Catching cod for tagging experiments

Abstract

The purpose of this study was to evaluate fishing gears designed to catch live cod in order to tag a representative part of the cod populations in two fjords in northern Norway. Hand line, fish pots and fyke nets were used at shallow rocky bottom (<50 m depth); in deeper waters, bottom and pelagic trawls were used. Fish pots were more efficient in catching cod than both hand line and fyke nets. Fish pots and hand line caught cod which mostly ranged from 30 to 50 cm in length, in contrast to fyke nets which caught smaller sized cod (10–30 cm in length). More than 90% of the cod longer than 20 cm and captured by passive gears were viable and were tagged and released. For trawl-catches from deep water (>50 m depth), the percentage cod suitable for tagging (66–86%) rose with increasing fish length, but decreased with depth of capture. In passive gears (hand line, fish pot and fyke net), cod made up 60–70% of the catches, while in bottom trawl catches the proportion of cod ranged from 30% to 80%. The non-targeted species caught by hand line were exclusively gadoids, while fish pots and fyke nets also caught pleuronectid flatfishes. We conclude that fish pots, hand line and fyke nets can be used successfully to catch live cod for tagging in areas where the use of trawl, Danish seine and purse seine are restricted or impossible, e.g. at rocky bottom, or in areas with high abundance of non-targeted species.