Body temperatures of leatherback turtles (Dermochelys coriacea) in temperate waters off Nova Scotia, Canada

Abstract

The leatherback sea turtle, Dermochelys coriacea (Vandelli, 1761), has the most extensive range of any reptile, migrating from tropical and subtropical nesting areas to distant foraging habitats, including those in temperate and even boreal waters. This implies flexible thermal functioning. It has been inferred that leatherbacks support active foraging by keeping warm in cold water, rather than becoming lethargic as other marine turtles do. However, data consistent with this view have come from captive turtles in unnatural and stressful conditions. In the present case, foraging leatherbacks were captured at sea off Nova Scotia and their body temperature recorded within 10 min, before such large animals could change their body temperatures appreciably. Mean excess temperature over that of the sea surface (15.0-16.7°C) averaged 8.2°C. These results attest to, but underestimate, the capacity of free-swimming leatherbacks to keep warm in northern waters, as data from another turtle that was instrumented to record ocean temperature while diving revealed that leatherbacks foraging in this area at the same time of year may spend 40% of their time diving to waters cooler than the surface.Résumé : La tortue luth, Dermochelys coriacea (Vandelli, 1761), possède l'aire de répartition la plus étendue de tous les reptiles, car elle migre de son aire de nidification tropicale ou subtropicale vers ses habitats lointains de recherche de nourriture qui incluent les eaux tempérées et même les eaux boréales. Un tel comportement suppose un fonctionnement thermique flexible. On en a déduit que les tortues luths maintiennent leur recherche active de nourriture en demeurant chaudes en eau froide, plutôt que léthargiques comme les autres tortues marines. Cependant, les données qui appuient cette hypothèse proviennent de tortues en captivité dans des conditions artificielles et éprouvantes. Dans cette étude, nous avons capturé des tortues en train de se nourrir en mer au large de la Nouvelle-Écosse et nous avons mesuré leur température corporelle dans un délai de moins de 10 min, avant que des animaux de cette taille n'aient le temps de subir une modification de leur température corporelle. Leur température moyenne est de 8,2°C supérieure en moyenne à celle de la surface de la mer (15,0-16,7°C). Ces données confirment, tout en la sous-estimant, la capacité des tortues luths en nage libre à se maintenir chaudes dans les eaux nordiques; en effet, des données provenant d'une autre tortue luth porteuse d'un enregistreur de température pendant la plongée indiquent que les tortues luths qui recherchent leur nourriture dans la même région au même moment de l'année peuvent passer 40 % de leur temps à plonger dans des eaux qui sont plus froides que les eaux de surface.[Traduit par la Rédaction] James and Mrosovsky 1306

Comparative Health Assessment of Western Pacific Leatherback Turtles (Dermochelys Coriacea) Foraging Off the Coast of California, 2005–2007

“…As expected, all foraging leatherback turtles maintained a higher core body temperature than the ambient water temperature (13.8-16.9 C), with a mean differential temperature of 7.656 2.88 C and a maximum differential of 10.2 C. These findings are similar to those recorded in leatherbacks from Nova Scotia (8.262.4 C; James and Mrosovsky, 2004) and higher than the median of 3 C above water temperature reported in the tropics (Harms et al, 2007). The higher temperature differential seen in leatherbacks in temperate waters likely is a result of the colder ambient water and air temperatures in northern latitudes.…”

“…Body temperatures for foraging leatherbacks in California (22.8962.26 C) were similar to foraging turtles from the cold waters off Nova Scotia (24.3361.87 C) and were lower than temperature ranges in swimming and diving (30.260.7 C) and anesthetized (31.160.4 C) leatherbacks in tropical climates (James and Mrosovsky, 2004;Southwood et al, 2005;Harms et al, 2007). As expected, all foraging leatherback turtles maintained a higher core body temperature than the ambient water temperature (13.8-16.9 C), with a mean differential temperature of 7.656 2.88 C and a maximum differential of 10.2 C. These findings are similar to those recorded in leatherbacks from Nova Scotia (8.262.4 C; James and Mrosovsky, 2004) and higher than the median of 3 C above water temperature reported in the tropics (Harms et al, 2007).…”

“…Morphologic measurements were recorded, including curved carapace length (CCL, measured from the nuchal notch to the tip of the pygal), curved carapace width (CCW, measured between the most lateral ridges at the widest part of the carapace), and body weight. Foraging turtles with CCL ,145 cm were classified as subadults; all turtles with CCL $145 cm were considered to be adults (James et al, 2007). Sex for turtles $145 cm was determined using external sexually dimorphic features, such as the length of the tail relative to the pygal and position of the cloacal opening; direct visualization of the extruded penis was used for all age classes (Wyneken, 2001).…”

“…Leatherbacks undergo the longest migrations of any sea turtle species, crossing ocean basins to forage on cnidaria zooplankton such as jellyfish and salps (James and Herman, 2001;Hays et al, 2004;James et al, 2005;Benson et al, 2007a, b). Their large size and unique thermoregulatory adaptations allow them to inhabit tropical and temperate oceans (Frair et al, 1972;Greer et al, 1973).…”

Prey landscapes help identify potential foraging habitats for leatherback turtles in the NE Atlantic

“…The occurrence of leatherback turtles in habitats with sea temperatures that induce lethargy in hard-shelled species (Davenport 1997) supports the premise that leatherbacks have an endothermic capacity, thus remaining active in cool prey-rich waters (Davenport 1998, McMahon & Hays in press). Female leatherbacks foraging in northwest Atlantic waters (15 to 16.7°C) have been shown to support core body temperatures 8.2 ± 2.4°C (mean ± SD) above ambient sea temperature (James & Mrosovsky 2004). This endothermy is thought to be achieved through their considerable body mass (gigantothermy; Paladino et al 1990) and physiological adaptations including counter-current vasculature in the flippers (Greer et al 1973), insulating subcutaneous lipid layers (Frair et al 1972, Davenport et al 1990) and variable lipid composition and distribution (Davenport et al 1990).…”