Global climate change and increased pressure on marine ecosystems to provide protein for an ever-expanding global population puts pressure on the health of marine ecosystems. The balance between harvesting commercial species whilst leaving appropriate levels of prey for maintaining higher predator populations (e.g. fish, sea birds and marine mammals) requires a holistic approach to ecosystem management. The success lies in the use of ecosystem-based models which supply robust scientific advice to managers, stakeholders and policy makers. In the Southern Ocean, the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) adopts an ecosystem-based approach to sustainable harvest of marine living resources which takes into account the impact of potential fisheries on other components of the ecosystem. Key to this approach is understanding the complex ecological and environmental interactions which dictate community composition and ecosystem function. However, there is still a great deal of uncertainty in the ecological interactions between commercially targeted and non-targeted species. This is evident in relation to estimating appropriate biomass and consumption rates by higher predators for the ecologically important Antarctic krill and balancing these with biomass extracted through commercial fisheries so not to have a detrimental effect on the ecosystem.
Antarctic krill is a key-stone species within the Southern Ocean and performs an important role in biogeochemical cycles. It is harvested for human consumption as well as being used for agricultural and aquaculture animal feeds. Krill are found in the greatest abundance in the Atlantic sector of the Southern Ocean, from the Antarctic Peninsula, across the Scotia Sea and to north of South Georgia. At South Georgia, they sustain populations of higher predators where their recruitment success is dependent on the influx of krill from more southernly latitudes. This makes the management of krill complex because the fisheries management must take into consideration protecting the source of krill to South Georgia and the biomass harvested around the island. Furthermore, the southwest Atlantic is warming rapidly which has been implicated in the decline of krill. This is expected to result in a decrease in krill populations at South Georgia with potential knock on effects to higher predator populations.
The CCAMLR risk assessments, which are used to manage the krill fishery, require information regarding krill consumption by predators and the by-catch of larval and juvenile fish. This helps inform spatial management requirements. Most of the recent and current work to develop and refine them have been based on consumption estimates for higher vertebrate predators and have largely ignored demersal fish, which are thought to be significant consumers of krill. The combined pressures of commercial fishing and potential warming may have significant impacts on the structure and functioning of the South Georgia food web. Identifying a sustainable krill catch-limit and minimising the potential ecological impacts on the demersal fish community around South Georgia and the Shag Rocks requires a greater understanding of krill consumption across life history stages, larval and juvenile fish by-catch, a temporal and spatial understanding of resource partitioning amongst the fish fauna and a clearer understanding of the importance of krill in sustaining fish biomass. This information is currently unclear and will be investigated within the project. The proposed work will be an important contribution to the CCAMLR risk assessment process for the krill fishery. The work will be carried out around the island of South Georgia in collaboration with scientists at British Antarctic Survey, partner Aker BioMarine and with assistance from the UK overseas territory, the Government of South Georgia and the South Sandwich Islands (GSGSSI). Fisheries revenue accounts for over 70% of GSGSSI income of which the krill fishery provides an important contribution. These funds help GSGSSI with the environmental management of the islands within their EEZ and meeting important international obligations for the conservation of higher predators (e.g. birds and whales). A key goal of GSGSSI is the long-term marine sustainability within their EEZ. The fisheries around South Georgia and the South Sandwich Islands are managed under CCAMLR. The research will feed into GSGSSI’s management of the fisheries and into wider international policy implemented through CCAMLR.