School for Marine Science and Technology team aims to measure abundance, density, and size distribution to aid in management of the fishery
Last week scientists from UMass Dartmouth’s School for Marine Science & Technology (SMAST) and fishermen successfully deployed a new video survey system they believe can provide more accurate measurements of the Atlantic cod population, helping regulators manage the fishery.
The system, collaboratively developed by scientists and fishermen over the last four years, was tested on Stellwagen Bank, a fishing ground located in the Gulf of Maine about 15 miles southeast of Gloucester and six miles north of Provincetown. The system involves placing high resolution video cameras in an open-ended commercial trawl net to capture images of groundfish (focusing on Atlantic cod and yellowtail flounder) as they pass through unharmed. Periodically the net is closed to collect biological samples such as length and weight measurements. These cod are kept alive in wells and are returned to the sea alive and in good condition.
SMAST Professor Kevin Stokesbury and his research team – chief scientist and graduate student Travis Lowery and graduate student Nick Calabrese – designed the system so they could identify the species in every image. This allows researchers to approximate the abundance, density, size distribution, and the impacts of commercial fishing. “Our goal is to provide all stakeholders in this issue with trustworthy science that reduces uncertainty for the Gulf of Maine cod fishery,” Dr. Stokesbury said.
“The seven-day cruise was very successful,” Dr. Stokesbury said. “Atlantic cod were observed over much of the bank, and the largest closed tow collection was of 345 cod in a half hour, with individuals measuring up to 83 cm. The idea is to increase the amount of sea floor sampled per sea day without killing more fish.”
A key milestone of the cruise was reached last Friday morning when all project systems came together. Data were collected on the position and speed of the vessel, including how the net was performing (i.e. spread of the doors, spread of the wings, bottom temperature). “We captured video of the footrope as the net passed over the sea floor and of the fish entering the net, as well as extremely clear video of the fish as they pass through the net, and a very large school of cod,” said Stokesbury. “All systems worked for the remainder of the trip; collecting data on cod abundance, distribution, the sea floor over which they school, and the other fish they associate with, including large schools of sand lance a key prey.”
The most recent assessment for Gulf of Maine cod estimated that the spawning stock biomass is a small proportion of its historic size. In response to the low abundance, the total allowable catch has been drastically reduced, constraining the fishermen’s ability to harvest healthy stocks, such as haddock and pollock. “Increasing the amount of sea floor scientifically sampled and increasing the amount of the information collected during a day at sea should reduce the uncertainty in the stock estimate, and reduced uncertainty is ultimately in everyone's best interest,” Dr. Stokesbury said. “In the end I think it is a good proof of concept and should give a good estimate of the cod aggregated on Stellwagen Bank.”
The Baker-Polito Administration provided $96,720 in capital money through the state Division of Marine Fisheries to fund the research tows conducted on Stellwagen Bank. Dr. Stokesbury's research has also received support in state funding the past two years, receiving more than $800,000 through legislation supported by State Senator Mark Montigny, State Representative Antonio F.D. Cabral and the entire SouthCoast legislative delegation.