MIGRATING marine mammals and large fish will soon have a new companion on
their travels鈥攁 robotic kayak.
Cliff Goudey and colleagues at MIT鈥檚 centre for fisheries engineering
research want to use the kayak to help unravel the mysteries of fish migration
and improve estimates of fish populations. For years many researchers have been
attaching acoustic 鈥減ingers鈥� to large fish and marine mammals in order to track
them. Boatloads of researchers are usually given the job of following the quarry
but this is expensive, costly and often boring. Goudey says a small, autonomous
robotic boat could do the same job much more cheaply.
Goudey鈥檚 students have already tested a model kayak in the Charles River
basin beside the MIT campus. In a few weeks鈥� time the same kayak will be
tracking blue sharks in Massachusetts Bay.
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Goudey chose kayaks because they are light, cheap and can bear a heavy load
for their size. To make the robot, the team fitted an ordinary 3-metre-long
kayak with a keel, rudder and a small propeller with blades 35 centimetres long
driven by a motor inside the boat.
A pinger is still attached to fish, and this is monitored by an acoustic
sensor on the bottom of the vessel. The sensor relays depth and directional data
to an onboard computer, which is attached to a Global Positioning System
receiver. 鈥淯sing this information, the computer can send controls to the rudder,
turn the kayak, and head toward the source of the sound,鈥� says Goudey, 鈥淭he same
way a person listening with earphones [on a boat] would do it.鈥�
The model kayak can travel at a speed of 3 knots for up to 24 hours at a
time. Although fish can swim faster than this in short bursts, their average
speed should be slow enough for the robotic kayak to keep pace with them.
The next version of the kayak will be swifter and longer-running, designed to
track fast-swimming bluefin tuna.
杏吧原创s on fishing boats are exhausted after following tuna for 48 to 60
hours, says Molly Lutcavage of the New England Aquarium in Boston, who tracked
five tuna that way last summer. A robotic boat wouldn鈥檛 get tired, and with
larger or rechargeable batteries could stay at sea far longer, collecting data
essential to resolving disputes over tuna populations. Once the kayak has
collected data or is close to running out of fuel, it will return to its home
port.
Because refitting a kayak is relatively cheap鈥攃osting only a few
thousand dollars at most鈥攏o great sum is at risk if it never returns. 鈥淵ou
don鈥檛 want to be losing $100 000 worth of equipment because your boat
doesn鈥檛 come home,鈥� says Goudey.