Home range of green turtles Chelonia mydas at a coastal foraging area in the Gulf of California, Mexico

The green turtle Chelonia mydas is a circumglobal species that is susceptible to overexploitation as a food resource and incidental mortality in fisheries. Efforts to recover regional green turtle populations have been hampered by a lack of information on their biology. In particular, turtle movements and home ranges in neritic foraging habitats are not well understood. Thus, wildlife managers cannot accurately determine the habitat needs of green turtle populations. To address these understudied aspects, we carried out the first ever investigation of green turtle home range in neritic foraging habitats of the eastern Pacific Ocean. Twelve turtles, ranging from 50.9 to 82.5 cm in straight carapace length and from 17 to 70 kg in mass, were tracked with radio and sonic telemetry for 34 to 96 d at the Bahia de los Angeles foraging area in the Gulf of California, Mexico. Home range areas determined with minimum convex polygon and fixed kernel density estimator methods ranged from 584 to 3908 ha (mean = 1662 +/- 324 ha) and 409 to 3231 ha (mean = 1537 +/- 280 ha), respectively. There was no evidence that straight carapace length, mass, sex, tracking duration or number of re-sightings influenced the size of the home range. Green turtle home ranges contained from 1 to 3 activity centers ranging from 3.8 to 642.2 ha in area (mean = 178.8 +/- 62.0 ha). Turtles were re-sighted in all depth-class regions (0 to 10 m to 40+ m) in the study area but were not found with equal frequency among these regions. The distribution of re-sightings among depth classes varied significantly between diurnal (05:00 to 18:59 h) and nocturnal (19:00 to 04:59 h) periods. While the greatest frequency of diurnal re-sightings occurred in the 10 to 20 m depth class, nocturnal encounters were most frequent in the 0 to 10 m depth class. This study shows that Bahia de los Angeles remains an important feeding ground; thus, underscoring the need to develop conservation strategies that address the impacts of ongoing commercial marine-algae harvests and net fisheries that threaten green turtles in this region.