Journal of Thermal Biology 51 (2015) 15–22 Contents lists available at ScienceDirect Journal of Thermal Biology journal homepage: www.elsevier.com/locate/jtherbio Core and body surface temperatures of nesting leatherback turtles (Dermochelys coriacea) Thomas J. Burns n, Dominic J. McCafferty, Malcolm W. Kennedy n Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, Graham Kerr Building, University of Glasgow, Glasgow G12 8QQ, Scotland, UK article info abstract Article history: Leatherback turtles (Dermochelys coriacea) are the largest species of marine turtle and the fourth most Received 27 November 2014 massive extant reptile. In temperate waters they maintain body temperatures higher than surrounding Received in revised form seawater through a combination of insulation, physiological, and behavioural adaptations. Nesting in- 27 February 2015 volves physical activity in addition to contact with warm sand and air, potentially presenting thermal Accepted 1 March 2015 challenges in the absence of the cooling effect of water, and data are lacking with which to understand Available online 3 March 2015 their nesting thermal biology. Using non-contact methods (thermal imaging and infrared thermometry) Keywords: to avoid any stress-related effects, we investigated core and surface temperature during nesting. The Thermal biology mean7SE core temperature was 31.470.05 °C (newly emerged eggs) and was not correlated with en- Thermography vironmental conditions on the nesting beach. Core temperature of leatherbacks was greater than that of Non-invasive techniques hawksbill turtles (Eretmochelys imbricata) nesting at a nearby colony, 30.070.13 °C. Body surface tem- Core temperature Dermochelys coriacea peratures of leatherbacks showed regional variation, the lateral and dorsal regions of the head were Eretmochelys imbricata warmest while the carapace was the coolest surface. Surface temperature increased during the early nesting phases, then levelled off or decreased during later phases with the rates of change varying be- tween body regions. Body region, behavioural phase of nesting and air temperature were found to be the best predictors of surface temperature. Regional variation in surface temperature were likely due to alterations in blood supply, and temporal changes in local muscular activity of flippers during the dif- ferent phases of nesting. Heat exchange from the upper surface of the turtle was dominated by radiative heat loss from all body regions and small convective heat gains to the carapace and front flippers. & 2015 Elsevier Ltd. All rights reserved. 1. Introduction Casey et al., 2014). Thermoregulation is aided by counter-current heat exchangers within the front and rear flippers (Greer et al., Leatherback turtles (Dermochelys coriacea) are the largest spe- 1973), a vascular plexus lining the trachea to reduce respiratory cies of marine turtle, with adult females having a mean mass of heat loss, analogous to that of nasal turbinates found in birds and around 400 kg (Georges and Fossette, 2006). As adults they inhabit mammals (Davenport et al., 2009a), extensive adipose tissues in a broad range of water temperatures, migrating between high la- the head and neck, and major blood vessels buried deep within titude, prey-rich temperate waters and the tropics or subtropics, the insulated neck (Davenport et al., 2009b). where beaches provide the conditions for laying and development In addition to these physiological adaptations for controlling of eggs. Leatherbacks exhibit a range of physiological and beha- heat loss, behaviour plays a key role in temperature control. vioural adaptations to cope with different environmental tem- Swimming (and the consequent metabolic heating) maintains a peratures, allowing them to remain active in temperate waters and high body to water temperature differential (Bostrom and Jones, prevent overheating in the tropics. Their thermoregulatory strat- 2007) and turtles change flipper stroke rate in response to dif- egy likely involves aspects of both gigantothermy due to their ferent water temperatures (Bostrom et al., 2010). Furthermore, large body mass, extensive fatty insulating tissue layers and leatherbacks may dive to cooler waters to lose heat in tropical adaptable blood circulation system (Paladino et al., 1990), and waters (Southwood et al., 2005; Bostrom and Jones, 2007) and, endothermy due to internal heat production (Bostrom et al., 2010; conversely, in temperate seas may bring prey items to the surface to warm them before ingestion (James and Mrosovsky, 2004). n Nesting is the only time when female leatherbacks are known to Corresponding authors. E-mail addresses: [email protected] (T.J. Burns), return to land, the process may last over two hours, and requires, [email protected] (M.W. Kennedy). with the exception of egg laying, extensive use of the flippers http://dx.doi.org/10.1016/j.jtherbio.2015.03.001 0306-4565/& 2015 Elsevier Ltd. All rights reserved. 