Use Frequency and Duration Analysis for Determination of Thermal Habitat Thresholds: Application for Conservation of Alasmidonta Heterodon in the Delaware River, USA

A novel approach for setting thermal tolerance recommendations for an endangered aquaticspecies will be proposed in this paper. The method, Uniform Continuous Above Threshold (UCAT)analysis, evaluates the duration and frequency of continuous events where the temperature is higherthan a specified value and identifies temperature levels that, because of their rare occurrence in thepast, can be considered stressor thresholds. The UCAT analysis was applied to set thermal tolerancerecommendations for Alasmidonta heterodon, an endangered mussel species in the Upper DelawareRiver. We found that a maximum daily water temperature of 26.5°C lasting for more than 7 days is arare event in the A. heterodon population centers in Upper Delaware River and consequently thiscondition should be avoided by adjusting already regulated cold-water releases from upstreamreservoirs. Knowledge of temperature thresholds and their relationship with persistent low-flowperiods provided further decision support for the development of flow management recommendationsfor species protection. The case study of A. heterodon in the Upper Delaware River demonstrates that,in the absence of laboratory research on physiological temperature tolerance of a species, UCATanalysis provides an effective approximation of thermal tolerances. Due to quick and easy preparationand analysis this method may also have a broader application to habitat studies of other animal groups.