Are Antarctic minke whales unusually abundant because of 20th century whaling?

Department of Biology, Hopkins Marine Station, Stanford University, Pacific Grove, CA 93950, USA.
Molecular Ecology (Impact Factor: 6.49). 12/2009; 19(2):281-91. DOI: 10.1111/j.1365-294X.2009.04447.x
Source: PubMed

ABSTRACT Severe declines in megafauna worldwide illuminate the role of top predators in ecosystem structure. In the Antarctic, the Krill Surplus Hypothesis posits that the killing of more than 2 million large whales led to competitive release for smaller krill-eating species like the Antarctic minke whale. If true, the current size of the Antarctic minke whale population may be unusually high as an indirect result of whaling. Here, we estimate the long-term population size of the Antarctic minke whale prior to whaling by sequencing 11 nuclear genetic markers from 52 modern samples purchased in Japanese meat markets. We use coalescent simulations to explore the potential influence of population substructure and find that even though our samples are drawn from a limited geographic area, our estimate reflects ocean-wide genetic diversity. Using Bayesian estimates of the mutation rate and coalescent-based analyses of genetic diversity across loci, we calculate the long-term population size of the Antarctic minke whale to be 670,000 individuals (95% confidence interval: 374,000-1,150,000). Our estimate of long-term abundance is similar to, or greater than, contemporary abundance estimates, suggesting that managing Antarctic ecosystems under the assumption that Antarctic minke whales are unusually abundant is not warranted.

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    • "Instead, a population mean age is typically used (e.g. Roman & Palumbi 2003; Alter et al. 2007; Ruegg et al. 2010 "
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    ABSTRACT: Recent historic abundance is an elusive parameter of great importance for conserving endangered species and understanding the pre-anthropogenic state of the biosphere. The number of studies that have used population genetic theory to estimate recent historic abundance from contemporary levels of genetic diversity has grown rapidly over the last two decades. Such assessments often yield unexpectedly large estimates of historic abundance. We review the underlying theory and common practices of estimating recent historic abundance from contemporary genetic diversity, and critically evaluate the potential issues at various estimation steps. A general issue of mismatched spatio-temporal scales between the estimation itself and the objective of the estimation emerged from our assessment; genetic diversity-based estimates of recent historic abundance represent long-term averages, whereas the objective typically is an estimate of recent abundance for a specific population. Currently, the most promising approach to estimate the difference between recent historic and contemporary abundance requires that genetic data be collected from samples of similar spatial and temporal duration. Novel genome-enabled inference methods may be able to utilize additional information of dense genome-wide distributions of markers, such as of identity-by-descent tracts, to infer recent historic abundance from contemporary samples only.
    Molecular Ecology 11/2012; 22(1). DOI:10.1111/mec.12094 · 6.49 Impact Factor
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    • "It had been suggested that these populations had competed with penguins for the same food sources, mainly krill, and that the decreases in the populations of marine mammals allowed some species of seabirds, including penguins, to increase in abundance (Trivelpiece and Volkman 1979). This so-called krill surplus hypothesis has been challenged and does not appear to be valid for minke whales (Ruegg et al. 2010). However, it is still invoked to explain the population dynamics of other krill predators. "
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    ABSTRACT: Seabirds and their response to climate pertur-bations are important bioindicators of changes in Antarctic ecosystems. During 30 years of observations of two chin-strap penguin (Pygoscelis antarcticus) colonies, one on King George Island and the other on Penguin Island (South Shetland Islands, Antarctica), the size of the breeding populations decreased by 84 and 41 %, respectively. We applied analyses of amplified fragment length polymor-phisms to study the genetic structure of the two populations and to evaluate the influence of the sudden population decrease. Our data indicate that there were only weak genetic differences between the populations, which were not strong enough to support the hypothesis of population differentiation. Weak genetic differences observed between the two populations seem not to be determined by selection processes. We hypothesize that the very low level of between-population genetic structure can be explained by some extent of genetic drift, which is largely compensated by gene flow. Moreover, the two populations seem to remain in a stationary state. Our results support the hypothesis of limited natal philopatry in chinstrap pen-guins. The observed decrease in population size is probably caused by emigration or a rise in juvenile mortality due to the increasing krill limitation of the marine food web. However, detailed research is required to address this issue.
    Polar Biology 06/2012; 35:1681-1689. DOI:10.1007/s00300-012-1210-7 · 1.59 Impact Factor
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    • "Here, it seems our minimum census of 52 haplotypes from 183 individual Antarctic blue whales is low compared to the 68 haplotypes reported in 98 bowhead whales (Balaena mysticetus) or the 83 reported in 119 Antarctic minke whales (Balaenoptera bonaerensis) (Table 7). As the Antarctic minke whale represents the only abundant species that was little depleted by whaling, it represents perhaps the best proxy of ‘pre-exploitation’ genetic diversity [54]. Unfortunately, comparisons of haplotype richness are highly dependent on standardization of both the length of the sequence and sample size. "
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    ABSTRACT: The Antarctic blue whale (Balaenoptera musculus intermedia) was hunted to near extinction between 1904 and 1972, declining from an estimated initial abundance of more than 250,000 to fewer than 400. Here, we describe mtDNA control region diversity and geographic differentiation in the surviving population of the Antarctic blue whale, using 218 biopsy samples collected under the auspices of the International Whaling Commission (IWC) during research cruises from 1990-2009. Microsatellite genotypes and mtDNA sequences identified 166 individuals among the 218 samples and documented movement of a small number of individuals, including a female that traveled at least 6,650 km or 131° longitude over four years. mtDNA sequences from the 166 individuals were aligned with published sequences from 17 additional individuals, resolving 52 unique haplotypes from a consensus length of 410 bp. From this minimum census, a rarefaction analysis predicted that only 72 haplotypes (95% CL, 64, 86) have survived in the contemporary population of Antarctic blue whales. However, haplotype diversity was relatively high (0.968±0.004), perhaps as a result of the longevity of blue whales and the relatively recent timing of the bottleneck. Despite the potential for circumpolar dispersal, we found significant differentiation in mtDNA diversity (F(ST) = 0.032, p<0.005) and microsatellite alleles (F(ST) = 0.005, p<0.05) among the six Antarctic Areas historically used by the IWC for management of blue whales.
    PLoS ONE 03/2012; 7(3):e32579. DOI:10.1371/journal.pone.0032579 · 3.23 Impact Factor
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