Order- Carcharhiniformes Family- Sphyrnidae -hammerhead, bonnethead, scoophead sharks Etymology- Greek, sphyra = hammer

Order- Carcharhiniformes

Family- Sphyrnidae -hammerhead, bonnethead, scoophead sharks

Etymology- Greek, sphyra = hammer

Taxonomy- 2 genera, 9 species• Eusphyra- 1 species

– E. blochii- Winghead shark

• Sphyrna- 8 species – S. corona- Scalloped bonnethead– S. couardi- Whitefin hammerhead– S. lewini- Scalloped hammerhead– S. media- Scoophead– S. mokarran- Great hammerhead– S. tiburo- Bonnethead– S. tudes- Smalleye hammerhead– S. zygaena- Smooth hammerhead

Evolution of the Hammer

• Geneticist Andrew Martin used mtDNA sequence data to explore the origins and pattern of hammer development in 7 species of hammerheads.

• The molecular data strongly suggest that the Winghead Shark, not the Bonnethead (as was thought) was the first hammerhead to diverge from the group's common ancestor and that the bonnethead was, in fact, the most recent hammerhead to appear.

Average head width expressed as a percentage of body length (for comparison, in most carcharhinids, head width averages about 6-8% of body length).

Evolution of the Hammer• 2002 paper by Kajiura and Holland,

Electroreception in juvenile scalloped hammerhead and sandbar sharks, he tested 2 hypotheses, sensory based and hydrodynamic functions.

• Concluded that hammerheads can sample larger area which enables them to find more prey and the wing shape of the head acts as a stabilizer, giving them greater maneuverability.

General Characteristics• Unmistakable, hammer/shovel shaped

cephalofoil

• Eyes have well developed nictitating membrane. Eyes and nostril positioned at the tip of hammer.

General Characteristics• 2 dorsal fins, 2nd dorsal and anal much

smaller than 1st dorsal.

• Caudal fin strongly asymmetrical, subterminal notch well marked, and a small but well defined ventral lobe. Upper and lower precaudal pits present.

General Characteristics• Anterolateral teeth blade-like, with a single cusp

usually pointed toward the corners of the mouth. Posterior teeth may be modified into keeled, molariform crushing teeth without cusps.

• Back predominantly grey/brownish, underside white/light grey

• Sizes range from 0.9-6 m long (3-20 ft)

• Many species are migratory and are known to form schools containing hundreds of individuals

• Average lifespan in the wild thought to be 20 to 30 years

Reproduction• All species are viviparous (placental viviparous,

with a yolk-sac placenta), and have 4 to 42 young per litter.

• Gestation 10-12 months

Bonnethead with embryoscourtesy NOAA

Reproduction

• World record 1,280 pound female S. mokarran was carrying 55 pups.

Reproduction• 12/14/01, Omaha, Nebraska – Henry Doorly Zoo- S. tiburo gave birth to normally developed live female pup

• Parthenogenesis confirmed and announced in May 2007 after DNA analysis found no paternal genetic material

Habitat/Distribution• Inhabit all tropical and warm-temperate

seas, from the surface down to at least 275m in waters near continents, and oceanic islands.

• Small species are confined to coastal continental waters; juveniles of large species are coastal off continents; adults are primarily semi-oceanic, although they often approach coasts in search of food.

Food Habits• Feed on: teleosts, other elasmo’s, cephalopods,

gastropods, bivalves, and crustaceans, but do not feed on marine mammals or other very large marine vertebrates.

• Particularly fond of stingrays; hammerheads have been found with dozens of venomous stingray barbs imbedded in their mouth and jaws.

Fisheries• Commercial fisheries catch hammerheads for

their oil, meat and skin.• Flesh is consumed commonly in the tropics and

sold frozen, dried/salted, and smoked.

Fisheries• Schooling pattern makes them easy prey for

fishermen targeting large catches.• Popular sport fishery, hammerheads are caught

accidentally by longlining crews fishing for swordfish and tuna.

Eusphyra blochii (Winghead shark)

• Expanded lateral blades of head very narrow and wing-like, with a series of small bumps along edges in front of nostrils; width across head 40 or 50% of total length.

• Nostrils enormously expanded, each nearly 2 times the mouth width.

