Overview

The project’s primary goals are to research, protect, preserve and enhance the population of leatherback turtles (Dermochelys coriacea) nesting at the Sandy Point National Wildlife Refuge, St. Croix, U.S. Virgin Islands.  This is the largest nesting population of leatherbacks in the United States.  The project also provides an excellent opportunity to study the biology and reproductive physiology of one of the world's oldest living vertebrate species.  Long-term monitoring of a discrete population such as this one enables management measures to be developed and monitored for effectiveness.  The goals of this project follow the goals of the Recovery Plan for Leatherback Turtles in the U.S. Caribbean, Atlantic and Gulf of Mexico (NMFS and USFWS 1992).

During the twenty-three years of this project, we have answered many questions about this little-known reptile.  2004 results are summarized in Alexander et al. (2004).  For example, we know that the female leatherbacks nest on two to seven year intervals, and that while females lay 5 - 6 clutches per season on average, they may lay up to 11 clutches in a season (a clutch is all the eggs in one nesting event).  We have established sand and nest temperatures at various times during the nesting season, and from these data have been able to estimate corresponding hatchling sex ratios (Basford 1988).  We know that the adults are able to dive to depths of at least 1500 m (Eckert et al., 1986, 1989).  We have developed and greatly improved identification techniques such as Passive Integrated Transponder (PIT) tagging and photoidentification, and so are able to more accurately estimate population size, recruitment, and remigration rates (McDonald and Dutton 1996).  Using these techniques, we have re-identified many individuals thought lost to the population, and developed more complete biological profiles on these turtles.  Satellite telemetry and direct observations have shown that leatherbacks sometimes travel between islands during interesting movements (Keinath and Musick 1993).  Physiological studies have shown that leatherbacks store oxygen in blood and tissue during deep dives (Lutcavage et al., 1990).

Through this project we have developed management measures which have significantly increased (doubled in some years) the numbers of hatchlings that leave the beach.  We have reduced the number and degree of impacts (poaching, vehicles, horses, predation) on nests and hatchlings. In 2004 we continued utilizing a relocation protocol designed to mimic the random nesting patterns of females.  This helped alleviate predation problems due to unnaturally high densities of nests in the relocation area of the beach.  A major problem continues to be light disorientation of the hatchlings, which was the focus of Violeta Villanueva-Mayor’s Master of Science research in 2001.  We provided the U.S. Fish and Wildlife Service (USFWS) documented proof of this disorientation, which the Service used to fund equipment to reduce the effects of commercial lighting near Sandy Point.  Data from this project were used, and will continue to be used, to develop the Marine Turtle Management Plan at Sandy Point, which is used as a reference by the USFWS (McDonald Dutton, 1997).

Perhaps most significantly, long-term effects of management are now being realized. From 1991 – 1996, the Sandy Point population showed an increase in numbers, reaching a record high of 118 individuals.  The previous record was 55 (McDonald Dutton et al., 1997). Subsequent years have been similarly high, including the 2001 season which reached a record high of 186 individual females, and the 2003 season which boasted 172 individuals.  Although trends cannot be determined by one season alone, the high numbers evidenced since 1991 are extremely encouraging.  While leatherback populations worldwide, particularly in the Pacific, are declining dramatically (Betz and Welch, 1992; Chan and Liew, 1996; Sarti et al., 1996; Spotila et al., 1996), the Sandy Point population has increased by 560% from the first 4 years of the project to the last 4 years of the project.

All of this would not have been possible without the assistance the Earthwatch Institute provides in the form of logistic and, most importantly, volunteer support.  From 1982 to 2004, 1282 Earthwatch volunteers have assisted with this project.  They walked a total of nearly 103,000 miles and spent a total of over 97,780 volunteer-hours on the beach.  They assisted in tagging and measuring 761 leatherbacks and documenting over 6,900 nests.  They helped relocate over 2730 nests from erosion zones, resulting in around 155,200 hatchlings released to the sea that would otherwise never have survived the time from egg to hatchling.

Although this project has contributed greatly to our understanding of this species, there are many questions that remain unanswered.  Where do females go between nesting seasons?  What is the age of turtles at sexual maturity?  Do they return to their natal beach to nest?  Our ongoing, long-term tagging studies and communication with researchers in other areas, as well as genetic studies being undertaken on this population are beginning to provide information to answer these questions.  Our genetic studies have provided the first evidence for natal homing in leatherbacks and suggest that the St. Croix nesting population is part of a regional population that is relatively isolated from mainland Atlantic populations (Dutton, 1995, 1996; Dutton et al. in press).  These studies have also resulted in a greater understanding of stock structure and mating behavior (Dutton, 1996).

