Using Forensic DNA to Save Sea Turtles

An Interview with Brian Bowen

From the Environmental Review Newsletter Volume Three Number Four, April 1996

Introduction:

Sea turtles have existed for at least 100 million years and until recently, occurred in large numbers in tropical seas all around the world. Sea turtles enter the sea as three-inch-long hatchlings and return to the same stretch of coast to lay their eggs fifteen to fifty years later. Where do sea turtles go when they leave their nesting beach, and how to they find their way home? New techniques of forensic DNA analysis have helped fill in the gaps in our knowledge of these ancient mariners that until recently were so numerous in tropical seas.

     Brian Bowen received a Master's degree in marine biology from Virginia Institute of Marine Science and a Ph.D. in genetics from the University of Georgia. He is director of the conservation genetics core in the Biotechnology for the Evolutionary, Ecological, and Conservation Sciences program at the University of Florida. The purpose of the BEECS genetics core is to make modern methodologies of genetic analysis available to the conservation sciences.

     We spoke with Dr. Bowen about how his program has helped unravel some of the mysteries of the natural history of sea turtles and how genetic markers have uncovered previously unrecognized threats to these endangered species.

ER: Dr. Bowen, what are some examples of how DNA analysis can be applied to wildlife conservation?

BB: One example is where we are looking at the manatees in southern Florida. Manatees occur all the way down to Brazil, and except for a couple of groups in the Caribbean, the Florida animals are genetically unique. This fits in with what is known about manatee behavior. They hug the coast; when they are in open water manatees are shark bait; they are nearly defenseless, they are slow, they don't have teeth or claws. So the open-water channel between Florida and Cuba is a barrier to dispersal. That means if the Florida population of manatees is wiped out, it is not going to be replenished by animals coming in from somewhere else.      

There is a great story emerging about orcas, the killer whales in your area: There are two similar but distinct forms of orca along the West Coast; one form concentrates on eating salmon and the other concentrates on the marine mammals; seals and sea lions and otters. One of whales is resident, does not migrate much, but the second group, the salmon eaters, stay offshore and move around quite a bit more. Over the last twenty or thirty years a few researchers suggested that maybe they are separate species, even though they are in close proximity. Genetic analysis has recently shown that the two groups are genetically distinct. In fact, one of the forms was more closely related to the Atlantic orcas than to the other form of west coast orca.

ER: It sounds like this may be close to the separation of one species into two; that is, if they were one species to begin with.

BB: That's right. These are incipient species and probably the wellspring for future biological diversity.

ER: Why does Archie Carr have a marine research center named after him?

BB: When Archie Carr began to study sea turtles in the 1950s it was not even known how many species there were; the Kemp's ridley in the Atlantic was called the bastard turtle because it was believed to be a hybrid between the green turtle and the hawksbill turtle.      

These turtles came ashore on tropical beaches during the summer for nesting and the next time one would see them was when the adult females came back to nest. So biologists had to be able to piece together sea turtle life history from fragmentary observations; for most of their life history sea turtles were more or less unobservable. The first technique that cracked open sea turtle life history was tagging: Tom Harrison in Indonesia was the first. But it was really Archie Carr in the Atlantic that developed this technique into a high art form and did it systematically for years so that some aspects of life history could emerge. One of the first things that came to light was that sea turtles will nest three to five and even seven or eight times during the nesting season. They lay about a hundred eggs each in each nest. So they might put out between 500 and 800 eggs in a season. And they seem to come back every three or four years.      

Thanks to Archie's tagging operation on green turtles nesting in Costa Rica the life history was semi-complete for at least one species. The adults were moving back and forth between sea grass pastures and tropical nesting beaches. However, the juvenile life history remained obscure. The hatchlings leaving the beach are only three inches long, and nobody has yet come up with a tag that could be applied to those little guys that could be recovered later on the adults. So the link between the hatchlings and the adults remained obscure right up until the late 1980s.      

Where do the juveniles go? The answer came from field observations of loggerhead turtles in the southeast U.S. when Archie Carr in a landmark paper in 1987, showed that hatchling loggerhead turtles show up in driftlines on the edges of oceanic currents. Debris accumulates at the edge of these currents covered with invertebrates; arthropods, isopods, little crabs, shrimp and so forth, so it is a cornucopia for a juvenile loggerhead turtle.

ER: A growing sea turtle would find that good forage?

