A Hokkaido research institute predicts about a 4 percent drop in the catch of salmon in prefectural waters this autumn due to colder waters that make it harder for fry to survive.

Still, the total estimated catch represents less than half of the over 60 million salmon in Hokkaido waters recorded in 2004. While the catch of fall salmon has fluctuated in the past three decades, the overall trend for the previous 12 years has been one of decline.

The Salmon and Freshwater Fisheries Research Institute, part of the Hokkaido Research Organization, predicts that about 24.8 million salmon will be caught in Hokkaido waters during the autumn run, a 3.8 percent drop from 2016.

By area, the number of autumn salmon taken in the Tokachi and Kushiro areas will likely decline 29 percent from last year, while a 2.9 percent reduction is seen for the Sea of Okhotsk region, according to estimates. By contrast, a 13.1 increase in fall salmon catch from 2016 is expected for the Sea of Japan, and a 4.8 percent increase is predicted for the Nemuro area.

The institute also says 3-year-old and 4-year-old salmon have declined as a percentage of total catch in recent years. While 4-year-olds have accounted for between half and two-thirds of Hokkaido’s salmon stocks over much of the past three decades, they made up only 41 percent of last year’s catch. The average salmon size in 2015, the latest year for which data is available, was 3.38 kilograms, slightly more than the average 3.10 kilograms recorded in 2012.

The predicted decrease in the overall catch of fall salmon is attributed to colder sea temperatures in the spring months, when salmon fry, the fish’s juvenile stage, enter the ocean, making it more difficult for them to survive in larger numbers. The ideal sea temperature, in general, for salmon fry is 7-10 degrees, said Yasuyuki Miyakoshi, a researcher at the institute.

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