Greenland sharks- Age before beauty

by Matthew Norton

Getting older can be a daunting prospect for some people. It would certainly explain the popularity of  beauty products that claim to make you ‘look younger’. The same can be said for some marine animals, except they can actually slow down their biological clock and extend their lifespan, rather than just delaying the effects of the ageing process.

The Greenland shark is an excellent example because they have the longest lifespan of any vertebrate animal on earth (that we know of). We don’t know exactly how long they can live for with estimates ranging between 272 and 512 years old although the halfway figure of 400 years is often the reported figure in newspapers. But even at the ‘younger’ maximum age of 272 years, Greenland sharks still outlive any other animal with a backbone, even the impressively long lived bowed whale.

Greenland sharks typically live in the cold, deep waters of the Arctic and North Atlantic Ocean. These ice cold surroundings tend to slow everything down biologically speaking, including the ageing process. But even compared to their equally chilled out neighbours, their lifespan is way too long to be fully explained by their environment. Their mysterious biology must play a part somewhere in all this.

However they manage it, the ability of Greenland sharks to stay ‘young’ for decades is nothing short of incredible.  But there are drawbacks to taking an excruciatingly long time to reach adulthood. By only gaining about 1cm in length per year it will be a long time before they can grow big enough to know no fear from predators and make baby sharks of their own. It is estimated to take them around 130-150 years old to reach sexual maturity and such a slow reproductive cycle could put the species at a serious disadvantage if their circumstances suddenly change.

Greenland sharks are also incredibly slow and sluggish in the water, but let us not forget that they are impressively large animals who can grow to over five metres in length. This puts them well within the size range of great white sharks and are just as feared among the local wildlife. Analyses of their stomach contents have confirmed their ability to hunt, or at least scavenger, on a variety of animal prey, some of whom are fierce predators in their own right. Thankfully, there is no record of a Greenland shark ever attacking a human.

Size is also a significant advantage for Greenland sharks against other strangely long lived creatures, such as the 500 year old Icelandic Cyprine clam and the appropriately named immortal jellyfish. In comparison, a large shark has fewer enemies to fear and a greater chance of watching the centuries pass by and making lots of baby sharks along the way. However, for reasons that will soon become apparent, this ‘slow and steady’ approach may not work as well as it once did.

From a human perspective

Extending your life by a couple of centuries may be an attractive prospect, especially after seeing so many lives tragically cut short in recent months. But as I said before, there are drawbacks to living longer and ageing more slowly. And these drawbacks are multiplied once you introduce human beings into the equation. With their fantastically slow reproduction rate it is going to be difficult for them to withstand everything we can throw at them.

One would hope that their existence in cold, deep and often isolated waters would keep them out of harm’s way, but this has not been the case. For centuries, we have hunted them for their meat which today is usually marketed as an Icelandic delicacy called ‘Hákarl’. To be fair, this is just one of many examples of a fishery targeting a large, slow growing species. The scale of this particular fishing operation is also considerably smaller and far less wasteful than the worldwide slaughter of sharks for their fins.

But, Greenland sharks must be among the least capable of replenishing their numbers to keep up with demand and it probably wouldn’t take much to put them in genuine peril. Frankly, I’m surprised that they are only classified as ‘Near Threatened’ by the International Union for Conservation of Nature. Although, the most recent assessment was in 2006 and a lot can change in 14 years.

Then there a potential health risks for the human consumer. The meat from any top ocean predator, a title that any large shark would qualify for, could be contaminated with the pollutants that they were exposed to before reaching the dinner plate. Any animal can be exposed to pollution in the water, but those at the top of the food chain will accumulate more of these toxic chemicals from the animals they eat in a process called ‘bioaccumulation’. 

Consuming the meat of a Greenland shark may exacerbate this risk further simply because they can live longer than any other fish and have more opportunities to accumulate a variety of different toxins. Studies have already been conducted and have reported the presence of several pollutants in their flesh including PBDE’s, SCCPs and PCBs. The use of the latter has been banned for decades, but it still persists in the sea and its inhabitants. The younger Greenland sharks in the sea today could end up acting as unwilling time capsules in 200 years time for all the crap we are currently pumping into the ocean.

