Abstract

A simulation model constructed around the life history characteristics of Atlantic blue marlin (Makaira nigricans) was applied to generate several time series of catch histories for hypothetical fisheries using alternative assumptions about natural mortality and the stock-recruitment relation. Maximum sustainable yield (MSY), the biomass at MSY (Bmsy), the fishing mortality rate at MSY (Fmsy) and related parameters were computed for each of the simulated populations. The time series of simulated catches and indices of abundance were employed in simulated stock assessments using surplus the surplus production method solved by the computer program ASPIC, which was the method most recently applied by ICCAT for the species. The resulting estimates of MSY and Bmsy were highly correlated with the known true values from the simulations, but tended to be a somewhat higher. The production model estimates of Fmsy were also highly correlated with but were slightly lower than the true values. Estimates of the ratios of fishing mortality to Fmsy and stock biomass to Bmsy in the terminal year of the simulated assessment were slightly lower than the known values from the simulation. These results suggest that the surplus production model might produce results that are slightly optimistic with respect to fishing mortality rates and slightly pessimistic with respect to the status of the biomass of the stock in the most recent year of an assessment. However, the error is small for reasonable combinations of natural mortality and initial slopes of the stock-recruitment curve. These results suggest that the major sources of uncertainty in the stock assessment lie with the underlying catch and effort data and not with the use of the surplus-production model itself

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