Ten miles downstream of the 263-MW Cabinet Gorge hydroelectric development on the lower Clark Fork River, Lake Pend Oreille is a favorite Idaho freshwater fishing destination. The lake lies downstream of the hydro plant, about 25 miles northwest of Coeur d’ Alene in the state’s northern panhandle. Historically, anglers seeking kokanee salmon, rainbow trout, native bull trout, and cutthroat trout flocked to the lake each year. Lake trout (mackinaw), although introduced in 1925, did not contribute to the fishery until the early 1990s. The annual income of area businesses as a result of visiting anglers is estimated at $17 million.
The 94,000-acre lake is one of the deepest and largest freshwater lakes west of the Mississippi River. It supports one of North America’s most important lake-dwelling native bull trout populations. The bull trout is listed as a threatened species under the Endangered Species Act. An important food source for the bull trout in Lake Pend Oreille is kokanee, the land-locked variety of sockeye salmon.
However, for the past 40 years, the numbers of kokanee salmon in Lake Pend Oreille have been diminishing. Predation by introduced lake trout and rainbow trout threatened the kokanee population with collapse. Because of the low numbers of kokanee in the lake, in 2005, the Idaho Department of Fish and Game (IDFG) predicted that the population would collapse within four years. This likely would mean a subsequent drastic decline in the bull trout population.
So, Avista Utilities, which owns and operates the Cabinet Gorge plant, stepped in to help IDFG save the kokanee fishery. In 2006, the utility invested $831,100 to coordinate development of a plan to manage predation of kokanee and enable recovery of the species. The plan includes three major efforts: placing a bounty on predators; informing the public; and continuing netting of lake trout using commercial gear.
Implementation of the plan resulted in suppression of lake trout to a level where, if it can be sustained, will collapse the predator population in less than ten years. Based upon these results, Avista provided an additional $643,600 for the continuation of the efforts in 2007.
Seeing signs of trouble
The kokanee were established in the lake in 1933 and became central to the lake’s popularity as a sport fishing destination. Lake Pend Oreille became known as a world-class kokanee fishery, with anglers harvesting more than 1 million kokanee annually. Game fish in their own right, kokanee also are an important food source for rainbow trout, bull trout, and lake trout. Lake Pend Oreille gained fame in 1947, when a sport fisherman landed a 37-pound, world-record rainbow trout. Two years later, another angler caught a 32-pound, world-record bull trout.
But the glory days waned in the 1960s, when the U.S. Army Corps of Engineers began using more water from the lake to generate electricity at its 42.6-MW Albeni Falls hydro plant, located downstream and just west of the lake on the Pend Oreille River. Winter lake levels were lowered by an additional 5 feet, leaving kokanee shoreline spawning areas dry. The kokanee population began its decline.
In an effort to mitigate the effects of the drawdowns associated with the operation of the Corps’ Albeni Falls plant and to restore the kokanee in Lake Pend Oreille, in 1985 the Bonneville Power Administration (which markets electricity generated at Albeni Falls) and Washington Water Power (now known as Avista) built the Cabinet Gorge Fish Hatchery near Clark Fork, Idaho. The purpose of the hatchery was to rear kokanee salmon, then release them into the lake.
An average of about 9 million fry have been released annually since the hatchery was opened in 1986; in some years, kokanee fry releases have exceeded 15 million.
However, despite the influx of hatchery fish, the kokanee population continued to decline due, in a large part, to foraging by the three trout varieties. A rapidly expanding lake trout population upset the traditional kokanee/trophy trout fishery the lake supported for more than 60 years.
In 2000, IDFG closed the kokanee harvest. Conversely, it also increased or removed limits on the numbers of lake trout and rainbow trout that could be harvested. The idea was to reduce the bull trout’s competition for food. However, despite IDFG’s public information program to encourage anglers to catch rainbow trout and lake trout, the response did little to reduce the predator population.
In both 2003 and 2005, Avista hired Harbor Fisheries, Inc. of Baileys Harbor, Wisconsin, to experiment with commercial trap nets to quantify the lake trout population and begin lake trout suppression. Commercial netting proved to be highly controversial, however, and use of trap nets for lake trout suppression was suspended until additional information was collected.
Avista funded incentives for lake trout caught in fishing derbies, but trap netting operations in late 2005 showed increased lake trout numbers. At the same time, acoustic monitoring showed that the kokanee population was greatly reduced. Data reported in January and March 2006 estimated the total biomass of kokanee in the lake at 2.5 pounds per acre, compared with estimates of 10 to 15 pounds per acre in the past. Survival of kokanee between one and two years of age declined to only 10 percent in 2005, compared with historical average survival rates of 50 to 90 percent.
