Understanding the functional relationship between krill, the krill fishery and demersal sub-Antarctic fish populations


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.


The student will undertake a combination of laboratory-based analyses and modelling of large datasets. Data and samples will come from a series of sources: South Georgia groundfish survey database, frozen stomach samples, samples collected from the commercial fisheries (currently underway) and new material collected through the groundfish survey and with Aker BioMarine. There may be an opportunity for the student to participate in the groundfish survey and collect samples on a commercial krill vessel but as yet this cannot be confirmed. These data will be used to elucidate demersal fish trophodynamics and the importance of krill in sustaining the demersal fish fauna across life history stages. This will be done through a combination of stable isotope and stomach content analysis of key fish species and their associated prey as well as the developmenting ecosystem based models. Juvenile and larval fish by-catch in the krill fishery will also be assessed.

Project Timeline

Year 1
  • Conduct comprehensive literature review on fish trophodynamics.
  • Familiarisation, data extraction and analyses of key life history information from the South Georgia fisheries database
  • Begin stomach content analysis
Year 2
  • Potential fieldwork
  • Sample preparation for stable isotope analysis
  • Spatial and temporal analysis of juvenile and larval fish by-catch in the krill fishery
  • Present findings at UK conference.
Year 3
  • Stomach content and stable isotope data analysis
  • Prepare first and second PhD manuscripts
  • Modelling contribution of krill to sustaining demersal fish biomass
  • Present findings at international conference.
Year 3.5
  • Preparation of policy papers for CCAMLR and Aker BioMarine on krill consumption by demersal and juvenile and larval by-catch.
  • Thesis completion

& Skills

The student will receive training in fisheries related data collection, biochemical techniques, running an isotope ratio mass spectrometer and analysing data resulting in the following skills (i) database structure and interrogation; (ii) preparation of tissue samples for stable isotope analysis; (iii) species identification for stomach content analysis; (iv) statistical and ecological modelling; and (v) production of scientific and policy related papers. The student will receive in-post training in the statistical software R. They will benefit from working in tandem with research teams focusing on the marine environment, statistical modelling, and synthesising evidence for policy decisions at Newcastle University and BAS. The student will also have the opportunity to take specialist courses at Newcastle University. A key element of the training will be taking ecological data, either historical or new, right through to scientific and policy related outputs.

References & further reading

Tratham PN and Hill SL (2016) The Importance of Krill Predation in the Southern Ocean In Biology and Ecology of Antarctic Krill, Editor Siegel V, Springer, p321-350.
Morley SA et al. (2014) Geographical isolation and physiological mechanisms underpinning distributions at the range limit hotspot of South Georgia. Rev Fish Biol Fisheries 24: 485-492.
Hill SL et al (2012) A foodweb model to explore uncertainties in the South Georgia shelf pelagic ecosystem. Deep-Sea Research II 59-60: 237-252.
McCormack SA et al. (2019) Using stable isotope data to advance marine food web modelling. Rev Fish Biol Fisheries 29: 277-296.

Further Information

For further information, please contact Dr William Reid (william.reid@newcastle.ac.uk) and Dr Martin Collins (macol@bas.ac.uk). Students are encouraged to contact Dr Reid and Dr Collins to discuss the PhD prior to application.

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