78 
Fishery Bulletin 113(1) 
Residuals Theoretical quantiles 
Figure 7 
Graphs for the validation of the best model of the generalized additive model in age and fish density were used 
as explanatory variables. Residuals versus explanatory variables were (A) age and (B) density to assess homo- 
geneity and (C) a histogram of residuals and (D) a Quantile-Quantile (Q-Q) plot to assess normality. The model 
was developed from data for recruits of European hake ( Merluccius merluccius) caught in June 2011 during the 
Mediterranean International [bottom] Trawl Survey (MEDITS) in the Ligurian Sea and northern Tyrrhenian Sea. 
presents a potentially valuable feature for conserva- 
tion and management purposes — one that, for instance, 
could be leveraged to ensure long-term effectiveness of 
no-take areas: Colloca et al. (2009) estimated that the 
closure of highly persistent nurseries would result in a 
small reduction of the exploitable fishery area (around 
5%) and the protection of a considerable fraction (40%) 
of the estimated total number of recruits. 
In a recent study, Cannella et al. (2011) found high 
hepatosomatic index values, a proxy for body condi- 
tion, in recruits of European hake from areas of high 
density in the Tyrrhenian Sea, support the hypothesis 
that high-density nurseries around the shelf break are 
high-quality areas where juveniles find environmental 
conditions of food and temperature that are appropri- 
ate for survival and growth. 
The present study is limited to growth estimation 
from a single year. However, although a longer time 
series of multiyear data is needed to sufficiently under- 
stand the role of environmental variables and density- 
based factors on growth, the results from the present 
study provide a first baseline and rationale in corrobo- 
rating the key role played by high-quality nurseries 
for recruitment success. The results from this study 
indicate that European hake recruits grow faster in- 
side their main nurseries than outside them, thereby 
increasing their chance to survive before they migrate 
to shallower areas on the continental platform. Accord- 
ing to the definition by Dahlgren et al. (2006), these 
areas can be regarded as “effective juvenile habitats.” 
In the areas that were identified as effective juvenile 
habitats, environmental characteristics (e.g., food avail- 
