Climate change, caused by human activities, has impacts on all species, including fish, whether freshwater or marine. Fertility, survival, migration, etc. : the increase in water temperature affects all aspects of the life of aquatic fauna already harmed by other threats, also human. State of affairs… dark.
Studies have been carried out for several years to check whether the increase in water temperature influences the reproduction, growth and seasonal rhythms of fish. One of the most recent, carried out in 2020, was able to demonstrate that increasing temperatures, above certain thresholds, greatly reduced the fertility and survival of eggs of several species of fish, such as Atlantic salmon, trout or even the sculpin.
On the side of the International Union for Conservation of Nature (IUCN), a 2023 assessment report highlighted some rather alarming figures:
- 25% of freshwater fish (3,086 of the 14,898 species assessed) are threatened with extinction;
- at least 17% of threatened freshwater fish species are affected by climate change, including reduced river flow, rising sea levels leading to the upwelling of salt water in rivers, and seasonal changes.
Added to these climatic factors are the “usual” threats: pollution, overfishing, dams, etc. Other indicators are visible: species, such as shad, sea trout, salmon, eels and sea lampreys, are beginning to modify their migration periods in response to signals of climate change which affects the temperature and flow of rivers.
As with plants and certain mammals and birds, a shift is observed in the phenology or biology of a species. Thus, scientists notice that the fish mentioned above return to the rivers a few days earlier each decade.
Climate change affects these animals on two other levels. Firstly, the increase in temperatures also has effects on water quality, and although the phenomenon has been documented for a long time, its worsening is evident, as evidenced by faster and more accentuated eutrophication phenomena. Second impact: the availability of water resources. The average flow of rivers is decreasing, low water levels are more severe and longer, which strongly impacts the ability of migratory fish to move.
It is by following the migration of salmon, for example, that we can measure the impacts of climate change, not only on the migration period but also on the numbers of these fish.
We should not forget that fish also suffer from the stress induced by ongoing climate change, and that they will also have to cope with invasive species.
