They shell rise again

Sea tur­tles make a come­back, but their ex­is­tence is al­ways ten­u­ous

The Citizens' Voice - - HEALTH & SCIENCE - BY PA­TRICK J. MC­DON­NELL

PLAYA MORRO AYUTA, Mex­ico — They ap­pear as ghostly shad­ows rid­ing be­neath the surf, their beaks and shells il­lu­mi­nated in the moon­light as they drift in the swells.

As dawn ap­proaches, col­umns of the pri­mor­dial fig­ures emerge clum­sily from the sea, and by mid­morn­ing, the lum­ber­ing, 80-pound-plus am­phibi­ous in­vaders will have over­taken the beach, their flip­pers kick­ing up tufts of sand and the pound­ing of their shells against the wet sand com­ple­ment­ing the crash­ing waves.

Welcome to one of na­ture’s most cin­e­matic scenes: the syn­chro­nized mass nest­ing, or ar­rib­ada (ar­rival), of fe­male olive ri­d­ley sea tur­tles along Mex­ico’s Pa­cific coast.

Hun­dreds of thou­sands of gol­fi­nas, as they are known here, may hit the beach dur­ing ar­rib­adas, oc­cur­ring roughly once a month from July to Fe­bru­ary.

Still of­fi­cially listed as en­dan­gered, the olive ri­d­ley has none­the­less made a spec­tac­u­lar re­cov­ery. Con­ser­va­tion­ists credit both le­gal pro­tec­tions and a gen­er­a­tional shift in at­ti­tude among Mex­i­cans who once sus­tained the in­dus­trial-scale loot­ing of eggs, which were eaten and re­garded as a male aphro­disiac.

“We can see that this species of tur­tle is on the road to re­cu­per­a­tion,” said An­gel Guillermo Gonzalez Padilla, co­or­di­na­tor of the Mex­i­can en­vi­ron­men­tal agency’s pro­tec­tion ef­forts here, as he ob­served thou­sands of nest­ing olive ri­d­leys on a stretch of this white-sand beach.

While the species still faces threats such as float­ing fish­ing tackle, cli­mate change, beach ero­sion, plas­tic and other sources of pol­lu­tion, bi­ol­o­gists say the up­swing in nests here is a clear sign that the rep­tile’s num­bers may be sta­bi­liz­ing, if not in­creas­ing.

A nat­u­ral mys­tery

Some lit­tle-un­der­stood pri­mal im­print — pos­si­bly re­lated to the Earth’s mag­netic field, wave pat­terns, cur­rents and sin­gu­lar smells — drives egg-bear­ing fe­males to re­turn from pro­longed marine wan­der­ings to the beaches where they were born years ear­lier. They de­posit in­di­vid­ual clutches of about 100 eggs. Mass nest­ings also take place on beaches in Costa Rica and In­dia.

A record 4.6 mil­lion olive ri­d­leys nested last year on Mex­ico’s Pa­cific coast, mostly here at Playa Morro Ayuta in Oax­aca state and up the coast at Playa Es­co­billa.

It’s a stun­ning turn­around from the 1980s, an era of vast egg poach­ing and com­mer­cial tur­tle slaugh­ter in Mex­ico when the an­nual ar­rival of the tur­tles av­er­aged about 120,000.

In 1990, a pres­i­den­tial de­cree out­lawed the cap­ture of sea tur­tles and banned col­lect­ing their eggs in Mex­ico, where beaches pro­vide nest­ing sites for six of the world’s seven sea tur­tle species. Mex­i­can troops and en­vi­ron­men­tal teams now pa­trol nest­ing beaches to de­ter hueveros, the il­licit egg gath­er­ers.

While other sea tur­tles such as the en­dan­gered Kemp’s ri­d­ley have also staged come­backs in Mex­ico, the scope of the olive ri­d­ley nest­ing as­sem­blages is un­matched. Sci­en­tists view the phe­nom­e­non as an evo­lu­tion­ary adap­ta­tion — known as “preda­tor swamp­ing” — in which there is sim­ply more prey than preda­tors.

Last year, au­thor­i­ties say, 77 mil­lion olive ri­d­ley hatch­lings made their way to­ward the sea on Mex­i­can beaches, though only 1 in 1,000 are said to ac­tu­ally reach adult­hood.

Al­though hu­man poach­ing re­mains a prob­lem, it is now re­garded here as less of a peril to the tur­tles than other dan­gers, such as the “ghost nets,” the aban­doned fish­ing tackle float­ing in the sea that can en­tan­gle the tur­tles.

In late Au­gust, more than 300 olive ri­d­leys, ap­par­ently fe­males poised to nest, were snared in nets float­ing off the coast of Oax­aca. All drowned. Images of the trapped, help­less tur­tles drew global alarm.

