New Video System More Accurately Assesses Cod Population

A new video system designed by UMass Dartmouth School for Marine Science and Technology (SMAST) scientists to assess the population of cod has passed its first major test, giving the researchers confidence that they can use this new approach to help improve the accuracy of future scientific assessments of this iconic species. Recent stock assessments indicate that the Gulf of Maine cod population is low and struggling to recover. Members of the fishing industry contest those results, suggesting the stock is much healthier than depicted in recent assessments.

“Our goal is to provide all stakeholders in this issue with trustworthy science that leads to smart management of the Gulf of Maine cod fishery,’’ said Dr. Kevin Stokesbury, whose team conducted the test. “We are pleased with the initial results and are looking forward to scaling up our work.”

The Baker-Polito Administration provided $96,720 in capital money through the state Division of Marine Fisheries to fund research tows recently conducted on Stellwagen Bank. This work builds on similar research that Dr. Stokesbury’s team has conducted on yellowtail flounder, which is also facing difficulty. Of special note, Dr. Stokesbury’s approach has been successfully used over the last sixteen years to measure the scallop population of the east coast resulting in improved assessments integral to sustaining that fishery and keeping New Bedford the top-ranked fishing port in the U.S.

“The work by UMass Dartmouth School for Marine Science and Technology will complement work done by our federal partners by providing additional scientific data that will help us better understand what is happening to the cod stocks in New England,” said Governor Charlie Baker. “Improving the data used to make informed decisions is critical to preserving the economic viability of the Commonwealth’s fishing industry.”

The new video system uses an open-end fishing net with video cameras mounted on its frame to capture images of the fish passing through the net. Researchers then review the video to count the different species, and estimate the size of each fish.

The current practice of counting cod involves catching the fish in a net and hauling them onto the deck of the vessel, then counting, weighing and measuring them. Dr. Stokesbury believes this practice is less efficient because the nets are only left in the water for a short period of time (20-30 minutes), while the open-end net can be left underwater for hours at a time collecting a greater amount of data on fish populations across a larger portion of the ocean. In addition, the traditional survey method kills most of the fish that are caught, while the new open-net video method causes no damage to the fish.

The tests were conducted on Stellwagen Bank January 7 -9 aboard the F/V Justice, a New Bedford-based commercial fishing boat captained by Ron Borjeson. Dr. Stokesbury was joined on the excursion by graduate students Travis Lowery and Nick Calabrese, and technician Christa Bank.

The objectives of the test were to determine whether the video camera system design functioned properly; whether the video fish counts matched on-deck fish counts; and whether the system could be used to measure the population of cod in the area.

Eleven 30 minute tows with an open net were conducted, while seven half hour tows were made with a closed net. For closed net tows, the fish were carefully brought onto the boat, counted, measured, weighed, and returned to the sea. Fish survival was high due to the care shown by the research team.

A total of 6,423 fish, representing 21 species, were collected during closed tows, with the three most abundant species being haddock (2,062), yellowtail flounder (1,444) and Atlantic cod (1,096). Cod ranged from 28 cm (10 inches) to over 80 cm (32 inches). Numbers and size of each species observed during open net tows are currently being derived from video footage.

Biological samples of cod were collected for two collaborative research projects related to the genetics and evolution of cod. SMAST, Gulf of Maine Research Institute, University of New Hampshire, Massachusetts Division of Marine Fisheries and the Gloucester Marine Genomics Institute are participating in these studies.

“This experiment was successful beyond what I had hoped for,” Dr. Stokesbury said. “I was impressed with the abundance of cod and other species, particularly yellowtail flounder, winter flounder, and haddock.”