Pelagic cephalopods of the central Mediterranean Sea determined by the analysis of the stomach content of large fish predators

Abstract

The pelagic cephalopod fauna of the central Mediterranean Sea was investigated through stomach content analyses of large fish
predators. A total of 124 Xiphias gladius, 22 Thunnus thynnus, 100 Thunnus alalunga, and 25 Tetrapturus belone were analyzed. Overall, 3,096 cephalopods belonging to 23 species and 16 families were identified. The cephalopod fauna in
the study area is dominated by Sepiolidae, Ommastrephidae, and Onychoteuthidae. The sepiolid Heteroteuthis dispar was the most abundant species (n = 1,402) while the ommastrephid Todarodes sagittatus showed the highest biomass. They can be considered key-species in the pelagic food web of the study area. The neutrally buoyant
Histioteuthis bonnellii,
H. reversa, and Chiroteuthis veranyi seem to characterize the deeper water layers. Given the difficulty in sampling pelagic cephalopods, the presence of cephalopod
beaks in the stomach of predators represents a fundamental tool to assess the biodiversity and the ecological importance of
these taxa in the marine ecosystem.

Full text

ORIGINAL ARTICLE
Pelagic cephalopods of the central Mediterranean Sea determined
by the analysis of the stomach content of large fish predators
Teresa Romeo •Pietro Battaglia •Cristina Peda
`•
Patrizia Perzia •Pierpaolo Consoli •
Valentina Esposito •Franco Andaloro
Received: 14 March 2011 / Revised: 26 July 2011 / Accepted: 28 July 2011
ÓSpringer-Verlag and AWI 2011
Abstract The pelagic cephalopod fauna of the central
Mediterranean Sea was investigated through stomach
content analyses of large fish predators. A total of 124
Xiphias gladius, 22 Thunnus thynnus, 100 Thunnus ala-
lunga, and 25 Tetrapturus belone were analyzed. Overall,
3,096 cephalopods belonging to 23 species and 16 families
were identified. The cephalopod fauna in the study area is
dominated by Sepiolidae, Ommastrephidae, and Onycho-
teuthidae. The sepiolid Heteroteuthis dispar was the most
abundant species (n=1,402) while the ommastrephid
Todarodes sagittatus showed the highest biomass. They
can be considered key-species in the pelagic food web of
the study area. The neutrally buoyant Histioteuthis bon-
nellii, H. reversa, and Chiroteuthis veranyi seem to char-
acterize the deeper water layers. Given the difficulty in
sampling pelagic cephalopods, the presence of cephalopod
beaks in the stomach of predators represents a fundamental
tool to assess the biodiversity and the ecological impor-
tance of these taxa in the marine ecosystem.
Keywords Pelagic cephalopods Beaks Large pelagic
predators Mediterranean Sea
Introduction
Knowledge of the pelagic cephalopod community has
increased over the last decades thanks to improved tech-
niques. However, there is still a significant lack of infor-
mation on these animals’ biology, distribution, and
importance in the food web. This is mainly due to the
difficulties associated with sampling, as conventional gears
used in monitoring of the pelagic environment usually
collect juvenile cephalopods, while adult specimens gen-
erally avoid being captured (Clarke 1996a).
Despite the difficulties in sampling, the ecological
importance of cephalopods in the marine ecosystem has
already been emphasized by several authors (Clarke 1996b;
Bustamante et al. 1998; Piatkowski et al. 2001; Velasco
et al. 2001). In particular, muscular squids are able to
quickly convert their food into biomass and to grow rap-
idly. They, therefore, represent a significant source of
energy for predators. Moreover, while most mid-water
fishes do not grow bigger than 200 mm in length, many
pelagic cephalopods grow up to larger sizes. They thus fill
the gap between small fishes (i.e., myctophids, etc.) and
large pelagic organisms, linking secondary production with
higher trophic levels, as reported in energetic models of
pelagic food webs (Clarke 1996b; Olson and Watters
2003).
Studies on the feeding habits of oceanic predators,
including marine mammals and sea birds, revealed the
actual role played by cephalopods in the pelagic food web
(Amaratunga 1983; Clarke 1996b; Santos et al. 2001;
Cherel et al. 2004). The identification of this taxon in the
Communicated by H.-D. Franke.
T. Romeo (&)P. Battaglia C. Peda
`P. Consoli 
V. Esposito
Laboratory of Milazzo, ISPRA,
Italian National Institute for Environmental
Protection and Research, via dei Mille 44,
98057 Milazzo, ME, Italy
e-mail: teresa.romeo@isprambiente.it
P. Perzia F. Andaloro
ISPRA, Italian National Institute for Environmental
Protection and Research, c/o Residence Marbela,
via Salvatore Puglisi 9, 90143 Palermo, Italy
123
Helgol Mar Res
DOI 10.1007/s10152-011-0270-3

stomach content of top predators is often achieved via a
taxonomic classification of their beaks, because these are
quite resistant to digestive processes (Clarke 1962a,b). In
this way, it is possible to describe the occurrence of pelagic
cephalopods in an area and to obtain precious information
on the ecology and behavior of cephalopods (Bello 1996;
Tsuchiya et al. 1998; Cherel et al. 2004; Lansdell and
Young 2007). Although several studies underlined the
significant presence of cephalopod prey in the diet of large
Mediterranean pelagic fishes (Bello 1991; Bello 1999;
Salman 2004; Sinopoli et al. 2004; Peristeraki et al. 2005;
Sara
`and Sara
`2007; Castriota et al. 2008; Consoli et al.
