Climate change severely affects marine life worldwide with warming oceans generating unprecedented cascading effects that include the melting of polar ice, rising seas, marine heatwaves, and ocean acidification. Regardless of their body size, habitat, or ecology, marine mammals will have to deal with the consequences of this global warming. Climate change has already caused a range of direct and indirect effects on marine mammals including an increase in infectious disease outbreaks, a reduction in breeding success for some species because of rising temperatures and a subsequent sea ice loss, and habitat shifts likely driven by the need to track changes in prey availability (also due to climate change) [1-3]. These range shifts are expected to continue for several marine mammal species globally for the upcoming future as climate conditions will worsen [4, 5].
Marine mammals are keystone species contributing to various ecosystem functions responsible for the stability of the carbon cycle and the maintenance of biodiversity worldwide. As apex- and mesopredators, they control the abundance of their prey species, thus helping to maintain the often delicate balance between different species in the marine environment (i.e., top-down regulation) .
Cetaceans (especially the great whales) are also known to be ‘marine ecosystem engineers’: they facilitate the transfer of nutrients such as nitrogen and iron from deep waters to the surface, and across latitudes via migration from feeding to calving areas. This worldwide transfer of nutrients is known as the ‘whale pump’ [7, 8] and enhances the primary productivity and krill abundance in the marine ecosystem. When they die, whales further sequester large amounts of carbon to the deep sea which contributes to natural climate-change mitigation .
By shifting their distributions to other, more suitable areas in response to climate change, marine mammals also move these services which could affect wider ecosystem functioning and destabilize ecological processes, particularly at local scales in the areas that were abandoned by the cetaceans.
Depending on mobility and habitat requirements, some species/populations show strong site fidelity and may be unable to shift their distribution to track suitable habitat. This would constrain the species to remain in a suboptimal environment and/or exposing them to substantial habitat loss (e.g., due to reduction in sea ice crucial for breeding). For example, in response to sea ice loss, some ice-dependant coastal species such as seals, polar bears, and even small cetaceans, may not be able to traverse oceans to reach a more suitable different coastline. Therefore, these species may not be able to adapt their lifestyle without significant risk of biological consequences to health such as reduced body condition and potential immune suppression.
Even the species that are able shift their distribution to track newly suitable habitats (and avoid newly unsuitable habitats) and prey availability, are not necessarily safe. Moving to new areas can expose them to a broad range of new challenges such as dealing with suboptimal environmental conditions and contaminants, new predators, and having to compete for resources with indigenous species (interspecific competition). Those new challenges are cumulative, adding to the toll taken by the energy expenditure for these moving species to find new habitats.
Many of the ecosystem-level changes will impact humans as Humanity depends directly on Earth’s ability to support a complex variety of living species  The benefits provided by biodiversity include products, cultural services that give us aesthetic, spiritual or recreational value, and major ecological processes, which regulate everything from the climate to the carbon, water, and nitrogen cycles . However, there are also more direct implications of climate change on marine mammals for humans, such as the economic value marine mammal tourism brings to both local communities and nationally to many countries. Locations where both direct and in- direct employment demographics are reliant upon whale watching activities would be particularly impacted by climate change.
To incorporate management actions that help mitigate the impacts of climate change on marine mammals, the first step is to identify how the species in question may be affected by climate change. This information can then support management decisions specific to the relevant threat. For example, if a species suffers from loss of prey species due to climate-related shifts in prey distribution, increased regulation of fisheries in specific areas may be possible to mitigate resource depletion.
To gain an understanding how species may be affected, it is vital to collect long-term data on marine mammal distribution and abundance, and to monitor environmental variables such as sea surface temperature, sea ice concentration, and primary production, but also wider ecosystem data such as prey availability [2, 3]. This allows the establishment of a baseline in relation to which changes can be detected. By using tools such as habitat modelling, areas of high importance for the respective species can be identified within the MPA and thus give increased protection priority .
These approaches may require collaborative efforts across a range of disciplines, including marine mammalogy, marine ecology, oceanography, and climate modelling. Additional methods to explore the impact of climate change in recent decades including the exploration of physiological changes in marine mammals in respect to climate change should further explored.
To support any conservation actions targeted to mitigate the impacts of climate change on marine mammals, it is recommended to reduce non-climate-related stressors on marine mammals in an effort to increase species’ resilience, for example noise pollution and disturbance via recreational vessels, fisheries interactions including bycatch and entanglement in fishing gear, and pollution .
Sperm (Physeter macrocephalus) and blue (Balaenoptera musculus) whales are potential good indicator and sentinel species because of their extended life span and sensitivity to seasonal environmental shifts in their prey distribution and abundance [14,15,16]. Therefore, identifying how environmental shifts will shape the distribution of these species can serve as an early warning system to anticipate current or potential ecosystem changes.
