Sonar reveals how krill fishing is hurting Antarctic wildlife

Antarctic krill – the shrimp-like crustaceans that feed whales, seals, and penguins – sit at the heart of the Southern Ocean food web. Yet these tiny animals are also the target of a fast-growing commercial fishery.

A new study led by the Alfred Wegener Institute (AWI) and the Norwegian Institute of Marine Research used more than 30,000 hours of sonar recordings from krill-trawling vessels.

The analysis pinpointed when and where fishing fleets overlap with natural krill predators. The results highlight seasonal hotspots of competition that managers can no longer afford to ignore.

Using sonar for krill clues

Fishing vessels routinely run powerful echo sounders to locate krill swarms. By repurposing those same acoustic logs, scientists gained an unprecedented view of the submarine “traffic” beneath the ships.

The team analyzed over 30,000 hours of sonar data from three krill fishing vessels, gathered over six years in the Southern Ocean. Machine learning algorithms filtered the files for the distinctive signatures produced when whales, penguins, or seals dive under a vessel.

“During such encounters, ships and krill predators pursue the same krill swarms,” said lead author Dominik Bahlburg, a scientist at AWI.

“This allowed us to analyze the spatial and temporal dynamics of this competition in order to identify locations and time periods where the interaction between the two groups is particularly intensive.”

Where penguins, seals, and trawlers converge

Patterns emerged once the detections were mapped. Penguins and fur seals appeared alongside fishing gear in both summer and winter, especially around the South Orkney Islands and South Georgia.

Whales appeared most near the Antarctic Peninsula in autumn, when they fatten for their long migration north.

“The South Orkney Islands seem to be a real hotspot for encounters with penguins,” Bahlburg said. “Compared to the Antarctic Peninsula, they have received far less attention in the debate on the impact of krill fishing and many of the colonies affected there are currently not regularly monitored.”

Direct competition with penguins

The overlap is worrisome as trawlers fish near breeding colonies when adult birds must feed their chicks. Voluntary buffer zones aimed to ease this conflict, but sonar evidence reveals an unintended side effect.

This also suggests that fishing vessels continue to encounter penguins despite the voluntary restriction zones around the Antarctic Peninsula.

The vessels also continue to compete directly with penguins for krill during the breeding season. Instead, the pressure appears to have shifted to the South Orkney Islands.

Fishing overlaps persist in winter

One assumption had been that moving effort into winter – when breeding pressures ease – would spare wildlife. The new data challenge that view.

“We were able to show that fisheries and penguins as well as fur seals encounter each other just as frequently in the winter as in the summer season,” Bahlburg said.

Since animals roam farther from colonies in winter, the persistence of close encounters surprised the authors and may require a reassessment.

While penguins and seals were encountered less often near the Peninsula, autumn fishing there overlapped heavily with whales. These whales depend on krill to build blubber reserves before migrating to equatorial calving grounds.

Krill fleet data goes public

The team found little year-to-year fluctuation in their maps. “Remarkably, these patterns were quite stable for seals, penguins and whales over a six-year period,” noted study co-author Sebastian Menze, a scientist at the Norwegian Institute.

Such consistency implies the method can deliver rapid, reliable diagnostics as fishing tactics or quotas change.

“Consequently, our results show that acoustic data from fishing vessels and machine learning can act as a reliable foundation for rapid and convenient assessments of fisheries’ interaction with the ecosystem,” Menze added.

Collecting those data costs almost nothing extra; crews already archive echo-sounder files as part of normal operations. The largest krill harvester, Aker Biomarine, even makes its records public through the HUBOcean platform.

Positive changes in krill management

Until now, scientists mainly used fishery sonar to estimate krill biomass. The study’s broader ecological application opens fresh possibilities.

Bettina Meyer of AWI represents Germany on the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR).

“We are expanding the potential uses for ecological questions and demonstrating new, cost-effective ways in which fishing vessels can contribute to krill fishery management,” said Meyer, who’s also a senior author of the study.

“Acoustic data make it possible to quickly draw an initial picture of how changes in fishery management or fleet behavior impact on the Antarctic ecosystem.”

Supported by Germany’s Federal Ministry of Food and Agriculture, the project feeds directly into CCAMLR deliberations on updated catch limits and dynamic closure zones.

By revealing when and where krill fishing most conflicts with wildlife, the acoustic approach offers a blueprint for fine-tuned regulations. This could help ensure that the Southern Ocean’s keystone crustacean can sustain both its natural predators and the fishery that now depends on it.

The study is published in the journal Proceedings of the National Academy of Sciences.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–