OUR GEM: Protecting cutthroat trout in some lake bays

For those who love viewing wildlife, the southern end of Lake Coeur d’Alene can be a great vantage point in the spring for catching migratory tundra swans that are making a pit stop on their migration northward to their breeding grounds in Alaska.

However, in some cases, the white objects that you may see bobbing in the waters in the southern end of the lake may not be these majestic birds. Rather, they may only be buoys that mark gillnets that are being deployed in the lake to capture and remove northern pike, a non-native fish species that was illegally introduced into the Coeur d’Alene Basin back in the mid-'70s.

Since 2015, the Coeur d’Alene Tribe in conjunction with the Idaho Department of Fish and Game has been removing pike in two locations of Lake Coeur d’Alene, Windy Bay and the southern end that encompasses Heyburn State Park. Removing pike in these locations was perceived to have the most benefit toward increasing survival rates of native westslope cutthroat trout that use the lake as adult-rearing habitat. Populations of cutthroat trout that migrate between their natal streams and the lake have been substantially reduced from historical levels. Though a number of factors have contributed to their decline, a research study funded by the Coeur d’Alene Tribe 10 years ago indicated that predation by pike is likely a primary reason currently limiting population recovery.

The reason that pike pose a problem is because they congregate during early spring in shallow bays of the lake to spawn, and in some locations, cutthroat trout have to move through these same shallow areas when they are entering and exiting their natal streams in the spring - easy pickings for pike.

The fact that pike congregate in specific shallow locations in the spring also makes them vulnerable to be targeted by certain methods of capture. Gillnetting is one such method and has been shown to be highly effective in removing large numbers of pike. For example, 31 pike were once pulled out of a single net set in the southern end of the lake. The gillnets used by the Tribe’s removal program are curtains of mesh (150 feet long by 6 feet deep) that are suspended in the water column along the lake bottom and intercept fish that get stuck as they attempt to swim through the mesh openings.

Of course, these nets are not selectively "picking on pike" but can also catch other species of fish. However, specific measures have been taken to minimize the number of other species, called "bycatch," captured by the nets.

First, the nets used by the removal program have large mesh that capture the large pike but allow smaller fish to swim right through. Nets are only allowed to soak overnight so that bycatch species don’t spend much time stuck in the nets before they get released in the morning. Netting is also conducted primarily when water temperatures are cold to minimize the stress placed on captured fish. Experience has also identified certain areas to less frequently target where sensitive bycatch species are numerous, but pike are few.

Notably, survival rates of cutthroat originating from Lake Creek have improved since pike removal was introduced into Windy Bay, so our gillnetting efforts are producing positive results.

One word of caution, though, regarding the netting operation. If you happen to be boating in some of the shallow areas where nets are being set, keep an eye out for those white buoys. They mark the ends of the 150-foot net, and if you are planning on motoring between them, go slowly because the top of the net may be at or just below the water surface — getting a net wrapped up in a boat propeller can be a pain to disentangle.

Our Gem Collaborative contributing writer Jon Firehammer, Ph.D is a fisheries biologist with The Coeur d’Alene Tribe.