Association of amphibians with attenuation of ultraviolet-b radiation in montane ponds

Ambient ultraviolet-b (UV-B) radiation (280320 rim) has increased at north- temperate latitudes in the last two decades. UV-B can be detrimental to amp hibians. and amphibians have shown declines in some areas during this same period. We documented the distribution of amphibians and salmonids in 42 re mote, subalpine and alpine ponds in Olympic National Park, Washington, Unit ed States. We inferred relative exposure of amphibian habitats to UV-13 by estimating the transmission of 305- and 320-nm radiation in pond water. We found breeding Ambystoma gracile, A. macrodacotylum and Rana cascadae at 33 %, 31%, and 45% of the study sites, respectively. Most R. cascadae bred in fishless shallow ponds with relatively low transmission of UV-13. The relat ionship with UV-13 exposure remained marginally significant even after the presence of fish was included in the model. At 50 cm water depth, there was a 55% reduction in incident 305-nm radiation at sites where breeding popul ations of R. cascadae were detected compared to other sites. We did not det ect associations between UV-13 transmission and A. gracile or A. macrodacty lum. Our field surveys do not provide evidence for decline of R. cascadae i n Olympic National Park as has been documented in Northern California, but are consistent with the hypothesis that the spatial distribution of R. casc adae breeding sites is influenced by exposure to UV-B. Substrate or pond de pth could also be related to the distribution of R. cascadae in Olympic Nat ional Park.