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Notes on a rare case of bluntnose sixgill shark hexanchus griseus stranded on the coast of tuscany in the central tyrrhenian sea

Authors:
  • Centro Studi Squali - Sharks Studies Centre - Scientific Institute
  • Centro Studi Squali-Sharks Studies Center

Abstract and Figures

A rare stranding event involving a 297 cm long mature male bluntnose sixgill shark (Hexanchus griseus) occurred on the Tuscan coast in the central Tyrrhenian Sea. The stranded specimen had 6 rows of teeth indicating that it belonged to the H. griseus and not to the Hexanchus nakamurai species, which only has 5. Biometric data on two teeth of the left front region of the lower jaw were collected. The body of the specimen did not show evidence of capture, only a deep cut at the height of the orbital arch suggesting a crash or the ramming of a boat.
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Anali za istrske in mediteranske študije
Annali di Studi istriani e mediterranei
Annals for Istrian and Mediterranean Studies
Series Historia Naturalis, 31, 2021, 1
UDK 5 Annales, Ser. hist. nat., 31, 2021, 1, pp. 1-164, Koper 2021 ISSN 1408-533X
KOPER 2021
Anali za istrske in mediteranske študije
Annali di Studi istriani e mediterranei
Annals for Istrian and Mediterranean Studies
Series Historia Naturalis, 31, 2021, 1
UDK 5 ISSN 1408-533X
e-ISSN 2591-1783
ANNALES · Ser. hist. nat. · 31 · 2021 · 1
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ANNALES · Ser. hist. nat. · 31 · 2021 · 1
Anali za istrske in mediteranske študije - Annali di Studi istriani e mediterranei - Annals for Istrian and Mediterranean Studies
UDK 5 Letnik 31, Koper 2021, številka 1 ISSN 1408-53 3X
e-ISSN 2591-1783
VSEBINA / INDICE GENERALE / CONTENTS 2021(1)
BIOINVAZIJA
BIOINVASIONE
BIOINVASION
Luca CASTRIOTA & Manuela FALAUTANO
Reviewing the Invasion History of the Blue Crab
Callinectes sapidus (Portunidae) in Sicily (Central
Mediterranean): an Underestimated Alien Species ...
Revizija zgodovine invazije modre rakovice
Callinectes sapidus (Portunidae) na Siciliji
(osrednje Sredozemsko morje):
podcenjena tujerodna vrsta
Alan DEIDUN, Bruno ZAVA, Maria CORSINI-
FOKA, Johann GALDIES, Antonio DI NATALE &
Bruce B. COLLETTE
First Record of the Flat Needlefish, Ablennes hians
(Belonidae) in Central Mediterranean Waters
(Western Ionian Sea) .............................................
Prvi zapis o pojavljanju ploščate morske igle,
Ablennes hians (Belonidae) v vodah osrednjega
Sredozemskega morja (zahodno Jonsko morje)
Mohamed Mourad BEN AMOR,
Khadija OUNIFI-BEN AMOR,
Marouène BDIOUI & Christian CAPAPÉ
Occurrence of Reticulated Leatherjacket
Stephanolepis diaspros (Monacanthidae)
in the Central Mediterranean Sea,
and New Record from the Tunisian coast .............
Pojavljanje afriškega kostoroga,
Stephanolepis diaspros (Monacanthidae),
v osrednjem Sredozemskem morju in
prvi podatek za tunizijsko obalo
Sara AL MABRUK, Ioannis GIOVOS &
Francesco TIRALONGO
New Record of Epinephelus areolatus in the
Mediterranean Sea: First Record from Syria ..........
Novi zapis o pojavljanju rdečepikaste kirnje
(Epinephelus areolatus) v Sredozemskem
morju: prvi podatki za Sirijo
SREDOZEMSKI MORSKI PSI
SQUALI MEDITERRANEI
MEDITERRANEAN SHARKS
Primo MICARELLI, Francesca Romana REINERO &
Emilio SPERONE
Notes on a Rare Case of Bluntnose Sixgill Shark
Hexanchus griseus Stranded on the Coast of
Tuscany in the Central Tyrrhenian Sea .................
