“Never turn your back on a shark” is the
take home message from an article published in Springer’s journal Animal
Cognition. Erich Ritter of the Shark Research Institute and Raid Amin of the
University of West Florida in the US contend that sharks can comprehend body
orientation and therefore know whether humans are facing them or not. This
ability helps sharks to approach and possibly attack their prey from the blind
side – a technique they prefer.
To hunt successfully a predator needs to
correctly perceive the body form, size and movement of its potential prey.
Studies confirm this is also true when sharks hunt. Descriptions of a shark’s
approach to typical prey, as well as humans, indicate that these predatory fish
prefer to avoid the field of vision. In other words, a shark would tend to
approach a person from behind. These observations underlie the yet-untested
assumption that sharks are able to identify human body orientation and can use
such information in a self-serving manner.
Shark preferences studied
Ritter and Amin therefore set about to
deepen the understanding of how sharks select an approach pattern when
interacting with humans. A test was designed to evaluate if sharks show a
measurable preference based on body orientation when approaching a person, and
if they choose a certain swim pattern when close to a human being. In one
experiment, a diver in full scuba gear was positioned on the sea floor in a
kneeling position, looking forward. In another, two divers kneeled back-to-back
to eliminate the blind area.
To ensure the safety of the test subjects,
the preferences of the Caribbean reef shark (Carcharhinus perezi) were tested.
The animal is a typical type of reef shark frequently encountered by divers in
the Bahamas, and is not considered to be a dangerous species regarding
incidents with humans.
They found that when approaching a single
test-subject, significantly more sharks preferred to swim outside the person's
field of vision. The results suggest that sharks can identify human body
orientation, but the mechanisms used and factors affecting the nearest distance
of approach remain unclear.
“Our discovery that a shark can
differentiate between the field of vision and non-field of vision of a human
being, or comprehend human body orientation, raises intriguing questions not
only about shark behaviour, but also about the mental capacity of sharks,”
“The more research is conducted on how
sharks sense and interpret humans, the better we will understand how to cope
with them in their habitat,” adds Amin.