Meeting Abstract

48.6  Saturday, Jan. 5  Thermal tolerances in bottlenose dolphins YEATES, Laura C*; HOUSER, Dorian S; US Navy Marine Mammal Program; US Navy Marine Mammal Program yeatesl@spawar.navy.mil

Bottlenose dolphins are found worldwide in temperate and tropical waters but are generally absent from 45 degrees pole-ward in either hemisphere. Limitations to the distribution of bottlenose dolphins have been hypothesized to be due to thermal tolerances and/or prey distributions. Air temperature as a limiting factor is particularly intriguing since dolphins lack nasal turbinates for warming inspired air. To evaluate whether air/water temperatures potentially limit bottlenose dolphin distributions, we determined lower critical temperatures (LCT) to water and air in four adult male bottlenose dolphins acclimated to the temperatures of San Diego Bay, California. Subjects ranged in mass from 170 to 220 kg and were tested at different times of the year to account for seasonal variations in blubber depth. Dolphins rested in water temperatures ranging from 2 to 17 °C and air temperatures as low as -2 °C during metabolic rate measurements. The LCT of water ranged from 4.9 to 8.1 °C and depended on dolphin mass and blubber depth. No definitive LCT for air was found in animals resting in thermoneutral water temperatures but variability in resting metabolic rate increased with declining air temperature. Intramuscular, subcutaneous and rectal temperatures measured during the trials indicated regional heterothermy and a temperature gradient between the skin surface and core. The LCT for water measured in all body conditions is below water temperatures that occur outside the coastal range of the bottlenose dolphin. The results suggest that factors besides water temperature are important in determining dolphin distributions.