Climate change threatens growing number of fish species

Climate change threatens a growing number of species, from Atlantic salmon to green turtles, the latest update to the International Union for Conservation of Nature (IUCN)’s Red List of Threatened Species™ reveals. The IUCN Red List now includes 157,190 species, of which 44,016 are threatened with extinction.

Dr Grethel Aguilar, IUCN Director General, said: “Climate change is menacing the diversity of life our planet harbors, and undermining nature’s capacity to meet basic human needs. 

“This IUCN Red List update highlights the strong links between the climate and biodiversity crises, which must be tackled jointly. Species declines are an example of the havoc being wreaked by climate change, which we have the power to stop with urgent, ambitious action to keep warming below 1.5 degrees Celsius.”

IUCN President Razan Al Mubarak said: “Today’s update to the IUCN Red List shows the power of coordinated local, national and international conservation efforts. Success stories such as that of the scimitar horned oryx show that conservation works. To ensure the results of conservation action are durable, we need to decisively tackle the interlinked climate and biodiversity crises.” 

State of the world’s freshwater fish species

The update completes the first comprehensive assessment of the world’s freshwater fish species, revealing that 25% (3,086 out of 14,898 assessed species) are at risk of extinction. At least 17% of threatened freshwater fish species are affected by climate change, including decreasing water levels, rising sea levels causing seawater to move up rivers, and shifting seasons. This compounds threats from pollution, which impacts 57% of freshwater fish species at risk of extinction, dams and water extraction, which affect 45%, overfishing, which threatens 25%, and invasive species and disease, which harm 33%. 

For example, the large-toothed Lake Turkana robber (Brycinus ferox) – an economically important species in Kenya – has moved from Least Concern to Vulnerable on the IUCN Red List, due to overfishing, climate-change driven habitat degradation and dams reducing freshwater entering the lake.

Kathy Hughes, Co-Chair of the IUCN SSC Freshwater Fish Specialist Group, said: “Freshwater fishes make up more than half of the world’s known fish species, an incomprehensible diversity given that freshwater ecosystems comprise only 1% of aquatic habitat. These diverse species are integral to the ecosystem, and vital to its resilience. This is essential to the billions of people who rely upon freshwater ecosystems, and the millions of people who rely on their fisheries. 

“Ensuring freshwater ecosystems are well managed, remain free-flowing with sufficient water, and good water quality is essential to stop species declines and maintain food security, livelihoods and economies in a climate resilient world.” 

The Atlantic salmon (Salmo salar) has moved from Least Concern to Near Threatened, with new evidence showing the global population decreased by 23% between 2006 and 2020. Atlantic salmon are now restricted to a small portion of the rivers they inhabited a century ago across northern Europe and North America, due to multiple threats over the course of their long-distance migrations between freshwater and marine habitats. 

Climate change affects all stages of the Atlantic salmon’s life cycle, influencing the development of young salmon, reducing prey availability and allowing invasive alien species to expand their range. Dams and other barriers block access to spawning and feeding grounds, while water pollution and sedimentation, primarily from logging and agriculture, lead to higher mortality of young salmon. 

Breeding with escaped farmed salmon threatens many wild populations, and may weaken their ability to adapt to climate change. Mortality due to salmon lice (Lepeophtheirus salmonis) from salmon farms is also of great concern. A significant rising threat is the invasive Pacific pink salmon (Oncorhynchus gorbuscha), which is spreading rapidly across northern Europe.

Central South Pacific and East Pacific green turtles at risk of extinction

The Central South Pacific and East Pacific green turtle (Chelonia mydas) populations are respectively Endangered and Vulnerable to Extinction, according to IUCN Red List update. Climate change is a growing threat to green turtles throughout their life cycle, as high temperatures result in lower hatching success, rising sea levels threaten to flood nests and drown the young, and the seagrasses that green turtles eat are susceptible to ocean warming and changes in currents due to extreme weather. 

A major cause of green turtle mortality throughout these regions is incidental bycatch in industrial and artisanal fishing. Numbers have also decreased as people harvest green turtles and their eggs for their own consumption or to sell at markets.

“It is shocking that one quarter of all freshwater fish are now threatened with extinction and that climate change is now recognized as a significant contributing factor to their extinction risk, which was also recently reported to be a serious emerging threat to amphibians,” said Dr Barney Long, Re:wild’s Senior Director of Conservation Strategies. “It is critical that we better safeguard our freshwater systems as they are not only home to precious and irreplaceable wildlife, but also provide humans with so many services that only the natural world can.”

Photo credit: iStock/ piyaset

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