By TOMOYUKI YAMAMOTO/ Staff Writer
October 28, 2024 at 07:00 JST
Pacific saury caught in Nemuro, Hokkaido, in September (Tomoyuki Yamamoto)
Fears are being raised that Pacific saury, a seasonal specialty in Japan in autumn, will continue to shrink in size due to climate change that is depriving the fish of their primary food resource.
Researchers say the species of zooplankton that the fish feed on is becoming beyond their reach as sea temperatures continue to rise.
“As the planet becomes warmer, Pacific saury will probably become thinner,” said Atsushi Yamaguchi, an associate professor with Hokkaido University who specializes in the ecology of plankton and led the study.
Japan’s annual catch of saury has declined dramatically in recent years. Also, the fish are noticeably smaller.
In summer 2021, the research team collected various species of plankton in northern areas of the North Pacific where saury congregate.
The team members put the plankton in tanks with three different water temperatures at 3 degrees, 7 degrees and 11 degrees to observe their growth rate. Temperatures were set to simulate changes in water temperature likely to occur in the sea area where the plankton was collected.
The experiment showed that zooplankton species with low nutritional values, such as eucalanus bungii and metridia pacifica, grow faster as water temperatures rise.
But neocalanus plumchrus, a highly nutritious species that saury gorge on, was found to be poor at adjusting to higher sea temperatures.
Neocalanus plumchrus thrive when the water temperature is 7 degrees, but their growth rate dropped an average 52 percent when the temperature was raised to 11 degrees. The largest decline came to 98 percent.
Pacific saury swim at depths of up to 20 meters from the water surface.
The researchers said neocalanus plumchrus will move deeper in the ocean when the water temperature is high, spelling fewer opportunities for the fish to catch their favorite plankton in their habitat.
The team also said that frequently occurring ocean heat waves, a condition where extremely high sea temperatures continue, in the North Pacific in recent years may have contributed to the increase in smaller saury populations.
The study was published in the online edition of the scientific journal Frontiers in Marine Science on Oct. 2.
Sea temperatures around Japan hit record high for third year
April 16, 2024
Climate change turns up the heat on Japanese seafood industry
May 28, 2024
Japanese salmon lose out as rival moves north due to climate change
August 25, 2024
Southern fish survive winter off Izu amid warmer waters
May 30, 2020
Global warming reduces number, size of autumn specialty saury
November 29, 2023
Here is a collection of first-hand accounts by “hibakusha” atomic bomb survivors.
A peek through the music industry’s curtain at the producers who harnessed social media to help their idols go global.
Cooking experts, chefs and others involved in the field of food introduce their special recipes intertwined with their paths in life.
A series based on diplomatic documents declassified by Japan’s Foreign Ministry
A series about Japanese-Americans and their memories of World War II
