Using infrared thermography to assess seasonal trends in dorsal fin surface temperatures of free-swimming bottlenose dolphins (Tursiops truncatus) in Sarasota Bay, Florida

The temperature differential (ΔT) between a body surface and the environment influences an organism's heat balance. In Sarasota Bay, FL, where ambient water temperature (T w ) ranges annually from 11° to 33°C, ΔT was investigated in a resident community of bottlenose dolphins (Tursiops truncatus). Dorsal fin surface temperatures (T dfin ) were measured on wild, free-swimming dolphins using infrared thermography. Field and laboratory calibration studies were also undertaken to assess the efficacy of this non-invasive technology in the marine environment. The portability of infrared thermography permitted measurements of T dfin across the entire range of environmental temperatures experienced by animals in this region. Results indicated a positive, linear relationship between T dfin and T w (r 2 = 0.978, P < 0.001). On average, T dfin was 0.9°C warmer than T w across seasons, despite the 22°C annual range in T w . Changes in integumentary and vascular insulation likely account for the stability of ΔT dfin-w and the protection of core temperature (T core ) across seasons. The high thermal conductivity of water may also influence this ΔT. The use of infrared thermography is an effective, non-invasive method of assessing dorsal fin skin surface temperatures (±1°C) across large numbers of wild, free-swimming dolphins throughout their thermally dynamic aquatic environment.