Analysis of the foraging ecology of hawksbill turtles (Eretmochelys imbricata) on Hawai'i Island: An investigation utilizing satellite tracking and stable isotopes

Foraging studies on hawksbill sea turtles (Eretmochelys imbricata ) in Hawai'i are limited. Previous tracking investigations have identified the Hamakua Coast (northeastern shore of Hawai'i Island) as the main foraging habitat of hawksbill adult females; however, there is little information on the prey species from the area, though the species is thought to prefer sponges. Satellite transmitters were attached on post-nesting females (n=3) from Hawai'i Island to ascertain feeding periods and depth, and benthic surveys at one region within the Hamakua Coast were conducted to determine sponge percent cover. Further, carbon and nitrogen stable isotope analyses were conducted to verify the dominant prey organisms of female turtles foraging around Hawai'i Island. One of the three hawksbill females migrated to the Hamakua Coast foraging during the daytime at depths up to 30m. Results from a two-source mixing model suggest she fed primarily on sponges. Carbon isotopes of all adult females varied, which may indicate possible differences in prey preferences or habitat type. Differences of carbon isotopes were also indicated among the deceased hatchlings. Carbon and nitrogen isotopes of the few deceased hatchlings compared to known females were similar suggesting deceased hatchlings could be incorporated in future foraging studies, leading to a less invasive monitoring program.