A framework for evaluating Strike Limit Algorithms for populations reduced to small numbers

Résumé

A generic framework is outlined within which operating models for populations reduced to low numbers but still subject to exploitation (‘type 3 fisheries’) can be developed. This framework is founded on an individual-based operating model that includes temporally correlated environmental variation in births and survival as well as the possibility of occasional catastrophic reductions in survival. Methods are developed to specify the value of the parameter that determines the productivity of the resource from that for MSYR, to enable simulation trials based on this framework to be parameterised in terms of MSYR. Three potential candidate Strike Limit Algorithms are evaluated using 14 ‘generic’ simulation trials that capture a range of factors pertinent to type 3 fishery situations. The ‘Maximum-likelihood-like’ SLA developed for use in the management of the Bering-Chukchi-Beaufort Seas stock of bowhead whales performs adequately for many of these 14 trials, but not all. In contrast, a variant of the ‘PBR approach’ is shown to perform adequately in terms of achieving conservation objectives for all of the trials. The information needed to specify trials for actual type 3 fishery situations is outlined.