Modelling Southern Ocean ecosystems: krill, the food-web, and the impacts of harvesting

Abstract

The ecosystem approach to fisheries recognises the interdependence between harvested species and other ecosystem components. It aims to account for the propagation of the effects of harvesting through the food-web. The formulation and evaluation of ecosystem-based management strategies requires reliable models of ecosystem dynamics to predict these effects. The krill-based system in the Southern Models of the Southern Ocean ecosystem. 2Ocean was the focus of some of the earliest models exploring such effects. It is also a suitable example for the development of models to support the ecosystem approach to fisheries because it has a relatively simple food-web structure and progress has been made in developing models of the key species and interactions, some of which has been motivated by the need to develop ecosystem-based management. Antarctic krill, Euphausia superba, is the main target species for the fishery and the main prey of many top predators. It is therefore critical to capture the processes affecting the dynamics and distribution of krill in ecosystem dynamics models. These processes include environmental influences on recruitment and the spatially variable influence of advection. Models must also capture the interactions between krill and its consumers, which are mediated by the spatial structure of the environment. Various models have explored predator-prey population dynamics with simplistic representations of these interactions, while others have focused on specific details of the interactions. There is now a pressing need to develop plausible and practical models of ecosystem dynamics that link processes occurring at these different scales.Many studies have highlighted uncertainties in our understanding of the system, which indicates future priorities in terms of both data collection and developing methods to evaluate the effects of these uncertainties on model predictions. We propose a modelling approach that focuses on harvested species and their monitored consumers and that evaluates model uncertainty by using alternative structures and functional forms in a Monte Carlo framework.

Omega-3 long-chain polyunsaturated fatty acids and aquaculture in perspective

“…For instance, Antarctic krill are near the base of a food chain that includes whales and penguins that would suggest there could be opposition to greatly increased exploitation (Hill et al, 2006).…”

From strategic ambiguity to technical reference points in the Antarctic krill fishery: the worst journey in the world?

“…This fishery accounted for 91% of the total Southern Ocean catch in the 2010-2011 fishing season (CCAMLR 2012). The model used to project the future state of the krill stock performs multiple simulations with random variation in the parameters controlling uncertain processes (Hill et al 2006). CCAMLR uses these simulation results to identify a regional catch limit that has the required probability of satisfying two objectives for the state of the stock (Table 1; Constable et al 2000).…”

“…For example, macaroni penguins in South Georgia seem to be sensitive indicators of krill availability (Waluda et al 2012) while mackerel icefish are both a harvested species and an important alternative prey that buffers some penguins and seals through krill shortages (Hill et al 2005). It is appropriate to present unaggregated results for the most important components (deYoung et al 2004;Hill et al 2006). Nonetheless, Hill et al (2007a) advise using no more than seven separate pieces of information in decision making.…”

“…Any interpretation of the principle must be in the context of a changing ecosystem. The Southern Ocean ecosystem is changing in response to two centuries of largely unregulated harvesting, including the removal of up to 84% of baleen whale biomass (Laws 1977;Hill et al 2006), and to the changing climate (Flores et al 2012). Translating the reversibility principle into an objective with a relative reference point is a pragmatic approach to managing a single human activity (fishing) in this context.…”

Chapter 1 Impacts of the Oceans on Climate Change

“…This population is sourced at least partially from breeding and nursery grounds near the western Peninsula, and it was argued that the loss of sea-ice and warming of the ocean may be the cause of their decline (Atkinson et al, 2004;Meredith and King, 2005). Krill are a critical component of the Southern Ocean marine food web (Hill et al, 2006;Knox, 2007) with most higher trophic levels depending on them and some such as the baleen whales feeding exclusively on these crustaceans. Krill are also now targeted by commercial fishing and so are particularly vulnerable.…”