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Conservation and management efforts for white sharks Carcharodon carcharias remain hampered by a lack of basic demographic information including age and growth rates. Sharks are typically aged by counting growth bands sequentially deposited in their vertebrae, but the assumption of annual deposition of these band pairs requires testing. Age estimates were up to 40 years old for the largest female fork length [FL]: cm and 73 years old for the largest male FL: cm. Our results dramatically extend the maximum age and longevity of white sharks compared to earlier studies, hint at possible sexual dimorphism in growth rates, and raise concerns that white shark populations are considerably more sensitive to human-induced mortality than previously thought. This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

But there are many misconceptions about how radiocarbon works and how reliable a technique it is. Radiocarbon dating was invented in the s by the American chemist Willard F. Libby and a few of his students at the University of Chicago: inhe won a Nobel Prize in Chemistry for the invention. It was the first absolute scientific method ever invented: that is to say, the technique was the first to allow a researcher to determine how long ago an organic object died, whether it is in context or not.

Shy of a date stamp on an object, it is still the best and most accurate of dating techniques devised. All living things exchange the gas Carbon 14 C14 with the atmosphere around them - animals and plants exchange Carbon 14 with the atmosphere, fish and corals exchange carbon with dissolved C14 in the water.

Throughout the life of an animal or plant, the amount of C14 is perfectly balanced with that of its surroundings.

When an organism dies, that equilibrium is broken. The C14 in a dead organism slowly decays at a known rate: its "half life". The half-life of an isotope like C14 is the time it takes for half of it to decay away: in C14, every 5, years, half of it is gone. So, if you measure the amount of C14 in a dead organism, you can figure out how long ago it stopped exchanging carbon with its atmosphere.

Given relatively pristine circumstances, a radiocarbon lab can measure the amount of radiocarbon accurately in a dead organism for as long as 50, years ago; after that, there's not enough C14 left to measure. There is a problem, however.

Carbon in the atmosphere fluctuates with the strength of earth's magnetic field and solar activity.

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You have to know what the atmospheric carbon level the radiocarbon 'reservoir' was like at the time of an organism's death, in order to be able to calculate how much time has passed since the organism died. What you need is a ruler, a reliable map to the reservoir: in other words, an organic set of objects that you can securely pin a date on, measure its C14 content and thus establish the baseline reservoir in a given year.

Jan 06, Radiocarbon dating is one of the best known archaeological dating techniques available to scientists, and the many people in the general public have at least heard of it. But there are many misconceptions about how radiocarbon works and how reliable a technique it is. Jun 15, The cervical vertebra (museum number ) was AMS dated by The National Laboratory of Age Determination at the Norwegian University of Science and Technology in Trondheim in and the thoracic vertebra (museum number ) at Oxford Radiocarbon Accelerator Unit (ORAU) in Cited by: 1.

Fortunately, we do have an organic object that tracks carbon in the atmosphere on a yearly basis: tree rings. Trees maintain carbon 14 equilibrium in their growth rings - and trees produce a ring for every year they are alive.

Radiometric dating / Carbon dating

Although we don't have any 50,year-old trees, we do have overlapping tree ring sets back to 12, years. So, in other words, we have a pretty solid way to calibrate raw radiocarbon dates for the most recent 12, years of our planet's past.

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But before that, only fragmentary data is available, making it very difficult to definitively date anything older than 13, years. Dietary and DIC pools have distinctive isotope values in ocean environments [27][28]which can cause problems when conducting bulk isotope analyses of vertebral material. Varying degrees of mineralization along a vertebra may lead to unequal carbon contributions from organic and inorganic pools to different material sampled longitudinally from a vertebra.

Collagen extraction from vertebral samples was conducted following Tuross et al.

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Each sample consisted initially of approximately 0. The filtrate from this process was frozen and lypholized. White sharks are highly migratory [30][31] with variable feeding habits [32][33]. A coral carbonate chronology from Florida [34] showed a more immediate uptake of bomb radiocarbon compared to the NWA otolith curve [35]. The reference record from validated porbeagle shark data provided a reference for a potential phase lag between ocean radiocarbon curves and vertebral profiles [11].

Radiocarbon values from white shark samples were plotted against the reference chronologies under the assumption of annual band pair deposition.

This calculation was repeated after moving the vertebral years step-wise one year closer each time to the reference years.

