Session #2005

Abstract

There are seven species of sea turtles found worldwide. Sea turtles are found in all oceans except for the Arctic. All species of sea turtles that reside in US waters are listed as either “threatened” or “endangered” under the Endangered Species Act (ESA).¹³

The life history for each species of sea turtle is different and important to know when working with them medically or from a conservation perspective. Anthropogenic threats are common, including habitat loss and degradation, climate change, fisheries interactions, boat strike injuries, marine debris ingestion and entanglement, fibropapillomatosis, harvesting of eggs and adults for human consumption, and harmful algal blooms. Medical and surgical management of injured and ill sea turtles can be challenging and expensive. Successful outcomes depend not only on veterinarians knowledgeable in sea turtle medicine and surgery but also the application of excellent husbandry, nutrition, and water quality.

Introduction

Over the last decade, numerous advances have been made in sea turtle rehabilitation and conservation.¹ Understanding the unique life history of each species of sea turtle is critical for success in managing ill and injured sea turtles during the rehabilitation process. Anthropogenic threats are common, including habitat loss and degradation, climate change, fisheries interactions, boat strike injuries, marine debris ingestion and entanglement, fibropapillomatosis, harvesting of eggs and adults for human consumption, and harmful algal blooms. Medical and surgical management of injured and ill sea turtles can be challenging and expensive. Successful outcomes depend not only on veterinarians knowledgeable in sea turtle medicine and surgery but also the application of excellent husbandry, nutrition, and water quality.

Natural History, Conservation Status, and Threats

There are seven living species of sea turtles, which are found in all oceans except for the Arctic. Sea turtles have a complex life history.² Animals migrate from foraging sites to nesting beaches, a journey that may cover as much as 2,600 km. During this time, and for the duration of the breeding season, they do not feed and typically lose body condition. Breeding most commonly occurs offshore near the preferred nesting beaches and can involve violent fighting between males as they attempt to dislodge each other from females. The time of year that breeding and nesting occurs is dependent on geographical location. The female sea turtle drags herself ashore where she digs a nest chamber and lays a clutch of eggs. Incubation times vary slightly between species but average around 60 days. Cooler temperatures will lengthen the incubation, whereas warmer temperatures will decrease incubation time. Optimal incubation temperatures for all species are generally 29–33°C. Above or below those temperatures will typically compromise the incubation success. Once hatched, the hatchlings dig to the surface of the nest and head towards the ocean, using moonlight to orientate themselves. When they reach the ocean, they go through a swimming frenzy to make it to open water, utilizing their remaining yolk sac for energy. They may spend anywhere from 3–12 years navigating the ocean before they return to offshore foraging areas. This period was known as the “lost years.”

The life history for each species of sea turtle is different and important to know when working with them medically or from a conservation perspective.

Adult green sea turtles (Chelonia mydas) have a curved carapace length (CCL) between 78–112 cm and weigh between 70–190 kg. They occur worldwide in tropical and subtropical habitats with distinct populations that have little or no female-mediated interbreeding between major breeding aggregations.³ Green turtles are unique among sea turtles in that they are primarily carnivorous as hatchlings but then undergo an ontogenetic shift to become almost exclusively herbivorous as adults. The adult diet typically consists of algae and seagrass.³ They become sexually mature at around 30–35 years of age. Female green turtles may have between 4–6 clutches per season, with clutch sizes ranging from 80–150 eggs. Inter-nesting periods within a season are between 3–4 weeks and females only breed every 3–5 years due to the heavy physiological reproductive demands.⁴ They are considered endangered by the IUCN.⁴

The flatback turtle (Natator depressus) ranges in size from CCL: 75–100 cm and weighs between 70–90 kg. All recorded nesting beaches are restricted to Australia. Foraging occurs more widely through the waters over the Australian continental shelf to Papua New Guinea and Indonesia. The population can be subdivided into 4 distinct populations, with limited genetic diversity between the groups.³ They are carnivorous, feeding primarily on soft-bodied invertebrates, including corals, sea pens, holothurians, and jellyfish.⁵ Female flatback turtles have approximately 4 clutches per season with clutch sizes of about 50 eggs. These comparatively small clutch sizes lead to larger hatchlings compared to some other species. Inter-nesting periods within a season are between 13–18 days, and females may breed every 2–3 years. There is no evidence that hatchlings have an oceanic dispersal phase as with other sea turtles.⁵

