Senior Research Associate
This research is funded by proceeds from Florida's Protect Wild Dolphins specialty license plate.
Estuarine systems are among the most dynamic and biodiverse aquatic systems. Their shores are often centers of urban development and their waters the terminus of rivers and canals. As such, estuaries bear the brunt of anthropogenic (human-caused) activities both urban and rural. As a sentinel species, dolphins can be important indicators of ecosystem health and alert us to increasing anthropogenic threats and other ecosystem-wide impacts.
We are conducting a comprehensive study of the bottlenose dolphin population in the Indian River Lagoon estuarine system. This 150-mile ribbon of water spans fully one-third of Florida’s east coast and traverses a patchwork of dense urban centers, high agricultural runoff and near-pristine habitats. This long-term study of a top predator residing in a high human-use coastal ecosystem focuses not just on bottlenose dolphins themselves but also on their role in the larger ecosystem, an approach that fosters informed species management and greater understanding of ecosystem function. Our study was a vital component in the establishment of the Indian River Estuarine Stock in 2009, one of the first inland populations along the U.S. Atlantic seaboard recognized by the National Marine Fisheries Service. Our discovery of a separate community of dolphins in the nearby coastal waters of the Atlantic Ocean helped to establish the Western North Atlantic Central Florida Coastal Stock in 2010. The study was established in 1996 and is based on systematic boat-based photo-ID surveys that have documented more than 1,400 individually identified dolphins, providing an unprecedented level of detail on behavior, ecology and individual life histories. We are currently investigating annual trends in abundance, distribution, birth and death rates, social structure, and health trends in this unique population.
Epidermal lesions can often be an indicator of the health of an individual dolphin. Lacaziosis is an epidermal disease that has been shown to be endemic in the IRL dolphin population. Our study of lacaziosis in the IRL dolphins determined the sensitivity and specificity of photo-identification for diagnosis of lobomycosis in free-ranging dolphins, determined the spatial distribution of lobomycosis in the IRL and assessed temporal patterns of occurrence.
Figures 1 & 2 - Lacaziosis in IRL dolphins
We work closely with the Epidemiology and Population Health program by using spatial and social structure data to analyze health conditions in dolphins. Our findings of long-term site fidelity, geographic partitioning and social structure within different dolphin communities has enabled us to examine health and environmental risks to dolphins occupying diverse habitats. We have been able to link health conditions such as E. coli carriage rates and lobomycosis with specific environmental features such as septic tanks and water quality parameters in spatial analyses.
IRL dolphins have been found to have higher-than-normal concentrations of mercury and antibiotic-resistant organisms. We are currently exploring the spatial distribution and social dynamics of these individuals to determine whether point sources of exposure exist in the IRL.
Reproduction and Fecundity
An accurate estimate of fecundity rate and infant survival is vital to assessing the health and status of cetacean populations. Bimodal peaks in births in the IRL have recently been attributed to the linear distribution of dolphins, with females residing in the northern lagoon calving in the spring and southern residents giving birth in the fall. This may coincide with the distribution and seasonality of sharks in the lagoon, as well as with shifts in prey movement and abundance, as lactating females have increased nutritional and energetic needs. The group size preferred by IRL dolphins is consistently small across seasons (median= 3), suggesting that resource availability is patchy, which would account for the lack of preferred nursery or protected areas for cow-calf pairs. IRL dolphin calves have a shorter dependency period than other estuarine/coastal populations, possibly due to increased ecological pressures to produce more offspring due to the low survival rate of calves. We have also found our average interbirth interval (3.4 years) to be more than one year longer than the average bottlenose dolphin interbirth interval (2.3 years), meaning fewer calves are being recruited into the IRL population. We recently collaborated with the U.S. Environmental Protection Agency, National Ocean Service and other investigators in a study of relaxin, a reproductive hormone by providing pregnancy data based on photographic identification of maternal-calf pairs.
Movement and Vital Rates
In 2011, we organized a multi-agency consortium to compare dolphin movements in northeast Florida in order to delineate the boundaries between the IRL Estuarine Stock (IRLES) and the Jacksonville Estuarine Stock, and to determine community structure for development of detailed life histories. Recent photo-ID evidence confirms that dolphins in the northern Mosquito Lagoon community range beyond the northern terminus of our study area, and some may travel as far north as Jacksonville. These lines of evidence suggest that the currently defined IRLES should exclude the Mosquito Lagoon; this would make the impacts of IRL dolphin mortality (originally based on the combined populations of the ML and IRL) more severe than initially suspected.
Our investigation of more than 500 dolphin carcasses recovered in the IRL (2002-2012) revealed they were resident dolphins that died within their known home ranges with limited drifting of carcasses. These findings are essential to attributing cause as they allow us examine specific spatial areas for possible ecological disturbances. This will aid in determining the impacts of mortality on community structure and stock viability and the actions necessary to prevent human-caused injury and death under the Marine Mammal Protection Act.