The next four years will provide critical data needed to evaluate the status of this species, information necessary to understand leatherback population dynamics, and to determine how effective the conservation measures undertaken by this project have been.  Long-term research is crucial to studying long-lived species, especially when each individual is only encountered every 2 - 7 years.  Population trends of species like the leatherback turtle can only be detected through long-term monitoring.  Thanks to long-term support for this project, we are finally beginning to develop estimates for age at sexual maturity and patterns of mortality and recruitment of females (Dutton et al., 2000; in press), fundamental questions that have so far eluded population biologists.

Only through continued intensive management efforts combined with public education and international support will we be able to help ensure the Sandy Point leatherback turtle population's survival.

Objectives

The project objectives are to:

• identify turtle encountered
• tag all untagged turtles with both flipper tags and passive integrated (PIT) tags
• collect behavioral and biological data for each nesting female
• move all nests laid below the high water mark or in the erosion zones to stable and accreting areas of the beach
• collect morphological data on each turtle
• collect data of each nest laid

In addition, as this research is continued from season to season, vital population statistics such as remigration figures, recruitment rates and fecundity can be evaluated.  Long-term monitoring is necessary to evaluate success of the management methods (i.e., increase in numbers of nesting turtles).

We also collect blood and tissue samples for genetic analysis, to identify different populations of leatherbacks and test the theory that leatherbacks return to their natal beaches to nest when they mature.  Blood samples will also be collected for physiological studies to quantify the metabolic drain and physiological changes that these turtles experience before, during, and after nesting

PIT tagging and photo-identification of leatherbacks nesting on the nearby island of Culebra, Puerto Rico, began in 1997.  Through cooperation with the researchers on Culebra, we will compare data to get a better estimate of leatherback movement between the two areas.

2005 Research objectives include:

• Terrestrial predation - Terrestrial predation is a function of the length of time the hatchlings spend on the beach.
• Adult injuries – Record and identify injuries, rates of healing, correlate injuries with local marine activities.
• Dive Behavior – We will attach time/depth recorders to determine dive behavior of the turtle compared to her on-beach activities.
• Satellite Telemetry – We will attach satellite telemetry transmitters on select turtles to study their geographical movement during their “internesting period”.  This research in conjunction with the dive behavior research will combine to give a complete picture of the “internesting” behavior of nesting Leatherback turtles.
• Beach Sex Ratio’s – Temperature data loggers will be inserted into In Situ and Relocated nests as well as relocation areas to determine and maintain natural sex ratio’s.

Methods

Study Area Coverage

Project team members patrol Sandy Point on hourly intervals all night (2000 to 0500 hours) every night during the main part of the nesting season, April 1 until ten days after the last turtle nests.  All activities prior to April 1 (typically 10 - 30 per season) are recorded by U.S. Fish and Wildlife Service employees during morning patrols.  Earthwatch volunteers will participate in patrols during the peak nesting period of April 29 to July 15.  There will be seven teams consisting of up to ten volunteers per team, each participating for an eleven day period.  Volunteers will participate in all research activities except for tagging and blood/tissue sampling, which they will be able to observe, but conducted by field staff.

The teams will be divided into groups, each led by a Principal Investigator or Field Leader.  Each group will walk a portion of the study area at 45-minute intervals.  Since previous observations indicate that leatherbacks require at least 1 hour to complete nesting, this will ensure that all nesting turtles are observed and tagged.

Data Collection

Basic data collection procedures are similar to previous years, and follow the techniques described in the Manual of Sea Turtle Research and Conservation Techniques (Pritchard et al., 1983) and the Recovery Plan for Leatherback Turtles in the U.S. Caribbean, Atlantic and Gulf of Mexico (NMFS and USFWS 1992).  Some of the techniques developed here, such as PIT tagging, have been adopted by the Leatherback Task Force of the International Union for the Conservation of Nature (IUCN).

Each time we encounter a turtle, we will complete a separate data sheet.  Morphological, nesting, behavioral data, and nest parameters are recorded along with time and date of encounter.  Nests will be excavated after hatchlings emerge, and the contents categorized to determine hatching success.  Activities of other turtle species will also be documented.

a.  Tagging

For every untagged turtle, we will attach an Inkonel tag to the thin flesh between the rear flipper and the tail.  This tagging method was adopted on Sandy Point in 1981 and has become accepted practice worldwide on leatherback nesting beaches.