The loggerhead turtle (Caretta caretta) ranges in size from CCL: 70–95 cm and weighs between 80–200 kg. They occur worldwide with circumtropical and subtropical distribution. The loggerhead turtle nests over the broadest geographical range of any sea turtle.⁶ They feed on hard-bodied, slow-moving invertebrates.^2,6 Age of sexual maturity occurs between 30–35 years of age. Female loggerheads have 3–7 clutches per season with clutch sizes ranging from 50–190 eggs. Inter-nesting periods are 9–23 days (average 14 days) and females usually nest every 2–4 years. They are considered vulnerable by the IUCN.⁴

The hawksbill turtle (Eretmochelys imbricata) ranges in size from 80–90 cm (CCL) and weighs between 80–90 kg. They have a worldwide circumtropical and subtropical distribution. DNA analysis has revealed that there are distinct genetic differences between populations on a global scale, and that there is very little interbreeding between populations, even those that nest on the same continent.⁷ They are omnivorous and feed mainly on sponges (75–90% of diet) and a small amount of algae or seagrass.⁷ Age of sexual maturity is unknown but thought to be greater than 20 years. Female hawksbill turtles’ nest 1–6 times per year with an inter-nesting period of 2–17 days, depending on locality. Clutch size is also quite variable and may range anywhere from 80–220 eggs. Females breed every 2–9 years.⁷ They are considered critically endangered by the IUCN.⁴

The olive ridley turtle (Lepidochelys olivacea) ranges in size from 65–72 cm (CCL) and weighs between 40–50 kg. They have a worldwide circumtropical distribution. They have only very large nesting populations, with over 100,000 nesting females annually in Orissa on the east coast of India, and the western Pacific coast of Central America in Mexico and Costa Rica. The olive ridley sea turtles have an unusual breeding behavior where immense numbers of turtles will come ashore at once to lay eggs. These events are known as “arribadas.”^2,8 They also nest solitarily. They are carnivorous, feeding primarily on gastropod mollusks and crabs. Additionally, they may feed on jellyfish and urchins.⁸ Olive ridley turtles lay 1–4 nests every 1–3 years with internesting intervals of 14 days for solitary nesters and 28 days for arribada nesters. Between 100–160 eggs are produced during each nesting event.⁸ They are listed as vulnerable by IUCN.⁴

The Kemp’s ridley turtle (Lepidochelys kempii) ranges in size from 58–70 cm (CCL) and between 36–45 kg. One of the most unique aspects of this species is that 95% of all nesting occurs on a single beach at or near Racho Nuevo, on the east coast of Mexico. They are found most commonly in the Gulf of Mexico, although they are sometimes found as far north as Maine and Nova Scotia.⁹ They feed primarily on gastropods and crabs.¹⁰ They nest approximately three times per season with an internesting interval of 25 days. Each nesting event produces between 100–115 eggs.¹¹ They are considered critically endangered by the IUCN.⁴

The leatherback turtle (Dermochelys coriacea) ranges in size from 150–180 cm (SCL) and weighs between 250–700 kg. They have a worldwide distribution in tropical and temperate oceans. There are genetically discrete breeding populations on a global scale. Leatherbacks are unique among extant reptiles for their ability to maintain high body temperatures using metabolically generated heat which allows them to occupy colder environments.¹² They feed primarily on colonial tunicates, jellyfish, and other soft-bodied invertebrates.¹² They reach maturity at around 26–32 years of age. Females may have between 3–10 clutches per season with an internesting interval of 9–28 days. Approximately 60–90 very large eggs are laid each time. Re-migration interval is typically more than 2 years.¹² They are considered critically endangered. The Pacific leatherback is the most imperiled sea turtle species.

