Selection and survival in the Norwegian shrimp trawl fisheries

Abstract

Shrimp trawling has aiways been associated with large bycatches. The problems are solely due to the small mesh sizes generally used in shrimp trawl compared to mesh size in trawls used for various groundfish. During the last 25 years, a lot of experiments have been performed to reduce the bycatch in shrimp trawl, but so far one has only partly managed to solve the problem. It still remains to develop devices that effectively separate small fish from shrimp and small shrimp from larger shrimp, that is a combined solution for species and size selection in shrimp trawl. I The survival of one-year-old cod (Gadus morhua), haddock (Melanogrammus I aeglefinus) and whiting (Mer1rn1~ti.sm eriangius), excluded fiom a shrirnp trawl by a diagonal metal grid placed in front of the codend (the Northmrre grid), was studied during June 1993 and 1994. Fish leaving the gear in fiont of this grid during trawling were retained by a net covering the fish outlet, and led into a I - collecting cage. The colleding cages were released from the trawl at the fishing daily by underwater television, and in the second season aiso by divers. The escapees from separate trawl hauk were anaiysed for body darnage. No mortality was found among the young gadoids during the observation period, except for one haddock in the control group. There were almost no visible skin injuries or scale loss in cod, while in whiting and haddock there was a significantly larger occurence of these factors. No correlation was observed between fish size and the amount of scale loss.