The white shark, Carcharodon carcharias, is one of the largest marine predators in the northwest Atlantic, where some authors suggest it has declined precipitously due to overexploitation. This seems plausible, because from the 1970s onward this species was targeted by recreational anglers and featured as bycatch in expanding commercial shark fisheries. White sharks were subsequently fully protected in the northwest Atlantic by the National Marine Fisheries Service (NMFS) in 1997, although illegal harvest and trade is known to occur in this region. A resurgence of interest in the status of the northwest Atlantic white shark population has stemmed from recent high-profile sightings of this charismatic species. We are currently employing a multi-analytical approach to test the hypothesis that northwest Atlantic white sharks have experienced a recent loss of genetic diversity due to a population bottleneck. We show that contemporary northwest Atlantic white sharks are genetically distinct from other populations and comprise a demographically distinct unit (pairwise Φst ranging from 0.125 to 0.88) that has relatively low mtCR diversity (4 haplotyopes in 23 animals). We will present an ongoing analysis of nuclear microsatellite data that aims to determine if these markers register a signal of recent population decline (e.g. M-ratio testing). Lastly, we detail attempts to reconstruct the genetic diversity of white sharks in the 1960s and 1970s using DNA recovered from archived vertebrae. Historical genetic diversity will be directly compared to contemporary genetic diversity in this study, which could serve as a model for similar studies of other elasmobranchs.
Available at: http://works.bepress.com/mahmood-shivji/82/