Article by Jeffrey Gallant
This issue’s selection focuses on three records from Greenland, and on one of its most famous residents, the Greenland shark. With a surface area of 2,175,600 sq km (840,000 sq miles), Greenland is world’s largest island. The majority of the residents of this autonomous constituent country within the Kingdom of Denmark, are Inuit, whose ancestors migrated from what is now the Canadian territory of Nunavut during the 13th century. Approximately 80% of
Greenland is covered by the only permanent ice sheet outside Antarctica. Most of the ice sheet is more than 2 km (1.2 mi) thick, and over 3 km (1.9 mi) at its thickest point. If it melted away completely, the world’s sea level would rise by more than 7 m (23 ft).
If you think the Arctic Ocean is too cold for sharks, think again. The Greenland shark, Somniosus microcephalus, is the largest member of the Somniosidae (Sleeper) family. It is the second largest carnivorous shark after the great white and it is the largest Arctic fish. It is also the longest-living vertebrate animal with a life expectancy of at least 272 years.
Until recently, aging a Greenland shark was impossible since it does not have vertebral growth bands— counted like rings on a tree—as do many other shark species. Therefore, determining its age would require the capture and measurement of a newborn pup followed by periodical recapture and measuring until the end of its natural life. Doing so under controlled conditions—no Greenland shark has ever been kept in captivity for more than a month— would not reflect the natural growth rate of a shark living in an oceanic environment, and a study in the wild over a long period, say 200 years, would require several generations of researchers as well as an extreme range and ongoing tracking system, the likes of which does not yet exist.
The Greenland shark’s suspected yet hypothetical longevity was long debated by a rare encounter with a Greenland shark in the St. Lawrence Estuary, apparently confirmed in a study released in August 2016 by a science team led by Julius Nielsen at the University of Copenhagen.
According to the article published in the journal Science, Nielsen and his colleagues used radiocarbon dating to establish the age of 28 Greenland sharks. The age ranges of sharks born before atomic bomb testing in the 1950s—which nearly doubled the amount of carbon-14 in the atmosphere—revealed a life- expectancy of at least 272 years, that sexual maturity may not be reached before 156 ± 22 years, and that the largest shark (5.2 m / 17 ft) was 392 ± 120 years old. Considering that the largest known length for the Greenland shark is over seven metres (23 ft), there may be living specimens that were swimming in the St. Lawrence when Jacques Cartier laid claim to New France in 1534.
Although scientific debate on this discovery may linger for years—radiocarbon dating of deep- dwelling marine organisms is not very precise—, it is safe to say that even with the most conservative margin of error, the Greenland shark is currently and by far the longest- living vertebrate on the planet.
If sharks aren’t your thing, you need not worry about encountering this old-timer during a dive. The Greenland shark is very rarely observed by divers because of its bathybenthic environment that is inaccessible to humans unless they are traveling aboard a deep submersible.
Read the full stories and discover hundreds more diving records, outstanding diving personalities, and 6,000 years of diving history in the Diving Almanac! www.divingalmanac.com
About Jeffrey Gallant
Jeffrey Gallant is the Editor of the Diving Almanac and a shark researcher. He started diving at age 14 in 1982 and has since led scientific and training expeditions around the world. Among other accomplishments, Gallant was trained as an aquanaut in Romania in 1995 and he dove with Équipe Cousteau in 1999.
Want more? www.divingalmanac.com