Special Oceanography Seminar

May 15, 3:00pm - 4:00pm
Mānoa Campus, Pacific Ocean Science and Technology (POST) 723 Add to Calendar

Dr. Allen H. Andrews
Research Fisheries Biologist
NOAA Fisheries – PIFSC

“Maximum age and missing time in shark vertebrae: the limits and validity of age estimates using bomb radiocarbon dating”

Abstract: Bomb radiocarbon dating has become a common tool in determining valid measures of age for marine organisms and has led to some recent discoveries about the longevity of large shark species. This method relies on a conserved record of the radiocarbon (14C) signal, created by the atmospheric testing of thermonuclear devices in the 1950s and 1960s, as a time-specific signal that can be used to determine valid measures of age. The first use of bomb 14C dating to marine fishes was a direct comparison of the 14C record stored in otoliths (fish ear stones) to known-age hermatypic corals for temporal alignment. Since this inaugural application, numerous marine organisms have been age validated using this technique, but the approach is not as straightforward as it may appear to be. Successful use of this method requires a firm understanding of the requirements and necessary assumptions. In the latest research on large shark species, complications with using bomb 14C dating can lead to perplexing results and in some cases assumptions that were made may not have been valid.

For most shark species, estimates of age were made by counting growth-band pairs in vertebrae and usually in the corpus calcareum of vertebral cross-sections. These estimates of age have been either supported or refuted using measured 14C values (reported as ∆14C) that are equated to a year-of-formation, and subsequently compared to an appropriate ∆14C reference record. Two of the most important considerations are the sources of carbon available to the vertebrae and the use of a valid ∆14C reference to provide validated age estimates. Recent findings for some species indicate the vertebrae cease growth and as a consequence ages have been underestimated by decades (i.e. sand tiger shark, Carcharias taurus). However, proper alignment of the ∆14C measurements from vertebral samples to the ∆14C reference record does not always provide well-defined ages and many are still considered estimates that require some assumptions (i.e. white shark, Carcharodon carcharias). The aim of this presentation is to provide an overview of how bomb radiocarbon dating works and what the special considerations are for shark vertebrae, with some insight on how the method can fall short of expectations.


Ticket Information
Free

Event Sponsor
Oceanography, Mānoa Campus

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