Releasing too much fish into rivers reduces fish population, researchers say

TOKYO, Feb 15 (NHK) - A team of Japanese and US researchers says releasing too much young fish into rivers disrupts their ecosystems and reduces river fish populations.

The team used statistics to calculate how numbers of all species of river-dwelling fish change before and after releases of captive-bred cherry salmon.

The researchers based their study on data collected over a 21-year period through 2019 on the scale of fish releases and populations in 31 rivers of Japan's northernmost prefecture of Hokkaido.

They found that the more cherry salmon are released, the greater the decrease in river fish population.

They also found that repeated massive releases cause some species to die out.

The team concluded that when fish are released in quantities that surpass a river's acceptable level, the fish fight for food and habitats, disrupting ecological balance. ...continue reading

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