Krill: Small but Mighty
Despite their small size, krill are hugely important due to the place they occupy in the global food chain. They are a vital food source for many marine predators including whales and penguins, and they keep a top-down pressure on phytoplankton through grazing. Krill are also increasingly harvested for human consumption due to their nutritive qualities.
Figure 1. Euphausia superba (Antarctic krill). Credit: British Antarctic Survey; image taken onboard RRS James Clark Ross cruise JR230 (benthic pelagic coupling cruise).
Antarctic Krill Populations
The commercial krill fishery around South Georgia, well known for its productive waters and ability to support large krill populations, operates exclusively during the winter period. However, our knowledge of stock dynamics (affected by birth rate, growth rate, and mortality), as well as the distribution of krill during the winter, is sparse. In addition, competition between predators (e.g. penguins, seals, whales) and fisheries is a growing conservation issue which can only be addressed through effective ecosystem monitoring and management.
The Winter Krill Project
Based on these motivators, a British Antarctic Survey (BAS) research study led by Professor Martin Collins and Dr Cecilia Liszka is investigating (1) the winter distribution of krill around South Georgia and (2) assessing predator distribution, potential overlap and foraging in the fishery area.
This BAS study, The Winter Krill Project, is carrying out three winter surveys per year over two consecutive years (2022–2023). The vessel used is equipped with a scientific echosounder system (Simrad EK80) with 38 kHz and 120 kHz transducers used to gather acoustic information about krill density and distribution along a predefined series of transects (figure 2). The aim of this is to identify aggregations of Antarctic krill.
Figure 2. The transects surveyed in the first year of the project, with the aim being to repeat these same transects in 2023. Credit: Kate Owen.
Plankton nets are also used to measure the size and condition of krill. As for the predator part of the research, cetacean and penguin observations are made using expert marine mammal observers, passive acoustics, and satellite tracking telemetry.
An RBRconcerto3 C.T.D., provided by RS Aqua, is being used to calibrate the echo sounder data as well as to provide contextual oceanographic data such as salinity, conductivity, and temperature. This logger has been an ideal instrument for the project as it is easy to deploy from a small vessel (figure 3), withstands harsh conditions, and provides reliable oceanographic data. During the first of six field campaigns for the project, the BAS project team has also been able to easily offload data via WiFi, process it using Ruskin and analyse it with software including Excel and R. Powered using just eight AA batteries and with the ability to store up to 240 million readings, the RBRconcerto3 is a very power-efficient solution for a wide variety of applications.
Figure 3. The RBRconcerto3 being deployed from small vessel near South Georgia. Credit: Martin Collins.
Preliminary data from the project has evidenced that all survey aspects have proven successful and that following the completion of the project in 2023, all measurements collected should provide a great deal of scientific data for the understanding of the two overarching aims of the study.
Image Credit: BAS, Kate Owen, Martin Collins
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