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Researchers from the University of Tokyo have found that climate change is causing saltwater fish in the western North Pacific Ocean to shrink due to warmer waters affecting their food supply. This discovery has important implications for the local fishing industry and global seafood markets, given the region’s significant contribution to the world’s fish catch.

Fish population in western North Pacific declining due to global warming

Scientists examined the total biomass and individual weight of 13 different types of fish during two significant time spans: the 1980s and the 2010s. Their results reveal that fish weights were diminished during both eras in comparison to previous years.

During the 1980s, fish weight decreased due to an abundance of Japanese sardine, causing intensified competition for food. In the 2010s, despite moderate increases in Japanese sardine and chub mackerel populations, climate change became the main concern. Warming ocean waters caused stratification, hindering the ascent of cooler, nutrient-rich water to the surface and consequently limiting fish food sources.

Japan’s seafood industry, integral to its cultural identity, is experiencing a decline in self-sufficiency due to various challenges including reduced sales, labor shortages, and rising fisheries management costs. This highlights the necessity for adaptive management strategies to address the increasing impact of global warming on marine life.

The western North Pacific, adjacent to Japan’s eastern coast, is crucial for marine life, contributing nearly 25% of the world’s fish catch and trade in 2019 according to the UN Food and Agriculture Organization. Researchers have observed declining fish stocks in this region, accompanied by changes in ecosystem dynamics.

Global warming impacts plankton population

The warming of the ocean’s upper layer due to higher temperatures leads to increased stratification, as observed in previous studies. This results in a shift from larger to smaller plankton and less nutritious gelatinous species like jellyfish, according to Shin-ichi Ito, a professor at the University of Tokyo’s Atmosphere and Ocean Research Institute.

Climate change disrupts the timing and duration of phytoplankton blooms, potentially affecting fish life cycles. Fish migration patterns are also influenced, affecting interactions and resource competition among fish species.