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Applied Herpetology
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Amphibian decline and aquatic pollution: Effects of nitrogenous fertiliser on survival and development of larvae of the frog Rana temporaria
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Due to intensified agricultural practice, nitrate concentrations of surface waters have increased since the Second World War and are expected to continue to rise. Little is known about how these nitrate levels affect the early stages of amphibians in the field situation and if they contribute to the decline of amphibian populations. Exposure of Rana temporaria larvae to ammonium nitrate in a replicated pond experiment increased mortality, and mass at metamorphosis, but extended the larval period. In a second experiment exposure of both R. temporaria and Bufo bufo to elevated levels of nitrate but low levels of ammonium did not affect larval survival and larval period, but caused an increase in mass at metamorphosis for both species. When R. temporaria eggs were exposed to calcium nitrate in enclosures in a pond, survival at tailbud stage and at hatching did not differ from controls. The results suggest that ammonium nitrate can be detrimental to amphibian development but that increased nitrate levels have no direct adverse effects on tadpoles of R. temporaria and B. bufo and eggs of R. temporaria but indirectly enhance mass at metamorphosis.
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Toxicity of herbicide formulations to frogs and the implications for product registration: A case study from Western Australia
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Growing concern about the decline of amphibian populations has highlighted the need to assess the potential impact of agricultural chemicals on these animals. Although the relative sensitivity of amphibians to the toxic effects of pesticides and other environmental contaminants has yet to be established, the perceived vulnerability of amphibians to pesticide effects may actually be attributable to their specific habitat requirements. Shallow temporary ponds, essential to the life cycles of many amphibians, are also areas where pollutants may accumulate without substantial dilution. Research in Western Australia has highlighted the potential risk that agricultural chemicals may pose to fauna that inhabit low dilution environments, and indicates that the data currently required for pre-registration assessment of pesticides may be inadequate to effectively protect these environments.
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Leaf litterbags: Factors affecting capture of stream-dwelling salamanders
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Many standardized techniques are used to monitor terrestrial salamanders, but fewer protocols have been tested for inventorying stream-dwelling salamanders, especially larvae. One new method uses artificial refugia (leaf litterbags) placed in shallow streams. Totest the utility of litterbags, we sampled three transects of 6 litterbags each (2 large, 2 medium, and 2 small) placed in five small, medium, and large streams in Great Smoky Mountains National Park, an area of high aquatic salamander diversity. We captured 690 larval, juvenile, and adult stream-dwelling salamanders of 11 different species from June to November 2000 in the 90 litterbags. Large and medium-sized litterbags were most effective at sampling salamanders in small streams, but all bag sizes worked equally well in medium and large streams. The number of salamanders captured varied seasonally,with most captures in June and July. The depth of bag submergence significantly influenced litterbag use by adult and larval salamanders, but had no effect on juvenile salamanders. Although the technique was effective for determining the presence of many salamander larvae, variation in the numbers of individuals captured and the inability to relate captures to overall abundance make it impossible to monitor trends without considerable additional effort. The ease of deployment and non-destructive methodology suggest that litterbags could be useful in determining salamander presence during inventory programs, especially when the time to sample a large number of sites is limited.
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Surveying for hellbender salamanders, Cryptobranchus alleganiensis (Daudin): A review and critique
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Wereview the wide array of techniques and their variants used in studying a cryptobranchid salamander and discuss their advantages and disadvantages. Electroshocking surveys are strongly discouraged because of the great potential for damaging reproductive success, immune systems, and their questionable effectiveness. Because successful Cryptobranchus alleganiensis nesting sites appear to be quite limited, the use of Peavy hooks and crowbars to breakup bedrock or dislodge large cover rocks should be restricted. Currently, skin-diving surveys coupled with turning objects is the only method shown to obtain all sizes of gilled larvae and multiple age groups of non-gilled and adult C. alleganiensis in brief periods.
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Ecotoxicology of crocodilians
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All species of crocodilians are long-lived, top-level carnivores that are integral components of aquatic, wetland, and marine/estuarine ecosystems. However, they are often excluded from studies on environmental contamination and ecological risk assessments. Available organic (including endocrine disrupters), inorganic, and radionuclide contaminant accumulation and effects studies for crocodilians were reviewed and summarized to facilitate the use of existing data, reveal the primary information gaps, promote the inclusion of crocodilians in environmental contamination studies and ecological risk assessments, encourage further ecotoxicological studies, and assist in the development of future research priorities. Environmental contamination studies were not available for more than half of the world's 23 crocodilian species. The majority of information available (almost 70% of reviewed studies) concerning environmental contaminants and their accumulation and effects on crocodilians was for the American alligator (Alligator mississippiensis) as a result of the considerable research effort on the effects of endocrine-disrupting contaminants (EDCs) on the alligator population inhabiting Lake Apopka, Florida and the many studies concerning mercury contamination in the southeastern United States, considered to be the most serious environmental threat to that area. With the exception of the extensive research on the effects of EDCs on Lake Apopka's alligators, research on the effects of environmental contaminants on crocodilians is lacking. The review indicated that the effects of EDCs on crocodilians are not confined to Lake Apopka and may occur in crocodilians in many parts of the world, especially in developing tropical areas where organochlorine pesticides are used extensively. For inorganic contaminants, determining the effects of mercury on crocodilians should be the highest research priority.
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