Testing an “Open Top Intermediate” to Exclude Pollock from Flatfish Trawls (NMFS-97-1)

In August of 1997, the Groundfish Forum conducted a test under a NMFS Experimental Fishing Permit (NMFS-97-1) to determine the effectiveness of a radically different trawl net designed to reduce pollock catches in flatfish trawls. The new net is supposed to allow pollock to escape the net unharmed through an open panel in the intermediate section of the trawl.

High discards have created a great need for innovative methods that reduce pollock bycatch in flatfish trawls.  Although some pollock discards are required by directed fishing regulations, most is discarded by H&G vessels due to its low price compared to flatfish and the limited frozen product hold capacity on the smaller vessels.  Starting in 1998, however, all pollock must be retained in Bering Sea/Aleutian Island and Gulf of Alaska groundfish fisheries, creating a new incentive to avoid catching pollock.

In order for most head and gut vessels to survive economically under the new regulations, it is critical that the fleet devise ways to avoid catches of pollock. Preliminary evidence from NMFS gear research (Rose 1995), suggested that an opening in the net intermediate would significantly reduce pollock bycatch by allowing the fish to swim out of the net while preventing the escape of target flatfish species. Groundfish Forum decided to apply for a permit to test this new net under actual fishing conditions.

The Test

In August 1997, six H&G vessels that applied to participate in the experiment, made 25 tows with both the open intermediate and traditional gear. Vessels in the experiment had two NMFS observers on board to sample all tows and record species and size composition data, which would be used to compare gear effectiveness. During some tows, nets were also equipped with low-light underwater cameras to observe the effectiveness of the open top intermediate during the experiment.

Preliminary Results

Data from the experiment are currently being compiled and analyzed. Preliminary results indicate that the performance of the open top intermediate depended greatly on the location of the opening and towing speed. Although statistical analyses are still being undertaken, it appears that the rate of reduction in pollock bycatch may be as great as 50-60% on some vessels and less than 10% on others. All vessels caught less flatfish with the new net but in some cases the reduction in pollock may have outweighed the reduction in flatfish; indicating that the open top device was of some benefit. A more refined statistical analysis will hopefully reveal the reasons why the device failed on some vessels as well as identifying the ideal placement and towing speed combinations.