A Day in the Life

Numerous studies have attempted to observe and understand a range of behavior in sharks; however there remain many unanswered questions. Sharks are notoriously difficult to observe and the costs associated with satellite tracking have led to a relative dependence on acoustic telemetric tools to achieve research goals. This provides data on spatio-temporal elements well but defines actual behavior poorly i.e. we know where an animal is and at what time but not what it is doing. Accelerometer technology combined with traditional acoustic telemetry allows for a more precise study of natural behavior than has previously been attainable. This project aims to identify and delineate a range of fine-scale behaviors of Bimini lemon sharks in space and time, thus producing ‘a day in the life of a shark’.

1. How do juvenile and sub-adult lemon sharks behave on a day to day basis? What patterns in activity do they display and what factors drive these observed patterns i.e abiotic and biotic factors ?

2. What predatory tactics do lemon sharks employ? How often do they hunt and how successful are they?

3. How important is predator avoidance in the decision making process of young lemon sharks? How often do individuals attempt to avoid predators?

Sharks occupy important roles in marine food webs and are fundamental in maintaining stability and productivity within marine ecosystems. In many instances, however, we still know little about the natural behavior of sharks and consequently have a limited understanding of their impacts on ecosystem dynamics. This is largely due to the elusive and cryptic nature of sharks and the inherent difficulties of studying large predators at liberty without impeding on what would be considered ‘natural behavior’. The use of varying remote and direct observational methods is critical in providing accurate behavioral and life history data, necessary to inform management policy. This study will shed light on the otherwise secretive lives of these key predators through attachment of small acceleration data loggers. These data loggers will log fine-scale movements and thus behaviour of the tagged animal. The study will help to define the roles that sharks play in coastal ecosystems, highlighting factors intrinsic to their fitness and provide a model for similar future studies focusing on species of critical conservation concern.
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 (Figure 1).
 
 
 
Deployment of accelerometers on wild sharks
Juvenile lemon sharks (100-120cm total length, n = 4) 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 (Research Techniques - Biotelemetry) 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 the summer season and the station is half way through the winter season for this species.  A number of individuals have been tagged during both seasons to see how behavior changes with water temperature.
 
Results show distinct patterns in resting and active swimming behaviors. Tested sharks rested for periods of several hours in sheltered areas over the high tides. During periods of swimming sharks have been found to occupy open lagoon areas and exhibit prolonged burst swimming events, hypothesized to be predatory behavior.
Principal Investigator
Rob Bullock - University of Hull, UK
 
Collaborators
Prof. Mike Elliott - University of Hull, UK
Prof. Ian Cowx - University of Hull, UK
Dr. Samuel Gruber - University of Miami, US
Dr. Tristan Guttridge - Cardiff University, UK
Dr. Adrian Gleiss - Stanford University, US
Dr. Nick Whitney - Mote Marine Labaratory, US
PhD Candidate Mark Bond - Stony Brook University, US
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