Importance of water contaminant testing in amphibian reintroduction programs

Abstract

Amphibians face various threats, including habitat loss and contamination, disease, unsustainable harvesting, invasive species, and climate change (Luedtke et al., 2023). Population declines have prompted conservation initiatives, including conservation breeding (i.e., captive breeding) and translocation (i.e., reintroduction) programs, to prevent extinction. Yet, the effectiveness of these programs depends greatly on the survival of the released amphibians. Consequently, the health status of individuals prior to reintroductions and the quality of the reintroduction habitat are key factors influencing survival after reintroduction. To enhance criteria used for release-site selection, we recommend measuring contaminants in site water, conducting ex situ exposures to site water, or both to screen for toxic levels of anthropogenic contaminants and assist in predicting amphibian survival at reintroduction sites. Contaminant screening is not a focus of the IUCN Guidelines for Amphibian Reintroductions and Other Conservation Translocations (IUCN/SSC, 2013; Linhoff et al., 2021) or the reintroduction guidelines of AmphibianArk (2018), except for screening of nitrogen and phosphorus (Egea-Serrano & Tejedo, 2014; Grant et al., 2014; Gustafson et al., 2009).

Chemical pollution is a large and growing global problem. Over 140,000 new chemicals and pesticides have been synthesized since 1950, and, of these, 5000 are produced in high volumes and are widely dispersed in the environment (Landrigan et al., 2018). Several environmental contaminants have negative impacts on amphibians, including reduced reproductive success, growth, immune function, and survival (Blaustein et al., 2018; Sparling et al., 2010). There is evidence of interactive effects of contaminant exposure and disease susceptibility that suggest higher prevalence of disease with contaminant exposure (e.g., Ranaviruses and pesticides [Blaustein et al., 2018]). Therefore, it is critical to avoid reintroduction sites with concentrations of chemical contaminants that exceed environmental quality guidelines set by regulatory authorities that could lead to one of or both short- and long-term adverse health outcomes in amphibians.

Collection of Oregon spotted frog reintroduction site water for contaminant testing. Photo by P. Sardari

Currently, there are few reintroduction programs for amphibians that prescreen for potential contaminants unless significant contaminant spills have occurred or it is a well-known contaminated site, although some programs do measure basic water quality parameters (e.g., hardness, dissolved organic carbon, pH, nutrients [Pollard et al., 2017]). Only 2 programs in British Columbia (northern leopard frog [Lithobates pipiens] and Oregon spotted frog [Rana pretiosa]) have examined contaminants at current and potential larval reintroduction sites to determine whether contaminants are present at concentrations above Canadian and US regulatory authority environmental quality guidelines and have used this information to select sites (danis et al., 2019; McKibbin et al., 2008). Through contaminant screening, contaminants of concern to larval amphibians can be identified prior to reintroduction. For example, Glooschenko et al. (1992) found that amphibian presence is negatively correlated with metal contamination at certain concentrations and recommended no reintroductions in these locations. We recommend that during pretranslocation planning and risk assessment (Linhoff et al., 2021), practitioners identify land uses, current and historical, to determine which contaminants may be present and, thus, which contaminants to measure. In addition, if restoration of the site is planned, contaminants in surrounding soil or sediments may be released into reintroduction habitat; thus, postrestoration contaminant measurements should be conducted. Monitoring of general water chemistry parameters and contaminants should be conducted during periods when aquatic larvae are present and after large water influxes to provide the most relevant data to predict site suitability for reintroductions.

Although standard exposure protocols were not followed, the findings of Pollard et al. (2017) suggest that ex situ followed by in situ exposures to site water is an effective screening approach to assess site water quality. The Organisation for Economic Co-operation and Development's (OECD's) larval amphibian growth and development assay (LAGDA) and amphibian metamorphosis assay (AMA) offer a structured ex situ methodology for assessing the effects of chemicals or site waters on growth, development, and survival of larvae in a laboratory setting (OECD, 2009, 2015). Furthermore, there are differences in naturally enriched substances (e.g., metals, nutrients), anthropogenic contaminants (e.g., pesticides, flame retardants), and basic water quality parameters across aquatic habitats relative to the treated water typically used for captive-breeding conditions. As a result, animals may not be acclimated to reintroduction site water, which may cause reduced survival. Therefore, OECD methods may also be considered for acclimation assays of larval amphibians prior to release at reintroduction sites to optimize survival. For example, hatchery-reared salmon show reduced acclimatization and adaptation compared with wild populations at release sites (Araki & Schmid, 2010; Chittenden et al., 2010; Christie et al., 2016). Acclimatization and adaptation provide mechanisms for populations to reduce the potential negative effects associated with elevated levels of environmental contaminants (Flynn et al., 2019; Whitehead et al., 2011). Conservation practitioners can use these assays to isolate and assess the potential risks of poor-quality site water, better predict survival after reintroduction, and ensure animals are acclimated to reintroduction site waters.

As an alternative to using declining or rare species in these ex situ exposures to site waters, the use of closely related species with similar ecological attributes may be substituted. Although the IUCN's guide on amphibian translocation and reintroduction covers various aspects of reintroduction, such as physical habitat and disease risk assessment and postrelease health surveillance (Linhoff et al., 2021), using these standardized preexposure tests, such as the LAGDA or AMA, will provide useful data for assessing the impacts of complex site water characteristics (i.e., contaminants, basic water quality parameters) on survival, growth, and development. Although surrogate species can be used, sacrificing small numbers of larvae may be justified when the information gained could significantly increase the success of reintroduction efforts.

We recommend 2 steps to increase the effectiveness of amphibian reintroduction programs—first, assess contaminant risks that naive larvae might encounter by measuring contaminants in water and sediments and determining whether concentrations exceed local environmental quality guidelines. Second, we recommend preexposure of captive-bred offspring (embryos, larvae, or both) to site water through OECD protocols to determine the potential impacts of reintroduction site waters on survival, growth, and development and to acclimate animals to site waters prior to release. Integrating these steps into existing reintroduction protocols would strengthen current conservation approaches, ensuring that reintroduced populations have the best possible conditions for success.