Zapis o redkem primeru morskega psa
šesteroškrgarja Hexanchus griseus, ki je nasedel
na toskanski obali v osrednjem Tirenskem morju
Alen SOLDO
The Occurrence of the Common Angel Shark
Squatina squatina in the Adriatic Sea ...................
Pojavljanje navadnega sklata (Squatina squatina)
v Jadranskem morju
Hakan KABASAKAL, Deniz AYAS &
Deniz ERGÜDEN
Intentional Stranding of a Blue Shark,
Prionace glauca (Carcharhiniformes:
Carcharhinidae), in Pursuit of Prey .......................
Namerno nasedanje sinjega morskega psa,
Prionace glauca (Carcharhiniformes:
Carcharhinidae), med zasledovanjem plena
Patrick L. JAMBURA, Julia TÜRTSCHER,
Alessandro DE MADDALENA,
Ioannis GIOVOS, Jürgen KRIWET,
Jamila RIZGALLA & Sara A. A. AL MABRUK
Using Citizen Science to Detect Rare
and Endangered Species: New Records
of the Great White Shark Carcharodon
carcharias Off the Libyan Coast ........................
Uporaba ljubiteljske znanosti za
pridobivanje podatkov o redki in
ogroženi vrsti: novi podatki
o pojavljanju belega morskega volka
Carcharodon carcharias
ob Libijski obali
51
1
9
23
37
31
17
45
ANNALES · Ser. hist. nat. · 31 · 2021 · 1
IHTIOLOGIJA
ITTIOLOGIA
ICHTHYOLOGY
Sihem RAFRAFI-NOUIRA, Christian REYNAUD &
Christian CAPAPÉ
A New Record of Clinitrachus argentatus
(Osteichthyes: Clinidae) from the Tunisian
Coast (Central Mediterranean Sea)............................
Novi zapis o pojavljanju srebrnice Clinitrachus
argentatus (Osteichthyes: Clinidae) iz tunizijske
obale (osrednje Sredozemsko morje)
Mauro CAVALLARO, Giovanni AMMENDOLIA,
Ignazio RAO, Alberto VILLARI & Pietro BATTAGLIA
Variazioni pluriennali del fenomeno dello
spiaggiamento di specie ittiche nello stretto
di Messina, con particolare attenzione alle
specie mesopelagiche ..............................................
Večletne spremembe v nasedanju ribjih
vrst v Mesinski ožini s posebnim ozirom
na mezopelaške vrste
Sihem RAFRAFI-NOUIRA, Christian REYNAUD &
Christian CAPAPÉ
Skeletal and Pughead Deformities in the Saddle
Bream Oblada melanura (Osteichthyes: Sparidae)
from the Tunisian Coast (Central Mediterranean Sea)
...
Deformacije skeleta in glave pri črnorepki, Oblada
melanura (Osteichthyes: Sparidae) iz tunizijske
obale (osrednje Sredozemsko morje)
Murat BILECENOGLU & Seydi Ali DOYUK
Uncommon Thermophilic Fishes
from the Marmara and Black Seas ............................
Nenavadne toploljubne ribe iz
Marmarskega in Črnega morja
Christian CAPAPÉ, Adib SAAD, Ahmad SOLAIMAN,
Issa BARAKAT & Waad SABOUR
First Substantiated Record of Armless Snake Eel
Dalophis imberbis (Osteichthyes: Ophichthidae)
from the Syrian Coast (Eastern Mediterranean Sea) ...
Prvi dokumentiran primer pojavljanja kačaste jegulje,
Dalophis imberbis (Osteichthyes: Ophichthidae),
vzdolž sirske obale (vzhodno Sredozemsko morje)
Khaled RAHMANI, Fatiha KOUDACHE,
Amaria Latefa BOUZIANI & Alae Eddine BELMAHI
Length-Weight Relationships and Metric Characters
of the Atlantic Horse Mackerel, Trachurus trachurus
(Perciformes: Carangidae), Caught in Béni-Saf Bay,
Western Mediterranean (Algeria) ................................
