Research Article

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

¹ Natural Resources Institute (Luke), Wolffintie 35, Vaasa FI-65200, Finland
² Natural Resources Institute (Luke), Helsinki FI-00791, Finland
³ Department of Biology, University of Turku, Turku FI-20014, Finland
⁴ Natural Resources Institute (Luke), Laivurintie 6, Keminmaa FI-94450, Finland

^* Corresponding author: lari.veneranta@luke.fi

Handling Editor: AE Richard Nash

Received: 27 July 2020
Accepted: 7 March 2021

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.