Escapement of gadoid fish beneath a commercial bottom trawl: Relevanceto the overall trawl selectivity

摘要

Escapement of Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus) and saithe (Pollachius virens) beneath a commercial bottom trawl, rigged with a 60 cm diameter rockhopper gear, was studied in the Barents Sea. The study was performed off the coast of north Norway in March/April 2003. In order to collect the escapees, three sampling bags were attached behind the rockhopper gear. Approximately one third of the cod and a quarter of the haddock available to the trawl escaped. Cod escape rates were highly length-dependent, following a sigmoid curve with an estimated length at 50% escape of 38.5 cm and interquartile width of 34.1 cm. Length dependence was less pronounced in haddock. The escape rate of saithe was not length-dependent, and on average 7% passed under the trawl's fishing line. Fish abundance had no observable effects on escape rates. Both video observations and scale abrasions on the fish caught in the collecting bags showed that some of the escaped fish had been overrun by the gear.