Determining the energetic costs of distinct behaviours is important for understanding the behavioral ecology of animals in their natural habitat and therefore aiding their conservation. The choices animals make in allotting energy to different life functions are fundamental to their success. This study utilises CEFAS G6a accelerometers (CEFAS) to determine metabolic rates through the theory of “Overall Dynamic Body Acceleration” (ODBA) whereby energy is required for muscles to contract, in turn creating body movement i.e. limb acceleration. These accelerometers record up to 30 acceleration data points per second in each of the three planes to give a thorough overview of body movement as well as providing a temperature and pressure reading every second. This study is being conducted in collaboration with Mote Marine Laboratory (MML) on three species with differing lifestyle strategies: sedentary nurse sharks (Ginglymostoma cirratum), intermediate lemon sharks (Negaprion brevirostris) and active blacktip sharks (Carcharhinus limbatus).
1. What is the relationship between ODBA and oxygen consumption (VO2, a direct measure of metabolic rate), for aerobic and anaerobic metabolism in the model species N. brevirostris and G. cirratum?
2. How does ambient water temperature affect metabolic rate in these species (i.e. determination of the Q10 value)?
3. What is the Field Metabolic Rate (FMR) for each of the model species?
Bioenergetics modeling for fish has had a lively history and has played an important role in addressing research and management questions relating to stocks, populations, food webs, and ecosystems. Understanding bioenergetics of elasmobranchs is fundamental to the facilitation of sustainable fisheries management. Due to their life history traits these ‘k’ strategist species are vulnerable to overexploitation and their diminution can cause complex trophic food web alterations. Understanding the energetic requirements of a species can aid in determining their minimum food requirement and the extent to which they influence their ecosystem structure. Apex predators, both terrestrial and aquatic, mediate their prey abundance and distribution through direct predation and risk effects. However few studies have determined the FMR of top marine predators and consequently there is a broad gap in knowledge of ecological energetics.
Categorising behaviors through captive studies
Accelerometer-equipped lemon sharks were monitored in semi-enclosed pens in order to develop a catalogue of discrete behaviors (Research Techniques - Captive Experiments). Sharks were observed for 6hr periods during which resting, steady swimming, burst swim and chafing behaviors were recorded. Following removal of the device, data was downloaded and analysed alongside the visual recordings to characterize the signal output for the behaviors observed.
Deployment of accelerometers on wild sharks
Juvenile lemon sharks (max size 90cm total length, n = 10) were captured in a known aggregation site (Aya’s Spot). Accelerometer tags (with tracking device) were attached and sharks monitored at liberty. During this time individuals were tracked through static acoustic receivers and observed from towers enabling us to calibrate actual behaviors with those recorded on the tags. After 5 days sharks were located using active tracking (Research Techniques - Biotelemetry) and captured with seine and gill nets to retrieve the accelerometer for data download (Research Techniques - Capture Methods). Successful deployments have been completed for both the summer season and the winter season for lemon sharks with the main focus currently being on juvenile nurse sharks. Some individuals have also been tagged during both seasons to see how behavior changes with water temperature.
Nurse shark ‘wrangling’
In preparation for the nurse shark deployments and due to the limited knowledge of their resting sites, we have invested time over the past year in PIT tagging and color coding individuals of the appropriate size range (<90cm TL). By conducting snorkel checks along the mangroves and around shallow ledges to identify individuals and their locations we hope to increase the chances of tag retrieval.
Lauran Brewster - University of Hull, UK
Prof. Mike Elliott - University of Hull, UK
Prof. Ian Cowx - University of Hull, UK
Dr. Samuel Gruber University of Miami, US
Dr. Tristan Guttridge - University of Miami, US
Dr. Adrian Gleiss - Swansea University, UK
Dr. Nick Whitney - Mote Marine Laboratory, US
Gleiss AC, Gruber SH, Wilson RP. 2009. Multi-Channel Data-Logging: Towards Determination of Behaviour and Metabolic Rate in Free-Swimming Sharks. In: Nielsen JL, Arrizabalaga H, Fragoso N, Hobday A, Lutcavage L, Sibert J eds. Tagging and Tracking of Marine Animals with Electronic Devices. 9:211-228.
Gleiss, A.C., Wilson, R.P., and Shepard, E.L.C. 2010. Making overall dynamic body acceleration work: on the theory of acceleration as a proxy for energy expenditure. Methods in Ecology and Evolution. 2(1): 23-33. DOI: 10.1111/j.2041-210X.2010.00057.x
Whitney, M.N., Papastamatiou, Y., Holland, K.N., and Lowe, C. 2007. Use of an acceleration data logger to measure diel activity patterns in captive whitetip reef sharks, Triaenodon obesus. Aquatic Living Resources 20(4): 299-305.
Whitney, N.M., Pratt Jr, H.L., Pratt, T.C., and Carrier, J.C. 2010. Identifying shark mating behaviour using three-dimensional acceleration loggers. Endangered Species Research 10:71-82. Doi: 10.3354/esr00247