COMMERCE
Subscriber Services
Classified Ads
Subscribe
Advertise
NEWS
This Month
Editorial
Letters
F/V Safety
Past Issues
ABOUT US
Contact Us
Latest Issue
Subscribe
History
MORE CONTENT
CFN Archives
Links
Each month exclusively in the PRINT edition of CFN
Along the Coast
Ask the Lobster Doc
Bearin’s
Classifieds
Coming Events
Editorial
Enforcement Report
FISH SAFE
Fleet Additions
Letters
Lobster Market Report
New Boats
News Catch
Quahog Market Report
|
Left, the catch from Tow 14 with the standard commercial shrimp net. Right, the catch from Tow 15 with the UNH experimental topless shrimp trawl.
Topless shrimp trawl reduces pelagic bycatch
DURHAM, NH – During the 2006 shrimp season, Pingguo He of the University of New Hampshire (UNH) and fisherman David Goethel of Hampton tested a “topless” trawl designed to reduce pelagic fish bycatch in the northern shrimp fishery in the Gulf of Maine.
Mandatory use of the Nordmore grate has greatly reduced finfish bycatch in the shrimp fishery. However, the grate cannot reduce bycatch of small pelagics, juvenile groundfish species, and small shrimp that can pass through the 1" bar spacing of the grate, so small fish such as herring, whiting, and red hake are often caught when they are present on the fishing grounds.
A conceptual drawling of the topless shrimp trawl. The net sea trials were carried out aboard David Goethel’s Ellen Diane in 2006.
The goal of the project was to test a net without square and top belly (with pulled-back headline) so that pelagic fish can escape over the headline before entering the trawl.
The trawl design is a reversal of a fish trawl design that uses overhung netting to prevent fish from escaping. In other words, the experimental trawl was much like a conventional trawl fished upside down.
The project was funded by the Northeast Cooperative Research Partners Program, which is administered by the National Marine Fisheries Service, and was a true joint effort between the industry partner and UNH.
Harold DeLouche of the Centre for Sustainable Aquatic Resources at Memorial University in Newfoundland, Canada assisted with the design. The model of the trawl was tested in the flume tank at the centre in December 2005. Trawlworks Inc. of Narragansett, RI manufactured the full-scale gear.
Sea trials took place on board Goethel’s Ellen Diane during February and March of 2006 off New Hampshire. After initial adjustments, 10 pairs of tows were made comparing the topless trawl to a commercial trawl.
Gear design, methods
The new topless trawl has a headline length of 105' and a sweep length of 91'. The comparison commercial trawl had a headline length of 52' and a sweep length of 70'. Other length and dimensions are shown in the accompanying table.
With the experimental trawl designated as “E” and the commercial trawl designated as “C,” an alternating tow method was used following a “CEEC” and “ECCE” sequence.
Four tows per day were made at similar fishing locations. During 10 pairs of tows, the exact same specifications of Nordmore grate and codend were used for both control and experimental gear. The Nordmore grate was made of stainless steel and measured 36" long by 29" wide. The grate spacing was 1" and it was installed at a 50° angle. The codend was made of 2" mesh nylon material, 99.5 meshes long and 150 meshes on the round.
Results
There was no problem in handling the new topless shrimp trawl with the existing deck machinery on board the Ellen Diane. Power needed to tow the new net was similar to that required for the commercial trawl as indicated by engine rpm readings. The new topless trawl seemed practical in terms of operation and handling.
The average catch of 10 tows with the topless trawl was 202 pounds per half-hour tow compared to 178 pounds per tow with the commercial trawl. That’s an average increase of 13.6% for the topless trawl over the commercial trawl.
The major bycatch species was Atlantic herring. Other bycatch species included blueback herring, whiting, American plaice, and winter flounder. Very few cod and haddock were caught as bycatch during the fishing period.
For the experimental gear, shrimp represented 90.6% of the catch while herring only accounted for 4.1% of total catch. For the commercial trawl, shrimp accounted for 69.5% of the total catch, while bycatch accounted for 30.5%, of which herring represented the majority.
The experimental gear was much “cleaner” and required less labor to sort the catch.
The experimental topless trawl caught significantly less herring than the commercial trawl with an average reduction of 87%. There were no differences in bycatch rates for blueback herring and whiting, but there was a slight increase in bycatch of American plaice and winter flounder, though their catch rates were generally low. The increase in flounder bycatch may be due to a longer sweep length and wider wingend spread in the topless trawl.
Conclusions
The new topless shrimp trawl performed very well in terms of operation, reducing herring bycatch and maintaining shrimp catch. It may be used when herring is plentiful on the shrimp fishing grounds.
The future plan is to test whether commercial shrimp trawls currently used in the Gulf of Maine can be modified into the “topless” design and whether such modification would still maintain catch rates and reduce pelagic species bycatch.
Pingguo He
Pingguo He is a research associate professor of fisheries at the Ocean Process Analysis Laboratory of the Institute for the Study of Earth, Oceans, and Space at the University of New Hampshire and a commercial fisheries extension specialist at New Hampshire Sea Grant.
For more information on the topless shrimp trawl or on other fishing gear issues, call He at (603) 862-3154 or e-mail him at <pingguo.he@unh.edu
Back to story list
|
|
Tell us what you think.
