Underwater behaviour of green turtles monitored with video-time-depth recorders: what's missing from dive profiles?

We used a turtle-mounted video and data-logging system (Crittercam; National Geographic Society, USA) to study underwater behaviour and dive patterns of green turtles, Chelonia mydas, at a coastal foraging area in the Gulf of California, Mexico, Between August 1997 and June 2002, units were deployed 36 times on 34 green turtles ranging from 64.1 to 96.7 cm in straight carapace length and 38.6 to 120.5 kg in weight. A total of 89.5 h of video was recorded with corresponding dive data (1065 total dives). Foraging was observed during 8 deployments (28 events) at depths of 3.0 to 32.0 m and occurred while turtles were swimming in the midwater column and stationary on the seafloor; 4 marine algae and 5 invertebrate prey species were identified. Resting behaviour was seen during 9 deployments (33 dives) as turtles set on the seafloor at depths of 7.0 to 26.5 m. Overall, 6 dive types were observed and labeled Type 1 to Type 6 dives. Green turtles foraged during Type 1, Type 3, and Type 5 dives, whereas they rested only during Type 1 dives. In addition to elucidating the importance of specific habitats and resources in neritic foraging areas, our results confirm that a variety of underwater behaviours can be reflected by 1 specific dive profile. These data indicate caution should be exercised when ascertaining in-water activity solely based on the appearance of dive profiles.