Age Validation Studies

Chronology of bomb radiocarbon

Validation of the periodicity of growth zone deposition patterns observed within vertebrae or other calcified structures is essential to determine the accuracy of age estimates. Although banding patterns may be evident within an ageing structure such as vertebra, the patterns may not be deposited in an annual or predictable manner. The PSRC will advance the analysis of radiocarbon isotopes (14C) as a novel method of age validation for chondrichthyan fishes. Testing of nuclear bombs in the 1950’s and 1960’s released large amounts of radiocarbon into the atmosphere. As a consequence, radiocarbon has entered the ocean through gas exchange of carbon dioxide, spread through the water column, and has been readily incorporated into animals that were growing during this time. Since the original rapid increase introduced by bomb testing, there has been a constant decrease of radiocarbon in the atmosphere and marine environment that is readily detectable in carbonate structures such as vertebrae. The level of 14C within a calcified structure can serve as a chemical tag, allowing the age of a specimen to be confirmed from a vertebral core or other structure. This method is well suited for long-lived species, such as many sharks and rays. Samples are currently being obtained from pre- and post-bomb era specimens. Primary species under investigation are the shortfin mako (Isurus oxyrinchus) and white shark (Carcharodon carcharias); the first of which is commercially important while the second, already protected, is an apex predator about which little is known. Successful completion of this research will provide definitive growth characteristics for these commercially important species and promote more effective fisheries management.