Anali za istrske in mediteranske študije
Annali di Studi istriani e mediterranei
Annals for Istrian and Mediterranean Studies
Series Historia Naturalis, 35, 2025, 1
UDK 5                       Annales, Ser. hist. nat., 35, 2025, 1, pp. 1-170, Koper 2025  ISSN 1408-533X
KOPER 2025
Anali za istrske in mediteranske študije
Annali di Studi istriani e mediterranei
Annals for Istrian and Mediterranean Studies
Series Historia Naturalis, 35, 2025, 1
UDK 5                    ISSN 1408-533X 
                e-ISSN 2591-1783
ANNALES · Ser. hist. nat. · 35 · 2025 · 1
Anali za istrske in mediteranske študije - Annali di Studi istriani e mediterranei - Annals for Istrian and Mediterranean Studies
ISSN 1408-533X     UDK 5  Letnik 35, leto 2025 številka 1
e-ISSN 2591-1783
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ANNALES · Ser. hist. nat. · 35 · 2025 · 1
Anali za istrske in mediteranske študije - Annali di Studi istriani e mediterranei - Annals for Istrian and Mediterranean Studies
UDK 5                                                      Letnik 35, Koper 2025, številka 1                                      ISSN 1408-53 3X
e-ISSN 2591-1783 
VSEBINA / INDICE GENERALE / CONTENTS
BIOTSKA GLOBALIZACIJA
GLOBALIZZAZIONE BIOTICA
BIOTIC GLOBALIZATION
Okan AKYOL, Oğuzhan TAKICAK & 
Hasan TARUN
A Fugitive Lessepsian Fish in a Sea-Cage 
Farm in the Aegean Sea: Stephanolepis 
diaspros (Monacanthidae) ................................
Ubežni lesepski migrant iz ribogojnice 
v Egejskem morju: Stephanolepis 
diaspros (Monacanthidae)
Nicola BETTOSO, Lisa FARESI, Valentina 
TORBOLI & Jose A. CUESTA
Additional Record of the Pea Crab 
Pinnotheres bicristatus (Brachyura: 
Pinnotheridae) in the Adriatic Sea ....................
Dodatni zapis o pojavljanju stražne 
rakovice vrste Pinnotheres bicristatus 
(Brachyura: Pinnotheridae) 
v Jadranskem morju
Alan DEIDUN, Sarah BAUMANN, 
Bruno ZAVA & Maria CORSINI-FOKA
Confirming the Occurrence of the 
Non-Indigenous Pteragogus trispilus 
(Actinopterygii: Labridae) within 
Maltese Waters ................................................
Potrditev pojavljanja tujerodne ustnače 
vrste Pteragogus trispilus (Actinopterygii: 
Labridae) znotraj malteških voda
Deniz ERGÜDEN, Yusuf Kenan BAYHAN, 
Sibel ALAGÖZ ERGÜDEN & Deniz AYAS
A New Ichthyological Record and 
Distributional Update for Epigonus 
denticulatus Dieuzeide, 1950 in 
Turkish Mediterranean Waters ...........................
Nov ihtiološki zapis in podatki o 
razširjenosti rjavega veleokca, Epigonus 
denticulatus Dieuzeide, 1950 v turških 
sredozemskih vodah
Sara LADOUL, Farid HEMIDA, 
Christian REYNAUD & Christian CAPAPÉ
On the Occurrence of Cornish Blackfish 
Schedophilus medusophagus 
(Osteichthyes: Centrolophidae) 
from the Maghreb Shore 
(Southwestern Mediterranean Sea) ...................
Potrjena prisotnost meduzojeda 
Schedophilus medusophagus 
(Osteichthyes: Centrolophidae) 
z magrebske obale (jugozahodno 
Sredozemsko morje)
Christina MICHAIL & Francesco TIRALONGO
First Occurrence of Ariidae in 
Cypriot Waters – a Major 
Contribution to Biodiversity .............................
Prvo pojavljanje predstavnikov iz 
družine Ariidae v ciprskih vodah – 
velik prispevek k biodiverziteti
SREDOZEMSKE HRUSTANČNICE
SQUALI E RAZZE MEDITERRANEE
MEDITERRANEAN SHARKS AND RAYS
Lovrenc LIPEJ, Riccardo BATTISTELLA, 
Borut MAVRIČ & Danijel IVAJNŠIČ
An Insight into the Diet of the Bull Ray, 
Aetomylaeus bovinus (Geoffroy 
Saint-Hilaire, 1817) in the 
Northern Adriatic Sea ......................................
Vpogled v prehranjevalne navade 
kljunatega morskega goloba, 
Aetomylaeus bovinus (Geoffroy 
Saint-Hilaire, 1817) v severnem Jadranu
Cem ÇEVİK, Deniz ERGÜDEN & Deniz AYAS
A New Capture Record of Alopias 
superciliosus Lowe, 1841 from the 
Turkish Coast (Northeastern Mediterranean) ......
Nov ulov velikooke morske lisice 
Alopias superciliosus Lowe, 1841 
iz turške obale (severovzhodno Sredozemlje)
1
7
13
21
35
27
43
55
ANNALES · Ser. hist. nat. · 35 · 2025 · 1
Cem DALYAN, N. Bikem KESİCİ, Elif YÜCEDAĞ 
BAKIR, Yunus GÖNÜL & Hakan KABASAKAL
No Longer as Common as its Name: a Review 
of the Occurrence of Torpedo torpedo 
(Linnaeus, 1758) (Chondrichthyes: 
Elasmobranchii) in Turkish Waters, 
with Photographic Evidence .............................
