White shark age validation using bomb radiocarbon dating REVISED & UPDATED...

Publication years 2006/2015

Andrews and Kerr (2015)

Validated age estimates for large white sharks of the northeastern Pacific Ocean: altered perceptions of vertebral growth shed light on complicated bomb Δ14C results

Age validation studies of large shark species using bomb radiocarbon (14C) dating have revealed that the growth of vertebrae can cease in adults. In a previous study of white sharks (Carcharodon carcharias) of the northeastern Pacific Ocean the latest growth material (leading edge of the corpus calcareum) was assigned a known date-of-formation assumed to coincide with the individual’s date of capture. This perspective prevented the assignment of older years of formation (a shift in age) to this material, leading to complicated results and no validated age estimates. A reanalysis of the bomb 14C data, in light of the recent findings for other species, has led to a validated lifespan estimate exceeding 30years for white sharks of the northeastern Pacific Ocean.

Publication: Andrews and Kerr (2015)

Kerr et al. (2006)

Investigations of Δ14C, δ15N, and δ13C in vertebrae of white shark (Carcharodon carcharias) from the eastern Pacific Ocean

The white shark, Carcharodon carcharias, has a complex life history that is characterized by large scale movements and a highly variable diet. Estimates of age and growth for the white shark from the eastern North Pacific Ocean indicate they have a slow growth rate and a relatively high longevity. Age, growth, and longevity estimates useful for stock assessment and fishery models, however, require some form of validation. By counting vertebral growth band pairs, ages can be estimated, but because not all sharks deposit annual growth bands and many are not easily discernible, it is necessary to validate growth band periodicity with an independent method. Radiocarbon (14C) age validation uses the discrete radiocarbon signal produced from thermonuclear testing in the 1950s and 1960s that is retained in skeletal structures as a time-specific marker. Growth band pairs in vertebrae, estimated as annual and spanning the 1930s to 1990s, were analyzed for Δ14C and stable carbon and nitrogen isotopes (δ15N, and δ13C). The aim of this study was to evaluate the utility of Δ14C age validation for a wide-ranging species with a complex life history and to use stable isotope measurements in vertebrae as a means of resolving complexity introduced into the Δ14C chronology by ontogenetic shifts in diet and habitat. Stable isotopes provided useful trophic position information; however, validation of age estimates was confounded by what may have been some combination of the dietary source of carbon to the vertebrae, large-scale movement patterns, and steep 14C gradients with depth in the eastern North Pacific Ocean.