Leatherback Sea Turtles

An Ancient Species in Distress

 

by

Marcus P. Borom

 

          May 3rd, 1992 - Fredericksted, US Virgin Islands.  High noon.  The sun soaks into my body as I recline on a chaise lounge at beachside.  The turquoise water rhythmically caresses the white sand beach that is devoid of people except for a few local children.  Three sailboats lie at anchor at the end of the Fredericksted pier with their masts sweeping back and forth as if in an attempt to paint the thin clouds overhead.  The intensity of the sun is disguised by the constant, cooling breeze which climbs onto the beach from the sea and runs in rivulets along the full length of my body.

          It is hard to imagine that such a paradise for humans can be the site of a battle for survival for a species that has lived and bred successfully on the face of the earth for 250 million years.  The continued existence of the Leatherback Sea Turtle is, however, in question, and one of those battlefields is in the midst of the splendor of the Virgin Islands.

          One of the forces acting in the behalf of these wondrous and mysterious creatures is Earthwatch, an organization which sponsors approximately 120 scientific research projects around the world every year.  Volunteers, like myself, not only pay their own expenses to remote corners of the earth but also pay a share of the project costs for the privilege of working toward the betterment of our environment.

          There are around 100,000 Leatherback sea turtles worldwide.  Monitoring their numbers is difficult since from the time they hatch and make their wild frenzied dash for the surf only the females return again as adults to make their nests on their natal beach and lay their clutch of up to 150 eggs to start a new generation of Leatherbacks.  From tagging and monitoring of the nesting females it has been learned that a female Leatherback nests every two years and may lay as many as 10 clutches of eggs in a single season.  Prior to the beginning of tagging programs, the breeding population of the Leatherbacks was overestimated since only the number of nests was monitored rather than the number of individual nesting females.

          On an average, an adult female Leatherback will lay around 500 eggs a year.  Her breeding life is unknown, but assuming 30 years she will lay around 15,000 eggs which will produce less than 100 breeding females.  In the race for survival, hatchlings face severe predation.  In their infantile dash to the sea they have to run a gauntlet of ghost crabs, sand traps and tangles of vegetation.  Once these sea cookies with flailing flippers hit the water's edge, they encounter an armada of hungry reef fish who lie in wait in the shallows.  In the open ocean they are sought out by albacore, amber jacks, tuna, dolphins and sharks.  But the greatest and most damaging predator is man.

          Without protection every Leatherback sea turtle nest in the Caribbean would be robbed by poachers.  Sea turtles remain in a sexual embrace for hours.  This behavior has spawned the belief among Caribbean islanders that eating sea turtle eggs enhances sexual prowess.  Turtle eggs sell for around $5 each.  A single nest with 100 eggs is more than a good night's wage for a poacher.  The continuity of the nesting population is very misleading since the loss of new hatchlings through poaching may not be felt for 30-40 years.   When the current and unreplenished population of adult sea turtles begins to die off, their population will precipitously decline.  One of the goals of the Earthwatch project is to eliminate poaching by constant patrolling of the beach and by educating St. Croix residents regarding the plight of the Leatherbacks.

          Earthwatch teams of 6-10 volunteers led by biologists Peter Dutton, Donna McDonald and Rafe Boulon patrol a 2 mile stretch of traditional nesting beach on Sandy Point on the island of St. Croix in the US Virgin Islands.  Starting in February, the patrol begins at 7:30 p.m. each evening and continues until around 5:00 a.m.  A nesting turtle can occupy as much as an hour of research team time.  After 10 miles of walking in deep, soft sand with the aid of only the moon or starlight, Earthwatch volunteers look forward to falling into bed for a well deserved rest.  With the rising sun signalling approaching sleep, it is understandable that fatigued volunteers give those inconsiderate Leatherbacks who ignore the approaching dawn and ascend the beach anyway the accolade of "the dreaded dawn turtle."

          Even though we were aware that Leatherback Sea Turtles are enormous reptiles up to 7 feet long and weighing up to 2000 lbs., the first encounter is an event of sheer wonder and excitement.  Our dark-adapted eyes strain to pick out tell-tale signs of sea turtle activity in the sand ahead of us (flashlights are used only when working with the turtles).  It is amazing that we are able to distinguish shape and form in the light provided only by stars.  A subtle change in the coloration of the sand from dry and white to damp and dark indicates that one of these amazing sea nomads has struggled ashore.  Her flippers have left a broad swath of turned, damp sand like the tread of a giant tractor.  If we are lucky enough to see her emerge from the ocean we are struck by her determination to carry out an age-old program of reproduction against what seems to be overwhelming odds.

          The Leatherback is a marvelous swimmer.  Tagged adult Leatherbacks from Sandy Point have been observed in Arctic waters and as far away as the west coast of Africa (almost 4000 miles from St. Croix).  Depth-time recorders have been strapped on female Leatherbacks nesting on Sandy Point and retrieved when they return 10 days later to lay another clutch of eggs.  The records have shown that the Leatherbacks are among the deepest diving air breathing creatures in the world.  They reach depths of over 4000 ft. to feed on jelly fish and salphs found in the biostrata known as the deep scattering layer.