Sea Turtle Emergency Medicine and Critical Care

Ill and injured sea turtles are usually, either found stranded on a beach or floating in the water. Live stranded sea turtles should be placed in an appropriately sized container with foam padding and towels and transported in a temperature-controlled vehicle for evaluation and stabilization. A thorough history and detailed physical examination should be performed on newly arrived patients and on a regular basis while the turtle is being rehabilitated.^13,14 A visual examination of the turtle before handling can provide important information.^13,14 Body weight and a body condition score should be recorded before therapy, and then measured serially during treatment.^13,14 Weight trends can be a good indicator of hydration status. Body condition index, a more quantitative assessment, is calculated using body weight and maximum straight carapace length (BCI=([weight (kg)/SCL (cm³)]×1000).¹⁴ Deep cloacal temperature may be representative of the sea turtle’s recent environmental temperature and is an important parameter to obtain and monitor in hypo- and hyperthermic patients. A digital laser thermal monitoring device directed at the pre-femoral or prescapular areas correlates well with core body temperature.¹⁴ Heart rate and rhythm can be assessed with a Doppler, or an ultrasound probe placed in the region of the thoracic inlet.^13,14 The skin, eyes, and shell should be checked carefully for evidence of fibropapillomas. Healthy loggerhead sea turtles will have some epibiota (especially barnacles) on the shell. When they become ill and more lethargic, the epibiota will often become more diverse and numerous. Moderate to heavy loads of small barnacles, leeches, and other epibionts on the skin is considered abnormal.¹³ The neurological status of the patient should be assessed.^13-15

The preferred blood collection site in most sea turtle species is the external jugular vein (also known as the dorsal cervical sinus). The lateral jugular vein is an alternative venipuncture site for green turtles and the femoral and interdigital vessels are alternatives in leatherbacks.^14,16 Although uncommon, lymph contamination may occur during the blood collection process, thus invalidating many of the clinical pathology parameters. A minimum database should consist of a hematocrit, total protein (TP), glucose, and a complete blood count and plasma biochemical analysis. Blood gas and electrolyte analysis are helpful in developing a prognosis and therapeutic plan. Ideally, a blood culture should be collected before initiating antimicrobial therapy. Healthy sea turtle patients can tolerate taking a blood volume of 0.5 ml/100 g body weight, while a reduced sample volume is recommended for debilitated patients. Lithium or sodium heparin is the anticoagulant of choice, because EDTA will cause red blood cell lysis in sea turtles.

Radiography is an important initial diagnostic tool used to assess the extent of external trauma, fractures, foreign body detection (e.g., fishhooks, chitinous and shell obstructions), respiratory tract, and internal fibropapillomas.^14,17 Radiopaque materials such as barnacles should be removed from the shell before performing a radiographic study. Three radiographic views should be routinely performed, including anterior-posterior and lateral projections using a horizontal x-ray beam and a dorsoventral (DV) view. Larger turtles may require multiple radiographs to assess the entire coelom, flippers, and head. Ultrasonography can be used to assess various internal organs but is particularly valuable in assessing whether plication is present in sea turtles that have ingested fishhooks and line.^14,17 Computed tomography has proven very useful in sea turtles with traumatic injuries involving the head or spine and internal fibropapillomatosis because of the increased detail provided over radiography.^14,17

Most sea turtles presented for rehabilitation are dehydrated.^14,18 Physical examination findings indicative of dehydration include sunken eyes, changes in skin turgor, skin tenting, loss of skin suppleness, dry mouth with ropey, thick oral secretions, depression, and a slow and difficult to find heartbeat. Elevation of hematocrit and TP can be helpful in determining the extent of dehydration. However, ill sea turtles are often anemic and hypoproteinemic, which may mask the extent of dehydration. Serial hematocrits and TP help assess the status of the patient and target the most appropriate therapeutic regimen. Hypoglycemia or hyperglycemia are often present in sick sea turtles; thus, blood glucose determination is essential.^14,18 Over-hydration is of concern in hypoproteinemic patients; thus, colloidal fluids may be more appropriate in these cases. Whole blood transfusions are indicated in cases of acute hemorrhage and life-threatening anemia (5% or less).^14,18,19 Fluid therapy, iron supplementation (in cases of blood loss anemia), and other supportive measures are often successful in less severe cases. The blood types in sea turtles have not been determined, but it is known that transfusion reactions do occur, and that cross matching is critical.¹⁹ The donor and recipient should be of the same species. An agglutination test between the recipient and donor blood is recommended. Acid-citrate-dextrose (ACD) solution or heparin can be used to collect blood for transfusion.

