Mountain Yellow-legged Frog Breeding Dynamics in Dusy Basin, Kings Canyon Nat'l Park: ... Snowpack ... Lake Water Level (and) recruitment...

Krishna Feldman

USDA Forest Service, Pacific Southwest Research Station

Berkeley, CA

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ABSTRACT

MATTHEWS, KATHLEEN R.1, KRISHNA V. FELDMAN1*, and IGOR LACAN2
1USDA Forest Service, Pacific Southwest Research Station, Berkeley, CA, kmatthews@fs.fed.us; 2University of California, Berkeley, Department of Environmental Science, Policy and Management, Berkeley, CA

Mountain Yellow-legged Frog (Rana muscosa) Breeding Dynamics in Dusy Basin, Kings Canyon National Park: How do Variable Snowpack and Lake Water Levels Affect Recruitment?

Our 1997-2005 surveys of mountain yellow-legged frogs in Dusy Basin found that most breeding (>70% of egg masses) occurred in shallow (<3m) lakes prone to late summer drying. Up to 4 years of tadpole recruits can be lost when lakes dry due to their extended tadpole phase. In upper Dusy Basin, more than 60% of egg masses were found in one shallow lake (max depth = 1m) that often undergoes a dramatic decrease in volume during years with low snowpack and precipitation. This breeding lake was totally dry by the end of the summer in 4 of 9 years; presumably, all tadpoles died because there was no connectivity to other water bodies. More breeding may now occur in shallow lakes vulnerable to drying because the largest lake in upper Dusy Basin has fish. Few egg masses were found in this larger, deeper lake (max depth = 10 m) either because frogs no longer breed in this lake or egg masses are quickly eaten by fish and not observed in surveys. Other lakes used for breeding are deeper and did not totally disappear in the low snowpack years. In lower Dusy Basin, over 90% of egg masses are found in one (max depth = 1.5 m) of four adjacent lakes; this lake has not dried up in surveys conducted from 1998-2005. To determine if there is a link between water availability and recruitment into adults, we compared the number of metamorphs in breeding lakes prone to drying with those breeding lakes not prone to drying. The lakes that intermittently dry up show low recruitment of metamorphosed frogs. The exclusion of successful frog breeding from the deepest lakes where recruitment may be more successful is another impact of introduced fish on this declining frog population.