South SFV Today

Human harvesting of krill in the Southern Ocean could threaten the recovery of whale species that were nearly wiped out by industrial whaling in the 20th century, according to a Sept. 10 study in Nature Communications.

The tiny, shrimp-like crustaceans known as krill are the essential food source for baleen whales such as blues and humpbacks. To feed, these giant marine mammals take in great gulps of ocean water, filtering krill through bristly mouth structures. Booming demand for krill as fish meal and omega-3 fatty acid nutritional supplements, however, could leave whales without enough victuals to sustain even their diminished numbers.

“Our calculations suggest an alarming possibility that we might harvest krill to the point where we do real damage to recovering whale populations,” said lead study author Matthew Savoca, a research scientist in the lab of Jeremy Goldbogen, associate professor of oceans in the Stanford Doerr School of Sustainability.

The results highlight a need for scientists, regulators, and industry to carefully assess the impacts of krill harvesting in the Southern Ocean at current levels before expanding. “With this study, we want to draw attention to how there likely isn’t enough krill to support fully recovered whale populations, and now on top of that, we’re harvesting krill and plan to harvest more krill in the near future,” said Goldbogen, the study’s senior author.

The new research grew out of a prior Stanford study documenting how baleen whales gobble up significantly more krill than scientists had previously estimated. A paradoxical finding of that study was that as whale populations plummeted by roughly 90% in the Southern Ocean during whaling’s grim heyday, so too did krill populations.

The researchers worked out that baleen whales effectively fertilize the ocean through their prodigious droppings, providing nutrients for phytoplankton that krill eat. The upshot: The krill population must have been much larger—perhaps five times greater—than it is currently to have sustained pre-whaling whale populations in the early 20th century.

“Krill is the foundation of the entire Southern Ocean ecosystem. They’re really the only thing that large whales eat down there,” Savoca said.

In nearly 40 years since a global whaling moratorium went into place in 1986, some Southern Ocean species—particularly humpbacks—have made an impressive comeback. Yet this recovery has taken place against increasing competition with humans for whales’ critical food source; over the past 30 years, the krill catch has quadrupled to around 400,000 tons annually and is set to expand further.

Savoca and colleagues calculated how much krill is left in the Southern Ocean for baleen whales, seabirds, and other predators after industrial krill harvesting at current rates compared to before industrial whaling began. “The basic math makes it pretty clear that current krill biomass cannot support both an expanding krill fishery and recovery of whale populations to pre-whaling size,” said Savoca.

The study offers suggestions for how the Commission for Conservation of Antarctic Marine Living Resources (CCAMLR), an international organization established in 1980 managing Southern Ocean fisheries can help avert disaster.

Regulation on areas and times commercial boats can operate minimizing competition with whales is a starting point. The most important region is west Coronation Island South Orkney group prime fin whale feeding ground where about 30% all fished since 2000 overlap drives welfare concerns researchers also suggest expanding use marine mammal exclusion devices prevent accidental bycatch entangled nets occurred recently documented deaths least four humpback across seasons

As for improved monitoring data hotspots identify zones ban or limit fishing vessels sample avoid harvesting midst spawning periods

Researchers hope prompt rigorous accounting deeper investigations predators ultimately forging path preserves delicate ecological balance

“It’s not foregone conclusion suffer higher levels careful management saving continue success.”

Additional co-authors include Hopkins Marine Station researcher Mehr Kumar PhD student Max Czapanskiy University Colorado Boulder University California Santa Cruz Alfred Wegener Institute Polar Marine Research Bremerhaven Germany Carl von Ossietzky University Oldenburg Germany Goldbogen member Stanford Bio-X

Research supported National Aeronautics Space Administration National Science Foundation MAC3 Impact Philanthropies Pew Charitable Trusts

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