SUITABILITY OF MOTORIZED UNDER-ICE SEINING IN SELECTIVE MASS REMOVAL OF COARSE FISH

The efficiency of modem, fully motorized under-ice winter seining tech nique was studied in the selective mass removal of coarse fish in the eutrophicated Lake Vesijarvi, southern Finland in 1992-1994. The total catch in 57 seine hauls was 69 000 kg and the average catch per haul 1210 kg (250-6500 kg). The average biomass removed from the fishing ar ea per haul was 120 kg ha(-1) (SD 116) in the deepest basins(depth > 1 5 m), where smelt (Osmerus eperlanus L.) dominated the catches. The co rresponding catch was 192 kg ha(-1) (SD 187) in a shallower basin (<15 m) where the catch comprised mainly cyprinids, all age classes of bre am (Abramis brama L.) and bleak (Alburnus alburnus L.) and juveniles ( 1 + and 2 +) of roach (Rutilus rutilus L.) and bleak. The catches were composed of aggregated fish since there was no correlation between th e length of the haul and weight of the catch and the biomass removed f rom the fishing area was high. The under-ice pelagic schooling pattern of fish distribution was confirmed by scanning sonar monitoring which was effectively utilized in fishing. Winter seining is a suitable met hod for selective fish removal both in fisheries management and in bio manipulation of temperate lakes which are ice-covered for several mont hs during a year. (C) 1997 Elsevier Science B.V.