Pacific Southwest Research Station

Pacific Southwest Research Station
800 Buchanan Street
West Annex Building
Albany, CA 94710-0011

(510) 559-6300

Research Topics: Invasive Species

Research by PSW scientists demonstrates that introduced trout and other species have caused major changes in abundance and distribution of native amphibians, zooplankton, and benthic invertebrates, changes likely to result in federal endangered species listings. Scientists are looking at the impacts of introduced fishes on invertebrates, amphibians, reptiles, birds, and bats.

In many ecosystems throughout California and worldwide, the success and effects of invasive species can strongly influence the dynamics of valued aquatic resources, and perhaps significantly interact with other influential factors. We are attempting to determine what characteristics of forest ecosystems reduce the probability of successful establishment and minimize the effects of aquatic invasive species. Another key component of this invasive species research is the evaluation of genetic constraints on the invasion process. In collaboration with Dr. Andrew Kinziger at Humboldt State University, we are identifying source populations and population bottlenecks for three cyprinid fishes that have become established in the Eel River of northwestern California.

Sacramento pikeminnow: a native of the nearby Sacramento-San-Joaquin drainage, is the invasive fish of interest in the Eel River, primarily because of its propensity to consume fish, including salmonids, and its broad distribution in the invaded system. Research by USDA FS PSW scientists has revealed that predation on salmonids by pikeminnow is localized, but that competition among juvenile pikeminnow and salmonids may also be significant. Further research has revealed that eradication of this invasive species is not feasible but the importance of water temperature to the interactions between pikeminnow and salmonids indicates that management actions focused on shifting parts of the system toward cooler, historic thermal regimes could significantly reduce the influence of invasive fishes on native salmonids.

Publications

• Harvey, Bret C.; White, Jason L.; Nakamoto, Rodney J. 2004. An emergent multiple predator effect may enhance biotic resistance in a stream fish assemblage. Ecology 85(1): 127-133.
• White, Jason L.; Harvey, Bret C. 2003. Basin-scale patterns in the drift of embryonic and larval fishes and lamprey ammocoetes in two coastal rivers. Environmental Biology of Fishes 67: 369-378.
• Harvey, Bret C.; White, Jason L.; Nakamoto, Rodney J. 2002. Habitat relationships and larval drift of native and nonindigenous fishes in neighboring tributaries of a coastal California river. Transactions of the American Fisheries Society 131: 159-170.
• Reese, Carl D.; Harvey, Bret C. 2002. Temperature-dependent interactions between juvenile steelhead and Sacramento pikeminnow in laboratory streams. Transactions of the American Fisheries Society 131: 599-606.
• White, Jason L.; Harvey, Bret C. 2001. Effects of an introduced piscivorous fish on native benthic fishes in a coastal river. Freshwater Biology 46(7): 987-995.
• Harvey, Bret C.; Nakamoto, Rodney J. 1999. Diel and seasonal movements by adult Sacramento pikeminnow (Ptychocheilus grandis) in the Eel River, northwestern California. Ecology of Freshwater Fish 8: 209-215.

Introduced trout: Trout are not native to most high elevation ecosystems and have been extensively used to stock lakes for recreational fishing, including the Sierra Nevada and Klamath-Siskiyou Wilderness Areas. According to Executive Order 13112, an "invasive species" is defined as a species that is 1) non-native (or alien) to the ecosystem under consideration and 2) whose introduction causes or is likely to cause economic or environmental harm or harm to human health. Considerable published information now exists to demonstrate that non-native trout have caused environmental harm to high elevation aquatic ecosystems. PSW studies have demonstrated that trout have caused major changes in abundance and distribution of native amphibians, zooplankton, and benthic invertebrates, changes likely to result in federal endangered species listings. Moreover, amphibian declines caused by trout introductions have also lead to declines in predators (example: the mountain garter snake, the only snake native to high elevation ecosystems), thus trout introductions have resulted major disruption and cascading effects throughout the ecosystem. When trout are not native to aquatic ecosystems, and their introductions result in major environmental changes, they can be considered invasive species. Future work must include developing ways to manage fish stocking to minimize deleterious effects and restore native species.

Klamath-Siskiyou Bioregion

High Mountain Lake Fish Stocking Studies

Research is being conducted by:

• Bret Harvey
• Hartwell Welsh
• Kathleen Matthews