Predicted length of individual anadromous female (F) and male (M) whitefish (Coregonus lavaretus) in relation to time (months) spent at sea in two year-class periods (1996–2002, 2003–2009; symbols: 1990 and 2000, respectively) in the Gulf of Bothnia according to linear regression model. The whitefish captured by trap and gill nets in the third-sixth sea year (25–72 months; 25–36 months = the third year; 37–48 = the fourth year, 49–60 = the fifth year, 61–72 = the sixth year) are included (sample size = 12653). The length is log-transformed (natural) in the model, but transformed back to linearity in the figures. Sample size for earlier and later periods, n = 6151 and n = 6516, respectively (Tab. A.4).