Elasmobranch Longevity

The longevity of sharks and rays remains an enigma for the vast majority of species. In 1998, Susan Smith, David Au and Christina Show published a paper in the journal Marine and Freshwater Research looking at the intrinsic rebound potential (i.e. how rapidly they recover from intense fishing pressure) of 26 species of pelagic sharks. Their results showed that many of these sharks didn’t reach maturity until they were more than ten years old, leading to a considerable length of time being required to rebuild over-exploited populations. Indeed, it is now well known that elasmobranchs grow and mature slowly; probably growing continually throughout their lives. It has been estimated that many elasmobranch species may replace as little as two-percent of their population annually.

The task of ageing elasmobranchs is also more difficult than it is for bony fishes because they don’t have otoliths (ear stones) and their continual replacement of teeth means that dental wear and tear can’t be used as an indication of age as it can in mammals. As such, most elasmobranch ageing studies rely on staining of vertebrae, in which distinctive bands are laid down as the shark grows. Dark bands are deposited in winter and light during the summer and the vertebrae can be stained (typically with silver nitrate) and the bands counted in a similar fashion to gauging the age of a tree.

Tagging studies are a big help in contributing to our data pool on shark longevity, especially when tagged sharks are injected with tetracycline upon landing; tetracycline is a broad-spectrum antibiotic that fluoresces under ultraviolet light. Consequently, if that shark is re-captured two years later, a sample of vertebrae will show how many bands have been deposited in that time and thus allow us to gauge an estimate of the shark’s age. Of course, there are some inherent pitfalls with this method, primarily the fact that band deposition is almost certainly related to the growth rate, which itself is related to environmental conditions. Thus, it is possible that a shark will lay down more bands during plentiful years than in years when pickings are slimmer. Another way of estimating age is using mathematical equations (e.g. von Bertalanffy growth curves), but the mathematical details of these are well out of the scope of this website!

Pitfalls aside, we do have age information for some of the more frequently encountered species. The great white shark, for example, is estimated to live to 60 years old, and calculated to reach maturity at 15 years old. Of the UK shark species, probably the longest-lived is the spiny dogfish (Squalus acanthias), the oldest recorded individual being 75 years old. Tope sharks (Galeorhinus spp.) can apparently live for as many as 55 years, whilst the oldest smoothhounds (Mustelus spp.) live for about 25 years. The pelagic blue shark (Prionace glauca) has been known to live as long as 20 years, and probably longer. A paper in Fishery Bulletin by Lisa Natanson and two colleagues, gave the maximum age for porbeagle sharks (Lamna nasus) based on vertebral band readings as 24 to 25 years old. Interestingly, the scientists found that, on the basis of longevity calculations, porbeagles in an un-fished population may live as long as 46 years.

A Greenland shark (Somniosus microcephalus) photographed during a dive in the Northeast U.S. Canyons and at Mytilus Seamount in the Pacific Ocean in 2013. - Credit: NOAA Okeanos Explorer Program

The record for longest-lived shark species is currently held by the Greenland shark (Somniosus microcephalus). In a paper to the journal Science in 2016, a team of biologists led by Julius Nielsen, at the University of Copenhagen, presented the results of their radiocarbon dating of the eye lenses of 28 female Greenland sharks caught as bycatch off Greenland between 2010 and 2013. They found that the two smallest animals (less than 1.5m/5ft long) had the highest radiocarbon levels in their eye lenses, suggesting they were born at some point after the early 1960s, after the nuclear bomb tests of the 1950s. Estimates for the two largest animals, both females around 5m (16.5 ft.) long, turned out to be much older; one was at least 260 and the other at least 272 years old. 

Age data for batoids are more difficult to come by. However, estimates for the common stingray (Dasyatis pastinaca) have been as high as 100 years, although Ali Ismen, of the Canakkale Onsekiz Mart University in Turkey, estimated a maximum age of ten years—using longevity calculations—in his recent paper in the journal Fisheries Research. Tagging studies involving the common skate off Scotland are suggesting a maximum age of as much as 40 years, an age close to the 50 years proposed by Marie-Henriette Du Buit in her 1972 paper.