This catch from the FV North Star is dominated by Maine shrimp, with juvenile Atlantic herring and silver hake also visible. Researchers hope the acoustic data will fill an information void created by the shrimping moratorium. Adam Baukus photos

This winter, a small fleet of Maine fishermen will head out to hunt for northern shrimp, even though the fishery itself has been closed for three years.

They won’t be landing the New England delicacy so it can be eaten. The fishermen will use acoustic transducers, and a few nets and traps, to help the Gulf of Maine Research Institute learn where these small pink crustaceans congregate in our near-shore waters over the winter, where they lay their eggs. Using sound waves to survey a species as small as shrimp is a new challenge for scientists.

“We have found low-frequency sound waves are good at detecting big fish, like cod, and high frequencies are good at detecting small organisms like shrimp,” said research associate Adam Baukus of GMRI. “The technology allows us to cover a lot more of the ocean than we can with trawls or traps alone. With sound, we can do 40 miles at a time. … Traditional (trawl) surveys are lucky to cover a quarter mile.”

To collect the data, GMRI has outfitted 10 lobster boats with echosounders, high-tech fish finders, to conduct monthly surveys of near-shore waters from Kittery to Cutler in January, February and March, which is the height of what used to be a $70 million fishing season. The lobstermen, who receive small stipends to cover fuel costs, will survey the same 40-mile-long stretch of water each time.

The data can’t immediately be used to determine whether the population of shrimp is growing because the sampling is being done in places that haven’t been surveyed before, so there is no history that can be used for comparison, Baukus said. GMRI just started doing acoustic surveys last year, using a $300,000 grant from the Saltonstall Kennedy program, which is funded by a federal tax on imported seafood.

But over time, if interstate fishery managers trust the accuracy of the acoustic survey data, the results can be used, in conjunction with the federal and state offshore summer trawl data, to determine whether Maine shrimp has recovered from its record low biomass and whether it is once again abundant enough in local waters to reopen the fishery, Baukus said.

Acoustic survey data could help determine whether Maine shrimp has recovered and is once again abundant enough in local waters to reopen the fishery, which used to be a $70 million January-through-March season.

TESTS AND RESULTS

Initial results suggest that the technology works, even for a species as small as shrimp, Baukus said. Whenever the transducer picks up a signal for a big school of shrimp, the lobstermen who are doing the actual survey will drop a few traps and nets to confirm that what looks like a shrimp school echo is in fact northern shrimp. Trap and trawl checks have helped confirm most of the acoustic results, he said.

GMRI even outfitted the federal shrimp trawl survey boat with a transducer over the summer to test it in open waters, and it worked there, too. This isn’t all that surprising, as acoustic surveys have been used by scientists and even fishery managers to document the health and abundance of other larger ocean species, but there had been some concern that it wouldn’t be able to detect shrimp.

Baukus said GMRI hopes its results will disprove that concern and add acoustic surveys to the data that interstate fishing officials can use when managing the fishery in the future. The Atlantic States Marine Fisheries Council’s northern shrimp board is meeting Thursday in New Hampshire to consider recent federal trawl data and decide whether to allow shrimp fishing again; its scientists are calling for it to remain closed for now.

In the meantime, however, GMRI hopes to use the acoustic survey data to determine if the shrimp are moving east, abandoning the warming waters in southern and midcoast Maine for the colder northeastern waters. Initial results suggest this may be the case, with a surprising number of shrimp found earlier this year around Mount Desert Island, Baukus said. Traditionally, the heart of Maine’s shrimp population was found off Pemaquid Point.

Sea surface temperatures in the Gulf of Maine have been rising over the past 35 years, and at nearly the fastest rate on the planet over the last 10. Half of the commercial fishing stocks tracked by federal managers in the northwest Atlantic Ocean have been shifting north, and scientists expect that trend to continue. Shrimp would be just one more species moving northeast, but an important one, as so many other species rely on it for food.

Without a fishery, the shrimp board is now without winter landing reports, which it had used in conjunction with the federal summer trawl data to evaluate the health and abundance of the stock and its suitability for fishing in the future. GMRI hopes its acoustic data will fill an information void created by the shrimping moratorium, and help fishery managers guide their future sampling efforts, Baukus said.