This week’s featured species needs no introduction: the Pelagic Thresher shark (Alopias pelagicus) has a narrow snout, large eyes, and long, straight pectoral fins with broad tips (Ebert, Fowler, & Dando, 2015). But what the thresher sharks are known for is their strikingly long tails. The upper lobe of their tails can be as long as the length of their entire body (Ebert, Fowler, & Dando, 2015). This extreme exaggeration of the of unequal tail lobes is called heterocercal (Parker, 2008).
The pelagic thresher shark is a member of the Alopiidae family. This family contains three species in one genus, Alopias. The largest of thresher sharks is the Common Thresher Shark (Alopias vulpinus); these sharks can reaches lengths of 20 feet (6 m) from snout to tip of the tail and can be found in subtropical and tropical waters world wide (Skomal, 2016). The Bigeye Thresher Shark (Alopias superciliosus) is also found world wide in subtropical and tropical waters and can reach lengths of 15 feet (4.5 m) in length. But these sharks are defined by their extremely large eyes with deep set ridges surrounding them (Tricas et al, 1997). The pelagic thresher is the smallest of the thresher sharks, measuring around 12 feet (3.65 m). They also have the smallest home range, only being found in the tropics and subtropics of the Indo-Pacific Oceans; there are no reports of this species in the Atlantic Ocean (Ebert, Fowler, & Dando, 2015).
The pelagic thresher shark is sometimes referred to as the small-tooth thresher shark (Reardon, Márquez, Trejo, & Clarke, 2009). The pelagic thresher shark has at least 30 rows of small teeth set in both the upper and lower jaws. Each smooth tooth has a distinct central cusp that is angled posteriorly, or towards the back of the jaw (Tricas et al, 1997). The shape and position of the pelagic thresher shark’s teeth are ideal for snaring their favorite prey: squid (Reardon, et al, 2009).
The pelagic thresher shark don’t only rely on their teeth for hunting and catching their prey. They have been documented hunting schools of fish and squids in pairs, working together to herd their prey into tighter and tighter groups (Parker, 2008). Then the thresher shark strikes out in the most unique fashion in the shark- and possible the animal- world. They slash their tails forward with incredible speed and stunning their prey (Parker, 2008). This technique is called tail-smacking. Until recently, it was only speculated that the thresher sharks used their tails to hunt in this way. But in 2010, a team of researchers captured this behavior for the first time by the pelagic thresher shark at Pescador Island in the Philippines (Oliver, Turner, Gann, Silvosa, & Jackson, 2013). The study was subsequently published in 2013.
PLOS Media (Videographer). (2013). Hunting Strategies of Thresher Sharks: Overhead Tail-Slap [Video Clip]. Retrieved from https://youtu.be/
Unlike other species of sharks which are cold blooded and rely on the surrounding water temperature to thermoregulate their bodies, the sharks in the family Alopiidae, which as well as family Alopiidae, as well as the sharks of family Lamnidae, which includes the Great White and the shortfin mako, are warm-blooded – sort of. These endothermic sharks have a modified circulatory system that allows them to elevate the temperatures of certain organs (such as the eyes, brain, heart, stomach, and trunk muscles) through a process called counter-current heat exchange. The arteries and veins run parallel over the trunk muscles. The incoming cold blood in the veins is warmed by the outgoing warm blood in the arteries (Klimley, 2013).