Odnos med dolžino in maso in metrični znaki
navadnega šnjura, Trachurus trachurus
(Perciformes: Carangidae), ujetega v zalivu
Béni-Saf, zahodno Sredozemsko morje (Alžirija)
Tülin ÇOKER & Okan AKYOL
On the Occurrence of Pomadasys incisus
(Haemulidae) in the Turkish Aegean Sea
(Eastern Mediterranean Sea) .....................................
O pojavljanju vrste Pomadasys incisus
(Haemulidae) v turškem Egejskem morju
(vzhodno Sredozemsko morje)
Sihem RAFRAFI-NOUIRA, Mohamed Mourad BEN
AMOR, Khadija OUNIFI-BEN AMOR, Marouène
BDIOUI & Christian CAPAPÉ
First Substantiated Record of Opah, Lampris
guttatus (Osteichthyes: Lamprididae), from
the Tunisian Coast (Central Mediterranean Sea)........
Prvi dokumentiran zapis o pojavljanju svetlice,
Lampris guttatus (Osteichthyes: Lamprididae), iz
tunizijske obale (osrednje Sredozemsko morje)
FLORA
FLORA
FLORA
Claudio BATTELLI & Marcello CATRA
First Report of Cystoseira aurantia (Sargassaceae,
Fucophyceae) from the Lagoon of Strunjan
(Gulf of Trieste, Northern Adriatic) ............................
Prvo poročilo o vrsti Cystoseira aurantia
(Sargassaceae, Fucophyceae) v strunjanski
laguni (Tržaški zaliv, severni Jadran)
Amelio PEZZETTA
Le Orchidaceae di Pinguente (Buzet)........................
Kukavičevke Buzeta
FAVNA
FAVNA
FAVNA
Ahmet ÖKTENER & Ivan SAZIMA
Caligus minimus (Copepoda: Caligidae)
Parasitic on the Gills of a Remora Echeneis
naucrates Attached to a Seabass Dicentrarchus
labrax in Köyceğiz-Dalyan Lagoon Lake,
Aegean Sea, Turkey ..................................................
Caligus minimus (Copepoda: Caligidae),
zajedavec na škrgah prilepa (Echeneis naucrates),
pritrjenega na brancina (Dicentrarchus labrax) v
laguni Köyceğiz-Dalyan v Egejskem morju, Turčija
Kazalo k slikam na ovitku ....................................
Index to images on the cover ...............................
159
165
165
139
129
63
69
95
101
147
123
107
85
ANNALES · Ser. hist. nat. · 31 · 2021 · 1
31
received: 2020-12-24 DOI 10.19233/ASHN.2021.05
NOTES ON A RARE CASE OF BLUNTNOSE SIXGILL SHARK HEXANCHUS
GRISEUS STRANDED ON THE COAST OF TUSCANY IN THE CENTRAL
TYRRHENIAN SEA
Primo MICARELLI & Francesca Romana REINERO
Centro Studi Squali – Istituto scientifico Loc. Valpiana Massa Marittima (GR), Italy
e-mail: direzione@centrostudisquali.org
Emilio SPERONE
Dipartimento di Biologia, Ecologia e Scienze della Terra. Università della Calabria (CS), Italy
ABSTRACT
A rare stranding event involving a 297 cm long mature male bluntnose sixgill shark (Hexanchus griseus) occurred
on the Tuscan coast in the central Tyrrhenian Sea. The stranded specimen had 6 rows of teeth indicating that it
belonged to the H. griseus and not to the Hexanchus nakamurai species, which only has 5. Biometric data on two
teeth of the left front region of the lower jaw were collected. The body of the specimen did not show evidence of
capture, only a deep cut at the height of the orbital arch suggesting a crash or the ramming of a boat.
Key words: bluntnose sixgill shark, Hexanchus griseus, shark stranding, teeth, Mediterranean Sea
NOTE SU UN RARO CASO DI SPIAGGIAMENTO DI CAPOPIATTO HEXANCHUS
GRISEUS LUNGO LA COSTA TOSCANA NEL MAR TIRRENO CENTRALE
SINTESI
Un raro evento di spiaggiamento che ha coinvolto un capopiatto maschio maturo lungo 297 cm (Hexanchus
griseus) si è verificato lungo la costa toscana nel mar Tirreno centrale. L’esemplare spiaggiato presentava 6 file di
denti che indicavano l’appartenenza alla specie H. griseus e non alla specie Hexanchus nakamurai, che ne ha solo
5. Sono stati raccolti dati biometrici su due denti della regione anteriore sinistra della mascella inferiore. Il corpo
dell’esemplare non mostrava segni di cattura, solo un profondo taglio all’altezza dell’arco orbitale che suggeriva una
collisione o lo speronamento di una barca.
