First satellite tracks of neonate sea turtles redefine the ‘lost years’ oceanic niche

Katherine L Mansfield,Jeanette Wyneken,Warren P Porter,Jiangang Luo

doi:10.1098/rspb.2013.3039

Abstract

Few at-sea behavioural data exist for oceanic-stage neonate sea turtles, a life-stage commonly referred to as the sea turtle ‘lost years’. Historically, the long-term tracking of small, fast-growing organisms in the open ocean was logistically or technologically impossible. Here, we provide the first long-term satellite tracks of neonate sea turtles. Loggerheads (Caretta caretta) were remotely tracked in the Atlantic Ocean using small solar-powered satellite transmitters. We show that oceanic-stage turtles (i) rarely travel in Continental Shelf waters, (ii) frequently depart the currents associated with the North Atlantic Subtropical Gyre, (iii) travel quickly when in Gyre currents, and (iv) select sea surface habitats that are likely to provide a thermal benefit or refuge to young sea turtles, supporting growth, foraging and survival. Our satellite tracks help define Atlantic loggerhead nursery grounds and early loggerhead habitat use, allowing us to re-examine sea turtle ‘lost years’ paradigms.

Highlights

Classic sea turtle life-history models assume discrete shifts in habitat use during different life stages [1,2,3]
Sea turtles hatch from nests on coastal beaches, enter near-shore waters and swim offshore, transitioning to oceanic habitats where they remain for a minimum of 1–2 years [1,2,3,4,5,6]
Seawater reflectivity was obtained from literature and satellite-based measures [27,28]. These data were applied to a heat balance equation: Qin þ Qabs 1⁄4 Qout þ Qst, where heat in (Qin) is by long wavelength infrared thermal radiation (IR) from the sky and clouds, Qabs is by solar radiation absorption, Qout is by conduction, convection, evaporation and emitted IR, and Qst is stored heat

Summary

Introduction

Classic sea turtle life-history models assume discrete shifts in habitat use during different life stages [1,2,3]. We infer that higher Argos location accuracies and greater charge rates relate to longer periods of transmitter exposure to air and to sunlight, enabling the tags to effectively communicate with overhead satellites or exposing tags to the solar energy required to successfully recharge We use these data as a proxy to determine whether the turtles occupied sea surface habitats. These data were applied to a heat balance equation: Qin þ Qabs 1⁄4 Qout þ Qst, where heat in (Qin) is by long wavelength infrared thermal radiation (IR) from the sky and clouds, Qabs is by solar radiation absorption, Qout is by conduction, convection, evaporation and emitted IR, and Qst is stored heat We used these calculations to determine whether any observed differences between ambient (transmitter-derived) and satellite- or model-derived SST measures could be explained by reflectivity differences between ambient seawater and turtles, tags or Sargassum. Temperature data from the data loggers were overlaid to compare thermal profiles among treatments

Results

Discussion

Findings

Methods