Thanks for Basking

Last week I found myself on the Hawaiian island of O‘ahu, part of — I swear! — a very arduous and intellectually demanding book-reporting trip. (More on that…someday.) After my grueling days of reportage, Elise and I headed up to the island’s North Shore, where, to our astonishment, we found the beaches positively littered with relaxing green sea turtles. Although I’d seen turtles come ashore to deposit their eggs — in fact I once spent a blissful season on a North Carolina barrier island, monitoring laying loggerheads and protecting their nests — I’d never seen one hauled out for the sole purpose of lying in the sun, and didn’t even know they engaged in that behavior. (NOAA claims it’s unique to Hawaii, and it is most common there, but scientists have also observed the phenomenon in Australia, Mexico, and the Galapagos Islands. Only green turtles do it.) They were spectacular in the way of all turtles, of course, sculpted and gleaming and placid, practically geologic in their ancient solidity.

I assumed that the basking had an obvious thermoregulatory function — warming up speeds reptilian digestion, among other functions. But it may not be entirely that simple, as a herpetologist named Hunter Howell pointed out to me in the graveyard once called Twitter. Green turtles often bask well into the evening (and indeed, I saw them lounging long after sunset), by which time the air is actually colder than the ocean, and we beach-lazing humans have long since gone back to our cabanas to take a hot shower and throw on a sweatshirt. So if the point isn’t solely to get warm, what else might motivate a turtle to drag its carapace ashore? Researchers have postulated that turtles leave the water to escape sharks, recuse themselves from competition over seagrass beds, or, in the case of females, avoid the unwanted advances of amorous males. Perhaps the simplest explanation is also the right one: You just save a lot more energy lying around than you do swimming. Or it’s all of the above. Whatever the purpose, Hawaii’s turtles do it a lot; one monitored turtle basked for a whopping 945 minutes in a single session, nearly sixteen hours. Hopefully she’d applied plenty of sunscreen.

(Oh, and a word about good turtle protocol — give the sunbathing reptiles their space, and report sightings through Honu Count, a volunteer-science portal.)