The Lakes of the Colville Reservation

Twin Lakes are located about 8.5 miles west of Inchelium, Washington on the Colville Confederated Tribes Reservation. In 2004 and 2005, Washington State University and the tribe conducted a study to determine prey selectivity and population dynamics of the Twin Lake fish community. The primary goal was to determine if largemouth bass were controlling golden shiners through predation and if that predator-prey relationship could be enhanced. Another objective was to determine if trout growth and condition are being compromised by the presence of golden shiners.

The data suggests that bass are predating extensively on golden shiners and are a key factor in controlling shiner populations. Trout growth rates and condition are relatively good despite the presence of golden shiners. This may be due to the presence of bass predating on shiners and preventing their population from reaching a point in which the trout community would be affected.

The information contained below is a brief results summary from the sampling conducted in 2004 and 2005. After data was collected all fish were released back into the lakes.

Trophic state: Mesotrophic (mesotrophic means the lakes are in an intermediate productivity level. There is a natural aging process in which sediment, organic, and nutrient inputs cause a lake to age and become nutrient rich (eutrophic). Poor land management practices can enhance and accelerrate this natural aging process. The trophic staus of a lake often dictates what type of fish species can live in it).

A native aquatic plant called watershield (Brasenia schreberi) dominates the plant community in Twin Lakes. Watershield in North Twin Lake can cover approximately 68 acres and around 19 acres in South Twin Lake. These plants provide important habitat for fish and wildlife, reduce bank erosion caused by waves, and uptake deleterious nutrients. Bass predation on shiners and fish distribution can be impacted by dense watershield beds like those observed in North Twin Lake.

View of watershield from channel between North and South Twin Lakes.

Fish Community

Brook Trout Salvelinus fontinalis: Are nonnative to Twin Lakes. The native range of brook trout is the eastern region of the United States and Canada south through the Appalacian Mountains, Great Lakes and parts of the Missouri River System. Brook Trout are fall spawners when temperatures and daylight begin to decline. The tribe stocks both lakes annually with brook trout. There is also a naturalized reproducing population of brook trout in both lakes.

Our samples indicate that brook trout represent 12-15% of the total trout population in both lakes. Approximately 83-88% of our samples in both lakes were wild fish. The mean length for brook trout in our sample was 13.4 inches with a range of 9.05-18.1 inches. Although feeding behavior varies throughout the year in Twin Lakes brook trout feed primarily on fantom midges, scuds, and zooplankton.

Rainbow trout Oncorhynchus mykiss: Rainbow trout are native to the west coast of the United States north through Canada and into Southern Alaska. Their range also extends as far south as northern Mexico and into parts of eastern Russia such as the Kamchatka Penninsula. Rainbow trout are spring spawners as water temperatures and daylight begin to increase.

Historically, a redband rainbow trout form may have existed in Twin Lakes but is now displaced by hatchery coastal rainbow trout. The tribe is considering stocking the lake in the future with redbands that may survive and grow better in Twin Lakes than the present coastal form.

Our samples indicate that rainbow trout represent 85-88% of the total trout population. Our samples also indicate that approximately 1-4% are naturally reproducing fish. The mean length of rainbow trout in our sample is 12.36 inches with a range of 8.66-18.5 inches. Although feeding behavior varies throughout the year in Twin Lakes the rainbow trout feed primarily on fantom midges, zooplankton, and scuds. We occasionally sampled small shiners from larger trout stomachs.

Largemouth Bass Micropterus salmoides: Are nonnative to Twin Lakes. Largemouth bass are native to the Missouri and Mississippi River Drainages, the Great Lake Region, south through Georgia and Florida and southeastern Canada. Largemouth bass are spring spawners. Largemouth bass were introduced illegally into Twin Lakes, most likely in the early 1980's.

Largemouth bass are well established in Twin Lakes and inhabit the weed beds and adjacent shoreline habitats in large number. In Twin Lakes, bass over 10 inches feed primarily on golden shiners and crawfish. Smaller bass eat primarily aquatic insects and smaller crustaceans.

The mean length of largemouth bass sampled from Twin Lakes was 7.25 inches with a range of 2.4-20.67 inches.

This bass was sampled and released in South Twin Lake.

Golden Shiners Notemigonus crysoleucas: Are nonnative to Twin Lakes. Their native range is very similar to that of the largemouth bass. Golden shiners spawn in the spring but under good conditions can spawn into late summer. Golden shiners are a natural prey organism for bass in much of their native range. Golden shiners were introduced illegally, most likely in the early 1990's. Bass appear to be limiting golden shiner numbers in Twin Lakes.

Golden shiners are omnivorous, feeding on both plant and animal tissue. In Twin Lakes, approximately 50% of their diet is algae and plant debris. The other 50% of their diet consists of scuds, midges, snails and clams, mayfly and caddisfly, and zooplankton.

Golden shiners grow quikly and can tolerate a wide range of water temperatures and dissolved oxygen levels. They are also very prolific and can deposit up to 250,000 eggs in one season. Depending on temperatures the embryos can hatch in 5-7 days. Without a predator to feed on them they can often overpopulate a water body and cause reduced growth rates in other species such as trout.

Mean golden shiner length in our Twin Lakes samples is 6.14 inches with a range of 1-9.25 inches.

Golden shiner sampled from Twin Lakes. The large circle shows a deeply depressed lateral line distinctive of golden shiners. The small circle shows sickle shape anal fin also indicitive of golden shiners.

Graph represents the estimated number of golden shiners consumed by largemouth bass over the 90 day sampling period. The x-axis represents the size classes of largemouth bass sampled. Values are an average for 2004 and 2005 estimates.

Bridgelip sucker Catostomus columbianus: Are native to Twin Lakes. Their native range is the Columbia and Fraser River systems. Bridgelip suckers are common throughout the Columbia River ecosystem. They generally spawn from April to June. Juveniles feed on zooplankton and aquatic insects. As they mature, their mouth parts develop into a sucker and begin to feed primarily on detritus, algae, and crustacean/insects on the lake bottom. Bridgelip suckers can play an important role of nutrient recycling of dead and dieing material in an aquatic ecosystem. Only one bridgelip sucker was sampled from Twin Lakes.

Are native to Twin Lakes. Their native range extends throughout the Pacific Northwest. Their range also extends into parts of Utah, Nevada, Wyoming, and Montana. Redside shiners do well in both streams and lakes but prefer calm waters with associated weed beds. Redside shiners also tend to move in schools. They can be a good forage fish for large predatory fish. Redside shiners feed on zooplankton and aquatic insects. In Twin Lakes only a few showed up in our samples. Their populations may be depressed by the presence of golden shiners.

Redside shiner. Photo courtesy the State of Utah Natural Resources Division of Wildlife Resources.

A copepod parasite called salmoncula occurs naturally in Twin Lakes. It appears the most frequently on hatchery fish released within the year. These newly released fish are lessed able to withstand the parasite. The wild trout and holdover fish are less affected because they have adapted to the parasite. The parasite becomes most active in July-September when surface temperatures increase. With high temperatures trout often become stressed and are less able to fight off the parasite.

Much of the general fish identification, habitat, range, and life history traits were found in the book "Inland Fishes of Washington." Reference information is found below.

Wydoski, R.S., and R.R. Whitney. 2003. Inland fishes of Washington. American Fisheries Society, Bethesda, Maryland.

Twin Lakes Fact Page