Conserving and Recovering Vulnerable Marine Species: A Comprehensive Evaluation of the US Approach for Marine Mammals

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Coastal Sciences, Gulf Coast Research Laboratory


Human-caused mortality due primarily to bycatch in fisheries is considered a major threat to some long-lived, slow-growing, and otherwise vulnerable marine species. Under many jurisdictions these species are designated as “protected”, and fisheries are subject to a management system that includes monitoring and assessment of bycatch impacts relative to management objectives. The US management system for marine mammals is one of the most sophisticated in the world, with a limit on human-caused 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 (TRPs) when bycatch exceeds PBR. The default values of the parameters of the PBR formula were selected in the late 1990s using management strategy evaluation (MSE), but the system, in particular the classification of fisheries, 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 TRPs. The level of error associated with fisheries classification was found not to impact the ability to achieve the conservation objective established for a stock under the US Marine Mammal Protection Act (i.e. maintain or recover the stock to/at optimum sustainable population). However, this ability is highly dependent on the life history and absolute abundance of the species being managed, as well as on the premise that bycatch is reduced if bycatch is estimated to exceed the PBR. The probability of correctly classifying fisheries depends on both the coefficient of variations (CVs) of the estimates of bycatch and the marine mammal stock’s abundance because classification depends on the ratio of the estimate of bycatch by fishery-type to the stock’s PBR, and the precision of the former depends on the bycatch CV and the latter on the abundance estimate CV. Moreover, the probability of correctly classifying a fishery decreases for smaller populations, particularly when a fishery has low to moderate impact.

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ICES Journal of Marine Science





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