Ni več tako pogost kot njegovo ime: pregled 
pojavljanja okatega električnega skata Torpedo 
torpedo (Linnaeus, 1758) (Chondrichthyes: 
Elasmobranchii) v turških vodah s 
fotografskimi dokazi
Deniz ERGÜDEN, Cemal TURAN, Servet Ahmet 
DOĞDU & Deniz AYAS 
Disc Deformity in a Juvenile Female Brown Ray, 
Raja miraletus (Family: Rajidae), from 
Northeastern Mediterranean (Türkiye) .................
Deformacija diska pri juvenilni samici modropege 
raže, Raja miraletus (družina: Rajidae), iz 
severovzhodnega Sredozemskega morja (Turčija)
Farid HEMIDA, Christian REYNAUD & 
Christian CAPAPÉ 
On an Old Record of the Smalltooth Sand Tiger 
Shark Odontaspis ferox (Chondrichthyes: 
Odontaspididae) from the Algerian Coast 
(Southwestern Mediterranean Sea) ........................
O starem zapisu o drobnozobem morskem biku 
Odontaspis ferox (Chondrichthyes: Odontaspididae) 
z alžirske obale (jugozahodno Sredozemsko morje)
Hakan KABASAKAL, Uğur UZER & 
F. Saadet KARAKULAK
Plastic Debris-Induced Fin Damage 
in the Smoothhound, Mustelus mustelus ..............
Poškodbe plavuti pri navadnem 
morskem psu, Mustelus mustelus, 
zaradi plastičnih odpadkov
Nicolas ZIANI, Florane TONDU, 
Rémi BRU, Chloé MOSNIER, 
Sarah FOXONET, Ruben Bao GALLIEN, 
Mathias POULY, Modan Lou TONIETTO, 
Lucille VERDON, Eloïse DEYSSON, 
Alessandro DE MADDALENA & 
Hakan KABASAKAL 
Bite Marks Observed on a Large Female 
White Shark Carcharodon carcharias 
Off Camargue, France Provide Potential 
Insights into the Reproduction of the 
Mediterranean Population ................................
Sledovi ugrizov na veliki samici 
belega morskega volka Carcharodon 
carcharias pri Camargu (Francija) 
kažejo na možno razmnoževanje 
sredozemske populacije
MORSKA FAVNA
FAUNA MARINA
MARINE FAUNA
Sihem RAFRAFI-NOUIRA, RIMEL 
BENMESSAOUD, Mourad CHÉRIF, 
Christian REYNAUD & Christian CAPAPÉ
Morphological Deformities in a 
Common Two-Banded Sea Bream, 
Diplodus vulgaris (Osteichthyes: Sparidae), 
from Northern Tunisian Waters 
(Central Mediterranean Sea) ............................
Morfološke deformacije pri fratru, 
Diplodus vulgaris (Osteichthyes: Sparidae), 
iz severnih tunizijskih vod 
(osrednje Sredozemsko morje)
Abdelkarim DERBALI, Aymen HADJ TAIEB & 
Wassim KAMMOUN
The Current Status of Polititapes aureus 
(Mollusca: Bivalvia) in the Coastal 
Zone of Sfax, Tunisia 
(Central Mediterranean) ....................................
Trenutno stanje vrste Polititapes aureus 
(Mollusca: Bivalvia) na obalnem 
območju Sfaxa v Tuniziji 
(osrednje Sredozemlje)
Neža LEBAN & Valentina PITACCO
Current Knowledge on the Distribution 
of the Poorly Known Echiurid Species 
Maxmuelleria gigas (M. Müller, 1852) 
in the Slovenian Sea .........................................
Trenutno poznavanje prostorske 
razporeditve manj poznane vrste 
zvezdaša Maxmuelleria gigas 
(M. Müller, 1852) v slovenskem morju
Jan MALEJ, Tjaša KOGOVŠEK, 
Martin VODOPIVEC, Janja FRANCÉ, 
Patricija MOZETIČ, Matevž MALEJ & 
Alenka MALEJ
Long-Term Study of Zooplankton 
Biomass in the Gulf of Trieste (Adriatic Sea) ......
Dolgoročna študija zooplanktonske 
biomase v Tržaškem zalivu 
(Jadransko morje)
Sihem RAFRAFI-NOUIRA, 
Rimel BENMESSAOUD, Mourad CHÉRIF, 
Christian REYNAUD & Christian CAPAPÉ
Occurrence of the Longjaw Snake Eel, 
Ophisurus serpens (Ophichthidae), in 
Tunisian Waters (Central Mediterranean Sea) .....
Pojavljanje zobate jegulje, Ophisurus 
serpens (Ophichthidae), iz tunizijskih 
voda (osrednje Sredozemsko morje)
83
73
91
65
125
117
109
133
145
97
ANNALES · Ser. hist. nat. · 35 · 2025 · 1
FLORA
FLORA
FLORA
Martina ORLANDO-BONACA, Artur BONACA, 
Diego BONACA & Ana ROTTER
Seagrasses: a Promising Source of 
Bioactive Compounds for Human 
Health Applications ..........................................
Morske cvetnice: obetaven vir 
bioaktivnih spojin za uporabo 
v zdravstvu
OCENE IN POROČILA
RECENSIONI E RELAZIONI
REVIEWS AND REPORTS
Shin-ichi Uye
Book review: Mirrors of the Sea: When 
Science and Art Meet. 30 Years of the 
Unesco Intergovernmental Oceanographic 
Commission in Slovenia ...................................
Kazalo k slikam na ovitku ...................................
Index to images on the cover ............................
