Predicting the responses of animals to environmental changes is a fundamental goal of ecology and is necessary for conservation and management of species. While most studies focus on relatively gradual changes, extreme events may have profound and lasting impacts on populations. Animals may respond to major disturbances such as hurricanes by seeking shelter, migrating, or they may fail to respond appropriately. We assessed the effects of Hurricane Irma (2017) on the behavior and survival of juvenile bull sharks (Carcharhinus leucas) within a nursery of the Florida Coastal Everglades using long-term monitoring and acoustic telemetry. Specifically, we investigated the environmental cues sharks use to sense and respond to an impending storm, determined the factors that impact the timing of return to behaviors similar to those found before the storm, assessed whether demographic factors influenced behavioral responses, and established if the hurricane affected macrohabitat use patterns.
Results/Conclusions
All 14 tagged sharks attempted to leave the shallow waters of the Shark River Estuary before the hurricane impact, but individuals varied in the timing and success of these movements. Three sharks moved downstream relatively late and may have died before leaving the system. Nine of the remaining 11 sharks (~82%) eventually returned to the array within weeks or months of the storm. Six of these returning individuals were detected in a different coastal array in nearshore waters ca. 80 km away from the mouth of the estuary during their absence. We also used binomial generalized linear mixed models to estimate the probability of presence (i.e., detection) within the array as a function of several environmental variables. Flight from the array was predicted by declining barometric pressure and increasing rate of change of pressure, but not fluctuations in river stage. Extreme events causing mortality and shifts in distribution and foraging patterns can consequently have impacts on food webs and potentially ecological processes. Understanding movements, behavior, and population fluctuations of sensitive demographics and species could be important for effective ecosystem management.