Their prototype appropriately named Shadow III (and painted a bright yellow that belies its sleuthy assignment) includes a video camera and hydrophones to track its prey.

Undergrads at Colorado School of Mines are developing the hydrophones that will create biaural hearing. This will let researchers determine the direction from which a sound originates.

Shadow III completed 10 dives in Prince William Sound, with a communications cable linking it to a mother boat on the surface. UA Professor Emeritus Tom Vincent anticipates it will be ready to track octopi next year.

Before then, this year's student design team will build a wireless communications system to free Shadow from a 100-ft-long coaxial cable to the mother boat. The team also will modify Shadow's buoyancy system. Water flows into a ballast ring that circles the center of the sub. Compressed air tanks on the sides of the sub blow this water out to bring Shadow to the surface.

"Right now the buoyancy system is under manual control, but we hope to have it under automatic control next time," Vincent said. "We'll just type in the depth we want on the computer and Shadow will automatically submerge to that depth."

In autonomous mode, the submarine would operate on its own, following an octopus using its hydrophone sensors. It would decide when to turn on its video camera, transmitting video to a remote receiver. This would require the submarine to know something about the topography of the ocean bottom in its area so it wouldn't run into a big rock or other obstacle while following the octopus.

The advantage of fully autonomous tracking is that octopi spend a lot of time in their dens vegging out, which is pretty boring for researchers. Instead of waiting for hours on the surface, biologists could set up the robot to wait quietly for an octopus to emerge.