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- A Re-Evaluation of the Size of the White Shark (Carcharodon carcharias) Population off California, USA,
- White sharks are highly migratory and segregate by sex, age and size. Unlike marine mammals, they neither surface to breathe nor frequent haul-out sites, hindering generation of abundance data required to estimate population size. A recent tag-recapture study used photographic identifications of white sharks at two aggregation sites to estimate abundance in ‘‘central California’’ at 219 mature and sub-adult individuals. They concluded this represented approximately one-half of the total abundance of mature and sub-adult sharks in the entire eastern North Pacific Ocean (ENP). This low estimate generated great concern within the conservation community, prompting petitions for governmental endangered species designations. We critically examine that study and find violations of model assumptions that, when considered in total, lead to population underestimates. We also use a Bayesian mixture model to demonstrate that the inclusion of transient sharks, characteristic of white shark aggregation sites, would substantially increase abundance estimates for the adults and subadults in the surveyed sub-population. Using a dataset obtained from the same sampling locations and widely accepted demographic methodology, our analysis indicates a minimum all-life stages population size of .2000 individuals in the California subpopulation is required to account for the number and size range of individual sharks observed at the two sampled sites. Even accounting for methodological and conceptual biases, an extrapolation of these data to estimate the white shark population size throughout the ENP is inappropriate. The true ENP white shark population size is likely severalfold greater as both our study and the original published estimate exclude non-aggregating sharks and those that independently aggregate at other important ENP sites. Accurately estimating the central California and ENP white shark population size requires methodologies that account for biases introduced by sampling a limited number of sites and that account for all life history stages across the species’ range of habitats., Downloaded from: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0098078 (8 July 2014)., , ,
- Burgess, Bruce, Cailliet, Goldman, Grubbs, Lowe, MacNeil, Mollet, Weng, O'Sullivan
- Biology of the White Shark (Carcharodon carcharias) in Aquaria
- Since 2004, the Monterey Bay Aquarium, California, has displayed six juvenile white sharks, Carcharodon carcharias (Linnaeus, 1758), in the 3,800 m3 Outer Bay exhibit. Upon capture, the sharks (132 - 164 cm total length (TL) and 19.6 - 47.0 kg body mass (BM)) were held in a 13,800 m3 ocean pen to initiate feeding prior to transport. Oxygen consumption rates of free-swimming C. carcharias during transports were analyzed, yielding one of the highest reported mass-specific muscle oxygen consumptions (MO2) for any shark species (246 ± 13 mg O2/kg/h). While on display (70 - 198 days), four of the C. carcharias fed consistently at a daily ration of 747 ± 46 g, or 1.62 ± 0.15% BM/day. One shark did not feed and was released after 11 days; another shark fed intermittently and was released after 55 days, but died immediately post-release. Mean mass growth rate for C. carcharias at the Monterey Bay Aquarium was 71.6 ± 8.2 kg/yr, with a corresponding mean dietary gross conversion efficiency of 27.1 ± 3.8%. The mean length growth rate (64.9 ± 8.5 cm/yr), was approximately twice the rate estimated from a published von Bertalanffy growth function. All C. carcharias were fitted with pop-up archival satellite tags upon release, which provided evidence of post-release survivorship.
- Ezcurra, Lowe, Mollet, Ferry, Murray, O’Sullivan