16 T.J. Burns et al. / Journal of Thermal Biology 51 (2015) 15–22 Table 1 Published values for leatherback body temperature shown alongside values derived from this study. o Mean TB7SE (range) C Method of measurement Location (turtle activity) n Source 31.4 70.05 (30.6–32.5) Egg surface temperature (corrected) Trinidad (nesting-laying) 65 This study 29.170.23 (27.3–30.6) Sub-carapace Costa Rica (inter-nesting) 3 Southwood et al. (2005) 30.270.35 (27.1–33.2) Gastrointestinal Costa Rica (inter-nesting) 4 Southwood et al. (2005) 28.370.07 (28.1–28.7) Gastrointestinal USVI (inter-nesting) 8 Casey et al. (2010) 31.1n (30.5–33.5) Egg temperature Mexico (nesting) 10 Mrosovsky (1980) 30.6 (29.8–31.4) Egg temperature French Guiana /Suriname (nesting) 24 Mrosovsky, Pritchard (1971) 3370.45 (32–34) Not specified Costa Rica (nesting-restrained post laying) 5 Lutcavage et al. (1992) 31.6 70.3 Inserted 25–30 cm into body through drilled hole Costa Rica (nesting-restrained post sand scattering) 10 Paladino et al. (1996) 30.870.2 Inserted 25–30 cm into body through drilled hole Costa Rica (nesting-laying) 3 Paladino et al. (1996) 31.4 70.4 Inserted 25–30 cm into body through drilled hole Costa Rica (nesting-‘exercising’)10Paladino et al. (1996) 31.5 Gastrointestinal (juvenile- 37 kg) Laboratory (in water tank) 1 Bostrom et al. (2010) 31.8 Gastrointestinal (juvenile- 16 kg) Laboratory (in water tank) 1 Bostrom et al. (2010) 26.470.23 (25.4–27.3) Gastrointestinal Northwest Atlantic (foraging) 7 Casey et al. (2014) 24.3370.94 (21.6–25.8) Cloacal Nova Scotia (restrained) 4 James and Mrosovsky (2004) n Represents a median value, values from this study are shown in bold. (Eckert et al., 2012). Flipper movement has been suggested as the the nest hole; 4-laying; 5-refilling the nest hole; 6-sand scattering primary source of heat production at sea (Bostrom and Jones, (also termed ‘camouflaging’ and ‘disguise’ elsewhere in the lit- 2007; Bostrom et al., 2010) and it is likely that flipper activity erature); 7-return to the sea (for a full description of nesting during nesting will result in substantial heat production. Biophy- phases see Table S1). sical modelling suggests that core temperature of leatherbacks increases throughout the nesting process and rises in core tem- 2.2. Body core temperature perature during nesting are predicted as a result of future rising temperatures in their breeding range (Dudley and Porter, 2014). The surface temperature of freshly laid eggs was used as a non- However, measurements on land of core temperature in this contact proxy of core body temperature. Measurements were ta- species are, surprisingly, relatively scarce (Table 1). þ The aims of this study were, first, to estimate the core tem- ken using a Fluke 62 Max portable infrared thermometer ¼ – m ¼ ° perature of nesting leatherbacks, second, to examine spatial and (spectral range 8 14 m, accuracy 1 C or 1%, thermal ¼ ° temporal variation in surface temperature through all phases of sensitivity 0.1 C) set to an emissivity of 0.98, which is within the nesting behaviour, and, third, to estimate the relationships be- range of previously used values for emissivity of living tissues tween both core and surface body temperatures and the en- (McCafferty et al., 2013; Rowe et al., 2013; Mortola, 2013). Infrared vironmental conditions on the nesting beaches. An important and thermometers were calibrated against a thermocouple, which had novel aspect of this study was that all measurements were made itself been calibrated against a mercury thermometer of 0.1 °C with minimal or no disturbance using non-contact thermometry sensitivity. The recorder lay in the sand with one arm extended and thermal imaging. For comparison we also estimated the core into the nest hole (some sand was removed from one side of the temperatures of ectothermic nesting hawksbill turtles (Eretmo- nest hole to allow better access) and observed the eggs as they chelys imbricata). were laid. Measurements were taken only on eggs that were freshly laid (within one or two seconds of emergence) and had no sand attached to the side which was being measured. As mea- 2. Materials and methods surements of surface temperature were taken so soon after the eggs emerged from the female the effects of variation in cooling 2.1. Study area and discrimination of nesting phases rates between eggs will be negligible. Measurements were also taken for nesting hawksbill turtles (to provide a smaller ec- Fieldwork on leatherback turtles was carried out at Fishing tothermic comparator) at Hermitage Bay, Tobago (approximately Pond Beach (approximately 10.58° N, 61.02° W) on the East coast 11.31° N, 60.57° W) using the same methods. of Trinidad, West Indies. Fishing Pond is one of three protected To correct for potential post-laying cooling and/or inaccuracy beaches on the island which receive high densities of nesting fe- due to imprecise emissivity setting, a correction factor for egg male leatherbacks during the nesting season which runs from surface temperature was estimated and applied to all measure- March to the end of August, peak nesting occurring during April ments of both study species.