In severely compromised sea turtles, intravenous (IV) fluid administration allows for rapid rehydration. Ultrasound has proven helpful in placing IV catheters in sea turtles.¹⁸ In this author’s experience, bolus IV fluid therapy via the cervical sinus is very useful in stabilizing most patients.^14,18 Subcutaneous fluids are typically placed in the pre-femoral fossa and medially in the front limb fossa. Mildly dehydrated sea turtles may benefit from placement in fresh water for rehydration and reduction of epibiota load. General recommended maintenance fluid rates range from 10 to 25 ml/kg/day, depending on the patient’s size and condition.¹⁴

Patients respond more quickly to therapy if their nutritional status is positive.^14,18 The critically ill sea turtle is often immunosuppressed, hypoglycemic, hypoproteinemic, and anemic. These turtles often have decreased gastrointestinal (GI) motility and poor digestion of solid food. Thus, GI nutritional support should not be instituted until the patient has been rehydrated, attains normal blood glucose, and has some evidence of active GI motility.^14,18 Total parenteral nutrition (TPN) has been successful in providing nutritional support in debilitated patients until GI motility returns.²⁰ Tube feeding can be a challenge in sea turtles. It is best to begin with smaller volumes and more dilute solutions and steadily increase the volume and concentration to meet the turtle’s nutritional requirements. An esophagostomy tube is an option for sea turtles that are difficult to tube feed.²¹ Tube feeding formulas may vary depending on the turtle’s condition, tendency to regurgitate, presence of hypomotility, intestinal blockage, or enterocolitis. Commercially available herbivore and carnivore tube feeding formulas have proven useful in smaller patients. Critically ill carnivorous sea turtles, just starting to eat, can be fed filleted fish until they are defecating regularly.¹⁴ Bones, beaks, and chitinous materials can be slowly added back to the diet as the turtle starts defecating more regularly. Finicky eaters may require special attention by holding food in front of their nostrils to get them to start eating. Initially, an ill green turtle diet may be predominantly fish based to improve body condition, then slowly changed to include dark green vegetation. Nutritionally complete gelatin diets are recommended as part of the diet for hatchlings and green turtles but have palatability issues in most patients.¹⁴

Drugs with available pharmacokinetic data should be chosen when possible.²⁰ Recent studies have shown that extrapolating drug dosages and frequency between species of sea turtles might not be accurate.²² Sick chelonians do not absorb drugs well, so correct hypothermia, dehydration, hypoglycemia, acid-base, and electrolyte imbalances, prior to or in conjunction with starting other therapeutic agents. Drugs and dosages commonly used in sea turtles have been reported.²⁰

Debilitated turtles are often dry docked on a padded surface initially.^14,18 These turtles are kept moist by regular misting of the skin and shell. Another option is to have recirculated temperature-controlled, filtered water sprayed over the turtle to keep them wet but to prevent drowning. Weak turtles that can lift their heads to breathe and swim should be kept in an appropriate depth of water for the patient. Dehydrated turtles and those covered with excess epibiota (e.g., leeches, barnacles) should initially be placed in fresh water for 2–4 hours, which will allow for rehydration and will eventually kill the epibionts. Water temperature should be kept warmer for newly arrived and ill patients at 27–28°C (80–82°F) to improve immune function and then slowly decreased as the turtle’s condition improves. Ideally, patients suffering from hypothermia (“cold stunning”) should be placed in water or air temperature that is only 2–4 degrees C warmer than the ambient water temperature where the turtle was found.^14,18 Increasing the body temperature 3°C (5°F) per day until reaching 24°C (75°F) is recommended but may not be feasible in large mortality events.¹⁴

It is also wise to quarantine new arrivals in a rehabilitation facility, especially if receiving patients with fibropapilloma (FP).²³ Ideally, each tank should have its own life support system (LSS) and separate equipment. At the Georgia Sea Turtle Center, green turtles are segregated from other species of sea turtles regardless of their FP status.

It is important for the veterinarian to understand the different life support system options.²³

Radiology and Advanced Imaging

Plain radiography is an important diagnostic tool used to assess ill and injured sea turtles.^14,17 Digestive tract radiographic contrast procedures are often necessary to document intestinal obstruction, motility, and foreign bodies. Normal transit times have been established and are extremely variable. The contrast media can be administered via a stomach tube or with an enema under endoscopic guidance to evaluate fishing line presence and location.^14,17 Barium-impregnated beads can be placed in a food item with subsequent serial radiographs to assess gastrointestinal motility.¹⁴

Ultrasonography has been used for diagnostic purposes such as assessing cardiac activity, identifying internal fibropapillomas, abdominal fluid, and gastrointestinal motility. Acoustic windows that are typically used include pre- and post-femoral, axillary, dorsal and ventral cervical, and right and left cervical brachial.¹⁷

Computed tomography (CT) has proven very useful, although very large sea turtles will not fit in most CT chambers.¹⁷ It is important to measure the CT chamber and the turtle prior to transporting to an offsite facility. Applications include diagnosing spinal and head injuries that have not been apparent or well defined on plain radiography, visualizing free air pockets in coelom, pneumonia, bronchiolar blockage, and internal FP. The procedure is usually quick, so sedation is often not necessary. Magnetic resonance imaging (MRI) takes longer than CT scanning, so may require sedation. Open MRI imaging is useful for larger sea turtles that cannot fit into CT and closed MRI chambers. Normal MRI internal anatomic structures have been established in loggerhead sea turtles.

