Investigating the influence of ‘minor’ krill-predators on the krill-predator dynamics of the Antarctic ecosystem.
Presentation to the PISCES/ICES Small Pelagic Fish: New Frontiers in Science for Sustainable Management Symposium, Lisbon, Portugal, 9 November 2022: 24pp, titled: Investigating the influence of ‘minor’ krill-predators on the krill-predator dynamics of the Antarctic ecosystem.
Krill (Euphausia superba) is a small pelagic crustacean and constitutes the largest forage fish resource in the Antarctic ecosystem. Over recent decades, a krill fishery has slowly expanded in this region. As a result, there is an increasing interest in how to harvest krill optimally without unduly impacting its natural predators. Many whale, seal, penguin and fish populations feed primarily on krill and share similar feeding grounds south of 60°S around Antarctica. In 2006, the Mori-Butterworth ecosystem model attempted to explain the population dynamics of the major krill-eating species in the Antarctic through predator-prey interactions only. Roughly ten years later, this krill-predator model was refined in Moosa (2017). Moosa found the important krill-predators south of 60°S to be the Antarctic blue whale (Balaenoptera musculus), fin whale (Balaenoptera physalus), humpback whale (Megaptera novaeangliae), Antarctic minke whale (Balaenoptera acutorostrata), Antarctic fur seal (Arctocephalus gazella), crabeater seal (Lobodon carcinophagus), leopard seal (Hydrurga leptonyx), Adélie penguin (Pygoscelis adeliae), marbled rockcod (Notothenia rossii) and mackerel icefish (Champsocephalus gunnari). However, as with the Mori-Butterworth (2006) model, Moosa also considered only the main krill-predators in her analysis. These main predators were determined to be the blue, fin, humpback and minke whale species, and the crabeater and Antarctic fur seal species, based on each of their annual circumpolar krill consumption by weight being estimated to exceed one million tonnes. The aim of this paper is to expand the ecosystem model developed by Moosa so as to include the ‘minor’ krill-predators, i.e. the leopard seal, Adélie penguin and the two fish species; the marbled rockcod and mackerel icefish. The region of focus, in contrast to the Antarctic-wide level considered in Moosa (2017), is a smaller area, the IWC (International Whaling Commission) Management Area II (60°W - 0°), which includes the Antarctic Peninsula and the area around South Georgia. This is also the only region for which abundance information is available for all the krill-predators considered. Furthermore, whereas these ‘minor’ krill-predators have a negligible influence on the ecosystem dynamics at an Antarctic-wide level, for this single management area this may not be the case as abundances of many of these ‘minor’ predators is rather greater relative to the major predators. Outputs from the analysis in this paper are compared to those from Moosa (2017). The overall aim is to identify any appreciable differences in results when these ‘minor’ krill-predators are incorporated.