Fish
There are 6 species of fish native to the lower elevations in Yosemite NP, and 9 non-native fish (7 species and 2 hybrids) throughout the park. The non-native count includes rainbow trout (Oncorhynchus mykiss) living at higher elevations.
Blocked by high waterfalls, native fish species were originally limited to the lower elevations of Yosemite. Today, about 245 of the water bodies in Yosemite (including many at high elevations) have non-native fish because of earlier fish stocking. More than 33 million fish were planted in many of Yosemite's aquatic ecosystems between 1887 and 1990. Most of these were trout for sport fishing. Initially, these fish were carried in jugs and coffee cans by people and were even hauled in by mules. By 1952, the procedure evolved to loading the fish into airplanes, flying over lakes, and dropping them into lakes from the sky.
Because most bodies of water in Yosemite were naturally fishless, many of its aquatic species evolved without fish. These introduced fish act as predators and have a significant impact on native species such as the Sierra Nevada yellow-legged frog. This same story has occurred throughout much of the high country in the Sierra Nevada. However, the National Park Service, Forest Service, California Department of Fish and Wildlife and other agencies have undertaken efforts to remove fish from some originally fishless lakes using large nets that catch the fish by the gills. Multiple years of successive netting are required to completely remove fish from a lake.
More information:
National Park Service- Fish: http://www.nps.gov/yose/learn/nature/fish.htm
National Park Service- Fish List: http://www.nps.gov/yose/learn/nature/fishlist.htm
