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 reduced compared with summer. In very cold periods, individuals can become winter quiescent. The extent to which the activities and movements of many fish species reduce in winter is unknown, including how these decrease in relation to environmental conditions. Acoustic biotelemetry was applied here to measure the body temperatures and movements of European barbel Barbus barbus (barbel) across winter 2020/2021 and 2021/2022, and common bream Abramis brama (bream) in winter 2022/2023 in the River Severn, western Britain. Body temperatures of barbel were measured from 1.9 to 11.3 °C and bream 0.4 to 12.8 °C. The tagged fish generally remained active throughout the winters, including when water temperatures were at their lowest. 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 temperate fishes thus remained active throughout winter, did not become quiescent in the coldest periods, and their winter movements were similar to those measured in summer.