Optimizing Dynamic Ocean Management Strategies to Reduce Whale Ship Strikes

The oceans are an increasingly crowded space due to human activities, where the pace and magnitude of climate impacts are accumulating. Highly migratory species, such as large whales, integrate across all of these changes. In recent years, the risk of whale mortality due to ship strikes has become ever more prominent; ship strikes continue to be a leading cause of mortality for Endangered blue whales (Balaenoptera musculus). New tactics to mitigate ship-strike risk are crucial. In the North Pacific, the Southern California Bight is a hotspot for blue whale-ship strikes where two highly trafficked ports intersect with whale feeding habitat. Currently, a static vessel slowdown period is enacted annually to minimize strike risk, however, advances in habitat modeling offer new tools to support dynamic management strategies that can better adapt to changing environmental conditions. We identified and assessed dynamic approaches to reduce whale-ship strikes in the Southern California Bight. We used daily projections of habitat suitability for blue whales to determine whether and when to institute a vessel slowdown period. We evaluated the utility of alternate approaches by quantifying the number of whales that would have received protection, using sightings data (2002-2018), versus the number of unrestricted shipping days permitted. Partial and fully dynamic strategies outperformed the interannually static approach, protecting an additional 6.42 and 10.74 percent of observed blue whales, respectively, with no additional shipping restrictions. Conservatively, this translated into an additional 84 and 141 protected whales, well above the 2.3 Potential Biological Removal limit for the species. With increasing ecosystem variability due to climate change, highly mobile species can no longer be effectively managed solely with interannually static strategies. By utilizing models that predict on relevant spatiotemporal scales, dynamic ocean management approaches can be used for conflict avoidance and mitigation between human and conservation goals.