Sorting grid trials to improve size selectivity of red mullet (Mullus barbatus) and annular sea bream (Diplodus annularis) in Turkish bottom trawl fishery

Summary Sorting grids with two different bar spacings (12 mm and 14 mm) were tested to improve size selectivity of the commercially important fish species, red mullet (Mullus barbatus) and annular sea bream (Diplodus annularis), in Turkish bottom trawl fishery. Fishing trials were carried out with R/V ‘Egesuf’ between April and May 2003 in Izmir Bay, Aegean Sea, using a traditional bottom trawl. Selectivity data were collected by the top cover method and analyzed by means of a logistic equation with the maximum likelihood method. Selectivity parameters for individual hauls were obtained with the software program cc 2000. Mean selectivity was also estimated and compared using the EC Model software that takes between-haul variations into account. The codend catch size as an additional explanatory variable was used in the comparison. The Kolmogorov–Smirnov (K–S) test was also applied to detect differences between length-frequency distributions in the upper and lower bags of the 12 and 14 mm bar spacings for red mullet and annular sea bream. The mean L50 values of red mullet were 8.7 and 10.0 cm with the 12 and 14 mm grids, respectively. The L50 value of 14 mm was comparable with the L50 value of the codend mesh size; however, the 12 mm value was rather low. The mean L50 values of 12 and 14 mm bar spacings were 8.8 and 10.4 cm for annular sea bream, respectively; the value of 14 mm bar spacing was very close to 50% size at sexual maturity of the species (10.5 cm). The K–S test indicated length distributions of red mullet and annular sea bream in the 12 and 14 mm upper and lower bags as significantly different (P < 0.05). These results show that improving the size selectivity in a multi-species fishery using a single selective device is rather difficult. However, higher size selectivity can be obtained when considering the minimum landing size or the 50% sexual maturity size for a given species.

[1]  L. Hendrickson,et al.  Effectiveness of the Nordmore grate in the Gulf of Maine Northern shrimp fishery , 2006 .

[2]  F. Sardà‐Palomera,et al.  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 Mediterranean , 2006 .

[3]  Aida Campos,et al.  Potential use of a Nordmøre grid for by-catch reduction in a Portuguese bottom-trawl multispecies fishery , 2005 .

[4]  Aida Campos,et al.  Using a modified Nordmøre grid for by-catch reduction in the Portuguese crustacean-trawl fishery , 2005 .

[5]  F. Sardà,et al.  Preservation of juvenile hake ( Merluccius merluccius L) in the western Mediterranean demersal trawl fishery by using sorting grids , 2004 .

[6]  H. Özbilgin,et al.  Effect of PA and PE material on codend selectivity in Turkish bottom trawl , 2004 .

[7]  H. Özbilgin,et al.  Body shape and trawl cod end selectivity for nine commercial fish species , 2003, Journal of the Marine Biological Association of the United Kingdom.

[8]  H. Özbilgin,et al.  Determination of the Appropriate Hanging Ratios to Ease the Escape of Juvenile Red Mullet (Mullus barbatus L., 1758) and Annular Sea Bream (Diplodus annularis L., 1758) from a Trawl Codend , 2003 .

[9]  H. Özbilgin,et al.  Comparison of the selectivities of double and single codends , 2003 .

[10]  Norman Graham,et al.  By-catch reduction in the brown shrimp, Crangon crangon, fisheries using a rigid separation Nordmøre grid (grate) , 2003 .

[11]  N. Rawlinson,et al.  Assessment and benefits of damage reduction in prawns due to use of different bycatch reduction devices in the Gulf of Carpentaria, Australia , 2000 .

[12]  T Moth-Poulsen,et al.  Selectivity experiments with escape windows in the North Sea Nephrops (Nephrops norvegicus) trawl fishery , 1999 .

[13]  R. G. Halliday,et al.  Evaluation of separator grates for reduction of bycatch in the silver hake (Merluccius bilinearis) otter trawl fishery off Nova Scotia, Canada , 1999 .

[14]  R. Ferro,et al.  Cod-end selectivities of a modified bottom trawl for three fish species in the Aegean Sea , 1998 .

[15]  N. Rawlinson,et al.  An assessment of Bycatch Reduction Devices in a tropical Australian prawn trawl fishery , 1998 .

[16]  R. Ferro,et al.  The effects of different cod-end design on bottom trawl selectivity in Turkish fisheries of the Aegean Sea , 1997 .

[17]  K. Stergiou,et al.  Size selectivity of diamond and square mesh codends for four commercial Mediterranean fish species , 1997 .

[18]  A. Engås,et al.  Survival of young gadoids excluded from a shrimp trawl by a rigid deflecting grid , 1997 .

[19]  Bjørnar Isaksen,et al.  Reduction of fish by-catch in shrimp trawl using a rigid separator grid in the aft belly , 1992 .

[20]  R. Fryer.  A model of between-haul variation in selectivity , 1991 .

[21]  H. Polet,et al.  Selectivity experiments with sorting grids in the North Sea brown shrimp (Crangon crangon) fishery , 2002 .

[22]  D. L. Alverson,et al.  By-Catch: Problems and Solutions , 2000 .

[23]  Alejandro D. Pettovello.  By-catch in the Patagonian red shrimp (Pleoticus muelleri) fishery , 1999 .