Featured Species Friday: Great Hammerhead (Sphyrna mokarran)

I know that I am not supposed to play favorites, however this week’s Featured Species ties for my favorite shark species – don’t tell the others! Growing to a maximum length of 20 feet (6 m), the Great Hammerhead (Sphyrna mokarran) is the largest of the 10 species of the hammerheads. If the image you conjure up when you think of hammerheads is massive schools of hundreds of hammerheads, you’ve got the wrong species. The Great Hammerhead is a solitary predator with a very tall dorsal fin on a brown-gray back and a sickle like tail.

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Discovery Channel Sharkweek (2014). Monster Hammerhead [Screen Capture]. Retrieved from http://sharkopedia.discovery.com/

There are 10 species of hammerheads in the family Sphyrnidae.

Common Name

Scientific Name

IUCN Status

Winghead Shark Eusphyra blochii Endangered
Great Hammerhead Sphyrna mokarran Endangered
Whitefin Hammerhead Sphyrna couardi Endangered
Scalloped Hammerhead Sphyrna lewini Endangered
Smalleye Hammerhead Sphyrna tudes Vulnerable
Smooth Hammerhead Sphyrna zygaena Vulnerable
Scalloped Bonnethead Shark Sphyrna corona Near Threatened
Bonnethead Shark Sphyrna tiburo Least Concern
Scoophead Shark Sphyrna media Data Deficient
Carolina Hammerhead Sphyrna gilberti Yet To Be Assessed

One species recently discovered in 2013, the Carolina Hammerhead (Sphyrna gilberti), is considered a cryptic species. It can only be told apart from the Scalloped Hammerhead (Sphyrna lewini) by the number of precaudal vertebrate (Quattro, Driggers III, Grady, Ulrich, & Roberts, 2013). However, the other remaining species of hammerheads are identifiable by, not only their size for many species, but their head wings referred to as a cephalofoil (Skomal, 2016). The Great Hammerhead’s cephalofoil is large and broad that is almost straight across except for a central notch (Skomal, 2016).

20170817132006_001
Drawings 1 to 9: Hammerhead sharks (fam. Sphyrnidae) are easily recognizable by the typical highly depressed, wide head with eyes on the outer side of the two lobes. The individual species, whose common denominator is this unusual head, can be distinguished by differences in horizontal profile, which can be almost straight or markedly curved. (1) Eusphyra blochii (2) Sphyrna tudes (3) Sphyrna couardi (4) Sphyrna corona (5) Sphyrna tiburo (6) Sphyrna mokarran (7) Sphyrna lewini* (8) Sphyrna zygaena (9) Sphyrna media (Mojetta, 1997). *Since publication Sphyrna gilberti has also been discovered as a cryptic species, and is only distinguishable from S. lewini by number of precaudal vertebrae (Quattro, Driggers III, Grady, Ulrich, & Roberts, 2013).

 

The hammerheads are relatively new in the shark world. They are actually the most recent shark family to evolve around 20 million years ago (Mojetta, 1997). So how did that unusual head evolve? DNA testing of modern hammerheads have revealed that big hammerheads most likely evolved into smaller hammerheads, and the smaller hammerhead species actually evolved independently… twice (Lim, Motta, Mara, & Martin, 2010). The winghead shark evolved very early on in the waters around Australia; while the lineage that would produce the bonnethead shark evolved later on in the Caribbean and eastern Pacific (Lim, Motta, Mara, & Martin, 2010). It is suspected that the ancestor of the hammerhead lived in the Miocene epoch about 20 million years ago, with the modern Great Hammerhead first appearing around 10 million years ago (Lim, Motta, Mara, & Martin, 2010).

Untitled
Fig. 3. Inferred phylogeny based on mixed model Bayesian analysis of the concatenated data and BEST analysis for species of the genus Sphyrna, Eusphyra blochii (Eusphyra) and the outgroup Carcharhinus acronotus. Number above nodes are the posterior probabilities (100x) from the mixed model analysis that contained the group and the numbers below the nodes are BEST credibility values (100x). (Lim, Motta, Mara, & Martin, 2010).

 

Scientists believe that the cephalofoil of the hammerheads allow for these sharks to utilize their sixth sense: the Ampullae of Lorenzini (Skomal, 2016; Parker, 2008). These jelly filled pores are electroreceptors that line the hammerheads cephalofoil that allow sharks to sense the slightest movement in the water – like the heartbeat of a fish or stingray hiding the in the sand (Parker, 2008).  The tiny black dots along the underside of the hammerheads snout are the Ampullae of Lorenzini.

