Coeur d’Alene eagle numbers low, mirroring lake’s kokanee population

Larger-than-normal kokanee in Lake Coeur d’Alene are sending migratory eagles wheeling on to better hunting grounds this winter.

“I think that explains why the eagle numbers are so different,” Bureau of Land Management biologist Carrie Hugo said. “When there aren’t as many, it’s hard to have 300 eagles competing for a smaller number of fish.”

Hugo counted 45 adults and six juvenile eagles on Wednesday. Last year around the same time, Hugo counted 234 adults and 25 juveniles.

Kokanee size is highly dependent on kokanee density (known by the experts as density-dependent growth). If, for instance, there are fewer fish, they grow larger taking advantage of abundant food. If the lake is teeming with kokanee, the fish are on average smaller in response to tight competition.

This year, kokanee numbers in Lake Coeur d’Alene are unusually low, leading to larger-than-average fish.

In 2020, the average size of males was 15.4 inches and females averaged 14.8 inches, according to an Idaho Department of Fish and Game news release. 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.

This is not common in Lake Coeur d’Alene and biologists don’t expect it to continue.

“In years with fewer adult kokanee, there are generally fewer bald eagles than in years with many adult kokanee,” IDFG fisheries biologist Carlos Camacho wrote.

The migratory birds flock to Wolf Lodge and Beauty bays to feast on spawning kokanee salmon. Their numbers generally peak during the third week of December. After spawning in the shallow waters of Wolf Lodge and Beauty bays, the adult kokanee die.

The BLM has conducted a weekly count since 1974. This is the fewest eagles Hugo has counted in her 11 years doing so, she said.

In 2017, 372 eagles were counted, setting a record for the most birds spotted in one count. At that time, biologists believed the higher-than-normal numbers were due to a particularity cold winter in Canada – which led to lakes freezing earlier – coupled with a strong spawning year for kokanee.

Hugo thinks that a milder-than-normal winter may be impacting eagle numbers, although the lack of kokanee is likely the main culprit.

“There is some possibility that they haven’t been in as much of a hurry to get down here,” she said.

The lower-than-normal numbers of fish shouldn’t be a problem for eagles, though. They will likely continue on to the Snake River plain in southern Idaho or Oregon’s Klamath River watershed.

“They’re just missing a bonus opportunity to fatten up a little bit,” Hugo said. “But there are no concerns about their population or anything.”

The best places to view eagles are Higgens Point, Mineral Ridge Boat Ramp or the Mineral Ridge Trailhead. Stopping along Highway 97 is dangerous. Eagle watchers should find a parking area before stopping and exiting their vehicles.