Collecting information on the pelagic phase of marine turtles from at-sea observations: The case of purse seine fisheries in the Indian Ocean

Observations of turtles in the open-ocean are essential to complement the information collected at nesting sites and rookeries, especially during the ‘lost years’ of their surface-pelagic juvenile phase. We used a large dataset of observations at sea collected onboard Seychelles, Spanish and French purse seiners over the period 2003-2019 to describe the occurrence of five species of turtles in the Western Indian Ocean: green ( Chelonia mydas ), loggerhead ( Caretta caretta ), leatherback ( Dermochelys coriacea ), Olive ridley ( Lepidochelys olivacea ) and hawksbill ( Eretmochelys imbricata ). A total of 895 turtles were recorded by human observers, 487 turtles after having been caught in the purse seine and hauled onboard the vessels and 408 turtles swimming around or lying on floating objects. An additional 86 turtles were recorded from images collected by cameras deployed on some purse seiners but could not be identified at the species level. Information collected on the status of turtles indicates that the very large majority (>90%) hauled on deck were released alive. Size data show that most turtles observed in the open ocean were juveniles and that the ones caught in association with free swimming schools of tuna were smaller than the ones caught in schools associated with drifting floating objects, these latter representing the majority of the observations. Through the turtles’ example, we aim to describe the availability of metadata and data standards widely used to share species occurrence data and key to foster collaborative science in the Indian Ocean and beyond.