Sea floor off the coast of San Luis Obispo County yields its secrets

ABOARD THE RESEARCH VESSEL FULMAR — The remotely operated vehicle Beagle descends more than 500 feet into the ocean off Morro Bay. As it nears the bottom, it passes through a cloud of translucent jellyfish.

Suddenly, the sea floor looms into view through the vehicle’s video camera — a vast muddy plain covered with millions of feathery scale worms. At a speed of a half a knot, the ROV begins a daylong journey of gliding nearly two miles over the ocean floor.

The high-resolution video and digital photographs the ROV collects will give scientists a rare, detailed view of the ocean floor off the Central Coast. It will also become part of a five-year collaborative research project designed to help marine scientists and fisheries managers better understand how the commercial fishing technique of bottom trawling affects the ocean ecosystem and thereby help them craft better rules for fisheries management.

“The juggernaut of fisheries management is moving ahead, but we don’t have a lot of scientific data to back it up,” said CSU Monterey Bay professor James Lindholm, the project’s chief scientist.

Lindholm was one of a group of six scientists sitting in a darkened compartment aboard the Fulmar Sept. 29, floating some 535 feet above the ROV three miles off Montaña de Oro State Park. They stare mesmerized at computer screens as a video feed from the ROV’s forward-looking camera shows the sea floor.

ROV supervisor Dirk Rosen guides the ROV using a control console. A thick yellow electrical cable tethers the ROV to the ship like an umbilical cord and allows Rosen to control it while digital data are continuously sent back to the ship.

On this day, the ROV will traverse three-kilometer-long monitoring plots. In addition to the video feed, a digital photograph is taken every minute. Fish and other animals of interest are also photographed individually as the ROV cruises by.

Soon, a pattern emerges. Scale worms form an almost unbroken blanket across the seafloor. Worms kicked up by currents float briefly in the water. Overlapping scales make the worms look like feathers.

The profusion of scale worms is a surprise, said Mary Gleason, chief scientist with The Nature Conservancy. Other bottom-dwelling creatures don’t seem to be interested in feeding on the worm bounty.

The cameras also regularly photograph a variety of other marine animals, some common, others not so familiar. One of the most abundant is a flat, elongated fish called an eelpout.

Octopuses, squid and anchovies also frequently skitter away from the approaching ROV. Sea cucumbers, urchins, anemones, sea stars and sea slugs are also abundant, as well as long, spindly sea whips, clusters of anemone-like animals, which stick straight up from the bottom.

Finding flatfish

Occasionally, the ROV encounters a trench or depression in the bottom. These often contain small rockfish, which use these depressions as a refuge from predators and strong currents.

At one point, the ROV startled a large fish of some kind, which bolted away in a blur, leaving behind a cloud of silt. Researchers may be able to identify the fish by examining the video frame by frame in the laboratory.

The fish type that sparks some of the greatest interest among the scientists is the flatfish. Jean de Marignac, a field scientist with the Monterey Bay National Marine Sanctuary, said most of the flatfish the ROV encounters are petrale sole and sand dabs.

Flatfish are of interest to scientists because they are one of the main reasons the research is occurring. Bottom trawling is the only commercially viable way to catch flatfish, highly valued as seafood.

But trawling comes at a price to the environment. One of the problems with trawling is called “by-catch.” A trawl net dragged across the ocean floor can scoop up the eelpouts, octopuses and other animals in addition to the targeted flatfish.

These unwanted species will be thrown back, but they are unlikely to survive being hauled up 500 feet from the ocean floor. Trawling also knocks over sea whips and fills in those depressions in which rockfish take refuge.

Some of the goals of the research are to determine how much trawling alters the seafloor and how quickly it recovers after trawling stops. With this kind of information in hand, fisheries managers can craft fish quotas and other regulations that allow economically important fish to continue to be caught without depleting fish stocks, Gleason said.

“Fortunately, advances in ROV technology are expanding our ability to explore and understand deep underwater realms where divers can’t reach,” she said.

Future studies

The researchers have established eight research plots in a north-south line just outside state waters, which end at three miles from shore. Half the plots will be trawled by Morro Bay commercial fisherman, Ed Ewing, using a fishing boat and trawl permits owned by The Nature Conservancy. The other half will not be trawled.

The ROV will make 30 to 40 dives per year for the next five years to monitor these plots. Scientists will be able to compare changes that occur in the trawled areas with those that are left untouched.

The trawl-effects research is a collaborative effort among The Nature Conservancy, CSU Monterey Bay, the National Marine Fisheries Service, Marine Applied Research and Exploration, the Monterey Bay National Marine Sanctuary and Morro Bay fishermen.

A big chunk of the money to purchase the ROV Beagle — named after the ship that took Charles Darwin to the Galapagos Islands for his famous research into evolution — was provided by the state Ocean Protection Council.

In all, the ROV and the array of electronics it uses cost nearly $500,000, Gleason said. The vehicle has the ability to dive to 1,600 feet and will also be used for a variety of deep-water research in Monterey Bay, Big Sur and the Channel Islands.

Reach David Sneed at 781-7930.