2008; Karakulak et al. 2009; Salman and Karakulak 2009;
Romeo et al. 2009), data on the specific composition and
distribution of pelagic cephalopod communities in the
Mediterranean are still poor.
In the present paper, stomach content analyses of large
predators were performed to assess the occurrence and
distribution of cephalopods in the Central Mediterranean
Sea (southern Tyrrhenian Sea and Strait of Messina). To
select for the most effective ‘‘cephalopod collectors,’’ data
on the species’ different ecology and feeding strategy were
considered. Large pelagic species usually hunt across a
specific water layer at varying—although sometimes over-
lapping—depth levels. Considering differences between
species in diving behavior, feeding strategies, and occur-
rence in the study area, the following top predators were
selected: (1) swordfish, Xiphias gladius Linnaeus 1758; (2)
blue-fin tuna, Thunnus thynnus (Linnaeus 1758); (3) alba-
core, Thunnus alalunga (Bonnaterre 1788); and (4) Medi-
terranean spearfish, Tetrapturus belone Rafinesque 1810.
Materials and methods
Study area
This study was carried out between 2002 and 2008 in the
central Mediterranean Sea (southern Tyrrhenian Sea and
Strait of Messina) (Fig. 1). A very small continental shelf
and the presence of important fish resources (Palko et al.
1981; Di Natale et al. 2005; Andaloro 2006; Battaglia et al.
2010) consolidated a fishing tradition targeting large
pelagic species, which use these areas for reproduction and
nursery purposes (Palko et al. 1981; De Metrio et al. 2005).
In fact, since ancient times this area has represented an
important fishing ground for the local populations, where
several types of fisheries have been employed: harpoon,
hand lines, tuna traps, and in the last decades also driftnets
and longlines (Lentini and Romeo 2000; Di Natale and
Mangano 2008; Battaglia et al. 2010). The Strait of Mes-
sina, in particular, is well known as an important migration
and feeding area of large pelagic species, where upwelling
phenomena result in high nutrient concentrations and prey
biomass (Guglielmo et al. 1995).
Data collection
Stomachs were collected during commercial fishing activ-
ities within different research projects between 2002 and
2008 aboard boats using drifting long-lines (three different
types of equipment targeting T. alalunga,T. thynnus, and
X. gladius, respectively) and harpoon (‘‘feluca’’ boats tar-
geting X. gladius and T. belone). Each predator specimen
Fig. 1 Study area in the central
Mediterranean Sea
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123

was measured and weighed (TW =total weight in kg) on
board. Lower jaw fork length (LJFL, expressed in cm) was
recorded for swordfish and Mediterranean spearfish, while
fork length (FL, expressed in cm) was recorded for blue-fin
tuna and albacore. Stomachs were immediately removed
from the fish specimens and preserved in order to stop the
digestion process, using three methods: (1) preservation in
formalin/sea water solution for 24 h and subsequent
transfer into 80% ethanol; (2) conservation in 70% ethanol;
(3) freezing at -20°C.
Laboratory analyses
Stomachs were dissected in the laboratory, and their con-
tent was examined under a stereomicroscope. Entire
specimens or partially digested cephalopods were identi-
fied to the lowest possible taxa, following taxonomic fea-
tures reported by Roper et al. (1984), Jereb and Roper
(2005), and Guerra (1992). When classification turned out
to be difficult, beaks were taken as the best means to
identify the species. A large portion of cephalopods was
determined by lower beak identification, since the beaks
were often the only structures found in stomachs. Their
classification was performed by identification keys (Wolff
1982,1984; Clarke 1986; Lu and Ickeringill 2002) and by
comparison with beaks of the ISPRA reference collection
(Peda
`et al. 2009).
The identified preys were counted and weighed; entire
specimens were preserved in 70% ethanol, while beaks
were immersed in a mixture of ethanol, glycerin, and
water.
Data analyses
In order to trace back cephalopods’ size and fresh weight,
the lower rostrum length (LRL) for Teuthida and the lower
hood length (LHL) for Sepiolidea and Octopoda were
measured to the nearest 0.1 mm. When the wet mass of
prey was not available (i.e., when it had already been more
or less digested), this value was calculated using equations
available from Wolff (1982,1984), Clarke (1962a,1986),
Lu and Ickeringill (2002), Zumholz and Piatkowski (2005)
or calculated from specimens preserved in the ISPRA
reference collection (Table 1).
To assess the cephalopod abundance in the study area
through diet information, the percent abundance (%N=
number of prey i/total number of prey 9100), estimated
weight percentage (%eW =weight of prey i/total weight
of prey 9100), and frequency of occurrence (%F=
number of stomachs containing prey i/total number of
stomachs containing prey 9100) were calculated for each
cephalopod prey taxon (Pinkas et al. 1971; Hyslop 1980),
and for each predator species.
