Kemp's ridley was a puzzle in mid-century herpetology: adults were familiar in the Gulf of Mexico, but no nesting beach had been documented. The Mexican engineer Andrés Herrera filmed an arribada at Rancho Nuevo, Tamaulipas, in 1947. When the footage came to the attention of biologists in the early 1960s, counts from it indicated on the order of forty thousand females nesting in one day.
By the mid-1980s the annual count of nests had fallen to a few hundred. Egg collection and drowning in shrimp trawls were the principal causes. A binational protection programme, beach patrols and turtle excluder devices in trawl nets followed.
Numbers rose through the 1990s and 2000s and then stalled. Unlike other sea turtles, Kemp's ridleys nest mainly in daylight, which makes them easier to count but also easier to take.