Research Document - 2009/093

A preliminary evaluation of the performance of the Canadian management approach for harp seals using simulation studies

By M.O. Hammill and G.B. Stenson

Abstract

The Precautionary Approach (PA), provides a framework within the context of fisheries management which attempts to take into account the uncertainties related to the status of the resource when setting harvest levels. In 2003, Fisheries and Oceans Canada (DFO) adopted a precautionary framework for the management of seals in Atlantic Canada. This framework is PA-like in that it identifies limit and precautionary reference levels, and explicitly incorporates uncertainty in our estimates, but the behaviour of the framework under simulated uncertainty in the parameters has not been examined. For marine mammals two basic frameworks have been developed (International Whaling Commission (IWC), Potential Biological Removal (PBR)), and these Management Procedures have been tested. Although both frameworks provide a guide to the simulation approach, they are not appropriate for management within the Canadian context. The model used to assess the Northwest Atlantic harp seal examined the impact of extending the modelled population from 1960 back to 1952, adjusting the within-year correlation in reproduction among cohorts, and assessing how alternative methods of applying the management plan impact the estimated population. Simulations to examine the impact of an unknown mortality of young animals related to poor ice conditions were also conducted. Failure to consider ice-related mortality in an Assessment model has a significant impact on perceptions of the resource. The preliminary simulations indicate that the current management framework is robust to avoiding a decline in the resource below the spawner stock biomass limit reference point (B_lim), thus satisfying a conservation objective, but can result in harvest closures after 10-20 years if the entire harvest was taken in every year. Adjustments in the approach are needed if industry would like to see long-term stability in harvest levels as a management objective.

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