Order: Carcharhiniformes Family: Sphyrnidae (hammerhead, bonnethead, scoophead sharks) Etymology




Дата канвертавання26.04.2016
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Heather Jewett-11/6/07
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 seven 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.

  • In a 2002 paper by Kajiura and Holland, they 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.

  • Anterolateral teeth blade-like, with a single cusp usually pointed toward the corners of the mouth. Posterior teeth similar to anterolateral teeth or modified into keeled, molariform crushing teeth without cusps.

  • 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.

  • 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: 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, pups fend for themselves after birth. Each litter contains 4-42 pups.

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

  • 12/14/01, Omaha, Nebraska – Henry Doorly Zoo- S. tiburo gave birth to normally developed live female pup (later killed by stingray in same tank)

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

Diagnostic Features

      • 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.

      • 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.

      • S. couardi (Whitefin hammerhead)- poorly known; found in E. Atlantic (34°N-6°S). Grows up to 3 m.

      • S. lewini (Scalloped hammerhead)- marked central indentation on anterior margin of head. 1st dorsal fin rear tip doesn’t reach level of pelvic fins, long second dorsal fin. Teeth triangular and smooth-edged. 5th gill shorter than others. Inshore and offshore (up to 275 m) Grows to ~ 365 cm (12 ft).

  • S. 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).

  • S. 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).

      • S. tiburo (Bonnethead)- Shovel/bonnet shaped head evenly rounded between the eyes. Smallest of sphyrnids, max size is ~150 cm (~5 ft).

      • S. 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, and free rear tip of 1st dorsal reaching level of pelvic fins. Reaches at least 152 cm (~ 5 ft).

      • S. zygaena (Smooth hammerhead)- Anterior margin of head lacks central indentation. 1st dorsal fin free rear tip doesn’t reach level of pelvic fins. Max size is 370-396 cm (12-13 feet).



Habitat/Distribution/Food Habits

  • inhabit all tropical and warm-temperate seas, from the surface, surf-line, and intertidal down to at least 275m in waters near continents, continental islands, and oceanic islands

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

  • Feed on a wide variety of bony fishes, other sharks (including batoids), cephalopods (squids, octopi, and cuttlefish), gastropods, bivalves, and crustaceans (shrimp, mantis shrimp, brachyurid crabs, lobsters, barnacles, and isopods), 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/Conservation

  • Commercial fisheries catch hammerheads for their oil, meat and skin.

  • Flesh is consumed commonly in the tropics and sold frozen, dried/salted, and smoked.

  • 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.

  • 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. . Downloaded on 12 October 2007.



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


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