BB: Good forage and good cover. Sargassum and sea weed protects them from sea bird predation. So we know they have a pelagic life stage: after they leave the beach juvenile loggerheads drift around in these currents at least for a while. Work by Alan Bolten here at University of Florida, and Luc Laurent in France, has documented the presence of larger juvenile turtles around the Azores and in the Mediterranean. Once they get up to about twenty centimeters, the turtles that hatch out in Florida may be feeding in the East Atlantic. And once they get above fifty centimeters, they may end up back on the East Coast of the U.S.; thousands of these large juveniles come into Chesapeake Bay during the summer.

ER: That's a long swim. Do they ride the currents?

BB: That is indeed a long swim. The North Atlantic gyre is a clockwise current that will shunt turtle hatchlings off the beaches up into the northern end of the Atlantic and then down along the coast of Africa and then back towards the U.S. So they can ride the currents.

ER: How many species of sea turtle are there?

BB: There are seven recognized species. The most abundant species in the North Atlantic is the loggerhead turtle. The green turtles also have a pelagic stage but people are not finding them out in the mid-Atlantic like the loggerheads. Green turtles swim offshore but they are not found out in the mid-Atlantic; possibly they end up feeding near shore within a few years of departing the nesting beach.

ER: Do sea turtles have overlapping ranges?

BB: Very much so. The waters of southern Florida are inhabited by at least five species. The truism is, if you sit on a tropical beach long enough anywhere in the world, eventually you will see a sea turtle come up to nest. They nest in large numbers on the coast of Saudi Arabia, in Oman; they nest in large numbers in India and in Northern Australia, and historically in large numbers on the Pacific coast of Mexico. The turtles that are seen in California are usually loggerheads, greens,and occasionally the giant leatherback. Leatherback turtles will reach a thousand pounds, and they migrate all the way up to the Gulf of Alaska to feed. Florida which has reefs and lagoons and good surf built beaches hosts up to 10,000 nesting loggerheads a year, which may be the largest nesting area for loggerheads in the world. Florida also hosts a few hundred green turtles, maybe fifty hawksbill turtles, maybe fifty leatherback turtles and an occasional Kemp's ridley. The Kemp's ridley nests almost exclusively in one location in the western Gulf of Mexico in the State of Tamaulipas, just south of the Texas-Mexico border.

ER: What is the status of the population if there are 10,000 individuals nesting?

BB: The Florida loggerheads appear to be stable although there is cause for concern. The green turtles are so few in number here that it is hard to say; they may be on the increase. Other habitats like the Yucatan nesting areas are being developed as tourist resorts. So their populations are a source of concern to conservationists.      

The most endangered sea turtle in the Atlantic is the Kemp's ridley. Archie Carr wrote about trying to find the nesting area for the Kemp's ridley. In 1963 Henry Hildebrant acquired a film clip taken in 1947 by a Mexican surveyor in Tamaulipas and in one sweep of the beach you can see an estimated 40,000 Kemp's ridleys nesting at once. So the nesting aggregate was probably at least 100,000 turtles. Since then, through the 1950s and 1960s, there was an unregulated nest harvest possibly taking the majority of eggs that were laid there.      

Scientists were unaware of this until 1963. Soon thereafter the Mexican government took action; they put marines on the beach and they protected it. But at the time this was going on, there was a shrimp fishery developing offshore. The adult kemp's ridleys were being captured in shrimp nets and drowned. They were considered to be a pest by the fishermen because the shrimp are fairly fragile and a big old turtle can damage their catch. I think a common response to a turtle in the net was to slit the turtle's throat before throwing it overboard. So the double whammy of the unrestricted egg harvest and the adult mortality reduced the nesting population from about 100,000 in 1947, to a few hundred turtles in the 1990s. This species is right on the edge of extinction.

ER: What predators do sea turtles have besides humans?

BB: Sharks and wild dogs. I have sat on nesting beaches on Pacific Costa Rica and watched coyotes make a picnic out of a nest. Raccoons. I have seen cases in Georgia where a nesting sea turtle is surrounded by a little coven of six or seven raccoons waiting for the turtle to finish laying.  And in some areas these predators may get damn near all the nests. That is just the start. If the hatchlings make it into the water, the gulls, crabs, and sharks prey on them.

ER: How plentiful were sea turtles before humans came along?

BB:  Before Columbus arrived, sea turtles occurred in the millions in the Caribbean. Everywhere else in this kind of warm tropical habitat in the world sea turtles were extremely abundant. They were a successful form until the advent of systematic human harvesting. Turtles are abundant in the fossil record throughout the last 100 million years, so they have been successful for a long time.

