Krill: the tiny creature with a huge ocean footprint

As nations seek increased catches in the Southern Ocean, scientists are trying to track the impacts of fishing and climate change on this vital part of the Antarctic food chain
<p>Krill are tiny creatures, but crucial to the Antarctic food chain. The small crustaceans help feed the region&#8217;s penguins, seabirds, seals, fish and whales. (Image: Justin Hofman / Alamy)</p>

Krill are tiny creatures, but crucial to the Antarctic food chain. The small crustaceans help feed the region’s penguins, seabirds, seals, fish and whales. (Image: Justin Hofman / Alamy)

At the height of the Cold War, a hungry Soviet Union launched an unlikely strategy to reduce its reliance on grain imports from the West: the superpower despatched hundreds of fishing boats to Antarctica and told them to come back with krill.

Krill – small crustaceans related to the prawn and lobster – do not carry much meat on a single body. But added together, the world’s krill population weighs in at between 300 and 500 million tonnes. Beyond single-celled organisms like bacteria and viruses, the hundreds of trillions of krill in our oceans represent the greatest biomass of any wild animal on the planet.

With little competition, the Russian vessels netted as much of this bounty as they could carry and returned to the motherland, where Soviet scientists mashed up the protein-rich creatures into a nutritious paste called Okean. Citizens were expected to mix it into their vegetables and soups. British officials got hold of some in 1973 and reported its taste as “very pleasant”. But the idea never really caught on and, by the 1980s, the Soviets were turning much of the krill they caught into animal feed.

By the early 1990s, of course, the Soviet Union – and its appetite for Okean – were no more. Left undisturbed, the krill were free to swim and drift around Antarctic waters, where they help feed other kinds of life – they serve as an important prey species for the unique region’s penguins, seabirds, seals, fish and whales.

who takes the most krill?
Data was compiled from various sources. (Graphic: Manuel Bortoletti / China Dialogue Ocean)

“I am a little bit frightened about the local effects of the increasing fishing effort because the fishery is nowadays very concentrated in space and time,” says Bettina Meyer, a krill researcher at the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany. “Due to the very high level of krill biomass that we currently have, and the krill management measures in place, we are not in big danger. But we do have to keep a very, very careful eye on it.”

Antarctic krill

Several different species of krill are found across the world’s oceans, but the Antarctic variety (Euphausia superba) is by far the plumpest and so the most valuable catch. Often found in massive swarms, which can number millions of animals and stretch for several miles of ocean, Antarctic krill haven’t been routinely studied in all seasons over the years, and scientists don’t understand some key features of their life cycle. That can make it difficult to predict their numbers and distribution from year to year, as well as the impact of fishing them in the era of accelerating climate change.

Krill abundance in some regions is known to fluctuate greatly, but the reasons for this aren’t clear. Another issue not understood fully is population dynamics: how many mature krill need to spawn to provide enough offspring to keep numbers sufficiently high. Finally, little is known about where the young krill migrate to in their first year of life.

These uncertainties help to explain why researchers are cautious about judging the possible impact from the fishing industry, Meyer says.

“We have a lot of knowledge gaps,” she says. “When you compare for example the maps of distribution of the krill larvae to the distribution of the entire population, then it might be that only a small proportion is responsible for replenishing the entire population.”

In other words, although a relatively small proportion of krill are pulled from the Southern Ocean each year, if those catches happened to target breeding adults, then such fishing could have an oversized impact.

Officially that should not happen. The Antarctic krill fishery is well managed and branded as sustainable. And unlike some contested areas around the world, scientists, conservationists and the fishing industry there enjoy a largely co-operative and constructive relationship. “I think the relationship is very friendly and also very open,” Meyer says.


Along with other species, the Antarctic krill fishery is managed by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), made up from a group of 26 nations (including the European Union) with an interest in the region. The commission monitors stocks, assesses the health of the fishery and sets limits on how much krill can be taken each year.

CCAMLR splits the waters surrounding Antarctica into three large areas. The limits on fishing are based on an estimate made in 2010 that krill stocks in one of these large areas – Area 48 on the Atlantic side of the continent – totalled 60.3 million tonnes. This allowed the commission to set an absolute cap on catches – called the “precautionary catch limit” – of 5.61 million tonnes each year. The actual annual take is nowhere near that figure. Fishing is only allowed in seven “sub-areas” and divisions, each of which have their own caps – added together, the total catch from each of these sub-areas cannot exceed 620,000 tonnes – the so-called “trigger level”. However, at present, fishing is only taking place in four of the sub-areas, all in Area 48. The most popular of these, sub-area 48.1 around the Antarctic peninsula, has an annual catch limit of just 155,000 tonnes.

Source: CCAMLR (Graphic: Manuel Bortoletti / China Dialogue Ocean)

In 2020, a total of 450,781 tonnes of krill were taken across the sector, a figure that has doubled in the last five years but is still comfortably below the trigger level.

So, all is good? Not necessarily.

Fishery management strategies that permit what look like relatively low catch levels across large regions could still prove to be unsustainable, says Philip Trathan, head of conservation biology at the British Antarctic Survey in Cambridge, the United Kingdom. “It matters where you take it from,” he says. “Say for the sake of argument you are allowed to take 100 tonnes from a defined area. That limit is set with an assumption you are going to take it evenly from across that area. But you’re not going to do that. You’re going to go to the areas where it’s most predictable and most profitable. And those are probably also the regions where the penguins, seals and whales go as well.”

