Vulnerability to predation of small cod (Gadus morhua) that escape from a trawl

Abstract

Studies of the vulnerability to gear damage of fish that have been caught in a trawl but have escaped through the codend meshes have focussed on determining survival rates. This study examines the risk of predation in small cod (Gadus morhua) (18.2 cm mean total length) escaping a small-scale trawl. Trawling was simulated in a circular tank by towing a small mock-up of a trawl (70 mm codend meshes) for 30 minutes. Escaped fish were retained in a small-meshed net (16 mm) covering the codend. After each towing period, three or four of these fish and the same number of fish from a control group were immediately transferred to a tank holding five large. cod (56.3 cm mean total length). Predation by the large cod was recorded for 30 min or until 50% of the small cod had been taken. In a total of nine experiments, equal numbers of escaping fish and fish from the control group were eaten by the large cod. This indicates that small cod escaping from a trawl do not have increased risk of predation under these experimental conditions. However, the stressed fish were not physically exhausted and the predation experiment was conducted under conditions where the predator could easily capture both stressed and control fish.