| Popis: |
In the last 125 years numerous invasive species have been introduced into Lake Tahoe. In recent years there has been an invasion of warm water fishes including largemouth bass [Micropterus salmoides (Lacepede, 1802)], and bluegill [Lepomis macrochirus (Rafinesque, 1820)]. These species threaten to displace and decrease native fish populations, and reduce nearshore water clarity. It is believed, with the help of climate change increasing lake temperature, these species are spreading to other areas from established populations on the south shore. Our objective was to determine current distribution and the potential impacts of warm water nonnative fishes. Snorkel surveys were conducted bi-weekly from May to November 2006 and electrofishing was conducted four times within the snorkel survey period at locations where warm water species are already established. Snorkel surveys and electro-fishing revealed that 57% of monitored sites contained warm water nonnative fish species. At electro-fish sites, number of native fish decreased with increasing nonnative fish species. Comparing historical and current diet data of natives and nonnatives indicated the latter are consuming the same diet items that native fish consumed historically. As a result, where nonnative and native fish habitats overlap, predation on and competition with native fish is likely. Current distributions of nonnative species found during this study are where the next established populations can be expected if their spread is not controlled. |
