LIVE FISH FROM THE OCEAN FLOOR

An intricate trap that calls to mind the fantastical devices of cartoonist Rube Goldberg has been developed in Moss Landing to do what nobody has done before: bring deep-sea fishes back to the surface alive.

Normally, as fish are hauled up from the deep ocean the air in their swim bladder expands because of the lower pressure at the surface. Their organs are crushed, their eyes bulge, and the fish are dead on arrival.

Biologists Jeff Drazen and Jim Barry and engineer Larry Bird at the Monterey Bay Aquarium Research Institute have built a pressurized trap for deep-sea fish, whose behavior is not well-known even as the fishing industry heads to deeper waters.

Their main target is the rattail, also known as grenadier, one of the most common fish in the deep sea. The 2-foot-long fish has a head like a cod and a long, tapering tail. Scientists have studied dead specimens and watched videos from the deep ocean, but they've never been able to experiment on a live animal.

In the 1980s two researchers in Southern California built a trap to bring fish up at pressure but the longest one survived was two days. The instrument was eventually lost at sea and the researchers moved on to other projects.

Drazen arrived at MBARI as a post-doctoral researcher determined to try again.

"I was studying dead things," Drazen said of his research experience. "You can only learn so much from studying dead animals."

Marine engineer Larry Bird worked closely with the biologists in designing and building the trap. The first challenge was the immense pressure it had to contain -- up to 6,000 pounds per square inch. Factoring in a three-to-one safety margin, Bird said, the trap was built to withstand 18,000 pounds per square inch of internal pressure, or 1.5 million pounds of force on the trap door.

The MBARI group's 4-foot, stainless-steel trap, built to catch a single fish at a time, weighs three-quarters of a ton. It's attached to buoys affixed to a large scaffold to offset its weight.

Avoiding enclosed spaces|

Apart from high pressure, Bird said, the main design challenge was the fishes' behavior.

"Unlike reef-dwelling fishes that would typically seek shelter, these fishes actually avoid enclosed spaces," he said. "So it becomes necessary to catch the fish outside the trap and pull it in."

The mechanism is familiar: A baited hook is attached to the end of a line. However, the trap is set on the ocean floor outside the control of researchers who are at the surface, 2 miles up.

When a fish goes for the bait it will struggle and tug on the line, setting off a series of events. It first trips a spring-loaded reel that hauls the fish into the trap. A secondary trigger then releases two large springs that shut the door. A sharp blade clamps on the line, cutting the fish free once inside the trap.

In an increasingly high-tech world, Bird calls the trap a "dumb mechanism" since it uses no electronics. The energy is stored entirely in springs.

His collaborators have praise for the device.

"This isn't a straightforward design," Barry said. "There are little intricacies of the trap and little details that require quite a lot of creative thought."

Before a recent deployment, Bird and Drazen were checking pressure seals in the MBARI workshop and carrying the floats on a small forklift down to the dock.

Bird was worried about some modifications: A spring tension he'd changed to pull the fish in more gently, and a new snipping device to cut the line and reduce stress on the animal. Each additional improvement to the trap, he explained, is a trade-off, another possible point of failure.

Three hours to ocean floor|

Out on the water, the researchers lower the trap into the water and it sinks, taking about three hours to reach the ocean floor. When the ship returns the next day the scientists press an underwater buzzer that triggers an acoustic sensor and releases the anchor. The trap floats slowly back up to the surface.

Only then do the researchers find out whether they've been successful in catching a fish. December's trip was a disappointment--a spring they'd replaced was a few thousandths of an inch too large, jamming the reel and sending the team back to the workshop. Of seven deployments over the last year, three have brought up a live fish, and a five-day series of experiments yielded the most information gathered on the deep-sea animal.

When he catches a live fish, Drazen experiments by changing the pressure and gas concentrations inside the trap, using electronic sensors and a video camera to monitor the effect and study the fish's tolerance.

Ultimately, Drazen hopes he may be able to decompress fish so they can survive outside the trap, in an aquarium or research lab. If the pressure is reduced very slowly, he believes, the fish could absorb gas from their swim bladders into their bloodstream, the same way that a scuba diver can adapt to changing pressures if it's done slowly enough.

"If it works, it may allow us to exhibit some fishes that nobody has ever seen before," said Randy Kochevar, a spokesman for the Monterey Bay Aquarium, which donated ship time to the project. "That's a very exciting prospect."

Kochevar cautioned that even if the procedure works, it would take years to put together a display for deep-sea fishes.

The research is partly funded by the Department of Energy, which wants to learn how deep-sea animals respond to changes in carbon dioxide levels to determine the effect of storing carbon dioxide in the deep ocean.

Meanwhile, Drazen will bring the trap to his new job at the University of Hawaii, where he will continue his experiments.