Changes in age and maturity of anadromous whitefish (Coregonus lavaretus) in the northern Baltic Sea from 1998 to 2014

Abstract

The maturation of anadromous whitefish (Coregonus lavaretus) was analysed from samples taken from commercial coastal fishing in 1998–2014 in the Gulf of Bothnia. Whitefish matured at a younger age from year to year. The proportion of older (5–12 sea years) mature males decreased from 79% to 39% in the northern Gulf of Bothnia (66°N–64°N) and from 76% to 14% in southern (64°N–60°30'N) during the study period. At the same time, the proportion of young males (2–4 sea years) increased. Whitefish matured younger: the proportion of mature fish at age four increased in both the north and south among females (13% → 98%; 6% → 85%) and males (68% → 99%; 29% → 89%). The catch length of four-year-old fish increased during the study period in both sexes. In contrast, the length of six-year-old females decreased from year to year. Sea surface temperatures increased during the study period, and were possibly associated with a decrease in the age of maturation and faster growth.

Acoustic seal deterrents in mitigation of human–wildlife conflicts in the whitefish fishery of the River Iijoki in the northern Baltic Sea area

“…Under natural conditions, larvae of anadromous European whitefish (whitefish) end up in the sea within weeks after hatching in a river (Lehtonen et al., 1992). After the sea phase, sometimes foraging hundreds of kilometres from their natal river, they mature and return to spawn, usually in the same river, 4–5 years later (at the length of ≥35 cm) (Veneranta et al., 2021). In most rivers running into the northern Baltic Sea, the upstream spawning migration is blocked or shortened by hydroelectric dams, which has decimated natural reproduction.…”