Dynamic Thermal Corridor May Connect Endangered Loggerhead Sea Turtles Across the Pacific Ocean

Dana K Briscoe,Tomomi Saito,Larry B Crowder,Masanori Kurita,Jeffrey J Polovina,Calandra N Turner Tomaszewicz,Marc R Rice,Hitoshi Okamoto,Denise M Parker,George H Balazs,Jeffrey A Seminoff

doi:10.3389/fmars.2021.630590

Abstract

The North Pacific Loggerhead sea turtle (Caretta caretta) undergoes one of the greatest of all animal migrations, nesting exclusively in Japan and re-emerging several years later along important foraging grounds in the eastern North Pacific. Yet the mechanisms that connect these disparate habitats during what is known as the “lost years” have remained poorly understood. Here, we develop a new hypothesis regarding a possible physical mechanism for habitat connectivity – an intermittent “thermal corridor” – using remotely sensed oceanography and 6 juvenile loggerhead sea turtles that formed part of a 15 year tracking dataset of 231 individuals (1997–2013). While 97% of individuals remained in the Central North Pacific, these 6 turtles (about 3%), continued an eastward trajectory during periods associated with anomalously warm ocean conditions. These few individuals provided a unique opportunity to examine previously unknown recruitment pathways. To support this hypothesis, we employed an independently derived data set using novel stable isotope analyses of bone growth layers and assessed annual recruitment over the same time period (n = 33, 1997–2012). We suggest evidence of a thermal corridor that may allow for pulsed recruitment of loggerheads to the North American coast as a function of ocean conditions. Our findings offer, for the first time, the opportunity to explore the development of a dynamic ocean corridor for this protected species, illuminating a longstanding mystery in sea turtle ecology.

Highlights

Conservation of long-lived pelagic organisms, like sea turtles, that navigate whole ocean basins remains one of the most daunting challenges in marine science
25 years ago, many assumed that loggerheads found in the eastern North Pacific Ocean originated from undiscovered nesting sites in the region, as it was hard to imagine a juvenile sea turtle undertaking a 12,000 km transpacific migration from its natal beaches in Japan to the North American coast (Nichols et al, 2000; Seminoff et al, 2012)
Based on our previous findings of the behavior of the 231 juveniles, the well-established relationships between movement and temperature, and an exploration of ocean conditions within the region identified by our 6 sentinel loggerheads, we explored the hypothesis that years with anomalously warm conditions could facilitate the recruitment of juvenile loggerheads into the eastern North Pacific and to the Baja California foraging habitat

Summary

Introduction

Conservation of long-lived pelagic organisms, like sea turtles, that navigate whole ocean basins remains one of the most daunting challenges in marine science. For turtles queued up in the eastern CNP, we posited that exceptionally warm conditions may provide the environmental cues and thermal requirements necessary to create an ecological bridge - a temporary pathway known to connect two suitable but disparate and distinct habitat regions for highly migratory species (Fromentin et al, 2014; Briscoe et al, 2017) – facilitating movement into the CCLME.

Results

Conclusion