Finally, in order to evaluate the importance of the prey
mass for the diet of each predator, all cephalopods were
grouped into four weight classes (small =0–50 g; medium/
small =51–100 g; medium =101–300 g; large C300 g)
and also into the following categories: muscular squids,
buoyant squids, sepiolids, pelagic octopuses, and demersal
octopuses. The percentage of each category per each mass
group was calculated for each predator diet.
Results
Overall, 3,096 cephalopods belonging to 16 families and
23 species (Table 2) were identified through the analysis of
the stomach content of 124 swordfishes (LJFL range
65–225 cm), 22 blue-fin tunas (FL range 45–270 cm), 100
albacores (FL range 48–91 cm), and 25 Mediterranean
spearfishes (LJFL range 120–189 cm). In terms species
number, the most represented families in the study area
were the Ommastrephidae (4) and the Octopodidae (3).
With 1,402 specimens, the sepiolid Heteroteuthis dispar
(Ru
¨ppell, 1845) was the most abundant species in the area,
although its biomass was low due to the small maximum
size of this species. Ommastrephidae, especially Todarodes
sagittatus (Lamarck 1798) and Illex coindetii (Ve
´rany
1839), and Onychoteuthidae as Onychoteuthis banksii
(Leach 1817) and Ancistroteuthis lichtensteinii (Fe
´russac
and d’Orbigny 1835) represented a consistent part of the
local cephalopod fauna. The highest values of biomass
were estimated for T. sagittatus (46,098.2 g). Similar val-
ues were reached by Thysanoteuthis rhombus Troschel
1857, but these resulted from just a few (n=6) large
individuals (Table 2).
A total of 1,032 cephalopods were recorded from
swordfish (8.3 prey/predator), 131 from bluefin tuna (5.9
prey/predator), 1,876 from albacore (18.8 prey/predator),
and 57 from Mediterranean spearfish (2.3 prey/predator)
(Table 3). The cephalopods T. sagittatus,O. banksii,I.
coindetii,Histioteuthis reversa (Verrill 1880), Ancistroc-
heirus lesueurii (Fe
´russac and d’Orbigny 1842), and Arg-
onauta argo (Linnaeus 1758) were preyed by all pelagic
fish species studied. In contrast, some taxa were found only
in the stomachs of a single predator species: Abralia ver-
anyi (Ru
¨ppell 1844), Galiteuthis armata (Joubin 1898), and
Octopoteuthis cfr. sicula (Ru
¨ppell 1844) in swordfish;
Todaropsis eblanae in bluefin tuna; Alloteuthis subulata
(Lamarck 1798) and Scaeurgus unicirrhus (Delle Chiaje
1840) in albacore. Table 3also shows the average values of
beak size (LRL or LHL in mm) and body mass (eW in g)
for each cephalopod.
The abundance percentage (%N), estimated weight per-
centage (%eW), and frequency of occurrence (%F)of
cephalopod species and families are listed in Table 4.
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123

Table 1 Equations used to rebuild body mass from beak size (LRL or LHL) for each species
Superorder and order Family Species Equation References No. of individuals
Octopodiformes
Octopoda Octopodidae Eledone cirrhosa ln W =1.68 ?2.85 * ln LHL Clarke (1986) 214
Pteroctopus tetracirrhus W=0.951 ?0.928 * LHL Present paper (only juveniles) 11
Scaeurgus unicirrhus W=0.943 ?0.937 * LHL Present paper (only juveniles) 6
Argonautidae Argonauta argo ln W =-0.545 ?3.26 * ln LHL Present paper 10
Ocythoidae Ocythoe tuberculata ln W =-1.05 ?2.51 * ln LHL Lu and Ickeringill (2002)16
Tremoctopodidae Tremoctopus violaceus ln W =0.390 ?2.829 * ln LHL Present paper 8
Decapodiformes
Oegopsida Brachioteuthidae Brachioteuthis riisei ln W =-0.81 ?2.94 * ln LRL Lu and Ickeringill (2002)25
Chiroteuthidae Chiroteuthis veranyi ln W =-0.241 ?2.7 * ln LRL Clarke (1980)14
Cranchiidae Galiteuthis armata ln W =0.700 ?2.233 * ln LRL Present paper 5
Ancistrocheiridae Ancistrocheirus lesueurii ln W =-0.194 ?3.56 * ln LRL Clarke (1980)21
Enoploteuthidae Abralia veranyi ln W =0.979 ?2.304 * ln LRL Present paper 5
Histioteuthidae Histioteuthis bonnellii ln W =1.594 ?2.31 * ln LRL Clarke (1986)–