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We identified the optimal shift for each white shark chronology by minimizing the summed squared differences for all the points Table S2. See supporting information for data and calculations.

Band pair counts in vertebral thin sections provided age estimates of years for female white sharks and years for male white sharks Figure 1Table 1. Post-peak radiocarbon values ranged from below the NWA otolith curve to nearly the same amplitude as the coral reference curve from Florida. A Upper section of vertebra taken from WS B WS vertebra; first dot is the birth band.

Visible band pairs are marked by dots on the corpus calcareum. The lines indicate the vertebral radius Vertebral radius is measured at the angle of the vertebra where the intermedialia meets the corpus calcareum.

Results from male A, B and female C, D white shark vertebrae. Dotted line is porbeagle data smoothed with a Loess curve. We found good agreement between the reference curves and band pair counts in three sharks WS57, WS, WS28 with nominal ages of 44, 9, and 6 years, respectively.

The two youngest white sharks WS and WS28 aligned closely with the coral curve. Figure 2B, D.

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We kept the terminal data point of WS at the year of collection because it reflected the most recently deposited material in the vertebra. Moving the vertebral values back to the reference curves led to an increase of estimated age to 40 and 73 years for the female and male, respectively Figure 2B, D.

These data stand in contrast to earlier studies in the Pacific and Indian Oceans which suggested that the individual white sharks examined were no older than 23 years [18][20][22][23] with concomitantly faster growth rates. Therefore, either white sharks are living significantly longer and growing slower in the NWA than either the Pacific or Indian Oceans or longevity has been underestimated in previous studies.

Results from this earlier study were generally inconclusive for several reasons. Kerr et al. However, the concept of missing growth in the outer margin was not considered because the idea had not yet been described [13]. Our results were substantively different from those derived from the Pacific samples. The NWA white sharks in our study with nominal ages up to 44 years aligned well with reference chronologies, confirming that these sharks deposited one band pair per year up to this age.

This observation is consistent with results from the eastern Pacific that found juvenile white sharks tend to stay in shallow water close to the coast [31].

Similar results have also been recently reported for great hammerhead [15]young tiger [14]and young sandbar [16] sharks in the NWA, indicating that these sharks are also using shallow, well-mixed habitats in coastal or oceanic waters. We found a significant phase lag in larger white sharks that, based on the alignment of young sharks with reference chronologies, was evidence for significant underestimation of age based on band pair counts in these individuals.

This result is not necessarily surprising as band pair counts appear to also underestimate age in older individuals in other shark species [13][16][17][37]. Given that band pairs are apparently laid down on an annual basis in small to medium sized NWA white sharks, we suggest that the largest individuals may experience a change in the rate of deposition of vertebral material at some point after maturity, or that the band pairs becomes so thin as to be unreadable.

This second hypothesis was supported by the shaved terminal sample that we were able to extract from WS that was clearly post-bomb and close to the NWA reference value for the year of capture. Andrews et al. We would also note that it is difficult to constrain the deposition date of material at the terminal edge of large white shark vertebrae even with the fine-scale sampling that we used here.

Based on the available data, we cannot determine if the results of our study are applicable to white sharks in other locations as age and growth can vary between different shark populations [11][13]but further studies are clearly warranted. While fish otoliths obtain most of their carbon through uptake from DIC [10][38] diet is likely the primary source of carbon in vertebral collagen of elasmobranchs [11][37].

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This difference in carbon source may lead to problems when comparing radiocarbon curves between inorganic carbonate structures and organic cartilaginous tissues. Equilibration of carbon isotopes incorporated through trophic transfer is likely to be slower than uptake from DIC and this would, in turn, act to reduce the rate of increase and perhaps the amplitude of the radiocarbon rise depending on the variability of tissue turnover rates in food sources.

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This effect is likely to increase with the trophic level or age of the prey [11]at least to the degree that either variable correlates with carbon turnover rates in muscle tissue of individual prey species. The synchronization between the coral reference chronology and WS28 and WS demonstrates that white sharks must quickly reach carbon isotopic equilibrium with their diet, or feed on prey that is isotopically equilibrated with ambient DIC.

Vertebral samples from other shark species that lag carbonate reference chronologies [11] presumably reach isotopic equilibrium with their environment considerably more slowly than white sharks.

