By-catch in a 40 mm PE Demersal Trawl Codend
Demersal trawling in Turkish waters yields a considerable amount of by-catch and discard. Data presented in this study were collected during a demersal trawl codend selectivity trial carried out on board the RV Egesüf (27 m, 500 HP) between August 9 and September 4, 2002, in İzmir Bay. In total, 52 species of fish and invertebrate from 40 mm nominal mesh size commercially used PE codend and 24 mm cover were identified, separately weighed, and classified as commercial and non-commercial. In addition, for red mullet (Mullus barbatus), hake (Merluccius merluccius), common pandora (Pagellus erythrinus), axillary sea bream (Pagellus acarne), annular sea bream (Diplodus annularis), and picarel (Spicare smaris), length measurements were taken to the nearest half centimeter, and percentages of by-catch, in terms of numbers of individuals, were calculated using Minimum Landing Size (MLS) or, if this was not defined, Length at First Maturity (LFM). Levels of by-catch for these species were also calculated in terms of weight, using length-weight relationships reported in the literature. The results showed that, on average, 63% (93 kg) of codend catch was composed of commercial species, while the rest, 37% (56 kg), was unmarketable species. Moreover, although they are commercial species, 5% of red mullet, 92% of hake, 32% of common pandora, and 33% of axillary sea bream were below MLS in terms of weight. In conclusion, it is stressed that the Aegean Sea demersal trawl fishery has a multi-species nature, its by-catch level is rather high, and therefore there is an urgent need for introducing more selective fishing practices.
By-catch in a 40 mm PE Demersal Trawl Codend
Demersal trawling in Turkish waters yields a considerable amount of by-catch and discard. Data presented in this study were collected during a demersal trawl codend selectivity trial carried out on board the RV Egesüf (27 m, 500 HP) between August 9 and September 4, 2002, in İzmir Bay. In total, 52 species of fish and invertebrate from 40 mm nominal mesh size commercially used PE codend and 24 mm cover were identified, separately weighed, and classified as commercial and non-commercial. In addition, for red mullet (Mullus barbatus), hake (Merluccius merluccius), common pandora (Pagellus erythrinus), axillary sea bream (Pagellus acarne), annular sea bream (Diplodus annularis), and picarel (Spicare smaris), length measurements were taken to the nearest half centimeter, and percentages of by-catch, in terms of numbers of individuals, were calculated using Minimum Landing Size (MLS) or, if this was not defined, Length at First Maturity (LFM). Levels of by-catch for these species were also calculated in terms of weight, using length-weight relationships reported in the literature. The results showed that, on average, 63% (93 kg) of codend catch was composed of commercial species, while the rest, 37% (56 kg), was unmarketable species. Moreover, although they are commercial species, 5% of red mullet, 92% of hake, 32% of common pandora, and 33% of axillary sea bream were below MLS in terms of weight. In conclusion, it is stressed that the Aegean Sea demersal trawl fishery has a multi-species nature, its by-catch level is rather high, and therefore there is an urgent need for introducing more selective fishing practices.
___
- Cook, R.: The Magnitude and Impact of By-catch Mortality by Fishing Gear. In Reykjavik Conference on Responsible Fisheries in the Marine Ecosystem, Reykjavik, Iceland, October 1-4, 2001.
- Alverson, D.L.: Some Observations on the Science of By-catch. MTS Journal, 33, No. 2, 13 p., 2000.
- Bailey, K., Williams, P.G., Itano, D.: By-catch and Discards in Western Pacific Tuna Fisheries: A Review of SPC Data Holdings and Literature. South Pacific Commission, Ocean Fisheries Programme. Technical Report, No. 34, 1996. 4. Crowder L.B., Murawski, S.A.: Fisheries by-catch: Implications for management. Fisheries, 1998; 23: 8-17.
- McCaughran, D.A.: Standardized Nomenclature and Methods of Defining By-catch Levels and Implications. In Proceedings of the National Industry By-catch Workshop, February 4-6, Newport, Oregon. ed. Jacobson R.W.: Natural Resources Consultant Inc., Seattle, Washington. 1992.
