This week’s featured species is thought to be the longest living vertebrate on the planet. The Greenland Shark (Somniosus microcephalus) is a deep sea arctic shark that can live up to 400 years, only reaching sexual maturity after 150 years (Nielsen, et al., 2016)!
Butler, P. (Author). (2016). Greenland Shark [Digital Image]. Retrieved from https://scroll.in/article/
There have been many attempts to determine the longevity of sharks. Bony fishes (teleosts) are aged using the patterns on the bony otoliths, which are the calcium carbonate structure of the inner ear (NOAA, n.d.). In elasmobranchs, the vertebrae have been the most widely used and accepted method of dating the age of sharks. Just like the rings on a tree, elasmobranchs have growth rings on the vertebrae (NOAA, n.d.). However recently, bomb radiocarbon dating has become one of the most reliable techniques for age validation of long-lived species. This technique uses the radiocarbon pulse in the environment, caused by the nuclear bomb testing in the 1950’s and 1960’s, as a marker (NOAA, n.d.). This technique was the basis of the study published in 2016 by Nielsen, et al. which used the radiocarbon dating of the Greenland sharks eye lens nuclei.
U.S. Department of Defense (photographer). (1945 July 16). The expanding fireball and shockwave of the Trinity explosion, seen .053 seconds after detonation on July 16, 1945 [Digital Image]. Retrieved from https://www.theatlantic.com/
The eyes of the Greenland shark give us a glimpse into more than just their potential longevity. Their eyes are typically infested with a parasite known as Ommatokoita elongate (Skomal, 2016). This copepod bores into the sharks cornea, rendering the shark virtually blind (Skomal, 2016; Tricas, et al., 1997).
A parasite anchored in a Greenland shark’s (Somniosus mircocephalus) eye [Digital Image]. (2016). Retrieved from http://dinoanimals.com/
The Greenland shark rivals the great white shark (Carcharodon carcharias) in both size and appetite (Parker, 2008). So how does a shark hunt when it is blind by a parasite? There is little evidence as to how the Greenland shark is able to catch prey such as seals, belugas, fast moving bony fishes, other sharks and even giant squid (Skomal, 2016; Yano, Stevens, & Compagno, 2007). The Greenland shark was once thought to be primarily a scavenger; however recent studies of the stomach contents of Greenland sharks suggests that while carrion is a part of their diet, they are active predators (Yano, Stevens, & Compagno, 2007; Nielsen, Hedeholm, Simon, & Steffensen, 2014) But there are a few hypotheses behind the hunting strategy of the Greenland shark. The Greenland shark is a sluggish, slow moving shark; however there is some evidence that supports the claim these sharks are ambush predators (Skomal, 2016). Their broad caudal fin suggests they may be capable of short bursts of speed (Parker, 2008). The copepods that infest their eyes may also give the Greenland shark a hunting advantage. The parasite may help to attract prey to the shark with their wiggly, bio-luminescent bodies (Tricas, et al., 1997).
Greenland shark feeding on seal [Digital Image]. (n.d.). Retrieved from http://otlibrary.com/greenland-shark/
The Greenland shark’s jaws are also very similar to the cookiecutter shark (Isistius brasiliensis). They have suctorial lips that cover sharp grasping teeth in the upper jaw and cutting teeth in the lower jaw (Skomal, 2016). These impressive teeth allow for the shark to grip their prey, such as a seal, while also dealing the fatal blow (Skomal, 2016).
Geerg.ca (Author). (n.d.). Greenland shark jaw [Digital Image]. Retrieved from http://www.geerg.ca/
The meat of the Greenland shark is poisonous, causing drunkenness and paralysis when consumed. The toxicity is due to trimethylamine oxide (TMAO) in the tissue of Greenland shark flesh. This helps them stabilise their enzymes and structural proteins against the debilitating effects of severe cold and high water pressure. Their meat can be prepared in a fermentation process that removes the TMAO. This dish, known as Hákarl or kæstur hákarl, is prepared by hanging the meat of the Greenland shark up for four to five months and removes the adverse effects of the neurotoxins. The Greenland shark has also been harvested for their livers and their teeth (Skomal, 2016; Tricas, et al., 1997). The liver is rich in vitamin A and oils. Their teeth have been used by the Inuit people to create tools and weapons (Skomal, 2016; Parker, 2008).
