Avoidance of Atlantic cod (Gadus morhua) with a topless trawl in the New England groundfish fishery

• A topless trawl reduced catches of Atlantic cod while maintaining catches of commercially-important flatfish.
• The topless design included a greater headrope to footrope ratio and more flotation than previously-tested designs.
• Success of topless trawls implies rising behavior of cod during the trawl capture process.
• Greater layback distance of the headrope from the footrope did not seem to reduce bycatch of any species.
• Flotation, particularly in the center of the headrope, appears to reduce flatfish escape.

Low quotas of Atlantic cod in the New England groundfish fishery may restrict fishing with trawls for mixed stocks of groundfish. Previous studies using topless trawls (i.e. trawls with a headrope more than 20% longer than the footrope) in this region showed reductions of cod, but also reductions in species of flatfish. In May and June 2011, we tested a topless trawl on a commercial trawler with a much greater headrope to footrope ratio and greater flotation than previous studies in the region. Thirty haul-pairs were successfully conducted and demonstrated a 51% reduction in the catch of cod, with no significant loss of any flatfish species, except for a significant loss of sublegal American plaice. Our results suggest that a topless trawl can be an effective method of cod avoidance for fishermen in the region, without substantial loss of landable flatfish. We infer from the results that: cod rise in response to an approaching trawl footrope and sand cloud; headrope layback may not be a critical value in the effectiveness of topless trawl designs; and, headrope flotation, particularly in the center of the headrope, may be an important factor in retaining flatfish.