The krill-fishing industry is "waging a tug-of-war for food" with penguins, seals and whales in the already-vulnerable Antarctic region, campaigners said.
The tiny shrimp-like creatures are one of the most important in the Antarctic food web, being eaten by species ranging from blue whales to Adelie, emperor and king penguins, elephant and fur seals and albatrosses.
But tracking of ships targeting krill, which are caught for products such as Omega-3 tablets, fishmeal for fish farms and even pet food, has revealed vessels close to wildlife feeding grounds, Greenpeace warned.
A new report from the environmental group said that, despite the fishery being presented as one of the best managed in the world, the data also suggests vessels are anchoring close to protected areas, which could damage wildlife and the fragile seafloor.
The tracking information suggests vessels were engaging in risky fishing practices such as transferring the catch from one ship to another at sea, which has been linked to poor environmental and labour protections.
And the report warned of potential environmental damage from fuel spills, fires on board and grounding of vessels in the pristine waters of the Antarctic.
Krill, like many Antarctic species, are already under threat from fast-rising temperatures due to climate change, which could destroy much of their habitat with knock-on effects for the region's wider wildlife, the report said.
Greenpeace is calling for all vessels krill fishing in the region to stay out of all Antarctic areas which are being proposed as marine sanctuaries, and for businesses which buy krill to avoid those that continue to fish in those places.
Countries that are members of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), which protects Antarctica, have put forward proposals for a number of areas to be protected.
These include the waters of the Weddell Sea, which has so far escaped the focus of the krill fisheries and if it secures protection would become the biggest marine reserve on Earth.
The West Antarctic peninsula has also been proposed as a sanctuary, which would conserve Adelie penguins and killer whales and protect essential krill nurseries, while countries have failed to reach consensus on plans to protect East Antarctica.
Frida Bengtsson, of Greenpeace's "protect the Antarctic" campaign, said vessels were fishing from the bottom of the food chain near the feeding grounds of whales, penguins and other animals.
"They're waging a tug-of-war for food with animals in the region, in an area already struggling with change.
"Climate change is impacting on krill numbers and Antarctic wildlife shouldn't have to be directly competing for food with trawlers just so these companies can sell health pills on the other side of the world.
"If the krill industry wants to show it's a responsible player, then it should be voluntarily getting out of any area which is being proposed as an ocean sanctuary, and should instead be backing the protection of these huge swathes of the Antarctic," she urged.