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Thu Jan 24, 2019 8:23am

Antarctic krill population contracts southward as polar oceans warm

January 22, 2019, British Antarctic Survey

Antarctic krill population contracts southward as polar oceans warm

Credit: British Antarctic Survey
The population of Antarctic krill, the favourite food of many whales, penguins, fish and seals, shifted southward during a recent period of warming in their key habitat, new research shows.

Antarctic krill are shrimp-like crustaceans which occur in enormous numbers in the cold Southern Ocean surrounding Antarctica. They have a major role in the food web and play a significant role in the transport of atmospheric carbon to the deep ocean.

Important krill habitats are under threat from climate change, and this latest research – published today (21st January 2019) in Nature Climate Change – has found that their distribution has contracted towards the Antarctic continent. This has major implications for the ecosystems that depend on krill.

An international team of scientists, led jointly by Dr. Simeon Hill at the British Antarctic Survey and Dr. Angus Atkinson at Plymouth Marine Laboratory, analysed data on the amount of krill caught in nets during scientific surveys. The data covered the Scotia Sea and Antarctic Peninsula – the region where krill are most abundant. The team found that the centre of the krill distribution has shifted towards the Antarctic continent by about 440 km (4° latitude) over the last four decades.

The team took great care to account for background noise in the data. Many factors, in addition to long-term change, influence the amount of krill caught in any one net. Even after accounting for these factors the team found a consistent trend throughout the data, indicating a substantial change in the krill population over time.

The study provides support for a proposed mechanism behind these changes – an increasingly unfavourable climate leading to fewer young krill replenishing the population. This has led to a smaller population dominated by older and larger krill.

Antarctic krill population contracts southward as polar oceans warm
A fur seal at Bird Island in South Georgia. This is one of the main krill predators likely to be impacted by the krill population contracting south. Credit: British Antarctic Survey
"These northern waters have warmed and conditions throughout the Scotia Sea have become more hostile, with stronger winds, warmer weather and less ice. This is bad news for young krill."
Dr. Atkinson added: "This is a nice example of international cooperation in Antarctica. It is only when we put all our data together that we can look at the large scales of space and time to learn how populations of key polar species are responding to rapid climate change."

Dr. Hill continued: "The surveys which provided these data weren't intended to monitor change over large spatial scales or over 90 years. The fact that we see a signal amongst all of this noise is an indication of how much the population has changed over time. These changes appear to be driven by the global climate. Continued precautionary management of the krill fishery is important, but is no substitute for global action on climate change."

Antarctic krill mainly live in the upper water column of the Southern Ocean, but are also found in deeper water and at the seabed. They feed on small plankton organisms and are themselves staple food for fish, penguins, seals and whales. Krill are also harvested by commercial fisheries for human consumption. There are an estimated 100-500 million tonnes of krill in the Southern Ocean – similar to the weight of the world's human population.

Antarctic krill supports an important international fishery, which currently catches around a quarter of a million tonnes per year. It is managed by the Commission for the Conservation of Antarctic Marine Resources (CCAMLR) with catch limits that are well enforced and conservative, compared to the current stock sizes. However, the major fishery is in the Scotia Sea and Antarctic Peninsula region which is undergoing rapid climatic warming. This warming is projected to continue, with unknown consequences for krill. In order to understand the repercussions for the food web, for biogeochemical cycling and for fisheries management it is imperative to understand how krill are responding to the ongoing changes observed within this sector.

The team compiled two large datasets of krill population density and size structure records from scientific surveys dating back to 1926. As well as published datasets, the authors retrieved information from old notebooks, creating a valuable database featuring thousands of net hauls over nearly a century.

Explore further: Business as usual for Antarctic krill despite ocean acidification

More information: Angus Atkinson et al. Krill (Euphausia superba) distribution contracts southward during rapid regional warming, Nature Climate Change (2019). DOI: 10.1038/s41558-018-0370-z
Journal reference: Nature Climate Change

Provided by: British Antarctic Survey

Read more at:

Krill fisheries and sustainability
Related Pages
Krill – biology, ecology and fishing
Antarctic krill (Euphausia superba)
Krill are small crustaceans of the order Euphausiacea, and are found in all the world's oceans.

