Department of Biological Sciences
Florida Atlantic University
Figure 1. T. Todd Jones holding a 1 year old leatherback that he raised
from a hatchling at the University of British Columbia. This turtle is in
excellent health and obviously well fed. It took years to determine how to
raise these very delicate and highly specialized turtles in captivity.
Advances in our understanding of marine turtle biology depend upon two broad lines of inquiry: field studies to determine where and how the turtles live, and laboratory studies to appreciate how they function. Some studies, such as those that investigate behavior, are routinely done in both locations.
Field studies give us an appreciation of what natural resources (e.g., food and shelter) and problems (disease, predators) sea turtles face, and therefore insights into how their environment must be protected if populations of these animals are to recover from their currently worldwide threatened or endangered status. Laboratory studies can seek cures and treatments for sick or injured animals, are used to determine dietary requirements, and can provide baseline information for what constitutes normal function, useful for diagnosing abnormal function. Laboratory studies can also determine how human activities affect marine turtles and their environment. For example, there is presently concern that the release of large quantities of anthropogenic sources of carbon dioxide into the atmosphere will increase temperatures and cause weather patterns around the globe to become less predictable. Those changes might affect the sex ratios of marine turtles, which are determined by the moisture and temperature conditions experienced by the developing embryos inside nests placed on oceanic beaches. To determine whether changes in weather are actually affecting those sex ratios, hatchlings must
be collected from nests exposed to known temperature and humidity regimes, and then raised to a size where their sex can be determined. Studies of that nature are currently ongoing at the Florida Atlantic University (FAU) Marine Laboratory, under the direction of Prof. Jeanette Wyneken.
Turtles can also be raised in the laboratory to test the efficacy of certain management practices. For example, the shrimp fishery in coastal U.S. waters was almost closed down because so many endangered sea turtles were accidentally trapped in the trawl nets, where they drowned. Hundreds of these dead turtles eventually washed up on shore so it became a problem that could not be ignored. An invention known as the turtle excluder device (or “TED”), was designed to promote the escape of trapped turtles from trawl nets but their design required modification and testing as the TEDs had to exclude the turtles but not the shrimp! At a laboratory in Galveston, Texas, the National Marine Fisheries Service raised hundreds of loggerhead and Kemp’s ridley turtles (the most vulnerable species) to a size where their ability to escape using the TED could be documented. Ultimately, several good designs were approved. The result was a win-win outcome; shrimp fishing could continue without any longer posing a major threat to the turtles.
While these examples indicate that we can learn a great deal by raising marine turtles in the laboratory, it’s also true that some species are easier to rear than others. It’s that fact that brings us to the subject of this article. The “hard-shelled” turtles (loggerheads, green turtles, Kemp’s ridley, hawksbills) are relatively easy to raise; some of have been kept on public display for years. These species have in
common well-understood dietary requirements that are easily met by common grocery store items. They also have a hardy physiology that resists most diseases, and respond well to surgical interventions and antibiotic treatment (when required). But the leatherback, one of the most endangered of the marine turtles, is a different story altogether. Sporadic attempts to grow these animals in captivity date back to the 1930’s, but the results at best have been single survivors from a large group of hatchlings, and even the survivors rarely lived for more than a year or two. At the same time, leatherbacks are fascinating because they are so different from other marine turtles. They feed in cold waters because as adults, they can retain heat and elevate their body temperature. But in addition, they are difficult to observe in nature because they commonly feed by diving to great depths (hundreds of meters) in pursuit of their prey (jellyfishes). Thus, of all the species of marine turtles, less was known about leatherbacks. At the same time, there was a real need to observe and study them in captivity. Early efforts to do so failed. What were the problems and what progress has been made to solve them?
Figure 3. Three juvenile leatherbacks in a tank while being reared at the FAU Marine Laboratory.
Each turtle can swim in any direction and dive below the water surface but a tether glued to its back at one
end, and attached to a wood dowel at the other end, restricts its movements so it can’t touch the tank sides
or bottom. This precaution is required because leatherback turtles do not recognize barriers.
For starters, leatherbacks are the most “specialized” of the marine turtles in terms of their habits, habitats and physiology. They feed only on gelatinous prey, either on the surface or deep in the ocean, and swim continuously to find food. They do not recognize barriers. If placed in a tank, they repeatedly ram the tank walls and bottom, abrading their delicate skin. Those abrasions soon become infected, suggesting the turtles have a compromised immune system.
