Vulnerability to climate change of marine mammal and sea turtle populations

Changing ocean conditions and extreme weather events associated with climate change may be especially harmful to marine species that already experience acute human impacts such as fisheries interactions, vessel strikes, and habitat degradation. Marine mammals and sea turtles are expected to respond to these changing conditions in a variety of ways that may result in shifts in distribution, abundance, and/or phenology. Climate change has already been shown to affect individual elements of marine mammal and sea turtle life history, but there is a need to assess impacts across the different stages of the species life history at multiple temporal and spatial scales.

NOAA Fisheries manages multiple marine mammal stocks and sea turtle populations across broad geographic areas that experience different environmental and anthropogenic pressures.

A systematic approach is needed to identify marine mammal stocks and sea turtle populations vulnerable to climate change to inform strategic research and conservation actions. Climate vulnerability assessment is one approach that allows us to characterize the effects of climate change and compare impacts and potential responses across a variety of taxonomic units and locations. Adapting from existing frameworks, NOAA Fisheries has developed a trait-based climate vulnerability assessment framework to characterize the relative vulnerability of marine mammals and sea turtles to climate change, hereafter the Marine Mammal Climate Vulnerability Assessment (MMCVA) and the Sea turtle Climate Vulnerability Assessment (STCVA).

The MMCVA framework has been used for marine mammals in the western North Atlantic, Gulf of Mexico, and the Caribbean. The STCVA framework is currently being used for sea turtles across the globe and the MMCVA framework will be applied to marine mammals in the Pacific and Arctic.

The frameworks combine existing published information with expert elicitation to characterize the sensitivity and adaptive capacity of selected stocks and populations to climate change. To characterize exposure to climate change, projected climate and ocean conditions were measured against historical conditions within current stock and population geographic distributions. To characterize sensitivity/adaptive capacity, experts scored species, stock, and/or population life history characteristics against a predefined rubric. The climate exposure and climate sensitivity/adaptive capacity scores were combined to calculate a climate vulnerability score and relative vulnerability index.

Forty-one subject matter experts scored climate sensitivity/adaptive capacity and climate exposure for 108 U.S. marine mammal stocks and stock groups. Of the marine mammal stocks scored, 33% had very high sensitivity to climate change, 18% had high sensitivity, 34% had moderate sensitivity, and 15% had low sensitivity. The majority of stocks scored (72%) had very high exposure to climate change, whereas 24% had high exposure, approximately 4% had moderate exposure, and no stocks had low exposure. When these factors were combined, the climate vulnerability index score was very high for 44% of the stocks (e.g., North Atlantic right whale, Gulf of Mexico Bryde’s whale), high for 29% (e.g., Nova Scotia sei whale, western North Atlantic hooded seal), moderate for 20% (e.g., Gulf of Mexico spinner dolphin, western North Atlantic harbor seal), and low for 7% (e.g., western North Atlantic offshore common bottlenose dolphin, western North Atlantic striped dolphin). Factors including temperature, ocean pH, and dissolved oxygen were the primary drivers of high climate exposure, with effects mediated through prey.

Twenty sea turtle experts are currently completing the STCVA scoring process for 51 sea turtle populations. Populations were defined based on the Distinct Population Segment (DPS) framework defined by the Endangered Species Act, and Regional Management Units (RMUs) where DPSs have not been designated. Results are expected in late 2019.

Result from these assessments can inform management decisions related to statutory mandates, provide hypotheses for further research, and identify potentially vulnerable stocks and populations as candidates for advanced modeling, monitoring, research, and conservation. These assessments will provide managers and researchers with population-specific climate vulnerability information that fill information gaps, inform protected species management actions, and influence future research.