Endoscopy

Endoscopy is an indispensable diagnostic tool in sea turtles.²⁴ Rigid endoscopy has been used for sex determination in juveniles, evaluation of reproductive activity, exploring the coelomic cavity, organ biopsy for histopathology, and for confirming the presence or absence of internal fibropapillomas. Furthermore, rigid and flexible endoscopy can be used to evaluate the cloaca, bladder, and distal gastrointestinal tract. Both can be used to visualize the location of fishhooks in the esophagus. Flexible endoscopes can be used to evaluate the upper and lower gastrointestinal tract, the trachea, bronchi, and anterior lung. Bronchoscopy has been used to remove granulomatous material that may partially or completely fill the bronchial lumen.

Analgesia and Anesthesia

Meloxicam, a non-steroidal anti-inflammatory drug (NSAID), has been used most extensively in sea turtles. Pharmacokinetic studies indicate the drug is not useful in loggerheads, but a dose of 1 mg/kg SQ every 12 hours in kemps ridleys and every 48 hours in greens maintains appropriate plasma levels to reduce pain and provide anti-inflammatory effects.²² Ketoprofen (2 mg/kg once daily, maximum 5 days consecutively, with 5 days off before resuming if needed) is preferred in loggerheads.²⁵ Adequate hydration and renal function should be assured prior to NSAID administration.²⁶ Efficacy studies for tramadol in red eared sliders demonstrated analgesic effects for 96 h at a dose of 10 mg/kg when given orally. Pharmacokinetic studies have been conducted for this drug and it is used routinely by the author for pain management in sea turtles at 5 mg/kg every 48 hours or 10 mg/kg every 72 hours orally or SQ.²⁷ For heavy debridement, low-dose dexmedetomidine (5–10 micrograms/kg) IV has been beneficial in selected patients, while some sea turtles require much higher doses. Lidocaine, at a maximum dose of 8–10 mg/kg, is particularly helpful in reducing the level or avoiding gas anesthesia when removing FP tumors via laser surgery. Intrathecal lidocaine has been used successfully to provide local analgesia for FP removal surgery in pre-femoral, cloaca, and tail regions. Ring and splash blocks are commonly used for removing FP tumors. Lidocaine can be diluted with sodium bicarbonate and saline to increase the volume of drug in patients with heavy tumor loads.

A thorough diagnostic workup should occur prior to anesthesia. The author’s preference for injectable anesthetics includes the use of a combination of dexmedetomidine (50 to 75 micrograms/kg), butorphanol (0.4 mg/kg), and ketamine (1–2 mg/kg) (D-B-K) or dexmedetomidine and midazolam (0.2 to 0.4 mg/kg) combination or propofol IV (5–7 mg/kg IV, top up with 3 mg/kg) for short relatively non-invasive procedures or for induction of general anesthesia. Local anesthetic use in combination with injectable anesthetics can assist in avoiding general anesthesia, especially for FP tumor removal surgery. Inhalant anesthetics are used for invasive or prolonged procedures. Ventilation and thermoregulatory support should be maintained during the procedure and throughout the recovery period. Monitor heart rate via a Doppler, ultrasound, or ECG. Venous blood gases are often performed pre-, intra-, and post-operatively and are invaluable in monitoring anesthesia and determining the frequency of ventilation. Both sevoflurane and isoflurane have been utilized with success in sea turtles.²⁶

Surgery

Common surgical procedures in sea turtles include the removal of fishing line and hook and other gastrointestinal foreign bodies, fibropapilloma removal, and various procedures related to traumatic injuries such as amputation of flippers and long bone and carapace fracture repair.²¹ The coelomic cavity is most commonly approached through an inguinal incision; however, supraplastron, axillary, and lower esophageal approaches have been described allowing access to the lower esophagus and stomach.²¹ Similar to other reptiles, sea turtles do not have the enzymes to break down many of the commonly used suture materials in mammals. Poliglecaprone 25 and polyglyconate cause the least tissue reaction in sea turtles.²¹

