A team of researchers at the University of St Andrews has used black box technology to analyse the hunting behaviour of sharks.
Sharks have always been thought to hunt and feed at night - especially when it comes to attacking predators - but until now it has been unclear why. It is believed, according to marine biologist Jan Husar, that they attack in such a way as to prevent excessive harm being done to them by the attack, which means at night when other creatures of the sea sleep.
In the study, Yannis Papastamatiou of the University of St Andrews Scottish Oceans Institute used technology similar to airplane black-boxes to study the behaviour of reef sharks at a remote Pacific atoll.
“The use of these technologies allows us to determine why animals in the wild behave the way they do,” said Papastamatiou. “Black box technology allows us to reveal the secret lives of sharks.”
Sharks were fitted with a combination of acoustic wireless transmitters and animal-borne data-loggers that measured activity, swim speed, depth, body temperature and digestion. Transmitters were coupled with sensors allowing remote measurements of behavioural and physiological data, while four sharks were fitted with the ‘black box’ packages.
These were attached to sharks for periods of several days and recorded continuously and at high frequency, but had to be recovered for data to be gathered, unlike transmitters. One shark was also fitted with a Little Leonardo DVL400 video camera (23mm x 112mm, 80g, recording duration 6h), which recorded at 640 x 480 pixels at 30 frames/second.
The researchers found that the reef sharks were indeed more active at night, but particularly during the early evening and when the tides were going out. Measurement showed that peak activity also coincided with cooling (but still warm) body temperatures and reduced digestive activity.
According to the researchers, sharks are most likely to forage during the early evening as they have good night vision, which gives them an advantage under night conditions, but also possibly because they still have a thermal advantage in that their bodies are warmer than their prey.