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

Abstract

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.

Seasonal distribution of an opportunistic apex predator (Tursiops truncatus) in marine coastal habitats of the Western Mediterranean Sea

“…In the southern Mediterranean Sea, chlorophyll-a was found to be the second strongest predictor for bottlenose dolphin spatial distribution patterns, representing a good proxy for prey availability and thus a highly useful parameter in identifying relevant aggregation hotspots for dolphins (La Manna et al, 2016). Most likely, it is not by chance that the main estuaries in the study area were sites with the greatest predicted bottlenose dolphin densities, as estuaries have been shown to act as significant habitats for the genus Tursiops worldwide (e.g., Sprogis et al, 2016;Hartel et al, 2020). Estuaries are key aspects of the coastal ecosystems because of their unique characteristics and the variability induced by mixing and stratifying fresh and saltwater (McLusky and Elliott, 2004;Lin et al, 2013).…”

Abundance and demography of common bottlenose dolphins (Tursiops truncatus truncatus) in the Indian River Lagoon, Florida: A robust design capture-recapture analysis

“…Individuals inhabiting the periphery of the study region, with home ranges extending beyond the IRL border, may have contributed to such temporary emigration. Resident dolphins have also been documented utilizing oceanic habitat [ 49 ]. Availability bias [ 94 ] may also occur due to dolphins utilizing the labyrinth of canals, freshwater creeks, and shallow waters surrounding islands throughout the IRL [ 49 , 64 ].…”

“…Resident dolphins have also been documented utilizing oceanic habitat [ 49 ]. Availability bias [ 94 ] may also occur due to dolphins utilizing the labyrinth of canals, freshwater creeks, and shallow waters surrounding islands throughout the IRL [ 49 , 64 ]. This bias could be potentially mitigated by including covariates that model detection heterogeneity such as distance from shallow labyrinth or inlets.…”

“…This is most obvious in portions of the lagoon near inlet access, particularly in response to dramatic declines in water temperature [21,23] which may influence dolphin movement [45][46][47][48]. Satellite telemetry has further corroborated oceanic habitat usage in resident IRL dolphins [49]. Photo-identification surveys further support transience occurrence, documenting dolphin movements between the northern portion of the IRL (Mosquito Lagoon) and the St. Johns River (Jacksonville Estuarine system stock-JES), [24,25,50] with a 13% exchange in the individuals examined [25].…”

Staying close to home: Marine habitat selection by foraging yellow-eyed penguins using spatial distribution models

“…We further sub-sampled one valid dive event per hour (first point/hour) for each foraging trip from 135 individuals tracked over 164 deployments to reduce temporal redundancy and spatial clustering (Hartel et al, 2020). We chose this method over other methods (e.g., distance sampling, random sampling), because it increased spatial and temporal independence while mitigating sampling differences (Boria et al, 2014).…”