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Abstract
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.
Highlights
Nonnative fish introductions are commonly associated with reduced food web efficiency, extirpation or reduction of native species, and decreased sport fishery production (MacRae and Jackson 2001; Pimentel et al 2000; Vander Zanden 1999)
The objectives of this paper are to: a) determine current distribution and relative abundance of two warm water nonnative fish species, largemouth bass and bluegill, within Lake Tahoe, b) sample established populations in Tahoe Keys and Taylor creek by electrofishing to determine their abundance compared with native fishes, and c) discuss potential impacts of nonnative fish on native fishes
A total of 11 species were captured by electrofishing in the Tahoe Keys in 2006 (Table 1) with largemouth bass and bluegill in highest abundance
Summary
Nonnative fish introductions are commonly associated with reduced food web efficiency, extirpation or reduction of native species, and decreased sport fishery production (MacRae and Jackson 2001; Pimentel et al 2000; Vander Zanden 1999). Lake Tahoe, with an extensive history of nonnative aquatic species introductions, has exemplified all the post invasion impacts mentioned above (Vander Zanden et al 2003b; Tassell et al 2000; Goldman et al 1979). Aquatic species introductions before the 1980’s were done intentionally to increase sport fishery production, but the opposite effect resulted when growth rates of top fishery species were reduced (Clarke and Bennett 2002, Tassell et al 2000). In the late 1980’s a suite of warm water fish species were observed in a near shore marina, the Tahoe Keys. These species are thought to have been illegally introduced by anglers (Reuter and Miller 2000).
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