Title: Selectivity of gillnet series of the pearch (Perca Fluviatilis L.) and roach (Rutilus Rutilus L.) in the coastal sea of Estonia

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The selectivity pattern of perch and roach for a six net gillnet series (mesh sizes 17, 21, 25, 30, 33 and 38 mm) was studied using the gamma model. Data was collected between 1995 and 2004 during routine coastal fish monitoring surveys in Estonia covering six permanent monitoring areas along the coastline. Gamma curves were fitted to the length distributions of different mesh sizes using all strata and relative abundances of the length groups in the gillnet catches were derived. Based on relative abundances, the estimated length distributions were calculated and the representative length distributions from the gillnet series was evaluated.
Size groups in the range of 17-27 cm of both species are overrepresented using the gillnet series, i.e. the length distribution of raw data is biased. Adding nets with smaller mesh sizes to the series would solve the problem of insufficient coverage of smaller (less than 12 cm in length) size groups and small-sized species without affecting long-term data series. For better evaluation of selectivity, experimental studies in recording different ways fish are captured and tagging experiments are recommended.

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