Nonetheless, this observation further supports our contention that age under-estimation is the most likely cause of the phase lag between the reference chronologies and the vertebral profiles. Atlantic white sharks are poorly studied in terms of diet and movement when compared to their Pacific, Australian, and South African counterparts. We found that male sharks aligned more closely with the NWA otolith reference record than the Florida coral record, suggesting that these individuals spent a significant amount of time in northern shelf waters.

Sex-specific differences in habitat use have been documented for Pacific white sharks [39]as has individual diversity in feeding strategy. Using stable C and N isotopes in vertebrae, Kim et al.

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White sharks in our study also displayed marked sexual dimorphism in size at age, assuming our age interpretations are correct. The largest male and female WS and WS81 in this study were similar in size FLs: cm and cm respectivelyyet their ages, as estimated by radiocarbon analyses, differed by up to thirty-three years. WS81, the largest female, is almost a meter longer and yet still four years younger than the second largest male in our study WS The smallest sharks in our study males: WS, WS; female: WS28 are also very similar in size, yet the two males are 3 and 8 years older than the female, respectively.

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Sexual dimorphism in growth rates is common in lamnids [13]although it is usually thought that larger females are also older. While our sample is limited, the NWA white sharks in this study appear to show the opposite trend. Since the lifetimes and sampling dates of these sharks span several decades, changes in habitat quality may also have influenced this trend. Assuming a lifespan estimate of 70 years or more, white sharks may be among the longest-lived chondrichthyan fishes [42].

Population projections for white sharks based on earlier age and growth data will, therefore, need to be revisited in the NWA. Modeling of elasmobranch populations has found that age at maturity accounts for most of the variance in population growth rates; sharks that mature late, have long lifespans, and small litters have the lowest population growth rates and longest generation times [43][44].

While increased overall longevity implies that each individual has greater potential lifetime productivity, modeling studies suggest that the ability of a shark species to recover from fishing pressure is little affected by overall longevity [43]and changes in juvenile survival actually have the greatest effect on population growth rates [44].

We predict that age at maturity for NWA white sharks will be substantially higher than estimates from other areas, using our age data. Earlier work concluded that white sharks have low rebound potential when exposed to fishing pressure [43] and high intrinsic vulnerability to extinction [45].

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Thus an increase in age at maturity would make white sharks even more sensitive to fishing pressure than previously thought. While already protected in many nations, even low levels of bycatch mortality are likely to have significant impacts [46] on attempts to rebuild white shark populations from historical over-fishing in the NWA [47] but see [48] and potentially other populations in the Pacific and Indian Oceans.

Radiocarbon dating vertebrae

A Florida coral reference chronology, used to correct WS Calculating the summed squared differences for optimal chronology shifting.

The top line for each chronology is its original placement based on band pair counts. We thank M. Lardie Gaylord, A. Thanks to the fishermen that allowed us to sample their catches and tournament officials that gave us the opportunity to sample at their events.

We are grateful for discussions with A.

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Andrews and G. Cailliet; A.

Are radiocarbon dating vertebrae accept

Andrews additionally provided valuable assistance with data interpretation and manuscript edits. We appreciate the helpful comments and suggestions provided by the editor and two anonymous reviewers.

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Abstract Conservation and management efforts for white sharks Carcharodon carcharias remain hampered by a lack of basic demographic information including age and growth rates. Fulton, The Australian National University, Australia Received: August 15, ; Accepted: November 11, ; Published: January 8, This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose.

Results Band pair counts in vertebral thin sections provided age estimates of years for female white sharks and years for male white sharks Figure 1Table 1.

Jan 08, Radiocarbon values in vertebral samples from before the bomb ? 14 C rise were generally consistent with regional ? 14 C reference chronologies (mean = ? (SD)) (Figure 2A, B, D). Post-peak radiocarbon values ranged from below the NWA otolith curve to nearly the same amplitude as the coral reference curve from by: 50 years based on vertebral ageing and bomb radiocarbon assays. The Hoenig estimated rate of instantaneous natural mortality was year -1, while the estimate from Then et al. ( Radiocarbon dating (also referred to as carbon dating or carbon dating) is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon. The method was developed in the late s at the University of Chicago by Willard Libby, who received the Nobel Prize in Chemistry for his work in

Download: PPT. Figure 2. Table 1. Collection and sampling information for individual sharks. Figure 4. Supporting Information.

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