Climate driven changes in the spawning of roach (Rutilus rutilus (L.)) and bream (Abramis brama (L.)) in the Estonian part of the Narva River basin

Increasing water temperature in spring in Estonian inland waters has affected differently the spawning of roach and bream. Within forty years (1951–1990), the spawning of bream shifted, on average, to a ten days earlier period but the range of spawning temperature remained unchanged, while there was no shift in the spawning time for roach, which started to spawn at about three degrees higher water temperature than earlier. The difference between spawning times of roach and bream decreased from an average 22 to 13 days and the difference in average temperatures at the onset of spawning by about 3 °C. Besides water temperature, the timing of spawning was also related to the water level in spring: in years with higher water levels in March or April both fish species started to spawn earlier. The effect of water level changes on spawning was more pronounced in shallower Võrtsjärv than in Lake Peipsi.