Effect of mesh size and codend circumference on selectivity in the Mediterranean demersal trawl fisheries

Sala, Antonello; Lucchetti, Alessandro

doi:10.1016/j.fishres.2011.04.012

Cited by 54 publications

(47 citation statements)

References 22 publications

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“…This finding is consistent with the results of the other studies conducted in the Mediterranean waters (Lök et al, 1997;Özbilgin et al, 2005;Sala et al, 2006;Kaykaç, 2007;Sala and Luchetti, 2010;. The only common species between the present and the other studies (Lök et al, 1997;Sala et al, 2006;Kaykaç, 2007;Sala and Luchetti, 2011) is the red mullet for which all the investigations clearly conclude that the narrow codend has higher L 50 values. However, because of the differences in the mesh material, mesh size, mesh diameter, presence and types of knots, number of meshes around the codend and tunnel, towing duration and populations fished, the results of the present study and the other investigations on the effect of codend circumference on selectivity are not directly comparable in terms of selection parameters.…”

Section: Discussionsupporting

confidence: 93%

“…In general, for the same mesh size, reducing the number of mesh around the codend might improve codend selectivity (Reeves et al, 1992;Broadhurst and Kennelly, 1996;Lök et al, 1997;Broadhurst et al, 2004;Özbilgin et al, 2005;Sala and Luchetti, 2011). Because during the haul, when the codend fills, diamond meshes elongate under tension, the end meshes are blocked, water flow is diverted and the codend forms a typical bulge which expands to a maximum diameter (Robertson and Stewart, 1988).…”

Section: Introductionmentioning

confidence: 99%

“…Underwater observations show that most of the fish mainly escape through open meshes just in front of the bulge and meshes ahead of these are partially or totally closed along the length of the codend, which leads to retention of juveniles of round-bodied fish (Özbilgin et al, 2005). Narrow codends should expand to form a smaller bulge and it takes less time to achieve the maximum diameter (Sala and Luchetti, 2011). As a result of this, with reduced number of meshes around the codend, the individual meshes should be more open during the tow (Robertson and Emslie, 1985).…”

Section: Introductionmentioning

confidence: 99%

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Eryaşar¹,

Özbilgin²,

Gökçe³

et al. 2014

Turk. J. Fish. Aquat. Sci.

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Poor selectivity and high discard rate of hand-woven slack knotted codend is a serious problem for north eastern Mediterranean demersal fish stocks. This study investigates the effect of codend circumference on bottom trawl selectivity for red mullet (Mullus barbatus), bogue (Boops boops), goldband goatfish (Upeneus moluccensis), Randall's threadfin bream (Nemipterus randalli) and picarel (Spicara smaris). A total of 18 valid hauls were conducted using covered codend method between 08 October and 26 December 2012 in Mersin Bay. Results show that selectivity of commercially used standard codend (300 meshes around its circumference) is rather poor and the narrow codend (150 meshes around its circumference) significantly increases selectivity for tested species. However, it is not selective enough to avoid the individuals of five commercial species under the MLS or FMS.Keywords: Narrow codend, trawl selectivity, hand-woven slack knotted codend, Mersin Bay. Kuzey Doğu Akdeniz Demersal Trol Balıkçılığında Torba Çevresinin El Örmesi Gevşek Düğümlü Torba Seçiciliğine Etkisi ÖzetEl örmesi gevşek düğümlü torbanın zayıf seçiciliği ve yüksek ıskarta oranı Kuzey Doğu Akdeniz demersal balık stokları için ciddi bir problemdir. Bu çalışmada torba çevresindeki göz sayısının dip trol seçiciliği üzerine olan etkisi barbun (Mullus barbatus), kupes (Boops boops), Nil barbunyası (Upeneus moluccensis), merbun (Nemipterus randalli) ve izmarit (Spicara smaris) için araştırılmıştır. Mersin Körfezi'nde 08 Ekim ve 26 Aralık 2012 tarihleri arasında örtü torba yöntemi kullanılarak toplam 18 çekim gerçekleştirilmiştir. Sonuçlar test edilen türler için ticari olarak kullanılan standart torbanın (çevresinde 300 göz olan) seçiciliğinin çok zayıf olduğunu ve dar torbanın (çevresine göz sayısı 150 olan) seçiciliği önemli ölçüde arttırdığını göstermektedir. Bununla birlikte, dar torba beş ticari tür için minimum yakalanma boyu veya ilk üreme boyunun altındaki bireyleri kaçırmada yeterince seçici değildir.Anahtar Kelimeler: Dar torba, trol seçiciliği, el örmesi gevşek düğümlü torba, Mersin Körfezi.

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Section: Discussionsupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Untitled

Eryaşar¹,

Özbilgin²,

Gökçe³

et al. 2014

Turk. J. Fish. Aquat. Sci.