In other words, the fishing industry could be taking their permitted and precautionary amounts of krill out of the mouths of predators that rely on them. That’s important because rises and falls in krill population from year to year, including those influenced by fishing, are believed to have a knock-on effect on the predators that eat them – notably penguins. A 2020 study of penguin colonies in the South Shetland islands, which lie about 120 kilometres north of the Antarctic peninsula, suggested a link between levels of krill fishing in surrounding waters and declining health of the birds.

Using decades of data going back to the 1980s, the research, led by George Watters at the US National Oceanic and Atmospheric Administration in La Jolla, California, found that when local fishing catches of krill spiked, penguins took longer to find food and had fewer healthy chicks.

One problem with the current fishery management approach, Trathan says, is that it sets up an annual free-for-all that pits fishing vessel against fishing vessel to scoop up as much krill in the shortest time possible. For example, this year the cap for zone 48.1 was reached in early June, so the area is now closed until December. Such an “Olympic-style” management plan can force fishing activity into smaller areas and shorter fishing seasons.

Many scientists and conservation groups would like to see tighter controls on exactly where and when the krill can be caught. Those measures could include dividing the existing sub-areas into smaller zones, each of which would then be allocated its own (smaller) maximum take.

Some countries have gone further and backed the establishment of new marine protected areas, including one around the Antarctic peninsula, which could lead to stricter controls and even outright bans on krill fishing in the most sensitive regions.

Keen to avoid such regulation, the krill fishers have taken steps to show they can manage the threat themselves. In December last year, an industry group called the Association of Responsible Krill Harvesting Companies voluntarily suspended fishing close to three penguin colonies on the Antarctic peninsula for 12 months. This adds to a series of existing buffer zones the industry has established around penguin colonies in which local krill fishing is halted during the incubation and chick-rearing season.

CCAMLR is due to discuss possible new restrictions in November, but Trathan, who sits on the commission’s scientific advisory group, says it’s unlikely much progress will be made. “I think it’s a tall order and it sort of depends on the process as well as the science, making sure that we’ve got enough time to discuss it in the detail that is needed.”

The current focus is on keeping the existing protection in place. The management system that divides the trigger-level catch limit between the seven sub-areas and divisions is due to expire this year. If not renewed, fishers would technically be able to take up to 620,000 tonnes of krill from wherever they liked: including the sensitive waters around the peninsula.

Who fishes?

Krill fishing is currently dominated by Norway. Helped by technology that continuously pumps the contents of submerged nets onboard, Norwegian vessels bagged almost 250,000 tonnes last year, which is more than double its nearest competitor. Chile, South Korea and Ukraine also take significant amounts of krill. An important new player is China. The country landed almost 120,000 tonnes of krill last year (up from 41,000 in 2018 and 50,000 in 2019).

who are the world's top krill fishers?
Annual catches fell off in the early 1990s after the dissolution of the Soviet Union, previously the main player in Antarctic krill fishing (the decline in 1983/4 is an anomaly attributed to technical difficulties with the fleet or an increase in the number of krill predators). Japan took over as the biggest krill fisher in the 90s and early 2000s, but it quit the arena in 2013. The increase in catches since 2010 has largely been driven by Norway. Source: CCAMLR. (Graphic: Manuel Bortoletti / China Dialogue Ocean)

“[Krill fishing] fits with the Chinese policy to develop its distant water fishing fleet,” says Nengye Liu, director of the Centre for Environmental Law at Macquarie University in Sydney, Australia.

“The gap between the number of krill allowed to be caught and the number actually caught is of interest to Chinese policymakers as having potential to grow or even just maintain that fleet,” Liu adds.

Climate change

As nations target increased krill catches in coming years, scientists are anxious about another possible pressure on stocks. A cold-water species, researchers aren’t sure how the crustaceans will manage as the waters around Antarctica steadily warm.

“Change will happen, but it will happen slowly, so maybe they will be able to adapt. We don’t know,” says Katharina Michael, a krill researcher at the University of Oldenburg in Germany.

To try to find out, Michael and her colleagues caught krill off the Antarctic coast and put them in giant tanks filled with different temperature seawater for eight months. They found that krill responded differently when the water was 3.5C or higher: their metabolism significantly increased, they used more oxygen and they grew to be significantly smaller.

“There is an increased energy demand, which may have implications for long-term processes. So, energy might be taken away from growth and reproduction,” Michael says. “We don’t know that yet. We have to investigate. But there is something going on.” Water temperature in krill habitats changes a lot with the seasons and weather, but currently range from -1.8C to 5.5C.

The Alfred Wegener Institute’s Meyer says the possible effects of warmer temperatures on krill body size is something that should be closely monitored in the future, along with other important information such as the distribution and density of krill stocks.

To gather real-world data, Meyer hopes to take advantage of the currently good relations between krill researchers and krill fishers. With limited slots available aboard scientific research ships and field stations, Meyer hopes that more fishing vessels could help, either by hosting scientists or by taking samples themselves.

With more reliable measurements, the management system could be made more responsive, with catch limits tightened or relaxed from year to year to match the real-world state of the fishery. “What CCAMLR needs to find is a way to reduce the risks to predators like penguins, seals and whales, while recognising that fishing is allowed,” Trathan says. “But ultimately the more krill you take out the more likely you are to see an effect.”