Survival of young gadoids excluded from a shrimp trawl by a rigid deflecting grid

Abstract

The survival of one-year-old cod (Gadus morhua), haddock (Melanogrammus deglefinus) and whiting (Merlangius merlangus), excluded from a shrimp trawl by a diagonal metal grid placed in front of the codend (the Nordmore grid), was studied during June 1993 and 1994. Fish leaving the gear in front of this grid during trawling were retained by a net covering the fish outlet, and led into a collecting cage. The collecting cages were released from the trawl at the fishing depth and anchored for 5 to 12 days. The fish in the cages were then observed daily by underwater television, and in the second season also by divers. The escapees from separate trawl hauls were analysed for body damage. 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 incidence of these factors. No correlation was observed between fish size and the amount of scale loss.