153 167
169
169
ANNALES · Ser. hist. nat. · 35 · 2025 · 1
43
received: 2025-04-17                 DOI 10.19233/ASHN.2025.07
AN INSIGHT INTO THE DIET OF THE BULL RAY, AETOMYLAEUS BOVINUS 
(GEOFFROY SAINT-HILAIRE, 1817) IN THE NORTHERN ADRIATIC SEA
Lovrenc LIPEJ 
Marine Biology Station, National Institute of Biology, Piran, Slovenia 
University of Primorska, Faculty of Mathematics, Natural Sciences and Information Technologies, Koper, Slovenia 
e-mail: Lovrenc.lipej@nib.si
Riccardo BATTISTELLA
via S. Stefano 47, Este, Provincia di Padova, Italy
Borut MAVRIČ
Marine Biology Station, National Institute of Biology, Piran, Slovenia
Danijel IVAJNŠIČ
Faculty of Natural Sciences and Mathematics, University of Maribor, 2000 Maribor
Faculty of Arts, University of Maribor, 2000 Maribor
ABSTRACT
This study provides baseline information on the feeding habits of the bull ray, Aetomylaeus bovinus (Geof-
froy Saint-Hilaire, 1817), in the Gulf of Venezia. Among 1557 prey items isolated from the stomachs of bull 
ray specimens, gastropods represented the overwhelming majority (93.8%). Within gastropods, Aporrhais 
pespelecani was the dominant species, followed by Gibbula magus and Bolinus brandaris – all characteristic 
elements of the biocoenosis of the muddy detritic bottom. We observed differences in prey structure between 
juveniles and adults, as well as sexes. Among fishes that proved to be particularly important in terms of bio-
mass, the majority of prey items consisted of small pelagic fish, including pilchard (Sardina pilchardus) and 
horse mackerel (Trachurus sp.). This paper contributes new data on the feeding ecology of a lesser known 
and critically endangered batoid species.
Key words: myliobatids, feeding ecology, nursery, Gulf of Venice
APPROFONDIMENTI SULLE ABITUDINI ALIMENTARI DELLA VACCARELLA, 
AETOMYLAEUS BOVINUS (GEOFFROY SAINT-HILAIRE, 1817) NELL’ADRIATICO 
SETTENTRIONALE
SINTESI
Lo studio riporta le abitudini alimentari della vaccarella, Aetomylaeus bovinus (Geoffroy Saint-Hilaire, 1817), 
nel Golfo di Venezia. Tra le 1557 prede isolate dagli stomaci, i gasteropodi costituivano la grande maggioranza 
(93,8%), dominati dalla specie Aporrhais pespelecani, seguita da Gibbula magus e Bolinus brandaris. Queste 
specie sono elementi caratteristici della biocenosi del fondo detritico fangoso. Sono state osservate differenze 
nella struttura delle prede tra giovani e adulti e tra i sessi. Tra i pesci che sembravano essere particolarmente 
importanti in termini di biomassa, i piccoli pesci pelagici come la sardina (Sardina pilchardus) e il sugarello 
(Trachurus sp.) rappresentavano le prede più grandi. Questo lavoro contribuisce a fornire nuove informazioni 
sull’ecologia alimentare di una specie di razza meno conosciuta e in pericolo critico.
Parole chiave: vaccarella, ecologia alimentare, nursery, Golfo di Venezia
ANNALES · Ser. hist. nat. · 35 · 2025 · 1
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Lovrenc LIPEJ et al.: AN INSIGHT INTO THE DIET OF THE BULL RAY, AETOMYLAEUS BOVINUS (GEOFFROY SAINT-HILAIRE, 1817) ..., 43–54
INTRODUCTION
The bull ray, Aetomylaeus bovinus (Geoffroy 
Saint-Hilaire, 1817), is a benthopelagic species 
inhabiting coastal and warm temperate waters, oc-
casionally found offshore, at depths of 10–150 m 
(Capapé & Quignard, 1975). Bull rays can tolerate 
greatly reduced salinities (Ebert & Stehmann, 2013) 
and therefore occasionally enter shallow lagoons (El 
Kamel et al., 2009) and semi-enclosed bays (Zogaris 
& Dussling, 2010; Bilgili & Kabasakal, 2023). As a 
longevous species with late maturity and low repro-
ductive rates – signature traits of a K-selected life 
history strategy (Stevens et al., 2000) – the bull ray 
is vulnerable to overfishing, especially in nearshore 
habitats, where it forms small aggregations to feed 
(Seck et al., 2002; El Kamel et al., 2010, Zogaris 
& Dussling, 2010; Akyol et al., 2017). The bull ray 
is poorly studied in terms of feeding ecology. The 
only comprehensive study on the feeding habits of A. 
bovinus was conducted by Capapé (1977) in Tunisian 
waters, based on analyses of 568 specimens at differ-
ent stages of development.
Bull rays are observed in the northern Adriatic 
Sea between late spring and early autumn, while 
in winter they migrate towards southern areas (La 
Mesa et al., 2017). Due to its longevity, A. bovinus 
was previously considered an indicator species for 
pollution with heavy metals such as Hg and MeHg 
(Horvat et al., 2013), arsenic (Šlejkovec et al., 2014), 
and selenium (Faganeli et al., 2018). Though not 
commercially targeted, the species is often caught as 
by-catch and discarded. It is currently considered a 
critically endangered ray species on the global scale, 
whose populations suffered substantial depletion in 
the last years due to overfishing (Jabado et al. 2021). 
Recently, this status was also confirmed by Soldo & 
Lipej (2022), who evaluated the species as rare in the 
Adriatic Sea.  
