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

Francisco Sardà; Nixon Bahamon; Balbina Molí; Francesc Sardà-Palomera

doi:10.3989/scimar.2006.70n3347

Authors

Francisco Sardà Institut de Ciències del Mar (CMIMA-CSIC), Barcelona
Nixon Bahamon Institut de Ciències del Mar (CMIMA-CSIC), Barcelona
Balbina Molí Institut de Ciències del Mar (CMIMA-CSIC), Barcelona
Francesc Sardà-Palomera Institut de Ciències del Mar (CMIMA-CSIC), Barcelona

DOI:

https://doi.org/10.3989/scimar.2006.70n3347

Keywords:

Mediterranean Sea, sorting grid, square mesh, selectivity, multispecies fishery, bottom trawl, European hake, Atlantic horse mackerel, Atlantic mackerel, red mullet

Abstract

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.

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References

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.