Why are leatherbacks Critically Endangered in the Pacific Ocean yet designated as Vulnerable globally?

Experts use Regional Management Units (RMUs) to distinguish thriving sea turtle populations from threatened ones.

Leatherback turtles exist throughout the world’s oceans. The East and West Pacific leatherback populations are designated Critically Endangered by the International Union for Conservation of Nature (IUCN). Scientists estimate fewer than 650 breeding females remain in the East Pacific leatherback population and fewer than 1500 in the West Pacific leatherback population. Globally, leatherbacks are designated as Vulnerable. This variation in designation is because experts distinguish sea turtle populations by region.

When all leatherbacks are considered as a single unit, scientists argued it radically obscured regional differences. Regional leatherback populations appear to exhibit little cross-over in habitat or gene flow. For these reasons, managing distinct turtle populations separately makes sense.

The Marine Turtle Specialist Group gathered during the 2008 and 2009 IUCN conventions to define Regional Management Units (RMUs) in an effort to promote more targeted conservation measures tailored to the needs of each sea turtle population.

RMUs are fundamental units in sea turtle conservation. Each RMU represents an independent population of sea turtles. The boundaries of RMUs are defined by the geographic distribution of turtles in geographies relevant to each life history stage (e.g., nesting sites, foraging habitats, migration corridors) as well as representation of distinct genetic stocks (i.e., an evolutionarily significant degree of reproductive isolation).

The U.S. Endangered Species Act (ESA) does not use these same fundamental RMU units, but the principles behind its population divisions are the same. In short, the Distinct Population Segments used by the U.S. ESA are functionally equivalent to RMUs since they are based on the natural isolation of various populations.

Ultimately, RMUs improve opportunities for conservation by providing more detailed data on regional populations than global trends or status. To ensure the genetic diversity of the species as a whole, successful conservation requires robust population numbers across RMUs.