Wildlife experts in Oregon have begun investigating the mass die-off of salmon migrating from the state toward Washington through the Columbia River.

Fisheries manager John North of the fish and wildlife department of Oregon said that out of the 507,000 sockeye salmon that had swum through the two dams between lower Columbia River, only 272,000 of them were able to survive the journey. He said that they have never had a scale of mortalities on this magnitude before.

The die-off of salmon in Oregon comes after several other states in the West Coast region of the United States struggle with the effects of a drought and the Columbia River is experiencing the third-highest population of sockeye salmon making the journey from the ocean in order to spawn since the 1960s.

Experts believe the increased heat in the air coupled with the abnormal melting of mountain snow have resulted in an increase in water temperatures in the area. This led authorities to impose fishing restrictions and to launch conservation efforts to help save the fish, such as trucking the sockeye salmon to cooler waters.

North said that they were able to detect a 70-degree Fahrenheit reading in the Columbia River, a month earlier than what was usually observed in the river. The salmon did not have enough time to adjust to this sudden increase in water temperatures.

Hatchery officials say increases in temperatures of the water have caused the death of around 400,000 additional salmon this year.

The population of sockeye salmon was measured between the Columbia River's McNary Dam and Bonneville Dam, located around 150 miles upstream toward the tributary of the Snake River.

The sockeye of the Snake River was the first species of salmon included in the U.S. Endangered Species List in 1991.

In 1992, wildlife experts only counted 15 sockeye salmon swimming toward the Lower Granite Dam of the Snake River. Only one of these fish, which was given the name Lonesome Larry by local officials, survived the journey to the Redfish Lake in Idaho. The lake is where this particular species of salmon historically spawn, according to North.

The fisheries manager said that there were 2,788 sockeye salmon that passed through the Lower Granite Dam last year. Many local leaders believed that this was proof that their efforts at restoring fish habitats and boosting the population of the salmon were making a difference.

The vulnerability of the salmon species to warm waters has resulted in the death of hundreds of sockeye and hundreds of thousands of fish spawned through hatcheries. Only 363 of the salmon have survived the journey past the Lower Granite Dam this year.

Compared to the sockeye, less than 2,000 wild salmon known as Chinook have died because of the increase in water temperatures in rivers from the estimated 109,000 that journeyed through the Bonneville Dam, North said.

He believes that the sockeye salmon are not as hardy as other species of salmon, and that they do not prefer to make the journey upstream when the waters become too warm for them.

Photo: Elsie Hui | Flickr 

ⓒ 2021 TECHTIMES.com All rights reserved. Do not reproduce without permission.