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ESR 9:105-116 (2010)  -  DOI:

Size-class partitioning and herding in a foraging group of green turtles Chelonia mydas

Michael J. Bresette1,*, Blair E. Witherington2, Richard M. Herren1, Dean A. Bagley1, Jonathan C. Gorham1, Steve L. Traxler1, Carrie K. Crady1, Robert Hardy3

1Inwater Research Group Inc., 4160 NE Hyline Dr., Jensen Beach, Florida 34957, USA
2Florida Fish and Wildlife Research Institute, FWC, 9700 South A1A, Melbourne Beach, Florida 32951, USA
3Florida Fish and Wildlife Research Institute, FWC, 100 Eighth Avenue SE, St. Petersburg, Florida 33701, USA

ABSTRACT: To collect data on green turtles Chelonia mydas near the Marquesas Keys, Florida, USA, we conducted haphazard, unmarked, nonlinear transect (HUNT) surveys from a moving vessel. During HUNTs, we recorded green turtle locations and made opportunistic captures. We found a unique foraging assemblage of subadult and adult green turtles in open-water seagrass habitat (3 to 5 m deep) at the eastern Quicksands, west of the Marquesas Keys. At an adjacent area in the Marquesas Keys (Mooney Harbor), we observed juvenile green turtles foraging in shallow seagrass habitat (<2 m). During 267 km of HUNTs, 370 green turtles (153 adults, 216 subadults, 1 juvenile) were recorded from the eastern Quicksands. At the Mooney Harbor site, 190 juvenile green turtles were sighted during 309 km of transects. Green turtles captured at the eastern Quicksands were adult and subadult animals that ranged from 69.3 to 108.5 cm straight carapace length (SCL; mean ± SD = 88.4 ± 10.6 cm, n = 31). Green turtles captured in Mooney Harbor were juveniles ranging from 27.0 to 59.3 cm SCL (mean = 44.0 ± 7.8, n = 41). Six repeatable, linear transects were surveyed during 3 sampling events at the eastern Quicksands. During these transects, 238 green turtles were observed. These spatial data were used in a nearest-neighbor analysis, which indicated that the distribution of green turtles at the eastern Quicksands was non-random and clumped. We hypothesize that adult and large subadult green turtles use deeper water habitats than juveniles, and this size-class partitioning may be due to differing habitat requirements and predation risk. Our analyses indicate that green turtles found at the eastern Quicksands form foraging herds.

KEY WORDS: Green turtle · Foraging ground · Partitioning

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Cite this article as: Bresette MJ, Witherington BE, Herren RM, Bagley DA and others (2010) Size-class partitioning and herding in a foraging group of green turtles Chelonia mydas. Endang Species Res 9:105-116.

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