The aim of this study is to investigate the feeding 
habits of the bull ray in the northern Adriatic Sea 
(the Gulf of Trieste and neighbouring areas along the 
western Istrian coast). The feeding ecology of this 
species is significantly understudied, making any 
data in this regard vital. Such research is also nec-
essary and useful in elucidating the impact of such 
predation on the structure of epibenthic macrofaunal 
assemblages.
MATERIAL AND METHODS
The stomachs of bull rays were collected between 
2005 and 2015 from rays caught as by-catch by com-
mercial trawlers. Fishing was conducted at depths of 
10 – 50 m in the Gulf of Trieste and along the western 
Istrian coast (Fig. 1). The sample was comprised of 
neonates, adult males, and adult females, including 
several pregnant specimens. After being defrosted in 
the lab, each individual was sexed. The specimens 
were measured (disk width – DW) and weighed. Each 
stomach was weighed full and emptied. Stomach con-
tents were washed on the sieve and conserved in 95% 
ethanol. Prey items were analysed using an Olympus 
SZX16 stereomicroscope and photographed using an 
Olympus camera DP 74. 
Prey items were identified to the lowest taxonomic 
level (species level where possible), using taxonomic 
keys and field guides (Riedel, 1991; Falciai & Min-
ervini, 1992), and subsequently counted. A reference 
collection of gastropod opercula preserved at the 
Marine Biology Station proved extremely valuable 
for determination, providing additional diagnostic 
support. The counting of prey items was based on typi-
cal anatomical parts: claws and legs for crustaceans, 
carapaces for decapods, shells and feet for bivalves, 
opercula for gastropods (Fig. 2), and partial remains 
(including otoliths) for teleost species. 
Data analysis
Opercula from isolated benthic gastropods were 
precisely measured (max length and width) and 
photographed under the microscope. To assess the 
approximate weight of each gastropod, a correlation 
length-weight curve obtained from the data of live 
collected specimens (pulled from the shells) was used. 
Length-weight correlation curves were calculated for 
the gastropod species that dominated the bull ray’s 
diet: Aporrhais pespelecani (Linnaeus, 1758), Bolinus 
Fig. 1: Map of the studied area and its position in the 
Adriatic Sea. Areas where bull rays were caught are 
depicted as red dots. Catch density is additionally 
presented as a heat map.
Sl. 1: Zemljevid obravnavanega območja in njegov 
položaj glede na Jadransko morje. Predeli, kjer so ujeli 
kljunate morske golobe, so označeni z rdečimi krogci. 
Gostota ulova je prikazana kot kolobarji. 
ANNALES · Ser. hist. nat. · 35 · 2025 · 1
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Lovrenc LIPEJ et al.: AN INSIGHT INTO THE DIET OF THE BULL RAY, AETOMYLAEUS BOVINUS (GEOFFROY SAINT-HILAIRE, 1817) ..., 43–54
brandaris (Linnaeus, 1758), Gibbula magus (Linnaeus, 
1758), and Hexaplex trunculus (Linnaeus, 1758).
The opercula of B. brandaris and H. trunculus 
exhibit numerous morphological similarities, making 
them challenging to distinguish. To ensure accurate 
identification, every operculum assignable to either 
species was carefully examined under the microscope 
and compared against reference specimens collected 
from the natural environment (those used for the cor-
relation length-weight curves). The majority of muricid 
opercula were conclusively identified as B. brandaris. 
In addition to opercular shape, the width-to-length ratio 
proved valuable for species discrimination in ambigu-
ous cases (Fig. 3), as B. brandaris and H. trunculus have 
different opercular proportions. For the few specimens 
that could not be confidently identified, we recorded 
them as generic Murex sp. 
The feeding habits of the bull ray were described 
using relative frequency of occurrence (PF = number 
of stomachs containing prey i/total number of full 
stomachs × 100), relative numerical abundance (PN 
= number of prey i/total number of prey × 100), and 
relative gravimetric composition (PB = weight of prey 
i/total weight of all prey x 100). To minimise potential 
errors inherent in individual parameters, all measures 
were integrated into a single composite Index of Rela-
tive Importance (IRI%) calculated as: 
[IRI =PF × (PN + PB)] (Pinkas et al., 1971),
which reduces potential misinterpretations from 
relying on any single given value. Prey biomass was 
obtained either from species-specific correlation 
diagrams (length-weight relationships) or literature 
estimates (Ravara, 2012). According to Capapé & 
Quignard (1974), we defined sexual maturity at 800 
mm disk width (DW) for males and 900–1000 mm for 
females, classifying individuals below these thresholds 
(DW< 800 mm in males and DW< 900 mm in females) 
as juveniles. Dietary diversity was assessed using the 
Shannon-Wiener diversity index: 
Fig. 2: Opercula of various gastropods present in the diet 
of the bull ray. Legend: a and b – Bolinus brandaris, c and d 
– Hexaplex trunculus, e – Cerithium vulgatum, f – Turritella 
communis, g – Aporrhais pespelecani, and h – Gibbula 
magus. Scale bar = 1 mm.  
Sl. 2: Poklopci (operkuli) različnih polžev, ki se pojavljajo 
v prehrani kljunatega morskega goloba. Legenda: a in b 
– Bolinus brandaris, c in d – Hexaplex trunculus, e – Ce-
rithium vulgatum, f – Turritella communis, g – Aporrhais 
pespelecani in h – Gibbula magus. Merilo = 1 mm.  
Fig. 3: Relationship between width and length of oper-
cula of two similar species Hexaplex trunculus (blue 
diamonds) and Bolinus brandaris (orange squares), 
obtained from specimens as by-catch from the fish-
ermen. This relationship was useful to discriminate 
the opercula of the two muricid species found in the 
stomachs of the bull rays. 
