The effect of twine thickness on cod-end selectivity of trawls for haddock in the North Sea

Lowry, Nicholas; Robertson, Julie

doi:10.1016/0165-7836(95)00418-1

Cited by 54 publications

(49 citation statements)

References 4 publications

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“…It was determined that various factors can affect the selectivity, such as, twine material (Tokaç et al, 2004) and thickness (Lowry and Robertson, 1996;Herrmann and O'Neill, 2006;Sala et al, 2007), codend circumference (Reeves et al, 1992;Broadhurst and Millar, 2009;Hermann et al, 2007;Graham et al, 2009;Wienbeck et al, 2011), towing speed (Dahm et al, 2002). Apart from these, total and codend catch, and species catch and haul durations which were evaluated in the present study affected L50 and SR values (Table 6).…”

Section: Discussionmentioning

confidence: 99%

Untitled

Dereli̇¹,

Aydın²

2016

Turk. J. Fish. Aquat. Sci.

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This paper compares the selectivity of 44 mm diamond mesh codend used in commercial fisheries (D44) and alternative codends 50 mm diamond (D50), a 40 mm square (S40) and a 40 mm 90° turned mesh (T40) for red mullet Mullus barbatus, European hake Merluccius merluccius, Morocco dentex Dentex maroccanus, Atlantic horse mackerel Trachurus trachurus in the Eastern Mediterranean demersal trawl fishery. Sea trials were carried out in the international waters between Turkey and Greece (Aegean Sea), with commercial trawler. Selectivity data were collected using the covered codend method and analysed by means of a logistic equation with the maximum likelihood method. Mean selection curves were estimated and compared using the between-haul variations model. The mean 50% retention total length values (L50) of D44, D50, S40 and T40 codends are 11.1, 12.9, 12.9 and 13.6 cm for red mullet, 12.3, 14.4 and 14.3 cm for hake, 10.0, 10.7, 10.3 and 8.4 cm for Morocco dentex and 16.2, 14.2, 15.3 and 17.1 cm for mackerel, respectively. The results show that there are statistically differences between L50 values of four codends for only red mullet. S40 and T40 codends improve the selectivity of red mullet when considering commercially D44 codend.Keywords: Codend selectivity, mesh shape, Eastern Mediterranean, demersal trawl. Doğu Akdeniz Dip Trol Balıkçılığında Dört Tür İçin Ticari ve Alternatif Torbaların Seçiciliği ÖzetBu çalışmada Doğu Akdeniz demersal trol balıkçılığında ticari olarak kullanılan 44 mm baklava gözlü torba (D44) ile 50 mm baklava gözlü (50D), 40 mm kare gözlü (S40) ve 40 mm 90° döndürülmüş (T40) alternatif torbaların barbunya Mullus barbatus, bakalyaro Merluccius merluccius, Fas mercanı Dentex maroccanus ve istavrit Trachurus trachurus için seçicilikleri karşılaştırılmıştır. Denemeler ticari trol teknesi ile Türkiye ile Yunanistan arasında kalan uluslararası sularda (Ege Denizi) yürütülmüştür. Seçicilik verisi çemberli örtü torba tekniği ile toplanmış ve lojistik eşitliğin maksimum olabilirlik yöntemi ile analiz edilmiştir. Ortalama seçicilik eğrileri, çekimler arası varyasyon modeli kullanılarak tahmin edilmiş ve karşılaştırılmıştır. D44, D50, S40 ve T40 torbalarındaki ortalama % 50 yakalama boyları (L50) barbunya için sırasıyla 11,1; 12,9; 12,9 ve 13,6 cm, bakalyaro için 12,3; 14,4 ve 14,3 cm, Fas mercanı için 10,0; 10,7; 10,3 ve 8,4 cm ve istavrit için 16,2; 14,2; 15,3 ve 17,1 cm olarak tespit edilmiştir. Bulgular, dört torbanın L50 değerleri arasında istatistiksel farkın sadece barbunya için bulunduğunu göstermektedir. S40 ve T40 torbalar, ticari olarak kullanılan D44 torbaya göre barbunyanın seçiciliğini geliştirmiştir.Anahtar Kelimeler: Torba seçiciliği, göz şekli, Doğu Akdeniz, demersal trol.

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Section: Discussionmentioning

confidence: 99%

Untitled

Dereli̇¹,

Aydın²

2016

Turk. J. Fish. Aquat. Sci.

