Garcia-Rodriguez et al.: Ontogenetic shifts and feeding strategies of Gadiformes in the Mediterranean Sea 
Table 3 
Volume index (%V) values for prey groups identified in the stomach contents of specimens of 7 key species 
of Gadiformes caught in the western Mediterranean Sea during 2011-2017. The %V value for a prey group 
represents the volume of that prey item compared with the total volume of all prey ingested by specimens 
of that species. The 7 species are the silvery pout (Gadiculus argenteus) (GAD), Mediterranean bigeye rock- 
ling (Gaidropsarus biscayensis) (GAI), Mediterrenean ling (Molva macrophtalma) (MOL), European hake 
(Merluccius merluccius) (MER), blue whiting (Micromesistius poutassou) (MIC), greater forkbeard (Phycis 
blennoides) (PHY), and poor cod (Trisopterus minutus) (TRI). A dash indicates that no consumption of that 
prey group was recorded for that species. An asterisk indicates the prey group with the highest %V value 
for each species. Information on niche breadth and the number of prey items is also reported. 
Information type 
Niche breadth 
No. of prey items 
Prey group 
Small plankton 
Large plankton 
Polychaeta 
Cephalopoda 
Crab, lobster, and mantis shrimp species 
Shrimp species 
Peracarida 
Demersal fish species 
Pelagic fish species 
Benthopelagic fish species 
provided in Supplementary Table 1 (online only) documents 
in detail the different prey items found in stomachs and 
identified to the lowest taxonomic level in this study. 
Regarding the ontogenetic variation in diet, for each of 
the studied species, the graph indicates trends in trophic 
strategies for 2 prey groups that were the opposite of the 
other, and this observation of different trends enabled us 
to establish a cutoff between the 2 size classes: the size at 
which a trophic shift occurred (Fig. 2). Only in the case of 
the silvery pout did the selected cutoff between size classes 
seem to be related to size at first maturity. For the Mediter- 
ranean bigeye rockling, no data are available on size at first 
maturity in the study area. 
The results obtained for species and size classes indi- 
cate that silvery pout fed mainly on large plankton 
(%GU=51.2%, %V=51.6%, %ZFO=50.9%), with EHuphau- 
sia krohnii as the most predominant prey species. The 
diet of Mediterranean bigeye rockling was based pri- 
marily on crab, lobster, and mantis shrimp species 
(%GU=44.9%, %V=51.5%, %FO=38.2%) and _ species 
of Peracarida (%GII=27.4%, %V=17.5%, %FO=37.3%), 
represented mainly by Calocaris macandreae and 
Lophogaster typicus, respectively. Benthopelagic fish 
species (%GII=57.0%, %V=73.8%, %FO=40.2%) com- 
posed the major prey group for Mediterranean ling, for 
which the most commonly consumed prey was another 
species of Gadiformes, the silvery pout. Pelagic fish spe- 
cies (%GII=29.0%, %V=40.8%, %FO=17.2%) and large 
plankton (%GII=15.1%, %V=12.0%, %FO=18.3%) were 
the main prey groups for European hake, with European 
JN 
anchovy (Engraulis encrasicolus) and euphausiids being 
the most important of the consumed prey, respectively. 
Blue whiting fed mainly on large plankton (%GII=39.3%, 
%N=40.3%, %FO=38.3%) and benthopelagic fish species 
(%GII=36.5%, %V=37.4%, %FO=35.6%), of which euphau- 
siids and the myctophid horned lanternfish (Ceratoscope- 
lus maderensis) were the main prey, respectively. Similar 
prey items were also found in the diet of both greater fork- 
beard and poor cod: prey species were primarily shrimp 
species (%GII=61.8%, %V=60.6%, and %FO=62.9% and 
%GU=65.7%, %V=65.5%, and %~FO=65.6%, respectively), 
with red snapping shrimp as the most-represented prey. 
Results of the one-way analyses of similarity indicate 
that there were significant differences in trophic compo- 
sition between size classes (P<0.05) for all species studied 
except for the Mediterranean bigeye rockling and poor cod 
(Suppl. Table 3) (online only). Moreover, results of the simi- 
larity percentage analysis for the 5 species that had onto- 
genetic shifts identify the contribution of each prey item to 
the mean Bray—Curtis dissimilarity for each species. The 
average dissimilarity between size classes ranged from 41% 
for Mediterranean ling to 75% for European hake. These 
differences were a result of the distinct contribution of 
major prey groups to the stomach contents in specimens 
examined for each species (Suppl. Table 4) (online only). The 
major prey groups contributing the most to the ontogenetic 
shifts in the diet of silvery pout were large plankton and 
Peracarida, and for Mediterranean ling, the major prey 
groups were teleosts, such as demersal and benthopelagic 
fish species. Pelagic fish, large plankton, and shrimp species 