Sl. 3: Odnos med dolžino in širino poklopcev pri dveh 
sorodnih vrstah volekov Hexaplex trunculus (modri karo) 
in Bolinus brandaris (oranžni kvadratki), na podlagi živih 
primerkov, ulovljenih kot prilov ribičev. Ta odnos je bil 
uporaben za razlikovanje poklopcev obeh volekov, na-
jdenih v prehrani kljunatega morskega goloba.  
ANNALES · Ser. hist. nat. · 35 · 2025 · 1
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Lovrenc LIPEJ et al.: AN INSIGHT INTO THE DIET OF THE BULL RAY, AETOMYLAEUS BOVINUS (GEOFFROY SAINT-HILAIRE, 1817) ..., 43–54
H’ = - (Σ pi*ln pi)
Diversity was also assessed separately according 
to sex and size classes. To evaluate the diet overlap 
between juveniles and adults and between males and 
females, we used the Morisita-Horn index (Krebs, 
1989): 
CH = 2*(∑pij pik) / (∑p
2
ij + ∑p
2
ik)
where CH is the simplified Morisita-Horn index 
representing the overlap between predators j and k; Pij 
is the proportion of prey i in the total prey consumed 
by predator j; Pik is the proportion of prey i in the total 
prey consumed by predator k; and n is the total number 
of prey categories. The index ranges from 0 (no dietary 
overlap) to 1 (complete dietary overlap), with values 
over 0.6 indicating significant resource sharing.
To assess the trophic level of the bull ray, a TROPH 
index was calculated using TrophLab software (Pauly 
et al., 2000), available through FishBase (www. fish-
base.org):
TROPHi =1+Σ G j=1 DCij ×TROPHj
TROPHj represents the fractional trophic level of 
prey j, and DCij denotes the proportion of j in the 
diet of consumer species i.
RESULTS
Biometry
A total of 42 bull ray specimens were measured 
and weighed, of which 19 were identified as males 
and 22 as females, while in one juvenile specimen 
the sex could not be determined. Maximum record-
ed disc width (DW) was 222 cm for females and 115 
cm for males, with minimum DWs of 27 cm and 
37 cm, respectively. The correlation between size 
and weight was statistically significant (y=0.0233x2 
+ 10.49x-11590; r2=0.92). Females were larger 
and heavier than males (Figure 4), with individual 
weights exceeding 100 kilograms.  
Overall diet
The feeding habits of a total of 41 bull ray 
specimens were analysed. In one specimen, 
stomach content analysis was not possible, and 
10 stomachs (24.4%) were found to be empty. Of 
the 1557 prey items isolated from the stomachs, 
gastropods represented the overwhelming majority 
(93.8%). Analysis of the opercula against the com-
parative collection confirmed Bolinus brandaris as 
the highly predominant muricid species. The most 
preyed upon gastropod was Aporrhais pespelecani 
(PN%=50.61%), present in 75% of all stomachs, fol-
lowed by B. brandaris (PN%=19.33%; PF%=60.71), 
and Gibbula magus (PN%=18.37; PF%=53.57). 
Other gastropods, including Hexaplex trunculus, 
Turritella communis, and Cerithium vulgatum, 
were negligible in terms of relative abundance 
and only occurred in a single stomach. In adult 
bull rays, fish represented a substantial portion of 
prey biomass (45.30%), second only to gastropods 
(52.86%), while in juveniles, gastropods prevailed 
(PB=86.08%).
Among other taxonomic groups, teleosts ac-
counted for 2.70%, hermit crabs 1.99%, and poly-
chaetes 1.16%. Sipunculids and bivalves were neg-
ligible in terms of relative abundance (0.19% and 
0.13%, respectively). Fish prey mostly consisted of 
small pelagic species, including pilchard (Sardina 
pilchardus) and horse mackerel (Trachurus sp.), and 
even a few specimens of anchovy (Engraulis encra-
sicolus) and gilt sardine (Sardinella aurita). The bull 
ray’s TROPH value was calculated as 3.40±0.58. 
Diet differences between sexes
Both sexes specialise in gastropod predation, 
with males predominantly catching Aporrhais 
pespelecani (PN – 70.5% vs. 36.1%; IRI% – 29.4 
vs. 3.7%) and females favouring muricids such as 
Bolinus brandaris (PN – 31.9% vs. 11%; IRI% – 
28.9% vs. 4.3%). Notably, fish – a secondary food 
category – were only preyed on by females (Figs. 5 
and 6). Females exhibited greater dietary diversity 
than males (The Shannon-Wiener diversity index H’; 
1.73 vs 1.02). However, the Morisita-Horn index 
showed substantial dietary overlap between sexes 
(0.79) which indicates shared prey resources. The 
calculated TROPH values for males were 3.37±0.58 
and 3.43±0.58 for females.
Diet differences between juveniles and adults
Both juveniles and adults primarily consume 
gastropods, the dominant prey category in their 
diets. Juveniles mainly feed on Gibbula magus 
(PN – 34.5% vs. 5.5%; IRI% – 77.9 vs. 32.2%), 
while adults show preference for Bolinus brandaris 
(PN – 33.4% vs. 1.6%; IRI% – 33.4% vs. 0.4%). 
Juveniles prey more heavily upon anomurans (es-
pecially Paguristes eremita) than adults (Fig. 7), 
which is evident when we compare the frequency 
of occurrence. Adults consumed more fish – which 
are more important in terms of biomass – suggesting 
an ontogenetic dietary shift (Fig. 7). The pattern mir-
rors intersexual differences, likely influenced by the 
fact that females represent the majority of the adult 
population. In the sample examined, adults had a 
more diversified diet than juveniles (H’; 1.44 vs. 