Though now con­sid­ered the most abun­dant sea tur­tle, the olive ri­d­ley — 2 to 2½ feet long and weigh­ing 80 to 110 pounds — is still listed as “in threat of ex­tinc­tion” in Mex­ico.

“Yes, we have suc­ceeded in in­creas­ing the num­ber of nest­ing tur­tles, but that is not to say that this species is out of dan­ger,” said Va­le­ria Towns, who over­sees threat­ened species for Mex­ico’s Na­tional Pro­tected Ar­eas Com­mis­sion.

Added Christine Figgener, a marine bi­ol­o­gist at Texas A&M Univer­sity: “We need a lot more an­swers to ques­tions about how many olive ri­d­leys are out there and what threats they are fac­ing.”

What’s in a name?

The olive ri­d­ley in­hab­its trop­i­cal and warm waters of the Pa­cific, Atlantic and In­dian oceans, feed­ing on crus­taceans, jel­ly­fish and mol­lusks. Its name de­rives from the pale green hue of its roughly heart-shaped top shell, though the et­y­mol­ogy of “ri­d­ley” re­mains un­clear.

Less than a gen­er­a­tion ago, the olive ri­d­ley in Mex­ico seemed to be hurtling to­ward doom.

Divers caught mul­ti­tudes at sea each year dur­ing the 1980s and ear­lier to be har­vested for meat, skin and shells, and coastal slaugh­ter­houses served as a grisly fi­nal stop for the peri­patetic tur­tles.

Grainy footage from the era re­cently aired on the Tele­visa net­work showed a grotesque scene with a row of cap­tive olive ri­d­leys ar­rayed on a ta­ble where a worker would fire a pis­tol into the an­i­mals’ heads. An­other clip dis­played a pile of butchered tur­tles, some with their limbs still flap­ping spas­mod­i­cally.

“The blood ran into the ocean,” re­called Miguel Garcia Lopez, 70, who worked in a tur­tle slaugh­ter­house at San Agus­tinillo, a beach-side ham­let up the coast from here. “It was quite hor­ri­ble, yes. But the fac­tory pro­vided work.”

Now, San Agus­tinillo and neigh­bor­ing Mazunte are thriv­ing beach re­sorts lack­ing any trace of the old tur­tle killing grounds.

On a re­cent morn­ing, the ar­rib­ada com­mences be­fore dawn un­der the glow of a full moon. Soon the beach is teem­ing with tur­tles, their tracks criss­cross­ing the sand like tank tread mark­ings.

Ping­pong-ball-size eggs lit­ter the area. In their ex­er­tions, the moth­ers reg­u­larly dig up in­cu­bat­ing eggs left by pre­vi­ous waves of olive ri­d­leys.

Dogs stalk the beach seek­ing tur­tle egg snacks. Vul­tures and preda­tory birds hover.

The tur­tles ad­vance be­yond the high-tide line, find an ap­pro­pri­ate spot and be­gin ex­ca­va­tion with both sets of flip­pers, seem­ingly obliv­i­ous to the pres­ence of oth­ers, some­times in shell-to-shell prox­im­ity on the beach. They pound down with their shells to cre­ate oval-shaped body pits. Hind flip­pers spade out cav­i­ties for the eggs.

The crea­tures go into a kind of trance as they re­lease their eggs, then use their hind flip­pers to cover them with sand, hid­ing them from preda­tors and en­sur­ing the eggs re­main moist and main­tain proper in­cu­ba­tion tem­per­a­ture.

The nest­ing tur­tles gen­er­ally spend an hour or so on land.

There is no mother’s care for the hatch­lings, which will emerge as dark-toned diminu­tives in about 50 days, fac­ing as­tro­nom­i­cal odds against sur­vival.

Done with their ma­ter­nal du­ties, the wea­ried olive ri­d­leys of­ten pause at the shore­line, con­tent to let the tide carry them back to sea, where they are grace­ful swim­mers, not plod­ding ter­res­trial beasts driven by in­stinct to ful­fill their evo­lu­tion­ary bur­den.

ALAN BERNER / TRI­BUNE News SER­VICE

Mon­i­tors are at­tached to an olive ri­d­ley sea tur­tle be­ing re­ha­bil­i­tated at the Seat­tle Aquar­ium in March 2016. In Mex­ico, the en­dan­gered olive ri­d­ley sea tur­tle is bounc­ing back.

AS­SO­CI­ATED Press FILE

An olive ri­d­ley sea tur­tle hatch­ling plods to­ward the sea in Sayulita, Mex­i­can state of Na­yarit, on Dec. 2.

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