The Fins United Initiative is excited to bring back the loved "Underrated Elasmobranch Spotlight" series through TFUI officer Jess Myers. Learn about the Chondrichthyans not shown on the big screen through her beautiful artwork... and check out the new name.
Swimming in with two more gill slits than most, is our next uncommon Chondrichthyan, the bluntnose sixgill shark (Hexanchus griseus).
Bluntnose sixgill sharks can be found all over the world in tropical and temperate waters. Juveniles will stick to shallower waters closer to the shore but as they age, adults will drift to waters as deep as 2,000 meters (~6,600 feet). They are the largest shark in the Hexanchidae family (six and sevengill sharks), growing up to 4.8 m (~16 feet) although some report up to 8 meters (26 feet). Like the broadnose sevengill (Notorynchus cepedianus) from the 2018 lineup, they have only one dorsal fin that is set farther back than most sharks. Dorsal fins help fish stay stable in the water column, so having a less prominent fin set farther back allows a shark to twist their body more easily.
A study from 2016 by Brian McNeil et al. looked at the feeding behavior of subadult sixgill sharks and noticed that bluntnose sixgill sharks have multiple styles of feeding. For instance, they use their unusually shaped serrated teeth combined with a back-and-forth motion to cut the chunks from larger prey. Other than biting and sawing through prey, Elasmobranchs can also ram feed, coming at their prey with an open mouth and swallowing it whole (like sand tiger sharks (Carcharias taurus) or suction feed by pulling their prey into their mouth using negative pressure (think nurse sharks (Ginglymostoma sp.). The scientists in this study noticed that the sixgills exhibited these three feeding behaviors. They theorize that the diverse feeding styles allow these sharks to live successfully in a variety of habitats.
Despite giving birth to up to 100 pups at a time, bluntnose sixgill sharks don’t mature until they’re about 3 meters (10 feet) long. This reproductive rate in combination with demand for their liver and meat leaves them Near Threatened according to the ICUN Red List’s 2019 survey.
TFUI Founder Melissa C. Marquez is author of all animal bios and "Behind the Fins" segments.
SEE MELISSA'S TEDx TALK HERE:
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