H漫画

Tragedy struck False Bay this past April when a young champion bodyboarder was attacked and killed by a great white shark in the popular surfing area near Cape Town, South Africa.

David Lilienfeld, 20, was surfing with his younger brother in an area known as 鈥渢he Caves鈥� when the shark was spotted, and was pulled underwater by the five-metre long shark. Onlookers watched as he tried to fend off the attack with his board. Paramedics responded to calls from witnesses, but Mr. Lilienfeld sadly died at the scene. 聽

Within a week, Ocean Tracking Network Executive Director Fred Whoriskey received a request for immediate assistance from Cape Town Waterman Pierre De Villiers. 鈥淚n the light of a very recent a tragic event I have gotten proactive,鈥� wrote Mr. De Villiers. 鈥淭he event mentioned here was the death of Mr. David Lilienfeld鈥� I said to myself, 鈥楾his must never happen again.鈥欌��

The shark alert system used in Cape Town currently depends very little on technology. Spotters with binoculars and radios are posted in elevated areas overlooking the Cape peninsula. When a shark is spotted, they radio partners positioned on the beach who raise a flag or sound a siren depending on the risk to swimmers and surfers in the area.

Tagging and tracking

Mr. De Villiers鈥� proposed approach is as pragmatic as it is proactive: expand OTN鈥檚 tracking system to remotely alert people in real-time to the presence of nearby sharks.

OTN鈥�$168-million mega-research project supported by the Canada Foundation for Innovation, the Natural Sciences and Engineering Research Council of Canada and the Social Sciences and Humanities Research Council of Canada鈥攊s hosted at H漫画, and involves more than 200 international researchers in a global network tracking marine species using acoustic telemetry technology.

These strategically positioned 鈥渓istening lines鈥濃�攆ixed acoustic receivers with overlapping detection ranges laid out on the ocean floor鈥攃apture movements of animals fitted with acoustic tracking tags, from eels and salmon, to cod, seals and sharks. The receivers store data from the tags that researchers use to analyze the movement, migration and survival of marine species.

This past June, OTN assisted in positioning telemetry lines that will document shark and other fishes鈥� behavior in Algoa Bay and Mossel Bay, South Africa. These areas are frequented by both resident and transient great white sharks. OTN and its partners will place another line in False Bay, also known for its big shark sightings.

These South African deployments present an opportunity to implement the shark alert system Mr. De Villiers鈥� imagines, and similar to one currently deployed on the Australian coast.

Down under, Australian scientists and OTN collaborators Rory McAuley and Matias Braccini have sonically tagged a few of their problem sharks. The monitoring system there can detect these sharks within 500 metres of special satellite-linked receivers that alert both scientists and beach authorities simultaneously. The detections provide immediate notice when sharks swim close enough to pose a risk to humans so that lifeguards can clear the water 鈥� important in a country where, according to a study published last year, shark attacks have doubled in the past decade.

The problem is about how best to tag sharks.

鈥淲e clearly want our technology to act in the service of people, however it鈥檚 difficult and dangerous to tag sharks, and there are too many to fit all of them with tags,鈥� says Dr. Whoriskey.

So while tagging and monitoring systems can help alert swimmers to the presence of some sharks, their long-term value will be in helping us better understand sharks鈥� movement patterns, thereby taking pre-emptive measures to minimize interactions between sharks and humans.

Exploring biodiversity

Sharks aren鈥檛 the only species tracked in OTN collaborations. Australia is a hotspot of marine animal migration. The extreme biodiversity off of Australia鈥檚 coasts makes the region the world鈥檚 third largest fishing zone, generating more than $2.5 billion annually. OTN listening lines on the west coast, where ocean currents sweep southward from waters around Indonesia, provide researchers with an eclectic mix of species observations to back sound resource management by policy makers 鈥� including efforts to protect shark populations.

OTN recently partnered with IMOS (Integrated Marine Observing System) to expand Australia鈥檚 role in the global ocean observing network. Collaborators from the University of Tasmania will install a listening line north of Tasmania this fall to complement two existing lines; one off of Perth and another south of Melbourne.

As for South Africa, the False Bay line of 20 acoustic receivers is scheduled for deployment this fall.

鈥淗aving all this instrumentation in the water now provides us with an opportunity to collect very powerful data, which I am sure, with time, will provide insights into the behaviour of great white sharks that can be used to mitigate shark attacks,鈥� said Paul Cowley, principal investigator of the OTN South African lines.