ER: It seems odd that nobody would notice when 50 thousand turtles come up on the beach all at once to nest. Was the arribada a trade secret or was it because there is a lot of coastline out there?

BB: It is because there is a lot of coastline out there. The olive ridleys - the other ridley species - were nesting numbers exceeding 100 thousand turtles on the western coast of Mexico. Archie toured the West Coast of Mexico looking for green turtles and was not aware that ridleys also nested in the same region in these arribadas. It is a testament to how little was known that thirty years ago these wonders of nature were unknown to science. [Turtle nesting in large aggregates is called an arribada. Probably a strategy to overwhelm nest predators. ed.]

ER:  How long does an arribada last?

BB: Am arribada can go on for several days. These massive nesting events will occur every month or so during the nesting season. Some of the nesting efforts will be arribadas and some will be solitary nesters coming up during the day or during the night.

ER: What about the males? Do they migrate like the females?

BB:     The males also migrate from the feeding grounds to the nesting area. Generally there is a courting area near the nesting beach, and a few weeks before the nesting starts, the males and females will show up there and initiate courtship and mating. Once the mating is concluded - after the first couple of weeks of the mating season - the males disappear and probably go back to the feeding grounds.

ER: How do sea turtles return to their natal beach after being away for twenty years?

BB: That is the million dollar question. Archie Carr and his colleagues looked at how they navigate from several angles: Is their eyesight good enough for celestial navigation? The answer is apparently no. Could they smell their way to the location? They apparently have a keen sense of smell, but whether they can smell their way to a location is still an open question. The breakthrough in how sea turtles navigate the open ocean was by Ken Lohmann and Mike Salmon and Jeanette Winecen. They demonstrated that these animals have magnetic sense, like some birds do. The experiments that demonstrated this were elegantly simple: They put hatchlings in a tank and applied a magnetic field around the tank, and the turtles would all go to one end of the tank and when they tilted the magnetic field, the animals would go to a different part of the tank. That means that sea turtles can tell not only which way is north, but how far north they are by the angle of the magnetic field relative to the angle of their horizon. That is probably the main reason why they can navigate accurately across open water.

     Green turtles nest on Ascension Island, 2,000 kilometers from where they feed in Brazil. The mature animals migrate halfway across the Atlantic and hit this small solitary island which is less than eight kilometers wide.  Archie Carr and his student Jean Mortimer tagged the turtles on Ascension Island and recovered them off the coast of Brazil.  Archie Carr's tagging data also showed that green turtles always go back to within a few kilometers of the beach where they were born. Archie proposed that turtles have a homing instinct to return to their natal beach. But John Hendrickson - another well known sea turtle biologist - proposed a different scenario; that is, perhaps adolescent females follow the adult females back to a nesting beach, and once they are there they fix on that nesting beach for the rest of their lives. He labelled this hypothesis social facilitation; this idea would explain adults always going back to the same nesting beaches without invoking this seemingly unlikely idea that turtles remember where they are born and return there thirty years later.     

 Unfortunately, evidence for either hypothesis was lacking because unlike migratory birds, where one can band the fledglings before they leave the rookery, this was not possible with sea turtles; the hatchlings would shed the tags. But now we can get at this question with DNA technology and population genetic theory. Under a social facilitation hypothesis, a hatchling could leave a Florida nesting beach and then as an adult end up nesting in Costa Rica or Mexico, and there would be genetic mixing between the nesting beaches. But under Archie Carr's natal homing hypothesis, animals should only go back to the nesting colony where they were born. There should not be any gene flow or movement between nesting colonies, and hence each nesting colony should be genetically distinct.

ER: Why would there be mixing?

BB: Imagine a hatchling leaving a Florida nesting beach and ending up on a feeding ground. Under social facilitation they would follow some female to whatever nesting beach they were going to.

ER: So it would be a random choice who it followed.

BB: Exactly. That hatchling when it matures, might end up back in Florida but it might end up in Mexico. So under social facilitation we would expect that all the regional nesting beaches would be genetically pretty much the same, and under natal homing they should be markedly different. When I started this research in 1987, I thought we would probably be disproving Archie Carr's theory, because I didn't think a three-inch-long hatchling could remember where it came from thirty years later. But the data from Florida and Costa Rica and Ascension Island and Venezuela was unequivocal. We would see genotypes at high frequency in Venezuela that did not occur anywhere else in the Caribbean; very strong evidence of natal homing; each nesting beach is genetically distinct.      

