Bluntnose sixgill shark
Bluntnose sixgill shark | |
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Chondrichthyes |
Subclass: | Elasmobranchii |
Subdivision: | Selachimorpha |
Order: | Hexanchiformes |
Family: | Hexanchidae |
Genus: | Hexanchus |
Species: | H. griseus
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Binomial name | |
Hexanchus griseus (Bonnaterre, 1788)
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Range of bluntnose sixgill shark (in blue) |
The bluntnose sixgill shark (Hexanchus griseus), often simply called the cow shark, is the largest hexanchoid shark, growing to 20 ft (6.1 m) in length.[2] It is found in tropical and temperate waters worldwide and its diet is widely varied by region.
The bluntnose sixgill is a species of sixgill sharks, of genus Hexanchus, a genus that also consists of two other species: the bigeye sixgill shark (Hexanchus nakamurai) and the Atlantic sixgill shark (Hexanchus vitulus). Through their base pairs of mitochondrial genes COI and ND2, these three species of sixgills widely differ from one another.[3]
Taxonomy
The first scientific description of the bluntnose sixgill shark was authored in 1788 by
Description
The bluntnose sixgill shark has a large body and long tail. The snout is blunt and wide, and its eyes are small. There are 6 rows of saw-like teeth on its lower jaw and smaller teeth on its upper jaw.
The bluntnose sixgill shark resembles many of the fossil sharks from the
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Jaws, male
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Upper teeth, male
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Upper teeth, female
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Lower teeth, male
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Lower teeth, female
Growth and development
In general, the size (in length and weight) of the sixgills increase with maturity. With the male sharks specifically, their sexual maturity is usually determined by the length of their claspers. While juveniles have short and flexible ones, mature male sixgills have rigid, calcified longer ones.[9] On the other hand, the length-weight relationship of females tend to increase very rapidly as they get to the onset of their sexual maturity.[10]
Distribution and habitat
With a global distribution in tropical and temperate waters, the bluntnose sixgill shark is found in a latitudinal range between
On December 2, 2017, the ROV camera of
.Being in such a deep area of the ocean, these sharks have developed the behavior of undergoing diel vertical migration (DVM) in order to have more access to food. Research has found that it takes more time for the sixgills to have to swim back down to their natural habitat of the bathypelagic rather than to swim up during the night to find food in the more populated zones. As such, it can be inferred that they have some sort of adaptation that aids buoyancy to ensure that these sharks are able to float more easily.[20] An example of this DVM occurrence was found off the coast of Oahu, Hawaii, whereby 4 sixgills' behaviors were studied. At around midnight to 3–am, the 4 sharks swam up to a minimum depth of 300 m (980 ft) whereas at about noon, they reached their maximum depth of between 600 and 700 m (2,000 and 2,300 ft).[21] This shows a daily pattern whereby the sixgills are going up during the nights when it is darker and colder to forage for food up in the shallower depths but as morning comes and light and higher temperatures starts to come in more intently again, the sharks go back down to their original habitat to maintain a lower metabolic rate, ensuring that they will be able to use the nutrients from whatever they ate during the night slowly, reducing the need for them to search for more food throughout the day. Another study found that the motivating factor for the bluntnose sixgill sharks' DVM behavior was foraging. Researchers were able to rule out predator and competitor avoidance as potential reasons for the vertical movement patterns because they found pairs of sharks with synchronized movements, indicating that the sharks were responding to the same stimuli. The sharks demonstrated distinct and consistent patterns of vertical migration despite size, sex, and spatial scales, showing that foraging behavior can most likely be seen as the reason for the diel vertical patterns of sixgill sharks.[22] Lastly, the bluntnose sixgill shark has consistent seasonal movements. They move north during the winter and spring and south during the summer and fall. In this study as well, researchers were able to determine that these movement patterns can be attributed to the seasonal movements of prey over other reasons.[23]
Feeding behavior
Sixgill sharks possess variability in their feeding mechanisms that could have contributed to their evolutionary success and global distribution. These sharks are able to protrude their jaws and vary their methods of feeding depending on the situation. They utilize sawing and lateral tearing techniques to manipulate food. Sixgill sharks also lower their pectoral fins right before they strike in order to stop forward progressions, making it easier for them to forage.[24]
Biology and ecology
Although sluggish in nature, the bluntnose sixgill shark is capable of attaining high speeds for chasing and catching its prey using its powerful tail. Because of its broad range, it has a wide variety of prey, including
Bluntnose sixgill sharks are also positively buoyant as hypothesized earlier. During vertical movements, the sixgill sharks demonstrate more swimming efforts for the descent than the ascent. This is indicated by the greater number of tail beats and the sharks' ability to glide upwards for several minutes. The positive buoyancy can help the sharks to hunt stealthily by approaching prey from below undetected since the upward gliding permits minimal movement. It can also be advantageous for their diel vertical migrations. Since the sharks spend their days in colder water, their metabolic rates decline. Positive buoyancy can help them to glide upwards with minimal swimming involved during their evening migrations.[28]
Reproduction is
Human interaction
The bluntnose sixgill shark is listed as
This species is rather harmless to humans unless provoked.[4]
Recent research
Blue Planet II
Blue Planet II, a documentary on marine organisms produced by the BBC, featured an episode focusing on deep sea organisms and environments. In this episode, bluntnose sixgill sharks were filmed feeding on a whale fall. In behind-the-scenes footage, the sharks attacked the deep sea submersible as crew members tried to collect the video footage. Thinking that they were competition, the sharks used their bodies to try to fend off the submarine, only leaving it behind once they realized that the sub was not there to feed.[30][31] The film crew was able to obtain useful video footage of the sixgills that they later featured in the episode. As a worldwide, well-known, scientific platform, it hence helped with the awareness of the existence of these species of sharks.
