Knotless Codend Mesh Sensitivity
Extension Associate Dana Morse is working with Boothbay Harbor fishermen Kelo Pinkham and Stanley Coffin, in their efforts to reduce bycatch, improve energy efficiency, and improve mesh size enforceability in trawl nets. The study, entitled “Sea Trials to Assess Knotless Mesh Codend Selectivity,” is enabled through a $46,180 grant from the Northeast Consortium.
The size, shape and materials used in mesh netting of trawls has much to do with escapement of fish during trawling, and on the species and sizes of fish that come up in the net. Traditionally, twine is knotted, which decreases the space available for fish to escape, and uses more energy to tow than knotless netting. This study will help to evaluate escapement by undersized fish, and any energy savings that might occur by using the newer mesh. Captains Pinkham and Coffin are running at-sea operations aboard Capt. Coffin’s 54-foot vessel, the F/V Bad Penny, with Morse as the scientific partner and PI.
Eight days at sea are planned for these trials, using an alternate tow strategy to evaluate the control codend (knotted) against the experimental (knotless). A standard-type groundfish net is used for the trials, with the codend being switched between tows. Sea trials began in late March 2003, and will run through May 2003.
The selectivity of knotless twine used in the codend of a groundfish trawl was tested, relative to a standard codend constructed of knotted twine. Between April and July of 2003, 13 tow pairs (26 tows) tests were conducted aboard the F/V Bad Penny, berthed in Boothbay Harbor, Maine. Analysis of catch per unit effort (CPUE) and length frequency by species detected a small difference between catches from the knotless and knotted codends. Larger sample sizes and covered codend experiments would help to more fully describe the selectivity of knotless twine in the Northeast groundfish fishery. Evaluations were somewhat hampered by a low catches in both control and experimental tows.
Video footage suggests a general tendency for the knotless twine to remain more fully open during trawling, and escapees from knotless codends may suffer less scale loss and other damage during the escape process. The knotless twine is lighter, easier to handle, and more supple. Future work should focus on the health of escapees, and on continued field trials, including square mesh arrangements.
For more information, contact Dana Morse.