Dynamic strategies offer potential to reduce lethal ship collisions with large whales under changing climate conditions

Abstract

Dynamic ocean management (DOM), a type of marine spatial planning in which management decisions are updated in response to changing environmental, biological, or socioeconomic conditions, holds promise for balancing tradeoffs between conservation and marine resource use. However, as climate change continues to drive unprecedented oceanic changes, it is critical to evaluate how such tradeoffs may vary under different environmental regimes to ensure management strategies remain robust. To address this need, we explored blue whale ship strike management scenarios in the Southern California Bight, USA, an area that currently uses voluntary vessel speed reductions to mitigate risk of lethal ship collisions. We compared two simulated DOM strategies – a ‘daily strategy’ that implemented speed reductions in response to whale habitat conditions on a daily basis, and a ‘seasonal strategy’ that implemented speed reductions in response to whale habitat conditions on a seasonal basis – with a ‘fixed strategy’ that implemented speed reductions for a fixed time period each year, irrespective of environmental conditions. We evaluated the capacity of these strategies to balance tradeoffs between whale conservation and shipping activities over a 17-year study period. Critically, we assessed these tradeoffs before, during, and after a record marine heatwave to evaluate the relative utilities of these strategies during anomalous ocean conditions. Over the 17-year study period, seasonal and daily DOM strategies achieved a 6.4–10.7% improvement in expected whale protection from lethal collision, respectively, without the need for additional vessel speed reductions, as compared to the fixed strategy. The benefit of DOM strategies has grown in the last decade and was accentuated during and after the marine heatwave event, with the daily DOM strategy seeing a 16.2% increase in whale protection compared to the fixed strategy in the five years prior to the event, versus a 26.5% increase in the five years during and after the event. Such results indicate that dynamic ocean management is a valuable strategy for coping with anomalous environmental conditions, which will become increasingly important as the climate continues to change. Moreover, our study emphasizes the importance of assessing tradeoffs between conservation goals and human activities over a range of environmental conditions in order to evaluate the robustness of management strategies to climate change.