A weight-of-evidence approach for defining thermal sensitivity in a federally endangered species

Managing for threatened and endangered species under changing environmental conditions is a challenge faced by resource managers worldwide. Lack of basic knowledge of the biology and habitat requirements of these species can contribute to this difficulty but is exacerbated by the limitations of working with rare species (i.e. few individuals) or unrefined and non-lethal methods for evaluating stress. A weight-of-evidence approach was used to evaluate the thermal biology of the federally endangered dwarf wedgemussel (Alasmidonta heterodon), using cumulative results from multiple experimental assessments, co-occurring species, and their host fish to begin defining the thermal limits and optimal conditions for the species. Results suggest that dwarf wedgemussel and its host fish are thermally sensitive species compared with other Atlantic-slope mussels, with a lower critical thermal maximum (CTM) and the selection of reduced temperatures during choice experiments. Physiological studies resulted in a lack of statistical significance, primarily owing to low power, which was a function of sample size - an unavoidable problem when studying rare species. Given these limitations, thermal choice and CTM may be more useful end points than physiological processes such as clearance and respiration rates when dealing with sample-size limitations. These results suggest that management strategies that avoid exposing dwarf wedgemussel and its thermally sensitive host fish to extreme temperatures could be important for species conservation.