Assessing Data Requirements for Calculating Sustainable Marine Mammal Bycatch Limits

May E (2022) Assessing Data Requirements for Calculating Sustainable Marine Mammal Bycatch Limits. Masters Thesis, Duke University

The Marine Mammal Protection Act (MMPA) sits at the forefront of marine mammal conservation in the United States, focusing on management aspects such as population abundance, strandings and injuries, and fishery interactions and impacts. Within the Act, the recently implemented Fish and Fish Product Import Provisions extend several domestic marine mammal management tools to foreign fisheries wishing to export their products to the United States. Representing the most extensive effort by a single nation to influence environmental regulations of many other nations, these Provisions hold significant potential to alter global marine mammal conservation efforts. This study set out to further explore the Provisions, looking at one specific requirement they outline for foreign, exporting fisheries. This requirement is the calculation of bycatch limits for marine mammal populations impacted by said fishing operations. It sits amongst several other requirements, both regulatory and scientific in nature, that exporting fisheries will have to comply with to continue accessing lucrative US seafood markets. These requirements necessitate the distribution of a significant amount of information to the US government, and we hoped to reveal the extent of obligatory data collection for this specific requirement.
Fisheries bycatch, or the incidental injury and death during fishing efforts, of marine mammals represents the largest global threat to these species. In the United States, bycatch limits are calculated using the Potential Biological Removal (PBR) framework, a modeling formula created for low data scenarios that only requires a recent population abundance estimate. However, several methods exist for these calculations, and the Provisions call for the use of PBR or a “comparable scientific metric.” This study explores all calculation methods available in current literature, along with their data requirements, and categorizes methods based on model structure, technical difficulty, and input data. Government documents, international and multilateral management organization and agreement reports and guidelines, and scientific literature were used to search for methods used to calculate bycatch and targeted removal limits for marine mammals. We specifically focused on models used for cetaceans (whales, dolphins, porpoises) and pinnipeds (seals, sea lions, walruses), as the Provisions’ implementing agency – the National Marine Fisheries Service (NMFS) – manages these taxonomic groups in the US.
Our findings revealed that measures and concepts of population size are most crucial to creating bycatch limit models across existing methods. Five general categories of calculation methods were created*, all of which required information about marine mammal population size. Some methods require much more information than PBR, including catch history estimates, demographic parameters, and the impact of natural and anthropogenic stressors on populations. Other methods had similar or less intensive data requirements compared to PBR. The term ‘comparable’ is not defined in the text of the Provisions, creating difficulty in speculating which methods can be used in the context of this requirement. It is our recommendation that NMFS should not deem methods that are less robust than PBR as comparable, and the use of outdated population abundance estimates in any limit calculation method holds considerable conservation risks and should not be encouraged.
All but one currently implemented bycatch or targeted removal limit calculation method stem from Western management authorities. This finding may have implications for the preparedness of other nations – without limit calculation methods or marine mammal population data collection programs in place – in the context of this portion of the Provisions. Exporting fishery managers in low-data environments should focus on collecting population abundance data for this specific regulatory requirement.
Though this study focused on data, our findings indicate that other factors are also important to consider. In collecting population abundance and other data, fisheries managers should be mindful of aspects such as data uncertainties in limit calculation models, how robust data collection methods are, and how marine mammal conservation objectives may modify model parameters or results. The Provisions’ outline of multiple requirements encourages the construction of more extensive marine mammal regulatory schemes in foreign contexts, which improves the effectiveness of limit calculation models and methods. Further, these models are most accurate and impactful when they are updated and grown as more data about marine mammal populations are collected, and several examples of this process were found in the literature. Data availability is the primary limiting factor in implementing bycatch limit methods, and this work has important implications for comparability determinations for foreign fisheries under the new Import Provisions.