BLUE HILL, Maine — Cod that are spawned in Maine waters tend to stay there, and they grow larger but more slowly than their counterparts in other regions.
That was one of the findings of a six-year study designed to track the movements of Atlantic cod in the Gulf of Maine and beyond.
The Northeast Regional Cod Tagging Program is the largest and most widespread study of its kind to date and provides a snapshot of the cod population and how it moves, according to Shelly Tallack, a research scientist with the Gulf of Maine Research Institute in Portland and lead investigator for the study. Tallack reviewed the results of the study on Thursday at the Marine Environmental Research Institute as part of its Ocean Environmental Lecture Series.
The study involved five research organizations, coordinated by the GMRI, and about 250 volunteer fishermen who tagged and released a total of 114,473 cod in locations throughout the three large cod management zones in the U.S. and Canada — the Gulf of Maine, Georges Bank and the Scotian Shelf area which includes the Bay of Fundy.
More than 1,000 individual fishermen have recaptured the tagged fish and reported specific information about the fish, providing valuable details about the movement and growth patterns of the fish.
The fish were captured, tagged following a specific method developed for the study, then released in the same area where they initially were captured. The study had been designed to last two years, but Tallack said it was extended and, although returns have dwindled, they still are receiving reports of recaptures six years after the start of the project. To date, she said, they have received reports of 6,600 recaptures.
The study had some limitations, Tallack said. The tags served as an ID for each individual fish, but did not track a fish’s movements in real time.
“We can track where it was released and where it wound up,” she said, “but we don’t know where it was in between.”
The recaptures also were influenced by where fishermen were fishing. Very little information came from areas north of Portland, where little cod fishing is being done anymore. Most of the recaptures came in areas that are more heavily fished, such as coastal areas south of Portland, Georges Bank and the west coast of Nova Scotia.
Tallack provided some fish facts for the MERI audience. The average maximum distance traveled by the cod was 300 to 500 kilometers. One fish traveled a distance of about 1,054 km or close to 700 nautical miles. The fish was tagged in the Bay of Fundy and was recaptured off the coast of Virginia.
The smallest cod tagged was 8.7 inches, the largest, 52.8 inches. The smallest fish recaptured was 13 inches and the largest, 55.9 inches.
While the information on growth and mortality may prove helpful to stock assessment efforts, the study was focused on fish movement. It showed different migration patterns for different groups of cod.
Cod tagged in the Gulf of Maine tended to remain in the same area. According to Tallack, few fish tagged in that area were recaptured outside of those waters. Instead, they seemed to move generally north and south along the New Hampshire and Maine coastline.
“The cod tagged inshore in the Gulf of Maine stayed in the same area,” she said.
In addition, the fish tagged and recaptured in the inshore area tended to be larger. The largest fish in the program were tagged in the Gulf of Maine, and the study indicated that while those cod grew more slowly than fish in the other areas, their growth period continued longer and the fish overall were larger than any of the other areas.
Cod tagged on Georges Bank tended to remain there but move northward into the Bay of Fundy in the spring and summer, returning to Georges Bank in fall and winter. Likewise, fish from the Bay of Fundy tended to remain there during the spring and summer, but in the fall they headed south to Georges Bank.
The real surprise for Tallack was what happened with fish tagged in the area around Cape Cod. Most of these fish were young when they were tagged and initially stayed in the local area. As they matured, the fish tended to move in different directions.
“They split,” Tallack said. “One group moved north into the Gulf of Maine, while others moved eastward onto Georges Bank.”
The fish obviously are not staying within the different management zones. Although the tagging program did not delve into the reasons for their migrations, Tallack speculated that the fish were moving for reasons that most species move: food and spawning.
The information from the program has been provided to fishermen and to authorities in Canada and the U.S., including the Northeast Fisheries Science Center at Woods Hole, Mass., and the Canadian Department of Fisheries and Oceans in New Brunswick. It was available for the most recent groundfish assessment review last year.
Funding for the program has run out, Tallack said, but she and co-workers have continued to gather information and to combine information with smaller, more localized studies in order to provide a broader set of data for scientists.