Distribution of Introduced Fishes and Their Effects on High Elevation lake Communities in Lassen Volcanic National Park, CA, USA>

Parker, Michael; Welsh, Hartwell; Sarr, Daniel

Stocking of nonnative fishes into historically fishless lakes represents one of the most widespread manipulations of high elevation aquatic ecosystems throughout mountainous regions of western North America (BAHLS 1992, DUNHAM et al. 2004, PISTER 2001). Ecological impacts of nonnative fish introductions have been well documented and include dramatic reductions and extirpations of large, mobile benthic invertebrate and zooplankton species (BRADFORD et al. 1998, CARLISLE & HAWKINS 1998, PARKER et al. 2001; but see WISSINGER et al. 2006 for contrasting results from New Zealand lakes) and amphibian populations (BRADFORD 1989, KNAPP 2005, PILLIOD & PETERSON 2001). These massive alterations of lake communities can lead to large-scale changes in ecological processes (SCHINDLER et al. 2001, WALTERS & VINCENT 1973) and may extend into the terrestrial environment (MATTHEWS, et al. 2002). Cessation of fish stocking in the 1970s and 80s within national parks and wilderness areas has resulted in many smaller lakes returning to a fishless condition, but self-sustaining fish populations continue to persist in most larger lakes (DONALD 1987, PARKER et al. 2001). Lack of systematic surveys in many areas limits knowledge of current fish distributions and ongoing impacts on native biota (BAHLS 1992). In this study we surveyed permanent lakes and ponds within Lassen Volcanic National Park (LVNP) to (1) describe current fish distributions 20-30 yr after stocking ceased, and (2) assess continuing effects of introduced fishes on the distribution and abundance of zooplankton and littoral benthos. Because most, if not all, natural lakes >2 m deep within LVNP were stocked in the past, current fishless lakes would have lost their fish populations after the cessation of stocking. Differences in invertebrate distribution and abundance between fish and fishless lakes should, therefore, reveal changes in response to fish loss and show whether communities within previously stocked lakes are resilient to major shifts in top predator abundance. This study was done in conjunction with a survey of amphibian distribution within LVNP reported elsewhere ( J. E. STEAD et al., U.S. Forest Service, unpubl.) and is the first complete survey of lakes within LVNP.

Distribution of Introduced Fishes and Their Effects on High Elevation lake Communities in Lassen Volcanic National Park, CA, USA>

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