Histioteuthis reversa ln W =1.41 ?2.35 * ln LRL Lu and Ickeringill (2002)10
Octopoteuthidae Octopoteuthis cfr sicula ln W =0.23 ?2.54 * ln LRL Lu and Ickeringill (2002)9
Ommastrephidae Illex coindetii ln W =1.174 ?2.47 * ln LRL Clarke (1962a,b)14
Ommastrephes bartrami ln W =1.834 ?2.07 * ln LRL Wolff (1982)–
Todarodes sagittatus ln W =0.783 ?2.83 * ln LRL Clarke (1962a,b)–
Todaropsis eblanae ln W =1.066 ?2.724 * ln LRL Zumholz and Piatkowski (2005) 313
Onychoteuthidae Ancistroteuthis lichtensteinii ln W =0.09 ?3.23 * ln LRL Lu and Ickeringill (2002)18
Onychoteuthis banksii ln W =0.58 ?3.7 * ln LRL Wolff (1984)–
Thysanoteuthidae Thysanoteuthis rhombus ln W =2.855 ?3.06 * ln LRL Clarke (1962a,b)7
Myopsida Loliginidae Alloteuthis subulata ln W =2?2.75 * ln LRL Clarke (1986) 116
Sepioidea Sepiolidae Heteroteuthis dispar ln W =1.033 ?2.527 * ln LRL Present paper 14
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123

T. sagittatus (%N=30.52; %eW =36.53; %F=62.9) and
A. lichtensteinii (%N=19.57; %eW =8.69; %F=48.4)
were the most important cephalopods detected in swordfish
stomachs, whereas blue-fin tuna preyed mainly on Tremoc-
topus violaceus Delle Chiaje 1830 (%N=36.64; %eW =
37.86; %F=36.4) and T. sagittatus (%N=19.85; %eW =
6.80; %F =59.1). H. dispar (%N=65.03; %eW =24.04;
%F=66.0) was found to be the preferential prey for
albacore, followed by T. sagittatus (%N=11.78; %eW =
24.10; %F=46.0) and O. banksii (%N=9.65; %eW =
24.43; %F=57.0). Mediterranean spearfish preyed mostly
on the epipelagic cephalopod T. violaceus (%N=24.56;
%eW =22.29; %F=1.8) and the ommastrephid I. coind-
etii (%N=22.81; %eW =23.08; %F=1.5).
The analysis of cephalopod body mass in predator diet
shows a clear dominance of muscular squids of all weight
classes (0–50 g; 51–100 g; 101–300 g; [300 g) in sword-
fish and blue-fin tuna food items (Fig. 2). These
cephalopods were less represented in samples collected
from Mediterranean spearfish, as this fish also preyed on
pelagic octopuses and buoyant squids. The pelagic octo-
puses constituted a consistent part of blue-fin tuna prey for
all weight classes. The albacore showed selective feeding
on small prey (99.6% of total prey), in particular sepiolids
(65.0%). Moreover, this predator is able to collect also
juvenile specimens of demersal octopuses (5.1%), which
have not yet settled on the bottom.
Discussion
The present study investigated the presence and distribu-
tional patterns of pelagic cephalopods by assessing the
importance of these species in the diet of large predatory
fish, which are considered efficient ‘‘cephalopod collec-
tors.’’ In fact, the analysis of the stomach content of apex
Table 2 Total number (N) and estimated weight (eW) of each cephalopod species identified from the stomach contents of large pelagic predators
caught in the central Mediterranean, together mean values of beak size (LRL or LHL in mm) and estimated cephalopod weight (eW)
Superorder
and order
Family Cephalopod species NeW(g) LRL/LHL (mm) eW (g)
Mean SD Mean SD
Octopodiformes
Octopoda Octopodidae Eledone cirrhosa (Lamarck, 1798) 2 4.8 0.8 – 2.4 –
Pteroctopus tetracirrhus (Delle Chiaje, 1830) 67 104.2 0.7 0.2 1.6 0.2
Scaeurgus unicirrhus (Delle Chiaje, 1840) 30 45.1 0.6 0.1 1.5 0.1
Argonautidae Argonauta argo Linnaeus, 1758 47 456.2 2.1 1.5 8.6 12.2
Ocythoidae Ocythoe tuberculata Rafinesque, 1814 18 106.7 2.1 1.8 5.5 7.5
Tremoctopodidae Tremoctopus violaceus Delle Chiaje, 1830 81 11,192.6 2.5 1.5 138.2 509.9
Decapodiformes
Oegopsida Brachioteuthidae Brachioteuthis riisei (Steenstrup, 1882) 6 38.8 2.4 0.4 6.5 2.7
Chiroteuthidae Chiroteuthis veranyi (Fe
´russac, 1835) 20 260.1 2.4 1.1 13.0 18.6
Cranchiidae Galiteuthis armata Joubin, 1898 16 178.1 2.6 0.9 11.1 17.4
Ancistrocheiridae Ancistrocheirus lesueurii (Fe
´russac
and d’Orbigny, 1842)
16 1,493.7 2.0 2.1 92.9 189.5
Enoploteuthidae Abralia veranyi (Ru
¨ppell, 1844) 4 8.7 1.5 0.4 2.2 1.2
Histioteuthidae Histioteuthis bonnellii (Fe