Parole chiave: capopiatto, Hexanchus griseus, spiaggiamento di squalo, denti, Mediterraneo
ANNALES · Ser. hist. nat. · 31 · 2021 · 1
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Primo MICARELLI et al.: NOTES ON A RARE CASE OF BLUNTNOSE SIXGILL SHARK HEXANCHUS GRISEUS STRANDED ON THE COAST OF TUSCANY ..., 31–36
INTRODUCTION
The bluntnose sixgill shark Hexanchus griseus
(Bonnaterre, 1788) is a deepwater, benthic, littoral and
semi-pelagic shark (Compagno et al., 2005), listed as
near threatened (NT) by the Red List of the International
Union for Conservation of Nature (I.U.C.N.) (Finucci et
al., 2020). Juveniles may approach the coast in cold
water, while adults live in shallow waters close to sub-
marine canyons (Compagno et al., 2005). H. griseus is
found in the Pacific and Indian Oceans, off the eastern
and western Atlantic coasts, and in the Mediterranean
Sea (Bass et al., 1975), up to 1875 meters deep (Com-
pagno et al., 2005). The bluntnose sixgill shark makes
day and night excursions, moving from a depth of 250
m up to 20 m, near the surface (Andrews et al., 2009).
The biology of H. griseus in the Mediterranean is poor-
ly known and the little information published focuses
mostly on its ichthyological characteristics (Capapé et
al., 2003). Cases of hermaphroditism, although rare
in elasmobranchs, seem to be present in bluntnose
sixgill shark (Daniel, 1928). The maturity is reached at
309–330 cm of total length (TL) in males and 350–420
cm TL in females, while the maximum size reached is
probably 550 cm TL (Compagno et al., 2005). In the
present article, authors report an incident of a stranded
bluntnose sixgill shark found on the Tuscan coast (cen-
tral Tyrrhenian Sea) and provide information on the
examined specimen. Furthermore, the authors review
the occurrence status of H. griseus in the Mediterrane-
an Sea in light of available data.
MATERIAL AND METHODS
On 16 March 2016, a bluntnose sixgill shark was
found on the beach of Marina di Grosseto in Tuscany
(coordinates: 42°43’24.5”N 10°58’19.4”E), Italy (Fig.
1a). This area, located in the northwestern Mediterra-
nean, more precisely, in the central Tyrrhenian Sea, is
characterised by a sandy bottom that slowly degrades
Fig. 1: (A) Hexanchus griseus; (B) tooth measurement; (C) teeth; (D) MEDLEM report; (E) claspers; (F) damaged eye.
Sl. 1: (A) Hexanchus griseus; (B) merjenje zob; (C) zobovje; (D) MEDLEM poročilo; (E) klasperja; (F) poškodovano oko.
ANNALES · Ser. hist. nat. · 31 · 2021 · 1
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Primo MICARELLI et al.: NOTES ON A RARE CASE OF BLUNTNOSE SIXGILL SHARK HEXANCHUS GRISEUS STRANDED ON THE COAST OF TUSCANY ..., 31–36
before reaching significant depths. The specimen, fo-
und in late afternoon, was quickly collected and taken
to landfill by the local authorities, thus only allowing
for a collection of limited biometric data based on a
few samples of teeth, and checking the external con-
dition of the specimen. The shark was measured on
the beach and its total length (TL) was recorded as a
straight line extending from the tip of the snout to the
tip of the upper lobe of the caudal fin, with the latter
in the depressed position. This type of measurement
represents the maximum length according to Compa-
gno (1984). The available data were entered in the
MEDLEM reporting form (Fig. 1d).