Common Problems Encountered in Sea Turtle Rehabilitation

Trauma

Collisions with ships and boats represent a major source of mortality in a wide range of marine wildlife, including sea turtles, and are of increasing concern, because increased development in coastal areas is likely to result in increased recreational boat traffic. In the United States, the percentage of strandings that were attributed to vessel strikes increased from approximately 10% in the 1980s to a record high of 20.5% in 2004. Many vessel strikes have been documented in southeast Florida, with as many as 60% of stranded loggerheads displaying signs of propeller-related injuries. In 2020, 26% of the sea turtles found dead or injured in Georgia suffered injuries consistent with being hit by a boat. State and federal agencies monitor sea turtles and other threatened and endangered wildlife through the Marine Turtle and Marine Mammal Stranding and Salvage Networks. The information gleaned provides the primary index for threats to these animals.²⁸

Watercrafts are one of the few things in the marine environment that move with enough force in the water to produce severe blunt trauma. Characterizing the injuries on injured and dead sea turtles can lead to understanding the type and parts of the vessels that are causing the injuries. If a particular type of vessel is identified as being problematic, it may help in mitigating the problem. There is significant variation in the appearance of sharp and blunt force wounds resulting from vessel strikes due to the various components of vessels, the variety of types and configurations of propulsion and steering systems, and various types and sizes of vessels that may strike turtles. The most specific and recognizable wounds caused by vessels are multiple, approximately equidistant, parallel chop wounds produced by propellers. The shape of the wound can vary from straight to curved to sigmoidal depending on the depth of penetration, the movement of the turtle during the strike, and characteristics of the propeller. Larger propellers can completely transect turtles and produce blunter injuries than smaller blades, resulting in extensive fractures and tearing of tissue. Various parts of the watercraft, such as the hull, keel, and trim tabs, often cause blunt injuries. In some cases, paint from the hull may be transferred to the turtle during impact providing further evidence of a vessel strike.²⁹

Marine Debris Ingestion

The accumulation and persistence of plastic debris in the marine environment are of increasing concern.³⁰ Plastics are now the most common form of marine debris, with total annual production increasing from 1950 to 2013 from 1.5 million to between 275 and 299 million metric tons. All the life stages of all seven species of sea turtles have been reported to be affected by marine plastics. Most plastic debris in environments where sea turtles frequent have been shown to be disposable consumer plastics from land-based sources. After sea turtles hatch on the nesting beach, they go through a swimming frenzy to get to the Sargassum ecosystem, where they spend several years feeding, resting, and following currents. The post-hatchling life stage is most impacted by plastic ingestion because the Sargassum seaweed tends to occur in convergent zones, where heavy plastic pollution tends to accumulate. One study used stranded post-hatchling sea turtles as indicator species for the study of micronizing oceanic plastic.³⁰ They evaluated individuals that were washed back to shore where they were rescued for rehabilitation. Plastic debris in marine environments fragments into smaller particles due to photochemical transformations from UV exposure and mechanical degradation processes associated with hydraulic forces and other abiotic degradation processes. In this study, they characterized nanoparticles in the sub 200 nm range using atomic force microscopy. These plastic particles have the potential to be absorbed across the GI tract into the systemic circulation which may lead to metabolic disturbances, inflammatory diseases, and potentially other long-term effects. Sea turtles often ingest non-biodegradable human waste such as plastic, balloons, metal, and glass. Sometimes they may be asymptomatic and incidentally pass the debris in their feces. Some may develop impactions which may be successfully managed with supportive care and GI tract lubricants; however, more severe cases may require surgical intervention or lead to death through GI tract perforation and other issues.

Oil and tar may be found on the skin or shell or may be ingested by the turtle. Dilute Dawn dishwashing liquid and mayonnaise have been used to remove oil from sea turtles. Fishhooks with attached fishing line may become anchored in the oral cavity, esophagus, or other parts of the GIT and lead to intestinal plication or coelomitis. Conservative medical treatment, with enemas, parenteral fluids, and petroleum laxatives, may be all that is necessary for clinical resolution of these patients. However, surgical removal of the foreign body may be required in some cases.

