Biogeographic range shifts in dolphins and porpoises

Definition

Dolphins and porpoises are aquatic, carnivorous mammals found worldwide from polar to tropical waters. Most species are marine, with a few having freshwater populations; however, only the endangered South Asian river dolphin (Platanista gangetica), the endangered La Plata River dolphin (Pontoporia blainvillei), and the functionally extinct Yangtze (or Chinese) River dolphin (Lipotes vexillifer) are primarily found in freshwater habitats.

The term dolphin can be used to refer to the Odontoceti (toothed whales), but here, it refers to the dolphin family Delphinidae (approximately thirty-seven species), the four families of river dolphins (one species each), and the porpoise family Phocoenidae (seven species). Taxonomic uncertainty makes the exact number of species an open question.

Dolphins and porpoises face a variety of threats, including targeted hunting, entanglement in fishing gear, pollution, disease, habitat degradation, water diversion, acoustic disturbance, and competition with fisheries. The 2021 IUCN Red List named five species and six subspecies of the forty-one dolphin species as endangered, which a 2024 review confirmed. Extensive surveys suggest that the Yangtze River dolphin is almost or already extinct.

Significance for Climate Change

Global warming induces biogeographic range shifts in dolphins and porpoises, as water temperature is often a reliable predictor of their presence. For example, off the coast of Scotland, an increase in the number of warm-water species since the 1980s was coincident with an increase in water temperatures over the same period, while the abundance of cold-water species diminished. Around the British Isles in general, the white-beaked dolphin (Lagenorhynchus albirostris) prefers colder waters, and the short-beaked common dolphin (Delphinus delphis) prefers warmer waters. As these waters warmed further, the short-beaked dolphin expanded its range northward, encroaching on the white-beaked dolphin's habitat.

On global scales, the diversity of whales (including dolphins and porpoises) in deep water is maximum at sea surface temperatures of 21 degrees Celsius, which occur commonly at midlatitudes. When applied to warming scenarios from the Intergovernmental Panel on Climate Change, these results suggest that biogeographic ranges would shift, resulting in a decline in the diversity of whales in the tropics, while the diversity in higher latitudes would increase.

Climate change induces range shifts in dolphins and porpoises by affecting species lower in the food web and thereby making preferred food items less abundant. This also changes competitive relationships between species. For instance, the 1982-1983 El Niño-Southern Oscillation event caused a reduction in squid off of California and coincided with the displacement of short-finned pilot whales (Globicephala macrorhynchus) by Risso’s dolphins (Grampus griseus), which are able to dive more deeply to obtain scarce prey.

Climate change also fragments dolphin and porpoise populations, which has implications for genetic diversity and generally reduces population persistence. For instance, water diversions for shipping and irrigation have already fragmented the populations of the three freshwater river dolphins. As precipitation patterns change, so too does the demand for water withdrawals and impoundments, meaning that the ranges of these species could become further fragmented. Climate change could also fragment marine populations. For example, warming could enhance the degree to which the warm-water current flowing through the Bay of Biscay divides northern and southern populations of the harbor porpoise (Phocoena phocoena).

Ocean acidification, a result of carbon dioxide (CO₂) dissolving into marine waters, also impacts the food supply of dolphins and porpoises. Dolphins and porpoises are often the top predators in food webs based on organisms that have calcium carbonate (CaCO₃) body structures, which are susceptible to dissolution in acidified waters. For example, the pantropical spotted dolphin (Stenella attenuata) consumes pteropods, which are known to be sensitive to acidification. Moreover, many fish species that dolphins and porpoises eat depend on coral reef habitats, which are vulnerable to warming-induced bleaching and decalcification due to acidification. As these habitats degrade, less food is available, leading to population decline. The vaquita (Phocoena sinus) populations in the Gulf of California have experienced decline due to this, as well as water flow and salinity changes.

Another consequence of ocean acidification is that acidified water absorbs sound less effectively, making the environment “noisier.” Dolphins and porpoises depend on echolocation to locate prey, discern their environment, and locate one another. Many species already suffer from acoustic disturbances caused by boat traffic, seismic exploration, and military exercises, which can propagate tens of kilometers underwater, and such disturbances are associated with behavioral changes, strandings, internal injury, and death. Deep water and waters at high latitudes are expected to be especially affected since the acidification reaction is temperature-dependent.

Global warming could exacerbate the threats of disease and pollution. Warmer temperatures and shifting currents also extend the range of disease-causing agents. For example, warmer temperatures are associated with outbreaks of the bacterium Vibrio, known to infect dolphins. Climate change might also influence the frequency and severity of harmful algal blooms.

Bibliography

Arreguín-Sánchez, Francisco, et al. “State of Knowledge of the Population of the Vaquita (Phocoena Sinus) from the Upper Gulf of California: A Bibliometric Analysis.” Frontiers in Conservation Science, vol. 5, 2025, doi:10.3389/fcosc.2024.1480035. Accessed 15 Sept. 2025.

Burns, William C. G., and Alexander Gillespie, editors. The Future of Cetaceans in a Changing World. Transnational, 2003.

Butterworth, A. Marine Mammal Welfare: Human Induced Change in the Marine Environment and Its Impacts on Marine Mammal Welfare. Springer, 2017.

"Five Endangered Dolphins ." World Animal Protection, 19 Apr. 2024, www.worldanimalprotection.org.nz/news/five-endangered-dolphins. Accessed 15 Sept. 2025.

"Freshwater Dolphins and Porpoises." Marine Mammal Commission, www.mmc.gov/priority-topics/species-of-concern/freshwater-dolphins-and-porpoises. Accessed 15 Sept. 2025.

Probert, P. Keith. Marine Conservation. Cambridge UP, 2017.

Reeves, Randall R., et al., compilers. Dolphins, Whales, and Porpoises: 2002-2010 Conservation Action Plan for the World’s Cetaceans. International Union for Conservation of Nature, 2003.

Soulé, Michael E., et al. Marine Conservation Biology: The Science of Maintaining the Sea’s Biodiversity. Island Press, 2005.

Temple, Andrew H., et al. "Management and Research Efforts Are Failing Dolphins, Porpoises, and Other Toothed Whales." Scientific Reports, vol. 14, no. 7077, 25 Mar. 2024, doi:10.1038/s41598-024-57811-7. Accessed 15 Sept. 2025.

Weelden, Celine van, et al. “Impacts of Climate Change on Cetacean Distribution, Habitat and Migration.” Climate Change Ecology, vol. 1, 2021, p. 100009. doi:10.1016/j.ecochg.2021.100009. Accessed 15 Sept. 2025.

Werth, Alexander. Marine Mammals in a Changing World. Multidisciplinary Digital Publishing Institute, 2022.