Instituting emergency measures
In 2006, IDFG declared an emergency. Recovery of the kokanee and protection of the bull trout depended on the ability to reduce the numbers of lake trout and rainbow trout in the lake by 50 percent each year. To achieve this reduction, Avista provided funding toward implementing a plan to manage predation of kokanee.
Placing a bounty on predators
Efforts to reduce predator populations include encouraging sport fishermen to fish for lake trout and rainbow trout and to keep all predators they catch, no matter the size. This is contrary to traditional practice, in which anglers at Lake Pend Oreille release small fish. A monetary incentives program is proving effective in encouraging the anglers to keep the fish, rather than release them. In the first year of the program, the incentives were multi-faceted. For example, an angler who catches and checks in a lake or rainbow trout – no matter the size – gets a coupon entered into a monthly drawing. Each month, 40 winners win $100 each and one gets $1,000. In addition, IDFG embedded microchip tags in 600 rainbow trout and 200 lake trout. If an angler catches one of these tagged fish, he or she is eligible to receive a reward at check-in ranging from $100 to $2,000. And, each adult who checks in a rainbow or lake trout gets a free Idaho Lottery ticket. In the later half of 2006, a simple $10/fish incentive was offered to anglers who return fish heads to IDFG freezers located around the lake. During the winter months, the incentive was raised to $15/fish to encourage fishing. The bounty remains at $15/fish.
Informing the public
To persuade anglers that the exploitation and recovery action was necessary and to encourage them to participate in the predator bounty efforts, IDFG launched a public information campaign.
IDFG developed news releases about the trap net program, and submitted these to all news outlets in northern Idaho, eastern Washington, and northwestern Montana. IDFG sponsored several public information workshops to go over research data on the kokanee and predator populations, and had an interactive session to gather feedback from constituents.
Avista sponsored production of two videos to help anglers improve their rainbow trout and lake trout fishing skills. Avista also made free copies of the videos available to IDFG and to libraries throughout the state of Idaho.
IDFG worked to recruit anglers, marina owners, charter boat captains, and members of the general public to join a fishery recovery task force to help spread the word. IDFG also worked closely with area legislators to keep them informed about the status of the fishery and public information efforts. IDFG also held a workshop of lake trout experts to gather input on whether or not the predator suppression program was warranted.
Finally, Mike Hansen, PhD, a fisheries professor from University of Wisconsin, Stevens Point, and a world recognized expert on lake trout, was hired with Avista funds to spend a sabbatical in Idaho assisting IDFG with predator/prey modeling and public relations work.
Continuing professional netting of predator fish
By 2006, a more complete gill net population estimate indicated the lake trout population was considerably larger than previously estimated with trap nets alone. Indications were the population was expanding rapidly. Suppression of lake trout with all methods was now urgent despite complaints from some anglers.
In 2006, Harbor Fisheries was hired again to use trap nets, gill nets, baited cod traps, and set lines to suppress the lake trout population.
Between April 29 and November 30, 2006, sport fishermen removed 5,948 rainbow trout and 11,041 lake trout from Pend Oreille Lake. Harbor Fisheries personnel removed another 4,431 lake trout. By the end of 2006, exploitation (the percent of the population harvested) was estimated to be 45 percent and total annual mortality about 60 percent. Dr. Hansen predicted this type of intense harvest on lake trout – if it can be maintained – would collapse the lake trout population within ten years or less.
Future activities will include assessment of kokanee survival rates, population estimates of lake trout, evaluation of exploitation rates on rainbow and lake trout, and development of long- and short-term population reduction targets. That information will help determine future activities.
– By Joe DosSantos and Ned Horner. Mr. DosSantos is the aquatic program leader for Avista Utilities. Mr. Horner is a regional fisheries manager for the Idaho Department of Fish and Game. Mr. DosSantos may be reached at Avista Utilities, P.O. Box 1469, Noxon, MT 59853; (1) 406-847-1284; E-mail: joe. firstname.lastname@example.org. Mr. Horner may be reached at Idaho Department of Fish and Game, 2885 W. Kathleen, Coeur d’Alene, ID 83815; (1) 208-769-1414; E-mail: email@example.com.
In recognition of its efforts to save the fishery, in 2007, Avista received an Outstanding Stewardship of America’s Waters award from the National Hydropower Association.
Lake trout are harvested as part of a collaborative effort by Avista Utilities, Idaho Department of Fish and Game, and local anglers and marina owners to reduce the population of this fish in Lake Pend Oreille. Lake trout feed on the lake’s declining population of kokanee salmon, a food source for the threatened bull trout.