Eusphyra blochii (Winghead shark)

Sphyrna mokarran (Great hammerhead)

• Nearly straight anterior margin of head (slightly round in juve’s) with deep central indentation.

• High 2nd dorsal fin, pelvic fins with curved rear margins. 5th gill shorter than others.


• Triangular teeth with serrated edges.

• Largest of Sphyrnids, reported to reach 610 cm (20 ft).


Parasitic copepods of the underside of snout of a great hammerhead© Doug Perrine

Sphyrna couardi (Whitefin hammerhead)

• poorly known

• found in E. Atlantic (45°N-8°S).

• grows up to 3 m.

Sphyrna lewini (Scalloped hammerhead)

• marked central indentation on anterior margin of head.

• Teeth triangular and smooth-edged. 5th gill shorter than others.

Sphyrna lewini (Scalloped hammerhead)

• Inshore and offshore (up to 275 m) Grows to ~ 365 cm (12 ft).

Sphyrna zygaena (Smooth hammerhead)

• Anterior margin of head lacks central indentation.

• Max size is 370-396 cm (12-13 feet).

Sphyrna zygaena (Smooth hammerhead)

Sphyrna corona (Scalloped bonnethead)

• poorly known• broadly rounded anterior margin of head

sometimes with a shallow central indentation. • Free rear tip of 1st dorsal reaches level of pelvic

fins. • E. Pacific (southern Mexico to northern Peru;

Gulf of California?)

Sphyrna media (Scoophead)

• slightly round anterior margin of head with deep central indentation.

• 1st dorsal fin free rear tip extends to level of pelvic fins. Reaches at least 152 cm (60 inches).

• Western Atlantic: Panama to southern Brazil. Eastern Pacific: Gulf of California to Ecuador and probably northern Peru.

Sphyrna tudes (Smalleye hammerhead)

• aka Golden hammerhead due to yellowish/brown color.

• Anterior margin of head with a deep central indentation, well developed inner narial groove.


• Free rear tip of 1st dorsal reaching level of pelvic fins.

• Reaches at least 152 cm (~ 5 ft).


• Western Atlantic: Venezuela to Uruguay.

Sphyrna tiburo (Bonnethead)

• Shovel/bonnet shaped head evenly rounded between the eyes.

• Smallest of sphyrnids, max size is ~150 cm (~5 ft).



Comparison of hammerhead sharks:A. smooth hammerhead, B. scalloped hammerhead, C. great hammerhead, D. bonnethead©George Burgess

Conservation• All species listed in IUCN Red List except S. couardi

(Whitefin hammerhead).

– S. media (Scoophead)- listed as data deficient.– S. tiburo (Bonnethead)- LR(lc)– S. lewini (Scalloped hammerhead) & S. zygaena

(Smooth hammerhead)– LR(nt)– S. corona (Scalloped bonnethead)- NT– E. blochii (Winghead shark)- NT– S. tudes (Smalleye hammerhead)- VU– S. mokarran (Great hammerhead)- EN

-based on suspected decline of at least >50% over the past decade-urgent need for data collection-highly valued for fins, incidental bycatch, biennial reproducers

Bibliography• Carrier, J., Musick, J., & Heithaus, M. (2004). Biology of Sharks and Their Relatives.

CRC Press, Boca Raton, FL. pg. 74

• Castro, J.I. 1983. The sharks of North American waters. Texas A&M University Press,College Station, TX. pp.150-159.

• Compagno, L.J. 1984. FAO species catalogue. Vol. 4. Sharks of the World. An annotated and illustrated catalogue of shark species known to date. Part 2- Carcharhiniformes.. FAO Fish. Synop. 125(4/1): 88-96.

• IUCN 2007. 2007 IUCN Red List of Threatened Species. <www.iucnredlist.org>. Downloaded on 12 October 2007.

• Kajiura, S., & Holland, K. (2002) Electroreception in juvenile scalloped hammerhead and sandbar sharks. The Journal of Experimental Biology. 205: 3609-3621.

• Martin, R. Aidan. 2003. Copyright and Usage Policy. World Wide Web Publication, Retrieved November 3, 2007 from: www.elasmo-research.org/copyright.htm.

http://www.elasmo-research.org/education/students/citations

Documents

Order- Carcharhiniformes Family- Sphyrnidae -hammerhead, bonnethead, scoophead sharks Etymology- Greek, sphyra = hammer