Abstract
For imperiled marine turtles, use of satellite telemetry has proven to be an effective method in determining long distance movements. However, the large size of the tag, relatively high cost and low spatial resolution of this method make it more difficult to examine fine-scale movements of individuals, particularly at foraging grounds where animals are frequently submerged. Acoustic telemetry offers a more suitable method of assessing fine-scale movement patterns with a smaller tag that provides more precise locations. We used acoustic telemetry to define home ranges and describe habitat use of juvenile green turtles at a temperate foraging ground in the northern Gulf of Mexico. We outfitted eight juvenile green turtles with acoustic transmitters and tracked them from 14 to 138 days from September 2012 to February 2013 in St. Joseph Bay, Northwest Florida. Mean home range size was relatively small compared to other studies. For four turtles, we observed a moderate inverse relationship between water temperature and water depth which is consistent with the idea that turtles moved to deeper waters when temperatures cooled. On average distance to the channel from turtle locations were different by bottom cover type. These turtles appear to forage in shallow-water seagrass beds that border deep channels. When water temperatures dropped in winter, some of the tracked turtles moved to a deep-water channel on the western side of the study site. Turtles whose foraging sites were farther from the deep-water channel exhibited greater displacement than those with sites that were closer to the channel. Green turtles in St. Joseph Bay have relatively small home ranges and many contain multiple activity centers. The frequent use of channels by turtles suggests bathymetry plays a major role in habitat selection of juvenile green turtles, particularly as temperatures drop in winter. The quality and density of seagrass habitat in St. Joseph Bay and its proximity to deep channels appears to provide ideal conditions for juvenile greens. The results of this study help define characteristics of foraging habitat utilized by juvenile greens in the northern Gulf of Mexico that managers can use in creating protected areas such as aquatic preserves.
Highlights
For imperiled marine turtles, use of satellite telemetry has proven to be an effective method in determining long distance movements
Fewer studies have been conducted at temperate foraging grounds and a severe lack of data remains for green turtles foraging in the Gulf of Mexico (GoM)
Studies of juvenile greens conducted in Texas [19, 20] and the Florida Everglades National Park [11] have provided some information on juvenile green turtle habitat use, no information on home ranges, habitat use or movement patterns is available for populations in Northwest Florida
Summary
Use of satellite telemetry has proven to be an effective method in determining long distance movements. We used acoustic telemetry to define home ranges and describe habitat use of juvenile green turtles at a temperate foraging ground in the northern Gulf of Mexico. Research on marine turtles has increased over the past decade [1,2,3], gaps in our knowledge still exist, at in-water foraging grounds [4] This is a serious knowledge gap for species such as green turtles (Chelonia mydas) that are threatened or endangered throughout parts of their range [5] and which spend the major part of their lives in neritic foraging grounds [6, 7] that are often exposed to multiple anthropogenic impacts [8, 9]. Studies of juvenile greens conducted in Texas [19, 20] and the Florida Everglades National Park [11] have provided some information on juvenile green turtle habitat use, no information on home ranges, habitat use or movement patterns is available for populations in Northwest Florida
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