Table 2. Parameter estimates of the optimal univariate models for otolith carbon isotope ratios and increment width selected with AICc.

Estimates are given for all fixed effects with confidence intervals (CI) and significance (p). For the random effects residual variance (σ²), the variance associated with tested effects (τ₀₀) and their intraclass correlation coefficient (ICC) are given. The number of observations used to fit model and the amount of variance explained (marginal and conditional R²) are specified.

Predictors	δ13Coto			Increment width
	Estimates	CI	p	Estimates	CI	p
Intercept	-1.563	-1.648 –-1.477	<0.001	5.146	5.130–5.162	<0.001
Age (factor)*	0.036	-0.048–0.119	0.409
Age (factor)*:Stock**	0.071	-0.043–0.186	0.223
Year	-0.007	-0.010 –-0.004	<0.001
Year:Stock**	0.004	-0.000–0.008	0.080
TL	-0.203	-0.591–0.185	0.306	0.301	0.216–0.386	<0.001
Stock**	-0.404	-0.522 –-0.286	<0.001	0.041	0.018–0.063	<0.001
AnomT				0.020	-0.004–0.043	0.102
Age (continuous)				-0.649	-0.669 –-0.630	<0.001
Age (continuous):Stock**				0.133	0.105–0.161	<0.001
Random Effects
σ2	0.144			0.058
τ00	0.128 FishID			0.005 FishID
	0.034 StockYear			0.001 StockYear
ICC	0.418 FishID			0.076 FishID
	0.111 StockYear			0.021 StockYear
N of measurements	836***			4243
N of random groups	436 FishID			436 FishID
	183 StockYear			194 StockYear
Marginal R2 / Conditional R2	0.166 / 0.608			0.604 / 0.642

*estimates of the coefficient for increment formed at age 8 in relation to age 3.

**estimates of the coefficient for NEA stock in relation to Icelandic stock.

*** for 36 individuals only 1 measurement of δ¹³C was available.