Modeling the growth of recruits of European hake (Merluccius merluccius) in the northwestern Mediterranean Sea with generalized additive models

In this study, the growth pattern of juvenile European hake (Merluccius merluccius) was analyzed in relation to oceanographic and ecological factors in the Ligurian Sea and northern TyrrhenianSea, both part of the MediterraneanSea. The ages of juvenile European hake, collected during a trawl survey in June 2011, were estimated by reading otolith daily growth rings. The growth pattern (length-age relationship) of juvenile European hake recruited to the population (<1 year old) was analyzed by fitting a multivariate generalized additive model with explanatory variables: depth, bottom temperature, sea-surface temperature, scalar wind speed, chlorophyll-a concentration, and fishdensity (number of individuals per square kilometer). A significant effect of density on the length-age relationship was found, and an increased growth rate at densities>3000 individuals km -2. This observed positive effect of density on growth could be argued to be a consequence of favorable environmental conditions, such as food availability and temperature, where both fish density and growth are maximized. Conversely, areas of lower density correspond to habitats of low suitability, where growth is impaired.