The winter movements of two fish species in a temperate lowland river.

Abstract

Winter involves long periods of low water temperatures, with the activities and movements of many temperate fish species being much reduced compared with summer. In very cold periods, individuals can be winter quiescent. The extent to which activities and movements decrease in winter, is however, unknown in many fishes, including how these decrease in relation to water temperatures. Here, acoustic telemetry (using transmitters implanted internally) measured the body temperatures and movements of European barbel Barbus barbus (barbel) across winter 2020/21 and 2021/22, and common bream Abramis brama (bream) in winter 2022/23 in the River Severn, western Britain. The body temperatures of barbel were measured from 1.9 to 11.3oC and bream 0.4 to 12.8oC. The tagged fish generally remained active throughout the winters, including in periods of very low water temperatures (<4 oC). The median total distance moved by bream was 106 km, which was higher than that measured in summer (103 km). Barbel moved less than bream and had total ranges that were similar in winter and summer (median range: 3.9 km in both seasons). These two temperate fishes thus remained active throughout winter, with no quiescence even in the coldest periods, and with aspects of their movements being similar to summer.