There are many species for which maximum or even average life span is a question mark. This is a combination of too many species and too few researchers, especially when it comes to marine life, and the fact that for some negligibly senescent species there is no good way to measure age. Their vital statistics and biochemistry change so slowly over time that any estimate may be half a life span removed from the reality. This was the case for lobsters until quite recently, for example. In the research noted here, scientists attempt an new method of age estimation for Greenland sharks, another case in which determining the age of individuals - and thus the species life span - is both quite difficult and little worked on:
A large, almost-blind shark that lives in the freezing waters of the North Atlantic and Arctic oceans is officially the world's longest-living vertebrate. The Greenland shark (Somniosus microcephalus) has a lifespan of at least 272 years, and might live as long as 500 years1. That is older than the 211-year lifespan of the bowhead whale (Balaena mysticetus), the previous record-holder in the scientific literature. It also beats the popular - but unconfirmed - tale of a famous female Koi carp called Hanako, who supposedly lived to 226 years old. Marine scientists already knew that the Greenland shark was long-lived. The fish are enormous but grow slowly, suggesting a long lifespan. Adult Greenland sharks have been measured at more than 6 metres long - and researchers think that they could grow even longer. One 1963 study estimated that the species grows at less than 1 centimetre per year. Getting a definitive measure of the shark's age, however, has proved tricky. Conventionally, researchers count layers of calcified tissue that grow on a fish's fin scales or other bony structures - rather like counting tree rings. But Greenland sharks have small, spineless fins, and their vertebrae are too soft for countable layers to be deposited.
To assess age, the team decided to measure levels of radioactive carbon-14 in fibres in the centre of the shark's eye lens. Such measurements reflect levels of radiocarbon in the ocean when the lens was first formed. Measurements of 28 female Greenland sharks, made during surveys in 2010-13, suggested that the largest of them (at 5.02 metres long) must have been between 272 and 512 years old at the time. The shark's longevity probably arises because it expends very little energy, owing to its cold body temperature and enormous size. Not all cold, large species live to such an exceptional age, so it would be intriguing to know whether the shark has any particular quirks or molecular tricks that contribute to its long lifespan. The study also shows that Greenland shark females don't reach sexual maturity until around 150 years old - suggesting that a century of heavy fishing could wipe out the entire species.