- Alverson, D.L., Freeberg, M.H., Murawski, S.A., Pope, J.G.: A Global Assessment of Fisheries By-catch and Discards. FAO Fisheries Technical Paper, No. 339, 323 p., 1994.
- Kelleher, K.: Discards in the world’s marine fisheries: an update. FAO Fisheries Technical Paper, No. 470, Rome, 2004.
- Doğanyılmaz, Y.: Scup (Stenotomus chrysops) balığı hedef dıflı av miktarının azaltılmasına yönelik morfolojik incelemeler. Yüksek Lisans Tezi. E.Ü. Fen Bilimleri Enstitüsü, Su Ürünleri Avlama ve İflleme Teknolojisi ABD, Bornova-İzmir, 45 s., 2002.
- Matsushita, Y., Rosidi, A.: Investigation of trawl landings for the purpose of reducing the capture of non-target species and size of fish. Fish. Res., 1997; 29: 133-143.
- Tosunoğlu, Z., Doğanyılmaz, Y., Özbilgin, Y.D.: Body shape and trawl codend selectivity for nine commercial fish species. J. Mar. Biol. Assoc. UK, 2003; 83: 1309-1313.
- Wardle, C.S.: Fish behaviour and fishing gears. In Behaviour of Teleost Fishes, ed. T.J. Pitcher, Croom Helm, London and Sydney, Second Edition, pp 463-495, 1993.
- Tarım ve Köyiflleri Bakanlığı: Denizlerde ve içsularda ticari amaçlı su ürünleri avcılığını düzenleyen 2004-2006 av dönemine ait 36/1 numaralı sirküler. T.C. Tarım ve Köyiflleri Bakanlığı, Koruma ve Kontrol Genel Müdürlüğü, Ankara. 2004.
- Stewart, P.A.M.: A review of studies of fishing gear selectivity in the Mediterranean. FAO, COPEMED, 2001.
- Özbilgin, H., Tosunoğlu, Z.: Comparison of the selectivities of double and single codends. Fish. Res., 2003; 63: 143-147.
- Tokaç, A., Özbilgin, H., Tosunoğlu, Z.: Comparison of the selectivity of PA and PE codends. Fish. Res., 2004; 67: 317-327.
- Tosunoğlu, Z., Özbilgin, H., Tokaç, A.: Effects of the protective bags on the cod-end selectivity in Turkish bottom trawl fishery. Arch. Fish. Marine Res., 2003; 50: 239-252.
- Kınacıgil, H.T., Çıra, E., İlkyaz, A.T.: Taflucu Körfezi (Kuzeydoğu Akdeniz): karides trol avcılığında hedeflenmeyen ava iliflkin bir ön çalıflma. E.Ü. Su Ürün. Derg., 1999; 16: 99-105.
- Metin, C., Özbilgin, H., Tosunoğlu, Z., Gökçe, G., Aydın, C., Metin, G., Ulafl, A., Kaykaç, H., Lök, A., Düzbastılar, O., Tokaç, A.: Effect of square mesh escape window on codend selectivity for three fish species in the Aegean Sea. Turk. J. Vet. Anim. Sci., 2005; 29: 461-468.
- Metin, C., Tosunoğlu, Z., Tokaç, A., Lök, A., Aydın, C., Kaykaç, H.: Seasonal variations of demersal fish composition in Gülbahçe Bay (İzmir Bay). Turk. J. Zool., 2000; 24: 437-446.
- Özbilgin, H.: The seasonal variation of trawl codend selectivity and the role of learning in mesh penetration behaviour of fish. PhD thesis. Department of Zoology, University of Aberdeen, Scotland, 1998.
- Özbilgin, H.: Effect of temperature change on the maximum swimming speed of whiting, Merlangius merlangus (Linnaeus, 1758). Turk. J. Zool., 2002; 26: 255-262.
- Özbilgin, H., Wardle, C.S.: Effect of seasonal temperature changes on the escape behaviour of haddock (Melanogrammus aeglefinus) from trawl codend. Fish. Res., 2002; 58: 323-331.