Common
Names: Scalloped
Hammerhead
Latin
Name: Sphyrna
lewini
Family:
Sphyrnidae
Identification:
Leading edge of hammer
arched with well defined indentations. Pectoral fins have dark tips. Pelvic fins
not falcate. Body grey to greyish brown. Ventral
surface pale.
Size:
Maximum
length 420 cm. 42 - 55 cm at birth.
Habitat:
In shore to off shore sea mounts. Adults are pelagic. Intertidal to 275
meters.
Abundance
and distribution: Circumtropical/temperate.
Behavior:
One
of very few large sharks observed schooling in great numbers. Diet consists of
bony fishes, sharks, rays, crustaceans, and octopus.
Reproduction:
Viviparous.
The hammerhead are considered the most highly evolved of the shark families.
Observations:
Scalloped
hammerheads have been well documented swimming in huge schools around various
sea mounts off of central and South America. They apparently use cleaning
stations in these areas to rid themselves of parasites.
Photographs:
.
Similar species: Great
hammerhead distinguished by straighter leading edge of hammer, proportionately
taller dorsal fin, and often larger size.
Reaction to divers:
Shy. Very
difficult to approach when viewed in schooling behaviour. Most divers have
better success when using rebreathers. Can
be aggressive making close passes in baited situations.
Diving
logistics:
Various
operators go from La Paz to the sea mounts in the Sea of Cortez to view
schooling Scalloped hammerheads but in recent years the schools have dwindled
due to heavy over fishing. The Galapagos, Malpelo, and Cocos Island remain the
best places for close encounters but all stocks are stressed by longlining and
numbers vary from year to year. El Nino years may see less hammerheads as the
water becomes too warm at recreational scuba depths and the sharks stay deeper.
Following El Nino years may see the best schooling activity as the sharks are
then in dire need of the cleaning stations that they were unable to reach the
previous year. The undersea hunter out of Costa Rica travels to Cocos for 1-2
week long trips that also expose divers to silkies, whitetips, silvertips,
occasional whale sharks, marbled rays, and other species of elasmos.
Other diving locations submitted by
readers:
References
and further
reading:
Reef Sharks and Rays of the World. Scott W. Michael. Sea Challengers.
Sharks and Rays - Elasmobranch Guide of the World. Ralf M. Hennemann. IKAN.
