Direct estimation of gill-net selectivity for roach ( Rutilus rutilus (L.)) in a small lake

Abstract

Gill-net size selectivity for roach ( Rutilus rutilus (L.)) was estimated directly in a small eutrophic lake by fishing with littoral and pelagic gill nets. The number of roach in the population was estimated by a mark-recapture method. The estimated height of the selectivity curves increased with increasing mesh size, i.e. a pronounced size selectivity. In explaining the observed differences in catch efficiencies, the encounter probability may be less important than the probability of capture and retention. In assessment of length-frequency distribution of roach populations by gill-net sampling, the numbers of large roach will be considerably overestimated relative to small roach if the catch data are not corrected for size selectivity.