In the Southern Ocean, one species, the Antarctic krill, Euphausia superba, makes up an estimated biomass of around 379 000 000 tonnes1, more than that of the global population of humans. Of this, over half is eaten by whales, seals, penguins, squid and fish each year, and is replaced through reproduction and subsequent growth of the krill population. Krill can live up to 8 years in aquariums but in the wild they probably live for 3 to 4 years, spawning when they are 2 to 3 years old. Antony Miller, CCAMLR

They are important in the food chain because they feed on phytoplankton, and to a lesser extent zooplankton, making nutrients available to other animals for which krill make up the largest part of their diet. For this reason krill are considered a keystone species in the Southern Ocean ecosystem.

Krill undertake large daily vertical migrations, providing food for predators near the surface at night and in deeper waters during the day.

The size of the krill population is very variable from year to year and the changes observed appear to be driven mostly by how many young krill enter the population each year. This may be driven by variability in the amount of sea-ice, which is why there is a concern about the effects of climate change (although there is no actual evidence of any reduction in sea-ice around the whole of the Antarctic).

Commercial fishing of krill
Managing a sustainable krill fishery
CCAMLR was established in 1980 amid concerns that an expanding krill fishery could have a large impact on the ecosystem of the Southern Ocean. Since then krill harvesting has been managed in a very precautionary manner. This is in recognition of the critical role of krill in the Antarctic ecosystem, a keystone species, and uncertainties associated with environmental changes – including in respect of climate change.

Allowable catch limits
Sustainability of the krill fishery is ensured by setting limits on the fishery such that the catches taken by the fishery will leave enough krill to ensure that there is a healthy breeding population and also that there is enough for the predators (such as penguins and whales).krill oil capsules

Sustainability of the krill fishery is dependent on the size of the catch relative to the population. Basically, CCAMLR's approach to managing the krill fishery is to minimise the impact on the ecosystem rather than trying to maximise the size of the fishery.

Scientists use computer models that simulate the krill population (controlled by a set of equations for the number of births, the rate of growth and the rate of death) and then use this data to predict what might happen with different levels of fishing. Thousands of simulations are carried out in order to determine a catch level that is sustainable.

There are lots of pieces of information that go into projecting the future krill population and for many of these there are no precise values. A sensible range of values is defined and simulations are run using all values in the range. Simulations take into account what is known and what is not known about the ecosystem.

The total allowable catch for the southwest Atlantic is currently about 5.6 million tonnes annually. However, CCAMLR has decided that the catch will be regulated within a 620 000 tonne 'trigger' level which is distributed across four regions in the southwest Atlantic. This 'trigger' level represents approximately 1% of the estimated 60 million tonnes of the unexploited biomass, or virgin size, of the krill population in this region. The actual annual catch is around 0.3% of the unexploited biomass of krill. CCAMLR has agreed that any expansion in the krill fishery should not happen unless the scientific data indicate that it will continue to be sustainable.krill trawling net

CCAMLR also maintains a network of stations where information is collected on other components of the Antarctic ecosystem to monitor change. This program, the CCAMLR Ecosystem Monitoring Program (CEMP), was established in 1989. The information collected under this initiative contributes to CCAMLR’s efforts to develop what is called a 'Krill Feedback Management procedure' which will help inform decisions regarding acceptable total precautionary levels of krill harvest.

Video – Krill connections, Why is Hobart the krill capital of the world?
This presentation was held at CCAMLR Headquarters, Hobart, Australia, during National Science Week, 2017.


Dr Keith Reid (CCAMLR Secretariat)
Dr So Kawaguchi (Australian Antarctic Division)
Dr Laura Laslett (University of Tasmania/Menzies Institute for Medical Research)
A National Science Week (Australia) public seminar to help people understand the connections between commercially available krill products, human health claims and the biology and ecology of this tiny crustacean.

Find out why Hobart is the global centre of krill science and krill fishery management and how each of the relevant institutions are connected through international scientific and government networks.

Dr So Kawaguchi talked about his research on krill biology and ecology and Dr Laura Laslett discussed her research on the medicinal value of krill oil.

Dr Keith Reid, Science Manager for CCAMLR, outlined how fishing for krill is regulated by this international body and how fishing limits are informed by the best available scientific studies on krill and their ecosystems.

