Eastern Pacific leatherback turtle movements and area-use in the South Pacific

Leatherback turtles (Dermochelys coriacea) are highly mobile species that migrate across entire ocean basins, which makes them highly susceptible to several anthropogenic stressors.

Pacific leatherbacks form two distinct breeding population groups with different migration patterns. In the eastern Pacific, nesting populations are found along the coasts of Central America, while western Pacific populations nest primarily in the Solomon Islands, Papua New Guinea, and Papua Barat, Indonesia. Historically, both populations have been robust, but because of their long migrations and relatively long life cycle, they are highly sensitive to several anthropogenic stressors. These populations are currently in decline and listed as “critically endangered” on the International Union for Conservation of Nature (IUCN) Redlist.

Understanding migratory ranges

Understanding the political biogeography of these highly threatened populations is especially important, as their management is jurisdictionally complex. Female eastern Pacific leatherback turtles show consistent post-nesting dispersal from their Central American nesting sites along a southward migratory corridor towards the South Pacific Gyre (Figure 1). Much of this population’s transit time is spent traveling through Ecuadorian waters around the Galapagos and on the high seas, governance is fragmented and largely consensus-based. Along the most southern parts of their tracks in the southeastern Pacific, changes in both horizontal and vertical movements suggest foraging behavior. Leatherbacks in this offshore foraging area have been observed reaching average maximum depths over 600 m, mimicking the diel patterns of their prey of gelatinous zooplankton that move up to the epipelagic zone at night and return to the mesopelagic zone during the day.

However, these post-nesting tracking studies are just one glimpse into area-use by leatherbacks in the South Pacific. Fisheries data and published literature from fisheries indicate that South American coastal waters are also high-use areas for this population. Compared to other regions around the world, eastern Pacific leatherback sea turtle bycatch rates in net fisheries were among the highest. fisheries bycatch records show that large leatherbacks, which are of high reproductive value to the population, make up a large majority of the Chilean longline bycatch with 284 caught between the years 2001-2005 (Figure 2). Similarly, bycatch reports for the coastal waters off Peru contain high rates of leatherbacks as well. Therefore, the high rates of observation of leatherback bycatch both inside and outside of national jurisdiction need to be addressed through cooperative measures.

Although there is still uncertainty over the relative magnitudes of the impact from different fisheries on the population of eastern Pacific leatherback sea turtles, the waters off Peru and Chile are shown to be important foraging and migratory regions for these leatherbacks. In- water satellite tagging efforts in Peru by the NGO ProDelphinus working with fishermen have begun to give us a glimpse of where the juveniles are spending their time. Use of horizontal migratory corridors by these tagged individuals show drastic differences from previously cited telemetry studies of post nesting females from Central America, beginning to introduce a more complete picture of the various movement patterns within this population.

Connectivity between regions

The area-use patterns described in the literature summarized here connect life history stages of the eastern Pacific leatherback sea turtle population across EEZs in Central America (Mexico, Guatemala, El Salvador, Nicaragua, Costa Rica and Panama) to juvenile and adult foraging grounds in Peru and Chile, and migratory corridors through Colombia and Ecuador. Further, the tracking work on juveniles in Peruvian waters implies greater connectivity between national jurisdictions in Pacific South America and areas beyond national jurisdiction, including potential for connectivity between the eastern and western South Pacific. Conservation of this critically endangered population requires coordination among coastal states in Central and South America, as well as with governance frameworks with competency in areas beyond national jurisdiction (e.g., the South Pacific Regional Fisheries Management Organization [SPRFMO] and the Inter-American Tropical Tuna Commission [IATTC]).