Okanagan Lake kokanee kill called a natural phenomenon

Fisheries biologists complete testing of kokanee that died in Okanagan Lake, while Wood Lake fishery continues to rebound

  • Aug. 3, 2016 6:00 p.m.

A kokanee fish kill in Okanagan Lake is being blamed on warmer water being pushed lower in the lake.

Despite a kokanee fish kill in Okanagan Lake that saw more than 1,000 kokanee turn up dead, the kokanee fishery in Lake Country’s Wood Lake has not been affected by the same scenario and continues to show a strong rebound since fish numbers crashed in 2011.

Fisheries biologists have now completed testing to find out the exact cause of the fish kill in Okanagan Lake that was first reported on July 14, testing nearly 80 of the dead kokanee for evidence of disease.

The fish health tests came back negative for disease or evidence of IHNv, a virus that has affected kokanee salmon in Kootenay Lake in recent years. Biologists can’t be 100 per cent certain about the cause of the recent die off, however it is strongly suspected this is a recurring natural phenomenon caused by summer time temperature inversions in the lake.

“Strong winds can send warm surface water deeper into the lake…such sudden changes in water temperature can be deadly to kokanee,” a news release from the provincial government reported.

Ministry of Forests, Lands and Natural Resource Operations staff say there have been at least three other die-offs of this kind in the past eight years and this year’s event was relatively small by comparison adding the 2016 die-off is not severe enough to have a significant impact on Okanagan Lake’s overall kokanee population. Kokanee stocks in the lake have enjoyed a strong recovery over the past several years.

While kokanee were washing ashore in Okanagan Lake, no such impact was seen in Wood Lake, which continues to see excellent kokanee returns each year since 2011.

“Since then the population has been recovering,” reported Greig Bethel, media relations officer for the Ministry of Forests, Lands and Natural Resource Operations. “Last year over 21,000 kokanee returned to spawn in Middle Vernon Creek. Ministry staff are expecting another year of strong returns to Middle Vernon Creek.”

When it comes to angling, fishing on Wood Lake has been excellent this year, according to Oceola Fish and Game Club fisheries chair Danny Coyne, who reported the average size of kokanee caught this year is between 13 1/2 and 14 1/2 inches long.

“That’s a really good sign of a healthy kokanee fishery,” said Coyne. “In the past those fish have been bigger. If you have more kokanee in the lake they are smaller and if you have less kokanee they get bigger. But because we have middle-size kokanee that tells us the fishery is healthy.”

When stocks crashed in 2011 it was due to warm water in Wood Lake. Kokanee couldn’t find the proper temperature to survive as the water in the entire lake was too warm for them. But this year’s cooler than normal summer so far have kokanee thriving in Wood Lake, which is open for kokanee fishing from April 1 to Aug. 31.

Kokanee will begin their annual spawn into Middle Vernon Creek in September, where 90 per cent of stream spawning kokanee return each year. The creek suffers from low water levels that can affect kokanee; however, ministry staff are able to monitor the levels and release more water if needed from Duck Lake to allow the fish to spawn in the creek.

Each fall the Oceola club does fish counts. If you would like to help during these counts, contact Danny Coyne at danny@bcfishn.com

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