There is however, one chemical that accumulates naturally in the the bodies of Greenland sharks, but is toxic to us in high doses. Trimethylamine N-oxide (TMAO) helps Greenland sharks to cope with the high water pressure they experience in the ocean depths, but if ingested by human beings it can increase the risk of certain heart conditions.

Icelandic settlers got around this problem a long time ago by devising a simple, but effective method for processing the meat and removing as much of  this chemical as possible. However, human nature often dictates that mistakes will be made on occasions and patrons may end up consuming improperly processed Hákarl. Though sometimes people consume the raw meat of a Greenland land on purpose to get  ‘shark drunk’. The experience has been compared to drinking a ridiculous amount of alcohol, or taking hallucinogenic drugs. Not something I would recommend.   

So why do people still eat Hákarl at all? Just like whaling, the hunting of Greenland sharks is often justified on cultural grounds and the importance of this fishery to the survival of the country’s first settlers. This argument is understandable to some degree, but history is full of traditions and practices that would not be acceptable in the 21st century. Also, given the current state of the oceans, now is as good a time as any to be asking serious questions about this practice and try to at least work out a compromise between culture and conservation.

This was actually alluded to in an article about the culinary adventures of the late TV chef Anthony Bourdain in Iceland. Björn Teitsson, a cultural critic claimed that most Icelanders would only taste Hákarl during the annual Þorrablót celebrations. If true, this could be a good example of how we can strike a balance with the needs of the creatures of the sea. By scaling down the exploitation of Greenland sharks to (hopefully) sustainable levels, the species and its important role in Icelandic tradition wil survive for many years to come.

Sources

Best Life Editors. 2017. 20 Easy Ways to Look a Decade Younger. https://bestlifeonline.com/ways-to-look-younger/. Last accessed 08/05/2020

Silberman and Adamiyatt. 2019. 36 Beauty Expert-Recommended Secrets to Looking Younger. https://www.townandcountrymag.com/style/beauty-products/g19410418/how-to-look-younger/. Last accessed 08/05/2020

Wikipedia. 2020a. https://en.wikipedia.org/wiki/Greenland_shark#cite_note-IUCN-1. Last accessed 22/04/2020

Kyne, P.M., Sherrill-Mix, S.A. & Burgess, G.H. 2006. Somniosus microcephalus. The IUCN Red List of Threatened Species 2006: e.T60213A12321694. https://dx.doi.org/10.2305/IUCN.UK.2006.RLTS.T60213A12321694.en. Downloaded on 22 April 2020.

Morelle. 2016. 400-year-old Greenland shark ‘longest-living vertebrate’. https://www.bbc.co.uk/news/science-environment-37047168. Last accessed 22/04/2020

Nielson et al. 2016. Eye lens radiocarbon reveals centuries of longevity in the Greenland shark (Somniosus microcephalus)

Eagle et al. 2019. Somniosus microcephalus. https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/somniosus-microcephalus/. Last accessed 22/04/2020

Schrope. 2014. Mysterious giant sharks may be everywhere. http://www.bbc.co.uk/earth/story/20141028-the-mystery-shark-of-the-arctic. Last accessed 22/04/2020

Nielson et al. 2014. Distribution and feeding ecology of the Greenland shark (Somniosus microcephalus) in Greenland waters

Howden. 2008. Clash of the fiercest predators as shark eats polar bear. https://www.independent.co.uk/environment/nature/clash-of-the-fiercest-predators-as-shark-eats-polar-bear-891512.html. Last accessed 22/04/2020

Costantini et al. 2017. The Greenland shark: a new challenge for the oxidative stress theory of ageing?

