Ocean warming is now recognized as a growing threat to fish populations, with potentially devastating effects on marine ecosystems and coastal economies. A recent study, published on February 25 in the journal Nature Ecology & Evolution, highlights the profound repercussions of this trend on marine biodiversity. Relayed by The Guardian, this study highlights that the phenomenon could lead to a significant decrease in fish populations, which poses a major risk to global food security and livelihoods for the millions of people dependent on fishing.
Results that worry
Researchers, under the direction of Shahar Chaikin, a marine ecologist at the National Museum of Natural Sciences in Spain, analyzed data from 33,000 fish populations in the northern hemisphere from 1993 to 2021. The study compares the effect of progressive ocean warming with that of marine heat waves on fish biomass.
The figures show a 7.2% decrease in fish populations for each increase of 0.1 °C in seabed temperatures per decade. The loss of biomass, linked only to chronic warming, could reach 19.8% in one year. These values, according to Chaikin, may seem low taken in isolation but « are described as « stonishing and deeply worrying » » when they accumulate over time at the scale of oceanic basins.
It varies a lot depending on the region
The decline in fish biomass is not uniform. Some areas have been more affected than others. The coasts of China and Japan recorded declines of up to 35%. In comparison, global ocean warming has already caused a 4% decline in sustainable catches, resulting in a loss of 1.4 million tonnes of fish between 1930 and 2010. Regions such as the East China Sea and the Kuroshio Current in Japan experienced dramatic falls, with fish stocks plunging by 15% to 35%.
Conversely, some regions seem to be temporarily benefiting from warming: the province of Newfoundland and Labrador, the Baltic Sea, and the continental shelf of the northeastern United States have observed temporary increases in stocks.
Ocean warming, a direct consequence of climate change, remains the main cause of the decline in fish populations. However, overfishing accentuates this phenomenon, aggravating the consequences on the marine environment. Beyond the ecological risk, the effects are also economic and social. East Asian countries, which are heavily dependent on fishing, may have to import more fish, leading to higher prices and affecting accessibility for many populations.
The warming of the seabed not only affects the reproduction of fish, but also reduces the diversity of species capable of surviving in extreme conditions. Dr. Chris Free, a quantitative environmentalist at the University of California, points out that despite an apparent decline of 4%, this decrease represents a significant loss in metric tons, calling into question the sustainability of some fisheries.
source : RSE magazine
