Tokyo, Japan – Climate change is not only affecting the ocean environment, it is also causing the decline of saltwater fish. Scientists from the University of Tokyo have discovered that fish in the western North Pacific Ocean are brightening because warmer waters are affecting their food supply. This finding has major implications for the local fishing industry and global seafood markets, as the region is a major contributor to the world’s fish catch.
The researchers analyzed the individual weight and overall biomass of 13 fish species during two critical periods: the 1980s and 2010s. Their findings indicate that fish weights are lower in both seasons compared to other years.
The 1980s saw a decline in fish weight due to the abundance of Japanese sardines, which led to increased competition for food. However, the 2010s experienced a slightly different scenario; although Japanese sardine and chub mackerel populations have increased moderately, the main concern is the impact of climate change. Warming ocean waters have resulted in a stratification that prevents cooler, nutrient-dense water from rising to the surface, thus limiting the food available to fish.
This phenomenon has broader implications beyond fish size. Japan, known for its rich seafood culture, from sushi to grilled mackerel, is facing declining seafood self-sufficiency, facing challenges such as reduced sales, labor shortages, and rising fisheries management costs. The study underscores the urgent need for adaptive management strategies in the face of the worsening effects of global warming on marine life.
The western North Pacific, bordering Japan’s east coast, is an important marine area that accounted for nearly a quarter of all fish caught and sold in 2019, as reported by the UN Food and Agriculture Organization. Scientists have shown that fish stocks in this area are not only decreasing in weight but also facing a change in their ecosystem dynamics.
“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,” said study author Shin-ichi Ito, professor from the Atmosphere and Ocean Research Institute at the University of Tokyo, in a university release.
“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.
Ito’s team analyzed long-term data from 1978 to 2018 for six fish populations from four species, and medium-term data from 1995-97 to 2018 for 17 fish populations from 13 species, including seawater temperature data from 1982 to 2014. Their analysis highlights a clear connection between climate change and marine ecosystem health, emphasizing the need for innovative management methods to maintain fish populations.
The study’s findings serve as a call to action for fisheries managers and policy makers. With increasing impacts of climate-induced conditions on fish stocks, traditional management practices may no longer be sufficient.
“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,” concluded This. “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.”
The study was published in the journal Fish and Fishing.
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