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“…However, the 2003 comparison of the grid system (grid and 135 mm codend) with a 155 mm mesh codend might be confounded by the fact that the 155 mm codend was made of 6 mm double PA while the 135 mm codend was made of double 5 mm PE (the di erence due to logistic reasons). Material type and twine thickness have both been found to a ect L 50 for diamond meshes (Ferro and O'Neill, 1994;Lowry and Robertson, 1996;Kynoch et al, 1999). If the 155 mm codend had been made of a di erent material (e.g.…”

Section: Discussionmentioning

confidence: 99%

“…Parameters other than mesh size that a ect codend selectivity, such as twine thickness (Lowry and Robertson, 1996), codend extension length and codend diameter (Reeves et al, 1992) are not regulated. Such regulations would have to be considered in case the grid regulations will be abolished.…”

Section: Discussionmentioning

confidence: 99%

Size selection of cod by rigid grids—Is anything gained compared to diamond mesh codends only?

et al. 2006

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Size selective grids were introduced into the Barents Sea demersal trawl shery in 1997. It was believed at the time that in comparison to standard diamond mesh codends, grids had better selective properties, i.e. narrower selection range. Few studies have directly compared the selective properties of the combined grid and codend with that of the codend only. In this study we describe two experiments carried out in 2002 and 2003, where we directly compared the properties of codend selectivity for cod (Gadus morhua ) with the combined selectivity of a Sort-V grid and a codend. In 2002 we used small-meshed covers, whereas the twin trawl method was used in 2003. In both experiments we compared the selectivity of a 135 mm codend only with that of a trawl tted with a 135 mm codend and a 55 mm grid, which is the mandatory con guration. In 2003 we also estimated the selectivity of a 155 mm diamond mesh codend, having an L 50 similar to that of the grid and 135 mm codend combination. The results presented no evidence that the grid and mesh combination had sharper size selection than codend meshes. The introduction of the mandatory use of grid in the shery in 1997 therefore only increased L 50 , and corresponded to a mesh size increase of around 20 mm. Mean selection length of the grid was inversely related to catch rates in the 2002 experiment when large catches were taken. Grid selection appeared less a ected by seasonal variations in degree of stomach fullness or condition than mesh selectivity. Other situations where grid selection might perform better than mesh selection are discussed.

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“…6). Although prawncatching gears are constructed using similarlyproportioned mesh sizes (e.g., Vendeville 1990;Broadhurst et al 2000Broadhurst et al , 2003aSobrino et al 2000), variables such as the volume of netting attached to the fishing line (i.e., the hanging ratio), thickness of twine, angle of body taper, towing speed, and weight of catch in the codend ensures that meshes open at a fraction of their overall size (Reeves et al 1992;Lowry & Robertson 1996;Lök et al 1997;Broadhurst et al 2000). For example, underwater observations of codends and extension sections in demersal trawls have revealed lateral mesh openings typically between 0.15 and 0.25 of the stretched mesh length (Robertson 1986).…”

Section: Discussionmentioning

confidence: 99%

Atypical size selection of captive school prawns,Metapenaeus macleayi, by three recreational fishing gears in south‐eastern Australia

Broadhurst¹,

Millar

Young

et al. 2004

New Zealand Journal of Marine and Freshwater Research

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Three manipulative experiments were done to estimate the selectivity of conventional and new sizes and configurations of mesh for school prawns, Metapenaeus macleayi, in three south-eastern Australian recreational fishing gears (haul, push, and scoop nets). The treatment meshes examined were: (1) conventional-sized, diamond-shaped mesh used in all gears (20 mm in scoop nets and 30 mm in push and haul nets); (2) 30 mm in scoop nets; and (3) 40-mm diamond-and (4) quantities of school prawns (6-24 mm carapace length (CL)) were placed in purpose-built enclosures, monitored to ensure no experimental-induced stress (as measured by changes in L-lactate in their haemolymph) and the replicate treatments of the various gear configurations deployed. Escapees from the various treatment nets were collected from the enclosures using fine-meshed nets. Logistic selection curves were derived for all treatment nets and specific comparisons made within and among gears. All nets had 50% retention lengths (L 50 ) comparable to other penaeid-catching gears with similar mesh sizes, but most had selection ranges (SRs) that were atypically inflated. The large SRs were attributed to a combination of factors that included the mesh geometry and towing speed of the gears and the behaviour of school prawns. The 20-mm scoop net had the smallest selection parameters, retaining >99% of individuals larger than 13 mm CL. Mesh size in this gear would need to be increased to at least 30 mm to allow some maturing prawns (>18 mm CL) to escape.

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The effect of twine thickness on cod-end selectivity of trawls for haddock in the North Sea

Cited by 54 publications

References 4 publications

Untitled

Untitled

Size selection of cod by rigid grids—Is anything gained compared to diamond mesh codends only?

Atypical size selection of captive school prawns,Metapenaeus macleayi, by three recreational fishing gears in south‐eastern Australia

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