Cold Stunning

Hypothermia, or cold stunning, in sea turtles may occur when the water temperature suddenly drops below 10°C (50°F).³¹ They lose their ability to swim and dive, become buoyant and float to the surface. Traumatic wounds, dehydration, corneal ulcerations, dermal, carapace and plastron lesions, flipper tip necrosis, and buoyancy disorders are frequent findings. Secondary infections, especially bacterial and fungal pneumonia and osteomyelitis, are not uncommon and may not be apparent until several weeks after the initial event. Less severe cases are placed in shallow water, while more severe cases are dry-docked. If practical, the water or room temperature should initially be only 2–4°C warmer than the ambient water temperature where the turtle was found. Increasing the body temperature 3°C (37.4°F) per day until reaching 24°C (75.2°F) has been recommended. Treatment of open wounds, corneal lesions, and supportive care should be started immediately. Broad-spectrum systemic antibacterial and potentially antifungal therapy should be initiated when the turtle reaches 21°C (70°F). Large numbers of sea turtles stranding at one time may dictate alternative management approaches.

Buoyancy Disorders

Any condition leading to gas or air accumulation in the intestinal tract, the coelomic cavity, or pulmonary disease may cause abnormal buoyancy.^1,14 Common causes include pneumonia, gastrointestinal disease that leads to gas accumulation, and free air in the coelomic cavity from a lung tear. Clinical pathology, various diagnostic imaging modalities, and endoscopy may be helpful in diagnosing the primary problem. Free air should be aspirated by tilting the turtle on its side and directing the head ventrally to bring the air pocket up to the inguinal space. Laparoscopic surgery may be useful in repairing lung tears that do not heal on their own. A less invasive alternative is autologous blood patch pleurodesis. Some turtles, especially those with spinal injuries, may remain abnormally buoyant for life.

Starvation/Debilitation

Emaciated sea turtles usually have an underlying problem, which is often masked by secondary medical problems such as bacterial or fungal pneumonia, septicemia, and severe endoparasitism.^1,14 Excessive epibiota, especially barnacles and leeches on the skin, are common in these patients. These turtles may be critically anemic, hypoproteinemic, and hypoglycemic. They often have severe generalized edema, serous atrophy of fat, lymphoid depletion, and bone marrow suppression. Treatment consists of careful fluid and electrolyte replacement, TPN, broad-spectrum antimicrobial drugs, and tube feeding electrolytes and glucose initially and eventually small but increasing levels of calories and nutrition. Depending on the severity of the anemia, whole blood and synthetic erythropoietin analogues have been used. Freshwater soaks will kill and loosen the epibionts.

Internal Parasites

Wild, healthy sea turtles typically have parasites; however, endoparasites may be a contributing factor in an already compromised sea turtle, and in some cases, they may be the primary cause of debilitation.^1,14 Numerous species of digenetic trematodes of the family Spirochiidae are commonly found in the cardiovascular system and other primary sites in several species of sea turtles and are implicated as a cause of significant morbidity and potentially contribute to mortality. The eggs are released into the circulatory system, which eventually become trapped within the terminal arterioles in visceral organs and in peripheral structures such as the limbs and dermal bone of the shell. A granulomatous response is produced by the eggs in various tissues. Clinical signs are related to the pathology caused by the eggs and secondary bacterial infections. Praziquantel has been used to decrease the adult trematode burden but has no effect on the eggs.²⁰

Caryospora sp. are one of the few pathogens that are associated with episodic mass mortality events involving free-ranging sea turtles.³² Green turtle (Chelonia mydas) mortality events documented to be caused by these coccidia were reported in maricultured turtles in the Caribbean during the 1970s and in wild green turtles in Australia in 1991 and 2014. Clinical cases of Caryospora-like infections were reported in free-ranging green turtles from the southeastern US in 2012. Following these initial individual cases in this region, an epizootic and mass mortality of green turtles occurred along the Atlantic coast of southern Florida from November 2014 through April 2015, and additional sporadic cases continued to be detected in the southeastern US in subsequent years. The first stranding associated with infection by a Caryospora-like organism occurred in Hawai’i in 2018.³² Common clinical signs include weight loss, lethargy, dehydration, and hypoglycemia. Pathological findings include watery, gassy enteric contents, mucosal hyperplasia and ulceration, and the small and large bowel are usually involved and occasionally the stomach.^1,32 If the turtle presents in critical condition, it should be stabilized prior to starting treatment. If the turtle cannot handle oral medications, intravenous metronidazole should be started at 20 mg/kg IV. Ponazuril is the preferred treatment and preliminary pharmacokinetic studies and personal experience suggest a dose of 100 mg/kg orally every 7 days for 8 doses.³³ The organism may have a direct or an indirect life cycle; thus, direct transmission can occur. Ozone and UV sterilizers will kill the organism. Most disinfectants work poorly against coccidia. Ammonium hydroxide is effective at a 10% solution.

