National Marine 
Fisheries Service Fishery Bulletin First U.S. Commissioner aes 
WNP F F of Fisheries and founder Epa 
NUAA @ established in 1881 ~< of Fishery Bulletin ; 
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Abstract—The trophic ecology of 7 key 
species of Gadiformes, the silvery pout 
(Gadiculus argenteus), Mediterranean 
bigeye rockling (Gaidropsarus biscay- 
ensis), European hake (Merluccius 
merluccius), blue whiting (Microme- 
sistius poutassou), Mediterranean ling 
(Molva macrophthalma), greater fork- 
beard (Phycis blennoides), and poor cod 
(Trisopterus minutus), in the western 
Mediterranean Sea was explored. A 
total of 3192 fish stomachs were exam- 
ined during 2011-2017 to investigate 
ontogenetic shifts in diet, trophic inter- 
actions (both interspecific and intraspe- 
cific), and feeding strategies. The results 
from applying multivariate statistical 
techniques indicate that all investigated 
species, except the Mediterranean big- 
eye rockling and poor cod, underwent 
ontogenetic dietary shifts, increasing 
their trophic level with size. The studied 
species hold different trophic positions, 
from opportunistic (e.g., the Mediter- 
ranean bigeye rockling, with a trophic 
level of 3.51) to highly specialized pisci- 
vore behavior (e.g., the Mediterranean 
ling, with a trophic level of 4.47). These 
insights reveal 4 different feeding strat- 
egies among the co-occurring species 
and size classes in the study area, as 
well as the degree of dietary overlap. 
Such information on ecological patterns 
within a fish assemblage, including spe- 
cies interactions, is often requested by 
those who aim to implement ecosystem 
management. Therefore, these findings 
can be used to improve management of 
sustainable fisheries in this region. 
Manuscript submitted 25 May 2020. 
Manuscript accepted 9 March 2021. 
Fish. Bull. 119:50-65 (2021). 
Online publication date: 13 April 2021. 
doi: 10.7755/FB.119.1.7 
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. 
Spencer F. Baird 
Ontogenetic shifts and feeding strategies of 
7 key species of Gadiformes in the western 
Mediterranean Sea 
Encarnacion Garcia-Rodriguez (contact author)! 
Miguel Vivas' 
José M. Bellido' 
Antonio Esteban’ 
Maria Angeles Torres” 
Email address for contact author: encarnacion.garcia@ieo.es 
" Centro Oceanografico de Murcia 
Instituto Espanol de Oceanografia 
Calle el Varadero 1 
San Pedro del Pinatar 
30740 Murcia, Spain 
? Centro Oceanografico de Cadiz 
Instituto Espanol de Oceanografia 
Puerto Pesquero 
Muelle de Levante s/n 
11006 Cadiz, Spain 
One of the most important aspects of 
analysis of trophic interactions is the 
study of trophic levels, understood as 
a hierarchical way of classifying organ- 
isms according to their feeding relation- 
ships within an ecosystem, contributing 
to knowledge about the ecological role 
of a species (Cochran et al., 2019). This 
knowledge is critical in investigating 
predator—prey interactions and is nec- 
essary for an ecosystem-based approach 
to fisheries management (Christensen, 
1996; Garcia et al., 2003). Additionally, 
feeding patterns offer useful insights 
about the long-term stability of marine 
ecosystems (Trites, 2003; McDonald- 
Madden et al., 2016). 
In general, fish change their diets with 
size to optimize their energetic return 
(Scharf et al., 2000; Juanes et al., 2002). 
In addition, ontogenetic shifts can be 
considered a mechanism to avoid, or at 
least minimize, intraspecific competition 
by allowing exploitation of different food 
resources at each developmental stage 
(Marrin, 1983; Castro and Hernandez- 
Garcia, 1995). More broadly, fish species 
have a wide range of strategies, on both 
intraspecific and interspecific levels, 
that result in and maintain resource 
partitioning (Madurell et al., 2008; 
Fanelli et al., 2009, 2013). Such strate- 
gies include not only food selection but 
also habitat selection and temporal 
segregation (Schoener, 1974). Hence, 
resource partitioning occurs when fish 
species are segregated into at least 1 of 
3 niche dimensions. As a result, niche 
overlap is avoided and resource com- 
petition is minimized among fish spe- 
cies. This hypothesis is known as niche 
complementarity (Ebeling and Hixon, 
1991) and assumes that a particular 
species, which overlaps with others in a 
given niche dimension, would separate 
along another dimension, maintain- 
ing resource partitioning. Describing 
and comparing these relationships, by 
using indices that reflect niche overlap 
or niche breadth, can help to explain 
