Antarctic krill remain one of the most abundant animal species on Earth, with a total biomass estimated at roughly 130 million tonnes around the year 2000, but the population faces a tightening set of pressures from warming oceans, a growing fishery, and recovering whale populations that all want the same food. There is no single trajectory to report: some monitoring regions show stable biomass over the past decade, while habitat projections for the end of this century paint a more precarious picture, especially under high-emission climate scenarios. The story is further complicated by the fact that krill management has recently lost key safeguards, and the science needed to guide decisions is struggling to keep up.
How Much Krill Is Out There
Pinning down the total biomass of Antarctic krill is harder than it sounds. They live across roughly 19 million square kilometres of the Southern Ocean, and their distribution shifts with currents, sea ice, and seasons. The most widely cited circumpolar estimate combined decades of net-sampling data (collected from 1926 to 2004) with acoustic surveys conducted in the Scotia Sea in the year 2000. That work yielded a figure of about 133 million tonnes for the total post-larval stock, based on the finding that the Scotia Sea survey area alone held around 37 million tonnes and represented roughly 28 percent of the global population.1Deep-Sea Research Part I. A re-appraisal of the total biomass and annual production of Antarctic krill That number is now a quarter century old, and no comparable circumpolar acoustic survey has been repeated.
Regional monitoring, however, continues. Around the South Orkney Islands, one of the densest krill grounds in the Scotia Sea, surveys between 2011 and 2020 found average biomass within a 60,000-square-kilometre area ranging from about 1.4 to 7.8 million tonnes, with no statistically significant upward or downward trend over the decade.2ICES Journal of Marine Science. Distribution and biomass estimation of Antarctic krill (Euphausia superba) off the South Orkney Islands during 2011–2020 That kind of year-to-year swing is normal for krill. Recruitment depends heavily on ice conditions and food availability the previous winter, so biomass can double or halve from one season to the next without any long-term decline being underway. The absence of a trend in this particular region is reassuring but says little about the circumpolar picture, which remains genuinely uncertain.
A Single Connected Population
One of the more striking findings from recent genetics work is that Antarctic krill across the entire Southern Ocean effectively function as a single population. Studies using both whole mitochondrial genomes and nuclear genome-wide markers have found almost no genetic differentiation among krill sampled from locations thousands of kilometres apart, including the South Shetland Islands, South Georgia, the Ross Sea, and Prydz Bay.3PubMed Central. Complete mitogenomes reveal high diversity and recent population dynamics in Antarctic krill A complementary genome-level analysis similarly found very low differentiation between geographic groups, with extensive mixing and connectivity confirmed through multiple statistical approaches.4Cell. The Antartic krill genome and the evolutionary adaptation to the Southern Ocean
This matters for management because it means local depletion from fishing cannot easily be offset by the idea that a separate “reserve” population exists somewhere else. If krill are one big gene pool mixed by ocean currents, then any localized impact on abundance and any localized recovery both play out against the same interconnected stock. It also means that environmental pressures hitting one region, such as warming along the western Antarctic Peninsula, have implications for the broader population rather than just a local subset.
Climate Change Is Reshaping Krill Habitat
The Southern Ocean is warming, and for a cold-adapted species like Antarctic krill, that matters. Krill are ectotherms whose metabolic rate rises with temperature. Long-term acclimation experiments found that krill held above 3.5°C for eight months had significantly elevated oxygen consumption and were physically smaller at the end of the experiment, suggesting that sustained warming forces krill to burn more energy on basic metabolism, leaving less for growth and reproduction.5PubMed. Facing Southern Ocean warming: Temperature effects on whole animal performance of Antarctic krill (Euphausia superba) A broad review of krill species worldwide confirmed that warming affects moulting, growth, maturation, body size, lipid reserves, and mortality across multiple krill species, not just the Antarctic one.6ICES Journal of Marine Science. Ecological roles, climate-driven responses, and critical knowledge gaps of krill in the global ocean
The picture for krill larvae is mixed. Larvae depend on sea ice for shelter and on autumn phytoplankton blooms to build energy reserves before winter. Modelling work that tested climate-change scenarios found that reductions in autumn productivity drove the largest declines in larval survival, particularly in lower-latitude shelf habitats where all scenarios predicted negative outcomes.7ICES Journal of Marine Science. Untangling the complexities of larval Antarctic krill overwintering success under climate change Yet an earlier analysis suggested that as sea ice retreats under warming, the total area of suitable under-ice habitat for larvae could actually increase in some scenarios, since thinner and more dynamic ice may create more of the structurally complex habitat larvae prefer.8Geophysical Research Letters. Under ice habitats for Antarctic krill larvae: Could less mean more under climate warming? These findings are not necessarily contradictory: habitat area and habitat quality are different things, and a larva that has more ice to shelter under but less food to eat before winter may not be better off.