Bacterial and Fungal Infections

Debilitated and injured sea turtles often present with bacterial or fungal infections. Predisposing factors include debilitation, injury, malnutrition, poor husbandry, and other disease processes. Gram-negative bacteria cause the highest morbidity in sea turtles; however, anaerobic bacteria can cause serious disease. Shell infections can involve the superficial keratin or may extend into the bone of the carapace and plastron. Aerobic and anaerobic bacteria and mycotic agents are commonly isolated. Pathology attributed to Mycobacterium sp. has been documented with some frequency in Kemp’s ridley turtles and occasionally in other sea turtles. A mixed nocardial and unidentified fungal osteomyelitis was documented in a Kemp’s ridley turtle.¹ Enterococcus sp. is a common cause of septicemia, osteomyelitis, and pneumonia in sea turtles, especially Kemp’s ridley turtles.³⁴ Serratia marcescens is a common cause of osteomyelitis in sea turtles.³⁴

Pneumonia is a common problem in critically ill sea turtles.¹ Hypothermia, malnutrition, and aspiration of salt water are predisposing factors for pneumonia. Sea turtles can conceal clinical signs of pneumonia until the condition is severe. Opportunistic gram-negative bacteria are recovered from a large percentage of the cases. Anaerobic bacteria represent an important cause of pneumonia. Although less common, fungal pneumonias have been documented in sea turtles. Digenetic spirorchid trematodes may predispose sea turtles to bacterial or fungal pneumonia. Diagnosis of pneumonia is based on history, physical examination, radiology and advanced imaging, and bronchoscopy.^17,24 Cytology and culture should be performed on samples obtained. Fungal pneumonias often produce localized or diffuse granulomatous nodules, which makes recovery of the organism difficult without a biopsy. Septicemia is a relatively common sequela to more localized infections. Systemic and nebulized antibiotics and antifungal drugs are the treatment of choice.²⁰ Terbinafine and itraconazole are the preferred antifungal drugs.²⁰

Viral Diseases

Loggerhead genital-respiratory herpesvirus and loggerhead orocutaneous herpesvirus has been reported.³⁵ The author has documented similar cases in live sea turtles that have been responsive to acyclovir therapy (80 mg/kg SID orally).

Fibropapillomatosis (FP), also caused by an alpha herpesvirus, is the most significant infectious disease affecting sea turtle populations worldwide. The disease was first reported in 1938 and was only occasionally observed in green turtles found in South Florida until the mid-1980s. Since that time, FP has been observed with increased frequency with a very high local prevalence in some green turtle populations.¹ The disease occurs most commonly and is more severe in green turtles, but has been documented in several other sea turtle species. Pelagic turtles recruiting to near shore environments are free of the disease. After exposure to these benthic ecosystems, FP manifests itself. Field observations support that the prevalence of the disease is associated with heavily polluted coastal areas, areas of high human density, agricultural runoff, and/or biotoxin-producing algae.¹

Fibropapillomas may present as very mild solitary wart-like masses on the skin to numerous very large masses covering the skin, shell, eyelids, conjunctiva, and cornea. The disease may impair the turtle’s mobility and vision and subsequently may lead to severe emaciation and eventual death. Internal organs (e.g., gastrointestinal tract, lungs, heart, liver, kidneys, and gonad) may be affected. Turtles may present with moderate to severe emaciation, especially if internal FP is present. Radiography, advanced imaging, and laparoscopy are used to identify internal FP. Humane euthanasia is recommended for turtles with internal lesions and grade 3 stage of the disease. Initial treatment consists of correcting dehydration, low blood glucose, and malnutrition. Antimicrobial therapy is usually indicated. Laser surgery is the safest and most efficient surgical modality to remove the tumors.

Acknowledgements

T. Franciscus Scheelings, Monash University, Clayton, Victoria, Australia for assisting in providing information and writing some of the natural history sections.

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