How overfishing a large piscine mesopredator explains growth in Ross Sea penguin populations: A framework to better understand impacts of a controversial fishery

Abstract

We herein review the modeling approach of Pinkerton et al. (2016, Ecol. Modelling), who tested the hypothesis that fishery depletion of large, neutrally buoyant Antarctic toothfish (Dissostichus mawsoni) was implicated in the recent increase in the southern Ross Sea population of Adélie penguins (Pygoscelis adeliae). Toothfish are a trophic competitor of penguins for Antarctic silverfish (Pleuragramma antarctica) in the southern Ross Sea, hence Ainley et al. (2013) and Lyver et al. (2014) proposed that the effect of the removal of toothfish was through predation release of silverfish. Pinkerton et al. concluded that predation release could not provide sufficient energy to sustain the observed penguin population growth. Critically, however, they failed to consider certain spatial and size-by-depth aspects of diet overlap, and mechanisms associated with population dynamics that could cause the population growth through predation release. In order to effectively test the prey release hypothesis, we suggest a strong inference path that incorporates what we know about population dynamics in penguins and Ross Sea food webs into life history parameterizations of penguins, toothfish and silverfish population dynamics models.