PARENT SESSION
Poster Session 7: Invasive Species.

Monday, August 2 Presentations from 5:00 PM to 6:30 PM, Exhibit Hall A 1.

Seasonal removal of invasive stream predators to protect sensitive amphibian populations.

Watters, Tyler^*,1, Jones, Laura^*,1, O'Hare, Shawn^*,2, Kerby, Matthew¹, Kats, Lee¹, ¹ Pepperdine University, Malibu, CA² Mountains Restoration Trust, Calabasas, CA

ABSTRACT- The spread of invasive species is widely believed to be a contributing cause of amphibian population declines in numerous countries around the world. Invasive aquatic predators have been known to attack adult amphibians and consume both eggs and larvae. In Southern California, streams are increasingly invaded by exotic crayfish (Procambarus clarkii) that are sold as fishing bait throughout the state. Streams where crayfish have been established for decades have already seen the extirpation of amphibians. In streams where crayfish have invaded more recently, amphibians continue to attempt to breed. Given that crayfish are difficult or impossible to eliminate from stream habitats, we chose to reduce crayfish numbers using both natural and artificial barriers, traps and hand nets and thereby provide crayfish-free zones for amphibian breeding, oviposition and metamorphosis. Amphibian numbers and activity were monitored in two control regions and three crayfish removal areas. We found significantly more amphibian activity in crayfish-free zones when compared to two control regions where crayfish densities remained high. For amphibian species of concern, mean densities throughout all life history stages were greater in crayfish removal areas. California tree frog (Hyla cadaverina) tadpole densities were six times greater in crayfish removal areas and metamorph densities were two times greater in crayfish removal areas. Densities of California newt (Taricha torosa) larvae were up to ten times greater in crayfish free areas. These data indicate that exotic crayfish negatively impact amphibian survival throughout all stages of development and suggest that temporary restoration (removal) efforts can alleviate predation pressure on these sensitive native populations. While complete elimination of stream exotics may be difficult, management of exotic predators through natural flood events combined with manual removal efforts may prove an effective option.

Key words: amphibians, aquatic ecology, invasive species, rare species