The “barrier” problem was the first to be addressed. Each turtle is attached by a tether to restrict its movements so it can swim continuously or dive in any direction without ever contacting the sides or bottom of their enclosure (Figure 3). But what do you feed an animal that under natural conditions preys upon jellyfishes that are mostly water and of so little nutritional value that the turtles must search for food and feed all day?! The answer took years to perfect but the basic idea was to create an artificial food that resembled jellyfishes in texture and nutritional value. That diet is gelatin-based, low in calories, and contains sufficient protein and carbohydrate (in the form of small quantities of ground fish and French bread, plus reptile vitamins and minerals) to mimic natural prey. Unlike the hard shelled turtles that can thrive on a single large piece of raw shrimp or fish, leatherbacks must be fed small quantities of food by hand, minimally three times daily (breakfast, lunch and dinner!) because their digestive system is specialized for such a dietary regime. Feed them raw shrimp or fish and their kidney function is compromised by too much protein over too short a time period; death soon follows. So, rearing leatherbacks is a time-consuming process requiring several trained personnel working throughout the day to properly cultivate these animals.
Lastly, a serious obstacle is the problem of disease. Leatherbacks in captivity often get sick. Hatchlings may avoid that fate by swimming well offshore to locations where pollutants and microbes are far less concentrated. The leatherback immune system may be designed to function under those conditions. When the turtles are exposed to coastal water that contains pesticides, fertilizers, microbes from sewage and other impurities, most of the turtles die from fungal and bacterial infections. The solution is to purify coastal water using two kinds of “filters”: “protein skimmers” remove chemical impurities, and UV (ultraviolet) filters destroy water-borne bacteria and fungi. We had both filters at the FAU Marine Lab. but our UV filter was antiquated and only partially effective.
Thanks to a $7,500 contribution from the National Save The Sea Turtle Foundation, the FAU Marine Lab recently purchased a state-of-the-art UV filtering system by Emperor Aquatics (Figure 4). We plan to raise more leatherbacks this summer and are confident that their survival will be improved, thanks to this new technology.
Currently, the FAU Marine Lab is the only facility in the world where leatherback turtles are successfully and routinely raised. Those efforts were started more than 15 years ago by one of our undergraduate students (Todd Jones), who finished a doctoral degree at the University of British Columbia, Vancouver, Canada. There, he continued to rear leatherbacks to study their physiology (Figure 1). However, while at FAU he worked with me
Figure 4. The UV filter system. Seawater pumped into the lab. flows into the large grey pvc chamber through an intake on the left, and then through the UV (large, grey) chamber where it is exposed to a strong dose of UV radiation that kills fungi and bacteria. From there, the sterilized seawater flows to the tanks in the lab. that house the turtles. Black arrows show the direction of flow toward the UV chamber; white arrows show direction of flow through the UV chamber.
to determine how young leatherbacks recognized their jellyfish prey. Those studies revealed that the whole process was instinctive. Leatherbacks were reared in the laboratory without being exposed to a jellyfish, then were taken out to sea for a single trial. These juvenile turtles immediately made deep dives to feed on jellyfish! No experience was required (Figure 2 ).
That project was followed by others that explored other kinds of leatherback behavior, such as how the turtles use vision and smell to find food, how they respond to the colored lights and baits used in certain fisheries, their ability to detect light colors, where they go as hatchlings after they leave our beaches, and the ratios of males to females produced by nests placed on our beaches. Several technical publications have resulted (see the bibliography at the end of this article), with more to come. These are also available as downloads from the Foundation website.
None of the information gleaned from these studies would be available if, over the last 15 years, students and faculty working at FAU’s Marine Lab hadn’t dedicated themselves to the task of rearing these animals in captivity. Those efforts would not have succeeded without the generous support of the National Save The Sea Turtle Foundation.
Related FAU Marine Lab Publications:
T. T. Jones et al. 2000. Rearing leatherback hatchlings: protocols, survival and growth. Marine Turtle Newsletter 90:3-6.
M. Constantino & M. Salmon 2003. Role of chemical and visual cues in food recognition by leatherback posthatchlings. Zoology 106:173-181.
M. Salmon et al. 2004. Ontogeny of diving and feeding behavior in juvenile sea turtles: leatherback sea turtles and green sea turtles in the Florida Current. Journal of Herpetology 38:36-43.
J. M. Gless et al. 2008. Behavioral responses of juvenile leatherbacks to the lights used in the longline fishery. Endangered Species Research 5: 239-247.