The estuarine waters of the St. John’s River in Jacksonville, FL may provide critical habitat for Atlantic bottlenose dolphins (Tursiops truncatus). However, this population of estuarine dolphins has not yet been well studied. This lack of information is concerning; given the urban location of this population the risk of anthropogenic (human) disturbance is high. In September 2010, an Unusual Mortality Event (UME) was declared for Jacksonville dolphins in response to an unprecedented number of dolphin strandings/deaths in the St. John's River. Unfortunately, the investigation into potential causes for these strandings was inconclusive due to limited existing knowledge of this population. Our project strives to fill this knowledge gap through a systematic study of the distribution, abundance and behavior of the dolphins that inhabit the St. John’s River in Jacksonville, Florida.
Through weekly vessel-based photo-identification and behavioral surveys, our research team has identified over 300 individual dolphins in the St. John’s River. Of these individuals, 27 dolphins have been re-sighted on ten or more survey days, with some individuals re-sighted as often as 14 survey days. Dolphins are consistently sighted throughout our survey route, Mayport Inlet to Hart Bridge, approximately 25 miles up-river and our preliminary data suggest that some individuals prefer particular portions of the river. However, continued data collection is necessary to determine seasonal patterns of habitat use and if the dolphins in the St. John’s River are year-round residents or if their home ranges extend beyond the river. Such information is critical for assessing the potential impact of anthropogenic disturbances on this population.
Our main objective is to continue developing a local photographic catalog and sighting history database of individual dolphins that can be utilized to address numerous research questions. These data will enable us to 1) identify critical habitat areas used for resting, mating/calving and foraging, 2) determine site fidelity and seasonal movement patterns, and 3) calculate life history parameters, particularly those related to reproductive success (calving rates, calf survival, and weaning age), as these are important indicators of the health and sustainability of the population. As founding members of the Northeast Florida Dolphin Research Consortium, we are also working collaboratively with eight other research groups to determine the population abundance of bottlenose dolphins throughout the northeast Florida region (Fernandina Beach to Ponce Inlet). Participation in this large-scale effort will clarify the larger ranging patterns of the St. John’s River dolphins, and thereby their cumulative exposure to anthropogenic disturbance.
Once we have achieved a basic understanding of the dolphins in the river (i.e., their seasonal abundance, distribution, and the sex of regularly sighted individuals), we intend to expand the behavioral component of our project by investigating social structure (association patterns) and complexity (e.g. male alliances), maternal care strategies, and calf development.