RESULTS
The male specimen displayed a pair of calcified
claspers and was probably mature (Fig. 1e). Its size
was 294 cm TL, it had no external abrasions or signs
of capture by fishing gear; the mouth was free and
without hooks. At the level of the left eye socket
there was a deep horizontal cut and the eye was
damaged (Fig. 1f). Six dental rows were observed and
the dental formula 20/13 corresponded to that of H.
griseus according to Last & Stevens (2009). Biometric
analyses of two teeth A1 and A2 (Fig. 1c) of the front
left region of the lower jaw were performed using a
caliper (Fig. 1b). The biometric measurements, taken in
mm, are shown in Table 1. The sixgill shark species H.
griseus (Bonnaterre, 1788) and Hexanchus nakamurai
(Teng, 1962) stand out for the presence of six rows of
distinctly comb-shaped teeth in the lower jaw in the
former and five rows in the latter species; moreover,
H. griseus has a short, blunt, broadly rounded snout
and a dorsal-caudal distance approximately equal to
its dorsal fin base length, while H. nakamurai has a
relatively longer snout that is more pointed and nar-
row, and a dorsal-caudal distance that is much longer
than the dorsal-fin base length (Ebert et al., 2013). In
addition, Adnet (2006) stated that H. griseus and H.
nakamurai are hard to distinguish, especially because
of the similarity between the lower teeth of juvenile or
sub-adult specimens in both species.
DISCUSSION
A historical survey of Mediterranean reports since
1892 shows that H. griseus has been captured in
restricted areas of the western basin more common-
ly than in the eastern one (Capapé et al., 2003). H.
griseus is included in the I.U.C.N. Red List, and even
though its populations are considered stable, they still
require careful monitoring; in fact, species with similar
life histories, often called ‘K-selected’ (Camhi et al.,
1998), can be affected by deepwater fishery (Walls
et al., 2015). Between 1666 and 2014, the MEDLEM
(Serena et al., 2014) database for the Mediterranean
Sea recorded occurrences of bluntnose sixgill shark (H.
griseus) in Maltese waters (20 specimens; GSA 15); in
the northern Tyrrhenian Sea (45 specimens; GSA 9); in
the southern Adriatic Sea; in the northern Ionian Sea;
in the southern waters of Sicily (21 specimens; GSA 18,
19, and 16 respectively); along the coasts of Tunisia
(GSA 13 and 14) (Capapé et al., 2003; 2004); and in
Turkish waters (24 specimens). The Mediterranean Sea
has been divided into 30 geographical sub-areas, cal-
led GSAs, by the General Fishery Commission for the
Mediterranean - GFCM. Kabasakal (2013) states that
150 specimens of H. griseus were caught by commer-
cial fishing vessels in the seas of Turkey between 1967
and 2013, 90 of which were recorded in the Marmara
Sea. Based on an analysis of internet-based media
reports on rare and large sharks of Turkey, Kabasakal
& Bilecenoğlu (2020) indicated that nearly 52 percent
(139 out of 268 specimens) of sharks captured between
2006 and 2020 were H. griseus. The bluntnose sixgill
shark is also regularly captured along the coast of
Lebanon (Lteif, 2015) and along the coasts of Calabria
(21 specimens; GSA 10 and 19), (Leonetti et al., 2020).
Stranding of bluntnose sixgill sharks in the Mediterra-
nean Sea is rare, particularly in consideration of their
presence at great depths. Kabasakal (2006) reported a
female specimen (450 cm TL) stranded in the Dardanel-
les Strait on 5 June 1999. Although in the present case
it was not possible to collect all the samples needed to
provide a more useful contribution to the knowledge of
the biology of this species, it was nevertheless possible
to establish that the number of rows of teeth equalled
6, which excluded the possibility that the shark could
be a H. nakamurai, whose maximum TL does not
Tab. 1: Five measurements were collected for each
tooth: CH, crown height; RH, root height; TH, total
height; BWT, basal width of the tooth; HC, height of
the cusp.
Tab. 1: Za vsak zob je bilo opravljenih pet meritev:
CH, višina krone; RH, višina korenine; TH, celotna
višina; BWT, bazalna širina zoba; HC, višina grbice.
