Kemp's Ridley Sea Turtle

Because it started from a tiny base and depends on a single place. It has the smallest population of any sea turtle, and almost all of its nesting is concentrated on one beach in Mexico, so a disaster there, whether a storm, a disease outbreak, or renewed poaching, could affect the entire species at once. It was also hit exceptionally hard in the twentieth century, first by industrial-scale collection of its eggs, which are easy to gather in bulk during the mass arrivals, and then by accidental capture and drowning in shrimp trawl nets across its Gulf of Mexico range. It came within a whisker of disappearing before protection began.

Arribada is Spanish for arrival, and it describes the mass synchronised nesting seen in the two ridley turtle species and almost no other. Instead of females coming ashore alone and at night, as most sea turtles do, ridleys gather offshore and then land in large groups, often in daylight, over one or two days, sometimes with thousands of turtles nesting shoulder to shoulder on a single beach. The likely benefit is safety in numbers for the eggs and hatchlings — predators such as crabs, birds, and mammals can only eat so many, so flooding the beach with nests at once means a higher proportion survive.

Through a sustained joint effort by Mexico and the United States. Mexico made Rancho Nuevo a protected reserve and stationed people on the beach to guard nests, move them to safe corrals, and protect the hatchlings on their way to the sea. A programme moved some eggs to Padre Island in Texas to try to establish a second nesting site. Crucially, the United States, after years of resistance from the shrimping industry, required turtle excluder devices, trapdoors in trawl nets that let a turtle escape, throughout the Gulf and south Atlantic. Nesting numbers responded, rising from a few hundred to tens of thousands of nests over about 25 years.

The turnaround around 2010 coincided with the Deepwater Horizon oil spill, which released a very large amount of oil into the northern Gulf of Mexico, exactly where adult and juvenile Kemp's ridleys feed and migrate. Oil exposure, the loss of prey, and the effects of the response effort are thought to have set the population back, and nesting numbers have been flat or slightly falling since. Continued trawl bycatch despite the excluder-device rules, boat strikes, marine debris, coastal development, and climate effects on the nesting beach and on hatchling sex ratios are all also implicated, and the species remains a focus of intensive conservation.