Abstract
Conservation planning traditionally relies upon static reserves; however, there is increasing emphasis on dynamic management (DM) strategies that are flexible in space and time. Due to its novelty, DM lacks best practices to guide design and implementation. We assessed the effect of planning unit size in a DM tool designed to reduce entanglement of protected whales in vertical ropes of surface buoys attached to crab traps in the lucrative U.S. Dungeness crab ( Metacarcinus magister ) fishery. We conducted a retrospective analysis from 2009 to 2019 with modeled distributions of blue ( Balaenoptera musculus ) and humpback ( Megaptera novaeangliae ) whales and observed fisheries effort and revenue to evaluate the effect of 7 planning unit sizes on DM tool performance. We measured performance as avoided whale entanglement risk and protected fisheries revenue. Small planning units avoided up to $47 million of revenue loss and reduced entanglement risk by up to 25% compared to the large planning units currently in use by avoiding the incidental closure of areas with low biodiversity value and high fisheries revenue. However, large planning units were less affected by an unprecedented marine heat wave in 2014–2016 and by delays in information on the distributions of whales and the fishery. Our findings suggest that the choice of planning unit size will require decision‐makers to navigate multiple socioecological considerations—rather than a one‐size‐fits‐all approach—to separate wildlife from threats under a changing climate.