Biometric measurements of the teeth (mm)
A1 A2
CH 10.3 9.84
RH 12.3 11.42
TH 19.97 19.49
BWT 28.99 28.06
HC 6.69 6.36
ANNALES · Ser. hist. nat. · 31 · 2021 · 1
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Primo MICARELLI et al.: NOTES ON A RARE CASE OF BLUNTNOSE SIXGILL SHARK HEXANCHUS GRISEUS STRANDED ON THE COAST OF TUSCANY ..., 31–36
exceed 180 cm. It is important to remember that it is
difficult to distinguish between specimens of the two
species without precise information on their body size
or maturity and only by comparing the teeth. In fact,
Adnet (2006) showed that the two recent species of the
genus Hexanchus have a similar dental development
but with a different growth rate: at same tooth width, H.
griseus retains a “young” morphology compared to that
of H. nakamurai and the distinction between the two
species in relation to dentition is currently limited to
the presence, in some individuals, of a vertical median
cusp on the symphyseal tooth in H. nakamurai, and dif-
ferent dental formulae. The size of the stranded animal
and the presence of hard and well-calcified claspers
indicated its probable maturity, although its body size
was slightly smaller than the minimum size at maturity
indicated by Compagno et al. (2005), which is 309 cm
for males. Observations suggest that H. griseus matures
at a smaller size in the Mediterranean than elsewhere
(Capapé et al., 2004). The examination of the collected
teeth confirmed the equation for establishing the size
of the animal based on the measurement of the tooth
base. As a matter of fact, in large shark species such
as H. griseus, the length of the body (Total Length
according to Compagno, 1984) and the width of the
teeth in each row are well correlated (R = from 0.95
to 0.98, p <0.001). A simple linear regression equation
expresses the relationship between the width of the
lower teeth and the length of the shark’s body, which
can be calculated as follows: shark’s length (in cm) =
111 × tooth’s width (in cm) + 3.9 (R = 0.97, p <0.001;
N = 243) (Adnet, 2006). If we were to apply the equa-
tion in this instance, it would have been possible to
estimate a length of about 325 cm, slightly greater than
the measured one, thus confirming the correctness of
the proposed equation. With regard to the reasons of
the stranding, the absence of apparent damages from
fishing tools and the presence of a deep cut at the
eye level may suggest the possibility that this male
specimen rose to the surface due to various reasons
that could have also caused its death by ramming such
as, for example, an accident with a boat. Injured sixgill
sharks may be at risk for post-release or post-accident
disability, or mortality due to long-term pathologic
consequences of anthropogenically induced scars
(Kabasakal, 2010). Andrews et al. (2009) found that in
Puget Sound (USA), sixgill sharks showed consistent
diel behavioural patterns throughout the year and
inhabited greater depths during the day than during
the night, being more active (with greater variation in
depth and greater rates of vertical movement) at night.
It is interesting to note that, in our case, the stranding
occurred in March, right at the beginning of the spring
season when, just like in Puget Sound, the movement
to the surface of these sharks is more frequent. Seaso-
nally, sixgill sharks occupy deeper habitats in autumn
and winter than they do in spring, and are more active
in autumn (Andrews et al., 2009). Moreover, in the
Mediterranean, little is known about the behaviour of
these sharks: Capapé et al. (2004) states that H. griseus
is probably able to live and reproduce in the Mediter-
ranean Sea; however, further observations are needed
to confirm that a sustainable bluntnose sixgill shark
population has been established here, especially off
the Maghrebi coast. Incidental capture of a new-born
specimen (60 cm TL) with an unhealed umbilical scar
(birthmark) between the pectoral fins suggested the
possibility of a nursery ground of H. griseus in northern
Aegean Sea bathyal grounds (Kabasakal, 2013). More-
over, another possible nursery ground was suggested in
the Marmara Sea, where several juveniles (120 to 250
cm TL) were incidentally captured (Kabasakal, 2013).
