Using bomb radiocarbon to estimate age and growth of the white shark from the southwestern Indian Ocean
Published online on 02. June 2016
Using bomb radiocarbon to estimate age and growth of the white shark, Carcharodon carcharias, from the southwestern Indian Ocean
Heather M. Christiansen, Steven E. Campana, Aaron T. Fisk, Geremy Cliff, Sabine P. Wintner, Sheldon F. J. Dudley, Lisa A. Kerr, Nigel E. Hussey
ABSTRACT:
Knowledge of age and growth parameters is vital to the conservation and management of white sharks (Carcharodon carcharias), but ages have not been validated for all populations and growth rates can vary regionally. Bomb radiocarbon (14C) analyses conducted on four individual white sharks [329, 414, 487, and 537 cm fork length (FL)] from the southwest Indian Ocean (SWI) were proximally aligned with Δ14C reference chronologies accepting established error, providing evidence to support annual band pair formation to 30–38 years for the SWI population. To enable comparison with previous studies on bomb radiocarbon in white sharks, a subset of specimens from the northwest Atlantic Ocean (NWA; 223.5, 441, and 493 cm FL) and northeast Pacific Ocean (NEP; 214, 365, and 429 cm FL) were also analyzed for 14C, revealing samples from the SWI were more enriched in 14C than samples from the NWA or NEP. Vertebral band pair counts were then determined for a larger set of white sharks from the SWI (140–422 cm FL, n = 51) resulting in age ranges of 1–38 years. The Gompertz growth model best described the SWI data, with an asymptotic size (L ∞ ) of 496.77 cm FL and length at birth (L 0) of 134.08 cm FL. The results of this study indicate white sharks in the SWI are longer-lived and grow more slowly compared to past estimates, but these data are more similar to recent age and growth estimates from other geographically distinct populations. This has important implications for the management of this species in the waters off southern Africa.
Marine Biology, June 2016, 163:144, doi:10.1007/s00227-016-2916-9