Testing satellite telemetry within narrow ecosystems: nocturnal movements and habitat use of bottlenose dolphins within a convoluted estuarine system

Background While cetaceans have been extensively studied around the world, nocturnal movements and habitat use have been largely unaddressed for most populations. We used satellite telemetry to examine the nocturnal movements and habitat use of four bottlenose dolphins ( Tursiops truncatus ) from a well-studied population in a complex estuary along the east coast of Florida. This also enabled us to explore the utility of satellite tracking on an apex predator within a very narrow and convoluted ecosystem. Our objectives were to evaluate (1) nocturnal home ranges and how individual dolphins moved within them, (2) nocturnal utilization of habitats surrounding ocean inlets, (3) nocturnal movements outside of the population’s known range (i.e., the study area), and (4) nocturnal use of select environmental variables. Results Satellite tags were active between 129 and 140 days (136 ± 4.99) during nocturnal hours (summer/fall 2012), yielding 3.3 ± 1.4 high-quality transmissions per night. Results indicated substantial individual variation among the four tagged dolphins, with home ranges varying in length from 53.9 to 83.6 km ( x̅ = 71.9 ± 12.9). Binomial tests and MaxEnt models revealed some dolphins preferred habitats surrounding inlets, seagrass habitats, and various water depths, while other dolphins avoided these areas. All dolphins, however, showed substantial movement ( x̅ = 5.8 ± 7.4 km) outside of the study area, including travel into rivers/canals and the adjoining ocean (6.0–8.6% and 0.8–2.9% of locations per dolphin, respectively). Conclusions This study was the first to utilize satellite telemetry on Indian River Lagoon dolphins and provided the first detailed insights into the nocturnal movements and habitat use of this population. Our findings suggest that while individual dolphin home ranges may overlap, they use different foraging strategies, feed on different prey, and/or exhibit intraspecific resource partitioning. In contrast with a prior study, all tagged dolphins showed considerable movement into the adjoining ocean and freshwater sources. This suggests this population has a much larger range than previously thought, which is important to consider for future research and conservation efforts.