Years ago, while sailing off Coast Rica, I saw something so amazing, I sometimes wonder if, having seen pictures of the event, I just dreamed I saw it. But Craig was there and confirms the facts: Floating in the water, looking like so many army helmets, were thousands of olive-green turtles, ranging as far as we could see. Unknowingly, we'd sailed into an arribada.

Arribada is the name of the olive ridley's nesting strategy, as well as that of its same-sized Gulf of Mexico cousin, the Kemp ridley. During an arribada, hundreds of thousands of these 2-foot-long turtles (the smallest in the world) gather off certain beaches, and over several days, come ashore to dig holes in the sand and lay eggs.

No one knows why these turtles congregate to nest in such numbers (both ridleys are the only ones that do it), but the system has serious drawbacks. One is that massive assemblies make it easy for hunters to kill thousands of turtles in one or two nights, which is what happened in the '60s and '70s.

Today, most countries protect their ridleys during arribadas, but both olive and Kemps are endangered species.

The other negative of nesting by the thousands is with so many females descending on a beach at once, they unintentionally dig up each others' nests, exposing, breaking or sending newly laid eggs flying.

But there is a good side to that. Since turtle eggs are in great demand by some people, this natural loss of eggs offers a conservation-sound opportunity. In Coast Rica, on the first day of an arribada, people are allowed to collect eggs and sell them in local markets. That way, collectors earn money, turtle-egg-eaters get a treat, and the next nesters have eggless sand in which to dig.

Some olive ridleys skip these big get-togethers and lay their eggs alone.

Although the species is rare in Hawaii, one of those loners recently chose Oahu for its nesting site. And for that nest's success, we can thank the Marines.

This summer, a beach walker at Marine Corps Base Hawaii in Kaneohe saw a turtle at Pyramid Rock Beach patting down the sand in a kind of dance. Although olive ridleys are known for energetic tamping down of the sand with their bottom shell, no one had to guess this turtle's species. The alert observer took pictures of the turtle mom as she headed back to the water.

Marine officials notified federal wildlife biologists, blocked off the beach to protect the nest and two months later, on Sept. 13, 55 tiny miracles popped out of their shells. Thirty-three olive-ridley hatchlings emerged on their own, with researchers giving a helping hand to 22 more.

This is only the third time an olive ridley has laid eggs in Hawaii. The first was near Paia, Maui, on 1985, and the second near Hilo in 2002.

Olive-ridleys forage for jellyfish, fish and crabs. When basking at sea, they can look like cartoon turtles because booby birds sometimes perch on their backs, hunting the fish that hide beneath the turtles' bodies.

I've not seen an olive ridley since I sailed into that arribada in the late '80s, nor did I see the recent hatching at Pyramid Rock. But that's OK. I'm just happy knowing that when I picture olive ridleys in a crowd in Costa Rica, or one alone in Hawaii, it's not just a dream.