The effects of different cod-end design on bottom trawl selectivity in Turkish fisheries of the Aegean Sea

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.

Section: Discussionsupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

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Eryaşar¹,

Özbilgin²,

Gökçe³

et al. 2014

“…It was due to the number of meshes around codend circumference as in 40T1 and 44T2. Findings from narrow codends provide higher L50 values like for some other species given by different study conducted in the Mediterranean waters (Lök, Tokaç, Tosunoğlu, Metin, & Ferro, 1997;Özbilgin, Tosunoğlu, Aydin, Kaykaç, & Tokaç, 2005;Sala, Priour, & Herrmann, 2006;Kaykaç, 2007;Luchetti, 2010 and. On the other hand, 40T1 and 44T1 showed to come close to the length at first capture value of L50 12.7 and 13.2 cm, considering the size at LFM (13 cm) of bogue.…”

Section: Discussionmentioning

confidence: 62%

Untitled

Ilkyaz¹,

Sensurat²,

Dereli̇³

et al. 2017

This study investigated the selectivity of 90° turned meshes of 40 mm mesh size with 165 meshes around codend circumferences (40T1), 44 mm meshes size with 300 meshes around codend circumferences (44T1) and 44 mm mesh sizes with 150 meshes around codend circumferences (44T2). Experiments were carried out in the Kuşadası Bay of the Eastern Mediterranean, between 19 January and 29 March 2015 with commercial stern trawler. Selectivity data were collected using the covered codend method and analysed by means of a logistic equation with the maximum likelihood method. Individual hauls and mean selectivity parameter were estimated by using the CC2000 and EC-Modeller software, respectively. The mean 50% retention total length values (L50) and selection range (SR) were 12.7 cm and 2.3 cm for 40T1, 13.2 cm and 3.5 cm for 44T1 and 13.8 cm and 3.0 for 44T2, respectively. Significant differences were determined among the L50 values of the codends (between 40T1 and 44T2) (P<0.05). However, there are no statistical difference between the 40T1 and 44T1, 44T1 and 44T2 (P>0.05). On the other hand, L50 values of 40T1 and 44T1 are very close considered to the 13 cm length at first maturity size of the species.

“…There are many studies carried out on the selectivity of red mullet in the Mediterranean and particularly, in the eastern Aegean Sea (Ferretti and Froglia, 1975;Kınıkarslan, 1976;Livadas, 1988;Jukic and Piccinetti, 1988;Gurbet, 1992;Stergiou et al, 1994;Gurbet et al, 1997;Lök et al, 1997;Tokaç and Tosunoğlu, 1997;Tosunoğlu et al, 1997;Tokaç et al, 1998;Çıra, 1999;Tosunoğlu, 2000;Akyol et al, 2000;Kınacıgil et al, 2001;Fiorentini and Leonori, 2002;Özbilgin and Tosunoğlu, 2003;Tosunoğlu et al, 2003a;Tosunoğlu et al, 2003b). Results obtained in these studies are rather variable.…”

Section: Discussionmentioning

confidence: 99%

Untitled

Özbilgin¹,

Tosunoğlu²,

Tokaç³

et al. 2011

Seasonal changes in the selectivity of 40 mm PE codend were investigated in the Eastern Aegean Sea. Selectivity of the same codend was tested for red mullet (Mullus barbatus), by using the same vessel, fishing ground, towing speed and duration. Four sets of data were collected in spring (4-18 April 2002), summer (10-25 July 2002), autumn (26 September-2 October 2002) and winter (22-23 January 2003). Data were obtained by using covered codend technique, and analysed by using logistic equation with the maximum likelihood method. Four sets of selection curves were analysed and compared using the model developed by Fryer. To investigate the seasonal changes in the condition of the fish, length and weight data were collected from samples taken to cover the whole length range in the catch. Results show that estimate of L 50 in spring is significantly lower than those for other seasons (P<0.05). There is about 10% difference between the mean L 50 values of the best and the poorest seasons, summer (11.1 cm) and spring (10.1 cm), respectively. The L 50 values of autumn (10.8 cm) and winter (11.0 cm) lay between these two. Fish were in their best condition and the water temperature was at its highest point of the annual cycle in autumn. Balığın kondüsyon faktöründeki mevsimsel değişimleri araştırmak amacıyla avdaki tüm boy aralığını kapsayacak şekilde alınan örneklerden boy ve ağırlık verisi toplanmıştır. Sonuçlar ilkbaharda hesaplanan L 50 'nin diğer mevsimlerdekinden belirgin derecede daha düşük olduğunu göstermektedir (P<0,05). En iyi ve en düşük L 50 değerleri arasında, sırasıyla yaz (11,1 cm) ve ilkbahar (10,1 cm), yaklaşık %10'luk bir fark vardır. Sonbahar (10,8cm) ve kışın (11,0 cm) L 50 değerleri bu iki değerin arasında kalmaktadır. Sonbaharda balıklar en iyi kondüsyon faktöründe ve su sıcaklığı yıllık döngüsünün en yüksek değerindedir.Anahtar Kelimeler: Trol seçiciliği, örtü torba, Ege Denizi.