Estimating total body heat dissipation in air and water from skin surface heat flux telemetry in Weddell seals

Abstract

Background: Accurate estimates of thermoregulatory costs in air and water are necessary to predict the impacts of changing habitats to individuals and populations of ice-obligate seals. Investigations that would provide such estimates of thermoregulatory physiology over natural activities in free-ranging marine mammals have been limited. This study describes a biotelemetry method for measuring skin surface heat flux in free-ranging Weddell seals. These data are then applied to estimations of thermoregulatory heat dissipation from multiple point measurements.Results: Data loggers collecting skin surface heat flux telemetry at four body locations (head, neck, axilla and flank) from 40 free-ranging Weddell seals were deployed and recovered over periods of 1-13 days in Erebus Bay, Antarctica. We derive equations for estimating total body heat dissipation from these point measurements and demonstrate the subsequent calculation of heat dissipated from obligate thermoregulatory costs. Heat lost to air or water was described by heat flux sensor data extrapolated across the whole-body surface, as informed by skin surface infrared thermal patterns. Heat lost directly to the ice surface during haul-out was best described by physical features of the seal, rather than environmental variables. Heat flux inputs from the four sensors could be reduced to two principal components, and corresponding regressions indicated that the axilla and flank sensors were most correlated with total body heat dissipation in air and water. Variability in head sensor heat flux was least described by the two principal components. Conclusions:This method can be used to estimate total body heat dissipation during daily activities in marine mammals, and under steady-state conditions, it can be used to identify obligate thermoregulatory heat costs. Ultimately this type of data will provide relevant empirical information for parameterizing models of thermoregulatory energetics in ice-obligate seals, which may improve our ability to predict outcomes of altered ice conditions at high latitudes.

Diving physiology of marine mammals and birds: the development of biologging techniques

“…The sensor used in most temperature biologging studies is the thermistor, which, when supplied with a constant current, experiences a drop in voltage owing to decreased resistance in response to a change in temperature. The placement of the thermistor is key because studies have revealed high regional heterothermy in diving animals, including the emperor penguin and Weddell seal [9,64,65].…”

“…Understanding how heat is released may also shed light on this question. Several methods for measuring heat exchange using heat flux sensors (thermopiles) attached to a biologger have been described for marine mammals [65,73,74]. Future studies that combine heat flux sensors and intravascular temperature could, theoretically, provide insight into whether heat dissipation is associated with reduced core body temperature.…”

Thermoregulatory Strategies of Diving Air-Breathing Marine Vertebrates: A Review

“…By comparing heat flux at multiple body sites in relation to water temperature and activity level in the lab, thermal windows have been identified in various species: dorsal fin and flippers in dolphins (Hampton et al, 1971;McGinnis et al, 1972;Heath and Ridgway, 1999;Noren et al, 1999;Williams et al, 1999b;Meagher et al, 2008), fluke and flippers in manatees (Erdsack et al, 2018), flippers in seals , and soft white skin areas in turtles (Heath and McGinnis, 1980;Standora et al, 1982). Unlike the dorsal fin of dolphins, heat flux sensors have not been attached to the highly maneuverable flippers of sea lions or fur seals and the wings of penguins to confirm the role of these appendages as thermal windows (Goldsmith and Sladen, 1961;Hindle et al, 2015).…”

“…IRT images of seals after exiting the water (Mauck et al, 2003;Erdsack et al, 2012) or during moments of heat stress (Norris et al, 2010;Codde et al, 2016) have revealed the dynamics of thermal windows while on land, verifying the role of broadly distributed AVAs to control heat exchange. Hindle et al (2015) used IRT on Weddell seals to determine the placement of heat flux sensors that best represented heat flux across the entire body and then extrapolated these measurements to estimate whole-body thermal dynamics. Similarly, IRT of dolphin dorsal fins revealed different surface temperatures that correspond to the underlying vasculature (Pabst et al, 2002).…”

Best practice recommendations for the use of external telemetry devices on pinnipeds

“…Photo © SM Steingass, 2015, NMFS #16691 transmit many behavioral, physiological and environmental variables and parameters, including dive depth, swim speed, acceleration and orientation, fine-scale movement, flipper stroking, heart rate and venous oxygen partial pressure [76,113,123]. ETDs can provide information on body temperature, heat exchange with surrounding medium, prey capture attempts and ingestion events, and proximity to conspecifics [24,49,51,54,65,70,87,90,124]. More recently, environmental data collected from animal-borne tags have supplemented data collected from other platforms, including vessel-based sampling, moorings, and various types of passive and active autonomous samplers [11,12].…”