Impacts of climate change on marine mammals

Information since 2010, when the last report card was published, indicate little change to the overall conclusions.

Globally, the impact of climate change on marine mammals remains poorly understood, due largely to the difficulty of obtaining substantive evidence. Most obvious impacts are loss of available habitat such as ice cover to ice-breeding pinnipeds. This already is thought to affect ringed seals and their main predator, the polar bear, but also the breeding success of harp and hooded seals in arctic regions.

In more temperate regions, environmental changes will likely be reflected mainly in responses to changes in prey abundance and distribution as a result of warmer sea temperatures, and enhanced stratification forcing earlier occurrence of the spring phytoplankton bloom and potential cascading effects through the food chain. There may also be effects through changes in the locations of fronts and water masses, and overall reduced primary and secondary plankton production.

Range shifts can be observed in a number of odontocete cetacean species, and these have been linked to increasing sea temperatures. However, the mechanisms causing those changes remain uncertain, and for some species, it is difficult to differentiate between short-term responses to regional resource variability and longer-term ones driven by climate change.

NW European species likely to be most affected in the future will be those that have relatively narrow habitat requirements – shelf sea species like the harbour porpoise, white-beaked dolphin and minke whale may come under increased pressure with reduced available habitat if they experience range shifts northwards. If overall secondary production is reduced, this could directly affect some baleen whale species that feed upon zooplankton, as well as have indirect effects on fish and cephalopod feeders. Although the main cause of widespread declines in the UK harbour seal population is not known, the prevalence in the population of domoic acid derived from toxic algae may be a contributory factor, and could be exacerbated by increased sea temperatures.