Abstract
Temperature affects most physiological processes which in turn impact animal behaviour and ecology. In ectotherms, both short- and long-term variations in temperature impact physiological (i.e. locomotor and metabolic capacity) and ecological (i.e. body condition and growth) performance and thus affect survival. It is therefore critical to understand the mechanisms driving these relationships. Here, we investigated the impact of seasonally changing temperature on the ecological and physiological performance of juvenile free-ranging largetooth sawfish (Pristis pristis) in its riverine nursery in North Western Australia. Animal-attached accelerometers, revealed that despite a 10°C increase in temperature, sawfish were active and displayed substantial burst-swimming capacity. Physiological performance, as ascertained by locomotory capacity, increased in the warmer late dry season conditions, whereas timing and duration of activity did not. Contrary to the physiological performance, late season sawfish were poorer condition that those in the early season. Activity was primarily crepuscular, irrespective of the season. This suggests that even though locomotory performance of juvenile sawfish increased at greater temperature, foraging activity and thus energy intake was not sufficient to maintain body condition, resulting in declining growth. Contrary to popular belief, seeking warmer temperatures can represent a disadvantage for juveniles under certain scenarios. Especially for individuals that are intake limited, greater temperatures and associated metabolic rates are disadvantageous and can result in lower growth rates and potentially starvation. Physiological and ecological performances may thus respond differently to warming temperatures, emphasizing that ‘optimal’ temperatures may be highly context dependent. Ecological scenarios responsible for mediating growth performance are discussed and integrated into a classic bio-energetics framework.