The impact fish stocking has on aquatic insects in mountain lakes can be rapidly reversed by removing non-native trout, according to a study completed by U.S. Forest Service and University of California, Davis, scientists.
Their findings appear in a current online issue of the journal Freshwater Biology where they describe experiments that examined some effects of fisheries management practices now in use in California mountain lakes where fish do not naturally occur.
The research has value because the vast majority of mountain lakes in the western United States have been stocked with trout for several decades. Studies following lake restoration to fishless conditions will help scientists and wildlife managers understand the impact of past actions and future decisions.
Since 2000, the California Department of Fish and Game has reduced the number of wilderness lakes it stocks by about half because non-native fish feed on declining species like the Sierra Nevada yellow-legged frog. Federal and state agencies have also begun removing introduced trout in some lakes because fish can survive for years and continue feeding on sensitive species, after stocking has ceased.
Until now, scientists seldom studied the response of aquatic insect populations to the removal of non-native trout.
"These highly-mobile predators don't naturally occur in small alpine lakes so they have significant top-down effects on ecosystems," said Karen Pope, a Forest Service scientist at the Pacific Southwest Research Station and one of the study's authors. "They prey upon aquatic insects that are also food for other insects, amphibians, birds and bats."
In 2003, Pope and her colleagues began testing the effects introduced fish had on lake ecosystems in 16 lakes in Northern California's Trinity Alps Wilderness.
The National Science Foundation, U.S. Forest Service, California Department of Fish and Game, and University of California funded the study, which mat
|Contact: Roland Giller|
US Forest Service, Pacific Southwest Research Station