The use of a square mesh codend and sorting grids to reduce catches of young fish and improve sustainability in a multispecies bottom trawl fishery in the MediterraneanEl uso de copo de malla cuadrada y rejillas separadas para reducir las capturas de pece
Keywords:Mediterranean Sea, sorting grid, square mesh, selectivity, multispecies fishery, bottom trawl, European hake, Atlantic horse mackerel, Atlantic mackerel, red mullet
In order to improve the capacity of bottom trawl fishing gears to reduce catches of young fish and discards in a highly exploited demersal trawl fisheries in the Mediterranean, the size-selection performance of a 36-mm square-mesh codend and two sorting grids with 20 and 15 mm bar spacing was assessed. Alternate hauls were used to assess the selectivity of 36-mm square-mesh codend. Selectivity of sorting grids was assessed using a double codend in which fish that escaped through the grid were captured in the lower codend while other fish were guided into the upper codend. The mean selection length (L50) for European hake was 18.5 cm and that for the Atlantic horse mackerel was 14.0 cm with the 36-mm square-mesh codend . These values are close to their current minimum landing sizes (20 cm for hake and 12 cm for horse mackerel). The sorting grid with 20-mm bar spacing showed L50 value of 13.3 cm for hake, suggesting that a larger grid-spacing would be needed to obtain sufficient sorting performance. Similarly, for Atlantic mackerel the estimated L50 of 14.3 cm indicates that larger grid spacing is required to attain an L50 that would be close to the current MLS (18 cm). For Atlantic horse mackerel and red mullet, the L50 obtained with the sorting grid with 20-mm bar spacing was close to the MLS of these species (the MLS of red mullet is 11 cm). The selectivity of the sorting grid with 15-mm bar spacing was generally very poor. Size-selection performance of sorting grids was assessed for the first time in the local fisheries. In order to effectively improve size-selection, seasonal and depth-dependent differences between target and by-catch species must be taken into account, which is a good indicator of the difficulty of implementing a single mesh size or grid spacing in the Mediterranean demersal trawl fishery.
Caddy, J. – 1993. Some future perspectives for assessment and management of Mediterranean fisheries. Sci. Mar., 57: 121-130.
Guijarro, B. and E. Massuti. – 2006. Selectivity of diamond- and square-mesh codends in the deepwater crustacean trawl fishery off the Balearic Islands (western Mediterranean). ICES J. mar. Sci., 63: 52-67. doi:10.1016/j.icesjms.2005.08.011
Larrañeta, M., P. Suau and J. San Felíu. – 1969. Experiencias de selectividad en la pesquería de arrastre en el Levante español. Inv. Pesq., 33: 15-53.
Lleonart, J. – 2001. Impact of fishery and environment on hake recruitment in Northwestern Mediterranean. EU FAIR CT-97-3522 (1998–2000), Barcelona.
Madsen, N. and K.E. Hansen. – 2001. Danish experiments with a grid system tested in the North Sea shrimp fishery. Fish. Res., 52: 203-216. doi:10.1016/S0165-7836(00)00234-4
Martín, P., A. Carbonell and P. Belcari. – 2001. Estimation of trawl discards in the western Mediterranean. European hake (Merluccius merluccius) as case study. EC DG Fisheries Study 00/009. Final Report (mimeo): 135 pp.
Millar, B.R. and R.J. Fryer. – 1999. Estimating the size-selection curves of towed gears, traps, nets and hooks. Rev. Fish Biol. Fisher., 9: 89-116. doi:10.1023/A:1008838220001
Millar, R. – 1992. Estimating the size-selectivity of fishing gear by conditioning on the total catch. J. Am. Statist. Assoc., 87: 962–968. doi:10.2307/2290632
Polet, H. – 2002. Selectivity experiments with sorting grids in the North Sea brown shrimp (Crangon crangon) fishery. Fish. Res., 54: 217-233. doi:10.1016/S0165-7836(00)00289-7
Sánchez, P., M. Demestre and P. Martín. – 2004. Characterisation of the discards generated by bottom trawling in the northwestern Mediterranean. Fish. Res., 67: 71-80. doi:10.1016/j.fishres.2003.08.004
Sardà, F., N. Bahamón, F. Sardà-Palomera and B. Molí. – 2005. Commercial testing of a sorting grid to reduce catches of juvenile hake (Merluccius merluccius) in the western Mediterranean demersal trawl fishery. Aquat. Living Resour., 18: 87-91. doi:10.1051/alr:2005010
Sardà, F., B. Molí and I. Palomera. – 2004. Preservation of juvenile hake (Merluccius merluccius, L.) in the western Mediterranean demersal trawl fishery by using sorting grids. Sci. Mar., 68: 435-444.
Stergiou, K., C.-Y. Politou, E. Christou and G. Petrakis. – 1997. Selectivity experiments in the NE Mediterranean: the effect of trawl mesh size on species diversity and discards. ICES J. mar. Sci., 54: 774-786. doi:10.1006/jmsc.1997.0231
Steward, P. – 2002. A review of studies of fishing gear selectivity in the Mediterranean. A review of studies of fishing gear selectivity in the Mediterranean. Report No. 9, (mimeo): 57 pp. Aberdeen, Scotland.
Tokai, T. – 1997. Maximum likelihood parameter estimates of a mesh selectivity logistic model through SOLVER on MSExcel. Bull. Jpn. Fish. Oceanogr., 61: 288-298.
Valdemarsen, J.W. and P. Suuronen. – 2003. Modifying fishing gear to achieve ecosystem objectives. In: M. Sinclair and G. Valdimarsson (eds), Responsible Fisheries in the Marine Ecosystem, pp 426. FAO and CABI International Publishing. Rome.
Wileman, D., R. Ferro, R. Fonteyne and R. Millar. – 1996. Manual of methods of measuring the selectivity of towed fishing gears. ICES Coop. Res. Rep. No. 215, pp 126. Copenhagen.
How to Cite
Copyright (c) 2006 Consejo Superior de Investigaciones Científicas (CSIC)
This work is licensed under a Creative Commons Attribution 4.0 International License.© CSIC. Manuscripts published in both the printed and online versions of this Journal are the property of Consejo Superior de Investigaciones Científicas, and quoting this source is a requirement for any partial or full reproduction.
All contents of this electronic edition, except where otherwise noted, are distributed under a “Creative Commons Attribution 4.0 International” (CC BY 4.0) License. You may read here the basic information and the legal text of the license. The indication of the CC BY 4.0 License must be expressly stated in this way when necessary.
Self-archiving in repositories, personal webpages or similar, of any version other than the published by the Editor, is not allowed.