Listening or sniffing – On the hunt for krill | Polarjournal
The most sought-after creature in the Southern Ocean is this crustacean, Euphausia superba, which is around 6 centimetres in size. Its abundance depends on the phytoplankton in the ocean, its food. Krill accumulate in huge swarms and thus drift with the current. But finding it is no simple matter. Picture: Michael Wenger

Krill is probably the most important animal representative in the Southern Ocean. Because everyone is after the little crustacean, from penguins to blue whales and recently even humans. But tracking krill in the vastness of the ocean is no simple matter. Nevertheless, Australian researchers have managed to learn more about krill and discover it on an expedition to East Antarctica. Help also came from whales and seabirds. An international team of researchers has discovered how the animals manage this and why they are superior to us despite our technical aids.

The research voyage of the RV Investigator, which spent two months between Africa and Australia in the Southern Ocean in search of krill, has come to a successful end. The Australian scientists of the Australian Antarctic Division AAD had to detect and study krill in this region with new detection and observation methods within the framework of the TEMPO project. The ship covered more than 17,000 kilometres before returning to the port of Hobart. Not only did the researchers have to endure heavy seas, but they also had to hope that the technical means they had developed to track the krill would work. After all, the goal was to collect enough data to be able to estimate the amount of the precious marine animals.

“At a time when commercial krill fishing is looking to expand into new areas, this research will play a critical role in ensuring sustainable catch limits.”

Sussan Ley, Australian Minister for the Environment

This is an important aspect, on the one hand to protect the animals, but at the same time to allow the CCAMLR (Commission for the Conservation of Antarctic Marine Living Resources) to set fishing quotas for the emerging krill fishery in the region. This is to counter illegal krill fishing. Australian Environment Minister Sussan Ley agrees: “At a time when commercial krill fishing is looking to expand into new areas, this research will play a critical role in ensuring sustainable catch limits.”

AAD’s video shows a summary of the expedition. In the course of it, new findings were made in the middle of krill swarms with the help of special cameras and it was also shown that krill can be found at depths of up to 1,500 metres. The researchers also received help from whales and seabirds. Video: AAD

Among the successes of the expedition are certainly the tests with cameras for stereoscopic recordings in the middle of krill swarms and the realization that krill undertake large vertical migrations. Animals were still found at depths of 1,500 metres and in various areas. Fixed probes with cameras will provide recordings and data on krill in different areas during one year. The researchers were also lucky enough to encounter several super swarms, including one 3.2 kilometres long, 300 metres wide and around 100 metres thick. There they could also observe the impact of whales, seals and seabirds on such swarms and learn more about the feeding behaviour of animals that depend on krill. In total, the scientists sighted more than 1,400 whales, hundreds of seals and penguins during the expedition.

Such echograms, which are produced with the aid of sonar from the ship, show the extent of a krill swarm. This one was over three kilometers long and about 100 meters “thick”. The blue areas branch off where whales had dived into the swarm. Picture: Gavin Macaulay, Australian Antarctic Division

“Now our challenge is to turn all this data into a reliable estimate of krill biomass in this region,” explains Dr. So Kawaguchi of AAD and leader of the expedition. “These research voyages are crucial to help us better understand Australia’s vast marine environment and ensure the prosperity of our growing blue economy,” says the Tara Martin, head of CSIRO, Australia’s government agency for scientific and industrial research. The term “blue economy” refers to the sustainable use of marine resources. But krill fishing is controversial because it is the fishing nations that are blocking efforts at Antarctic Treaty meetings to establish large-scale marine protected areas in the Antarctic.

Aggregations of whales and seabirds indicate the location of a krill swarm in the Southern Ocean from afar. While we rely primarily on visual and auditory detection and are limited by distance, animals can smell swarms of krill at great distances. Picture: Michael Wenger

But despite all the technical successes of the expedition, the scientists had to count on help from the animal world to discover the krill swarms. Although krill are found in huge quantities in the Southern Ocean, their distribution is patchy and difficult to detect in the vastness of the ocean. Super swarms could theoretically be recorded with the help of satellites. But such swarms are the exception rather than the rule. But how do those species that depend on krill for food manage to track down their food? An international team of researchers from Japan and the USA investigated this question and discovered that the animals probably detect zooplankton by means of a specific odour: dimethyl sulphide, also called the “scent of the sea”. This sulphur-containing substance is produced when krill eat phytoplankton, releasing DMSP (dimethylsulphoniopropionate) stored in the plant cells. Thereby, the typical smell of the sea, which one knows from beaches with seaweed, is generated. The more zooplankton graze, the higher the concentration of DMS should be in the air and water.

To this end, the research team developed an instrument that analyses and quantifies the amount of various sulphur compounds in the air and water on board of ships. The team was able to determine that in places with large amounts of zooplankton there are also large amounts of DMS and DMSP. The researchers took this data to a pilot study in Antarctica, where humpback whales were tagged to study their movement patterns. The evaluations of this work are still in progress. But the researchers are convinced that in further studies they will find out more about how the giants of the seas track the tiny krill… and in the process serve as a signal to us.

Numerous penguin species also live almost exclusively on krill. Macaroni penguins swim in groups, called rafts, into the open sea to the krill swarms. They probably follow chemical clues. Picture: Michael Wenger

Dr Michael Wenger, PolarJournal

Links to the studies:

Owen, K., Saeki, K., Warren, J.D. et al. Natural dimethyl sulfide gradients would lead marine predators to higher prey biomass. Commun Biol 4, 149 (2021).

Okane, D., Koveke, E., Tashima, K., et al (2019) Anal. Chem., 91, 16, 10484-10491 High Sensitivity Monitoring Device for Onboard Measurement of Dimethyl Sulfide and Dimethylsulfoniopropionate in Seawater and an Oceanic Atmosphere;

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