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

P>The temperature differential (delta T) 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 degrees to 33 degrees C, delta T 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) (r2 = 0.978, P < 0.001). On average, T(dfin) was 0.9 degrees C warmer than T(w) across seasons, despite the 22 degrees C annual range in T(w). Changes in integumentary and vascular insulation likely account for the stability of delta T(dfin - w) and the protection of core temperature (T(core)) across seasons. The high thermal conductivity of water may also influence this delta T. The use of infrared thermography is an effective, non-invasive method of assessing dorsal fin skin surface temperatures (+/- 1 degrees C) across large numbers of wild, free-swimming dolphins throughout their thermally dynamic aquatic environment.