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

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.

Ethnobiological methods enhance our capacity to document potential climate sentinels: a loggerhead sea turtle (Caretta caretta) case study

“…Loggerheads' close connection to temperature variability makes them valuable climate sentinels, either as indicators of temperature anomalies or expanding species range as a result of climate change (Hazen et al, 2013(Hazen et al, , 2019. The close association between loggerheads and SST changes has led to policies based on dynamic-fisheries management to prevent increased loggerhead bycatch in the California Current Large Marine Ecosystem during anomalous warm-water periods thorough a time-area closure enacted when an El Niño event is forecasted or declared (NOAA, 2001;Eguchi et al, 2018;Briscoe et al, 2021). ENSO dynamicsparticularly El Niño events-may drive periodic loggerhead presence in the Southern California Bight.…”

“…As ectotherms, loggerheads rely on thermal cues for habitat selection and avoidance, and temperature is a critical driver of their distribution and migratory patterns (Abecassis et al, 2013;Briscoe et al, 2016). Importantly, Pacific loggerheads exhibit strong fidelity to the 18°C isotherm, a widely-used proxy for the highly-productive Transition Zone Chlorophyll Front (Polovina et al, 2017;Briscoe et al, 2021; Figure 1). Thermal cues and patterns are closely linked to ocean temperature, which is dynamic and operates on various temporal scales including annual variations, irregular events like the El Niño Southern Oscillation (ENSO).…”

Ecological Trap or Favorable Habitat? First Evidence That Immature Sea Turtles May Survive at Their Range-Limits in the North-East Atlantic

“…The loggerhead turtle (Caretta caretta) is the most studied of the seven sea turtle species (Hays and Hawkes, 2018) and has a complex life cycle, being distributed in oceanic waters during its juvenile stage before recruiting to coastal habitats (Bolten, 2003). The movements and habitat use of immature individuals directly caught at-sea at their developmental habitats have been largely documented in the Mediterranean Sea (Cardona et al, 2005;Revelles et al, 2007;Casale et al, 2012;Abalo-Morla et al, 2018;Chimienti et al, 2020), Pacific (Polovina et al, 2001(Polovina et al, , 2004(Polovina et al, , 2006Kobayashi et al, 2008;Briscoe et al, 2016bBriscoe et al, , 2021, Indian (Dalleau et al, 2014;Bousquet et al, 2020), and Atlantic Oceans (Mansfield et al, 2009(Mansfield et al, , 2014Varo-Cruz et al, 2016;Chambault et al, 2019). However, the spatial patterns of individuals after rehabilitation in unusual habitat (outside their geographical range-limit) remain undocumented in most regions, in particular in Western Europe.…”

Local Ecological Knowledge enhances our capacity to document potential climate sentinels: a loggerhead sea turtle (Caretta caretta) case study

“…Loggerheads are categorised as Vulnerable on the IUCN Red List, and their close connection to temperature variability makes them valuable sentinels of temperature anomalies or shifting species range due to climate change (Hazen et al, 2019). North Pacific loggerheads nest exclusively in Japan and forage in highly productive pelagic zones in the Central North Pacific and Baja California Sur, Mexico (Briscoe et al, 2021) (Figure 1). As ectotherms, their distribution and migratory patterns are largely driven by ocean temperature, with important links to annual variations, irregular events (El Niño Southern Oscillation, ENSO), and decadal patterns (Pacific Decadal Oscillation) subject to climate change-driven alteration (Almpanidou et al, 2019; Briscoe et al, 2021).…”

“…Loggerhead movement is strongly correlated with SST variations, especially ENSO dynamics which may drive transient loggerhead presence in the temperate North Pacific (Figure 1). Loggerhead strandings have been reported in British Columbia, Canada, and the Gulf of Alaska during El Niño events (Halpin et al, 2018), and 15,000+ loggerheads were recorded in the Southern California Bight (SCB) during the 2015 El Niño event (Eguchi et al, 2018; Briscoe et al, 2021) (Figure 1). Loggerheads’ close association with SST has led to dynamic-fisheries management policies for by-catch reduction in the SCB through a time-area closure during El Niño events (Eguchi et al, 2018).…”