Variability of Fish Defensive Reaction to Netting with Mesh of Different Sizes

Selectivity aspects related to the mesh size of active fishing gears are studied in detail and primarily taken into consideration in the current fishing practices. On the contrary, selectivity aspects associated with individual behavioral traits are still poorly understood. Laboratory study on behavioral response of several freshwater fish species (roach, bream, perch and others) to moving net panels with different mesh size showed pronounced intra- and interspecific variability of defensive reaction. In terms of behavior, selectivity of fishing gear was conditioned by differences in the intensity of response to netting which appeared due to different reactivity of single individuals and various species. The more reactive individuals preferred to pass through meshes with perimeter greatly exceeding their own maximum girth or avoided contact with netting at all, irrespective of mesh size. It is probable that fish with less pronounced defensive reaction would be caught first causing significant shifts in abundance of more and less reactive individuals in intensively exploited populations. The behavior-related selectivity effects found in the study performed should be taken into account in commercial fishing and stock assessment surveys as well.