We will also tag turtles with a small (14 mm long x 2 mm diameter) glass-encased electromagnetically coded microchip, or Passive Integrated Transponder (PIT) tag.  We will inject these tags directly into the left or right shoulder muscle of each turtle, using the technique described in Dutton and McDonald (1994) and McDonald and Dutton (1996).  The tags are detected with a small portable scanner passed over the area, and the number is displayed on a digital screen on the scanner.  Tags and scanners are manufactured by AVID, Inc.

b.  Morphology

We will use a metal tape to measure over-the-carapace (o.c.) length and width.  Carapace length will be measured from the nuchal notch to the posterior tip alongside the vertebral ridge.  Width will be measured to each side ridge at the widest point of the carapace, which is just posterior to the front flippers.  Individuals will be measured each time they are encountered, and the measurements averaged for the season.  We will examine each turtle for diagnostic markings, deformities and ectobiota (living organisms attached to the turtle’s body or carapace), and photograph injuries and the pink spot on the head of each adult to aid in identification of re-emigrants that lose flipper tags between nesting seasons.

c.  Nesting

Nest digging is observed whenever possible.  Field staff will note any anomalies in digging or nest cavity structure, or whether the nest cavity is excessively moist or dry.  The location of each nest is measured as the distance from the center of the nest to each of the two nearest marker stakes.  We will also record distances from the nest to the stake line or vegetation line and to the high water mark.

D.  RELOCATED NESTS

We will collect the eggs and rebury them in a stable area of the beach if a nest appears threatened by imminent erosion or inundation, if it is situated in a previously identified erosion zone, or if there is standing water in the nest at the time of laying.  We will attempt to duplicate the dimensions and shapes of the original nest as much as possible.  Relocated nest depth and overburden (depth of sand over the eggs, measured from the top of the egg mass to the sand surface) will be recorded.  The number of yolked and yolkless eggs in all relocated nests will be recorded.  We will leave in situ all nests we consider to be “marginal” (i.e., will likely experience some wave washover but will probably not be washed away) as this may help create a more natural sex ratio.

E.  EMERGENCE AND EXCAVATION

Teams will monitor nests nightly starting three days before the expected emergence date.  After emergence, we will record the location, date, time, and number of hatchlings seen.  Hatchlings will be guarded from potential predators until they enter the water, and any beach debris will be removed from their path.  Disoriented hatchlings (i.e., those wandering up in the vegetation or along the beach away from the water) or those trapped in vegetation will be assisted to the water's edge.

After emergence, volunteers will assist in the excavation of nests and categorizing the contents to determine hatching success.  Field staff will open unhatched eggs to determine stage of development, using criteria developed by Whitmore and Dutton (1985).  We will note the condition of the nest cavity to determine possible causes for poor hatch success, such as flooding, extremely dry sand, closely packed or compressed eggs (such as are often found in high public use areas), hatchlings trapped by root growth, etc.  We will release any live hatchlings found in the nest.  We will release most hatchlings within one hour after nest excavation, after they become vigorous and active.  Hatchlings with a large protruding yolk-sack will be kept overnight in a box with damp sand on the bottom.  We will release hatchlings either near the site of the excavation or on the grassy side, where there appears to be less fish predation.

f.  Blood and Tissue Samples

Field staff will take blood or tissue samples from some individuals for genetic and physiological.  Blood samples are taken from the sinus in a rear flipper using a 21 gauge needle.  Tissue samples will be taken using a small (6 mm) tissue biopsy punch, using the technique described in Dutton and Balazs (1995).  Volunteers will be able to observe and act as a scribe during these activities.

G. DIVE BEHAVIOR

We will identify and record each sub-activity of select nesting females.  Activity times and turtle temperature will be noted during each sub-activity.  A time/depth recorder flipper tag will be attached to the rear flipper of the turtle while she lays her eggs.  Dive profiles will be downloaded upon each return to the beach.  We will then compare these profiles to the energy expended and her specific beach activities.  This information along with the Geographical Movement (see Item H) information will form a complete internesting behavior picture.

H. GEOGRAPHICAL MOVEMENT

We will attach satellite telemetry transmitters on select nesting females.  These transmitters send geo-location information through a satellite link.  We will identify and track the movement of these turtles during there “internesting period”.  This information along with the Dive Behavior (see Item G) information will form a complete internesting behavior picture.

I. DETERMINE AND MAINTAIN SEX RATIO’s

Temperature data loggers will be inserted into both In Situ (natural nests) and relocated nests.  The data loggers will monitor temperature throughout the incubation period.  Once the nests are removed, any dead hatchlings will be collected and sent to the lab for sex determination.  This will allow us to determine Sandy Point’s natural sex ratio temperature.  Temperature data loggers will also be inserted into various areas of the beach (not in a nest) to develop a beach temperature transect.  This will allow us to maintain sex ratio’s when relocating nests.

K. INJURY DOCUMENTATION

We will identify, photograph, and record all injuries on the nesting turtles.  Returning turtles will be monitored to estimate rates of healing.  Additionally the cause of the injury will be correlated to marine activities. For example, turtles have been identified with deep gashes associated with boat propellers. Turtles have come ashore tangled in fishing line, with hooks embedded in them, or with scarring in a net pattern across their head and shoulders. We will use this information to determine the location the injury occurred so that local marine advisories can be made if necessary.

West Indies Marine Animal Research and Conservation Service, Inc.

Copyright © 2004-2008

All Rights Reserved.