Bomb Radiocarbon Dating - Sandtiger shark
Sand tiger shark - Maximum age and missing time
Published in Marine and Freshwater Research 2014
I GOT THE JOURNAL COVER IMAGE - I made the image above from a set of images using Photoshop (See caption at bottom)
Bomb radiocarbon dating of sand tiger shark (Carcharias taurus)
Bomb radiocarbon analysis of vertebral growth bands was used to validate lifespan for sand tiger sharks (Carcharias taurus) from the western North Atlantic (WNA) and southwestern Indian Oceans (SIO). Visual counts of vertebral growth bands were used to assign age and estimate year of formation (YOF) for sampled growth bands in eight sharks from the WNA and two sharks from the SIO. Carbon-14 results were plotted relative to YOF for comparison with regional Δ14C reference chronologies to assess the accuracy of age estimates. Results from the WNA validated vertebral age estimates up to 12 years, but indicated that ages of large adult sharks were underestimated by 11–12 years. Age was also underestimated for adult sharks from the SIO by 14–18 years. Validated lifespan for C. taurus individuals in the present study reached at least 40 years for females and 34 years for males. Findings indicated that the current age-reading methodology is not suitable for estimating the age of C. taurus beyond ~12 years. Future work should investigate whether vertebrae of C. taurus record age throughout ontogeny, or cease to be a reliable indicator at some point in time.
Publication: Maximum age and missing time
Maximum age and missing time in the vertebrae of sand tiger shark (Carcharias taurus): validated lifespan from bomb radiocarbon dating in the western North Atlantic and southwestern Indian Oceans by M. S. Passerotti, A. H. Andrews, J. K. Carlson, S. P. Wintner, K. J. Goldman and L. J. Natanson
Sand tiger sharks are a common shark that lives in habitat from the surf zone and shallow bays to the outer continental shelf. Its distribution is circum-subtropical and is an important food fish throughout its range. Sand tiger sharks can reach 2.3 meters in length and are estimated to live up to about 20 years. Reductions to stocks worldwide have led to the species being placed on the IUCN Red List of Threatened Species. In the east and southeastern United States, sand tiger sharks have been listed as a species of concern because of its vulnerability SOC_sandtigershark_detailed.pdf.
Because of concerns over the health of sand tiger shark populations, NOAA Fisheries - Species of Concern has provided grant funding to determine the longevity of this species. Based on the present maximum age near 20 years, a late age at maturity, and low fecundity, the potential lifetime productivity of individuals is much lower than would be expected. Hence, the maximum age is thought to be greater, but to date there is no proof to validate this hypothesis.
Use of bomb radiocarbon dating on the vertebrae of sand tiger shark from the southeastern United States and from South Africa has revealed the first evidence of greater longevity. Preliminary results indicate maximum age may greatly exceed 30 years. Missing time is evident in the growth bands of vertebrae, as was the case with sandbar shark, and it remains to be seen how many years may be missing. The latest round of samples were processed to answer this question and a publication is is progress.
Above is a view of the computer screen during a micromilling extraction series. Pictured is a vertebra section that has been sampled by isolating small age specific samples from the vertebra. Youngest to oldest shark age (bottom to top on right) were sampled (n = 5) for radiocarbon analysis. Each of this small blocks were separated from the vertebra and cleaned prior to analysis at Woods Hole Oceanographic Institute. Below is a spot plate with 30 clean samples. All extractions were performed with New Wave Research micromilling machine (Elemental Scientific Lasers, Bozeman, MT, USA; http://www.nwrlasers.com/milling/micromill/).
Above are some of the small extracted samples drying in a spot plate.
This project was a national and international effort with colleagues at NOAA Fisheries - Panama City Lab (Michelle Passerotti (Lead) and John Carlson) and the KwaZulu-Natal Sharks Board, South Africa (Sabine Wintner).
