Great white sharks, top predators throughout the world's ocean, grow much slower and live significantly longer than previously thought, according to a new study led by the Woods Hole Oceanographic Institution.

In the first successful radiocarbon age validation study for adult white sharks, researchers analyzed vertebrae from four females and four males from the northwestern Atlantic Ocean. Age estimates were up to 73 years old for the largest male and 40 years old for the largest female.

“Our results dramatically extend the maximum age and longevity of white sharks compared to earlier studies,” said Li Ling Hamady, lead author of the study published in PLOS ONE. “Understanding longevity of the species, growth rate, age at sexual maturity, and differences in growth between males and females are especially important for sustainable management and conservation efforts.”

Age determination in fish relies primarily on analyzing growth increments in mineralized tissue, such as ear bones, vertebrae, and fin rays. These grow throughout a fish’s life, adding annual rings, similar to growth rings in trees.

Estimating age in white sharks can be challenging. While vertebrae are constructed of layers of tissue, laid down sequentially over an individual’s lifetime, the alternating light/dark banding patterns can be narrow and less distinct than in other species, and the bands don’t necessarily signify annual growth.

“Traditionally, aging sharks have relied on the assumption that band pairs are annual. In many cases this has been proven correct for part or all of a species life, however in more and more cases this is being disproven,” said coauthor Lisa Natanson, a fisheries biologist at the Northeast Fisheries Science Center lab in Narragansett, Rhode Island.

In previous studies, which assumed annual deposition of growth bands, the oldest white shark individuals identified were from the southwestern Pacific Ocean at 22 years old and the western Indian Ocean at 23 years old.

For this study, researchers took advantage of radiocarbon produced by thermonuclear device testing done during the 1950s and 1960s. Radiocarbon mixed from the atmosphere into the ocean, and was incorporated into the tissues of marine organisms living during that time period. The rise in radiocarbon gave researchers a specific spot in time pinpointed in the vertebra layers, which can be used as a time stamp to help determine the age of an animal.

Researchers conducted radiocarbon analysis on collagen in the white shark vertebrae. All of the vertebrae samples came from white sharks caught in the northwestern Atlantic Ocean from 1967 to 2010.

Researchers found that band pairs are laid down on an annual basis in small to medium-large sized white sharks in the northwestern Atlantic. However, the largest individuals may experience a change in the rate of vertebral material deposition at some point after maturity, or the bands may become so thin that they are unreadable.

Assuming a lifespan estimate of 70 years or more, white sharks may be among the longest-lived cartilaginous fish. While they are predominantly found in temperate and subtropical waters, white sharks migrate long distances and can be found throughout the global ocean. White sharks are considered vulnerable worldwide. Since individuals are slow growing and mature late, white shark populations could be even more sensitive to fishing, environmental and other pressures.

Government shortsightedness
makes life hard for retirees

Dear A.M. Costa Rica:

Your editorial entitled "Campaigns ignore issues close to hearts of expats" surfaced some of the many problems facing Costa Rica today.

As someone who came to Costa Rica in 2004 with my wife, made our home here and spent most of our income in Costa Rica for over nine years we fully agree with your editorial.

During this time we hired many Costa Ricans giving them a living wage where they would not have had work. We also endured the problem of having an attorney steal one of our properties from us and resell it without the courts doing anything about it.

We have finally given up hope that the government will change and pass laws that protect foreigners' property and allow them to subsist  without harassment in their country of choice for retirement.

The shortsightedness of the government during two regimes has not changed, and we do not believe without a wholesale movement of expats to other countries the government will recognize the amount of money expats spend in Costa Rica.

If the government is intent to subsist only on tourism that will not bring in enough to improve the lives of all Costa Ricans as do expats living full-time in Costa Rica and giving them full-time work. So we will bid goodbye to Costa Rica and hope that in our exodus and the many others doing the same today that someone will see the problems and correct them for other expats who may choose Costa Rica in the future.

Bring back the rail signal
to avoid mishaps with trains

Dear A.M. Costa Rica:

With the train accidents that occur, I have a suggestion.  The crossing on the south side of Heredia is quite dangerous, since there is a big Rotario Club sign near or on the railroad right of way. Since it is hard to see, cars often pull up and stop ON the track. One day I saw the train stop because of a car on the track.

Years ago the red signal blinked ONLY when a train was coming. So everyone stopped.  Much safer and even would save electricity.  The old was better.