Ecology and Vulnerability

Blue Whale

Marine mammals, particularly the large migratory whales and porpoises that comprise the Northeast RSGCN, are experiencing high rates of ocean warming, acidification, and other climate impacts to affect their distribution, phenology, and population dynamics (Letrick et al., 2023). Relatively few studies of marine mammal responses to climate change exist in part due to the difficulties in detecting and tracking their populations over the broad spatial scales that constitute their geographic ranges. Several of the large migratory whale RSGCN have shown shifts in range and phenology over recent decades; however, the rate, magnitude, and direction of these shifts vary widely across sub-regions of their range and studies (Ramp et al., 2015; Charif et al., 2020; Pendleton et al., 2022). These conflicting patterns of earlier or later arrival may be due to the different methods used to monitor populations (e.g., acoustics vs aerial visual observations) with different detection abilities and spatial coverages.

Shifts in the distribution of marine mammals are largely attributed to the indirect effects of climate change, as prey availability, abundance, and quality are altered due to ocean warming and acidification. Planktivorous species like North Atlantic Right Whales, which depend on seasonally reliable concentrations of highly nutritious and lipid-rich Calanoid copepods, are more sensitive to bottom-up changes in primary and secondary production compared to piscivorous whales (Pendleton et al., 2022). However, rapid warming in the Gulf of Maine is having broad impacts on regional food webs with ramifications not only for whales but many other marine fish and seabird RSGCN that consume zooplankton or planktivorous forage fish such as sand lance and herring (Staudinger et al., 2019; Pershing et al., 2021). Most notably, increasing SSTs are negatively affecting cold-adapted subpolar copepod species, including Calanus finmarchicus through decreased growth, productivity, and shifts in overwintering phenology schedules (Staudinger et al., 2019; Staudinger et al., 2020; Pershing et al., 2021).

As food resources become increasingly unpredictable, migratory whales are occurring in unexpected locations and at unexpected times or showing elevated mortality and stranding rates, as indicated by the declaration of Unusual Mortality Events in the region (NOAA, 2024)1 . This increases the potential for conflict and the incidence of injury and mortality of these already atrisk and endangered species with human activities such as shipping, fishing, and wind energy development.