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What Can You Find in Our Lake?

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By Woostermike at en.wikipedia [Public domain], from Wikimedia Commons By Woostermike at en.wikipedia [Public domain], from Wikimedia Commons

A round-up of fish in Lake Pend Oreille

Have you ever wondered what was swimming around our lake with you? Not the Pend Oreille Paddler of legend, but the tail you feel brush against your leg, or the tug you feel on the end of your line? The likely subjects include the native species such as  bull trout (a federally listed Threatened species for which no harvest is allowed), the mountain whitefish, and westslope cutthroat trout (State Species of Special Concern, catch and release only). While there are many other species of native fish that call Lake Pend Oreille home, they are not likely to find their way to the end of your line. We also host several other game fish, such as walleye, crappie, pike, bluegill, catfish, perch and bass, but they are not native to this system. 

 Lake trout (mackinaw) were introduced by the federal government as a game fish in 1925. Kokanee made their way to the Pend Oreille system from Flathead Lake during extreme flooding in 1938. Although kokanee are considered non-native, they provide a vital food source for threatened bull trout. In the 1940s Gerrard rainbows (aka Kamloops) were introduced from Kootenai Lake in British Columbia.  

The Idaho Department of Fish and Game has made intense efforts in recent years to help kokanee populations recover. Hatcheries trap, spawn, and rear fry for release back into the system to augment naturally spawning fish and help perpetuate resident populations. Important spawning habitat is protected, and lake trout, which prey heavily on kokanee, and have had a devastating effect on populations, are being removed from the lake through bounties and trapping. These efforts are paying off with growing kokanee populations and we saw an incredible number of adults return to natal streams such as Trestle Creek and Granite Creek to spawn over the past few years. 

Shoreline spawning kokanee have also seen a successful return and our recent surveys have indicated a roughly threefold increase of shoreline spawners. In addition, kokanee are utilizing spawning habitats that have not been used in recent years, signifying a saturation of traditionally used sites. 

Native and non-native were living somewhat harmoniously until a multitude of events occurred.  In the late 1950s the Cabinet Gorge and Albeni Falls dams were built, and the naturally fluctuating water levels in Lake Pend Oreille were manipulated for power generation. In 1965 the US Army Corps of Engineers began manipulating lake levels, impacting the survival of shoreline spawning fish, such as kokanee.  In the late 1960s mysis shrimp were introduced, allowing lake trout populations to explode, thereby throwing off the delicate balance that existed prior to their arrival. 

Shoreline alternations, such as docks, riprap and boat houses, provide hiding cover for predatory fish that prey on young native fish. A more recent proliferation of septic systems, increased runoff, and the introduction of fertilizers and excess nutrients potentially changes water quality in the near shore area and increases algae that can ultimately deplete the amount of available dissolved oxygen fish depend on to breath. Cold water species, such as those native to Lake Pend Oreille, are impacted disproportionately because they require higher levels of dissolved oxygen. 

So how is this connected to fishing and what does fishing mean to Bonner County and the people of Idaho? For one thing, in 2003 400,824 people bought fishing licenses and/or permits which in turn generated over $437.6 million in retail sales. In Bonner County alone there was an estimated $25 million spent on fishing trips, $18 million on Lake Pend Oreille with $7 million on food, beverages and motels.

In Bonner County a healthy fishery leads to a healthy economy and we ask everyone to help keep our waters clean and fish populations healthy. 

How do my actions around the house affect the lake? All living things depend on their ecosystem to provide basic life necessities such as food, shelter, and oxygen to breath. Fish need oxygen to survive and they depend on their aquatic environment to provide it. As water moves past their gills, microscopic bubbles of oxygen in the water called dissolved oxygen (DO) are transferred from the water to their blood. 

There are many factors that affect the amount of DO in the water. Cold water holds more DO than warm water, and as waters warm, less and less DO is available to the fish living there. The DO concentrations change seasonally with runoff, temperature changes, the decomposition of aquatic plants, and pollution level along with lake depths.

Pollution, sewage, lawn clippings, eroded soils, and runoff entering the lake contribute nutrients that stimulate the growth of organic matter, causing a decrease in DO concentrations available to resident fish. Eutrophication exacerbates the decrease in DO in the lake by adding organic matter to the system, which accelerates the rate of oxygen depletion in the colder, deeper portions of the lake. 

Cold water species, such as native Bull Trout, which are federally listed as Threatened, and the Kokanee they depend on, can tolerate temperatures up to 70 degrees. In addition to a lower availability of DO as water warms, trout have difficulty using the oxygen that is present in the water even if concentrations are high when water temperatures are above 75 degrees. During different life stages, fish require different levels of DO in the water. 

Allowing excess sediment to enter the water not only causes water quality problems associated with pH and DO, but can also smother food sources, such as invertebrates, interfere with gills and respiration, reduce places for fry to hide, and by covering spawning gravels. 

Landowners can take measures that will help keep DO levels in the lake and streams high for our resident fish. Maintaining a buffer of vegetation along the shoreline will provide shade to keep water temperatures low, and will help filter sediment and nutrients running off from upland areas before entering the water. Keeping compost, pet and livestock waste, and lawn clippings as far from the shoreline as possible, maintaining septic systems, and not using commercial fertilizers in near shore areas will also help.  It doesn’t matter where you live; the health of the lake is in your hands.

Leave No Child Inside

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Author info

Matt Haag Matt Haag is an Idaho Fish and Game Conservation Officer.

Tagged as:

Lake Pend Oreille, fishing, kokanee, bull trout, The Game Trail, mountain whitefish, westslope cutthroat trout, walleye, crappie, pike, bluegill, catfish, perch, bass

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