Smooth Hammerhead Shark

Smooth Hammerhead Shark
Sphyrna zygaena
Lateral View (♀)
Ventral View (♀)
SYNONYMS
Sphyrna lewini (Griffith & Smith, 1834), Squalis pictus (Blainville,
1816), Squalus carolinensis (Blainville, 1816), Sphyrna zigaena
(Linnaeus, 1758), Spyrna zygaena (Linnaeus, 1758), Squalus malleus
(Valenciennes, 1822), Squalus zygaena (Linnaeus, 1758), Zygaena
malleus (Valenciennes, 1822), Zygaena subarcuata (Storer, 1848),
Zygaena vulgaris (Cloquet, 1830).
DISTRIBUTION
The Smooth
Hammerhead
Shark has a
widespread but
patchy distribution
in temperate and
tropical waters
worldwide. In the
east Atlantic it is
known from the
southern British
Isles to Senegal and
the Ivory Coast,
No Records
including the
Occasional
Mediterranean Sea.
Range
It is also known in
the west Atlantic,
the Indian Ocean
and the Pacific
(Compagno, 1984).
Map base conforms with ICES grid squares.
Text & Illustrations © Shark Trust 2009
•
Broad, narrow-bladed cephalofoil with no median indention.
•
Moderately sized first dorsal fin.
•
Second dorsal fin tiny and set above the anal fin.
•
Small pelvic fins with almost straight posterior edges.
•
Large, well developed caudal dorsal lobe with terminal notch.
•
Dark olive to grey brown dorsally.
•
White ventrally.
•
Maximum total length reported to 500cm.
The Smooth Hammerhead Shark is an easily recognised large
species. In European waters it could be confused with the Scalloped
Hammerhead Shark, Sphyrna lewini, or the Great Hammerhead Shark,
Sphyrna mokarran, although both of these species has an indent in
the very centre of the leading edge of the cephalofoil, a feature the
Smooth Hammerhead Shark lacks. The first dorsal fin is moderately
sized with large free rear tips. It originates just behind the pectoral fins
with the free rear tip ahead of the pelvic fins. The pelvic fins are small
and square. The second dorsal fin is tiny, comparable in size to the
anal fin over which it is positioned. The dorsal lobe of the caudal fin is
large and well developed with a strong terminal notch (Compagno,
1984).
Dorsal colouration is from dark olive to dark grey with no
patterning, although some individuals have dusky or black edged fins.
It is white ventrally. There are reports of the Smooth Hammerhead
Shark reaching 500cm in length, although 250-350cm individuals are
more common (Bester, Unknown).
NT
Smooth Hammerhead Shark, Common Hammerhead Shark, Round
Headed Hammerhead Shark, Requin-Marteau Commun (Fr), Cornuda
Cruz (Es).
NE ATL MED
APPEARANCE
SPZ
COMMON NAMES
Supported by:
SIMILAR SPECIES
Sphyrna lewini, Scalloped Hammerhead Shark
Sphyrna mokarran, Great Hammerhead Shark
(Not to scale)
Text & Illustrations © Shark Trust 2009
Smooth Hammerhead Shark
Smooth Hammerhead Shark
Sphyrna zygaena
TEETH
The teeth have very broad cusps
with smooth or weakly serrated
edges (Compagno, 1984).
ECOLOGY AND BIOLOGY
HABITAT
The Smooth Hammerhead Shark is found close inshore and over
the continental shelf to depths of at least 200m, although it prefers
to stay shallower than 20m. While it is more tolerant of temperate
waters than any other hammerhead shark, it does make migrations
towards warmer waters in the winter. This is reversed in the summer
and it migrates towards the poles into cooler water. During these
migrations adults may form small groups, and young sharks less
than 1.5m in length are known to form enormous schools. It is
usually a solitary animal however. It has been known to enter
freshwater on occasion (Bester, Unknown).
DIET
A 1999 study showed that cephalopods constitute (68.9%) of
the diet of the Smooth Hammerhead Shark, followed by teleost
fish (29.8%) with small amounts of other chondrichthyans and
benthic invertebrates (mostly crustaceans) (Cortés, 1999). However,
other studies have shown them to be primarily piscivores with a
preference for other elasmobranchs, especially in inshore areas
(Bester, Unknown). Compagno (1984) lists the main prey items as
herring, menhaden, sea catfishes, sea bass, mackerel, porgies and
also small sharks, skates, stingrays, shrimp, crabs, barnacles, squid
and other cephalopods (Compagno, 1984).
