Cosmopolitan pelagic species often show shallow genetic divergence and weak, or no, genetic structure across a species' range. However, there have been few such genetic studies for pelagic sharks. The pelagic blue shark (Prionace glauca) has a broad circumglobal distribution in tropical and temperate oceans. To investigate the population genetic structure and demographic history of this species, we analysed variation in the mitochondrial cytochrome b sequence for a total of 404 specimens collected from 10 locations across the Indo-Pacific region. The observed genetic diversities were comparable among sampling locations (h ¼ 0.77-0.87; p ¼ 0.17-0.23%). Spatial analysis of molecular variance (SAMOVA), pairwise F ST and conventional F ST estimates, and analysis of isolation with migration indicated weak or no genetic differentiation of this species across the Indo-Pacific region. The results of three phylogeographic analyses (i.e. mismatch distribution and parsimony haplotype network analyses and a neutrality test) suggested that the Pacific blue shark had historically experienced a sudden population expansion. These results, coupled with the biological properties of this species, imply that historical climate fluctuation has had only a minor effect on the genetic structuring of the blue shark.

t r a c tThe blue shark (Prionace glauca) is globally distributed, occupying the pelagic, open ocean in temperate and tropical waters. It is the most abundant shark in the north Pacific and is exploited in several fisheries. Catch size and sex composition in fisheries and research data, along with tagging and distribution patterns, have been used to infer the existence of distinct north and south Pacific stocks. The present study consisted of a comprehensive survey of nuclear genetic diversity at microsatellite loci within and among six regions encompassing the north Pacific blue shark distribution to rationalize current management practice which assumes a single stock. We tested microsatellite diversity at 14 loci in 786 tissue samples for east-west population differentiation, examined regional samples for evidence of population mixture, and estimated historical and contemporary effective population sizes (N e ). The results strongly supported the existence of a single population of blue shark in the north Pacific. Historical and contemporary N e values between 4500 and 5500 and the resultant low ratio of effective to census size (N c ) does not reflect recent population perturbation. However, it does highlight that the population may be more vulnerable to reduced reproductive success arising from natural or fishing mortality coupled with environmental change than total abundance would imply.Crown

Two minke whale species are recognized, the Antarctic minke (Balaenoptera bonaerensis) and the cosmopolitan common minke (Balaenoptera acutorostrata) whales. The latter is divided into three subspecies: North Pacific (NP) B. a. scammoni, North Atlantic (NA) B. a. acutorostrata, and the Southern Hemisphere 'dwarf' minke whales B. a. unnamed subsp. Genetic variation of two populations of dwarf common minke whales from the Western South Atlantic (WSA) and Western South Pacific (WSP) was assessed through analysis of mitochondrial DNA (mtDNA) control region sequences (313 bp) and microsatellite DNA (msDNA) (11 loci). For comparative purposes, the mtDNA analysis involved samples of Antarctic minke whales, NP, and NA common minke whales. The msDNA analysis included individuals from the WSA, WSP, and NP. There was no shared mtDNA haplotype among common minke whales, and the mtDNA haplotype phylogeny analyses placed WSA in a different cluster from WSP and closer or within the NA clade. The WSA population exhibited the lowest estimates of diversity for both markers. The estimate of Nei's net nucleotide substitution (d A ) between WSA and WSP (0.027) was larger than between WSA and NA (0.014) whales. Significant msDNA differences (based on F ST and D SW ) were found among NP, WSA and WSP, and the pattern of differentiation was similar to that of the mtDNA. Results suggested that the taxonomical status of common minke whales in the Southern Hemisphere should be revised and that regardless of their taxonomical status, dwarf common minke whales from WSA and WSP are unique populations that require separate management for conservation.