Projections looking out to 2100 converge on a broad theme: krill habitat is likely to shift poleward, retreating from the northern edges of the current range and potentially concentrating around higher-latitude coastal regions. Under high-emission scenarios, habitat faces severe contraction and loss, while low-emission pathways suggest partial recovery is possible by the end of the century.9PubMed. Antarctic krill habitat suitability changes: Historical trends and future projections under climate scenarios A circumpolar growth-potential model found that about 85 percent of the study area experienced only moderate change in krill growth conditions by 2100, but the regions likely to decline were concentrated near the northern limits of distribution and in the Amundsen-Bellingshausen seas in autumn, meaning krill will probably lose ground at the warm edges of their range.10Nature Climate Change. Circumpolar projections of Antarctic krill growth potential A separate modelling study identified the western Weddell Sea and parts of the Indian sector as among the few regions that would still reliably support successful krill spawning by the end of this century, warning that loss of spawning habitat could amplify adult population declines.11Geophysical Research Letters. Projected changes of Antarctic krill habitat by the end of the 21st century
The Fishery and a Management Gap
Antarctic krill are harvested primarily for krill oil (a growing health-supplement market) and aquaculture feed. The krill oil market alone is projected to reach roughly $1.4 billion by 2031, driven by demand for phospholipid-bound omega-3 fatty acids from health-conscious consumers, particularly in Asia.12Marine Policy. Research funding and economic aspects of the Antarctic krill fishery Despite increases in catch volume over the past decade, prices for krill meal and oil have continued to rise, signalling strong demand growth that is unlikely to plateau soon.
The fishery is managed by CCAMLR, the Commission for the Conservation of Antarctic Marine Living Resources, which sets catch limits for the Southern Ocean. The current interim catch limit for the southwest Atlantic krill fishery is 620,000 tonnes per year, a figure well below the estimated biomass of the stock. On paper, that sounds conservative. In practice, the problem is spatial and temporal concentration. Fishing vessels cluster in the same coastal areas where penguins, seals, and whales forage, and at the same times of year. Studies have documented significant overlap between krill fishing operations and krill-dependent predators at every spatial and temporal scale examined throughout the Antarctic Peninsula and South Orkney Islands.13PubMed Central. Identifying Risk: Concurrent Overlap of the Antarctic Krill Fishery with Krill-Dependent Predators in the Scotia Sea
CCAMLR had been working on a revised management framework to spread catches more evenly in space and time, but at its 2024 meeting, no progress was made. Part of the existing management approach, which had imposed catch distribution rules, was not renewed. As a result, the entire 620,000-tonne quota can now be taken from anywhere in the fishery area at any time, including places and seasons critical to breeding predators.14Marine Policy. The fishery for Antarctic krill – Conflicts between industrial production, protection of biodiversity, and legal governance This is a significant step backward. Previous protection measures designed to buffer penguin colonies at the Antarctic Peninsula have also been shown to simply push fishing pressure and predator-vessel encounters to the South Orkney Islands, where the affected colonies are not monitored.15Proceedings of the National Academy of Sciences. Mapping encounters between Antarctic krill fishing vessels and air-breathing krill predators using acoustic data from the fishery
Krill as a Keystone for Predators
Antarctic krill are the primary food source for a remarkable range of large animals: penguins, seals, whales, squid, and many fish species. When krill availability drops even temporarily, the effects cascade quickly. Chinstrap penguins studied on the Antarctic Peninsula had to dramatically increase their foraging effort during a year of low krill density, and their breeding success dropped as a result.16Scientific Reports. Contrasting environmental conditions precluded lower availability of Antarctic krill affecting breeding chinstrap penguins in the Antarctic Peninsula Southern right whales show a similar dependency: their reproductive success is strongly correlated with krill density on their Southern Ocean feeding grounds, with climate-driven variation in krill availability appearing to explain swings in calving rates thousands of kilometres away in their Brazilian breeding waters.17Scientific Reports. Southern Right Whale (Eubalaena australis) Reproductive Success is Influenced by Krill (Euphausia superba) Density and Climate
The recovery of baleen whales from 20th-century whaling adds a new dimension. Whale populations are growing, and their appetite for krill is increasing accordingly. A recent analysis argued that current krill biomass cannot support both an expanding krill fishery and the continued recovery of whale populations toward pre-whaling sizes, framing this as an emerging human-wildlife conflict over a shared resource.18PubMed Central. Whale recovery and the emerging human-wildlife conflict over Antarctic krill The relationship is not purely competitive, though. Research on baleen whale feeding suggests that whales recycle nutrients through their fecal plumes, which can fertilize phytoplankton growth and potentially boost the productivity of the waters krill depend on. The implication is that whale recovery could, over time, help restore ecosystem function rather than simply reducing the krill available for other claimants.19PubMed. Baleen whale prey consumption based on high-resolution foraging measurements
Krill and the Southern Ocean Carbon Pump
Beyond their role in the food web, krill are significant players in the ocean’s carbon cycle. They feed on phytoplankton at the surface and produce dense fecal pellets that sink, transporting carbon to depth. A year-long acoustic study in the East Antarctic estimated that the total carbon flux from krill fecal pellets was about 9.7 milligrams of carbon per square metre per day. However, only a quarter of krill migrated below 200 metres, and the deep transport accounted for less than 10 percent of the total pellet flux, with strong seasonal variation.20Science. Antarctic krill vertical migrations modulate seasonal carbon export That study cautioned that models assuming krill consistently migrate to depth and defecate there will overestimate carbon export if they miss the seasonal pattern.
