Mind’s Eye to Real Time Bottom View

by Fishermen’s Voice staff

What the bottom looks like 200 feet down, at least for what fishermen are looking for, has been a mix of many random small samples from soundings or a jumble of solids that make it to the surface in a dredge. This new image, right, is the bottom as was when the digital camera passed over. Some images show a three foot wide image the length of two football fields. Photo: Woods Hole Oceanographic Institute

For fishermen the view of the deep bottom has always been in the mind’s eye of the experienced captain. Scientists, who virtually never have a captain’s experience with the bottom, use trawls to decide what is on the bottom they cannot see. However, the definition of “scientific” alone would be enough to declare trawls not very scientific. They drag blindly along, scooping a mess of stuff from somewhere on the bottom. The captain’s sounding lead on the end of a line, with a wad of grease on it’s bottom that causes ocean floor particles to stick to it, was far more precise in determining what exactly was on the bottom in a specific place.

But technology has made it possible to replace the fairly blunt instrument that is the dredge with a not only precise, but real time, see it as it happens, view. Richard Taylor, a Gloucester fisherman who started fishing scallops in 1968 out of Hampton Virginia, and a research team from Woods Hole Oceanographic Institution, have been taking thousands of high-resolution digital still photos and making photo mosaics of scallop beds from the New Bedford scalloper Kathy Marie. Skipper Paul Rosonina knows the bottom, and Norman Vine, a former New Bedford dragger skipper, who turns the raw images into a something that can be looked at over the internet, round out the team.

The project can be traced back to 1994 when a 6600-square mile area was closed by the National Marine Fisheries Service (NMFS), to all gears capable of catching ground fish. These areas were also the most highly productive scallop fishing areas in New England. By 1996 scallops in the area remaining open to the fishery were in short supply, total landings were about 12,000,000 pounds. There were 100’ offshore vessels averaging just 400 to 500 pounds per day of fishing. At the same time the news was spreading on the docks that the scallops were rebuilding in the closed areas. The big question then was “how many scallops are in there?”

In 1998 a cooperative effort between the School for Marine Science and Technology (UMASS Dartmouth), Virginia Institute of Marine Science, and the National Marine Fisheries Service had six industry boats make 2,000 tows in Closed Area 2. Most of these tows were on a gridded survey pattern with a tow every 1.7 miles. They were gathering information – on scallops, fish and the bottom using the standardized NMFS tows (1 mile exactly). This survey found that there were more pounds of scallop meats in that one area than had been landed from all the open fishing grounds over the entire region in each of past three years.

However, there was disagreement concerning the actual amount since the calculation depended in great part on the “efficiency” of the dredge. What percentage of the scallops in the dredge path were actually caught? The published literature figured 10-20% and NMFS estimated 20-50%. In an effort to improve on the accuracy of the biomass estimate, Kevin Stokesbury, SMAST, developed a pyramid shaped device for taking point samples with a video camera. Lowered over the side from industry vessels, it took photos, not physical samples and therefore removed the “efficiency fudge factor” inherent in the NMFS dredge survey.

The NMFS scallop survey makes about 500 tows between Cape Hatteras and Canada every year. That’s in a 12,500 square mile area, which translates into about one eight-foot wide one-mile long tow every 25 square miles. In comparison the SMAST sampling method was 100% efficient since the camera recorded 100% what was there. With this equipment they made four drops of the camera within 100 to 200 yards depending on current and tide. After the fourth drop they moved to the next station, about 1, 3 or 5 km, for another drop. The camera shows where the scallops are exactly, whereas the dredge does not transmit this information. Fishermen, says Taylor, have a good notion of the bottom; but the pictures show it exactly.

Neither method was quite good enough, “I knew from fishing that moving over a tenth of a mike or half a fathom could bring a whole different tow. You might miss it jumping a mile”. So he set out to “ get the best people and equipment to measure the scallop beds.” He went to the best team he could find, the Woods Hole Oceanographic Institution Deep Submergence Lab, the ones who put together the tools and equipment to search for the Titanic. Their interest was in building the next generation of underwater imaging equipment. That meant, for them, working with fiber optics and networking to bring real time images up the tow cable to be viewed on the bridge.

The enormous difference between what this method does and what other surveys do, is apparent in just one fact alone. They tow the camera a fathom off the bottom at 5 knots, produce 14,000 detailed images every hour and cover 100 miles in a day. The next development, Taylor said, will be the use of side scan sonar from the camera vehicle. This would project 20 to 30 meters out on each side of the camera. It would not be a photograph, but it would be a data producing image of a much wider swath.

Taylor says that “the industry is united in not going overboard” in harvesting scallops and cites the recent experience in Hudson Canyon where the catch went down to nothing much faster than expected. “Fishing the closed areas in rotation is working, but we have a long way to go yet, there are a lot of details we just do not know. No one has ever tried anything like this on this scale before.”

The team continues to write funding proposals for producing the overlapping photo mosaics of the bottom. “There is no disaster money for scallops as there was for groundfish”, Taylor pointed out. However, 2% of the annual scallop catch is set aside to help fund scallop related research. “We have a great team, it took each and every one of us, and a lot of boats to support the effort. A great set of tools to see and photograph the bottom have been developed, over 3 million, 1 meter square pictures the first year. Now we need to concentrate on turning the images into useful information for both scallop biomass estimation and substrate.”