Marine heat waves have minimal impact on fish abundance and cause little change in the composition of fish populations in the Northern Hemisphere, according to a study published Wednesday in the journal Nature.
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“These results surprised me,” confirmed Alexa L. Fredston, assistant professor in the Department of Ocean Sciences at the University of California and lead author of the study, in an email to AFP.
“We know that fish communities have responded to long-term ocean warming by moving poleward, which can change the biomass and composition of fish in a given location. “I therefore expected similar results after these heat waves in the sea, such as a fish community with more warm-water species and fewer cold-water fish than usual,” explained the researcher.
The dozen American, Canadian and European researchers who conducted the study analyzed more than 82,000 fishing catches made using bottom trawls during scientific campaigns in the North Atlantic and northeast Pacific.
The catches, which included 1,769 demersal fish species caught between 1993 and 2019, were compared to 248 heat waves recorded during the same period in deep waters from the subtropical zone to the Arctic.
The authors noted some impacts of marine heat waves, such as a 22% loss of fish biomass in the Gulf of Alaska after the 2014–2016 heat wave or, conversely, a 70% increase in biomass in the northeastern United States after the 2012 heat wave.
These fluctuations, although significant, are less important than the natural variability of fish abundance. Furthermore, such changes have not been observed in other heat wave episodes that have been little studied.
At the end of their analysis, the researchers found no significant relationship between the cumulative intensity of marine heat waves and the evolution of demersal fish biomass.
They also found no rapid decline in cold-water fish or an increase in warm-water fish after these heat waves. “We couldn’t predict which fish would lose or gain biomass based on their biology or the temperatures at which they normally exist,” Fredston said.
“It should be emphasized that changes in fish biomass are often difficult to predict,” the researcher noted.