Garcia-Rodriguez et al.: Ontogenetic shifts and feeding strategies of Gadiformes in the Mediterranean Sea 51 
feeding behaviors that range from generalist to specialist 
in nature (Silva et al., 2014). 
This study aimed to investigate niche complementar- 
ity and co-occurrence of 7 fish species of Gadiformes in 
the western Mediterranean Sea off the coast of Spain. In 
particular, we analyzed ontogenetic shifts in diet, trophic 
interactions (both interspecific and intraspecific), feed- 
ing strategies, and the degree of dietary overlap among 
the studied species, to ascertain the ecological patterns of 
dietary interrelationships within the fish assemblage. 
The selected gadiform species can inhabit depths greater 
than 1000 m (Fanelli et al., 2013) and play an important role 
in the middle of the food web (i.e., in both bottom-up and 
top-down controls) within marine ecosystems (Libralato 
et al., 2006), indicating that they feed on different trophic 
levels (Miller et al., 2010). They are prey for many other fish 
species (e.g., Preciado et al., 2008; Rodriguez-Cabello et al., 
2014), and they occupy different substrates, ranging from 
sandy to rocky (Cohen et al., 1990). 
In the Mediterranean Sea, the biology and behavior of 
many species of Gadiformes are well-documented (Morte 
et al., 2001, 2002), and they are important commercially and 
ecologically. For example, the European hake (Merluccius 
merluccius) is one of the most common representatives of 
this group, considering the amount of landings, and is cur- 
rently experiencing overexploitation, with fishing mortality 
rates around 1.8—8.1 times higher than the assumed refer- 
ence level of fishing mortality that would provide maximum 
sustainable yield (Colloca et al., 2013). 
In the western Mediterranean Sea, studies of fish feed- 
ing habits usually focus on a few species and omit trophic 
interactions, information about which is essential for an 
effective implementation of an ecosystem approach to 
fisheries management (Garcia et al., 2003). For instance, 
off the coast of Spain, Macpherson (1978a) studied age- 
related seasonal feeding habits of blue whiting (Microme- 
sistius poutassou) in the Gulf of Valencia and of silvery 
pout (Gadiculus argenteus) in the Catalan Sea. He also 
investigated the diet of the Mediterranean bigeye rock- 
ling (Gaidropsarus biscayensis) and Mediterranean ling 
(Molva macrophthalma) (Macpherson, 1978b, 1981). 
Bozzano et al. (1997) reported seasonal feeding habits of 
European hake in the Gulf of Lion off the coast of France, 
and Morte et al. (2001, 2002) analyzed the diet of poor 
cod (Trisopterus minutus) and greater forkbeard (Phycis 
blennoides) in the Gulf of Valencia. Unfortunately, none 
of these studies have investigated further interactions 
between species and fish assemblage. 
Studies that address a broader geographic area and 
include ontogenetic shifts in diets of gadiform species, 
therefore, are scarce for the Mediterranean Sea off 
the coast of Spain, and it is necessary to fill this gap 
in knowledge as well as update current information. 
Additionally, the fish assemblage in the western Medi- 
terranean Sea is currently facing problems of not only 
overfishing and biodiversity loss but also environmental 
pressures, such as the massive urbanization of coast- 
lines, with increases in water pollution and decreases in 
sediments from principal rivers (e.g., Coll et al., 2010). 
Catch quality is decreasing, resulting in landings with a 
higher proportion of low-value species and a higher ratio 
of small to large fish. Furthermore, in the case of some 
of the most damaging and commonly used gear, namely 
bottom trawls, discard rates of low-value species are 
high (Bellido et al.'; Paradinas et al., 2016). Under this 
scenario of overfishing and environmental pressures, a 
declining trend in the landed biomass of the commercial 
species of Gadiformes investigated in our study has been 
observed in the area (MAGRAMA?; MAPAMA?: MAPA‘). 
Consequently, more local and updated data on intraspe- 
cific and interspecific interactions are needed to develop 
ecosystem models for an ecosystem-based approach to 
fisheries management (Christensen and Walters, 2004; 
Gascuel, 2005). 
Material and methods 
Study area and sampling procedure 
We carried out our study in the Mediterranean Sea off 
the coast of Spain from Cape Palos to Cape Creus (Fig. 1). 
According to the General Fisheries Commission for the 
Mediterranean, this area is also known as geographical 
subarea 06 (GSA-06), and it extends along 808 km of 
coastline, with a total area of 30,119 km? and depths of 
40-800 m. The study area is characterized by high biodi- 
versity (Garcia-Rodriguez et al., 2011) and oligotrophic 
conditions. Nevertheless, within the study area, certain 
zones (e.g., Ebro Delta) are exceptions because of their 
moderate levels of primary production (Estrada, 1996). 
The main fishery resources in this area are demersal 
and benthic organisms, such as fish species (Osteich- 
thyes and Chondrichthyes) and invertebrates (mollusks 
and crustaceans). Some of the fish species, such as the 
bogue (Boops boops) or blotched picarel (Spicara maena), 
are heavily discarded, or they are used as bait, although 
they are an increasing component of landings, mainly in 
the bottom-trawl fishery (Bellido et al.’). Most of these 
species, including the European hake and blue whiting, 
both of the order Gadiformes, are fully exploited or over- 
exploited (Coll et al., 2008; Cardinale, 2012, 2013; Coll 
et al., 2014; FAO, 2018). 
1 Bellido, J. M., A. Carbonell, M. T. Garcia, and M. Gonzalez. 
2014. The obligation to land all catches—consequences for the 
Mediterranean: in-depth analysis, 46 p. Policy Dep. B: Struct. 
Cohes. Policies, Dir.-Gen. Intern. Policies, Eur. Parliam., 
Brussels, Belgium. [Available from website.] 
2 MAGRAMA (Ministerio de Agricultura, Alimentacion y Medio 
Ambiente). 2013-2015. Estadisticas pesqueras: Noviembre 
[2013-2015]. Minist. Agric. Aliment. Medio Ambiente, Madrid, 
Spain. [Available from website.] 
3 MAPAMA (Ministerio de Agricultura y Pesca, Alimentacion y 
Medio Ambiente). 2016-2017. Estadisticas pesqueras: Noviembre 
[2016-2017]. Minist. Agric. Pesca Aliment. Medio Ambiente, 
Madrid, Spain. [Available from website.] 
4 MAPA (Ministerio de Agricultura, Pesca y Alimentacién). 2018— 
2020. Estadisticas pesqueras: Noviembre [2018-2020]. Minist. 
Agric. Pesca Aliment., Madrid, Spain. [Available from website.] 
