abstract
Marine mammals have many thermoregulatory mechanisms that allow them to live in very cold habitats. Thermal imaging has been previously reported as a useful tool in Veterinary Medicine and will be helpful in studying thermoregulatory mechanisms in marine mammals. This method, which is based on recording thermal radiations emitted by the body to identify and quantify superficial temperature, allows the diagnosis of diverse pathologies, as well as certain physiological processes which are undetected by the naked eye, such as thermoregulatory changes.
In this study, thermal patterns from the skin of walruses have been analyzed in order to understand the physiological processes leading to thermoregulation. Thermal images were taken from four female and one male walrus at L'Oceanogràfic (Valencia, Spain). All five animals are between four and five years of age. Thermographs were obtained using an I75 model FLIR Systems thermocamera during several sessions. The analysis of the thermal images obtained and treated by ThermoCAM QuickReport 1.0 software, show the areas of skin with higher registered temperatures.
Comparing the images in all five animals, it seems that these spots tend to appear in areas of the body which are not in contact with the ground, and mainly on the back and chest. These areas appear both in male and females, without a defined pattern of size, form and location among individuals. With time, these areas are modified for each individual. In spite of the remarkable difference of temperature between heated and non heated areas, this kind of pattern is considered completely physiological and should not be mistaken with areas of inflammation or trauma.
These results observed in walrus might correspond with the "thermal windows", described by Mauck et al.1 in harp seals (Phoca groenlandica), harbour seals (Phoca vitulina vitulina) and grey seals (Halichoerus grypus). Many investigators have been interested in understanding how walrus thermoregulatory mechanisms work, since there are evident changes mainly in the color of the skin depending on the environmental temperature.2 Thermal images suggest that these animals have developed mechanisms, if not equal to, than similar to the "thermal windows" described in seals1, probably related with changes in the blood flow limited to certain body areas, as a mechanism for heat dissipation by irradiation or evaporation of the water contained in the walrus skin.
acknowledgements
This work was supported by a grant from The Universidad Complutense de Madrid. The authors wish to thank L'Oceanogràfic staff for their assistance.
References
1. Mauck B, Bilgmann K, Jones DD, Eysel U, Dehnhardt G. 2003. Thermal windows on the trunk of hauled-out seals: hot spots for thermoregulatory evaporation? J of Experimental Biology 206:1727-1738.
2. Turco K. 1987. Why does a Walrus Blush? http://www.gi.alaska.edu/ScienceForum/ASF8/830.html.