The conservation implications of natal homing are that each colony is demographically independent. If the Florida nesting colony is depleted, it is not going to be replenished any time soon by turtles coming in from elsewhere. And in fact there is historical data that supports this conclusion. The large nesting colonies in Grand Cayman and Alto Villo in the Caymans and the Dry Tortugas were harvested extensively. There was a European industry that was focussed just on these nesting colonies; boats would come over and fill the holds up with green sea turtles for the soup kitchens of Europe. Some of these colonies were gone by the early 1700s and the rest were gone by the 1800s. Two centuries later those nesting areas have not been recolonized. So the historical data and the genetic data both indicate that each nesting colony is a unique component of sea turtle biological diversity.

ER: How did genetic studies apply to the other segments of sea turtles life history?

BB: For most of the last twenty years researchers have known the locations of some of the major sea turtle feeding grounds, but they did not know which nesting colonies were feeding there. In cases where the feeding populations were being harvested, this information was critical to conservation. For example, when a Miskito Indian harvests a green turtle off the coast of Nicaragua, is he affecting the large nesting colony in Costa Rica which may have several thousand turtles a year, or is he depleting the Florida nesting colony, which has only about one hundred turtles a year. Naturally occurring genetic markers provided an opportunity to look at this. The first nesting and feeding population we examined was loggerheads in the western Mediterranean, the turtles that nest in high frequency in Florida. Archie Carr and others had observed that there were more juvenile loggerhead turtles in the western Mediterranean than could be produced by the Mediterranean nesting colonies in Greece, Turkey, and Cyprus.

ER: Immature turtles swim across the Atlantic from Florida to feed in the Mediterranean?

BB: Yes. And Archie was one of the first people to suggest this but the idea was not widely accepted. It was a nice idea but there was no proof. However, we had a genetic marker we could use to detect the presence of Florida turtles in the western Mediterranean. So a French researcher - Luc Laurent - surveyed sixty turtles from the western Mediterranean, and genetic markers indicated that about half these turtles are from the nesting beaches in the Southeastern U.S. That is a remarkable piece of life history but right behind that is a pressing conservation concern: In the last twenty years there has been a developing long-line fishery and more recently, there have been extensive driftnet fisheries developing in the Mediterranean. The best estimates are that about 20 thousand loggerhead turtles a year are taken in these fisheries, and that between twenty-five and fifty percent of those turtles perish. By anybody's arithmetic, this is a severe conservation problem.

ER: Where are the nesting colonies for the rest of the Mediterranean loggerheads?

BB: Greece, Cyprus, and Turkey, and there is scattered nesting in Libya and the African side. But most of the nesting is in the eastern Mediterranean and it probably amounts to a couple thousand turtles a year.

ER: A couple thousand a year is not enough to keep the population going with those kind of losses.

BB: That is precisely the point. There is no way this bycatch is sustainable, and it is especially chilling that these fisheries are relatively young. With the twenty year generation time of loggerhead turtles, the impact of the bycatch has not been felt yet on the nesting beaches; it probably won't be felt for another five or ten years. But if the numbers are anywhere close to correct, it could be catastrophic loss of breeding turtles. In addition, if the Mediterranean colonies go under, they will not be recolonized over a time frame that is meaningful to conservation plans. Over a period of thousands of years they are likely to be recolonized by occasional strays, but not over a period of decades or hundreds of years. They will be essentially wiped out.          

 There is a similar problem building in the Eastern Atlantic where driftnet fleets are starting to fish heavily in an area occupied by loggerhead turtles. That fishery may also be killing thousands of loggerhead turtles. Alan Bolten at the Archie Carr Center is investigating this problem with the genetic markers.

ER: How about the Pacific populations? Are there conservation concerns in the Pacific?

BB: About twenty years ago, a Mexican researcher - Rene Marquez - noticed juvenile loggerhead turtles off the coast of Baja California. This was a mystery because loggerhead turtles do not nest anywhere in the Eastern Pacific. So where are the loggerheads coming from? There are only two known nesting areas for Pacific loggerheads: Japan and Australia. These two nesting populations are genetically distinct, so every turtle swimming out there in the Pacific Ocean is carrying a natural tag that says, I came from Japan or I came from Australia.  Itaru Yukida released an aquarium raised loggerhead turtle from Japan and it was recovered off Baja California. Based on that one observation he suggested that maybe the Baja California turtles are coming from Japan. This was widely dismissed because the distance is 10,000 kilometers, three times longer than the distance between Florida and the Mediterranean. And nobody believed that a three inch long hatchling could traverse a third of the planet.

