Challenges of Monitoring Headwater Amphibians: Searching for a Pattern Among the Warts

Lowell Diller

Green Diamond Resource Company

Korbel, California

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ABSTRACT

DILLER, LOWELL V., and LAURA L. BURKHOLDER
Green Diamond Resource Company, Korbel, CA
ldiller@greendiamond.com

Challenges of Monitoring Headwater Amphibians: Searching for a Pattern Among the Warts

As part of developing an aquatic habitat conservation plan on private timberlands, we attempted to use obligate headwater amphibian species to monitor potential impacts of timer harvest. Since 1997, we have been monitoring populations of southern torrent salamanders(Rhyacotriton variegatus) and coastal tailed frogs (Ascaphus truei). The goal was to compare changes in populations of these amphibians by employing a paired sub-basin design using randomly selected streams in sub-basins with (treatment) and without (control) timber harvest. The initial problem was to find a sufficient number of suitable streams with particular difficulty locating suitable control streams. To date, 30 and 18 monitoring reaches have been established for torrent salamanders and tailed frogs, respectively. Estimating relative abundance of torrent salamanders has proved problematic, because the process of searching for the animals appears to have lasting negative impacts on their habitat. The solutions may be a "lighter touch" survey approach and only attempting to determine presence/absence of salamanders. Estimating larval populations of tailed frogs has been successful, but high annual variation made interpreting the results problematic. In hopes of understanding this phenomenon, we began a mark-recapture study of post-metamorphic tailed frogs in 2002. The adults appear to be less variable compared to the larval populations, but it requires substantial effort to obtain a useful estimate through mark-recapture. The options are to have a large research budget that would allow an integrated approach to monitor both larvae and adult frogs or extend the larval monitoring to a longer interval (>10 years).