Distribution of introduced fishes and their effects on high elevation lake communities in Lassen Volcanic National Park, CA, USA

Abstract

Stocking of nonnative fishes into historically fish1ess 1akes represents one of the most widespread manipu1ations of high e1evation aquatic ecosystems throughout mountainous regions ofwestern North America (BAHLS 1992, DuNHAM et al. 2004, PISTER 2001). Eco1ogica1 impacts ofnonnative fish introductions have been well documented and include dramatic reductions and extirpations of 1arge, mobi1e benthic invertebrate and zoop1ankton species (BRADFORD et al. 1998, CARLISLE & HAWKINS 1998, PARKER et al. 2001; but see WisSINGER et al. 2006 for contrasting resu1ts from New Zea1and 1akes) and amphibian popu1ations (BRADFORD 1989, KNAPP 2005, PILLIOD & PETERSON 2001). These massive a1terations of 1ake communities can 1ead to 1arge-sca1e changes in eco1ogica1 processes (SCHINDLER et al. 2001, WALTERS & VINCENT 1973) and may extend into the terrestria1 environment (MATTHEWS et al. 2002). Cessation of fish stocking in the 1970s and 80s within nationa1 parks and wi1derness 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). Laek of systematic surveys in many areas limits know1edge of current fish distributions and ongoing impacts on native biota (BAHLS 1992). In this study we surveyed permanent 1akes an d ponds within Lassen Volcanic Nationa1 Park (LVNP) to (l) de seri be current fish distributions 20-30 yr after stocking ceased, and (2) assess continuing effects o f introduced fishes on the distribution an d abundance ofzoop1ankton and littoral benthos. Because most, ifnot all, naturallakes >2 m deep within LVNP were stocked in the past, current fishless 1akes would have 1ost their fish populations after the cessation o f stocking. Differences in invertebrate distribution and abundance between fish and fishless lakes should, therefore, reveal changes in response to fish 1oss and show whether communities within previous1y stocked lakes are resilient to major shifts in top predator abundance. This study was don e in conjunction with a survey o f amphibian distribution within LVNP reported elsewhere ( J.E. STEAD et al., U. S. Forest Service, unpubl.) and is the first complete survey oflakes within LVNP.