The Krill We Don’t See: Why a tiny crustacean you’ve probably never heard of matters beyond the Southern Ocean.

Written by Alana Wilson (with editorial direction from Leanne Hepburn).

For the second year in a row, the Antarctic krill fishery has closed months before the official end of its fishing season. On the 12th of August 2026, fishing in CCAMLR Area 48 ceased after reaching 620,000 tonnes of krill caught – the precautionary trigger set for the region. In 2025, the same threshold was reached on the 1st of August.

The official season runs from 1st December to 30th November every year.

Antarctic krill haven’t suddenly all disappeared! The 620,000 tonne limit acts as a management trigger, not an estimate of how many krill are in the Southern Ocean. But these figures do raise a bigger question…..

If the fishery can reach its precautionary limit months before the end of the season multiple years in a row, what does that tell us about how, where and when we’re fishing?

To understand why this matters, we need to look at something most of us have probably never even heard of …..krill.

Meet the krill

Antarctic krill (Euphausia superba) are really small marine creatures, generally only a few centimetres long. Individually, they’re not necessarily the most impressive thing to look at, but collectively they are one of the most important links in the Southern Ocean food web.

Penguins, seals, fish and seabirds all eat them.

Whales eat a LOT of them.

This makes krill a crucial mid-trophic species, transferring energy from the phytoplankton they feed on up through the food web. Remove enough of this link, in the wrong place and at the wrong time, and the consequences can potentially cascade through the wider food web.

Then we started fishing them…..

Commercial krill fishing is nothing new. Experimental catches began in the early 1960s and by the 1970s a multinational commercial fishery was operating in the Southern Ocean. The Soviet Union became the dominant player, catching over 500,000 tonnes a year by the 1980s.

Then the Soviet Union collapsed. Fishing effort dropped considerably, and for around 15 years Antarctic krill catches remained relatively low.

But the fishery has evolved….

Improvements in harvesting and processing technology made catching krill more practical. One example was the introduction of continuous fishing systems, allowing krill to be pumped continuously from nets onto vessels rather than repeatedly hauling catches onboard.

At the same time, the market changed. Krill was no longer simply a relatively low-value source of animal feed. Demand grew for aquaculture feed, fishmeal and nutritional products such as krill oil and omega-3 supplements.

From around 2007, catches began rising rapidly again, particularly as Norwegian fishing expanded. Area 48 went on to reach the 620,000 tonne trigger in both 2025 and 2026.

So when we say Antarctic krill fishing has increased, we’re not simply talking about fishing more. We’re seeing the combination of technology, economics and growing demand.

The 1% problem

Krill are not evenly distributed across the Southern Ocean. They form dense ‘swarms’, which are also important to predators like whales that need large quantities of food close to their feeding grounds.

This matters because 620,000 tonnes spread evenly across the Southern Ocean is unlikely to have the same ecological impact as 620,000 tonnes concentrated in a handful of productive areas.

CCAMLR’s management system recognised this. Spatial catch limits were introduced to distribute fishing pressure rather than allowing vessels to take most of their catch from high-density areas.

Here’s the catch… those spatial distribution limits expired at the end of the 2024 fishing season, and no replacement was agreed.

So while the 620,000 tonne trigger remained, the spatial distribution limits didn’t.

Around the Antarctic Peninsula, Subarea 48.1 had already repeatedly reached its local catch limit early.. on 27th June 2022, 16th June 2023 and 18th May 2024. Then in 2025 and 2026 the whole of Area 48 reached the 620,000 tonne trigger before the end of the season.

So I think the important question we should be asking, if a regional percentage is actually telling us the full story about the ecological impact of taking that 1%.

The whale-sized problem

For many whales in the Southern Ocean, krill are essential. Baleen whales are heavily reliant on krill, and several populations in the Southern Ocean are still recovering from the devastation of industrial whaling. That creates an unusual situation.

At a time when we’re seeing the recovery of animals that were historically removed from the ecosystem in huge numbers, we’re simultaneously seeing increasing demand for their vital food source.

A 2024 Nature Communications perspective explored this potential conflict, arguing that continued expansion of the krill fishery could increasingly put fishing and recovering whale populations in competition for the same resource. The question around who gets access to Antarctic krill therefore becomes increasingly important, particularly where fishing areas overlap with predator feeding grounds.

Climate changes the map

If this whole story was just about fishing it would already be complicated enough, but it’s not….

The Southern Ocean is changing; and I don’t just mean that the ice is melting…

The map is actually changing.