O’Sullivan. 2017. Greenland sharks beginning to shed their secrets on longevity. https://www.irishtimes.com/news/science/greenland-sharks-beginning-to-shed-their-secrets-on-longevity-1.3144480. Last accessed 04/06/2020

BBC News. 2007. Ming the clam is oldest mollusc. http://news.bbc.co.uk/1/hi/sci/tech/7066389.stm. Last accessed 22/04/2020

Wikipedia. 2020b. https://en.wikipedia.org/wiki/Turritopsis_dohrnii. Last accessed 27/05/2020

Wikipedia. 2020c. https://en.wikipedia.org/wiki/H%C3%A1karl. Last accessed 22/04/2020

MacNeil et al. 2012. Biology of the Greenland shark Somniosus microcephalus

Serena. 2018. Hakarl — Iceland’s National Dish Is Basically Rancid And Toxic Shark. https://allthatsinteresting.com/hakarl. Last accessed 16/05/2020

Skara et al. 2015. Fermented and ripened fish products in the northern European countries

Morris. 2019. Hákarl: How Fermented Shark Became Iceland’s National Dish. https://theculturetrip.com/europe/iceland/articles/how-fermented-shark-became-the-national-dish-of-iceland/. Last accessed 16/05/2020

Icelandic Magazine. 2019. When Anthony Bourdain visited Iceland to eat the worst food he’d ever taste. https://icelandmag.is/article/when-anthony-bourdain-visited-iceland-eat-worst-food-hed-ever-taste. Last accessed 08/05/2020

The F Word. 2011. James May eats Bull’s Penis and Rotten Shark – Gordon Ramsay. https://www.youtube.com/watch?v=-xhfJRdwHnU. Last accessed 08/05/2020

Laxson et al. 2011. Decreasing urea∶ trimethylamine N-oxide ratios with depth in chondrichthyes: a physiological depth limit?

Tang et al. 2013. Intestinal microbial metabolism of phosphatidylcholine and cardiovascular risk

Qi et al. 2018. Circulating trimethylamine N‐oxide and the risk of cardiovascular diseases: a systematic review and meta‐analysis of 11 prospective cohort studies

Velasquez et al. 2016. Trimethylamine N-oxide: the good, the bad and the unknown

NOAA. 2020. What are PCBs? https://oceanservice.noaa.gov/facts/pcbs.html. Last accessed 13/05/2020

Strid et al. 2007. Dioxins and PCBs in Greenland shark (Somniosus microcephalus) from the north-east Atlantic

Strid et al. 2013. Brominated and chlorinated flame retardants in liver of Greenland shark (Somniosus microcephalus)

Anthoni et al. 1991. Poisonings from flesh of the Greenland shark Somniosus microcephalus may be due to trimethylamine

Strøksnes. 2017. My Hunt for the 400-Year-Old Shark Whose Flesh Gets You High. https://www.vice.com/en_us/article/ywz8eg/my-hunt-for-the-400-year-old-shark-whose-flesh-gets-you-high. Last accessed 29/04/2020

Fulton. 6 ÞORRABLÓT FOODS FOR THE CULINARILY BRAVE. https://www.nordicvisitor.com/blog/6-thorrablot-foods-for-the-culinarily-brave/. Last accessed 16/05/2020

Image sources

Hemming1952. 2007. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:Greenland_shark_profile.jpg

Hans-Petter Fjeld. 2006. [CC BY-SA 2.5 (https://creativecommons.org/licenses/by-sa/2.5)]. https://commons.wikimedia.org/wiki/File:Gadus_morhua_Cod-2b-Atlanterhavsparken-Norway.JPG

Ecomare/Oscar Bos. 2016. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:Ecomare_-_sterrog_(sterrog-2481-ogb).jpg

Virginia State Parks staff. 2011. [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)]. https://commons.wikimedia.org/wiki/File:Harp_seal_at_False_Cape_(cropped).jpg

Alexandre Buisse (Nattfodd). 2007. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://commons.wikimedia.org/wiki/File:20070818-0001-strolling_reindeer.jpg

Arturo de Frias Marques. 2011. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)%5D. https://commons.wikimedia.org/wiki/File:Polar_Bear_AdF.jpg

Xfigpower. 2011. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://commons.wikimedia.org/wiki/File:H%C3%A1karl_in_store.jpg

Jóhann Heiðar Árnason. 2009. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://commons.wikimedia.org/wiki/File:H%C3%A1karl.JPG

Chris 73. 2007. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://en.wikipedia.org/wiki/File:Hakarl_near_Bjarnah%C3%B6fn_in_Iceland.JPG

All other images are public domain and do not require attribution