ER: Why? Is there some barrier?

BB: Actually there is a North Pacific current that picks up off Japan and comes across to California, but it is considered to be an oceanic desert between Japan and California with very low food supply. It was thought while the current offered a physical mechanism to carry the hatchlings from Japan to California they could not make it because there was not a food supply. When the National Marine Fisheries Service started putting environmental observers on the driftnet fleets north of Hawaii, they discovered that juvenile loggerhead turtles were being captured in the driftnets between Hawaii and the Gulf of Alaska, where nobody thought sea turtles could persist. We got samples off Baja California with the assistance of the Mexican researcher Alberto Abreu and it turned out that ninety-five percent of the turtles were from Japan.     

 This confirmed two facts: that loggerhead turtles could navigate 10,000 kilometers, and secondly, that the Japanese driftnet fleets were wiping out one of their own natural resources. Now on the surface one might consider that it is Japanese fleets killing Japanese turtles, so it is nobody else's business, but these turtles spend part of their lives in Mexican waters and so it is a concern to the Mexican government as well.

ER: The conservation of such a wide-ranging species can raise political problems.

BB: Our work on the Caribbean hawksbill turtle has been politically difficult. Historically hawksbill turtles occurred in the hundreds of thousands in the Caribbean, but by 1982 there were only about 10,000 nesting females left in the Caribbean region. And yet Japanese businesses were still importing thousands of these turtles a year, or more accurately, importing their shells, through Panama, Haiti, and other countries. The shells of the hawksbill turtle produce a beautiful brown and clear translucent material that was used for everything from combs to tortoiseshell glasses prior to the invention of plastics. Since the availability of plastics, only a few countries have persisted in using this material, prominent among them is Japan. The Japanese artisans who use this material have banded together in what is called the Bekko Corporation. Bekko is Japanese for tortoiseshell, and they have continued up until three years ago to legally import hawksbill turtle shell by taking an exemption on that species under the rules of the CITES treaty.     

 In 1992, in response to the ongoing demand, the Cuban government announced an intention to resume harvesting hawksbill turtles on the reefs around their nation. They maintained that the turtles that feed around Cuba were all from the Cuban nesting colonies so it was nobody's business but their own what happened to these turtles. The marine turtle biologists and conservationists were skeptical about this claim but since the hawksbill was already a scarce animal in the Caribbean, data to refute this fishery model was almost non-existent. Nothing was known about how hawksbills migrate, how far they go, and in fact there was some anecdotal evidence that maybe they did not migrate that much; maybe there was an element of truth to the Cuban model. To look at this we could not get into the Cuban feeding grounds for political reasons, but we set up a parallel test of their fishery model in nearby Puerto Rico. Researchers Carlos Diez and Prober Van Dam collected samples from forty-one hawksbill turtles - a couple drops of blood - and we compared the turtles in that feeding ground to turtles in an adjacent nesting colony - within a few hundred meters. If the Cuban model was correct, the turtles in that nesting colony and that feeding ground should be pretty much the same. We found that this feeding population was genetically different from the adjacent nesting colony, indicating that turtles were coming from somewhere else.      

At the same time, BEECS researcher Anna "Sam" Bass sampled nesting colonies from throughout the Caribbean. We could not get the Cuban nesting beaches but we got seven others from throughout the region, almost all the other major nesting colonies. Our analysis indicates that about twenty percent of the turtles on the feeding ground were coming from Yucatan, Mexico and a higher percentage were coming from the U.S. Virgin Islands at Buck Island. The feeding ground also contained turtles from Belize, Barbados, and elsewhere in the Caribbean. The numbers are approximate, but the point is that the feeding ground population contained turtles from nesting colonies throughout the region. Any feeding ground in the Caribbean is likely to be comprised of turtles from throughout the Caribbean region, and any harvest is going to affect the natural resources of half a dozen or more countries in the region.      Partially in response to this data, but also in response to public pressure, the Cuban government has backed down off the harvest plan. They are now talking about turtle ranching. But again, if they ranch the turtles and we have genetic samples from the brood stock, we can take samples of turtle in a market in Japan and determine whether they came from the ranch or not. So even if ranching goes through, genetic markers will be a valuable way to monitor the marketplace.

ER: How are the turtle populations doing in the U.S. now?

