A new study published in the open-access journal PLoS ONE has found that great white sharks live significantly longer than previously though.
Sharks are long-lived animals that grow slowly and do not produce many young. In many parts of the world they are fished commercially, requiring age and growth data for conservation and management efforts.
Validation of age in shark species is also critical in understanding their longevity as well as in estimating vital rates such as age at maturity, lifetime fecundity or fertility, growth rates, and differences in growth between males and females.
Sharks are typically aged by counting alternating opaque and translucent band pairs deposited in sequence in their vertebrae. It is unclear whether these band pairs are deposited annually, making it difficult to accurately estimate age or provide estimates for longevity for many shark species.
In the first successful radiocarbon age validation study for adult great white sharks (Carcharodon carcharias), scientists from NOAA’s Northeast Fisheries Science Center and the Woods Hole Oceanographic Institution analyzed vertebrae from four females and four males caught between 1967 and 2010 in the Northwest Atlantic Ocean.
Age estimates were up to 73 years old for the largest male and 40 years old for the largest female.
Previous studies of great white sharks from the Pacific and Indian Oceans suggested that none of the examined specimens were older than 23 years. Also, none of these earlier studies were able to document annual periodicity of the band pairs used to assign age.
The scientists suggest that either great white sharks are living significantly longer and growing slower in the Northwest Atlantic than either the Pacific or Indian Oceans, or longevity has been underestimated in previous studies.
“Ageing sharks has traditionally relied on counting growth band pairs, like tree rings, in vertebrae with the assumption that band pairs are deposited annually and are related to age,” said co-author Dr Lisa Natanson of NOAA’s Northeast Fisheries Science Center.
“In many cases, this is true for part or all of a species’ life, but at some point growth rates and age are not necessarily in sync. Growth rates slow as sharks’ age. Deposition rates in vertebrae can change once the sharks reach sexual maturity, resulting in band pairs that are so thin they are unreadable. Age is therefore frequently underestimated.”
“This research demonstrates the power of applying cutting-edge techniques in isotope geochemistry to answer fundamental questions in ocean ecology,” added senior author Dr Simon Thorrold from the Woods Hole Oceanographic Institution.
“The radiocarbon time stamp in white shark vertebrae provides irrefutable evidence of white shark longevity that had proved to be impossible to verify using traditional age estimation methods.”
Assuming a lifespan estimate of 70 years or more, great white sharks may be among the longest-lived cartilaginous fishes.
Hamady LL et al. 2014. Vertebral Bomb Radiocarbon Suggests Extreme Longevity in White Sharks. PLoS ONE 9 (1): e84006; doi: 10.1371/journal.pone.0084006