Abstract
BackgroundMisidentifications between exploited species may lead to inaccuracies in population assessments, with potentially irreversible conservation ramifications if overexploitation of either species is occurring. A notable showcase is provided by the realization that the roundscale spearfish (Tetrapturus georgii), a recently validated species, has been historically misidentified as the morphologically very similar and severely overfished white marlin (Kajikia albida) (IUCN listing: Vulnerable). In effect, no information exists on the population status and evolutionary history of the enigmatic roundscale spearfish, a large, highly vagile and broadly distributed pelagic species. We provide the first population genetic evaluation of the roundscale spearfish, utilizing nuclear microsatellite and mitochondrial DNA sequence markers. Furthermore, we re-evaluated existing white marlin mitochondrial genetic data and present our findings in a comparative context to the roundscale spearfish.ResultsMicrosatellite and mitochondrial (control region) DNA markers provided mixed evidence for roundscale spearfish population differentiation between the western north and south Atlantic regions, depending on marker-statistical analysis combination used. Mitochondrial DNA analyses provided strong signals of historical population growth for both white marlin and roundscale spearfish, but higher genetic diversity and effective female population size (1.5-1.9X) for white marlin.ConclusionsThe equivocal indications of roundscale spearfish population structure, combined with a smaller effective female population size compared to the white marlin, already a species of concern, suggests that a species-specific and precautionary management strategy recognizing two management units is prudent for this newly validated billfish.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-014-0141-4) contains supplementary material, which is available to authorized users.
Highlights
Misidentifications between exploited species may lead to inaccuracies in population assessments, with potentially irreversible conservation ramifications if overexploitation of either species is occurring
Population genetic structure of roundscale spearfish: population-level analyses The genotypes of 198 roundscale spearfish were determined at 13 microsatellite loci
Roundscale spearfish population structure We provide the first examination of the genetic population structure of the roundscale spearfish, a large, pelagic predator captured in international fisheries and whose existence has only recently been recognized
Summary
Misidentifications between exploited species may lead to inaccuracies in population assessments, with potentially irreversible conservation ramifications if overexploitation of either species is occurring. Identifying genetic conservation units of large-bodied, marine pelagic fishes remains challenging as a result of their often large population sizes, typically strong dispersal ability (via adult and/or larval phases) and few apparent physical barriers to gene flow. These parameters are generally associated with shallow levels of genetic differentiation across large geographic regions [1,2,3]. ? 2014 Bernard et al.; licensee BioMed Central Ltd Istiophorid (Istiphoridae) billfish species fall in this category, and in several cases are known to have declined to levels low enough to cause international concern about their population status [7,8,9,10]
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