Shadowing fishermen's nets with a robot sub
New research sheds light on life at 90 fathoms
On a cold, clear day in November, the Donna Kathleen rode a gelid swell off the central California coast. On the aft deck of the 58-foot vessel, a small knot of people in hard hats ministered to what looked like a glorified toboggan with a couple of thrusters bolted on.
The fridge-sized, black-and-seafoam-green machine, dubbed the Beagle, was a remotely operated vehicle, or ROV — essentially, a boxy, unmanned robot submarine. As a veteran ROV designer named Dirk Rosen fiddled with one of the video cameras mounted on it, he waxed decidedly un-lyrical about the machine’s inherent hydrodynamic flair.
“It’s a total brick," said Rosen. "It’s basically a pickup truck carrying a whole bunch of sensors.”
As Rosen paid out a thick umbilical cord attached to the Beagle, a crane lifted the machine over the deck railing and gently set it into the water, where it bobbed on the swell. Then the ROV burst to life. Like a dog sniffing out a scent, the Beagle zipped 20 feet through the water and then burbled into the dark depths below.
Rosen turned and ducked through a hatchway into the Box, a darkened, van-sized container lashed to the deck of the boat. Inside, James Lindholm, a professor from California State University Monterey Bay, sat crammed into a seat with what looked like a video-game controller in his hand. A miniature disco ball dangled over his left shoulder, and as his iPod shuffled through its play list, the groove of the Bee Gees’ “Night Fever” suddenly began bumping over the soft hum of electronics cooling fans.
Lindholm’s eyes were riveted on a bank of video monitors displaying a feed from the Beagle. Five hundred feet below, at the edge of the Continental Shelf, the ROV whirred along the path that a 240-foot-wide fishing net had left as it dragged along the sandy seafloor — an obvious furrow carved by the half-ton steel “doors” that had kept the net pressed to the bottom. As Lindholm “flew” the Beagle, Mary Gleason, a biologist from the Nature Conservancy perched on a seat next to him, clicking a joystick and taking one photo of the bottom after another.
Everything about the effort had been painstakingly choreographed, right down to the path of the drag net they were following. A week earlier, a trawler called the South Bay had intentionally towed its net through this experimental plot and three others, as part of a carefully constructed experiment to investigate the effects of trawling on the habitat of bottom-dwelling species such as soles and eel pouts.
Bottom trawling is notorious as the most destructive form of fishing; some fisheries scientists have likened trawling coral reefs to clear-cutting the rainforest. Yet while the impacts of trawlers on reefs has been exhaustively studied, scientists have only a sketchy understanding of what trawling does to other types of habitats, and how — or whether — those areas recover after they’ve been “dragged.”
“There’s just a handful of people doing trawl-related research worldwide,” says Lindholm, “and outside of really charismatic habitats, we don’t know very much.” Lindholm has eschewed Cousteauvian coral wonderlands to focus on “soft-sediment environments”: seemingly featureless, current-swept expanses that, he concedes, “are not exactly like what you see in National Geographic.”
Technically, soft-sediment environments are composed primarily of sand, although Lindholm tends to just call it mud. Whatever you call them, however, they are a very important chunk of the planet. They make up about 70 percent of the continental shelf off California and are the most abundant habitat on earth. “Even if we think mud’s not that exciting, said Lindholm, “we can’t ignore it.”
Still, the work is hardly the kind of thing that makes fifth-graders thrill with dreams of a degree in marine biology. “We’re down there just plowing through transects for eight hours straight,” Lindholm said. “That is a long time to be slowly moving over the mud.”
Up at the helm of the Donna Kathleen, Tim Maricich babied the throttles. His boat was a shrimper that has been repurposed as a research vessel, and Maricich conceded that he was still getting used to the new kind of work. “We’re working in friggin’ meters,” he groused. “My whole life has been feet and fathoms, and now everything’s in meters.”
Two years ago, The Nature Conservancy cut a deal to buy out the trawl permits for the struggling fleet of boats based in the Central Coast port town of Morro Bay. Working with the Pacific Fishery Management Council, the conservancy established 3.8 million acres of “essential fish habitat” — essentially a giant no-trawl zone.
A handful of Morro Bay boats are now back on the water, fishing not with trawl nets but more discriminating gear like longlines and traps. But with the end of dragging in the area, Lindholm and Gleason also realized that they had a ready-made, real-world laboratory for a controlled study of trawling. They teamed up with Rosen — who, after a career as an ROV engineer, now runs a nonprofit called Marine Applied Research and Exploration — and bought the Beagle with funding from the California Ocean Protection Council.
