MEET THE TWO SPECIES
Leatherback (Dermochelys coriacea)
Leatherbacks roaming the oceans today are virtually carbon copies of their ancestors from more than 100 million years ago; they lived among dinosaurs, even outlasting them.
By far the largest of all living sea turtles, leatherbacks can grow to a carapace length of nearly 2 m (7 ft) and a weight of up to 800 kg (1,760 lbs).
They are easily distinguished from other living sea turtle species by their massive size and lack of a completely fused, bony shell. They also have a teardrop-shaped body and a somewhat flexible, smooth-skinned shell with pronounced ridges on their backs (dorsal) and bellies (ventral). Together, these features give leatherbacks unparalleled hydrodynamics and swimming efficiency among turtles.
In addition to their unique body form, leatherbacks have a diet unlike any other sea turtle: they exclusively consume soft-bodied prey on the high seas, such as jellyfish, salps, and pyrosomes.
Regarding distribution, leatherback nesting occurs along the Pacific coast of the Americas from México to Ecuador, concentrating in México and Central America.
After nesting, most Eastern Pacific leatherbacks migrate to waters in the southeastern Pacific, south of the equator, offshore of countries like Ecuador, Peru, and Chile, and northward into the Gulf of California. The number of nesting female leatherbacks in the Eastern Pacific has declined by more than 90 percent over the past thirty years. However, leatherback nesting has stabilized, particularly in Mexico.
Ongoing bycatch in commercial and artisanal and driftnet and longline fisheries remains the biggest threat to the species, with leatherbacks most susceptible to fisheries interactions directly adjacent to their nesting beaches and in the foraging areas in the southeastern Pacific.
Loggerhead (Caretta caretta)
The loggerhead is an enigmatic species. For years, fishers and scientists had seen loggerheads in the waters of the Eastern Pacific, especially along the coast of Mexico, yet nesting beaches were unknown in the region. Nowadays, there is an awareness that all loggerheads found off Pacific Mexico originate from nesting beaches in Japan, nearly 10,000 km (6213.7 mi) away.
Hatchling loggerheads depart Japanese nesting beaches and move eastward to distant developmental and foraging habitats where they grow and mature. While in foraging areas, loggerheads are opportunistic omnivores, consuming a variety of benthic prey found in the mid-water and coastal regions.
Once individuals reach sexual maturity, they return to their natal nesting beaches in Japan for reproduction and remain in the Western Pacific for the remainder of their life cycle, never returning to the Eastern Pacific.
Relative to historical abundance, today's loggerhead nesting population in Japan is substantially low, although some encouragingly positive trends exist in increasing nesting abundance. The primary causes of these declines are loss of nesting habitat and, more so, bycatch in marine fisheries.
These loggerheads forage in the high seas of the Central Pacific, with an unknown proportion of the population moving to the eastern Pacific, off southern California U.S., and the coasts of Northwest Mexico, especially in the Gulf of Ulloa along the Pacific Coast of the Baja California Peninsula.
The Gulf Of Ulloa is of significant importance for the North Pacific loggerhead population, as it is one of the hotspots for fisheries bycatch in Mexico, where more than 1,000 dead loggerheads would wash ashore in any given year. Thankfully, conservation efforts prompted by the Mexican government and local community groups have reduced this mortality rate.