• Angela Warrior

June Elasmobranch of the Month: Common Thresher Shark


Name

Alopias vulpinus-also known as the Common Thresher Shark or Fox shark. Thresher sharks were first named after foxes by Aristotle in the book Animalia. He described them as intelligent and cunning as a fox due to what he believed to be their ability to bite through fishing lines to escape fishermen and swallow their young to protect them from predators. Although these behaviors were scientifically incorrect, they earned the Thresher Shark the Greek name Alopex, meaning fox.

Order-Lamnioforme

Family-Alopidae

Genus-Alopias

Species-vulpinus

Image: Richard Herrmann

Appearance

Common Thresher sharks range from 2-6 meters in length, averaging 2.74m. Up to 50% of this is due to their very long caudal fin, which gives the tail a whip-like appearance. They can weigh up to 500kg but the average is believed to be around 348kg. The thresher shark has a short head and a cone-shaped nose. Their mouths are generally small, they have small, razor sharp teeth with curved, smooth-edged cusps. Their coloration varies from coppery brown to blue on their dorsal sides and white on their ventral sided. They are warm bloodied, with endothermic capabilities. This means they have slow-oxidative muscles combined with counter current blood vessel exchange (when heat from warm arterial blood moves across the vessels to the cooler venous blood) which helps them regulate their blood pressure internally and maintain a blood temperature 3.6F warmer than the surrounding sea water. Being warmer means they can use their muscles more efficiently, making them quick swimmers and active hunters.

© FAO, Food and Agriculture Organization of the United Nations, Ebert, D.A. 2014.

Behavior

Common thresher sharks are solitary, known as free-range predators due their migratory behavior. There is little information on their migratory paths, however it is believed that during winter they will travel south towards the equator to warmer waters and in the summer they will travel north away from the equator to cooler waters. Thresher sharks are one of the fastest sharks in the ocean and can swim at a top speed of 30 mph! They are also seen jumping out of the water when catching their prey. Their long caudal fin which provides extra thrust and endothermic abilities give it extra strength and power.

Predation

Like most sharks, the common thresher is a carnivore. From an early age thresher will mainly feed on small schooling fish such as anchovies, sardines, mackerel, hake and squid from the deep ocean, which they corral and stun with strikes from their tails. As they grow into larger classes and stages of maturity they will feed on larger fish such as tuna. They are also keen predators of the larger squids found deep in the ocean.

Reproduction

Males become sexually mature at approximately 10-15 years of age, but females reach sexual maturity later. All three species of Thresher shark are believed to reproduce via aplacental viviparity where the embryos develop inside eggs that are kept within the mother’s body until they are ready to hatch. Gestation periods are unknown, but new born pups have been measured at around 5 feet. The pups usually keep to shallow nursery areas that are separate from adults to avoid predation from other sharks like makos, reef sharks and even older thresher sharks.

Threats

Common threshers are sold in many foreign fish markets, the meat is considered to be very tasty, as a result the demand for their meat is high. Because thresher sharks are often seen feeding close to shore, they offer sport fishers a shot at big-game-style fishing without the need to burn a lot of fuel. In many areas of the Atlantic Ocean, populations have declined by nearly 70% in the last ten years. Alopius vulpinus is now listed as “Threatened” on the IUCN Red-List.

References

AnimalDiversityWeb.Alopiasvulpinus.SeaFox.https://animaldiversity.org/accounts/Alopias_vulpinus

Pelagic Shark Research Foundation. Thresher sharks-Alopias sp.

http://www.pelagic.org/montereybay/pelagic/threshershark.html

IUCN Redlist Alopias vulpinus. https://www.iucn.org

Images

Pelagic Shark Research Foundation. Thresher sharks-Alopias sp.

#Threshershark #sharks #sharkfacts #Commonthreshershark #sharkeducation #sharkconservation #Sharkreproduction #shark

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