Last November, the South Bay dragged the experimental plots for the first time, and the Donna Kathleen followed two weeks later with the ROV. Earlier this year, the researchers returned for a six-month checkup, and they’ll return once more this fall. Then they’ll drag the plots again, more intensively, and repeat the process for the next three years.
For some time already, scientists have been investigating the effects of overfishing and accidental “bycatch” on specific species. Now they’re widening their field of view: “Understanding the ecological effects is the newer level of inquiry,” said Lindholm.
He and Gleason and several other researchers will use the video and still images gathered by the ROV to monitor the rate at which the seafloor recovers after being dragged. They hope to gain a better understanding of the post-disturbance population dynamics of the fish and invertebrates here.
That kind of research has been made possible only as ROVs have opened wide new windows on the denizens of the deep. Earlier efforts to understand population dynamics relied on relatively crude efforts like sampling species abundance with trawl nets. But as Lindholm said — using an analogy originally made by marine researcher Elliott Norse — that’s like sampling a rainforest by flying over it in a helicopter and dropping a net through the fog.
“You’ll get the squirrels and the hummingbirds and pieces of trees, but it’s all squished in the net. You won’t understand the interactions,” he said. “An ROV allows us to have our eyes underwater, looking at everything that’s going on.”
It turns out that even a seemingly featureless expanse of sand can be rich in “microhabitat” — hideouts created either by currents or by fish and invertebrates as they hunker down and burrow into the sand. If you’re a flatfish flopped over on your side on the bottom, it doesn’t take much of a divot to hide from predators and currents.
“Imagine you’re a fish that’s that flat” — Lindholm indicated something about the width of a chapati — “and then look at the bottom and think, ‘OK, I can use that. I could use that.’ ”
The video and photos from the ROV cruises will show changes in the topography of the bottom immediately after a trawl net sweeps over it, and then six months and a year afterwards. And, Lindholm said, they’ll show whether trawled areas are subsequently colonized by species that weren’t there before.
Back in the Box, Lindholm handed the Beagle’s controls over to Rosen. “To get calibrated,” joked Rosen, “you kind of have to bump into a few things.”
Rosen settled in and quickly attained a state of meditative oneness with the ROV. On the video monitor, soles hunkered down into the sand as the Beagle motored closer, until they accelerated ahead with surprising bursts of power.
“At some point, you really do transform yourself,” he murmured. Anything that breaks the trance can be extremely jarring. Once, a six-gill shark whipped around straight into the ROV’s camera lens. Hundreds of feet above, Rosen shot out of his seat on the boat.
A couple of hours doing a delicate do-si-do with the ROV can turn into a disembodied, bleary-eyed — and, if a good swell’s running — nausea-inducing ordeal, no matter how hot the playlist on Lindholm’s iPod. And the gruelingness doesn’t end once the boat ties up back in Morro Bay. To analyze the data collected, the researchers overlay each still photo and video frame with 50 random dots, and then count and identify habitat types and species under each dot. In May, Lindholm and the other researchers were still analyzing the data they’d gathered last November.
“It’s easy to fixate on the really cool stuff,” Lindholm said, “but there are hours and hours and hours in the video lab, days and days where you do go cross-eyed.”
Ultimately, this research could help fisheries regulators develop more sophisticated ways of managing fishing in California and elsewhere. Rather than outright bans on trawling, for instance, it may be possible to take a more nuanced approach and allow occasional trawling in areas that can withstand it.
And it’s already clear that people are watching Lindholm, Gleason and Rosen’s work with keen interest. “From my perspective, this kind of a study would prove that trawling is good in soft-bottom habitat,” said Maricich, the Donna Kathleen’s skipper.
The wheelhouse of the Donna Kathleen has a live video feed from the ROV, and he keeps a close eye on it. “Fishermen have always said that grounds that are trawled are better fishing than non-trawled grounds — a lot of the organic nutrients get stirred up and reintroduced to the ecosystem.”
Lindholm, for his part, is careful to not jump to any conclusions. It will be years before the team’s formal findings are ready. “If there’s one thing we’ve learned,” he said, “it’s to not make any judgment based on what we see live when we’re flying over the bottom.”
Late that afternoon, the setting sun left a habañero-red smear across the western horizon. Maricich maneuvered the Donna Kathleen with the current, and Rosen and one of his staffers, Steve Holz, used the crane to wrestle the Beagle back aboard the boat. Once the dripping ROV was secured on deck, Holz peeled off his hard hat with a look of relief.
“Every time you throw something into the ocean,” he laughed, “there’s a good possibility you’ll never get it back.”