Finally, lack of information on the movements of the
specimens along Turkish coasts reveals the necessity of
tagging surveys of H. griseus in the mentioned region
to understand the spatial and bathymetric movement
patterns of this species (Kabasakal, 2013). Meager &
Sumpton (2016) suggest that an integrated approach
of using stranding and bycatch data may provide an
indicator of long-term trends for data-limited cetace-
ans, and that stranding programs can give a faithful
representation of the species composition of cetacean
assemblages, while standardised bycatch rates can
provide a measure of relative abundance. Therefore,
in the long term, the stranding of elasmobranchs,
however rare and even in the case of animals living in
the deep but periodically venturing to surface waters,
could provide useful insights for an evaluation of their
health status. This information provides a useful contri-
bution to the biometric data available for this species,
with particular reference to teeth, and testifies to a rare
case of stranding.
ANNALES · Ser. hist. nat. · 31 · 2021 · 1
35
Primo MICARELLI et al.: NOTES ON A RARE CASE OF BLUNTNOSE SIXGILL SHARK HEXANCHUS GRISEUS STRANDED ON THE COAST OF TUSCANY ..., 31–36
ZAPIS O REDKEM PRIMERU MORSKEGA PSA ŠESTEROŠKRGARJA HEXANCHUS
GRISEUS, KI JE NASEDEL NA TOSKANSKI OBALI V OSREDNJEM TIRENSKEM MORJU
Primo MICARELLI & Francesca Romana REINERO
Centro Studi Squali – Istituto scientifico Loc. Valpiana Massa Marittima (GR), Italy
e-mail: direzione@centrostudisquali.org
Emilio SPERONE
Dipartimento di Biologia, Ecologia e Scienze della Terra. Università della Calabria (CS), Italy
POVZETEK
Avtorji poročajo o redkem primeru, ko je na toskanski obali v osrednjem Tirenskem morju nasedel 297 cm dolg
odrasel samec morskega psa šesteroškrgarja (Hexanchus griseus). Nasedli primerek je imel 6 nizov zob, po katerih
ga je bilo možno razlikovati od sorodne vrste Hexanchus nakamurai, ki ima 5 nizov. Avtorji so opravili biometrijo
na dveh zobeh levega sprednjega dela. Na telesu morskega psa ni bilo videti znakov ulova, le globoka rana v višini
očesnega loka priča o morebitnem trku s plovilom.
Ključne besede: morski pes šesteroškrgar, Hexanchus griseus, nasedli morski pes, zobovje, Sredozemsko morje
ANNALES · Ser. hist. nat. · 31 · 2021 · 1
36
Primo MICARELLI et al.: NOTES ON A RARE CASE OF BLUNTNOSE SIXGILL SHARK HEXANCHUS GRISEUS STRANDED ON THE COAST OF TUSCANY ..., 31–36
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Full-text available
Article
A biometric analysis of the lower teeth of Recent cow sharks (Hexanchidae) investigates the ontogenetic and phylogenetic aspects of the dental characters employed by many ichthyologists and palaeontologists. The dental characters currently used to separate two extant species of sixgill sharks (Hexanchus griseus and H. nakamurai) are analysed and the fossil record of their relatives reviewed. The main results suggest that the cusp number ratio (number of cusps per mm) is preferable to width of the lower tooth for inference of total body size, at least in species of Hexanchus. The presence of a serrated edge or an enlarged acrocone appears to depend on ontogeny and care must be taken when using these as taxomomic characters. Three Eocene species of Hexanchus, H. collinsonae, H. hookeri, and H. agassizi, and a new assemblage of fossil teeth from the late Ypresian/early Lutetian (Early/Middle Eocene) of south−western France, are also analysed. The first two of these species may be ontogenetic states of H. agassizi. Hexanchus agassizi, belonging to the vituliform lineage and closely related to the living H. nakamurai, is considered here to be the only species of Hexanchus in the Lower to Middle Eocene. A brief overview of Palaeogene Hexanchus, suggests no evidence of the grisiform group (closely related to living H. griseus) before the Late Eocene.
Post-release behavior and anthropogenic injuries of the bluntnose sixgill shark, Hexanchus griseus (Bonnaterre, 1788) (Chondrichthyes: Hexanchidae) in Turkish waters
  • H Kabasakal
Kabasakal, H. (2010): Post-release behavior and anthropogenic injuries of the bluntnose sixgill shark, Hexanchus griseus (Bonnaterre, 1788) (Chondrichthyes: Hexanchidae) in Turkish waters. Annales Ser. Hist. Nat., 20: 39-46.