Trawl bag selectivity in the Champsocephalus gunnari fishery
Experiments on trawl bag selectivity during fishing on pre-spawning concentrations of Champsocephalus gunnari were carried out in June 1990 in the South Georgia area concurrently with trawl surveys as part of the main biological and oceanic research program. The results presented here are based on 29 hauls and, due to the limited time available for experiments, should be considered as preliminary. L50% was 24.8 cm and the selectivity factor was 3.10 for a mesh size of 80 mm. Comparison of these results with results from previous years demonstrates close similarity. A significant increase in modal length (up to 34-35 cm) as well as earlier sexual maturation of fish were noted. It was suggested that the use of Polish type chafers and a reinforced outer cover on trawl bags reduces the stress on the mesh threads and increases mesh openings therefore enhancing their selectivity properties. Further experiments are recommended in order to fully understand the mechanism involved.