Tagging sixgills in their natural habitat
Since 2005, scientists have successfully been able to tag sixgill sharks as a means of studying their behavior. With this being said, however, as of 2019, there has yet to be a sixgill tagged in its natural deep-sea habitat. Researchers from Florida State University, the Florida Museum of Natural History, the Cape Eleuthera Institute, and OceanX hence decided to join forces to tag a deep-sea shark through use of a submersible, and they succeeded in doing so.[32] After 3 months of leaving the tag on the sixgill, the tag was thought to float up to the surface where scientists will be able to collect the data from that tag. Overall, this study showed how advancements in technology has helped scientists be better able to study marine life. Instead of having to go on an expedition for years at a time, the scientists here simply had to attach a tag onto the sixgill once and collect the data another time. The tag simply showed behavioral results of the sixgills.
References
- ^ doi:10.2305/IUCN.UK.2020-3.RLTS.T10030A495630.en. Retrieved 19 November 2021.)
{{cite journal}}
: CS1 maint: multiple names: authors list (link - ^ "Huge deep sea shark scavenges food". Newsweek. July 23, 2019.
- S2CID 46764519.
- ^ ISBN 0-7835-4940-7.
- ^ McFarlane, Gordon A. and King, Jacquelynne R. and Saunders, Mark W. (2002) Preliminary study on the use of neural arches in the age determination of bluntnose sixgill sharks (Hexanchus griseus). Fishery Bulletin, 100(4), pp. 861-864. http://fishbull.noaa.gov/1004/17mcfarl.pdf
- PMID 25649000.
- ^ Lineaweaver, Thomas, & Richard H. Backus. (1969). The natural history of sharks. Lyons & Burford, New York, p. 169.
- ISSN 1755-2672.
- ISSN 0001-5113.
- ^ Ebert, David (1986). "Biological Aspects of the Sixgill Shark (Hexanchus griseus)". Research Gate.
- .
- ^ a b c d Froese, Rainer; Pauly, Daniel (eds.) (2017). "Hexanchus griseus" in FishBase. 01 2017 version.
- ^ "Φωτογραφίες: Έπιασαν καρχαρία τεσσάρων μέτρων στον Αστακό Αιτωλοακαρνανίας" [4 meters Hexanchus griseus in Greece]. ProtoThema. 7 October 2017.
- S2CID 252512629.
- ^ McFarlane, G. A.; King, J. R.; Saunders, M. W. (2002). "Preliminary study on the use of neural arches in the age determination of bluntnose sixgill sharks (Hexanchus griseus)" (PDF). Fishery Bulletin. 100: 861–864.
- ^ Bauml, Jessica. "Hexanchus griseus (Bluntnose Sixgill Shark)". Animal Diversity Web. Retrieved 2020-10-31.
- ^ Catoto, Roel (20 December 2017). "Rarely seen shark sighted in Ormoc Bay | MindaNews". www.mindanews.com. Retrieved 2017-12-22.
- ^ "'Look at the shark': Shark swims over oblivious divers in underwater video". USA TODAY.
- ^ "Scientists studying remains of pregnant sixgill shark found on Vancouver Island". The Globe and Mail. The Canadian Press. Retrieved 2019-02-07.
- PMID 31978204.
- ISSN 0967-0645.
- S2CID 53161681.
- PMID 20838617.
- PMID 27243237.
- S2CID 209673396.
- ^ Ebert, David (1986). "Biological Aspects of the Sixgill Shark (Hexanchus griseus)". Research Gate.
- ISSN 0257-7615.
- PMID 26061525.
- OCLC 1042901090.
- ^ "Blue Planet II behind the scenes: The moment giant sharks attack crew submarine - BBC News". YouTube. 2017.
- ^ "Blue Planet II behind the scenes: The moment giant sharks attack crew submarine - BBC News". YouTube.
- ^ Gilliland, Haley (2019). "Scientists Tag Deep-Sea Shark Hundreds of Feet Underwater—a First". National Geographic. Archived from the original on September 7, 2019.
External links
- Media related to Hexanchus griseus at Wikimedia Commons
- Data related to Hexanchus griseus at Wikispecies
- "Hexanchus griseus". Integrated Taxonomic Information System. Retrieved 23 January 2006.
- Information on H. griseus from ReefQuest Center for Shark Research
- YouTube video (1:17) - 18' specimen filmed at 1000 m in Molokai, HI.
- YouTube Video 1:37 - Cape Eleuthera Institute
- BBC Video 1:54 multiple specimens feeding at 750 m