An integrated Bayesian evaluation of Hooker's sea lion bycatch limits

An integrated Bayesian evaluation of Hooker's sea lion bycatch limits

P.A. Breen, and S.W. Kim

An integrated Bayesian evaluation of Hooker's sea lion bycatch limitsThis is part of Sea Lions of the World
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Description

This paper extends previous work on the effect of New Zealand’s subantarctic squid fishery on the threatened Hooker’s sea lion at the Auckland Islands. The management goal is to rebuild and maintain the population above 90% of carrying capacity, K, and to maintain the population above 90% of the unfished level in years when it is less than 90% K.

We fitted a fully age-structured model, with density-dependent pup births, to seven sets of population data, including time series of estimated births, tag/re-sighting data, pup mortalities, and population and bycatch age structures. From these data the model estimated posterior distributions for survival, maturity, vulnerability, and pupping rate parameters. A prior distribution on the intrinsic rate of increase, λ, a derived parameter, was necessary to obtain biologically reasonable estimates.

The population appears to be near K already. The bycatch control rule used in New Zealand before 2004, based on the Permitted Biological Removal approach and different policy objectives from the goal listed above, was very conservative and incurred a high cost to the fishery. Simple alternatives are safe to the sea lion population, meet the management goal, and incur much lower economic cost.

The Bayesian model is an ideal tool for incorporating multiple data sets and prior information in such evaluations.

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