Winter behavior breams examined
Recently, for example, Czech researchers have better mapped the behaviour of bream in the winter in a lake (44 hectares, depth max. 8 m, with an inflowing river). Eight breams with a length of 25-30 centimeters were equipped with a transmitter and followed from 1 December. Even under a strong ice floor, the signal of the transmitters was still receiving a strong signal. All observations were mapped and then analyzed. As a measure of the activity, the researchers used the distance between two consecutive points (observations): the greater the distance, the more active the fish.
Up to 270 meters
The bream was observed in 34% of the lake. On average, the fish spent shorter distances in the night than during the day. But the variation between the breams was very large: the smallest displacement was 4 meters, the longest more than 270 meters. the fish generally did not stay in concentrations (in 85% of the observations more than 50 meters distance). And the distance between the fish was greater at night than during the day. By connecting each observation point with each fish, the researchers put together a kind of travel report for each fish. This showed that the breams showed a certain presence, with an average winter stay of 7.4 hectares per fish, with a variation of 2.8- 13.9 hectares. One bream is therefore clearly more homogeneous than the other. The bream appeared to have a clear preference for a stay in the middle of the lake, at a water depth of 3-5 m. Shoal and deeper water were much less popular.
The results do not exactly indicate behavior in which the bream forms large, static schools in the winter. However, there seem to be large differences in behavior between the bream. Even at very low temperatures (ice cover about 20 cm) a number of fish remained active. The fish seem more active during the day, but in a smaller area than in the night.
The researchers suspect that the breams avoid the zones with very cold water under the ice and with less oxygen in the deepest parts. Migration to the inflowing river was not observed. The behavior of the bream seems to be related mainly to active foraging, in particular with the search for mosquito larvae and other soil food.
Although the number of fish being tagged was not large, the results indicate that the existing picture of large, inactive bream schools may need to be adjusted in the winter. The specific characteristics of the investigated lake may influence the observed behavior. In other lakes, with different characteristics, it is not imaginary that the bream shows a different winter behavior. Comparable research in other waters can reveal more about this.
Source: Jurajda, P. et al. (2018). Winter activity of common bream (Abramis brama L.) in a European reservoir (Fish Manag Ecol 25: 163-171).