Population genetics of Australian white sharks reveals fine-scale spatial structure, transoceanic dispersal events and low effective population sizes

Abstract

Despite international protection of white sharks Carcharodon carcharias, important conservation parameters such as abundance, population structure and genetic diversity are largely unknown. The tissue of 97 predominately juvenile white sharks sampled from spatially distant eastern and southwestern Australian coastlines was sequenced for the mitochondrial DNA (mtDNA) control region and genotyped with 6 nuclear-encoded microsatellite loci. MtDNA population structure was found between the eastern and southwestern coasts (F ST = 0.142, p < 0.0001), implying female reproductive philopatry. This concurs with recent satellite and acoustic tracking findings which suggest the sustained presence of discrete east coast nursery areas. Furthermore, population subdivision was found between the same regions with biparentally inherited microsatellite markers (F ST = 0.009, p < 0.05), suggesting that males may also exhibit some degree of reproductive philopatry; 5 sharks captured along the east coast had mtDNA haplotypes that resembled western Indian Ocean sharks more closely than Australian/New Zealand sharks, suggesting that transoceanic dispersal, or migration resulting in breeding, may occur sporadically. Our most robust estimate of contemporary genetic effective population size was low and close to thresholds at which adaptive potential may be lost. For a variety of reasons, these contemporary estimates were at least 1, possibly 2, orders of magnitude below our historical effective size estimates. Population decline could expose these genetically isolated populations to detrimental genetic effects. Regional Australian white shark conservation management units should be implemented until genetic population structure, size and diversity can be investigated in more detail.

Population genetic structure and demographic history of Pacific blue sharks (Prionace glauca) inferred from mitochondrial DNA analysis

“…white shark (Carcharodon carcharias), Blower et al 2012; sandbar shark (Carcharias plumbeus), Portnoy et al 2010). In contrast, the few genetic studies of pelagic sharks that are predominantly distributed in the open ocean all suggest weak or no genetic structure at an inter-or intraoceanic scale (shortfin mako (Isurus oxyrinchus), Heist et al 1996; basking shark (Cetorhinus maximus), Hoelzel et al 2006; whale shark (Rhincodon typus), Castro et al 2007; silky shark (Carcharhinus falciformis), Cabrera-Chávez-Costa et al 2010).…”

Genetic analysis of stock structure of blue shark (Prionace glauca) in the north Pacific ocean

“…Coastally oriented shark species may exhibit strong population subdivision associated with limited vagility and female philopatry. Such species are additionally vulnerable to overexploitation due to their coastal residence, and these factors combined often result in low CN e values and CN e : N C ratios between 0.5 and 1.0 (Portnoy et al, 2009;Blower et al, 2012). In other coastal species that exhibit high vagility and/or low male philopatry, resultant higher levels of gene flow obscure differentiation at nuclear loci and lead to greater N e (Schultz et al, 2008;Karl et al, 2011).…”

Population dynamics of the reef manta ray Manta alfredi in eastern Australia

“…A strong female-biased sex ratio in Mozambique, in addition to higher site affinity by females, suggests that this area is a refuge habitat for females and may be an important breeding and/or pupping site for M. alfredi (Marshall et al 2011a). Molecular genetic analyses on several elasmobranch species suggest greater levels of philopatry in females than males (e.g., Schrey and Heist 2003;Blower et al 2012). Male M. alfredi may also roam more than females, which return more regularly to a natal or pupping site.…”