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

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.

Dividing up the pie: Whales, fish, and humans as competitors

“…Laws (1977) proposed that minke whales in the Antarctic may have increased as a result of the decimation of the larger species. However, more recent genetic analysis indicating large pre-and postexploitation minke whale populations in Antarctic waters does not support the idea that minke whales have been limited by competition with larger baleen whales for krill (Ballance et al, 2006;Ruegg et al, 2010). (Nor does it support the hypothesis that large minke numbers may be inhibiting recovery of large baleen whales today.…”

Genetic structure of declining chinstrap penguin (Pygoscelis antarcticus) populations from South Shetland Islands (Antarctica)

“…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.…”

Population Structure and Dynamics

“…Other scientists feel that this system is driven from bottom up control, with environmental conditions dictating the abundance of krill in the system. Debate continues on both sides of the discussion in marshalling evidence to support either "top down" or "bottom up" explanations (see Ruegg et al 2010, Huang et al 2014.…”