Buhler, M. (Author). (2017). Inuit tools with Greenland shark teeth, National Museum of Denmark, Copenhagen [Digital Image]. Retrieved from http://bestiarium.kryptozoologie.net/
Wonder how an arctic shark is studied by scientists? Mike Rowe found out first hand on an episode of Dirty Jobs (2008). Below is a short clip from the episode that gives some insight as to how scientists determine whether the Greenland shark is an active predator or a scavenger. Click here to view the full episode.
Scavenger or Active Predator?
Steve Perrault (2008, July 30). GLIER on Dirty Jobs [Video Clip]. Retrieved from https://www.youtube.com/
Authority: Bloch & Schneider, 1801
Family: Somniosidae (Sleeper Sharks); 17 species
Length: Maximum of 24 feet (7.3 m)
Weight: 880 lbs (400 kg)
Habitat: Continental and island shelves and slopes, coastal waters, deep waters, fiords, bays and inlets
Depth: Usually 1,000-2,000 feet (305-610 m), up to 6,500 feet (1,981 m)
Litter Range: 10 pups
Home Range: Temperate to polar waters of North America and Artic
Diet: Bony fishes, invertebrates, sharks, birds, marine mammals, carrion
IUCN Status: Near Threatened; population status unknown; taken by commercial fisheries as bycatch
(Skomal, 2016; Parker, 2008; Kyne, Sherrill-Mix, & Burgess, 2006)
Thanks for checking out this week’s Feature Species! If you missed last week, be sure to check out the Cookiecutter shark. Leave me a comment, let me know what other species you’d love to know more about!
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!
Remember you can make a difference for marine ecosystems by calling your Congress man or woman and tell them that you care about the quality of our waters! Sharks, rays, and other marine organisms cannot speak or be represented in Congress. They need your voice. Get involved and stand up for sharks. Until next time finatics!
Featured Image Source
Greenland Shark [Digital Image]. (n.d.). Retrieved from http://blogspot.com/
Kyne, P.M., Sherrill-Mix, S.A. & Burgess, G.H. 2006. Somniosus microcephalus. The IUCN Red List of Threatened Species 2006: e.T60213A12321694.
National Oceanic and Atmospheric Administration. (n.d.). NEFSC Apex Predators Program. Retrieved September 28, 2017, from https://www.nefsc.noaa.gov/nefsc/Narragansett/sharks/age.html
Nielsen, J., Hedeholm, R. B., Heinemeier, J., Bushnell, P. G., Christiansen, J. S., Olsen, J., … & Steffensen, J. F. (2016). Eye lens radiocarbon reveals centuries of longevity in the Greenland shark (Somniosus microcephalus). Science, 353(6300), 702-704.
Nielsen, J., Hedeholm, R. B., Simon, M., & Steffensen, J. F. (2014). Distribution and feeding ecology of the Greenland shark (Somniosus microcephalus) in Greenland waters. Polar biology, 37(1), 37-46.
Parker, S. (2008). The encyclopedia of sharks (2nd ed.). Buffalo, NY: Firefly Books Ltd.
Skomal, G. (2016). The Shark Handbook: The Essential Guide for Understanding the Sharks of the World. (2nd ed.). Kennebunkport, ME: Cider Mill Press.
Yano, K., Stevens, J. D., & Compagno, L. J. V. (2007). Distribution, reproduction and feeding of the Greenland shark Somniosus (Somniosus) microcephalus, with notes on two other sleeper sharks, Somniosus (Somniosus) pacificus and Somniosus (Somniosus) antarcticus. Journal of Fish Biology, 70(2), 374-390.