Climate change affects marine mammals directly and indirectly. Their habitats are being transformed and their food resources are decreasing.
The decrease in food resources
Greenhouse gases are mainly produced by the combustion of fossil fuels such as oil, gas and coal. Some of these gases are absorbed by the ocean, which acidifies the marine environment and increases the water temperature.
This acidification process can seriously affect marine mammal populations because of its impact on their prey. Many invertebrates, such as squid or zooplankton, which is made up of microorganisms at the base of the food chain, build and consolidate their internal or external skeleton (shell) through complex chemical processes. The acidification of the oceans disrupts these processes and weakens these structures, thus decreasing the survival and reproduction rate of these species. Their populations are decreasing and so is the stock of prey for marine mammals.
To escape from the rise in water temperature, certain species move towards colder waters. Krill, for example, the main food of certain whales, move closer to the Antarctic Peninsula. In other words, the surface area of the whale feeding ground is reduced. Climate change also influences krill reproduction, making it impossible for favourable reproduction conditions to occur regularly enough. The food stock of certain cetaceans is therefore also reduced.
As a result, marine mammals may have to travel 200 km to 500 km further to find food. This results in a greater expenditure of energy that could weaken their chances of reproducing. The Humpback Whale, for example, only gives birth when the conditions for feeding its young are favourable.
Changes in the distribution of populations
Marine mammals, like all living beings, are distributed on the surface of the globe according to geographical barriers defined by thermal differences between water masses (creating in particular the major ocean currents) and by environmental conditions linked to their life cycle. If these conditions change, then their distribution and movements will be affected. An entire food chain can be disrupted, from plankton to marine mammals, by altering ocean currents, the temperature and salinity, and by rising sea level due to melting sea ice.
Decline in breeding rates
This increase in temperature can also disrupt the reproduction of marine mammals, reducing their chances of procreation by not providing them with optimal conditions and by modifying their breeding habitats. Some species, such as the Humpback Whale, have different feeding and breeding grounds and make long migrations to reach one or the other. While they like to breed in the warm waters of the Caribbean, they cannot tolerate temperatures above 28°C. This can result in dispersing to new breeding sites.
Some species or populations could disappear from the warm waters of the Caribbean. This would have a substantial socio-economic impact since these animals are of interest to tourists.