Warming, sea-ice change, ocean circulation and food availability can all influence where krill live, feed and reproduce. Long-term research has found evidence of a poleward contraction in krill distribution in parts of the Southwest Atlantic, alongside changes in swarm density. These shifts matter because dense swarms are exactly what both predators and fisheries are looking for.

Recent research also shows that different krill life stages may respond differently to environmental change. Temperature, for example, appears to be particularly important in predicting juvenile krill distribution, while spawning adults respond to a wider range of factors.

Of course, when prey moves, predators are likely to move too. But different species may respond to warming at different rates, potentially reshaping long-standing feeding relationships.

Sea ice still plays a huge part in this story. Krill are closely connected to sea-ice-associated food and seasonal conditions, while many Antarctic predators also depend on sea ice during parts of their life cycle.

The main point is that none of these pressures are happening independently.

Warming can change where krill are. Changing sea ice can alter their habitat and food supply. Fishing can remove krill from areas where they are concentrated.

Predators are having to respond to all of it at once.

Krill and the carbon cycle

Ok, one more reason krill matter that actually doesn’t really have anything to do with whales.

Krill are key players in moving carbon through the ocean.

They feed near the surface on phytoplankton and other small organisms, and their faecal pellets can sink into deeper water, helping transport carbon away from the atmosphere.

A 2024 study estimated that Antarctic krill could move around 20 million tonnes of carbon into the deep ocean annually through this process, where some of that carbon may remain stored for decades or longer.

Let’s not get ahead of ourselves though, krill are not a magical climate solution.

Instead, they’re another great example of how a seemingly insignificant animal can play a much larger role in processes happening on a global scale.

From Antarctica to our shopping baskets

Now we’re looking at how you might actually recognise krill. Krill caught in the Southern Ocean can end up in omega-3 supplements, aquaculture feed, fishmeal, ornamental fish feed and pet products. That connection between a tiny crustacean in the Southern Ocean and a product on a shelf here in the UK isn’t always obvious. When we buy something containing ‘marine ingredients’, we probably don’t consider the ecosystem those ingredients came from.

Quite often the ocean is hidden several steps behind the final product.

And that makes supply chains an important part of ocean literacy.

So, is krill fishing sustainable?

Unsurprisingly, not a simple question to answer.

The 2026 FAO assessment reported that 100% of assessed stocks in Antarctic Areas 48, 58 and 88 were biologically sustainable, highlighting the region as an example of ecosystem-based management and international cooperation.

The fishing industry has pointed to the report as evidence that Antarctic fisheries, including krill, are being managed sustainably. Conservation organisations are challenging that interpretation.

In September 2026 the Blue Marine Foundation published an open letter signed by more than 30 conservation organisations and independent experts, calling on the FAO to reconsider its characterisation of Antarctic fisheries.

Their argument is that the assessment doesn’t adequately reflect rapid environmental change, high krill catches or the concentration of fishing activity in important wildlife feeding grounds.

On the surface, this can look like two extremes of an argument.

But maybe they aren’t actually asking the same question.

A fish stock can be assessed as being within chosen biological reference points while there are still concerns about where fishing happens, when it happens, how catches overlap with predators and how those relationships might change under climate change.

This is the important distinction.

Because ‘sustainable’ certainly isn’t a magic word that ends the environmental debate.

It depends on the scale, the indicator, the baseline, the assumptions and the uncertainty behind it.

This is where ocean literacy becomes way more than being able to name a marine species.

It’s understanding how decisions about the ocean are actually made, and questioning what the numbers we’re presented with are really telling us. 

The krill we don’t see

The Antarctic krill fishery is much more complicated than a story of good vs bad.

CCAMLR has a precautionary management system, and reaching a precautionary trigger and closing the fishery is very different from fishing without regulation.

BUT… reaching that trigger twice in two years, alongside concerns about where fishing is concentrated, tells us that the management system is operating in a changing Southern Ocean.

And maybe the biggest lesson from Antarctic krill is that the ocean doesn’t fit into neat boxes as we humans would like it to…

A krill swarm links phytoplankton to penguins, seals and whales. It connects fisheries to food webs and products on our shelves to far-away ecosystems. It connects climate change to decisions about who gets to use the ocean and how much.

We just don’t always see the connection.

Until we look for it…

Image credit: Meganyctiphanes_norvegica2 by Øystein Paulsen - MAR-ECO used under CC BY-SA 3.0 / Desaturated from original