Near-blind shark is world’s longest-lived vertebrate

From Scientific American:

The Greenland shark (Somniosus microcephalus) has a lifespan of at least 272 years, and might live as long as 500 years. 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, says Peter Bushnell, a marine physiologist at Indiana University South Bend and a co-author of the study, published in Science. 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, says marine biologist Julius Nielsen at the University of Copenhagen, who also worked on the study.

Instead, 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, Bushnell …

Continue Reading