Seasonal Variation in Trawl Codend Selectivity for Annular Sea Bream (Diplodus annularis L., 1758)
This study investigated the selectivity of a 40 mm mesh size polyethylene codend commonly used by Turkish demersal trawlers. Seasonal selectivity data were collected for annular sea bream (Diplodus annularis), which is the most abundant discard species in the catch composition in Gülbahçe Bay. 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). The selectivity of the same codend was tested under very similar conditions except for the seasonal variables. The data were obtained using the covered codend technique, and analysed by logistic equation with the maximum likelihood method. Parameters of mean curves for each trip were estimated using Fryer's between haul variation model. The results show that although there is a pattern of decrease in selectivity from summer (L50 = 9.3 cm, SR = 0.9 cm) to autumn (L50 = 9.2 cm, SR = 0.9 cm), winter (L50 = 8.9 cm, SR = 1.1 cm) and spring (L50 = 8.7 cm, SR = 1.1 cm), seasonal differences in selectivity for annular sea bream are not very high.
Seasonal Variation in Trawl Codend Selectivity for Annular Sea Bream (Diplodus annularis L., 1758)
This study investigated the selectivity of a 40 mm mesh size polyethylene codend commonly used by Turkish demersal trawlers. Seasonal selectivity data were collected for annular sea bream (Diplodus annularis), which is the most abundant discard species in the catch composition in Gülbahçe Bay. 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). The selectivity of the same codend was tested under very similar conditions except for the seasonal variables. The data were obtained using the covered codend technique, and analysed by logistic equation with the maximum likelihood method. Parameters of mean curves for each trip were estimated using Fryer's between haul variation model. The results show that although there is a pattern of decrease in selectivity from summer (L50 = 9.3 cm, SR = 0.9 cm) to autumn (L50 = 9.2 cm, SR = 0.9 cm), winter (L50 = 8.9 cm, SR = 1.1 cm) and spring (L50 = 8.7 cm, SR = 1.1 cm), seasonal differences in selectivity for annular sea bream are not very high.
___
- Tosunoğlu, Z., Özbilgin, Y.D., Özbilgin, H.: Body shape and trawl codend selectivity for nine commercial fish species. J. Mar. Biol. Assoc. UK., 2003; 83: 1309-1313. 2. Metin, C., Tosunoğlu, Z., Tokaç, A., Lök, A., Aydın, C., Kaykaç, H.: Seasonal variations of demersal fish composition in Gülbahçe Bay (Izmir Bay). Turk. J. Zool., 2000; 24: 437-446. 3.
- Devlet İstatistik Enstitüsü, Su Ürünleri İstatistikleri 2001. T.C.
- Baflbakanlık Devlet İstatistik Enstitüsü, Ankara, 62 s., 2003. 4.
- Tarım ve Köyiflleri Bakanlığı, Denizlerde ve içsularda ticari amaçlı
- su ürünleri avcılığını düzenleyen 2002-2004 av dönemine ait 35/1
- numaralı sirküler. T.C. Tarım ve Köyiflleri Bakanlığı, Koruma ve
- Tosunoğlu, Z., Özbilgin, H., Tokaç, A.: Effects of the protective bags on the codend selectivity in Turkish bottom trawl fishery. Arch. Fish. Mar. Res., 2003; 50: 239-252.
- Wileman, D.A., Ferro, R.S.T., Fonteyne, R., Millar, R.B. (eds.): Manual of Methods of Measuring the Selectivity of Towed Fishing Gears. ICES Cooperative Research Report, No. 215, Copenhagen, 126 p., 1996.
- Tosunoğlu, Z., Tokaç, A., Lök, A., Metin, C.: Trol seçicilik arafltırmalarında kullanılan örtü torba yönteminin farklı iki tekniğinin torba seçiciliğine etkilerinin karflılafltırılması. Turk. J. Vet. Anim. Sci., 1997; 21: 449-456.
- Tokai, T.: Maximum likelihood parameter estimates of a mesh selectivity logistic model through SOLVER on MS-Excel. Bull. Jpn. Fish. Oceanog., 1997; 61: 288-298.
- Fryer, R.J.: A model of between-haul variation in selectivity. ICES J. Mar. Sci., 1991; 48: 281-290.
- Kınacıgil, H.T., Akyol, O.: Effects on trawl selectivity of growth and reproduction in Diplodus annularis L. of Izmir Bay (Aegean Sea). Arch. Fish. Mar. Res., 2001; 49: 19-26.
- Özbilgin, H.: The seasonal variation of trawl codend selectivity and the role of learning in mesh penetration behaviour of fish. PhD Thesis in Department of Zoology, University of Aberdeen, Scotland, UK, 206 p., 1998.
- He, P.: Swimming speeds of marine fish in relation to fishing gears. ICES Mar. Sci. Symp., 1993; 196: 183-189.
- Özbilgin, H., Wardle, C.S.: Effect of seasonal temperature changes on the escape behaviour of haddock, Melanogrammus aeglefinus, from the codend. Fish. Res., 2002; 58: 323-331.
- Özbilgin, H.: Effect of temperature change on the maximum swimming speed of whiting, Merlangius merlangus (Linnaeus, 1758), Turk. J. Zool., 2002; 26: 255-262.
- Gurbet, R.: Farklı dip trol ağlarının seçiciliği üzerine arafltırma. E.Ü. Arafltırma Fon Saymanlığı, 1990/SUFA/003 Nolu Proje, Bornova-İzmir, 86 s., 1993.
- Lök, A., Tokaç, A., Tosunoğlu, Z., Metin, C., Ferro, R.S.T.: The effects of different codend design on bottom trawl selectivity in Turkish fisheries of the Aegean Sea. Fish. Res., 1997; 32: 149- 156.
- Tokaç, A., Tosunoğlu, Z.: Ağ göz flekli ve balık vücut formu arasındaki iliflkinin trol ağları seçiciliğindeki önemi. Akdeniz Balıkçılık Kongresi, (ed. B. Hoflsu), E.Ü. Su Ürünleri Fakültesi, ss. 51-58, İzmir, 1997.
- Tosunoğlu, Z.: Türkiye denizlerinde kullanılan dip trol ağlarında torba seçiciliğini arttırmaya yönelik yapısal uygulamalar. Doktora Tezi, E.Ü. Fen Bilimleri Enstitüsü, Su ürünleri Avlama ve İflleme Teknolojisi Bölümü, Bornova-İzmir, 121 s., 1998.
- İlkyaz, A.T., Metin, C., Kınacıgil, H.T.: Örtü torba yöntemi ile örneklenen sürütme ağlarında seçicilik parametrelerinin hesaplanması üzerine bir bilgisayar programı (L50 Sürüm:1.0.0). Ege Üniv. Su Ürün. Derg., 1998; 15: 305-314.