Assessment of Entanglement Risk: A Vertical Line Co-occurrence Model of Large Whales and the Commercial Fixed Gear Dungeness Crab (Cancer magister) Fishery Off the U.S. West Coast

Abstract

Since 2014, reports of whale entanglements have spiked along the U.S. West Coast from an average of 10 confirmed cases per year to up to 71 reported entanglements in 2016. The commercial fixed gear Dungeness crab (Cancer magister) fishery has been the most identifiable gear in confirmed whale entanglements. The continued high number of reported whale entanglements has warranted fishery managers, fishermen, and other stakeholders to look into solutions to reducing the number of entangled whales; however, a better understanding of where and why these entanglement rates have spiked is needed. Previous efforts by National Marine Fisheries Service (NMFS) to understand entanglement risk designed a co-occurrence model to assess entanglement risk along the West Coast by overlaying landings data with species-specific whale density and distribution patterns to produce relative co-occurrence scores as an indicator for risk. The purpose of this study was to create a vertical line co-occurrence model between large whales and the commercial Dungeness crab fishery; as NMFS indicated in their previous model, that the use of gear density instead of the number of pounds landed to represent fishing effort provides a better understanding of high entanglement risk areas. This research provides a comparison to previous co-occurrence modeling efforts, highlights the areas and months of high entanglement risk, and compares risk areas over several time periods. The vertical line co-occurrence models piloted in this study created a new understanding of areas of entanglement risk for large whales in recent years to aid future efforts by NMFS and fishery managers to mitigate large whale entanglements.