Effect of tow duration on length composition of trawl catches

Published source details Godø O.R., Pennington M. & Vølstad J.H. (1990) Effect of tow duration on length composition of trawl catches. Fisheries Research, 9, 165-179.
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This study is summarised as evidence for the following.

	Action	Category
	Reduce duration of fishing gear deployments Action Link

Reduce duration of fishing gear deployments

A replicated, paired, controlled study in 1985–1989 in three areas of seabed in the Barents Sea and Atlantic Ocean off Norway and USA (Godø et al. 1990) found that shorter bottom trawl tow durations did not improve the size-selectivity of Atlantic cod Gadus morhua, haddock Melanogrammus aeglefinus and long rough dab Hippoglossoides platessoides, and more small cod but not haddock were caught, for different tow durations between 5 min to 2 h. Across all three trials, the average fish length was similar between tow durations, for cod (trials 1 & 2, 15 min: 26–32 cm, 30 min: 29–32 cm, 60 min: 32–35 cm; trial 3, 5 min: 50 cm, 30 min: 50 cm), haddock (trials 1 & 2, 15 min: 18–33 cm, 30 min: 17–33 cm, 60 min: 19–32 cm, 120 min 33 cm; trial 3, 5 min: 27 cm, 30 min: 27 cm, 120 min: 33 cm) and long rough dab (trials 1 & 2 only, 15 min: 24–26 cm, 30 min: 24–25 cm, 60 min: 32–35 cm). In addition, in two of two trials there were no differences in catch rates of small haddock between tow durations (5–60 min), however, the catch rates of small cod increased with decreasing shorter tow durations (see original paper for data). Two trials (one and two) were done in the Barents Sea in October 1988 (nine parallel deployments by two vessels: three each of 15, 30 and 60 min) and February 1989 (24 deployments: 16 × 5 mins and 8 × 30 mins). Additional data from a trial on the Georges Bank in January 1985 (trial three)was also analysed (64 deployments: two each of 15, 30, 60 and 120 min at eight stations). Tow durations were based on the standard tow duration for trawl surveys (from 30 min to 2 h).

(Summarised by: Chris Barrett)