Nesting dynamics of hawksbill and leatherback turtles: a four-year photo-identification study in Martinique

Abstract

One major limitation in conservation studies is accurately estimating population size to adapt management efforts. Thus, avoiding individual duplicate counts is essential to prevent any overestimation of population size. Photo-identification (photo-ID) offers a low cost and non-invasive alternative for monitoring migratory animals, and yet, it remains generally under-implemented in marine species. In this study, we applied photo-ID with sea-turtle populations in the French Antilles for the first time, thereby contributing to global population survey efforts in the Caribbean while minimising stress or harm to turtles. We focussed on two species of concern, Dermochelys coriacea (leatherback) and Eretmochelys imbricata (hawksbill), identified through a semi-automated recognition method to analyse their nesting behaviour. Our multi-annual survey involved 5292 h of night monitoring across three Martinique beaches over four years, yielding valuable data on nesting behaviours, population dynamics and conservation needs. We recorded 57 occurrences of leatherback turtles with a recapture rate of 61 %, and 314 hawkbill observations with a recapture rate of 36 %. The microhabitat of each nest was recorded, providing insights on nesting site preferences. Additionally, leatherbacks exhibited a longer time interval between their arrival on the beach and the start of nesting activity compared to hawksbills. These results reveal significant behavioural differences and specific nesting habits underscoring the potential of expanding photo-ID combined with ecological analysis, as a valuable resource for the conservation management of threatened sea-turtle species.