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Johnson, G. (Photographer). (2017 January 1). Bimini’s Great Hammerhead season is in full swing [Digital Image]. Retrieved from https://www.instagram.com/

It is thought that hammerheads use their cephalofoil similar to a metal detector, swinging their heads back and forth over the sand, picking up the tiniest electrical signals from their favorite prey – stingrays (Skomal, 2016; Parker, 2008). Once detected, the great hammerhead is highly maneuverable, able to make hairpin turns while pinning their prey to the seafloor with their massive head. With the stingray pinned, the great hammerhead will rotate its head to the side and take a debilitating bite out of the ray’s pectoral fin (Tricas, Deacon, Last, McCosker, Walker, Taylor, 1997). Great hammerheads have often been documented with stingray barbs in their mouths and throat from consuming their prey whole (Skomal, 2016).

 

 

 

Smithsonian Channel. (2016 July 29). Hammerhead vs. Stingray [Video Clip]. Retrieved from https://www.youtube.com/

 

I’m delighted to announce a partnership with the wonderfully talented Julius Csotonyi! Julius creates stunning shark coloring sheets that are fun and educational for all ages. From time to time you’ll see Julius’ work featured right here and on my other social media platforms! You can find more coloring sheets in the store! You are welcomed to download these beautiful sheets and enjoy them with family and friends.

Sphyrna-mokarran-lewini-zygaena_Csotonyi_01_201903022358.jpg

 

Shark Stats

Authority: Rüppell, 1837

Family: Sphyrnidae; 10 species

Length: Maximum of 20 ft (6 m)

Weight: Average 550 lbs (249 kg), rarely over 800 lbs (363 kg), largest ever landed 1,100 lbs (499 kg)

Habitat: Shallow coastal waters to offshore oceanic areas; coral atolls and lagoons; island shelves and coral reefs

Depth: Surface to 260 ft (80 m)

Reproduction: Viviparous

Gestation: 11 months

Litter Range: 6 – 42 pups every 2 years

Home Range: Worldwide, tropical waters seasonally to warm temperate zones, not found in Hawaii

Diet: Wide variety of organisms including invertebrates, fishes, sharks, and their favorite prey: stingrays; documented cases of cannibalism

IUCN Status: Endangered

(Skomal, 2016; Parker, 2008; Denham, 2007; Frederico & Hassall, 1998)

Thanks for checking out this week’s featured species! If you missed last week’s Featured species, please check out the Whitetip Reef Shark. Haven’t seen your favorite species yet? Leave me a comment or send me a message! I’d love to hear from you!

The new Ocean For Sharks Shop is open! There’s handmade ocean inspired plush animals, canvas paintings, and of course my children’s book, Winifred the Wondrous Whale Shark, available in print and PDF. Be sure to stop by. Remember proceeds benefit shark research and conservation with a donation to Project AWARE!

Remember you can make a difference for marine ecosystems by calling your Congress man or woman and tell them that you care about the quality of our waters! Sharks, rays, and other marine organisms cannot speak or be represented in Congress. They need your voice. Get involved and stand up for sharks. Until next time finatics!

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Featured Image Source

Dargento, R. (Photographer).(2017 June 18). Great Hammerhead Shark [Digital Image]. Retrieved from https://www.instagram.com/

Literature Cited

Denham, J., Stevens, J.D., Simpfendorfer, C., Heupel, M.R., Cliff, G., Morgan, A., Graham, R., Ducrocq, M., Dulvy, N.K., Seisay, M., Asber, M., Valenti, S.V., Litvinov, F., Martins, P., Lemine Ould Sidi, M., Tous, P. & Bucal, D. 2007. Sphyrna mokarran. The IUCN Red List of Threatened Species 2007: e.T39386A10191938. http://dx.doi.org/10.2305/IUCN.UK.2007.RLTS.T39386A10191938.en

Frederico, L., & Hassall, G. (Eds.). (1998). Reader’s Digest Explores: Sharks (1st ed.). Reader’s Digest.

Lim, D. D., Motta, P., Mara, K., & Martin, A. P. (2010). Phylogeny of hammerhead sharks (Family Sphyrnidae) inferred from mitochondrial and nuclear genes. Molecular Phylogenetics and Evolution55(2), 572-579.

Mojetta, A. (1997). Sharks: History and biology of the lords of the sea. (E. McNulty, Ed.). San Diego: Thunder Bay Press.

Parker, S. (2008). The encyclopedia of sharks (2nd ed.). Buffalo, NY: Firefly Books Ltd.

Quattro, J. M., Driggers, W. B. I., Grady, J. M., Ulrich, G. F., & Roberts, M. A. (2013). Sphyrna gilberti sp. nov., a new hammerhead shark (Carcharhiniformes, Sphyrnidae) from the western Atlantic Ocean. Zootaxa3702(2), 159-178.

Skomal, G. (2016). The Shark Handbook: The Essential Guide for Understanding the Sharks of the World. (2nd ed.). Kennebunkport, ME: Cider Mill Press.

Tricas, T.C.; Deacon, K.; Last, P.; McCosker, J.E.; Walker, T.I.; Taylor, L. (1997). The Nature Company Guides: Sharks and Rays. (L. Taylor, Ed.). Hong Kong: The Nature Company, Time Life Books.

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