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Title image: An adult blue whale. (Credit: )

Antarctic krill fishing could threaten the recovery of whale species that were nearly wiped out by industrial whaling, according to led by CU Boulder and Stanford University, and published Sept. 10 in the journal Nature Communications.

Krill, small shrimp-like crustaceans, are an important food source for many animals in Antarctica, including seals, penguins, and blue and humpback whales. Scientists estimate that there are over 7000 trillion krill in the Southern Ocean.

Krill are about the size of an adult human pinkie. (Credit: )

“Because of the sheer number of krill in the Southern Ocean, they play a major role in storing carbon and recycling nutrients,” said Zephyr Sylvester, the paper’s co-author and a doctoral student in the Department of Environmental Studies at CU Boulder. “Those processes support the growth of microorganisms that many marine animals feed on.”

Driven by the rising demand for krill as fish meal and nutritional supplements, krill fishing in the Southern Ocean has quadrupled in the past two decades. According to a report by the United Nations Food and Agriculture Organization, commercial fisheries captured more than in 2020. 

Before the global ban on commercial whaling in the 1980s, many whale species in the Southern Hemisphere had plummeted to just 10% of their pre-whaling populations. Since the whaling moratorium took effect in 1985, some Southern Ocean species have made remarkable comebacks. For example, scientists estimate that the population of humpback whales in certain areas of the Southern Ocean has rebounded to about.

This recovery has occurred amid growing competition with humans for the whales' essential food source.

Sylvester added that fishing efforts in the Southern Ocean have become more spatially concentrated in recent years, with the same number of krill being captured from increasingly smaller areas. 

“This intensification can significantly increase the vulnerability of local ecosystems, amplifying the indirect impacts of fishing on the broader environment,” she said. 

In the new study, the team—including scientists at Stanford University—calculated how much krill is left in the Southern Ocean for whales and other predators to eat after industrial krill harvesting. Researchers found that the number is significantly lower than the estimated number of krill available before industrial whaling began, suggesting that krill populations in the Southern Ocean surrounding Antarctica are insufficient to support the full recovery of whales to pre-whaling levels.

“This study really highlights the need for maintaining enough krill in the Southern Ocean to feed current whale populations and to also support whale recovery,” said Cassandra Brooks, the paper’s senior author and associate professor in the Department of Environmental Studies. “This also emphasizes the critical need for more research on how much krill-eating whales need to recover and better understanding of competition with commercial fisheries.”

The research comes right before in Australia to make management decisions regarding krill fisheries in Antarctica.

“The committee is working on revising Antarctic krill catch limits, making this an opportunity to take precautionary steps to ensure that whales are considered in the management process,” Brooks said. 

Stanford University contributed to the story. This research was supported by the National Aeronautics and Space Administration, the National Science Foundation, MAC3 Impact Philanthropies, and the Pew Charitable Trusts.