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Idaho Fish & Game Reports From LCAA

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Coeur d'Alene Lake kokanee and Chinook Population Monitoring

      by Jim Fredericks, Regional Fishery Manager.

As everyone who fishes Coeur d’Alene Lake knows full well, the fishery is a delicate balance between predator (Chinook salmon) and prey (kokanee salmon). Further complicating the picture is the natural conditions in the lake, which can be very good for the fishery (good zooplankton production) or very bad (excessive runoff and flooding). Over the past 30 years, we’ve seen lots of ups and downs in both species. Fortunately for the past 3-4 years, we’ve seen excellent environmental conditions, and anglers are benefitting. All indications are that, for the foreseeable future, anglers should continue to enjoy a good balance in the kokanee and Chinook populations and a productive Coeur d’Alene Lake fishery.

Each year we monitor the kokanee population using a midwater trawl and hydroacoustic equipment. In 2013 we were once again encouraged to see continued high abundance of spawners, as well as juvenile year-classes. We estimated over 3.5 million age-1 kokanee. This continues to bode very well for both kokanee anglers and Chinook anglers alike, as the growth in the kokanee population has allowed us to begin building the Chinook population. In 2011 the regulations were changed to allow only 2 Chinook per angler, with a 20” minimum size. The rule, combined with the abundant prey base, appears to be making a difference. Angler catch rates and fish sizes in 2013 showed improvement, as evidenced by the success of the annual Big One Derby entries.

To monitor the Chinook population, we estimate spawner escapement by counting redds (spawning nests) the in tributaries to Coeur d’Alene Lake. Early surveys were done from a helicopter, but we now float the main spawning sections of the Coeur d’Alene and St. Joe rivers using canoes. Ideally, Chinook escapement will result in 100-120 redds-enough to produce enough juveniles to maintain a good fishery, but not so many that the kokanee population is jeopardized. This year we counted 129 redds—a bit high, but not cause for alarm.

In addition to counting numbers, we also assessed the age of spawning adults. Like all salmon, Chinook die after spawning.

To learn their ages, carcasses were recovered from the Coeur d’Alene River and otoliths (ear stones) were removed from the heads. Once removed, the otoliths are sanded and burned to help identify the annual growth rings. We were pleased to see that over half of spawners were 5-year-old fish, and only 2 of 16 were 3-year-olds. This suggests that harvest pressure is not forcing fish to spawn at younger ages, and smaller sizes.

Unfortunately, despite stocking 20,000 juvenile adipose-clipped Chinook each year, we’re still seeing very few hatchery Chinook in the fishery. We’ve made changes to release timing, and more recently to the rearing hatchery where the fish are raised, and we’ll continue to try to find a combination that works, but for the time being, the fishery continues to be primarily driven by natural reproduction. While that’s not a bad thing, it means that we’re at the mercy of Mother Nature, and it also means the late summer fishery is primarily concentrated at the south end of the lake.

Finally, many of you had the opportunity to meet and work with Melo Maiolie, the Regional Fishery Biologist who worked on Coeur d’Alene Lake. After a long and outstanding career with IDFG, he recently joined the ranks of the retired. Melo loved working on Coeur d’Alene Lake, and he very much appreciated the LCAA and their support. We’ll fill his position later this spring, but until then (and after) don’t ever hesitate to contact me if you have questions, thoughts or concerns. Happy fishing!


Idaho Fish and Game Report



LCAA