UW Aquatic & Fishery Sciences Quantitative Seminar

Andre Punt

Director of School of Aquatic and Fishery Sciences, University of Washington

Evaluating the US approach for Managing Human-Caused Mortality of Marine Mammals: Beyond the PBR Formula

Abstract

The US system for managing the human-caused mortality of marine mammals is one of the most sophisticated in the world, with a limit on such mortality computed using the Potential Biological Removal, PBR, formula. Fisheries are categorized according to their impact relative to PBR, and Take Reduction Teams established to develop Take Reduction Plans when bycatch exceeds PBR. The default values of the parameters of the PBR formula were selected using Management Strategy Evaluation, but the entire system has yet to be evaluated in its entirety. A MSE framework is developed that includes the PBR formula as well as the processes for evaluating whether a stock is ‘strategic’, assigning fisheries to categories, and implementing a Take Reduction Plan. Ignoring the latter two components of management (i.e. fisheries classification and implementation of TRPs) was found not to impact the predictions related to the ability to achieve the conservation objective established for a stock under the US Marine Mammal Protection Act [i.e. recover (or maintain) the stock to (at) its optimum sustainable population level]. However, this ability is highly dependent on the life history and absolute size of the species being managed. The probability of correctly classifying fisheries depends on both the CV of the estimates of bycatch as well as the CV of the survey estimates of the marine mammal stock’s abundance because classification depends on the ratio of the estimate of bycatch by fishery-type to the PBR, and the precision of the former depends on the bycatch CV and the latter on the abundance estimate CV.