Climate change shrinking fish | EurekAlert!

The weight of fish in the western North Pacific Ocean plunged in the 2010s due to warmer waters limiting food supplies, according to a new University of Tokyo study. The researchers analyzed the individual weight and overall biomass of 13 fish species. In the 1980s and 2010s, the fish were lighter. They attributed the initial period of weight loss to more Japanese sardines, which increased competition with other species for food. In the 2010s, while numbers of Japanese sardines and chub mackerel increased modestly, the effect of climate change warming the oceans appears to have resulted in more competition for food, as cooler, nutrient-dense water does not readily rise in surface. These results have implications for fisheries and policymakers trying to manage ocean resources under future climate change scenarios.

Whether it’s sushi, takoyaki (traditional octopus pancake ball) or grilled mackerel, seafood is an iconic and important part of Japanese cuisine. However, Japan’s seafood self-sufficiency has been gradually declining for several decades. Local fisheries are facing many challenges from reduced sales and lower prices, labor shortages, changing consumer preferences and rising costs. But perhaps one of the biggest threats comes from global warming.

Japan’s eastern coast is bordered by the western North Pacific Ocean, a highly productive marine area. According to the UN Food and Agriculture Organization, in 2019, the western North Pacific accounted for almost a quarter of the total total fish caught and sold. However, the results of new research at the University of Tokyo show that between the 1980s and 2010s, the weight of fish in the region changed significantly.

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

Ito, along with co-author Lin Zhen, a PhD student, analyzed fish weight and biomass data from Japan’s Fisheries Agency and the Japan Fisheries Research and Education Agency. Fish weight refers to individual fish (for example, a 200-gram mackerel), whereas biomass is the total weight of a species or group in an area (for example, 50,000 tons of mackerel).

The pair looked at long-term data for six fish populations from four species between 1978 and 2018, and at medium-term data for 17 fish populations from 13 species from 1995/1997 to 2018. Sea water temperature data between 1982 and 2014 were also analyzed to see if changes in the ocean’s surface and subsurface layers may have had an effect.

The results showed two periods of reduced fish body weight, first in the 1980s and again in the 2010s. The team attributed the decline in weight in the 1980s to the rise of Japanese sardines, which likely led to greater competition for food within and between fish species. In comparison, in the 2010s, although there was a modest increase in the population of Japanese sardines and chub mackerel, the team’s analysis shows that the supply of nutrients to the surface ocean from subsurface layers decreased, due to the impact of global ocean warming, is an influential factor.

“At higher temperatures, the upper layer of the ocean becomes more stratified, and previous research has shown that larger plankton are replaced by smaller plankton and less nutritious gelatinous species, such as jellyfish,” Ito explained. . “Climate change may alter the timing and length of phytoplankton blooms (explosive growth of microscopic algae at the ocean’s surface), which may no longer match important stages of the fish life cycle. Migration of fish has also been shown to be affected, in other studies, which affects fish interactions and competition for resources.

It is hoped that fisheries managers and policy makers will use research like this to better understand the changes occurring in the oceans around Japan to help make informed choices for the future. “Fish stocks must be managed differently than before, taking into account the increasing impact of climate-induced conditions. The situation experienced by fish is worse than decades ago,” he said. . “If we do not stop global warming, the quality of fish may decrease. So, we need to act so that we can enjoy healthy oceans and delicious fish.”

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Paper Title:

Lin Zhen and Shin-ichi Ito. Fish weight loss in response to intra- and interspecies competition under climate change. Fish and Fishing. DOI: 10.1111/faf.12818

Funding:

This study was conducted as an activity of the Joint PICES/ICES Working Group on the Impact of Warming on Growth Rates and Fishery Yields (GRAFY). This study was supported by The Japan Society for the Promotion of Science (JSPS) KAKENHI grant numbers JP21H04735 and JP22H05030.

Useful Links
Atmosphere and Ocean Research Institute (AORI): https://www.aori.u-tokyo.ac.jp/english/

Contact Research:

Professor Shin-ichi Ito

Atmosphere and Ocean Research Institute, The University of Tokyo

Kashiwanoha 5-1-5, Kashiwa, Chiba 277-8564, Japan

Email: [email protected]

Tel.: +81-4-7136-6240

Touch the contact:
Mrs Nicola Burghall
Public Relations Group, The University of Tokyo,
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan
[email protected]

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