Advancing length at first maturity estimation: evaluating models for Black Sea whiting ( Merlangius merlangus )

Length at 50% maturity (L50) is a key input to harvest control rules and spawning biomass calculations. We estimated female L50 for Black Sea whiting (Merlangius merlangus) from 757 individuals using nine candidate maturity ogives (logistic, probit, Hill, log-logistic, Gompertz, Weibull, Richards, Cauchy, exponential). Models were fitted under a binomial likelihood, with uncertainty quantified by non-parametric bootstrap and model support evaluated using AICc. We also derived L10, L90 and the transition width (L90–L10), assessed sensitivity to measurement resolution (rounding TL to 0.5 and 1.0 cm), and tested robustness to an isolated high-length immature observation (∼16 cm). Sigmoid models yielded highly consistent L50 estimates. AICc favoured the probit model (Akaike weight = 0.40), with logistic, Hill and log-logistic models similarly supported (ΔAICc ≤ 1.8). The model-averaged L50 was 13.66 cm TL (SE = 0.10; 95% CI = 13.46–13.86), with a transition width of ∼3.5 cm. Rounding total length to 0.5 or 1.0 cm shifted L50 by ≤ 0.03 cm, whereas excluding or re-coding the isolated ∼16 cm immature observation shifted L50 by ≤ 0.04 cm. These results demonstrate that standard sigmoid models provide robust and consistent L50 estimates for Black Sea whiting, and that a multi-model framework offers transparent uncertainty for fisheries management applications.