Global warming is causing fish to shrink, reveals a new study

Researchers studied 13 fish species using data from 1978 to 2018.

by | March 4, 2024

Filed Under Environment | Research | Trends

Nutritious phytoplankton blooms may no longer align with fish life cycles

By Isobel Williams/The Courier-Times
February 29, 2024

Global warming is causing fish to shrink, reveals a new study.

New research has discovered that climate change is decreasing the weight of fish, as warmer water is limiting their food supplies.

The University of Tokyo researchers analyzed the individual weight and overall biomass of 13 species of fish from Japan’s Fisheries Agency and the Japan Fisheries Research and Education Agency.

They looked at long-term data for six fish populations from four species between 1978 and 2018.

Seawater temperature data between 1982 and 2014 were also studied to see if changes in the ocean’s surface and subsurface layers 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.

This initial weight drop was originally attributed to greater numbers of Japanese sardine, which increased competition with other species for food.

However, further analysis revealed that the effect of climate change warming the ocean appears to have resulted in more competition for food, as cooler, nutrient-dense water could not easily rise to the surface.

Professor Shin-ichi Ito from the Atmosphere and Ocean Research Institute at the University of Tokyo said: “We investigated 17 fish stocks — that is, populations or groups of fish — from 13 species and found that many decreased in weight during this period.

“With higher temperatures, the ocean’s upper layer becomes more stratified, and previous research has shown that larger plankton are replaced with smaller plankton and less nutritious gelatinous species, such as jellyfish.

“Climate change can alter the timing and length of phytoplankton blooms, the explosive growth of microscopic algae at the ocean’s surface, which may no longer align with key periods of the fish life cycle.

“The migration of fish has also been shown to be affected, in other studies, which in turn impacts fish interaction and competition for resources.”

According to the UN Food and Agriculture Organisation, in 2019, the western North Pacific accounted for almost a quarter of the global total of fish caught and sold.

The researchers note that Japan’s seafood self-sufficiency has been gradually declining for several decades and global warming is one of the biggest threats facing local fisheries.

The team adds that their results have implications for fisheries and policymakers trying to manage ocean resources under future climate change scenarios.

Professor Ito said: “Fish stocks should be managed differently than they were before, considering the increasing impact of climate-induced conditions.

“The situation fish experience is much more severe than decades ago. If we cannot stop global warming, the quality of fish may decline.

“So, we need to take action so that we can enjoy a healthy ocean and delicious fish.”

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About Laine

Laine Welch has covered the Alaska fish beat for print and radio since 1988. She also has worked “behind the counter” at retail and wholesale seafood companies in Kodiak and on Cape Cod.

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