First successful head-start program of leatherback sea turtles (Dermochelys coriacea) in Thailand and proposed dietary strategy

Leatherback sea turtle (Dermochelys coriacea) hatchlings have previously been kept alive for over a year in captive conditions but these were the few survivors of initially larger groups. In this report, newly hatched leatherback sea turtles were randomly harvested from two nests in Thailand and successfully reared before release back to the wild. In captivity, the survival of the turtles decreased sharply during the first 4 or 5 months, and then steadied until the end of the 12-month trial. The survival of yearlings from one nest was 13.3% and from the other nest 46.7%. Their growth was exponential, reaching 1.36-3.35 kg (n = 9) at the end of program. The causes of death of the reared turtles were accidents (25.0-38.5%) and infections from water and live food (61.5-75.0%). The dietary requirements of the turtles were investigated by determining the digestibility of protein and carbohydrate in vitro, using enzymes from the digestive tracts of hatchlings that had died in an accident (70.1-92.9 g body weight). The results indicated that the most suitable source of protein was wheat gluten, followed by soybean meal, nonruminant meat and bone meal, fish meal, nonruminant meat meal, pork meal, and skimmed milk, while suitable carbohydrate sources were mashed cassava, corn, wheat flour, and alpha starch, followed by cereal meal and rice flour. Findings from the current report provide a practical protocol for head-starting leatherback sea turtles, and indicate the possible basis of an effective artificial diet for this species.

Physiological determinants of the internesting interval in sea turtles: a novel 'water-limitation' hypothesis

The internesting interval separates successive clutches of sea turtle eggs, and its duration varies both among and within species. Here, we review the potential physiological limits to this interval, and develop the hypothesis that desalination capacity limits the internesting interval owing to the requirement for water deposition in eggs. Sea turtles deposit 1-4 kg of water per clutch in egg albumen; for most species, this represents about 2% of adult body mass. We calculate how quickly turtles can recover this water by estimating maximal salt excretion rates, metabolic water production and urinary losses. From this water balance perspective, the 'water-limitation' hypothesis is plausible for green turtles but not for leatherbacks. Some plasma biochemistry studies indicate dehydration in sea turtles during the nesting season, although this is not a universal finding and these data have rarely been collected during the internesting interval itself. There is mixed support for a trade-off between clutch size and the length of the interval. We conclude that the 'water-limitation' hypothesis is plausible for most sea turtle species, but requires direct experimentation.

Evidence of accumulation and elimination of inorganic contaminants from the lachrymal salt glands of leatherback sea turtles (Dermochelys coriacea)

Plasma osmolalities of marine vertebrates are generally lower than the surrounding medium; therefore, marine organisms must cope with the osmoregulatory challenges of life in a salty environment. The salt glands serve to maintain osmotic and ionic homeostasis in a number of lower marine vertebrates. One marine reptile, the leatherback sea turtle (Dermochelys coriacea), ingests excessive amounts of salts due to their diet of gelatinous zooplankton. Outside of the normal osmoregulatory function of the salt gland, little research has been conducted on contaminant accumulation and excretion in this organ. Here, we established arsenic, cadmium, lead, mercury, and selenium concentrations in red blood cells (RBCs) and salt gland secretions (SGSs) of nesting leatherbacks. We also collected salt glands from different life stage classes of dead stranded leatherbacks from the western Atlantic Ocean to determine if inorganic contaminants accumulate in this organ. Using non-metric multidimensional scaling and regression analyses, we determined that RBC and SGS inorganic contaminant concentrations were not correlated. Additionally, RBCs showed significantly higher concentrations of these contaminants in comparison to SGSs, likely due to the affinity of inorganic contaminants for the heme group of RBCs. Lastly, we found that salt gland cadmium and mercury concentrations tended to increase with increasing curved carapace length (CCL) in stranded leatherbacks. Our results indicate that different physiological mechanisms determine the distribution of inorganic contaminants in blood and SGSs. Increases in salt gland contaminant concentrations with increasing CCL suggest this organ as a potential target for accumulation.