Winter activity of common bream (Abramis brama L.) in a European reservoir

As temperatures drop and fish metabolism slows, cyprinids are generally assumed to form dense, static shoals or migrate to suitable sites up tributaries to reduce predation risk. Using telemetry, common bream Abramis brama (L.) were observed to remain active and (presumably) foraged throughout winter in an area in the middle of an 8-m-deep valley reservoir coinciding with a 3-5 m zone of warmer, oxygenated water below an inverse thermocline. Tagged bream appeared to avoid cold, shallow zones (<1.5 m) at the inlet and banks and the deepest zone (5-8 m) near the dam/outlet, possibly due to poor food availability. Under certain conditions, bream populations showed higher levels of winter activity (and feeding) than previously assumed, with implications for both reservoir fisheries management and future studies assessing cyprinid behaviour, energy budgets and diet in lakes and reservoirs.