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Lovrenc LIPEJ et al.: AN INSIGHT INTO THE DIET OF THE BULL RAY, AETOMYLAEUS BOVINUS (GEOFFROY SAINT-HILAIRE, 1817) ..., 43–54
1.08). The Morisita-Horn index analysis revealed no 
significant difference between the diets of juveniles 
and adults, since the overlap in the diet was 0.74. 
The calculated TROPH values for juveniles were 
3.38±0.58, and 3.42±0.41 for adult specimens. 
DISCUSSION
The feeding habits of the bull ray were assessed on 
a rather small sample (41), consisting entirely of by-
catch specimens occasionally entangled in fishing nets. 
However, some studies suggest that as few as 15–30 
non-empty stomachs may be enough to adequately 
describe prey diversity in certain shark species (Alonso 
et al., 2002; Lucifora et al., 2006). Our analysis in-
cluded 41 stomachs, of which 10 were empty. The 
empty stomachs belonged to the smallest specimens 
– DW 27 cm (female) and DW 37 cm (male) – with 
DWs below the reported size of specimens at birth 
(Seck et al., 2002). We can therefore presume that 
pregnant bull rays aborted their pups during fish-
ing interaction, as cases of parturition induced by 
Tab. 1: Diet composition of bull rays in the study area: N – number of prey items of different species, PN – relative 
abundance (%), PB – relative biomass (%), PF – frequency of occurrence and IRI% – index of relative importance 
(%). Specimens which we were not able to identify as Hexaplex or Bolinus are grouped under Murex sp. and marked 
with an asterisk.  
Tab. 1: Prehrana kljunatega morskega goloba na obravnavanem območju: N – število različnih vrst plena, PN – rela-
tivna abundanca (%), PB – relativna biomasa (%), PF – frekvenca pojavljanja in IRI% – indeks relativne pomembnosti 
plena (%). Primerki, ki jih nismo uspeli določiti kot čokate ali bodičaste voleke, smo združili v kategorijo Murex sp. 
in jih označili z zvezdico. 
taxa N PN% PB% PF% IRI%
M
ol
lu
sc
a
Aporrhais pespelecani 788 50.61 20.03 75.00 53.24
Gibbula magus 286 18.37 10.91 53.57 15.76
Hexaplex trunculus 13 0.83 4.86 10.71 0.61
Bolinus brandaris 301 19.33 6.68 60.71 15.87
»Murex« sp.* 55 3.53 17.62 39.29 8.35
Muricidae 1 0.06 0.32 3.57 0.01
Turitella communis 1 0.06 0.02 3.57 <0.01
Cerithium vulgatum 1 0.06 0.06 3.57 <0.01
Cerithidae/Naticidae 15 0.96 0.97 14.29 0.28
Bivalvia 2 0.13 0.07 3.57 0.01
C
ru
st
ac
ea
Anomura 3 0.19 0.32 10.71 0.05
Paguristes eremita 19 1.22 3.09 17.86 0.77
Pagurus anachoretus 1 0.06 0.11 3.57 0.01
Paguridea 8 0.51 0.73 14.29 0.18
Annellida
Polychaeta 18 1.16 0.07 14.29 0.18
Sipunculida 3 0.19 0.05 7.14 0.02
Pi
sc
es
Engraulis encrasicolus 2 0.13 0.95 7.14 0.08
Sardina pilchardus 24 1.54 23.90 14.29 3.65
Sardinella aurita 1 0.06 0.21 3.57 0.01
Trachurus sp. 14 0.90 4.34 14.29 0.75
Solea sp. 1 0.06 4.69 3.57 0.17
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capture are well-documented (Adams et al., 2018; de 
Sousa Rangel et al., 2020).
The number of stomachs analysed in our study 
seems to be adequate to provide relevant insight into 
the feeding habits of the bull ray. Our results show that 
with 31 full stomachs, 90% of the asymptotic species 
richness was reached (see Fig. 8). Our results are gener-
ally consistent with one of the few available studies 
on the species’ diet published by Capapé (1977), who 
found the bull ray preying mainly on four food catego-
ries: bivalves, cephalopods, gastropods, and fish. In his 
study, which was based on a substantially larger sam-
ple of stomachs, additional, even peculiar animal taxa 
were identified among the prey items of the bull ray, 
such as polychaetes, sipunculids, and echinoderms.
Mollusc specialisation
The bull ray consumes gastropods and bivalves by 
crushing their shells with strong dental plates and can 
therefore be defined as a batoid specialised in duropha-
gous feeding (Wilga & Motta, 2000). The dominant 
gastropod species preyed upon by bull rays – Aporrhais 
pespelecani, Gibbula magus, and Bolinus brandaris – are 
characteristic and abundant in the biocoenosis of the 
muddy detritic bottom, where their shells also represent 
an essential substrate for the settlement of multi-species 
biogenic clumps (Stachowitsch & Fuchs, 1995). This bio-
coenosis geographically corresponds to the area where 
fishing vessels operated when catching bull rays, so we 
can assume that the diet of the bull ray reflects the avail-
ability of shelled prey species in the environment. Apor-
rhais pespelecani, the most frequently consumed and 
most abundant prey species, is known for its burrowing 
behaviour (Yonge, 1937). In a recent study carried out in 
the Sea of Marmara (Türkiye), hard-shelled molluscs were 
also identified as the main food items of another, closely 
related batoidean, Myliobatis aquila (Gül & Demirel, 
2020). Adult bull rays preyed on more muricids (Hexaplex 
trunculus, Bolinus brandaris, Murex sp.) than juveniles, 
both in term of relative abundance (PN%=40.8 vs. 2.3) 
and biomass (PB%=37.0 vs. 6.3). This may be explained 
by the fact that adults, having larger and stronger jaws, 
are better equipped to feed on muricids, which are char-
acterised by their thick shells. Juvenile bull rays showed a 
preference for other species, such as A. pespelecani and 
G. magus (PN%=56.81 vs. 34.49, respectively), which 
were also the overall most frequently consumed prey 
(PF%=92.86 vs. 57.14).
