By Jackie Reuder, M.S. Graduate Student, Nova Southeastern U & Shark Angels Intern
Scientific Study: Eye lens radiocarbon reveals centuries of longevity in the Greenland shark (Somniosus microcephalus) Julius Nielson et al.
Background
Greenland sharks are slow growing sharks that live in some of the coldest waters on Earth. They are found in the Arctic around the North Pole, around Greenland, northern Canada and Denmark. Because they are slow growing, determining their age is difficult. Radiocarbon dating is used to age objects ranging from animals to rocks. In the mid-1900s bomb testing left radioactive signatures in the atmosphere, waters, and soils. Animals born during this time have a signature in their tissues. Animals born before this time do not. In the middle of the eye, there is a protein that is formed before birth. This is where scientists look for the bomb signature, and to determine age.
Methods
28 females were sampled after they accidentally died because of bycatch (catching an animal you were not trying to catch). They took the center of the eye and extracted samples for analysis. To determine age, they looked at the radiocarbon levels. The higher the concentration, the closer they were born to the time of bomb testing. For those born before bomb testing, they used multiple statistical tests and other chemical tracers to determine age.
Findings & Conclusion
Of the 28 females sampled, three had the bomb signature which suggests they were born at the time of testing or after. The rest of the sharks did not have a bomb signature which suggests they were born before the testing. After analysis, the age of sexual maturity was determined to be around 156 years old. The oldest living Greenland shark of the 28 sampled was estimated at 392 years old. To date, this is the oldest known age of any vertebrate. There may be older Greenland sharks swimming around today. This technique is particularly helpful in determining ages of other hard to sample animals. For Greenland sharks, they are often tragedies of bycatch in commercial fisheries and this technique can determine more accurate age estimates of wild, living Greenland sharks.