Krill, a tiny shrimp-like creature commonly used in fish oil supplements due to its high ‘Omega 3’ oil content, has been the subject of considerable discussion in environmental circles. I’ve talked before about why there won’t be a sudden expansion of the krill fishery and today I’d like to address a different issue: is krill fishing harming penguin populations? The suggestion that krill fishing is damaging krill and penguin populations in the Antarctic should be taken very seriously and is a topic I feel it is important to address.
The key questions are:
- Are krill populations in decline?
- Are penguin population declines linked to krill availability? And finally,
- Is krill fishing to blame?
Are krill populations in decline?
Research from the mid-2000s suggested that krill populations around the Antarctic Peninsula had fallen significantly between the late 1970s and 2000.   Some suggest that these declines are linked to declines in penguin populations, and that fishing on krill is a cause of both declines. However, as usual the picture is more complex than that simple supposition.
More recent research suggests that krill populations are actually mainly influenced by decade-long ocean and atmospheric cycles, and the 1970s peak identified in the earlier research may have been simply an unusual series of bumper years for krill populations.   As a result, the krill population may now be very similar to what it was in the 1920s and 1930s. Studies in other areas of the Antarctic Peninsula have failed to detect the declines reported by Atkinson and others.  So, has the krill population been declining more recently, over the last decade? Here again there has been no reported change in abundance since the survey in the 2000 which indicated a krill population in the Atlantic of over 60 million tonnes. 
Are penguin population declines linked to krill availability?
Penguin population dynamics are complex, and while some are decreasing others are increasing.  Overwhelmingly the evidence is that these changes to krill and penguin population dynamics are being caused by oceanographic cycles and climate change, not fishing for krill. National Members of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) annually monitor penguin breeding success in the south Atlantic, and so far have not been able to detect any impact of localised krill fishing even when this is relatively concentrated close to monitored colonies. 
Is krill fishing to blame?
CCAMLR, the organisation that manages krill fishing in the Antarctic, is widely accepted to be the most precautionary of all organisations managing high seas fishing. Very precautionary measures have been put in place that aim to preserve enough krill for predators. For instance, the total catch of krill last year was less than 0.5% of the total population of about 62 million tonnes. By contrast, it is estimated that predators eat at least 20 million tonnes annually.
The total catch currently allowed from the entire south Atlantic is 1% of the population size or 0.62 million tonnes and the catch in the Antarctic peninsula is limited to 155,000 t, or 0.25% of the south Atlantic population. By any measure, these are extremely small catches of a very large krill population, so it is unsurprising that all the evidence suggests that krill fishing is having no impact on penguins.
We talk about catches being small in comparison to the krill population, yet the fishery’s critics talk about ‘hoovering up krill’. How can the two be the same? Well, there is some truth to the analogy of a vacuum cleaner, the fishing boats do pump the krill directly out of the net to stop them from getting squashed. But it is important to get a sense of the scale involved. If we imagine the whole Southern Ocean (CCAMLR) area shrunk to the size of a house, the Aker Biomarine ‘hoover’ would be tiny: just a few atoms long, a million times smaller than a full stop.
Taken together, the evidence is overwhelming: krill populations and predator populations of penguins, seals and whales are not being influenced by krill fishing. Current krill catch limits are so small in relation to the overall population as to be insignificant. However, this is no reason to be complacent. CCAMLR is well known for being extremely cautious in its approach to fishing impacts on ecosystems. The matter is kept under regular review by the Commission and scientists monitor krill, penguin, seal and whale populations to ensure a sustainable future for krill and the complex and beautiful ecosystem that depends on it.
An MSC certified fishery’s performance is reviewed regularly. Independent re-certification audits take place every five years and are reinforced by annual check-up or ‘surveillance’ audits every year. The Aker Biomarine Antarctic krill fishery was recertified in January this year.
 Atkinson et al 2004. Long-term decline in krill stock and increase in slaps within the Southern Ocean. Nature, 432, 100-103.
 Trivelpiece et al 2011. Variability in krill biomass links harvesting and climate warming to penguin population changes in Antarctica. Proceedings of the National Academy of Sciences, 108(18), 7625-7628.
 Valerie J. Loeb, Jarrod A. Santora. (2015) Climate variability and spatiotemporal dynamics of five Southern Ocean krill species. Progress in Oceanography 134, 93-122.
 Ward et al (2008). The summertime plankton community at South Georgia (Southern Ocean): comparing the historical (1926/1927) and modern (post 1995) records. Progress in Oceanography 78, 241–256.
 Steinberg et al (2015). Long-term (1993–2013) changes in macrozooplankton off the Western Antarctic Peninsula. Deep-Sea Research Part I: Oceanographic Research Papers 101, 54-70