Study

Size selectivity of hand and machine woven codends and short term commercial loss in the Northeastern Mediterranean

  • Published source details Özbilgin H., Eryaşar A.R., Gökçe G., Özbilgin Y.D., Bozaoğlu A.S., Kalecik E. & Herrmann B. (2015) Size selectivity of hand and machine woven codends and short term commercial loss in the Northeastern Mediterranean. Fisheries Research, 164, 73-85

Actions

This study is summarised as evidence for the following.

Action Category

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

Action Link
Marine Fish Conservation

Use a larger mesh size

Action Link
Marine Fish Conservation
  1. Modify the design or configuration of trawl gear (mixed measures)

    A replicated, controlled study in 2011 of a fished area of seabed in the Mediterranean Sea, Turkey (Özbilgin et al. 2015) found that three different designs of bottom trawl codend woven by machine instead of by hand, improved size-selectivity and reduced the discarded catches of five commercial fish species compared to a commonly used commercial hand-woven codend. The length at which fish had a 50% chance of escaping was higher in machine-woven codends than hand-woven codends for: red mullet Mullus barbatus (machine: 8–14 cm, hand: 7 cm); brushtooth lizardfish Saurida undosquamis (machine: 23–28 cm, hand: 8 cm); common pandora Pagellus erythrinus (machine: 12–15 cm, hand: 8 cm); goldband goatfish Upeneus moluccensis (machine: 12–21 cm, hand: 5 cm); and Randall’s threadfin bream Nemipterus randalli (machine: 10–14 cm, hand: 6 cm). In addition, the proportions of undersized fish retained for the five species were lower in machine codends compared to the hand codend design, however, there were also increased losses of commercial sizes for some species (see original paper for full data by species). Trials were done with three alternative machine-woven trawl codends (40 mm square mesh; 44 mm and 50 mm diamond mesh) and a commercial hand-woven codend (44 mm diamond mesh) on fishing grounds in Mersin Bay between January-December 2011. Data were collected from a total of 87 individual deployments (20–23 of each of the four codends) onboard a commercial trawler. Tow duration was 80–220 minutes at a speed of 2.3–2.8 knots. A small-mesh cover was fitted over each codend to collect the escaped fish. Catches in the codends and covers were sampled.

    (Summarised by: Rosslyn McIntyre)

  2. Use a larger mesh size

    A replicated, controlled study in 2011 on fishing grounds in Mersin Bay, Mediterranean Sea, Turkey (Özbilgin et al. 2015) found that a larger diamond codend mesh size in a trawl net improved size-selectivity and allowed a greater proportion of undersized and immature fish to escape compared to a smaller mesh size. The length at which fish had a 50% chance of escape was greater with a larger 50 mm mesh codend than a smaller 44 mm mesh codend for five of five species: goldband goatfish Upeneus moluccensis (large: 21 cm, small: 12 cm), red mullet Mullus barbatus (large: 12 cm, small: 8 cm), brushtooth lizardfish Saurida undosquamis (large: 28 cm, small: 23 cm), common pandora Pagellus erythrinus (large: 15 cm, small: 12 cm) and Randall’s threadfin seabream Nemipterus randalli (large: 12 cm, small: 10 cm). The likelihood of being retained in the codend for undersized or immature fish was also lower with the larger mesh for four of four species (data reported as retention efficiencies - see paper for individual data). Data were collected from 41 trawl deployments (80–220 min) in Mersin Bay on a commercial fishing vessel in January–December 2011. Two codends were tested: 50 mm diamond mesh codend (21 hauls, 265 meshes circumference) and a 44 mm diamond mesh codend (20 hauls, 300 meshes circumference). Small mesh covers attached over each codend collected fish escaping through the meshes. All fish in the covers and codends were identified and their lengths measured.

    (Summarised by: Rosslyn McIntyre)

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