The occurrence of anomurans in the diet of the 
bull ray is likely related to the frequent use of empty 
muricid shells as shelters by certain hermit crabs. 
Paguristes eremita, the dominant anomuran found in 
the diet of the bull rays from the present study, is the 
largest and most robust anomuran species in the area 
and is known to inhabit heavier gastropod shells with 
a wider aperture (family Muricidae) (Manjon-Cabeza 
& García Raso, 1999). In our study, anomurans were 
predominantly found in the diet of juveniles; how-
ever, it is difficult to assess whether the consumption 
of P. eremita and other anomurans was intentional or 
incidental. Other related species, such as the bullnose 
ray (Myliobatis freminvillei), have also been reported 
to occasionally feed on anomurans (Szczepansky & 
Bengtson, 2014). No data are currently available to 
Fig. 4: Size-weight relationships in the bull rays from the 
studied area. Legend: DW – disk width (mm), red circles – 
females, blue circles – males. 
Sl. 4: Dolžinskomasni odnos kljunatih morskih golobov 
na obravnavanem območju.  Legenda: DW – premer diska 
(mm), rdeči krogci – samice, modri krogci – samci. 
Fig. 5: Comparison of diet compositions in male (M) and 
female (F) bull rays from the studied area: PN – relative 
abundance (%), PB – relative biomass (%), PF – frequency 
of occurrence, and IRI% – index of relative importance (%). 
Sl. 5: Primerjava prehrane samcev (M) in samic (F) klju-
natega morskega goloba na obravnavanem območju: 
PN – relativna abundanca (%), PB – relativna biomasa 
(%), PF – frekvenca pojavljanja in IRI% – indeks relativne 
pomembnosti plena (%). 
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determine whether some myliobatids can discriminate 
between shells occupied by anomurans and those 
containing gastropods. 
The TROPH values for bull rays (3.37-3.43) were 
higher than those for a related durophagous species, 
the common eagle ray (Myliobatis aquila) (Lipej et al., in 
press) – calculated at 3.20±0.44 to 3.25±0.39 – but lower 
than the values reported for the blackspotted smoothound 
Mustelus punctulatus (3.70 ±0.6) (Lipej et al., 2012). 
The feeding habits of the bull ray are, to some ex-
tent, similar to those of its relative, the common eagle 
ray Myliobatis aquila, which is also specialised in hunt-
ing molluscs, which represent 75% of its diet (Lipej et 
al., in press). However, while the eagle ray is mainly 
targeting bivalves, our findings show that the bull ray 
feeds mainly on gastropods. Among gastropods, eagle 
rays primarily consume species such as Cerithium 
vulgatum and Turritella communis (collectively ~20% 
of relative abundance), which were rarely preyed on 
by bull rays (each less than 0.1% of PN%). This dietary 
divergence between two related species inhabiting the 
same environment may reduce their competition.
Fish in the diet
Although fish represented only a small amount 
in terms of relative abundance, this food category 
is important in terms of biomass. Our results dem-
onstrate an ontogenetic shift in the diet from gastro-
pods to fish (sensu Koen Alonso et al., 2002; Ellis & 
Musick, 2007).   
The species found in the diet of the bull ray are 
the dominant small pelagic taxa commonly caught in 
the study area. The only exception is the sole (Solea 
sp.), which is a benthic species. This aligns with find-
ings reported by Capapé (1977) from Tunisian waters, 
where small pelagic species frequently occurred in 
the diet of bull rays. Due to size and gape limitations, 
bull rays and their relatives may only prey on fishes 
smaller than 50 cm in total length (Wetherbee et al., 
2012), meaning small species or larger species at early 
Fig. 6: Differences/similarities in prey composition 
and abundance with respect to factor sex (blue circles 
=males, red circles=females) in the NMDS space.
Sl. 6: Razlike/podobnosti v vrstni sestavi in 
številčnosti plena glede na spol (modri krogci=samci, 
rdeči krogci=samice).
Fig. 7: Comparison of diet composition between juve-
niles (juv.) and adult specimens (ad.) of bull rays in the 
study area: PN – relative abundance (%), PB – relative 
biomass (%), PF – frequency of occurrence and IRI% 
– index of relative importance (%). 
Sl. 7: Primerjava prehrane mladičev (juv.) in odraslih 
primerkov (ad.) kljunatega morskega goloba na obrav-
navanem območju: PN – relativna abundanca (%), PB 
– relativna biomasa (%), PF – frekvenca pojavljanja in 
IRI% – indeks relativne pomembnosti plena (%). 
Fig. 8: The cumulative number of prey types identified 
with increasing sample size (number of stomachs). 
Sl. 8: Kumulativno število določenih primerkov plena 
glede na naraščajoč vzorec (število želodcev). 
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life stages. The presence of pelagic species in the diet 
of predominantly benthic-feeding bull rays may be 
related to the availability of these species as dead dis-
cards abandoned on the sea floor or bull rays feeding 
on specimens with which they were entangled in the 
fishing nets during trawling operations. Fish cages are 
also an important source of food that attracts elasmo-
branchs (Barash et al., 2018; Akyol et al., 2022; Kurtay 
et al., 2023). Akyol et al. (2022) reported bull rays 
feeding on dead fish around a sea-cage fish farm in 
Iskenderun Bay (Türkiye), noting that the rays showed 
no interest in the pellets used to feed cultured fish. 