´russac, 1835) 21 797.4 2.1 1.0 38.0 52.3
Histioteuthis reversa (Verrill, 1880) 27 1053.2 2.9 0.7 55.7 29.8
Octopoteuthidae Octopoteuthis cfr sicula Ru
¨ppell, 1844 1 935.3 – – – –
Ommastrephidae Illex coindetii (Ve
´rany, 1839) 152 11,259.8 3.1 1.6 74.1 65.2
Ommastrephes bartrami (Lesueur, 1821) 39 6,611.5 4.2 2.5 169.5 256.9
Todarodes sagittatus (Lamarck, 1798) 565 46,098.2 2.7 1.8 81.6 122.5
Todaropsis eblanae (Ball, 1841) 2 273.8 3.7 – 136.9 –
Onychoteuthidae Ancistroteuthis lichtensteinii (Fe
´russac
and d’Orbigny, 1835)
302 11,335.0 2.4 1.2 37.5 53.5
Onychoteuthis banksii (Leach, 1817) 270 2,587.1 1.2 0.6 9.6 22.5
Thysanoteuthidae Thysanoteuthis rhombus Troschel, 1857 6 45,192.0 5.6 3.7 7,532.0 11,263.5
Myopsida Loliginidae Alloteuthis subulata (Lamarck, 1798) 2 7.7 0.8 – 3.9 –
Sepioidea Sepiolidae Heteroteuthis dispar (Ru
¨ppell, 1845) 1,402 1,317.9 0.9 0.2 0.8 1.3
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Table 3 Number of specimens (N) and total and mean estimated weight (eW) of each cephalopod species identified from the stomach contents of large pelagic predators caught in the central
Mediterranean (SWO =Swordfish; BFT =Bluefin tuna; ALB =Albacore; MSP =Mediterranean spearfish), together mean values of beak size in mm (LRL or LHL)
Superorder and order Family Cephalopod species SWO BFT
NLRL/LHL (mm) eW (g) NLRL/LHL (mm) eW (g)
Mean SD Tot Mean SD Mean SD Tot Mean SD
Octopodiformes
Octopoda Octopodidae Eledone cirrhosa 1 – – 2.1 – – 0 0
Pteroctopus tetracirrhus 3 0.8 0.1 5.2 1.7 0.1 0 0
Scaeurgus unicirrhus 0000
Argonautidae Argonauta argo 14 2.5 1.2 124.3 8.9 11.9 4 3.8 0.9 86.9 21.7 12.0
Ocythoidae Ocythoe tuberculata 11 2.9 1.9 96.4 8.8 8.2 0 0
Tremoctopodidae Tremoctopus violaceus 19 2.7 2.2 4,979.8 262.1 901.1 48 2.5 1.3 5,502.0 114.6 348.0
Decapodiformes
Oegopsida Brachioteuthidae Brachioteuthis riisei 6 2.4 0.4 38.8 6.5 2.7 0 0
Chiroteuthidae Chiroteuthis veranyi 19 2.3 0.8 177.8 9.4 9.2 1 – – 82.3 – –
Cranchiidae Galiteuthis armata 16 2.6 0.9 178.1 11.1 17.4 0 0
Ancistrocheiridae Ancistrocheirus lesueurii 3 2.6 3.0 515.7 171.9 296.8 1 – – 1.0 – –
Enoploteuthidae Abralia veranyi 4 1.5 0.4 8.7 2.2 1.2 0 0
Histioteuthidae Histioteuthis bonnellii 13 2.1 0.6 393.9 30.3 21.3 1 – – 247.4 – –
Histioteuthis reversa 19 2.9 0.6 1,041.7 54.8 24.6 3 2.6 0.9 126.4 42.1 35.5
Octopoteuthidae Octopoteuthis cfr sicula 1 – – 935.3 – – 0 0
Ommastrephidae Illex coindetii 103 3.7 1.2 9,916.1 96.3 62.4 4 2.9 1.4 243.3 60.8 55.6
Ommastrephes bartrami 35 4.1 2.5 5,635.0 161.0 253.0 4 5.1 3.3 976.4 244.1 319,3
Todarodes sagittatus 315 3.8 1.6 43,923.1 139.4 138.0 26 2.3 1.1 988.5 38.0 50.9
Todaropsis eblanae 0 0 2 3.7 – 273.8 136.9 –
Onychoteuthidae Ancistroteuthis lichtensteinii 202 2.9 1.1 10,397.5 51.5 57.7 9 2.7 1.4 434.6 48.3 59.4
Onychoteuthis banksii 71 1.4 0.6 885.7 12.5 27.0 17 1.5 0.9 468.0 27.5 45.3
Thysanoteuthidae Thysanoteuthis rhombus 5 5.4 4.1 40,100.8 8,020.2 12,521.8 1 – – 5,091.2 – –
Myopsida Loliginidae Alloteuthis subulata 0000
Sepioidea Sepiolidae Heteroteuthis dispar 172 1.0 0.3 224.9 1.3 3.3 10 0.8 0.2 9.3 0.5 0.4
Total cephalopods per predator 1,032 119,580.8 131 14,531.2
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Table 3 continued
Superorder and order Family Cephalopod species ALB MSP
NLRL/LHL (mm) eW (g) NLRL/LHL (mm) eW (g)
Mean SD Tot Mean SD Mean SD Tot Mean SD
Octopodiformes
Octopoda Octopodidae Eledone cirrhosa 1 – – 2.7 – – 0 0
Pteroctopus tetracirrhus 64 0.6 0.2 99.1 1.6 0.1 0 0
Scaeurgus unicirrhus 30 0.6 0.1 45.1 1.5 0.1 0 0
Argonautidae Argonauta argo 18 0.6 0.2 51.7 0.1 0.1 11 2.1 0.9 193.4 17.6 13.0
Ocythoidae Ocythoe tuberculata 7 0.9 0.5 10.3 0.5 0.7 0 0
Tremoctopodidae Tremoctopus violaceus 0 0 14 2.0 1.0 710.8 50.8 71.9
Decapodiformes
Oegopsida Brachioteuthidae Brachioteuthis riisei 0000
Chiroteuthidae Chiroteuthis veranyi 0000
Cranchiidae Galiteuthis armata 0000
Ancistrocheiridae Ancistrocheirus lesueurii 8 0.7 0.3 9.4 0.4 0.6 4 4.4 1.8 967.5 241.9 243.6
