Lake Chelan Large Kokanee Explained
Mike Carey - 2/25/2014
There has been speculation exactly why anglers are seeing such large and healthy kokanee in Lake Chelan. Site member Toni (Wannafishalure.com) recently contacted WDFW Fish Management and got these two responses:
From Larry Phillips, Fishery Manager:
"My understanding of Kokanee (based on what I’ve read in the published literature) is that growth is closely related to density. More kokanee=smaller size. Because they are specialized feeders (almost exclusively daphnia which is a species of zooplankton), they can overgraze their forage base. I suspect that in the case of Lake Chelan we had a couple of weak year classes prior to the year-class that supported last year’s fishery. The weak year classes may have been the result of high water or high predation which limited overgrazing. This would have given the prey base a couple years to build and support much higher growth. Obviously this is a guess because I’m not the biologist for that area. Recall that all kokanee are genetically identical to sockeye and most naturally occurring sockeye populations have an associated resident (kokanee) component. Also recall that several 20+ inch kokanee were caught in American last year……so Whatcom Lake (our state source for kokanee) also has high growth potential.
When prey abundance is high kokanee have the potential to get very large. Several other factor can affect growth but it typically comes down to the relationship between kokanee abundance, prey availability, and prey size. Other issues include predation, temperature, and turbidity."
From Travis Maitland, Fish Biologist:
"Larry’s previous explanation to you of what has been going on with the Kokanee in Lake Chelan the last couple of years is “spot on”. I will only elaborate a bit more on a few points that I hope will help answer your questions.
Historical Lake Productivity: Lake Chelan is the textbook example of an oligotrophic body of water. Bodies of water like this tend to be relatively deep, nutrient poor, clear, light transmission is high and the euphotic zone is deep. Even though light penetrates to a considerable depth, primary production of phytoplankton is limited by the lack of nutrients, all of which results in a biologically limited body of water.
Lake Chelan Kokanee history: Although details (Strain and numbers) of stocking history prior to 1933 are missing….we do know that Kokanee were first stocked into Lake Chelan in 1917. WDFW stocked only this initial naturally reproducing stock of kokanee back into the lake from the early 1940's until about 1957. In 1957 Kootenay Lake stock kokanee were introduced as eyed eggs, and in 1966 Whatcom stock kokanee plus, Kootenay stock kokanee began to be stocked as eyed eggs and in later years as fry. Recently only lake Chelan stock (so, a conglomerate of Kootenay, Whatcom and what was originally stocked) are being stocked. There are no records that I know of that point to the ocean going form (Sockeye) ever being stocked into the lake and no genetics work has been conducted to my knowledge.
Recent year classes: During the last couple of years, the Kokanee available in the fishery came off of relatively low adult spawning escapements….and by that I mean the parents of these fish were in relatively low abundance by the time they made it to spawn. As Larry also mentioned, this can also be caused or compounded by things such as predation or high water events that may have taken place on the spawning tributaries.
All of this comes back around to numbers. So, for what information we have at this point…I am comfortable in saying that the fish have grown to some larger sizes in recent years because they have been present in relatively lower densities with the same available food source, thus giving them the opportunity to grow larger. There is no evidence that suggest this is genetically driven.
I have been hearing a few good angler reports as well of good sized Kokanee already this year…..12”-16”.
I hope this has helped and please feel free to contact me if you have any further questions."
Best regards
Travis Maitland
Washington Department of Fish and Wildlife
Dist. 7 Fish Biologist
Wenatchee District Office
3860 Hwy 97a
Wenatchee, WA 98801
(509) 665-3337
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