The western Pacific leatherback turtle (Dermochelys coriacea), one of three genetically distinct stocks in the Indo-Pacific region, has declined markedly during past decades. This metapopulation nest...

Effective conservation strategies for highly migratory species must incorporate information about long-distance movements and locations of high-use foraging areas. However, the inherent challenges of directly monitoring these factors call for creative research approaches and innovative application of existing tools. Highly migratory marine species, such as marine turtles, regularly travel hundreds or thousands of kilometers between breeding and feeding areas, but identification of migratory routes and habitat use patterns remains elusive. Here we use satellite telemetry in combination with compound-specific isotope analysis of amino acids to confirm that insights from bulk tissue stable isotope analysis can reveal divergent migratory strategies and within-population segregation of foraging groups of critically endangered leatherback sea turtles (Dermochelys coriacea) across the Pacific Ocean. Among the 78 turtles studied, we found a distinct dichotomy in δ¹⁵N values of bulk skin, with distinct “low δ¹⁵N” and “high δ¹⁵N” groups. δ¹⁵N analysis of amino acids confirmed that this disparity resulted from isotopic differences at the base of the food chain and not from differences in trophic position between the two groups. Satellite tracking of 13 individuals indicated that their bulk skin δ¹⁵N value was linked to the particular foraging region of each turtle. These findings confirm that prevailing marine isoscapes of foraging areas can be reflected in the isotopic compositions of marine turtle body tissues sampled at nesting beaches. We use a Bayesian mixture model to show that between 82 and 100% of the 78 skin-sampled turtles could be assigned with confidence to either the eastern Pacific or western Pacific, with 33 to 66% of all turtles foraging in the eastern Pacific. Our forensic approach validates the use of stable isotopes to depict leatherback turtle movements over broad spatial ranges and is timely for establishing wise conservation efforts in light of this species’ imminent risk of extinction in the Pacific.

Interactions with fisheries are believed to be a major cause of mortality for adult leatherback turtles (Dermochelys coriacea), which is of particular concern in the Pacific Ocean, where they have been rapidly declining. In order to identify where these interactions are occurring and how they may be reduced, it is essential first to understand the movements and behavior of leatherback turtles. There are two regional nesting populations in the East Pacific (EP) and West Pacific (WP), comprising multiple nesting sites. We synthesized tracking data from the two populations and compared their movement patterns. A switching state‐space model was applied to 135 Argos satellite tracks to account for observation error, and to distinguish between migratory and area‐restricted search behaviors. The tracking data, from the largest leatherback data set ever assembled, indicated that there was a high degree of spatial segregation between EP and WP leatherbacks. Area‐restricted search behavior mainly occurred in the southeast Pacific for the EP leatherbacks, whereas the WP leatherbacks had several different search areas in the California Current, central North Pacific, South China Sea, off eastern Indonesia, and off southeastern Australia. We also extracted remotely sensed oceanographic data and applied a generalized linear mixed model to determine if leatherbacks exhibited different behavior in relation to environmental variables. For the WP population, the probability of area‐restricted search behavior was positively correlated with chlorophyll‐a concentration. This response was less strong in the EP population, but these turtles had a higher probability of search behavior where there was greater Ekman upwelling, which may increase the transport of nutrients and consequently prey availability. These divergent responses to oceanographic conditions have implications for leatherback vulnerability to fisheries interactions and to the effects of climate change. The occurrence of leatherback turtles within both coastal and pelagic areas means they have a high risk of exposure to many different fisheries, which may be very distant from their nesting sites. The EP leatherbacks have more limited foraging grounds than the WP leatherbacks, which could make them more susceptible to any temperature or prey changes that occur in response to climate change.

The leatherbacks nesting at Bird's Head Peninsula, Papua Barat, Indonesia, account for 75% of the total leatherback nesting in the western Pacific and represent the last sizeable nesting population in the entire Pacific. Sporadic nest counts at Jamursba Medi Beach at Bird's Head have indicated a declining trend from the 1980s through 2004, although a relatively high amount of nesting has recently been documented at Wermon Beach, located 30 km east of Jamursba Medi. We used expanded year‐round nesting surveys from 2005 to 2011 at these two primary nesting beaches to obtain more robust estimates of the nesting population size and to evaluate long‐term nesting trends. We found a 29% decline in nesting at Jamursba Medi and a 52% decline at Wermon from 2005 through 2011. We found that the estimated annual number of nests at Jamursba Medi has declined 78.3% over the past 27 years (5.5% annual rate of decline) from 14,522 in 1984 to 1,596 in 2011. Nesting at Wermon has been monitored since 2002 and has declined 62.8% (11.6% annual rate of decline) from 2,994 nests in 2002 to 1,096 in 2011. Collectively, our findings indicate a continual and significant long term nesting decline of 5.9% per year at these primary western Pacific beaches since 1984. Mark‐recapture with PIT tags, initiated in 2003, resulted in the tagging of 1,371 individual nesting females as of March 2012. Observed clutch frequencies ranged from 3‐10 per season with a mean of 5.5 ± 1.6 and, based on nest counts, provide an estimate of approximately 489 females nesting in 2011. The persistent and long term decline we report for the Bird's Head leatherback population follows other dramatic declines and extinctions of leatherback populations throughout the Pacific over the last 30 years. These findings highlight the urgent need for continued and enhanced conservation and management efforts to prevent the collapse of what might be the last remaining stronghold for leatherbacks in the Pacific.

Hatching success for leatherback turtles (Dermochelys coriacea) was low at 4 important nesting beaches in Papua, with high rates of tidal inundation, pig predation, and possible temperature effects. Better protection from pigs and possible nest relocation may be needed to improve hatching success for leatherbacks.