What sharks do all day long?
What do sharks do when we’re not looking?
To answer this question, Murdoch University fish biologist Lauran Brewster attached accelerometers to the fins of 24 lemon sharks in the Bimini Islands, Bahamas to find out.
Similar to our wearable Fitbits, the accelerometer collects data about the sharks’ movements, which are then analysed using a statistical approach called machine learning. “Very basically, machine learning is a model that learns patterns in data and can be used to identify similar patterns in new data and make predictions from it,” said Brewster.
Of the 24 lemon sharks tagged, 20 were recaptured and the data from their accelerometers analysed.
“The model identified five different behaviours for lemon sharks, like swimming and resting. Also, successful prey capture (represented by the shark shaking its head from side to side), burst swimming and chafing behaviours, where the shark performs a barrel roll movement to scratch its back,” she added.
The results showed that the sharks did not spend much time at rest; during the warmer months, they spent one percent of their day resting, while during the colder months, the amount of time rose to just 10 percent.
In addition, they preferred to catch prey in the early evenings, and preferred not to eat during high tide. They also tended to eat more when the water is warm.
Such information will increase our understanding about the species and how human activity is affecting their behaviour. Brewster now intends to study the sharks’ behaviour in areas affected by human development.
“We have been able to determine the fine-scale activity budget of a wild shark species here in pristine conditions. We can compare it with the activity of other lemon sharks inhabiting waters degraded by human development as a means to assess the risks associated with coastal development and establish how to manage the impact development has on coastal species,” she said.