Realignment of sea turtle isotope studies needed to match conservation priorities

Abstract

Stable isotope analyses have become popular in sea turtle literature over the past decade, with an increasing year-to-year trend in published studies reporting insights into food web structure, diet, trophic interactions, ontogenetic shifts, geographic distributions, and more. Understanding the geographic distribution of migrating taxa within their sub-populations could enhance conservation and management, especially for threatened populations. For sea turtles, stable isotope analyses can potentially be used to quickly assess foraging distributions across large proportions of a nesting population, examining high numbers of turtles at low cost and/or effort relative to satellite telemetry and mark-recapture studies. We systematically assessed the literature, aiming to identify the current state of research into sea turtle isotope ecology, including key knowledge gaps and the level of geographic assessment within regional management units (RMUs). Sea turtle RMUs listed as Least Concern by the IUCN (6.5 studies per RMU) have been studied at a rate 13 times higher than those considered Threatened (0.5 studies per RMU). Loggerhead turtles Caretta caretta and green turtles Chelonia mydas are the most studied species. Comparatively, flatback Natator depressus and Kemp’s ridley Lepidochelys kempii turtles return a paucity of analyses. This is the first review of sea turtle isotope studies and helps to refocus future isotope research to prioritise conservation outcomes throughout the world. The mismatch between effort and conservation priority may be a testimony to the effectiveness of research and management in these areas but suggests a need to now realign the focus of sea turtle isotope ecological studies towards more threatened RMUs.