In the study area, discards of small pelagic fish from 
pelagic trawlers occurred regularly and may represent 
a significant food source for bull rays.
The importance of the Gulf of Trieste and adjacent 
areas as bull ray habitat
While the bull ray was once considered a rela-
tively rare batoid species in the Adriatic Sea (Jardas, 
1985), subsequent studies based on the capture of 
numerous specimens confirmed its presence in 
the Gulf of Trieste (Dulčić et al., 2008; Lipej et 
al., 2009) and throughout the broader northern 
Adriatic region (La Mesa et al., 2017). Dulčić et 
al. (2008) confirmed regular bull ray occurrence 
in the area, though like other elasmobranch spe-
cies of low or no commercial value, specimens are 
typically discarded at sea (Mavrič et al., 2004). The 
presence of several gravid females with developed 
embryos and numerous juvenile specimens indi-
cates the area’s importance for the reproduction 
of the species. Further investigation is needed to 
evaluate its potential nursery function, as specu-
lated by some authors (Dulčić et al., 2008; Lipej 
et al., 2009). This speculation gains support from 
Capapé & Quignard’s (1975) findings that the spe-
cies reproduces from March till October, with ges-
tation lasting six months. Notably, the study area 
hosted some record-sized individuals (1540–2220 
mm DW, 68–116 kg), the largest ever documented 
(Dulčić et al. 2008; Lipej et al., 2009). 
Over the recent years, increasing myliobatid 
sightings have been reported through social media, 
including observations of bull rays in shallow waters. 
The Gulf of Trieste – a rather shallow basin with many 
riverine inflows enhancing its productivity – appears 
to attract bull rays to brackish areas such as lagoons, 
river mouths, and estuaries. This behaviour aligns with 
reports by Zogaris & Dussling (2010) of two occur-
rences of bull rays in the Amvrakikos Gulf (Greece) 
in August 2000 (two dead specimens found, probably 
discarded by fishermen) and August 2004 (12 live 
specimens sighted). This giant shallow lagoon-like gulf 
supports a rich and abundant mollusc community that 
evidently attracts bull rays. Similarly, El Kamel et al. 
(2009, 2010) reported the captures of juvenile and 
adult A. bovinus in the Tunisian Lagoon of Bizerte, 
associating them with the local presence of abundant 
mollusc populations (Zaouali, 1979) – a known prey 
preference for the bull ray. Higher occurrences of bull 
rays have also been observed off the estuaries of three 
main river systems in northern Italy (the Po, Adige, and 
Brenta Rivers) (La Mesa et al., 2017) – areas productive 
due to riverine nutrient input and characterised by a 
high abundance of molluscs, crustaceans, and small 
pelagics (e.g., anchovies), which constitute major 
components of the bull ray’s diet. Recently, sightings 
of bull rays have also been reported by local media in 
the marine protected area of Miramare (Ciriaco, 2020; 
Anonymous, 2023) and at Punta Madona in Piran 
(2023–2025), where divers observed individual bull 
rays as well as “cemeteries” of broken mollusc shells 
close to the shore (pers. observations).  
ACKNOWLEDGMENTS
We would like to express our gratitude to many col-
leagues who helped us in this study, especially Jernej 
Uhan, Martina Orlando-Bonaca, Tihomir Makovec, 
Francesca Garaventa, Radoš Jenko and others. Many 
thanks also to Ariana Stojnić, M.Sc., SIC Company, 
Vabriga, who provided us with occasional specimens 
entrapped as a bycatch in the waters along the western 
coast of Istria. 
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VPOGLED V PREHRANJEVALNE NAVADE KLJUNATEGA MORSKEGA GOLOBA, 
AETOMYLAEUS BOVINUS (GEOFFROY SAINT-HILAIRE, 1817) 
V SEVERNEM JADRANU
Lovrenc LIPEJ 
Marine Biology Station, National Institute of Biology, Piran, Slovenia &
University of Primorska, Faculty of Mathematics, Natural Sciences and Information Technologies, Koper, Slovenia 
e-mail: Lovrenc.lipej@nib.si
Riccardo BATTISTELLA
via S. Stefano 47, Este, Provincia di Padova, Italy
Borut MAVRIČ
Marine Biology Station, National Institute of Biology, Piran, Slovenia
Danijel IVAJNŠIČ
Faculty of Natural Sciences and Mathematics, University of Maribor, 2000 Maribor
Faculty of Arts, University of Maribor, 2000 Maribor
POVZETEK
Raziskava poroča o osnovnih podatkih o prehranjevalnih navadah kljunatega morskega goloba Aetomylaeus 
bovinus (Geoffroy Saint-Hilaire, 1817) v Beneškem zalivu. Med 1557 primerki plena, izoliranimi iz želodcev, so 
veliko večino predstavljali polži (93,8 %). Med njimi je prevladovala vrsta Aporrhais pespelecani, sledili sta ji 
Gibbula magus in Bolinus brandaris. Te vrste so značilni elementi biocenoze muljastega detritnega dna. Opazili 
smo razlike v strukturi plena med mladimi in odraslimi primerki ter med spoloma. Med ribami, ki so se izkazale 
za pomembne predvsem z vidika biomase, so največ plena predstavljale male pelagične ribe, kot sta sardela 
(Sardina pilchardus) in šur (Trachurus sp.). Članek prispeva nove podatke o prehranjevalni ekologiji manj znane 
in kritično ogrožene vrste skatov.
Ključne besede: morski golobi, prehranjevalna ekologija, jaslice, Beneški zaliv
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