COUGAR — Kokanee found dead floating along the shore of Yale Reservoir probably died of oxygen deficiency caused by the lake’s shift from winter to summer conditions.
The Washington Department of Fish and Wildlife has received a half dozen telephone calls about dead kokanee at Yale, a 3,000-acre reservoir on the North Fork of the Lewis River.
Anglers netted some of the dead and dying fish and brought them to Speelyai Hatchery on Merwin Reservoir.
Bryan Quinton, a fish and wildlife health specialist for the department, examined the fish.
“My estimation for cause of death would be a case of acute toxicity or anoxia,’’ Quinton wrote in an email. “Kokanee are one of the most chemically sensitive fish that I work with. Any slight shift in water chemistry or clarity has a tendency to shake a few out. With the weather pattern we have had lately, I would assume that the reservoir water has inverted. This would induce a water quality change that could produce this type of loss. This has happened already at a couple of my lake and reservoir water stations.’’
Quinton added that a loss of kokanee in spring was common in Lake Whatcom in northern Washington. He also has seen it occur in Alder, American and Summit lakes.
Quinton also wrote about Yale: “These fish had no visible signs of trauma, infection or disease. Skin and gill tissue had no parasite or bacterial pathogens present. Fat level was good, all organs had normal coloration, texture and size. Stained tissue samples showed no internal parasites or bacteria present.’’
Spawning report — Kokanee spawning in Cougar Creek, a Yale Reservoir tributary, was well below average in 2015, according to a report by PacifiCorp, operator of the three dams on the North Fork of the Lewis River.
Last fall, biologists for the utility estimate 20,942 kokanee — a landlocked sockeye salmon — spawned in Cougar Creek in southern Cowlitz County. That’s well below the 10-year average of 28,483 and the 1978-2015 average of 63,981.
The 20,942 is a decrease from 33,626 observed in 2014.
Male kokanee averaged 12.1 inches, while females averaged 11.3 inches.
The report says predation, low reservoir productivity from water turbidity or dam operations, lack of access to portions of Cougar Creek due to logjams, harvest, disease or competition all could be dampening the kokanee production in Yale.
“It is difficult to quantify each factor and its specific effect on kokanee escapement,’’ the report conclude. “However, it is clear that kokanee escapement is much lower in Cougar Creek in recent year, especially when compared to historical records.’’
Cougar Creek is the main spawning area for Yale kokanee.
