Understanding how active animals are under different conditions can provide a wide range of important insights into their general ecology, and their physiological sensitivity to environmental variation. A key implication of an animal being more active is that its energy expenditure will tend to increase, so wild animals need to carefully partition activity into those periods that will maximise their foraging or reproductive success.
We use a variety of different methods to measure activity levels and rates of energy expenditure of marine animals in the wild, to explore the different challenges posed by variability in their environment – including changes caused by human disturbance.
Activity levels of wild fish
We use several approaches to measuring activity levels of marine animals in their natural environment. One of our preferred methods is to attach accelerometer devices to free-ranging animals and record ‘overall dynamic body acceleration’ – a proxy of mechanical work. We have deployed these devices on species ranging from hammerhead sharks and tiger sharks to sand whiting and mulloway, and measured how body acceleration varies with temperature, time of day, and with disturbance from humans (e.g. presence/absence of divers or boating activity).
Rates of energy expenditure
Estimating rates of energy expenditure in wild animals in notoriously difficult, but recent technological and logistical developments are providing the tools necessary to gain insights into the energetics of animals in their natural environment. For example, swim speed and dynamic body acceleration are useful proxies of energy expenditure, and if carefully calibrated in a laboratory or by hydrodynamic modelling, data from speed and accelerometer loggers can be used to estimates rates of energy expenditure in wild animals. We have used this approach to estimate how much additional energy sharks use on days that ecotourism operators are present compared to days when they are absent, and to estimate that great hammerhead sharks cut transport costs by ~10% if they roll onto their side instead of swimming in the traditional upright form.
Measuring rates of energy expenditure in aquatic animals is normally only possible for small (<10kg) specimens, but we recently designed and built a huge, submersible swim-tunnel respirometer that can measure the swimming metabolic rates of fish and sharks up to several hundred kg. We think this will be a valuable new tool for understanding how large fish (including sharks) manage their energy budgets, as we know very little about energy use in large-bodied marine animals in general.
Payne, N. L., Iosilevskii, G., Barnett, A., Fischer, C., Graham, R. T., Gleiss, A. C., & Watanabe, Y. Y. (2016). Great hammerhead sharks swim on their side to reduce transport costs. Nature communications, 7, 12289.
Barnett, A., Payne, N. L., Semmens, J. M., & Fitzpatrick, R. (2016). Ecotourism increases the field metabolic rate of whitetip reef sharks. Biological Conservation, 199, 132-136.
Payne, N. L., Smith, J. A., Van der Meulen, D. E., Taylor, M. D., Watanabe, Y. Y., Takahashi, A., . . . Suthers, I. M. (2016). Temperature dependence of fish performance in the wild: links with species biogeography and physiological thermal tolerance. Functional Ecology, 30(6), 903-912.
Brodie, S., Taylor, M. D., Smith, J. A., Suthers, I. M., Gray, C. A., & Payne, N. L. (2016). Improving consumption rate estimates by incorporating wild activity into a bioenergetics model. Ecology and evolution.
Payne, N. L., Van der Meulen, D. E., Suthers, I. M., Gray, C. A., & Taylor, M. D. (2015). Foraging intensity of wild mulloway Argyrosomus japonicus decreases with increasing anthropogenic disturbance. Marine Biology, 162(3), 539-546.
Payne, N. L., Snelling, E. P., Fitzpatrick, R., Seymour, J., Courtney, R., Barnett, A., . . . Semmens, J. M. (2015). A new method for resolving uncertainty of energy requirements in large water-breathers: the ‘mega-flume’ seagoing swim-tunnel respirometer. Methods in Ecology and Evolution, 6(6), 668-677.
Fitzpatrick, R., Abrantes, K. G., Seymour, J., & Barnett, A. (2011). Variation in depth of whitetip reef sharks: does provisioning ecotourism change their behaviour? Coral Reefs, 30(3), 569-577.