Behavior of some growth performance indexes for exploited Mediterranean hake

Exploited marine living resources are at present assessed in the Mediterranean by refer‐ ring to 26 geographical sub‐areas (GSA: GFCM, 2009), mainly delimited on the basis of politi‐ In this paper, some life‐history estimates concerning the females of the Mediterranean hake Merluccius merluccius (L., 1758), i.e. the parameters of the von Bertalanffy growth function (L∞, K, and t0), the maximum‐ever lengths (Lmx‐e), and the lengths at full maturity (Lmst) were gathered from the pertinent literature and used to derive 5 growth performance indexes (K, φ’, RL=Lmst/ L∞, t50% and ω). The original datasets (n= 70) and the corresponding growth performance indexes were organized and analyzed by various geographical units (GFCM’s geographical sub‐area, GSA; GFCM’s statistical division, GD; and biological province, BP). The parameter distribution resulted to be normal only for the growth performance indexes K and RL; a significant relationship correlation was detected between K and t50%, between φ’ and ω, and between K and ω. The examination of the available historical data showed a scattered and unbalanced geographical distribution by GSA (e.g. 13 of 20 GSAs had less than 5 datasets each), a variability which was higher intra‐GSA than inter‐GSAs (as evidenced by the box‐plots) and no clear geographical trend. GD and BP presented similar patterns, with significant geographical effects only in the RL. Present results suggest that, even if geographical effects are expected, they are obscured by the uncertainty of the original parameters, especially those related to the von Bertalanffy growth function (vBGF). Consequently, growth performance indexes should be used (and interpreted) with caution.