biomass (ecology) , fishery , population , thunnus , biology , geography , environmental science , ecology , demography , fish <actinopterygii> , sociology
Computer simulations of future parental biomass, recruitment, and surface and longline catches of southern bluefin tuna (Thunnus maccoyii) were performed to examine the effects of continuing the 1982 fishing regime for the following 20 years. The simulation model is based on a simple catch equation. It accounts for changes in the age structure of the southern bluefin tuna population and catches due to exploitation and the variability in recruitment to the fishable stock. Two alternative hypotheses regarding recruitment were designed to reflect (1) constant average recruitment with random variation independent of the parental biomass level and (2) average recruitment dependent on parental biomass with random variation independent of the parental biomass level. Substantial declines in at least parental biomass and longline catch are likely from about 1985. If average recruitment remains constant, stabilization occurs in the early 1990s with both parental biomass and longline catch being reduced to approximately 57% of their 1983 levels. This reduced parental biomass represents, at most, 17% of the unexploited parental biomass. Assuming constant average recruitment, the expected surface catch is stable, although its variability is higher than that of the longline catch. If average recruitment decreases in response to declining parental biomass, no stabilization occurs; parental biomass, recruitment, surface catch, and longline catch continue to decrease so that, by the end of the 20‐year simulation period, they are 46, 55, 57, and 41%, respectively, of their 1983 levels. Sensitivity analyses indicated that, while these trends are sensitive to some input parameters, the overall qualitative conclusion (substantial declines in at least parental biomass and longline catch) is not affected by varying input parameters within the ranges of their uncertainties. The probability and timing of future zero recruitment depend on the level of natural mortality used. Zero recruitment may occur within 50 years if natural mortality is less than 0.20 year −1.