Biology

Currently, 322 living species of tortoises and freshwater and marine turtles are in existence (Table 4-1). They are found in diverse habitats on all continents except Antarctica and in all oceans except the Arctic. The largest concentrations of turtle species occur in North America, more than in any other temperate region of the world. Ninety-eight species of chelonians are endangered or critically endangered because of habitat degradation, human encroachment, and harvesting for food, medicines, and the pet trade. Of the chelonians with known threat status in 2010, 53% of the species are considered threatened, making chelonians the most highly endangered of any of the major vertebrate groups.⁸

Feeding

The diverse species of chelonians demonstrate great diversity in diet and feeding habits. They may be omnivores, eating a broad spectrum of foods to constitute a complete diet, or they may be specialist feeders and have a strict, narrow spectrum of food items that they will accept. They may be herbivores, omnivores, or carnivores. Many have feeding strategies that change during different life stages. Wild-caught animals may be very difficult to acclimate to novel food items, and some may never willingly transition to captive foods. It is important to be familiar with the natural history of certain “specialized feeders” to provide familiar and acceptable food items while transferring animals to a balanced captive diet. Tortoises are herbivores that tend to graze on grasses and annual forbs but have very little natural exposure to fruits. Freshwater turtles are primarily omnivorous, consuming fish, crustaceans, snails, aquatic grasses, fallen fruits, and many other food items. Some are more carnivorous as juveniles but become more herbivorous with age. Complete rations have been formulated specifically for different groups of animals, and some may be used successfully for all life stages. Like other aquatic turtles, sea turtles may be omnivorous, carnivorous, or herbivorous. Green sea turtles feed on sea grasses and algae. Loggerhead and Ridley sea turtles prefer a diet of molluscs and crustaceans, whereas hawksbills specialize on sponges and leatherback sea turtles consume primarily jellyfish. Captive sea turtles will eat fish, crustaceans, and molluscs and may be acclimated to balanced diets in pellet or gelatin form. Obesity is not uncommon in captive turtles. One should remember that in nature, chelonians may spend a considerable amount of time foraging as a daily activity and such activity may provide benefits for well-being beyond simple nutrition. In general, hatchling chelonians of all species should be fed daily. Frequency of feeding may be reduced with age, but most species should be fed at least twice per week as adults.

Restraint and Handling

Most chelonia are relatively easily restrained. A potential risk exists for handlers from bites, scratches from claws, or cuts from projections of scales or points on the shell. Green sea turtles may flap their front flippers forcefully enough to fracture their humerus and may easily injure handlers while struggling. It is generally most safe to lift larger animals, placing one hand on the anterior carapace over the neck and the other hand on the caudal carapace over the tail. This minimizes the potential for bites or scratches. For species that may be lifted easily, care must be taken not to flip them upside down rapidly. This may cause immediate changes in hemodynamics that may cause distress to the animal, may impair ventilation because of compression of the lungs under the weight of coelomic viscera, or result in intestinal or uterine torsion. Aggressive animals may require diversion, immobilization, or blocking of the head to safely examine them. Materials such as rolls of tape or padded sticks or polyvinyl chloride pipes serve well as bite blocks placed in the mouth and secured with tape around the head. For small species, pushing the head under the carapace in a natural position and maintaining it there manually or with padding covered and taped to the shell allows nonpainful procedures on other portions of the body to proceed in safety. Many tortoises will not struggle if their eyes are covered or the heads are in the confines of their shells. Conversely, when chelonians are regressed completely into their shells, extricating limbs or the head without harming the animal is challenging. Some animals will extend their limbs when securely balanced on a pedestal, allowing for visual examination of the appendages and potentially permitting restraint of a limb or the head and neck. Using a small metal spatula, usually, even the tightest hinged plastron of a box turtle or the armored front leg of a tortoise may be breeched. Gentle, steady traction on the closed plastron or leg is usually rewarded by relaxation of the defense mechanisms. In extreme cases, chemical immobilization must be used to examine or treat the animal.

Surgery and Anesthesia

General anesthesia may be induced and maintained with parenteral agents given through intravenous or intramuscular routes (Table 4-2). Gas anesthetics may be used to induce and maintain anesthesia, but induction under voluntary respiration may be prolonged when animals hold their breath. Direct intubation of the glottis may be accomplished in the awake chelonian through use of an oral speculum. The glottis is located at the base of the tongue and is closed unless the animal is taking a breath. An appropriate sized endotracheal tube may be gently forced into the glottis and the animal induced using positive pressure ventilation until an acceptable level of anesthesia is achieved. The trachea bifurcates into paired bronchi in the cranial one third of the cervical area and has complete cartilagenous rings. Care should be taken to prevent unilateral bronchial intubation. Anesthetic agents are metabolized more slowly under low body temperatures, so special attention should be given to maintaining the anesthetized chelonian at or near its preferred optimal temperature range. The turtle’s ability to withstand prolonged anoxia may cause reduced ventilation, resulting in reduced exchange of anesthetic gases. Whenever possible, animals under anesthesia should be intubated and provided with assisted ventilation. Recovery after gas anesthesia may be prolonged because ventilation is not induced by hypercapnea and decreases during hyperoxia. The use of room air rather than oxygen will speed anesthetic recovery.⁷ The use of local anesthetic (lidocaine 2% or bupivacaine 0.5%) may be used as adjunct to general anesthesia. Epithecal anesthesia (2% lidocaine at 1 mL/20 kg) may be used alone or in conjunction with general anesthesia for surgeries of the cloaca and tail (Figures 4-1 and 4-2).⁶

Surgical procedures should be performed under appropriate anesthesia and aseptic conditions. Intracoelomic surgery such as ovariectomy, salpingotomy for removing retained eggs, or enterotomy for removing a foreign body may be achieved by accessing the coelom through the prefemoral fossa. Incision size may be kept to a minimum by using rigid endoscopy to retract the ovarian tissue, oviduct, or intestine and bring it to the skin incision. Intracoelomic access may be limited via this route, however, and surgical objectives may require cutting through the plastron. In brief, the shell is cut to make a beveled edge by using a drill or a saw while attempting to keep a portion of the cut shell attached by preserving the periosteum. Care is taken to identify the coelomic blood vessels before incising them. With the shell out of the way, surgery may proceed as for any routine abdominal procedure. After the primary surgical objectives are met, closure of the coelom is accomplished by replacing the shell with the use of the beveled edge to help position and stabilize the flap during closure. The flap is affixed to the plastron using materials such as bone cement, acrylic, screws, and cerclage wire, in combination or alone. As with any orthopedic manipulation, complete healing of the shell may take months. Plastrotomy is not advised in species having dynamic movement of the plastron during normal respiration or diving (e.g., sea turtles), as the surgery site will be in constant motion, impeding or preventing the healing process. Fish hooks are commonly ingested by sea turtles and frequently lodge in the lower esophagus near the base of the heart. These may generally be accessed through a ventral cervical incision, retracting the esophagus cranially to access the site where the hook has lodged (Figure 4-3).