Comparison of the selectivities of double and single codends

Published source details Özbilgin H. & Tosunoğlu Z. (2003) Comparison of the selectivities of double and single codends. Fisheries Research, 63, 143-147.
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This study is summarised as evidence for the following.

	Action	Category
	Modify the design or configuration of trawl gear (mixed measures) Action Link

Modify the design or configuration of trawl gear (mixed measures)

A replicated, controlled study in 2002 of seabed in a coastal bay in the Mediterranean Sea, off Turkey (Özbilgin & Tosunoğlu 2003) found that modifying the design of a bottom trawl net (single or double layer codends) resulted in improved size-selectivity and reduced catches of smaller fish in single codends for red mullet Mullus barbatus, annular sea bream Diplodus annularis, and common pandora Pagellus erythrinus, compared to a double layer codend. The length at which fish had a 50% chance of escape was greater in single layer codends than double codends for red mullet (single: 10 cm, double: 9 cm), annular sea bream (single: 9 cm, double: 8 cm) and common pandora (single: 11, double: 8 cm). The total number of fish that escaped capture was higher with a single codend for all three species (red mullet, single: 1,928, double: 599 fish; annular sea bream, single: 304, double: 53 fish; common pandora, single: 381, double: 82 fish). In April 2002, bottom trawl deployments were carried out in Izmir Bay in the eastern Aegean Sea; nine with codends of a single layer of netting (one codend) and nine with double layer codends (one codend mounted around another, see original paper for gear specifications). Gear was towed for 45 minutes at 2.2–2.6 knots and 25–30 m depth. Codends had 200 mesh circumferences and 40 mm mesh size. Covers attached over each codend type collected escaped fish. Both codend and cover catches were sampled, and fish lengths recorded.

(Summarised by: Natasha Taylor)