Here Fishy, Fishy: Tagging Prehistoric Sixgill Sharks

The sixgill shark is potentially the world’s most widely distributed large predator left on Earth today. And we hardly know anything about it.

Sixgill Shark. Photo by Lia Barrett.

Sixgill Shark. Photo by Lia Barrett.

Sightings of sixgills are rare as they tend to spend most of their time in deeper waters. Seattle, Washington, specifically Puget Sound, is one location where sixgills can be found at recreational scuba depths. Generally, young sixgills are found at these shallow depths, while adults tend to remain in deeper water farther off the coast. It’s thought that sixgills may be restricted to deeper depths due to light sensitivity and perhaps thermal sensitivity. In some parts of the world, sixgills can be found seasonally at shallower depths, usually when algae is in bloom, as the blooms tend to attenuate light penetration. In one unusual case, a sixgill was caught 30 km up a river in Tasmania!

Much of the research on sixgills and some of the only horizontal migration studies have been conducted in Puget Sound. Many studies have focused on diel vertical migration – the daily pattern of movement up and down the water column – and found that sixgills tend to vertically migrate several hundred meters into shallower water at night and return to deeper depths (the oxygen minimum zone) during the day. But no study has ever looked at the horizontal migration patterns of adult sixgills. One reason for this is that, well, they’re hard to catch. In most cases, a sixgill shark must be hauled up alongside a boat and a tagged via surgical insertion of a satellite tag underneath the skin. As you can imagine, it’s not that easy to selectively catch a deep water fish.

taggingdiagramBut what about tagging from a submersible? A graduate student at the University of Hawai’i at Manoa has just that idea. Brandon Genco is currently trying to crowd-fund his project and has also applied for a Waitt Institute grant. His main objective is to tag 3-5 adult female sixgill sharks from Idabel so we can figure out a thing or two about where these animals move and how far they swim. This will basically involve a glorified slingshot with a satellite tag attached. With a large helping of crowd-funded science and a sprinkle of renegade engineering, we plan to get it all on film, too.

Most sharks tend to migrate long distances, and these migrational movements can be extremely important for conservation efforts. For instance, studies in Puget Sound found that sub-adult sixgills stuck pretty close to home until they reached a certain size. A small home range for subadults is imperative for understanding how localized environmental effects (e.g. anthropogenic activities) could have serious consequences for these sharks. Establishing whether adults migrate long distances and congregate for mating events will be one critical to our understanding of this animal.

If you are having ANY doubts about funding this project, just take a look at when NatGeo was here a few years ago filming sixgills from Idabel. And did I mention that sixgills are prehistoric?! The majority of extant sharks today have five-gills – a hallmark of a more recent evolutionary history. Most members of the sixgill family tree no longer exist (they died off 200 million years ago), but a few aunties and sixth cousins half-removed still remain like the dogfish, greenland shark, and other six-gill and seven-gill sharks. So, if you’d like to give a hand to this unique project, please visit the crowd-funding page here!

 

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Sources

Andrews KS, Williams GD, Levin PS (2010) Seasonal and ontogenetic changes in movement patterns of sixgill sharks. PloS one 5: e12549. DOI:10.1371/journal.pone.0012549.

Barnett A, Stevens JD, Yick JL (2010). The occurrence of the bluntnose sixgill shark Hexanchus griseus (Hexanchiformes: Hexanchidae) in a river in south-eastern Tasmania. Marine Biodiversity Records, 3, e24 DOI:10.1017/S1755267210000199.

Comfort CM, Weng KC (2014) Vertical habitat and behaviour of the bluntnose sixgill shark in Hawaii. Deep Sea Research Part II: Topical Studies in Oceanography. DOI: 10.1016/j.dsr2.2014.04.005

http://psrc.mlml.calstate.edu/2008/11/featured-elasmobranch-bluntnose-sixgill-shark/

http://www.elasmo-research.org/education/topics/d_jurassic_shark.htm

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~ by twonakedapes on July 6, 2014.

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