Using the whales’ present distributions and a combination of mathematical models, we built a set of environmental “rules” that dictate where each species can live. Using climate-dependent data such as sea-surface temperature and chlorophyll A (a measure of phytoplankton growth), and static data such as water depth and distance to shore, we applied these rules to forecast future habitat suitability at the end of the century based on three climate change scenarios of differing severity outlined by the Intergovernmental Panel on Climate Change (IPCC).
Our results show a clear southward shift for both species, mostly driven by rising temperatures at the sea surface. The most severe climate change scenario tested generated 56% and 42% loss and decrease of currently suitable habitat for sperm and blue whales, respectively, mostly in New Zealand’s northern waters. These predicted changes will have a strong impact on the ecosystem functioning and services in New Zealand’s northern waters but also in coastal areas (critical for the species’ foraging and survival). Furthermore, a shift in sperm whale distribution causing fewer and less reliable sightings around Kaikōura on the South Island of New Zealand, would likely negatively impact both the tourism and wider hospitality industry in the region. Not only do these simulated range shifts help to identify future potential climate refugia to mitigate a global warming, they also generate a range of socioeconomic consequences for island nations relying on wildlife tourism, industry, and environmental protection.
International Whaling Commission: Climate Change and Cetaceans
 Simmonds, M.P. and S.J. Isaac, The impacts of climate change on marine mammals: early signs of significant problems. Oryx, 2007. 41(1): p. 19-26.
 Orgeret, F., et al., Climate change impacts on seabirds and marine mammals: The importance of study duration, thermal tolerance and generation time. Ecology Letters, 2022. 25(1): p. 218-239.
 Gulland, F.M.D., et al., A review of climate change effects on marine mammals in United States waters: Past predictions, observed impacts, current research and conservation imperatives. Climate Change Ecology, 2022. 3.
 Chambault, P., et al., Future seasonal changes in habitat for Arctic whales during predicted ocean warming. Science Advances, 2022. 8(29): p. eabn2422.
Peters, K.J., K.A. Stockin, and F. Saltré, On the rise: Climate change in New Zealand will cause sperm and blue whales to seek higher latitudes. Ecological Indicators, 2022. 142: p. 109235.
Estes, J.A. and D.O. Duggins, Sea otters and kelp forests in Alaska: generality and variation in a community ecological paradigm. Ecological monographs, 1995. 65(1): p. 75-100.
Roman, J. and J.J. McCarthy, The whale pump: marine mammals enhance primary productivity in a coastal basin. PloS one, 2010. 5(10): p. e13255.
 Nicol, S., et al., Southern Ocean iron fertilization by baleen whales and Antarctic krill. Fish and fisheries, 2010. 11(2): p. 203-209.
 Roman, J., et al., Whales as marine ecosystem engineers. Frontiers in Ecology and the Environment, 2014. 12(7): p. 377-385.
 Martin, J.-L., V. Maris, and D.S. Simberloff, The need to respect nature and its limits challenges society and conservation science. Proceedings of the National Academy of Sciences, 2016. 113(22): p. 6105-6112.
 Ricklefs, R.E., R. Relyea, and C. Richter, Ecology: the economy of nature. Vol. 7. 2014: WH Freeman New York:.
 Bailey, H. and P.M. Thompson, Using marine mammal habitat modelling to identify priority conservation zones within a marine protected area. Marine Ecology Progress Series, 2009. 378: p. 279-287.
 Nelms, S.E., et al., Marine mammal conservation: over the horizon. Endangered Species Research, 2021. 44: p. 291-325.
 Hazen, E.L., Abrahms, B., Brodie, S., Carroll, G., Jacox, M.G., Savoca, M.S., Scales, K.L., Sydeman, W.J., Bograd, S.J., 2019. Marine top predators as climate and ecosystem sentinels. Front. Ecol. Environ. 17, 565–574.
 Moore, S.E., 2008. Marine mammals as ecosystem sentinels. J. Mammal. 89, 534–540.
 Silber, G.K., Lettrich, M.D., Thomas, P.O., Baker, J.D., Baumgartner, M., Becker, E.A., Boveng, P., Dick, D.M., Fiechter, J., Forcada, J., Forney, K.A., Griffis, R.B., Hare, J. A., Hobday, A.J., Howell, D., Laidre, K.L., Mantua, N., Quakenbush, L., Santora, J.A., Stafford, K.M., Spencer, P., Stock, C., Sydeman, W., Van Houtan, K., Waples, R.S. 2017. Projecting Marine Mammal Distribution in a Changing Climate. Front. Mar. Sci. 4.