The notion that dolphins can simply move if their environment is disturbed reflects a common misconception of the marine environment as a uniform space and does not account for other influences on distribution and movement such as prey availability, predation risk, calf rearing, gender and social organization. Further, when negative impacts are not uniformly distributed some population units may be overexploited while others remain intact. During three NOAA declared Unusual Mortality Events in the IRL (2001, 2008, 2013) a record number of dolphins died within their home ranges in the north-central IRL, indicating that the causative agent was confined to geographic range and was not an epizootic event spread via overlapping communities.
IRL dolphins were found to have preferential companions, and associations are higher within – than between – sex class, indicating differential male-female survival strategies [Kent et al. 2008]. Males form loose bonds with each other during adolescence based on calf group acquaintances and then stable dyads at sexual maturity in order to herd females [Kent et al. 2008]. Breeding females have more social affiliations in order to rear similar-aged calves together, travel in larger calf bands using “helpers” to corral uncoordinated newborns and increase predator vigilance [Howells et al. 2009].
Nearly one-third of IRL dolphins bear evidence of shark encounters. It is also likely that habitat parameters shaping fish distributions in turn affect dolphin concentrations by driving group size down, increasing vulnerability to shark attacks. The high rate of shark bite scars from unsuccessful attack or interspecific competition indicates that risk of attack is substantial, and therefore fatal shark attacks may have a significant impact on dolphin survival within discrete communities existing within the estuary. Attacks are most prevalent among females with calves. Many calves (30%) disappear before age two, with most vanishing between one and three months of age, potentially indicating high predation rates. An alternate theory under investigation is fatal contaminant loads transferred to first born calves via lipid-rich milk provided by their mothers. Females will push and carry dead offspring on their backs for days, but the overall recovery of dead calves is low, suggesting that fatal predator attacks or scavenging of carcasses occurs at high rates.
Naïve first-time mothers are at greater risk of being struck by boats and losing offspring to fatal collisions. Our research has established correlations between risk of dolphin-vessel collisions and home ranges, with dolphins utilizing Martin and St. Lucie counties having the highest prevalence of boat strikes, leading to our recommendations to mitigate impacts with legislative and management initiatives including boater education and the implementation and enforcement of slow speed zones.
We found that all age classes (i.e., adult, juvenile and calf) are affected by entanglement with fishing gear, and that males are more likely to become ensnared. More than 30 cases of early intervention and rescue were successfully executed since our programs inception, with most distressed dolphins first reported during our photo-ID surveys. Our post-release radio-tracking of rescued dolphins has contributed to the development of criteria for determining if candidates can be successfully reintegrated into known social systems after lengthy (i.e., 3-6 month) rehabilitation periods.
A radio tracking study of bottlenose dolphins in the Indian River Lagoon was conducted during the summer of 2010 by the Dolphin Photo-ID and Population Biology Behavioral Ecology programs, in collaboration with Hubbs-SeaWorld Research Institute. Dolphins were chosen based on known individuals within the Photo-Identification catalogue that portrayed high sightability and local home ranges. Tracking was conducted primarily by boat-based surveys but additional data were acquired via aerial surveys. All four individuals were tracked within their respective known home ranges over a three-month study period. Future tracking studies will focus on behavioral interactions, male coalitions, and on equipment and attachment placement.
Figure 1. – Radio tag attachment before release
Figure 2. – Hole made from designed disassembly of radio tag (disregard roto tag mid fin)
Figure 3. – Migration of intact radio tag
Our team works closely with the Stranding, Health & Rehabilitation program by reporting entangled dolphins that are in need of rescue intervention. We identify the entangled dolphins, provide specific home ranges to narrow the search area for these animals, and perform scouting surveys prior to rescues to locate dolphins that have been targeted for invention.
We are part of a multi-agency consortium to compare dolphin movements in northeast Florida. Collaborators include the Georgia Aquarium Conservation Field Station, Hubbs-SeaWorld Research Institute, University of North Florida, St. Augustine Eco Tours, and Marine Mammal Behavioral Ecology Studies, Inc. Data from this research will help delineate the boundaries between the IRL Estuarine Stock and the Jacksonville Estuarine Stock, and to determine community structure for development of detailed life histories.
Current collaborative research includes investigators from the Dolphin Ecology Project, Florida Fish & Wildlife Conservation Commission, Georgia Aquarium (and its Conservation Field Station), Hubbs-SeaWorld Research Institute, Jacksonville University, Marine Mammal Behavioral Ecology Studies, Inc., NMFS, NOAA National Ocean Service, St. Augustine Eco Tours, St. Johns River Water Management District and University of North Florida.