          All the streamlined features that have evolved over eons to enable these turtles to become world class members of the sea community seem to fail them when the females emerge from the sea to nest.  Their struggle is incredible.  The egg laden mother throws her front flippers forward in a breast stroke motion and jams their leading edges into the sand for purchase.  With each stroke she drags her huge bulk only 4-5 inches.  After 5 or 6 strokes she must rest and gasp for air before attempting to move ahead another few feet.  Some of the obstacles these creatures scale to reach suitable nest sites are unbelievable.  On the NW shore of Sandy Point the sea can carve the beach into 7 ft. high vertical walls of sand.  These persistent reptiles driven by their reproductive clock will flail at these cliffs of sand until they have converted them to a manageable ramp with a slope of 1.  In the bright light of day, their efforts resemble the work of a bulldozer.

          Once a suitable nesting site has been selected, the female begins a process that has been genetically programmed.  A process that was not taught to her by her parents.  She has never known her father.  Her mother abandoned her before she ever hatched.  She has received no parental guidance for her whole life.  Yet, she, like her mother before her, will navigate to her natal beach, select a nesting site, excavate a nest, lay her eggs, camouflage the site and leave her hatchlings to their own devices.  Once the genetic tape has begun to play, there is not much that will stop it from running to completion.  Biologists have found, however, that a tug on the turtles' 4 inch diameter tail during egg laying is a sure fire STOP/ABORT button.  During the monitoring process, volunteers avoid contacting the tail at all costs.

          After site selection, the turtle begins to dig in with her front flippers alone - a procedure referred to as body pitting.  Without a firm purchase for the slender, powerful wing-like tapered front flippers, the turtle would slide unceremoniously into the nest cavity yet to be dug by her hind flippers.

          The nest cavity is excavated by the broad, stubby hind flippers which are effectively used as rudders when the turtle is in the sea.  During excavation they become powerful, flexible, dexterous scoops which perform their operation by touch alone.  The turtle never visually inspects the nest hole.  One rear flipper will scoop straight down, curl to the inside, lift up with about 1 pt. of sand, carefully rotate to the rear and outside and deposit the load beyond where the flipper will come to rest palm down.  The opposite flipper then repeats the procedure and then "the sequence" begins again.  During the digging the Earthwatch volunteers inspect the trailing edges of the rear flippers for tags and record their numbers or call to have tags placed on untagged turtles.

          When the expectant mother is satisfied with the depth (around 30 inches) and the undercut, elliptical post hole shape of the nest, she will drop one rear flipper alongside her tail to protect the eggs while they are being laid.  If the nest is in an erosion resistant section of the beach, the Earthwatch volunteers move the covering flipper aside, taking care not to touch her tail and use thumb operated counters to tally the billiard ball sized, yolked eggs.  The end of the clutch will include groups of smaller, infertile, yolkless eggs which are also tallied.

          Turtles sometimes select nest sites in beach areas which are known to be subject to severe tidal erosion.  Eggs laid in erosion prone areas are almost certain to be lost during the incubation period.  Under these circumstances, Earthwatch team members actually catch the mucous covered eggs as they are being laid, and relocate them to a safe site later in the evening.  Since site selection is a random geographical problem rather than a part of the genetic code, relocation is considered an act beneficial to species survival rather than one which would contribute to a strain of turtles too dumb to nest in the right spot.

          After the clutch has been laid, the turtle begins to cover the eggs by dragging sand into the hole with alternating flippers.  She keeps her tail pointing down into the hole as a gauge to monitor successful filling and packing as she fills and tamps.  Before the nest is backfilled, the research team makes precise triangulation measurements so that the nest can be located at a later time to measure hatchling success.  If triangulation measurements are not performed, the nest location becomes completely obscured by the next sequence in the genetic tape known as disguising.  With all her energy the new mother begins to throw sand with both front flippers.  She will continue to change direction and location as she also slings sand with her rear flippers.  She may cover a 10 yd. square area before beginning her final trek to the sea.

          Not all nesting attempts are successful and some have to be helped along in an attempt to maximize hatchling success.  There were some turtles with major portions of a rear flipper missing due likely to shark attack.  The genetic tape, however, continues to run its course.  The missing flipper goes through all the motions of digging and throwing sand even though nothing is happening.  Earthwatch team members "lend a flipper" in between scoops of the ghost flipper to complete the nest to the point that the turtle will initiate laying.

          A real feeling of success swept through the team on one of those starlit nights in May of 1992.  A fresh, never before tagged, young female Leatherback with no flipper damage or signs of distress struggled ashore to lay what we assumed was her very first clutch of eggs.  It was concluded that this turtle was the first returning hatchling saved from poachers twelve years earlier with the beginning of the protection and monitoring program.  Other young untagged females followed during the season to yield a new record for number of nesting Leatherbacks on Sandy Point.  The program is paying off.  The Leatherbacks are returning.

          In nature, some nesting attempts are totally unsuccessful.  Some turtles make "false crawls" several times without finding a suitable nesting site.  In a final act of desperation, like in a taxi on the way to the delivery room, a frustrated, expectant turtle will actually dig a nest in the surf.  Earthwatchers who lie face down in the froth of the surf, stretched out behind a desperate turtle to rescue otherwise lost eggs deserve a special badge of dedication.  Soaked in salt water, gritty with sand, chilled by the wind and with no hope for a shower and warm clothing until dawn - that is the measure of a lay person concerned about our environment and species survival - that is Earthwatch.