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The Prolific Mystery of Lake Pend Oreille

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Lake whitefish are ecologically and economically important to Lake Pend Oreille

Lake whitefish, Coregonus clupeaformis, are believed to be the most numerous fish species in Lake Pend Oreille. Consider this: in 2007, netting conducted by Idaho Department of Fish and Game to target lake trout landed just under 8,000 lake trout (target species), but nearly 80,000 lake whitefish. Over 125,000 lake whitefish are estimated to live in Lake Pend Oreille.

Lake whitefish, also known as the common whitefish, are members of the trout and salmon family. Lake whitefish are not native to the Pend Oreille drainage, and their relationships and interactions with other fish species are relatively unknown. They occur with lake trout throughout much of northern North America, but both species were widely introduced throughout the West where they were not native. Though known predators of lake whitefish eggs, larvae and juveniles include lake trout, northern pike, burbot, and walleye, the population in Lake Pend Oreille appears to be largely unfazed by predation.

This species is a cool-water species that moves from shallow to deep water when waters are warm in summer, and then back to shallow water when waters cool in autumn. Lake whitefish are found throughout much of Canada and the northern United States. From October to December, depending on water temperature, whitefish move from deeper water to littoral areas to broadcast their eggs in depths ranging from 2 to 4.5 meters over sand, gravel, flat stone, cobble, and boulder.

The coloration of lake whitefish is bronze to brown, becoming silvery on the sides; the underside is silvery white. They have a deeply forked tail and small mouth below a rounded snout On average, they reach 18 inches. Primarily bottom feeders, lake whitefish eat crustaceans, snails, aquatic insect larvae, mollusks, and other small aquatic organisms. They may also eat eggs of their own and other species, including lake trout. They have occasionally been reported feeding on other, small, bottom-oriented fish.

In 2006, IDFG hired Dr. Mike Hansen, Professor of Fisheries at the University of Wisconsin, Stevens Point to study lake trout on Lake Pend Oreille, a species that he has studied in the Great Lakes for more than 20 years. Dr. Hansen brought a couple of his graduate students on an extended field trip to the Panhandle to help out. One of them, Mike Hosack, studied and wrote his thesis on the lake whitefish in Lake Pend Oreille. Hosack recently graduated with a Master of Science in Natural Resources (Fisheries). His report, entitled "Population Dynamics of Lake Whitefish in Lake Pend Oreille, Idaho," was released in late 2007 to IDFG.

In the Great Lakes, where Hansen and his students spend most of their time, lake whitefish support a commercial fishery. In contrast to Lake Pend Oreille, lake trout are native in the Great Lakes, where they are protected but also support a large catch to lake whitefish commercial fishermen. Somewhat ironically, Hansen was hired to help IDFG knock out the lake trout, whereas historically he has worked to bring them back. Because of Hansen’s experience with commercial whitefish fishery’s effect on lake trout in the Great Lakes, he suggested that IDFG look into the feasibility of a commercial fishery on lake whitefish. This is, in part, what grad student Hosack’s work has done.

"IDFG has been looking for cost effective ways to reduce predation on kokanee and to protect native cutthroat trout and bull trout which are highly susceptible to competition and predation from lake trout," says regional supervisor Chip Corsi. "Thus, IDFG is interested in whether a commercial fishery for lake whitefish could be a useful and inexpensive tool to help restore Lake Pend Oreille’s prized sport fisheries for kokanee, trophy rainbow trout, and bull trout."

For a commercial fishery to be sustainable, the target species must be able to compensate well; that is, they must reproduce at a rate as high or higher than the rate at which they are removed from the population. Some species, such as lake whitefish, are better at this than others. On the other hand, a species that is slow-growing and long-lived, such as lake trout, would likely not be a good candidate for a sustainable commercial fishery. The theory is that lake whitefish could sustain a viable fishery, while the fishery was used to suppress lake trout. This concept is just in the idea phase right now, but could be a useful tool in keeping the lake trout population at bay.

"In the Great Lakes, commercial fisheries for lake whitefish must be rigorously enforced to limit the number of lake trout that are killed inadvertently while fishing for lake whitefish," says Hansen. "In the absence of such rigorous regulation of the lake trout harvest as by-catch in commercial lake whitefish fisheries, lake trout stocks declined sharply or remained low in many areas of Lake Superior. Only after by-catch of lake trout was controlled by strict quotas and gear restrictions have lake trout stocks recovered in Lake Superior."

To evaluate the biological potential of a lake whitefish fishery, Hosack estimated lake whitefish population attributes that control production and yield, as well as those that limit compensatory responses to harvest. He used information gathered on the species while IDFG was trap netting in autumn of 2005 and gill netting in spring 2006. He also conducted a thorough literature review on the species. Population dynamics, in the realm of fisheries management, includes estimation of changes in population composition, numbers, and biomass.

Some of the informational tidbits uncovered by Hosack include data on age of maturity (sexually mature between the ages of 6 to 8 years), distribution of males to females (more females), estimated natural mortality rates (low), growth rates (slow), and the likely presence of sub-populations (at least two). Hosack surmised that the lake whitefish in Lake Pend Oreille are indeed a good candidate for a commercial fishery, so long as harvest is maintained within sustainable limits.

Unexploited populations of whitefish are quite rare, mostly existing in small, remote lakes in northern Canada. Such populations have considerable potential for commercial fishery development. Slow growth rates, low rates of natural mortality, high density, and old age at maturity typically characterize unexploited populations.

Lake whitefish are an "ecologically and economically important freshwater fish throughout their range," notes Hosack. "The whitefish is currently the most valuable commercial fish species in lakes Michigan, Huron, Ontario, and Superior," he states in his thesis. "In 2005, commercial harvest of whitefish in these four lakes was 8.5 million pounds valued at $6.8 million dollars."

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Author info

Kate Wilson Kate Wilson was a Project Journalist for Avista's Clark Fork Project. She has been interested in environmental issues since she was a youngster.

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