BB: There are at least two loggerhead nesting populations: One is in south Florida, which is at 10,000 turtles and is probably stable. The second - the northern population - is in Georgia, South and North Carolina and that population has shown evidence of longterm decline. The Georgia population has been monitored now for about twenty years by Jim Richardson at the University of Georgia.

ER: What are the prospects of effective action being taken for the driftnets and long-line fisheries? Are there devices like turtle excluders?

BB: There is no mechanical solution yet. In many ways it is like the shrimp fisheries in the mid-1960s and early 1970s: the problem is just beginning to be recognized and solutions are just starting to be considered. And so any equivalent to a turtle excluder device is probably a decade away.      As far as government regulation, the U.S. National Marine Fisheries Service was initially unprepared for this genetic data; it is new technology and a new field. But in the last couple years they have really responded; the NMFS endangered species office in Washington and their turtle programs here in the Southeast, California, and Hawaii are helping us to conduct research, and they are concerned about it.

ER: What sea turtles are listed as endangered species?

BB: They all are considered endangered or threatened.

ER: But you are still seeing turtle eggs for sale in Central America and tortoise shell jewelry.

BB: Enforcement is patchy in Latin American countries. I think Costa Rica has done a really good job. And in parts of Mexico I have seen good enforcement, but by and large turtle products are readily available in most locations.

ER: How would you summarize the conservation status of sea turtles?

BB: I know that your readers are aware of human population issues, and this is at the heart of sea turtle conservation. Thanks to Archie Carr and his friends and students, almost everybody involved with sea turtles knows that we have to protect the nesting beaches. But in the last two decades, human encroachment on coastal and oceanic feeding grounds has expanded dramatically. Feeding ground harvests have gone from natives like a Miskito Indian in Nicaragua taking an occasional green turtle to industrial fishing fleets which are capable of killing sea turtles by the thousands. In the Pacific Basin alone, over 10,000 turtles a year are killed in driftnet and long-line fisheries.     

 In the case of loggerhead turtles there is a twenty year maturation period and in the case of green turtles, perhaps thirty to fifty years. So these fisheries are creating a vacuum that won't even be apparent on the nesting beaches for at least another decade.

ER: What can we do?

BB: One of the biggest sources of optimism is that you and your readers are aware of this problem. This information has been around for a little while in the scientific literature but it is only starting to reach into public awareness; and that is how changes are going to be effected. As long as our work is ivory tower stuff - DNA sequences and statistical tests - it is not going to cause changes. But I do feel optimistic because government agencies are starting to pay attention to this, and they are starting to support this work. The National Marine Fisheries Service is considering this problem and weighing their options about what to do. It may take a couple more years to establish a policy, but they have good people there and they are responding to this problem. 

ER: Are sea turtles important as an indicator of the health of our ecosystem?

BB: Turtles have definite ecosystem value, but one direction they are probably not valuable is as the canary in the coal mine. I have seen turtles come up and nest on beaches where you would not consider letting your children swim. In many respects they are magnificent creatures but they are not very aware creatures; they will keep coming back to a beach long after it is degraded and not a good place to nest.      The value of sea turtles to human interests is tremendous. For example, these animals in large part fueled the exploration of the New World. By the time Columbus got through his second voyage his crew was feeding on them. On one voyage there is a note in his log that these animals were so abundant in the Caribbean that the crew couldn't sleep. It was like hitting rocks in the water, they would be sailing along and whump, like a 200 pound rock hitting the hull. Turtles were incredibly abundant and the vitamin deficiencies associated with long sea voyages, that could send one body a day over the side, were healed by this endless source of fresh meat.     

 Aboriginal people here in the Americas and elsewhere have used turtles as a valuable and plentiful source of protein since time immemorial. And for tropical native low tech cultures these animals may be sustained continuously. The evidence from aborigines in Australia, the Philippines, from Indonesia, from Western Mexico was that native cultures could harvest these animals continuously for thousands of years as long as it wasn't done in a large scale or commercial format.      The second thing is of course that these turtles are a piece of the natural heritage of this planet. I have thought about this for ten years and I still have not figured out what the emotional appeal of turtles is. What is it? Living in a box? But it is something we all want our grandchildren to see. And if we are going to be good stewards of this planet then we want to preserve sea turtles for the same reason that historical societies want to preserve George Washington's home. These are a magnificent piece of our natural heritage. They outlasted the dinosaurs, they will probably outlast us if they are given a little bit of care and just enough room to survive.

Copyright 1996 Environmental Review