Fish are declining due to global warming, a new study reveals.
Warmer water means that smaller plankton (the microorganisms that fish feed on) float to the surface. This means the fish get fewer nutrients than they eat, the researchers found.
Researchers at the University of Tokyo analyzed the individual weight and overall biomass of 13 fish species, including mackerel, anchovy and sardines, analyzing long-term data from six fish populations of four species between 1978 and 2018.
Seawater temperature data between 1982 and 2014 were also studied to see if changes in the surface and subsurface layers of the ocean may have had an impact.
The results, published in Fish and Fisheries, showed two periods of reduced fish body weight, first in the 1980s and again in the 2010s.
The results, published in Fish and Fisheries, showed two periods of fish body weight reduction, first in the 1980s and again in the 2010s (pictured: sardines underwater).
This initial weight drop was originally attributed to increased numbers of Japanese sardines, which increased competition with other species for food.
However, closer analysis revealed that the effect of climate change warming the ocean appears to have resulted in greater competition for food, as colder, nutrient-rich water could not easily rise to the surface.
The findings in the Pacific support previous research in other areas of the world that has found that trophy fish caught in fishing competitions are also getting smaller, and that smaller fish species are also increasing in number at the expense of larger ones. big.
Professor Shin-ichi Ito of the University of Tokyo said: “With higher temperatures, the upper layer of the ocean becomes more stratified, and previous research has shown that larger plankton is replaced by smaller plankton and less nutritious gelatinous species. , like jellyfish.
‘Climate change may alter the timing and duration of phytoplankton blooms, an explosive growth of microscopic algae on the ocean surface, which may no longer coincide with key periods in the life cycle of fish.
Warmer water means smaller plankton, which means fish get fewer nutrients from what they eat, the researchers found (pictured: freshly caught herring at a fish market)
“Other studies have also shown that fish migration is affected, which in turn impacts fish interaction and competition for resources.”
According to the Food and Agriculture Organization of the United Nations, in 2019, the western North Pacific accounted for almost a quarter of the world’s total fish caught and sold.
The team adds that their results have implications for fisheries and policymakers trying to manage ocean resources in future climate change scenarios.
Professor Ito said: “Fish stocks should be managed differently than before, taking into account the increasing impact of climate-induced conditions.”
‘The situation that fish are experiencing is much more serious than decades ago. If we cannot stop global warming, the quality of fish may decline.
“Therefore, we must take action so we can enjoy a healthy ocean and delicious fish.”