69 
NOAA 
National Marine 
Fisheries Service 
Abstract— In this study, the growth 
pattern of juvenile European hake 
( Merluccius merluccius ) was ana- 
lyzed in relation to oceanographic 
and ecological factors in the Ligu- 
rian Sea and northern Tyrrhenian 
Sea, both part of the Mediterranean 
Sea. The ages of juvenile European 
hake, collected during a trawl sur- 
vey 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-sur- 
face temperature, scalar wind speed, 
chlorophyll-a concentration, and fish 
density (number of individuals per 
square kilometer). A significant ef- 
fect of density on the length-age 
relationship was found, and an in- 
creased growth rate at densities 
>3000 individuals km -2 . This ob- 
served positive effect of density on 
growth could be argued to be a con- 
sequence 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 suit- 
ability, where growth is impaired. 
Manuscript submitted 10 August 2013. 
Manuscript accepted 3 December 2014. 
Fish. Bull. 113:69-81 (2015). 
doi: 10.7755/FB.113.1.7 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Fishery Bulletin 
Hr established 1881 
Spencer F. Baird 
First U.S. Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Modeling the growth of recruits of 
European hake C Merluccius merluccius ) in 
the northwestern Mediterranean Sea with 
generalized additive models 
Alessandro Ligas (contact author ) 1 
Francesco Colloca 2 
Mathieu G. Lundy 1 
Alessandro Mannini 3 
Paolo Sartor 4 
Mario Sbrana 4 
Alessandro Voliani 5 
Paola Belcari 6 
Email address for contact author: alessandro.ligas@afbim.gov.uk 
1 Fisheries and Aquatic Ecosystems Branch 
Agri-Food and Biosciences Institute 
18a Newforge Lane 
BT9 5PX, Belfast, United Kingdom 
2 Istituto per I'Ambiente Marino Costiero 
Consiglio Nazionale delle Ricerche 
Via Vaccara 61 
91026 Mazara del Vallo (Trapani), Italy 
3 Dipartimento di Scienze della Terra 
dell'Ambiente e della Vita 
Universita delgi Studi di Genova 
Corso Europa 26 
16132 Genova, Italy 
4 Centro Interuniversitario di Biologia 
Marina ed Ecologia Applicata "G. Bacci' 
Viale Nazario Sauro 4 
57128 Livorno, Italy 
5 Risorse Ittiche e Biodiversita Marina 
Agenzia Regionale per la Protezione 
Ambiente della Toscana 
Via Marradi 1 14 
57126 Livorno, Italy 
6 Dipartimento di Biologia 
Univerisita di Pisa 
Via Derna 1 
56126 Pisa, Italy 
The European hake ( Merluccius mer- 
luccius) is a demersal fish widely 
distributed in the Mediterranean 
Sea and in the northeastern Atlantic 
(Murua, 2010). In the Mediterranean 
Sea, it is a major component of the 
demersal fish assemblages on both 
the continental shelf and the upper 
slope (Orsi Relini et ah, 2002; Col- 
loca et ah, 2004). Juvenile European 
hake aggregate in nursery areas lo- 
cated on the continental shelf break 
(Maynou et ah, 2003; Abella et ah, 
2005; Bartolino et ah, 2008a; Hidalgo 
et ah, 2008), and adult fish can be 
found in a wider depth range from 
the shelf to the upper slope (Alde- 
bert et ah, 1993; Sbrana et ah, 2007; 
Cartes et ah, 2009; Bartolino et ah, 
2011). Because of its abundance and 
wide spatial distribution, the Euro- 
pean hake is one of the most highly 
exploited species in the Mediterra- 
nean Sea, targeted by multigear fish- 
eries. The bulk of the catch of this 
species is obtained from trawl fisher- 
ies, which mainly exploit the young- 
est portion of the population (<30 
cm in total length [TL] ). However, 
there are still relatively high discard 
rates of undersize fish (Cardinale et 
ah, 2011) despite an amendment in 
2010 in the European Union Council 
Regulation to increase trawl codend 
mesh size (European Union Council 
Regulation 1967/2006). The adult 
fraction ( >40 cm TL) is exploited by 
gillnet and longline fisheries (Sbrana 
