investigation the selectivity of gillnet used in roach (rutilus rutilus l., 1758) fishery in uluabat lake, bursa-turkey

the purpose of this study was determine the selectivity properties of gillnet used in roach (rutilus rutilus) fishery in the lake uluabat. in the fishery works, 7 different gill net which were 100 meters in length and 32, 40,50, 60,70,80 and 90 mmmesh size with a same thickness and depth of 50 mesh as vertically have been used. field work was carried out monthly in a period of january 2011 and december 2011. length and weights of 434 samples were determined with 1mm and 1g precision measurement board and scale. select method was used in the determination of the selectivity parameters. obtained data were analyzed by pasgear ii v 2.5 computer software. the program calculates parameters of 5 different model (normal location, normal scale, log-normal, gamma and bi-modal) based on select method. normal scale yielded the best as a result of analysis. according to the this model optimum catch lengths and spread value of nets which have 32, 40, 50, 60, 70 and80 mm mesh size determined as 12.16-1.24 15.20-1.56 19.00-1.95 22.80-2.34 26.60-2.73 30.40-3.12 respectively. according to the kolmogorov-smirnov test results differences were determined between size frequency distribution of fish caught by all nets.