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“…In general, the codend catch size did not have a significant effect on L 50 or SR values of the fish species Merluccius merluccius , Merlangius merlangus, Trisopterus minutuscapelanus, Mullus barbatus and Pagellus erythrinus analysed by Sala et al. () and Sala and Lucchetti (). Sala, Lucchetti, Piccinetti, and Ferretti () report a positive effect of mesh configuration on L 50 , and a small but significant negative influence on catch size and depth on SR for P. longirostris .…”

Section: Discussionmentioning

confidence: 71%

Selectivity of 50 mm T0 and T90 codends for commercial shrimp species in the Turkish deepwater trawl fishery, Eastern Mediterranean

2016

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Summary The study compared the selectivity of 50 mm mesh size conventional (T0) and 90° turned mesh (T90) demersal trawl codends for four commercial shrimp species (Aristaeomorpha foliacea, Aristeus antennatus, Parapenaeus longirostris and Plesionika martia) in the Bay of Antalya in the eastern Mediterranean. Data were collected from 27 valid hauls using the covered codend method. Selectivity parameters were obtained using the logistic equation with the maximum likelihood method and by taking into account the between‐haul variations. Results show that changing the codends from T0 to T90 increases the percentage of escapees for all four targeted shrimp species. According to species, a change in the mesh configuration significantly increases L50 by 7–14%. However, for the two commercially important red shrimp species (Aristaeomorpha foliacea and Aristeus antennatus), even the L50 values obtained in the T90 codend (23.3 mm) remain rather low for the release of sufficient numbers of immature specimens. First maturity sizes (FMS) for these two species are 38 and 30 mm, respectively; therefore, for their sustainable exploitation, additional management measures must be investigated including larger mesh sizes.

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“…Very few empirical data are available describing the effects of SR on penaeid trawls (but see Broadhurst et al 2014b), although it is well established that the SR in benthic-teleost trawls can vary according to a (Sala et al 2008). …”

Section: Optimise Spread Ratiomentioning

confidence: 99%

Modifying penaeid-trawl spreading mechanisms to improve environmental efficiency

McHugh¹

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The environmental efficiency of demersal trawls can be defined within measures of three response variables: (i) species selectivity; (ii) extent and intensity of habitat impacts; and (iii) energy efficiency. All three variables affect all fisheries, but especially those targeting penaeid prawns (or shrimp).Penaeid-trawl fisheries are globally distributed in tropical and temperate latitudes and involve vessels (~8−25 m) towing small-meshed, single-or multi-funnel-shaped nets on the seabed, horizontally spread by hydrovanes (called 'otter boards'), and less commonly, rigid beams. To date, most of the efforts towards improving the environmental efficiency of penaeid trawls have concentrated on gear selectivity specifically, via bycatch reduction devices (BRDs) in the codend (to address i above).Although somewhat effective (30-70% reductions), BRDs offer few perceived benefits to fishers and, in many fisheries, there is resistance to their adoption.It is known that the anterior trawl section affects all three response variables above, which might concomitantly be mitigated through modifications that could potentially provide fishers with a realised benefit-increased energy efficiency (and therefore greater adoption). A primary objective of this thesis was to investigate the potential for holistically improving penaeid-trawl environmental efficiency through research focussed on the anterior section of the gear; specifically the spreading mechanisms (otter boards, sleds, beams and sweeps).The treatments tested comprised three broad categories: (i) revising otter boards and their rigging;(ii) substituting otter boards with a beam; and then (iii) amalgamating key concepts across both methods. Modifications within the first category included removing sweeps and testing a novel otter board (i.e. the batwing). Within the second category, beams were modified in attempts to maintain target catches while minimising bycatch, habitat contact and energy intensity. The third group of modifications involved exploiting the concepts underlying an identified inherently superior species selection of beam trawls to otter trawls via counter-herding devices, termed 'simple anterior fish excluders'-SAFEs.Where appropriate, the treatments were compared against controls for their utility in mitigating the three response variables. The overall results demonstrated that selectivity can be improved (i.e. bycatch reduction) by using a beam trawl, SAFE or by removing sweeps; habitat impacts will be reduced when using batwings; and, while overall energy intensity was not improved, an important component-drag-can be alleviated using a beam trawl or batwing otter boards. For targeted iii catches, the conventional otter trawls caught more total penaeids, but the beam trawls had comparable penaeid catches when corrected for fuel-to-catch ratios.A key conclusion from the thesis is that no single treatment will be effective for significantly improving all three response variables; however, anterior modifications lowering drag (the beam trawl an...

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Effect of mesh size and codend circumference on selectivity in the Mediterranean demersal trawl fisheries

Cited by 54 publications

References 22 publications

Untitled

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Selectivity of 50 mm T0 and T90 codends for commercial shrimp species in the Turkish deepwater trawl fishery, Eastern Mediterranean

Modifying penaeid-trawl spreading mechanisms to improve environmental efficiency

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