Enoploteuthidae Abralia veranyi 0000
Histioteuthidae Histioteuthis bonnellii 0 0 7 1.7 0.8 156.1 22.3 21.9
Histioteuthis reversa 1 – – 142.6 – – 4 2.8 0.6 192.6 48.1 21.3
Octopoteuthidae Octopoteuthis cfr sicula 0000
Ommastrephidae Illex coindetii 32 1.1 0.8 364.5 11.4 24.1 13 2.7 1.6 735.8 56.6 55.0
Ommastrephes bartrami 0000
Todarodes sagittatus 221 1.2 0.5 1,086.4 4.9 6.9 3 2.3 1.2 100.2 33.4 27.7
Todaropsis eblanae 0000
Onychoteuthidae Ancistroteuthis lichtensteini 91 1.2 0.6 502.9 5.5 18.5 0 0
Onychoteuthis banksii 181 1.1 0.5 1,101.3 6.1 12.8 1 – – 132.1 – –
Thysanoteuthidae Thysanoteuthis rhombus 0000
Myopsida Loliginidae Alloteuthis subulata 2 0.8 – 7.7 3.9 – 0 0
Sepioidea Sepiolidae Heteroteuthis dispar 1,220 0.9 0.2 1,083.6 0.7 0.5 0 0
Total cephalopods per predator 1,876 4,507.3 57 3,188.4
Helgol Mar Res
123

predators is a significant source of data to describe this
component of the marine fauna (Tsuchiya et al. 1998;
Lansdell and Young 2007). Limitations of this method
could be related to the retention of larger beaks in the
stomachs of predators for several days (Santos et al. 2001)
and to the migratory behavior of large pelagic predators.
To minimize potential biases, four ‘‘cephalopod-samplers’’
were considered which differed in size, feeding habits, and
preferential habitats were. In fact, the presence of cepha-
lopods in the diet of large pelagics is strictly related to the
water layer where the predator usually feeds and to its
capability to carry out vertical movements.
Much information on horizontal and vertical migration
was recently acquired by tagging experiments with sword-
fish (Carey and Robinson 1981; Takahashi et al. 2003;
Canese et al. 2004,2008), blue-fin tuna (Lutcavage et al.
2000; Block et al. 2001,2005), and albacore (Arrizabalaga
et al. 2002; Cosgrove et al. 2006). Swordfish perform ver-
tical excursions, reaching depths up to 800 m during day-
light and remaining near the surface at night (Carey and
Robinson 1981; Carey 1990; Takahashi et al. 2003). Their
diel vertical excursions are usually discontinouos and fre-
quently interrupted by vertical rises (Canese et al. 2008).
Blue-fin tuna follows a similar behavioral path, diving to
depth [600 m (Block et al. 2001), whereas the albacore
depth range varies from the surface layers to 450 m (Bard
2001). While these three species are usually able to explore
a large part of the water column, the Mediterranean
spearfish does not seem to dive deeper than the thermocline
(Nakamura 1985), as reported in studies on its feeding
Table 4 Abundance percentage (%N), estimated weight percentage
(%eW) and frequency of occurrence (%F) of cephalopod prey
(species and family) identified from the stomach contents of large
pelagic predators caught in the central Mediterranean
(SWO =Swordfish; BFT =Blue-fin tuna; ALB =Albacore;
MSP =Mediterranean spearfish)
Superorder and order Prey types SWO BFT ALB MSP
%N%eW %F%N%eW %F%N%eW %F%N%eW %F
Octopodiformes
Octopoda Octopodidae 0.4 \0.1 2.4 – – – 5.1 3.3 24.0 – – –
E. cirrhosa 0.1 \0.1 0.8 – – – 0.1 0.1 1.0 – – –
P. tetracirrhus 0.3 \0.1 1.6 – – – 3.4 2.2 24.0 – – –
S. unicirrhus – – – – – – 1.6 1.0 5.0 – – –
Argonautidae (A. argo) 1.4 0.1 7.3 3.1 0.6 18.2 1.0 1.1 10.0 19.3 6.1 2.0
Ocythoidae (O. tuberculata) 1.1 0.1 5.6 – – – 0.4 0.2 4.0 – – –
Tremoctopodidae (T. violaceus) 1.8 4.2 4.8 36.6 37.9 36.4 – – – 24.6 22.3 1.8
Decapodiformes
Oegopsida Brachioteuthidae (B. riisei) 0.6 \0.1 3.2 – – – – – – – – –
Chiroteuthidae (C. veranyi) 1.8 0.1 5.6 0.8 0.6 4.5 – – – – – –
Cranchiidae (G. armata) 1.6 0.1 6.5 – – – – – – – – –
Ancistrocheiridae (A. lesueurii) 0.3 0.4 2.4 0.8 \0.1 4.5 0.4 0.2 7.0 7.0 30.3 0.8
Enoploteuthidae (A. veranyi) 0.4 \0.1 2.4 – – – – – – – – –
Histioteuthidae 3.1 1.2 15.3 3.1 2.6 13.6 0.1 3.2 1.0 19.3 10.9 1.5
H. bonnellii 1.3 0.3 7.3 0.8 1.7 4.5 – – – 12.3 4.9 0.8
