Do boating and basking mix? The effect of basking disturbances by motorboats on the body temperature and energy budget of the northern map turtle

Abstract

Abstract Basking is the primary mechanism used by many freshwater turtles to maintain their body temperature (Tb) in a range that maximizes physiological performance. Basking turtles are easily disturbed by motorboats, but the consequences of the increasingly popular use of motorboats on turtles is largely unknown. In this work, predictive models built from field and laboratory data were used to assess the effects of the frequency of basking disturbance by motorboats on Tb and metabolic rate (MR) of female northern map turtles (Graptemys geographica), a species of conservation concern. Simulations revealed that the effects of boat disturbance vary seasonally. In early May, a conservative estimate of the disturbance rate (0.15 per hour) resulted in a 0.34°C decrease in mean daily Tb, which translated to a 7.8% reduction in mean MR. In June, July and August, owing to warmer lake temperatures, the effect of disturbance was less marked and the observed disturbance rates (0.32, 0.96 and 1.23 per hour, respectively) reduced the mean MR of an adult female by 2.1%, 0.5%, and 0.4 %, respectively. Reduction in MR decreases the rate of energy assimilation, which could translate into sublethal effects on turtles, such as reduced growth and reproductive output. Motorboat usage is increasing in many areas and is probably affecting other species of freshwater turtles that use aerial basking. This study offers important insights on the implications of disturbances for species that bask. Copyright © 2016 John Wiley & Sons, Ltd.