Krill swarms also exhibit a behaviour called satiation sinking: after feeding at the surface, well-fed krill sink passively, depositing fecal pellets at the bottom of the swarm where other krill are less likely to re-ingest and break them apart. This increases the efficiency of carbon transport to depth.21PubMed Central. Oceanic swarms of Antarctic krill perform satiation sinking A declining krill population would not just hurt predators; it would weaken one of the Southern Ocean’s biological mechanisms for sequestering carbon, with potential feedbacks on the climate system itself.
Ocean Acidification and Krill Reproduction
Rising carbon dioxide concentrations in the atmosphere are also making the Southern Ocean more acidic, and Antarctic krill embryos appear vulnerable to extreme conditions. Laboratory experiments found no significant effects on embryonic development or larval behaviour at carbon dioxide levels of 1,000 micro-atmospheres, roughly double pre-industrial concentrations. But at 2,000 micro-atmospheres, development was disrupted before a critical early stage in 90 percent of embryos, and no larvae hatched successfully.22PubMed Central. Will krill fare well under Southern Ocean acidification? Current projections suggest the Southern Ocean is unlikely to reach 2,000 micro-atmospheres globally this century, but localized upwelling zones and deep winter mixing could push some areas well above average levels. Whether those hotspots overlap with major krill spawning grounds is an open question that needs more research.
Microplastics and Nanoplastics
Plastic pollution has reached the Southern Ocean, and krill do ingest it. But laboratory evidence so far suggests the acute threat is limited. In ten-day toxicity tests, krill fed diets containing up to 80 percent microplastic showed no mortality and no dose-dependent weight loss. Krill that ingested microplastics eliminated most of their burden within five days, with no bioaccumulation over a 25-day observation period.23PubMed. Uptake and Depuration Kinetics Influence Microplastic Bioaccumulation and Toxicity in Antarctic Krill (Euphausia superba) Krill appear quite efficient at passing plastic fragments through their gut.
Nanoplastics, the much smaller fragments, may be a different story. Exposure to nanoplastic particles increased moulting rates in juvenile krill and reduced the sinking speed of their fecal pellets by roughly two-thirds compared to fresh controls.24PubMed. Nanoplastics affect moulting and faecal pellet sinking in Antarctic krill (Euphausia superba) juveniles Slower-sinking pellets are more likely to be consumed or broken apart by microbes before reaching the deep ocean, which could reduce the carbon-export function described earlier. No krill died in those experiments either, but sublethal chronic effects on moulting, feeding, and carbon cycling are where the real concern lies for nanoplastics.
Salps as Competitors
As the Southern Ocean warms, gelatinous organisms called salps are expanding into waters historically dominated by krill. Salps eat the same small phytoplankton krill rely on, and an individual-based modelling study found that the competitive impact is strikingly one-sided. When salps were introduced into the model, krill abundance crashed by essentially 100 percent and egg production dropped to zero, while salp density was unaffected by the presence of krill.25Ecological Processes. The impact of salps (Salpa thompsoni) on the Antarctic krill population (Euphausia superba): an individual-based modelling study Those are model results under specific conditions and should not be read as a forecast for the whole Southern Ocean, but they illustrate how asymmetric the competition can be. Salps reproduce explosively when conditions suit them, and unlike krill, they provide little nutritional value for the penguins, seals, and whales that depend on the Antarctic food web.
North Atlantic Krill Tell a Cautionary Tale
While much of the focus is on Antarctic krill, other krill species offer a glimpse of what sustained warming can do. In the North Atlantic, surface krill abundance has declined by about 50 percent over the past 60 years. The decline happened in place rather than through a range shift: warmer isotherms pushed southward from the north while cooler isotherms remained pinned by subpolar ocean fronts, squeezing the band of suitable habitat from roughly eight degrees of latitude to four.26Communications Biology. North Atlantic warming over six decades drives decreases in krill abundance with no associated range shift The krill could not track the shifting temperatures because their path was blocked. This “habitat squeeze” mechanism is a useful warning for Antarctic krill: even if warming proceeds gradually, physical oceanographic boundaries like fronts and continental shelves can prevent populations from simply relocating.
Body Size Trends From the Fishery
One practical indicator of population health is whether the average size of krill is changing. In the Bransfield Strait and around the South Shetland Islands, researchers analysing catches from recent years found that mean krill length declined around 2017 but recovered steadily afterward, reaching its highest recorded values in 2022. That year also showed the highest proportion of older krill (age four and above) in the dataset. The authors concluded that the sustained increase in fishing effort in recent years had not reduced the size of individual krill in this region.27PubMed Central. Population Dynamics and Body Size Structure of the Antarctic Krill Euphausia superba in the Bransfield Strait and South Shetland Islands That finding is geographically limited, and body size trends can lag behind population-level changes, but it is one of the few direct indicators we have that fishing pressure is not yet visibly degrading the stock in this particular area.