HARPSWELL — The Maine Department of Marine Resources, charged with regulating the scallop fishery, has never formally studied how shellfish dragging affects the seabed.
In the wake of an episode in April, however, there are questions about how dragging metal nets across the sea floor affects the health of the ocean bottom.
Scallops are primarily harvested in Maine using drag nets. Most fishermen now use New Bedford-style drags, which are essentially large chain nets attached to steel frames. Fishermen drag the nets across the ocean floor, collecting the shellfish.
Chain-sweep drag nets are also used to harvest oysters and mussels in Maine.
Many studies have found that a single drag can kill a lot of animals: the net scoops up shellfish, but disrupts other types marine life, including invertebrates, fish and seaweed.
“There is some level of incidental mortality,” associated with dragging, DMR scallop scientist Kevin Kelly said.
But studies have shown that in many places, habitats can recover in a matter of months. In a 2008 review done for Suffolk County, New York, shellfish scientist Robert Rheault cited several studies confirming this finding.
But resiliency in areas that have been dragged repeatedly over many years remains a question.
In a 1997 study of the Georges Bank, the large elevated area of sea floor in the Gulf of Maine, scientists from the University of Rhode Island and Woods Hole, Massachusetts, found that there were more organisms and more species diversity at sites that had been historically undisturbed by dragging.
“The cumulative effect and the intensity of trawling and dredging may generate long-term changes in (sea floor) communities,” the authors wrote.
There has been no study in Maine on the effect of dragging in the state’s coastal waters.
Questions were raised locally when a Harpswell homeowner complained to the town’s Board of Selectmen that an unmarked shellfish dragger – later confirmed to be an oyster dragger by the boat’s captain – upset an oyster bed off his property.
Selectmen referred the question to the town’s Marine Resources Committee.
But at the state level, the environmental effects of dragging are “not really being looked at at this time,” Kelly said.
Rotating closures are the DMR’s primary management tool for ensuring the sustainability of the scallop industry.
“(We’re) rotating the harvest, similar to crop rotation,” Trisha Cheney, DMR scallop resource coordinator, said. “That way, we allow some areas to rebuild with no bottom impacts, while others are harvested.”
In 2009, the DMR ordered 13 coastal areas closed to scallop dragging. One of those areas was a section of Casco Bay encompassing Harpswell and Merriconeag sounds.
That area reopened in 2012 for limited access. Starting in January 2014, it was open one day a week to draggers, and one day a week to divers.
A standard scallop season is about 70 days, starting in December, and can often be trimmed. This year, Zone 1, which includes Casco Bay, will only have a 60-day season, after a vote at the June 4 Scallop Advisory Council Meeting in Ellsworth.
DMR attributes the recent rebound in scallop landings to spatial management.
Scallop landings have bounced back from a historical low of 125 metric tons in 2005, to 2,207 tons in 2014, according to DMR data.
There are also technology limits on drag nets: the largest a net can be is 10 feet 6 inches in width, with a bag made of 4-inch metal rings.
“(That size) allows sub-legal product and byproduct to pass through while maintaining a pretty clean catch of just scallops,” Cheney said.
She acknowledged, though, that dragging the metal nets across the sea floor definitely has an impact to the bottom.
And to date, nobody knows what exactly that impact is.
In 2014, DMR licensed 545 commercial draggers and 82 commercial divers. Of that total, 483 were considered “active,” Cheney said.
The active number has increased from 168 in 2009, when scallop stocks were low.
The scallop fishery was valued at nearly $7.5 million last year, and fetched a historic high of $12.78 per pound, according to DMR.
“We’re definitely on a rebuilding trajectory,” Cheney said.