• The impact of climate change on marine mammals remains poorly understood. As a result, there has been a great deal of speculation but without very much substantive evidence. That evidence for marine mammals is very difficult to obtain, particularly when there are often synergistic effects from anthropogenic activities.
• 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, 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.

What is already happening: Low

What could happen: Low

Range shifts for particular species, reported in the 2007-08 Report Card, have persisted to the present. Research on climate change effects upon marine mammals has also expanded in recent years both in Europe and elsewhere, whilst there have been a number of meetings/workshop addressing this issue with respect to marine mammals (ICES WGMME, 2007; IWC, 2009; ECS, 2009), as well as a Special Publication of the journal Ecological Applications focusing upon on Arctic Marine Mammals and Climate Change (2008).

The top priority knowledge gaps that need to be addressed in the short term to provide better advice to be given to policy makers are:

1. A pre-requisite to assessing impacts of climate change on marine mammals at a population level is a long-term, wide-ranging, monitoring programme that can discriminate between regional population responses and those occurring on a wider geographical scale. This is presently lacking for all UK cetacean species, whilst for seals there remain regions (e.g. Irish Sea) with only patchy coverage.
2. Our knowledge of trends in basic life history parameters (growth rates, age at sexual maturity, reproductive rates, and mortality) for all cetacean species with the possible exception of harbour porpoise is woefully inadequate, based upon small sample sizes from a restricted number of areas, and without long-term continuity of data. For the majority of species, we are unlikely to obtain adequate information in the foreseeable future given how difficult they are to study and the resources available to do so. However, certain species could be targeted for more intensive study with some likelihood of success. In UK waters, these include (in addition to harbour porpoise) bottlenose dolphin, short-beaked common dolphin, white-beaked dolphin, Risso's dolphin, and minke whale. In particular, two long-term studies exist on coastal populations of bottlenose dolphins - Moray Firth (20 years) and Cardigan Bay (10 years), which could serve to provide a better understanding of the interaction between climate-mediated changes in the environment and changes in distribution, habitat use and demography. 
3. Functional responses to environmental change through physiological and behavioural mechanisms are also poorly understood for most marine mammal species. For this, seals are rather better suited to experimental studies where variables can be controlled. However, it is unclear whether data from seals can be generalised to cetaceans due to ecological differences between the two groups. Once individual responses are better understood, it may be possible to make predictions at the population level, but it will be necessary to conduct these studies across both seals and cetaceans.
4. Too little is known about how changes in fish, cephalopod and plankton dispersion, distribution and abundance may affect the foraging ecology of particular marine mammal species. Often, one of the major gaps in information lies in the lack of data for non-commercial fish and cephalopod species, although even for some commercial species, such information is lacking.
5. There is a need for better understanding of how predictions from climate models relate to changes most likely to impact upon marine mammals. Overall rises in sea temperatures, for example, need to be separated from changes in the timing and location of fronts, and in turn how these may affect prey resources (abundance, distribution, and availability) and the energetics of different marine mammal predators.
6. Models have routinely been used on marine mammal populations to better understand population dynamics and to forecast the implications of anthropogenic impacts. However, they generally face the limitations of inadequate real data, a poor understanding of mechanisms, and an inability to model those mechanisms adequately. On the other hand, they can be useful to compare alternative scenarios and hence to identify specific data gaps that if filled are most likely to allow discrimination between scenarios. Priority should be given to developing models that can integrate the demographic and spatial consequences of climate change, as well as developing full ecosystem models using bottom-down as well as bottom-up approaches.        

No marine mammal species in UK is exploited directly. However, changes in the status and distribution of marine mammals could potentially have commercial effects if species (e.g. minke whale, bottlenose dolphin) targeted by the ecotourism industry become scarce, or there are changes in competitive relations (e.g. an increase in seal predation upon commercially important fish).

If climate change affects human behaviour, for example by increased pressure on already depleted fish stocks or shifts to squid fisheries, those in turn could affect marine mammal species through their food supply. If there is increased usage of the coastal zone for particular human activities (e.g. recreation), these could impose pressures through disturbance and pollution. A greater emphasis upon offshore renewable energy sources such as wind and tide may result in greater conflicts with marine mammal species like the harbour porpoise, bottlenose dolphin, minke whale, and harbour seal, that often forage in coastal areas and within high energy sites around headlands and island archipelagos. Negative effects include sound disturbance particularly during pile driving construction activities in the case of wind farms or physical damage in the case of tidal turbines (Carstensen et al., 2006; Evans, 2008). On the hand, once wind farms are under production, it is possible they could have positive effects if they form safe havens for fish (Evans et al., 2008).

Evans, P.G.H., I.L. Boyd & C.D. MacLeod (2010) Impacts of Climate Change on Marine Mammals in MCCIP Annual Report Card 2010-11, MCCIP Science Review, 14pp. www.mccip.org.uk/arc