H. reversa 1.8 0.9 8.9 2.3 0.9 9.1 0.1 3.2 1.0 7.0 6.0 1.0
Octopoteuthidae (O. cfr sicula) 0.1 0.8 0.8 – – – – – – – – –
Ocythoidae (O. tuberculata) 1.1 0.1 5.6 – – – 0.4 0.2 4.0 – – –
Ommastrephidae 43.9 49.7 79.8 27.5 17.1 63.6 13.5 32.2 48.0 28.1 26.2 2.0
I. coindetii 10.0 8.3 37.9 3.1 1.7 13.6 1.7 8.1 18.0 22.8 23.1 1.5
O. bartrami 3.4 4.7 18.5 3.1 6.7 13.6 – – – – – –
T. sagittatus 30.5 36.7 62.9 19.8 6.8 59.1 11.8 24.1 46.0 5.3 3.1 0.5
T. eblanae – – – 1.5 1.9 9.1 – – – – – –
Onychoteuthidae 26.5 9.4 58.9 19.8 6.2 54.6 14.5 35.6 58.0 1.8 4.1 0.3
A. lichtensteini 19.6 8.7 48.4 6.9 3.0 31.8 4.9 11.2 33.0 – – –
O. banksii 6.9 0.7 21.8 13.0 3.2 31.8 9.6 24.4 57.0 1.8 4.1 0.3
Thysanoteuthidae (T. rhombus) 0.5 33.5 2.4 0.8 35.0 4.5 – – – – – –
Myopsida Loliginidae (A. subulata) – – – – – – 0.1 0.2 1.0 – – –
Sepioidea Sepiolidae (H. dispar) 16.7 0.2 33.9 7.6 0.1 13.6 65.0 24.0 66.0 – – –
Helgol Mar Res
123

behavior in the Mediterranean Sea (Castriota et al. 2008;
Romeo et al. 2009).
The analysis of cephalopod prey from a large number of
stomachs of X. gladius,T. thynnus,T. alalunga, and T.
belone provides a clearer picture of the pelagic cephalopod
fauna in a macro-area of the central Mediterranean Sea
(southern Tyrrhenian Sea and Strait of Messina). Cepha-
lopods in the study area are mainly dominated by Sepio-
lidae, Ommastrephidae, and Onychoteuthidae. The pelagic
Sepiolidae are only represented by H. dispar. The high
number of specimens (n=1,402) found in the present
study as well as the huge biomass of this species recorded
in other areas (Bello 1999; Salman and Karakulak 2009)
suggest this squid being a key-species in the Mediterranean
pelagic food web. In particular, H. dispar is an important
food item for T. alalunga since this fish usually hunts small
prey aggregated in schools (Bello 1999; Consoli et al.
2008). In fact, H. dispar is a small-sized sepiolid that
usually lives in groups in lower epipelagic and in meso-
pelagic zones, most commonly in depths between 200 and
300 m (Jereb and Roper 2005).
The greatest overall prey biomass was represented by
Ommastrephidae (especially T. sagittatus,O. bartramii,
and I. coindetii) and Onychoteuthidae (O. banksii and A.
lichtensteinii), highlighting the importance of these
widely distributed families in the pelagic ecosystem of the
area. Moreover, it is well known that these muscular fast-
swimming squids are high-speed growing active preda-
tors, which efficiently convert their prey into own bio-
mass (Clarke 1996b), thus representing a primary source
of energy for large marine fishes. The importance of the
Ommastrephidae in the study area, especially in the area
around the Aeolian Islands, is also confirmed by the
presence of a specific professional fishing activity by
squid hand-jig lines targeting T. sagittatus (Battaglia et al.
2010).
The neutrally buoyant and slowly swimming ammoni-
acal squids belonging to the Histioteuthidae, Histioteuthis
bonnellii (Fe
´russac 1835) and H. reversa, and to the Chi-
roteuthidae, Chiroteuthis veranyi (Fe
´russac 1835) seem to
characterize the deeper water layers in the study area. This
is confirmed by their morphological features (e.g., the
presence of light organs) as well as by their occurrence
mainly in swordfish stomachs (i.e., in that predator which
carries out feeding excursions to deep water layers). The
abundance of Histioteuthidae in deeper waters was also
recorded in other Mediterrranean areas, such as Spanish
waters (Quetglas et al. 2010), where H. bonnellii and H.
reversa show a spatial segregation with peaks of occur-
rence at 500–600 m and 600–700 m depth, respectively.
Moreover, Quetglas et al. (2010) reported an increase in
mean size of H. reversa with depth, indicating an ontoge-
netic migration to deeper waters. Therefore, the species’
abundance might be even higher than reported in the
present paper, because of the limited bathymetric range in
which predators are usually hunting.
