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Antarctic krill is a key species in the Antarctic marine ecosystem as an important food source for many species, such as whales, seals and penguins. However, the small crustaceans are increasingly targeted as part of a growing fishing industry, which has significant consequences for the entire Southern Ocean ecosystem. Therefore, ways to minimize the negative effects of fishing on the krill themselves and on the animals that feed on them are urgently needed.

A research team from the Alfred Wegener Institute and the Norwegian Institute of Marine Research in Bergen has now been able to use acoustic recordings, which fishing vessels routinely record, to identify areas and periods in which there is an increased overlap between fishing and krill predators. The results can contribute to developing effective management strategies to protect the Antarctic ecosystem. The study is in the Proceedings of the National Academy of Sciences.

"In conducting our study, together with our colleagues from Norway, we analyzed more than 30,000 hours of echo sounder recordings collected by three krill fishing vessels in the Southern Ocean over a period of six years," says Dominik Bahlburg from the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI).

Using a segmentation model and artificial intelligence, the researchers were able to filter out signals that whales, penguins and seals emit when they dive under fishing vessels. "During such encounters, ships and krill predators pursue the same krill swarms. This allowed us to systematically 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," Bahlburg says.

This technology revealed distinct seasonal patterns that were specific to the various krill predators. For example, the fishery encountered penguins and fur seals in summer and winter, particularly in the South Orkney Islands and South Georgia, while only rarely encountering whales. "The South Orkney Islands seem to be a real hotspot for encounters with penguins," says Bahlburg. "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."

This, however, would be ecologically significant, as fishing vessels encounter penguins here in summer during their main breeding season, in the immediate vicinity of their breeding colonies. This furthermore suggests that restriction zones on the Antarctic Peninsula, that have been established voluntarily by the fishery, do not really minimize the encounters of penguins and vessels and thus the direct competition for krill during the breeding season, but rather shifted them to the South Orkney Islands.

Another aspect took the authors by surprise: "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." As the animals are not tied to their colonies at this time and are often widely dispersed, the fact that krill fishing has increasingly focused on the wintertime was previously seen as a positive development. "However, the fact that the animals are now also encountering ships so frequently at this time may require a reassessment of this development."

Compared to the South Orkney Islands, seals and penguins were rarely encountered in the echo sounder data from the Antarctic Peninsula. Especially in the autumn, fishing here competes intensively with whales for krill. It is at this time that whales build up their fat reserves for their subsequent migrations to their breeding grounds towards the equator.

Reliable data for better protection of the Antarctic Ocean ecosystem

"Remarkably, these patterns were quite stable for seals, penguins and whales over a six-year period," says Sebastian Menze from the Norwegian Institute of Marine Research. "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."

They offer tremendous temporal and spatial coverage, as the vessels are traveling in different locations in the Southern Ocean almost all year round. What's more, recording the data is particularly cost-effective, as it can be collected as a kind of "by-product" of fishing. The data used in this study by the largest krill fishing company (Aker Biomarine) is even accessible via a public data platform (HUBOcean).

To date, echo sounder data from krill fishing has only been used sporadically for scientific purposes, for example, to estimate the biomass of krill. "Thanks to our approach, we are expanding the potential uses for ecological questions and demonstrating new, cost-effective ways in which fishing vessels can actively contribute to krill fishery management," emphasizes Bettina Meyer, scientist at the AWI and German scientific representative in the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR).

"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. This is particularly significant for periods of time or areas that are not well covered by existing research programs."

In the future, such analyses can also help to evaluate the effectiveness of existing and future management measures and optimize them where necessary.