Overwintering behavior and movement of immature green sea turtles in south Texas waters

Abstract

Overwintering behavior and movement of immature green sea turtles (Chelonia mydas ) in Lower Laguna Madre, Texas was characterized from October 1992 to March 1993 and November 1993 to March 1994. Radio and sonic telemetry was used to monitor nine juvenile greens ranging from 36 to 62 cm Straight Carapace Length (SCL) (mean = 48.6 cm SCL). Five turtles were tracked each period with one individual recaptured and tracked both years. Green turtles overwintered in and displayed a strong site fidelity for lower Laguna Madre habitats. Resting (remaining in the same location with little directed movement) dominated submerged behavior during periods of reduced air and water temperatures (<17 C). Activity, defined as progressive movements through the water column and surrounding habitat (i.e., foraging), was the most prevalent behavior during warmer months (>17 C) of both years. Resting also dominated nighttime behavior while increased activity was the norm during daylight hours. Surface and submergence durations typically were < 20 seconds and < 10 minutes long, respectively. One turtle's behavior appeared to be influenced by dredging activity and depth of the water column it occupied. Range of movement was related to size of turtle, with largest individuals traveling greatest distances. Turtle movement was greatest during the daytime and increased with rising air and water temperature. Mud and algal growth atop the carapace of greens recaptured during December-March may be indicative of prolonged intervals (> 2 hr) of reduced activity along the bottom.