Evaluating the constraints governing activity patterns of a coastal marine top predator

Abstract

How animals partition activity throughout the day is influenced by processes that affect supply and obtainability of resources. However, as resource supply and usability are often entrained by the same diurnal pattern, it has been difficult to disentangle their relative importance. Given the strong influence that tide has on the distribution and accessibility of resources, intertidal systems present opportunities to examine questions surrounding the drivers of activity patterns. Here, we used multisensory biologgers to study the activity patterns of a coastal marine predator, sicklefin lemon sharks (Negaprion acutidens), in a tidally driven environment. Hidden Markov models were used to identify relatively high and low locomotory activity states, which were used as proxies for behavioural–activity states and to examine the factors underpinning variation in activity patterns. Although tide governs the spatial distributions of this species and showed some effect on sharks’ activity, diurnal light patterns were the predominant factor influencing behavioural-activity patterns, with the probability of high activity peaking overnight. Temperature and body size also had minor negative influences on the probability of animals being in the high-activity state. Interestingly, sharks were least likely to be in a high-activity state during high tide, a time of presumed high resource supply, contradicting the common assumption that this species forages during high tide. We suggest that despite the importance of the accessibility of resources, functional constraints, such as sensory (e.g., visual) and mechanical (e.g., swimming) performance ultimately underpin the activity patterns of intertidal marine predators through their influence on foraging success.