Pesticides in mountain yellow‐legged frogs (Rana muscosa) from the Sierra Nevada Mountains of California, USA

Abstract

In 1997, pesticide concentrations were measured in mountain yellow-legged frogs (Rana muscosa) from two areas in the Sierra Nevada Mountains of California, USA. One area (Sixty Lakes Basin, Kings Canyon National Park) had large, apparently healthy populations of frogs. A second area (Tablelands, Sequoia National Park) once had large populations, but the species had been extirpated from this area by the early 1980s. The Tablelands is exposed directly to prevailing winds from agricultural regions to the west. When an experimental reintroduction of R. muscosa in 1994 to 1995 was deemed unsuccessful in 1997, the last 20 (reintroduced) frogs that could be found were collected from the Tablelands, and pesticide concentrations in both frog tissue and the water were measured at both the Tablelands and at reference sites at Sixty Lakes. In frog tissues, dichlorodiphenyldichloroethylene (DDE) concentration was one to two orders of magnitude higher than the other organochlorines (46+/-20 ng/g wet wt at Tablelands and 17+/-8 Sixty Lakes). Both gamma-chlordane and trans-nonachlor were found in significantly greater concentrations in Tablelands frog tissues compared with Sixty Lakes. Organophosphate insecticides, chlorpyrifos, and diazinon were observed primarily in surface water with higher concentrations at the Tablelands sites. No contaminants were significantly higher in our Sixty Lakes samples.

Pesticide concentrations in frog tissue and wetland habitats in a landscape dominated by agriculture

“…From a landscape perspective, many of the water soluble herbicides (atrazine) were detected frequently in water and less frequently in sediment and tissues, whereas several more hydrophobic compounds (DDE, pyraclostrobin) were detected predominantly in sediment and more frequently in tissues (Table 3). Wetland sediment can be a sink for hydrophobic contaminants and our results support previous work documenting the bioaccumulation of agrochemicals in amphibians (Smalling et al, 2013b;Fellers et al, 2004). Frogs are exposed to pesticides in both the aquatic and terrestrial environments and in many cases wetland habitats where they are captured do not completely explain their contaminant body burdens.…”

Mitigating amphibian chytridiomycoses in nature

“…However, without a solid understanding of host-pathogen dynamics and the biology of the host and pathogen in the landscape, translocations/reintroductions have little probability of success. Several attempts have been made to repatriate amphibians affected by chytridiomycosis in Europe, North America, the Caribbean and Africa but none have led to successful, long-term amphibian re-establishment [4,26,28,29] (but see [30] for evidence of shortterm post-release survival). Although the majority of failures have been associated with the re-emergence of lethal chytridiomycosis in the translocated/reintroduced species, the cause behind failure to re-establish in almost every case could not be attributed clearly [26,28] (but see [11]).…”

Deposition and accumulation of airborne organic contaminants in Yosemite National Park, California

“…The most dramatic decline has been observed for the mountain yellow-legged frog (Rana muscosa), which has disappeared from more than 90% of its historic range in the Sierra Nevada [7]. Several hypotheses have been proposed to explain these declines, including the introduction of nonnative fish species [8], elevated levels of ultraviolet radiation [9], recent emergence of the chytrid disease [5], and increasing pesticide use in adjacent agricultural areas [10][11][12]. Davidson and Knapp [13] suggested that multiple stressors may be involved, although upwind pesticide application appears to have had the greatest influence on amphibian declines in the Sierras.…”

“…Several studies have reported pesticide concentrations in fish and amphibians [6,11,[14][15][16][17][18], although measurements of pesticides in the atmosphere and aquatic habitats are relatively sparse. Pesticide concentrations in wet deposition [19] and in air, dry deposition, and surface water [2] were measured in Sequoia and Kings Canyon National Parks (Fig.…”