Pelagic thresher sharks are listed as a Vulnerable species to extinction by the International Union for the Conservation of Nature (IUCN). Like many species of sharks, they are threatened by the fin trade. In surveys of fishing markets in Hong Kong, thresher sharks were found to represent 2-3% of the fins at auction (Clarke, Magnussen, Abercrombie, McAllister, & Shivji, 2006). It is estimated that between 35,000 to 3.9 million thresher sharks are represented in the trade each year (Clarke, et al, 2006). It is difficult to determine the exact number of thresher sharks harvested each year because catches are vastly under reported globally. As a result, population trend data is largely lacking (Reardon, et al, 2009). It is suspected that current fisheries are unsustainable. Aside from targeted fisheries, the pelagic thresher shark is also taken as bycatch from the tuna fisheries. They are easily entangled in gillnets and longlines, and have even been snared on hooks by their long tails (Reardon, et al, 2009). All members of the family Alopiidae are listed as highly migratory species under the 1995 UN Straddling Fish Stocks Agreement. Under this agreement, coastal states are required to cooperate and adopt measures to ensure the conservation of all listed species (Reardon, et al, 2009). The FAO International Plan of Action for the Conservation and Management of Sharks (IPOA- Sharks) also recommends that regional fisheries organizations carry out regular assessments of these species (Reardon, et al, 2009).
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.
Authority: Nakamura, 1935
Family: Alopiidae; 3 species
Length: 10 feet (3.65 m); smallest of the thresher sharks
Weight: Maximum 153 lbs (69.5 kg)
Habitat: Epipelagic; oceanic, typically offshore; narrow continental shelves
Depth: Surface to 500 feet (152 m)
Reproduction: Ovoviviparous with oophagy stage
Gestation: Unknown gestation period
Litter Range: 2 pups
Home Range: Tropics and subtropics of the Indo-Pacific Ocean
Diet: Bony fishes and invertebrates with a preference for squids
IUCN Status: Vulnerable
(Reardon, et al, 2009; Ebert, Fowler, & Dando, 2015)
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!
Thanks so much for checking out the stunning Pelagic Thresher Shark! If you missed last week’s featured species, please be sure to check out the Salmon Shark! If there is a species of elasmobranch you’d love to know more about, leave me a comment or send me a message! I would love to do a feature on your favorite species. So connect with me on Instagram and Facebook for even more elasmo fun!
Conservation legislation needs public support in order to become law and help protect the environment and wildlife. Tell your representatives that you care about environmental and wildlife conservation. It only takes a moment to make a change that will last a lifetime. Until next time finactics!
Featured Image Source
Scarborough, J. (Photographer). (2017). Thresher Shark in Malapascua [Digital Image]. Retrieved from https://www.scubatravel.com/blog/wp-content/uploads/2017/08/Thresher-shark-Malapascua-4.jpg
Clarke, S. C., Magnussen, J. E., Abercrombie, D. L., McAllister, M. K., & Shivji, M. S. (2006). Identification of shark species composition and proportion in the Hong Kong shark fin market based on molecular genetics and trade records. Conservation Biology, 20(1), 201-211.
Compagno, L. J. (2001). Sharks of the world. An annotated and illustrated catalogue of shark species known to date, vol 2. Bullhead, mackerel and carpet sharks (Heterodontiformes, Lamniformes and Orectolobiformes). FAO species catalogue for fishery purposes, 1, viii+-1.
Dulvy, N. K., Baum, J. K., Clarke, S., Compagno, L. J. V, Cortés, E., Domingo, A., … Valenti, S. (2008). You can swim but you can’t hide: The global status and conservation of oceanic pelagic sharks and rays. Aquatic Conservation: Marine and Freshwater Ecosystems, 18(5), 459–482.
Ebert, D. A., Fowler, S. L., & Dando, M. (2015). Sharks of the world: a fully illustrated guide. Wild Nature Press.
Klimley, A. P. (2013). The biology of sharks and rays. University of Chicago Press.
Oliver, S. P., Turner, J. R., Gann, K., Silvosa, M., & Jackson, T. D. U. (2013). Thresher sharks use tail-slaps as a hunting strategy. PLoS One, 8(7), e67380.
Parker, S. (2008). The encyclopedia of sharks (2nd ed.). Buffalo, NY: Firefly Books Ltd.
Reardon, M., Márquez, F., Trejo, T. & Clarke, S.C. (2009). Alopias pelagicus. The IUCN Red List of Threatened Species. Retrieved from https://www.iucnredlist.org/species/161597/5460720
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.