Reproduction of Marine Life, Birth of New Life! Investigating the Mysteries of Reproduction

All seven extant species of sea turtles are considered endangered or threatened with extinction. Because of their commercial value for food (particularly the green turtle) and for craft materials (bekko or tortoiseshell from the hawksbill turtle) they have been heavily exploited around the world. Sea turtles are also charismatic animals to view in large aquaria and three species have proven easily reared in captivity. Initially, in the 1970s, the green sea turtle was bred in captivity by the Cayman Turtle Farm on Grand Cayman Island in the Caribbean. Subsequently, the loggerhead, Kemp’s ridley and hawksbill have also been bred in captivity at several aquaria and research labs around the world. Research on captive sea turtles has proven very important in improving our understanding of the reproductive biology of sea turtles. Our group, as well as other researchers, has made key original observations on captive animals, particularly at the Cayman Turtle Farm over the last four decades. These include the first evidence of temperature dependent sex determination in sea turtles, the first understanding of the ovulation cycle in any sea turtle, the first description of the hormonal control of reproduction 2 in turtles, the first quantitative description of mating and courtship behavior in a sea turtle, and the first captive breeding of the green, hawksbill, loggerhead and Kemp’s ridley sea turtles. In addition, multiple paternity has been observed in captive greens with as high as seven fathers in a single clutch. Proper nutrition in captive animals has permitted sea turtles to reach sexual maturity 2-5 times faster than they do in the wild. On the other hand, imbalanced free fatty acid ratios from the diet appear to cause a reduction in viability of captive bred embryos. Finally, unique observations of sea turtles in aquaria have improved our knowledge of physiological processes such as the occurrence and possible seasonal cycles of a softened plastron in adult males, an adaptation important in mating behavior. It can be argued that successful captive breeding of four species of sea turtles, while not favored as a current conservation strategy, has nonetheless reduced the prospect of extinction for these species. Captive breeding programs for the other three species would teach us much more about these turtles and improve the long term conservation options for these species as well. Introduction Sea turtles are visually spectacular when swimming, providing the appearance of underwater flight, very much like a large graceful bird on the wing. As air breathing vertebrates with their tough reptilian skin and shell, they are exciting as large and distinctive display specimens. When you combine the important Reproduction of Marine Life, Birth of New Life! Investigating the Mysteries of Reproduction Owens & Blanvillain: Captive Reproduction of Sea Turtles 24 “appearance factor” with the fact that sea turtles are very robust animals, having minimal disease problems, you have a combination of characters which make them very desirable for modern zoos and public aquaria. The second important factor adding to sea turtle’s general desirability is their economic value. Parsons (1962) once described the green sea turtle (Chelonia mydas) as the most valuable reptile on the earth. Indeed the meat, shell and skin have been important commercial products for millennia (Frazier, 2003). Because of the hardy nature of turtles, they were actually important in discovery and exploration of the new world since they could be carried alive aboard ships and used as fresh food as needed without requiring fresh water (see Carr, 1967 for discussion). Similarly, for centuries in several different cultures, the keratinized shell of the hawksbill (Eretmochelys imbricata) turtle has been commercially valuable for carvings, jewelry and as furniture inlays (Frazier, 2003). Considering this general interest in sea turtles, it is not surprising that they have long been maintained in captivity and that they have also been used in several attempts at captive culture and farming (Table 1) (Carr, 1967; Hendrickson, 1974; Ross, 1999). Indeed, in the 1960s the idea of sea turtle aquaculture seemed a very logical and practical extension of the popularity of these species for food and other commercial uses. Carr (1967) in his most popular book “So Excellent a Fishe” devoted part of the last chapter to evaluating options for sea turtle culture. He argued that such culture prospects could be valuable for the conservation of these species which he was becoming more and more concerned about in terms of over exploitation in the wild. Subsequently, in the 1970s, he modified his thinking and began to feel strongly that captive culture of sea turtles could work against the long term conservation strategies for sea turtles (Carr, 1967; Ehrenfeld, 1974; Fosdick and Fosdick, 1994). This change of philosophy was devastating to the commercial approach to turtle culture as it directly resulted in more restrictive changes in the US Endangered Species Act as well as in international thinking as evidenced by many CITES (Convention on International Trade in Endangered Species) policy decisions up to the present time. 4 The turtle farm at Grand Cayman Island and other places have had significant success with captive breeding and the remainder of this paper will focus on those results. The first author of this paper and three of his subsequent graduate students had the opportunity to conduct extensive reproductive biology experimentation at Mariculture, Ltd. (initial name) and the Cayman Turtle Farm, Ltd. (CTF) between 1973 and 1999 (Owens, 1976; Crowell Comuzzie, 1987; Rostal, 1991; Craven, 2001). Materials and Methods In addition to the Cayman Island facility, mentioned above, several public aquaria have had limited success with captive breeding of sea turtles. While the breeding facilities we have seen around the world range from very large as in the Cayman Islands (Fig. 1) to very modest as at the Miami Seaquarium (Fig. 2), the minimum requirements for success in breeding have included adequate depth for movement during mating and courtship, an associated sandy nesting beach and a good nutritional diet for the breeding animals. While we do not claim this to be a complete listing, the following facilities are known to have had at least some success with captive breeding of sea turtles: Cayman Turtle Farm, Ltd., Grand Cayman Island; Miami Reproduction of Marine Life, Birth of New Life! Investigating the Mysteries of Reproduction Owens & Blanvillain: Captive Reproduction of Sea Turtles 25 Seaquarium, USA; Xcaret, Mexico; Sea Life Park Hawaii, Oahu, Hawaii; Yaeyama Station, Ishigaki Island, Japan. An important advantage to the use of enclosed and protected facilities such as zoos and aquaria for research on captive breeding and reproductive biology, is the improved ability to track and carefully observe the animals aver an extended period. In addition, the captive situation is a good location to test the development of new technologies not yet proven in wild populations. While we will not go into detail on the following methods themselves, which are published elsewhere, most of these technologies were first used and adapted to sea turtle work in captive/farm situations: Radioimmunoassays (RIA) on sea turtle hormones were first used to determine the sex of juveniles (Owens et al., 1978) and reproductive condition of adult sea turtles (Licht et al., 1979) in experiments done at CTF. Safe and efficient blood and cerebral spinal fluid sampling techniques were first developed at CTF as pictured in Figure 3 (Owens and Ruiz, 1980). Sea turtle laparoscopy or endoscopy was first done by Dr. James Wood and collaborators at CTF (Wood et al., 1983). In addition, Dr. Fern Wood and her collaborators made significant improvements in the anesthesiology of sea turtles at CTF (Wood et al., 1982a). The nutrition of sea turtles in captivity, improving our understanding of nutritional requirements in the wild, was first studied in captivity (Wood, Figure 1. Cayman Turtle Farm breeding pond and nesting beach in 2009. Note tracks and nesting pits on the beach. (photo J.