Northeastern fishermen and scientists test ‘restriction rope’ for bottom trawl surveys

Scientists and fishers have worked together for many years to develop bottom trawl survey gear that performs consistently, ensuring accurate and reliable data for fisheries management in the United States.

This summer, they evaluated a potential way to better standardize survey gear – a “restriction rope” that helps keep the distance between trawl doors consistent while trawling in different conditions, depths, warp lengths and line configurations. gear.

A summary of the project from the Northeast Fisheries Science Center of the National Marine Fisheries Service describes experiments conducted in the spring and summer of 2022 at sea with scientists and fishermen with long experience of cooperative survey work.

Their main rig was F/V Darana R, with Captain Jimmy Ruhle, his son Bobby Ruhle and their crew. Homeported in Wanchese, NC, the Darana R has for years supported the bi-annual North East Area Monitoring and Assessment Program bottom trawl survey, conducted by the Virginia Institute of Marine Science at Gloucester Point, Virginia.

The NEAMAP program facilitates the collection of fishery-independent information in the northeast and standardizes survey procedures to improve data quality and accessibility.

Expanding offshore wind power development off southern New England will force changes to bottom trawl surveys in the next few years alone. The Vineyard Wind, South Fork Wind and Revolution Wind wind turbine arrays will be constructed between Martha’s Vineyard and the East End of Long Island.

“Existing studies will need to adapt to work in and around offshore wind farm areas,” according to the Northeast Fisheries Science Center. “Researchers will also need to develop new surveys to fill data gaps created when pre-existing survey locations are not accessible. A standardized gear configuration should be used so that data collected from existing and new surveys can be used and compared. »

For help with this redesign, the science center approached the Northeast Trawl Advisory Committee, a joint advisory group made up of members of the Mid-Atlantic and the New England Fishery Management Council, as well as experts from the fishing industry, academics, government and non-government. He identified the use of a restriction rope as a possible way to standardize all northeast bottom trawl surveys in the region. None have yet used restraint cords.

A restriction rope, marked with a C in the diagram, helps to maintain a constant distance between the trawl doors during tows. NEFSC chart.

Restriction ropes can provide better consistency in the performance of survey nets, the science center explained:

“Many factors can affect the way a trawl fishes through the water, including water depth, tides and currents, boat speed and warp length (the amount of towline left out ). These can influence the opening distance of the heavy doors of a trawl, which can change the shape of the net opening. For example, when the gates splay wide, the net opening can be flattened like a pancake. When they are not as wide, the opening takes on a more oval shape.

“Restriction ropes have the potential to reduce one of the most variable parts of trawl gear geometry – the door gap,” said scientist Mike Pol, a member of the trawl advisory committee and director of research at the Responsible Offshore Science Alliance.

“Preventing gates from overstretching helps prevent overstretching the net, and can help maintain consistent net shape and reduce catchability variation,” Pol said. “The variation in swept area is also reduced, which helps to make trawl survey indices more accurate.”

Scientists use the area-scanned values ​​to calculate and normalize catches. This means that catches at one location can be compared to catches at other locations.

In June, scientists from the Northeast Fisheries Center worked with the Ruhles and her crew on the Darana R, and scientists at Virginia Institute of Marine Science to begin the study of the restrictor cable.

Teaming up with NEAMAP veterans for the restriction rope research “is ideal, as they have long-standing expertise with trawl survey gear as well as a skilled team to execute the job,” said Anna Mercer. , head of the Northeast Fisheries Science Center Cooperative. Research Branch and member of the Trawl Advisory Committee.

Dustin Gregg, the VIMS chief of trawl survey operations, is optimistic about the study.

“The quality of survey data is inexorably linked to the performance of sampling equipment. Given the interest in adopting this set of equipment for a variety of new research projects, I hope that this study will allow the modification of the restrictor to help achieve cross-platform data uniformity in the future.” , said Gregg.

A 7/16″ green Tenex polyester restriction rope shown here is attached to the trawl door with a Viking hook. Photo NEFSC.

The first round of study experiments began May 30 in Rhode Island and Block Island Sound off the state’s coast. Over the course of eight days, the team completed a total of 80 bottom trawl tows – 40 with the restriction rope and 40 without. During restrictor rope tows, each end of a high-strength, low-stretch, 7/16-inch single-braided polyester Tenex rope was attached to the bottom panels of the trawl using hooks Viking. The team collected a variety of data, including:

  • Catches: Fish species, numbers, lengths, total weight per species
  • Hydrographic: water temperature, salinity, dissolved oxygen
  • Atmospheric: air temperature, wind speed and direction, barometric pressure, sea state, general weather
  • Towing: GPS location, direction, towing speed, towing depth, net geometry, warp length

Some of the species they captured during the experiment included Atlantic cod, black bass, butterflyfish, longfin squidnorthern blackbird, scup, silver hakespotted hake, Striped Bass, summer plaice, white hakeand winter flounder.

“Since species composition differs seasonally, the team will continue this research in the fall. In the coming months, scientists from the Institute, with the support of our fisheries scientists, will analyze the data and present the results of their research to the panel of experts in early 2023,” according to the science center.

Kathryn Ford, trawl panel manager for the science center, said she was excited about the continued collaboration.

“There are legitimate concerns about how to standardize trawl survey data collection so that we can integrate multiple data sources and understand the impacts of offshore wind on our fisheries resources. The panel has long focused its attention on research survey performance, and this study represents the first in which we examine how best to standardize survey gear deployed from commercial vessels.

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