The occurrence of some specimens of neutrally buoyant
squids in the diet of the surface-feeding predator T. belone
may be due to the upwelling currents in the Strait of
Messina that concentrates deep fauna in the area, and to the
species’ diel vertical migrations to shallow depths at night
(Quetglas et al. 2010).
Pelagic octopuses (T. violaceus,A. argo, and Ocythoe
tuberculata Rafinesque 1814), belonging to the Argonau-
thoidea, inhabit epipelagic waters of the study area and,
according to our results, seem to be more common than
previously thought. These cephalopods occur in near-sur-
face waters and rarely descend below the thermocline
0
10
20
30
40
50
60
70
0 -50 g 51 -100 g 101 -300 g > 300 g
% ind.
prey weight classes
Pelagic octopuses
Sepiolids
Demersal octopuses
(juveniles)
Muscular squids
Buoyant squids
SWO
0
10
20
30
40
50
60
70
0 -50 g 51 -100 g 101 -300 g > 300 g
% ind.
prey weight classes
Pelagic octopuses
Sepiolids
Demersal octopuses
(juveniles)
Muscular squids
Buoyant squids
BFT
0
10
20
30
40
50
60
70
80
90
100
0 -50 g 51 -100 g 101 -300 g > 300 g
% ind.
prey weight classes
Pelagic octopuses
Sepiolids
Demersal octopuses
(juveniles)
Muscular squids
Buoyant squids
ALB
0
10
20
30
40
50
60
70
80
0 -50 g 51 -100 g 101 -300 g > 300 g
% ind.
prey weight classes
Pelagic octopuses
Sepiolids
Demersal octopuses
(juveniles)
Muscular squids
Buoyant squids
MSP
Fig. 2 Prey species
composition (%) within the four
weight ranges (0–50; 51–100;
101–300; [300 g) in the
stomach content of predator
species (SWO swordfish, BFT
bluefin tuna, ALB albacore,
MSP Mediterranean spearfish)
Helgol Mar Res
123

(Voss 1953; Thomas 1977; Bello 1993). For this reason, T.
violaceus and A. argo represented a consistent part of the
cephalopods collected by the surface-feeding T. belone.A
clear preference for T. violaceus was showed for the
predator T. thynnus, as it was also reported also by Ka-
rakulak et al. (2009) for the eastern Mediterranean Sea.
The occurrence of small specimens of the demersal
species Eledone cirrhosa (Lamarck 1798), Pteroctopus
tetracirrhus (Delle Chiaje 1830), and S. unicirrhus is likely
to be due to the local presence of schools of juveniles
(Giordano et al. 2010). Pelagic predators can take advan-
tage of demersal octopuses as long as their young stages
have not yet settled on the bottom.
On the other hand, records of both adult and juvenile
individuals of a prey species in the stomachs of several
cephalopods (A. lichtensteinii, H. dispar, I. coindetii, O.
banksii, T. rhombus, and T. sagittatus) indicate that these
species are likely to complete their entire life cycle in this
area.
The present study also provided the opportunity to
improve our knowledge on the distribution of some scar-
cely known and rare cephalopod species. A large beak
(LRL =14.1 mm) probably belonging to a specimen of
the octopoteuthid Octopoteuthis sicula (Ru
¨ppell 1844) was
found in a swordfish stomach. Large individuals of this
species have never been recorded before, and among the
few specimens caught until now, most records remained
uncertain (Villari and Ammendolia 2009). This new data
suggest that O. sicula can reach a larger size and that the
growth of this species should be revaluated. Other rare
cephalopods recorded in the study area were A. veranyi and
G. armata.
The highest number of different prey species (20) was
recorded in swordfish stomachs. This indicates that X.
gladius can be considered the most efficient ‘‘cephalopod
collector’’ that probably relates to the species’ hunting
behavior during large vertical migrations (Canese et al.
2008). Both epipelagic (T. violaceus, A. argo, etc.) and
deep-water cephalopods (C. veranyi,H. bonnellii,H. re-
versa,O. cfr sicula, and A. veranyi) were recorded in its
diet. The intake of cephalopod prey species that follow a
dial vertical migration pattern seems to be important for all
predators except for T. belone. This species usually hunts
above the thermocline and mainly during daylight, there-
fore not exploiting the vertical migrations of several
cephalopods at night time (Castriota et al. 2008; Romeo
et al. 2009).
In the light of the results achieved so far, analyses of the
diet of pelagic predators are still the best tool to investigate
the cephalopod community in pelagic areas (Cherel et al.
2004). In this context, the collection of cephalopod beaks
in the stomachs of predators is a fundamental part in
assessing the importance of cephalopods in the marine food
web and in understanding the cephalopod diversiy in
pelagic waters. Therefore, as far as the Mediterranean Sea
is concerned, diagnostic tools for cephalopod beak identi-
fication (Clarke 1977) should be improved.
Acknowledgments The authors are grateful to Dr. G. Bello for his
help in the classification of some beaks and to A. Villari and G.
Ammendolia for their contribution in identifying rare species, thanks
to their personal cephalopod collections, made up from stranding
specimens in the Strait of Messina. The authors would also like to
acknowledge the collaboration of the fishermen during sampling
operations.
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