Text & Illustrations © Shark Trust 2009
REPRODUCTION
Like Carcharinidae and other Sphyrnidae species, the Smooth
Hammerhead Shark reproduces through placental, or yolk-sac,
viviparity. For about the first third of the gestation period, the
embryos are nourished by a yolk supply in a very similar way to the
60% of elasmobranchs which reproduce through normal viviparity.
However once this yolk supply is used up the yolk-sac changes,
becoming more folded and wrinkled. It now interlocks with the
lining of the mother’s uterus. The blood supply to both the yolk-sac
and the uterus wall increases allowing nutrients and oxygen to pass
from the mother to the embryo and vice versa for waste, very much
like a mammalian placenta (Martin, 1994).
Female Smooth Hammerhead Sharks reach sexual maturity
at around 270cm in length, males at around 210–250cm. Mating
and birth both occur during the summer with a gestation period
of 10–11 months. Litters of 20–40 pups have been reported with
each pup measuring around 50cm in length at birth. It gives birth
in inshore nursery areas such as lagoons and estuaries where the
young form large schools (Bester, Unknown).
Supported by:
COMMERCIAL IMPORTANCE
A common and fairly abundant species, the Smooth Hammerhead
Shark is taken with pelagic longlines, handlines and pelagic and
bottom trawls. Its meat is not considered to be high quality but it
is used fresh, dried salted and smoked for human consumption.
Its hide is used for leather, its liver oil for vitamins and its fins are
highly prized for sharkfin soup. Its carcass can also be processed for
fishmeal (Compagno, 1984).
THREATS, CONSERVATION, LEGISLATION
While the Smooth Hammerhead Shark is an abundant and
widespread species, population trends are poorly understood
and fishing mortality is likely to be significant. While there are few
targeted fisheries, it is taken as bycatch across its range by longline,
handline and trawl fisheries. Due to the high value of its fins,
animals taken as bycatch are unlikely to be returned alive (Casper et
al., 2005).
Text & Illustrations © Shark Trust 2009
Smooth Hammerhead Shark
IUCN RED LIST ASSESSMENT
Vulnerable (2005).
HANDLING AND THORN ARRANGEMENT
• Handle with care.
• Large, powerful shark.
• Sharp teeth and abrasive skin.
Smooth Hammerhead Shark
Sphyrna zygaena
REFERENCES
BESTER, C. Unknown. Smooth Hammerhead. Florida Museum of
Natural History. www.flmnh.ufl.edu/fish/.
COMPAGNO, L. J. V. 1984. Sharks of the World: An Annotated and
Illustrated Catalogue of Shark Species Known to Date. Volume
4, Part 1. Hexanchiformes to Lamniformes. FAO. Rome, Italy.
CORTÉS, E. 1999. Standardized Diet Compositions and Trophic
Levels of Sharks. ICES Journal of Marine Science. 56 (5): 707-717.
FERRETTI, F., MYERS, R. A., SERENA, F., LOTZE, H. K. 2008. Loss
of Large Predatory Sharks from the Mediterranean Sea.
Conservation Biology. 22 (4): 952-964.
MARTIN, R. A. 1994. From Here to Maternity. Diver Magazine, April
1994.
CASPER, B. M., DOMINGO, A., GAIBOR, N., HEUPEL, M. R., KOTAS, E.,
LAMÓNACA, A. F., PÉREZ-JIMENEZ, J. C., SIMPFENDORFER, C.,
SMITH, W. D., STEVENS, J. D., SOLDO, A., VOOREN, C. M. 2005.
Sphyrna zygaena. In: IUCN 2009. IUCN Red List of Threatened
Species. www.iucnredlist.org.
Text: Richard Hurst.
Illustrations: Marc Dando.
Citation
Shark Trust; 2010. An Illustrated Compendium of Sharks, Skates, Rays
and Chimaera. Chapter 1: The British Isles and Northeast Atlantic. Part
2: Sharks.
Any ammendments or corrections, please contact:
The Shark Trust
4 Creykes Court, The Millfields
Plymouth, Devon PL1 3JB
Tel: 01752 672008/672020
Email: [email protected]
For more ID materials visit www.sharktrust.org/ID.
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Text & Illustrations © Shark Trust 2009