Watch the video on YouTube (available in English only)

Krill connections screen shot


1A. Atkinson, V. Siegel, E.A. Pakhomov, M.J. Jessopp & V. Loeb (2009). "A re-appraisal of the total biomass and annual production of Antarctic krill". Deep-Sea Research I 56: 727–740.
Wikipedia – Krill
Will there be a new ‘Gold rush’ on krill? (The Marine Stewardship Council)
Photos: CCAMLR Secretariat
Commercial fishing for the tiny crustacean has increased in recent years to supply growing demand for nutritional supplements.

Krill oil, rich in heart-healthy omega-3 fatty acids, is a popular nutritional supplement around the world. However, according to a recent report from Greenpeace, growing demand is fueling commercial fishing in Antarctica's icy waters that could make it harder for all kinds of polar marine life to survive climate change threats.

A tiny cold-water-living crustacean, krill isn't eaten by humans. It is fished in parts of Antarctica's Southern Ocean to make nutritional supplements as well as pet, livestock, poultry, and aquaculture feed. But polar marine wildlife—including penguins, seals, whales, fish, and birds—also depend on krill as a major part of their diet. The Southern Ocean teems with an estimated 379 million metric tons of krill.

Regulators of Antarctica's krill fishery have already implemented rigorous rules to ensure sustainable fishing levels according to current available science, said Phil Trathan, a scientific adviser to the Commission for the Conservation of Antarctic Marine Living Resources and a senior scientist at the British Antarctic Survey. CCAMLR, the governing body that oversees krill stocks, asserts the fishery is one of the world's best-managed and includes a strict licensing and catch-reporting system.

But while the industry and its regulators might be focused on good management, Greenpeace argued that krill fishing is placing unnecessary pressure on sensitive ecosystems in a part of the world's oceans already greatly threatened by melting sea ice and rising ocean temperatures. These activities could also impede ongoing marine protection efforts, according to Luke Massey, global communications lead of Greenpeace's Protect the Antarctic program.

"There is a clear overlap between the countries most strongly opposed to marine protection and those with an active krill fishing industry in the region," he said in an email. "As the largest fishery in the Antarctic Ocean, the krill industry represents a significant lobby capable of transforming efforts to create ocean sanctuaries in the Antarctic."

In the report, Greenpeace detailed its use of public data to track five years of krill fishing vessel activities around the Western Antarctic Peninsula, the part of the continent that extends up toward South America and is both the major area for the krill fishery and a feeding ground for penguins and whales. Krill fishing levels have increased in the area in recent years. In 2010, according to the report, fishing hit the maximal allowed level of 120,000 metric tons for the first time in the West Antarctic Peninsula region and has several times since—triggering the early closure of season's fishing. In these years, the report said, vessels from Norway, South Korea, and China have ramped up activities and new ships are also being built.

In tracking vessel movements, Greenpeace noticed "a pattern of fishing activity increasingly close to shore and in the immediate vicinity of penguin colonies, which depend on krill." Their findings—based on analyzing automatic identification signals, which show movements of krill trawlers, and cargo and tanker vessels—found vessels that appeared to be transferring catch at sea to large refrigerated cargo ships, a practice called transshipment that has raised concerns about illegal fishing elsewhere. The report identifies at least two of these cargo ships, called reefers, as having been involved in previous pollution or safety violations. Some ships were anchoring close to a specially protected area, which can damage the seabed and is discouraged by the CCAMLR's rules, according to the report. Other concerns raised by Greenpeace include the risk of oil spills, fires, or groundings in relatively pristine waters.

Greenpeace, which is among a number of conservation groups and governments pushing for expanded marine reserves in the Southern Ocean, is calling on krill-buying companies to stop purchasing catch from vessels that fish in areas that are currently under consideration for protection by the CCAMLR. The environmental group is also urging ships to voluntarily stop fishing in sensitive areas and asking fisheries managers to support conservation goals.

In 2016, the CCAMLR voted to create the world's largest marine protected area in Antarctica's Ross Sea. It is also considering other protection proposals, including creating a 700,000 square-mile protected area in the Weddell Sea, as well as in the waters around the Western Antarctic Peninsula. The latter area is the ecologically important region that krill fishing boats currently frequent. Greenpeace, according to Massey, worries that there will be pressure for fishing efforts to expand beyond current levels.

Scientists Mark Belchier and Simeon Hill with the British Antarctic S

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