Many anglers on Coeur d’Alene Lake reported catching very large kokanee this year, so it is no surprise that this year’s spawning kokanee adults achieved near record size. Each year, Idaho Fish and Game staff conduct a netting survey to evaluate the size of spawning kokanee in Coeur d’Alene Lake. In 2020, the average size of males was 15.4 inches and females averaged 14.8 inches. Males were the third largest and females were the second largest on record since surveys started in 1954. The largest individual fish caught in the 2020 netting survey was an 18.3 inch male.
Kokanee size is highly dependent upon how many of them are in the lake. Fish biologists refer to this as density-dependent growth. When kokanee abundance is high, fish size is small. When kokanee abundance is low, fish size is large.
This occurs because the amount of food available changes based on the number of kokanee. In years with lots of kokanee, the fish compete for a limited food supply and slowly grow. In years with fewer kokanee, food is more plentiful and fish grow faster. In 2020, Coeur d’Alene Lake supported a lower abundance of adult kokanee that grew exceptionally well.
However, this is fairly uncommon in Coeur d’Alene Lake and is not expected to continue. Kokanee sampling completed during the summer indicated that younger kokanee are highly abundant. This means that adult kokanee should be more abundant in coming years, resulting in a return to more typical sized kokanee for anglers (often 9-11 inches).
Kokanee not only provide a popular fishing opportunity, but they are an important food source for other fish and birds. The high abundance of young kokanee signals good growing conditions for predator species that consume kokanee, such as Chinook salmon and smallmouth bass.
Kokanee are also a sought after food source for migrating bald eagles. Hundreds of bald eagles typically use Coeur d’Alene Lake as a stopping location to rest and feed on spawning kokanee before continuing their winter migration.
After spawning to produce the next generation of kokanee for the lake, adult kokanee will all die. These dead or dying kokanee provide easy meals for bald eagles. In years with fewer adult kokanee, there are generally fewer bald eagles than in years with many adult kokanee.