April 11, 2008

The Fish Stocking Program Loses Its Way

Following the end of World War II, the California Department of Fish and Game (CDFG) began experimenting with using airplanes to stock trout into High Sierra lakes. Following initial successes, this program was soon used to stock millions of fingerling trout into lakes in remote areas throughout the State. In the Sierra Nevada, the efficiency of aerial stocking allowed thousands of lakes to be stocked on a regular basis, including those too remote to have been stocked previously. As such, the aerial stocking program created abundant new opportunities for anglers, but also impacted the lakes and streams of the High Sierra on a scale not seen since the melting of the Sierran ice cap 12,000 years earlier. Mountain yellow-legged frogs, already in serious decline due to the smaller-scale fish stocking efforts that preceded the aerial stocking program, were now eliminated from hundreds of additional lakes. On national forest lands, where the CDFG had authority over fish and wildlife, virtually every water body that was suitable for trout was stocked, and mountain yellow-legged frogs were relegated to a handful of lakes that had for one reason or another never been added to the fish stocking list. In the Sierran national parks (Sequoia, Kings Canyon, Yosemite) where authority over fish and wildlife rested with the National Park Service, stocking was less intensive but still resulted in trout being introduced to the majority of water bodies.

Ironically, aerial fish stocking, a remarkable achievement in its time, led to the CDFG backcountry fish stocking program losing its way. Airplanes were a far more efficient means of stocking trout than the previously-used mules, and that efficiency brought with it a certain blindness. For example,
thousands of lakes were stocked every year or every other year without any thought being given to whether particular lakes needed to be stocked to provide angling opportunities. Some of these stocked lakes were so remote that they rarely received any human visitors. In other lakes, originally- introduced trout reproduced naturally in inlet and outlet streams and quickly developed self-sustaining populations. Ignorant of their self-sustainability, the CDFG added thousands of additional fingerlings with each stocking. Blinded by the success of the aerial stocking program, the program remained virtually unchanged for 50 years.

By the late 1990s, researchers studying amphibian declines in the Sierra Nevada and in other mountain ranges in the western U.S. were increasingly convinced that introduced trout were a major cause of frog disappearances. Surveys of thousands of water bodies in the High Sierra showed that the presence of trout greatly reduced the likelihood of finding mountain yellow-legged frogs and other vertebrate and invertebrate taxa. Furthermore, experimental removal of trout from a handful of lakes resulted in rapid recovery of mountain yellow-legged frog populations. With mounting evidence indicating that trout introductions had caused unintended but dramatic impacts to Sierra Nevada aquatic ecosystems, and with t
he potential listing of the mountain yellow-legged frog under the Endangered Species Act, pressure was building on the CDFG to modify the stocking program to reduce these impacts. After 50 years of tremendous public support, it was clear that the program had fallen victim to its own success.

Next week: How change finally came (or didn't come) to the stocking program....

For additional reading, check out the following papers (available at http://vesr.ucnrs.org/pages/knapp/publications/publications.html):

Knapp, R. A., and K. R. Matthews. 2000. Non-native fish introductions and the decline of the mountain yellow-legged frog from within protected areas. Conservation Biology 14:428-438.

Armstrong, T. W., and R. A. Knapp. 2004. Response by trout populations in alpine lakes to an experimental halt to stocking. Canadian Journal of Fisheries and Aquatic Sciences 61:2025-2037.

Knapp, R. A., D. M. Boiano, and V. T. Vredenburg. 2007. Removal of nonnative fish results in population expansion of a declining amphibian (mountain yellow-legged frog, Rana muscosa). Biological Conservation 135:11-20.

Back to The Mountain Yellow-legged Frog Site.

1 comment:

  1. Fascinating stuff. Thanks for the posts.