Pend Oreille Lake Levels Affect Kokanee
Monday, February 19, 2001 - 12:00 AM MST
by Melo Maiolie, Panhandle Region Fisheries Biologist Editor's note: the following is adapted from an article for a north Idaho sportsmans newsletter. It explains some of the important points in the continuing saga of one of the most popular large lake fisheries in Idaho. Most anglers in the region are familiar with the controversy over how lake levels in Lake Pend Oreille are managed. It is a tough subject that pits natural resources against economic interests and has been the subject of lawsuits and more than a few hard feelings. Fish populations are driven by the amount of habitat that is available to them, similar to most other wildlife species. In the case of kokanee in Lake Pend Oreille, it is the spawning habitat that is in limited supply. If we expand the amount of habitat, given time, the kokanee population will expand to fill this habitat. If spawning habitat stays scarce, then all of our efforts, no matter how expensive or time consuming, will do little on a long-term basis. One of our project findings was that the fluctuations of the lake are critical to maintaining abundant spawning habitat. The issue is not about one elevation being better than another, but more about having some variability in the minimum pool level between different years. Specifically, it appears that one of the best ways to keep good spawning areas is to lower the lake down to 2051 feet elevation during some winters and keep it at least four feet higher in others. Gravel around the perimeter of the lake is cleaned and re-sorted by wave action during the winter when the pool level is low. This gravel is available for kokanee spawning in subsequent years when the lake is held higher. It appears that one year of low pool level, followed by three years of higher pool level, could maximize benefits to the kokanee population. Lake level changes of four feet appear necessary. This is because wave action can move gravel down to a depth of three feet during severe winter storms. If kokanee eggs are buried in the shallow gravel, they are likely to become dislodged and die. The good news is that "fish friendly" lake level management is becoming more of a reality. The U.S. Fish and Wildlife Service has recently released their "biological opinion" for bull trout in Lake Pend Oreille. It calls for the lake to be drawn down to 2051 feet in 2001, and then held four feet higher (2055 feet) in 2002. The US Fish and Wildlife Service will then get an "independent scientific review" of the situation and, with input from Idaho Fish and Game, will decide on operations for 2003 to 2006. They will then come up with written recommendations for future management in 2007. The U.S. Fish and Wildlife Service hopes to strengthen the kokanee population and thereby benefit bull trout. So this is a case of protecting a threatened species (bull trout) and in the process helping other species such as kokanee, Kamloops rainbow trout, and bald eagles. (The full biological opinion can be seen at http://www.r1.fws.gov/finalbiop/biop.html.) In trawl surveys made in September, near record high numbers of fingerling and one-year-old kokanee were observed. Older fish, however, remained at extremely low levels. A point to remember is that predator management is a stop-gap measure to keep the depressed kokanee population from totally collapsing, but this cannot be considered a long-term solution. Kokanee population recovery ultimately depends on habitat - spawning gravel - restoration.