by H. Arnold Carr
This article is reprinted with permission of Commercial Fisheries News, the Northeast's fishing newspaper for over 30 years, ©2003 Compass Publications Inc. Commercial Fisheries News is published monthly; annual subscriptions are $21.95. To subscribe or request a sample issue: call (877) 263-4496; fax (207) 367-2490; e-mail (cfoster@fish-news.com); or click on the hot link.
Capt. Luis Ribas of Provincetown, MA and the Massachusetts Division of Marine Fisheries (DMF) Conservation Engineering staff each had an idea. They were working independently toward the same goal: How to catch flatfish, but not cod and haddock. Each developed their idea and submitted it to the Northeast Consortium for funding.
What resulted was a suggestion by the consortium that Capt. Ribas and DMF team up to test each of the two trawl designs. The award was granted last year to Capt. Ribas and DMF with Manomet Center for Conservation Sciences providing some support.
The beauty of these designs is that they consider the behavior of the fish species encountered and use that as a means to reduce the unwanted regulatory catch.
Both designs use the whole net system. The low vertical profile of the traditional net, the square mesh on the top of one net or the headrope setback of the other net, and the square mesh codend combine to allow escapement of round bodied fish while retaining the targeted flatfish.
The two designs are similar in that they modify the same sections of traditional flatfish nets. Capt. Ribas's design places 8" square mesh in the upper wings and behind the headrope -- all the way to the codend. DMF's design brings the headrope radically back to the extension piece. Both nets then have codends made of 6-1/2" webbing set on the square.
Both modified nets are designed to take advantage of the behavior of cod, haddock, and the target species, the flatfish. First, the flatfish nets have a low headrope height of 6' or less. This low headrope height, even with the headrope set radically back or with the large square mesh, should still maintain the flatfish catch of yellowtail, windowpane, winter flounder, American plaice, and skate.
The cod and haddock, however, typically rise up in the mouth of the net. The haddock are known to do this in a dramatic way, whereas the cod rise in a more subtle manner. The design of both nets is intended to give these species a chance to escape before they actually enter the codend. The 6-1/2" mesh in the codend then provides a further means of escape for the smaller or sublegal cod.
The idea of using a big piece of large square-mesh webbing on the net or dropping the headrope far back toward the codend have been seen before. Last year, Capt. Charlie Saunders in Maine successfully tried large square mesh pieces to reduce the catch of cod. The headrope design has also had some success in Europe.
Sea trials
DMF has and will continue to acquire more data on the two modified nets through underwater video observations and sea sampling the catch.
DMF's hardwire underwater video system, which is supported by a third winch on deck, is providing the means to observe the nets and the behavior of the fish around the mouth of the nets.
The catches of the two modified trawl nets are being compared to the traditional flatfish trawl net on a tow-by-tow basis and using standard sea sampling protocol. Each tow of one of the modified nets is compared to a tow of the traditional, or control, net in an alternating tow fashion.
Initial sea trials were undertaken aboard Capt. Ribas's fishing vessel Blue Skies between November and January. Underwater video observations and sea sampling of the catch done during the trips supported the expected behavior of these species. The target catch of flatfish does not appear to be reduced. The cod, which would be more problematic than haddock, was the only roundfish species observed and identified with the underwater video and they did escape.
How cod escaped
The escape path was seen by video observations to be over the headrope for many of the cod. Some of the cod, primarily the smaller ones, went into the net and escaped through the square mesh codend.
Capt. Ribas predicted a 70%-90% reduction in cod catch between the traditional flatfish net and his modified design. The first series of paired tows between the nets tends to support that prediction.
The actual catch data is presently limited and deemed preliminary. We would have liked to catch the fish and relate that directly to the underwater video taken on both nets, but time constraints and the regulatory permit process have precluded that activity to date. Access to the cod, which were in the closed areas when weather allowed video taping, was through a permit that required the codends to remain open.
More sea trails comparing the catch of the two experimental nets with the traditional net are planned for this spring. Sea sampling will provide the means to determine the future and implications of these net designs.
If the designs -- or even one design -- continues to sharply reduce the catch of cod and haddock, the proven net or nets should provide a means to fish for flatfish in the presence of cod. This would then greatly reduce the impact of fishing on cod.
Arne Carr is a senior marine fisheries biologist for the Massachusetts Division of Marine Fisheries.
