Multi-year tracking reveals extensive pelagic phase of juvenile loggerhead sea turtles in the North Pacific.

D K Briscoe,L B Crowder,T Saito,M Kurita,G H Balazs,H Okamoto,E Hazen,S Bograd,D M Parker,J J Polovina,M Rice,K Scales

doi:10.1186/s40462-016-0087-4

Abstract

BackgroundThe juvenile stage of loggerhead sea turtles (Caretta caretta) can last for decades. In the North Pacific Ocean, much is known about their seasonal movements in relation to pelagic habitat, yet understanding their multi-year, basin-scale movements has proven more difficult. Here, we categorize the large-scale movements of 231 turtles satellite tracked from 1997 to 2013 and explore the influence of biological and environmental drivers on basin-scale movement.ResultsResults show high residency of juvenile loggerheads within the Central North Pacific and a moderate influence of the Earth’s magnetic field, but no real-time environmental driver to explain migratory behavior.ConclusionsWe suggest the Central North Pacific acts as important developmental foraging grounds for young juvenile loggerhead sea turtles, rather than just a migratory corridor. We propose several hypotheses that may influence the connectivity between western and eastern juvenile loggerhead foraging grounds in the North Pacific Ocean.Electronic supplementary materialThe online version of this article (doi:10.1186/s40462-016-0087-4) contains supplementary material, which is available to authorized users.

Highlights

The juvenile stage of loggerhead sea turtles (Caretta caretta) can last for decades
Individuals deployed off Japan utilized the Kuroshio Extension Current (KEC) to disperse into pelagic areas (Fig. 2a)
North Pacific loggerhead sea turtles travel long distances and across entire ocean basins to reach developmental foraging grounds, yet connectivity between east-west movements has remained difficult. While individuals from this endangered population display a range of movement strategies, results from multi-year tracking reveals extensive use of the Central North Pacific

Summary

Introduction

The juvenile stage of loggerhead sea turtles (Caretta caretta) can last for decades. In the North Pacific Ocean, much is known about their seasonal movements in relation to pelagic habitat, yet understanding their multi-year, basin-scale movements has proven more difficult. While advancements in tracking have greatly enhanced our ability to understand how migratory animals move through their environment (seabirds, marine mammals, and sea turtles), it still remains a challenge to understand the degree of connectivity between the reproductive and foraging grounds [3] Environmental flows such as wind and currents are known to influence early animal movement into the open ocean, and can potentially impact the ontogeny of foraging and migratory patterns as animals develop [4,5,6]. The pelagic stage is inferred rather than empirically observed [8] This is especially true for sea turtles, as the oceanic period of early life history has been termed the ‘lost years’ [9]

Methods

Results

Discussion

Conclusion