Whales and humans tend to go after the same dense groups of krill in Antarctica’s Southern Ocean. Youenn Kerdavid/Sea Shepherd Global
While krill may be small to look at, these shrimp-like crustaceans play an outsized role in the global food web. They support the diets of several whale species, including the largest animals to ever exist, seabirds, seals, and more. Humans have also developed a taste for krill. They come in the form of some omega-3 supplements, despite their mostly speculative health benefits. This increased human demand for the krill could spell trouble for the whale species as they continue to recover from the days of industrial whaling.
A new perspective study published September 10 in the journal Nature Communications found that continuing to harvest krill in the Southern Ocean could threaten the whale’s continued recovery from whaling. The authors also call for new recommendations to protect the marine mammals and other Antarctic species that need these tiny ship-like crustaceans to survive.
Krill the mighty
Krill is a catchall term for roughly 86 species that are found throughout the world’s open oceans. They are only about the size of a human thumb, but play an important role in the global food web. Antarctic krill (Euphausia superba) is only found in the Southern Ocean and is among the most important animals in the Antarctic ecosystem. It makes up the diet of most marine mammals and seabirds and also stores carbon. Krill can remove as much as 23 megatons of carbon dioxide from the atmosphere annually.
The crustacean also plays an economic role and is the focus of the largest fishery in the Southern Ocean. Demand for krill as a dietary supplement skyrocketed from 104,728 metric tons in 2007 to 415,508 metric tons in 2022.
According to the Associated Press, 10 to 12 trawlers from Chile, China, Norway, South Korea and Ukraine harvest krill. Its largest commercial use is as an ingredient fed to farm-raised fish. Aker BioMarine from Norway, is responsible for roughly 70 percent of krill catch and is behind changes to how it is caught and marketed over the past several years. The small red krill oil capsules the company sells have omega-3 vitamins that claim to support brain, heart, and joint health.
During that same time, baleen whales including humpbacks (Megaptera novaeangliae), fin whales (Balaenoptera physalus), and Antarctic blue whales (Balaenoptera musculus ssp. Intermedia), have started to recover from 200 years of commercial whaling. Since they are not being hunted in large quantities, they’ve had a change to repopulate after they were almost wiped out.
[Related: Biologists vastly underestimated how much whales eat and poop.]
Stanford University conservation biologist Matthew Savoca and his team previously discovered that the whales in Antarctica are eating significantly more krill than scientists expected. Whale foraging in Antarctica also directly overlaps with human fishing for krill, with some proposals to increase the allowable catch of krill.
“Taken together this is all highly concerning,” Sovca tells Popular Science. “Antarctic krill is among the most biomassive macroscopic species on the planet. To give you an idea of how much mass this is: there are about 400 million tonnes of Antarctic krill in the Southern Ocean (and way more than that before whaling), while the entire human population weighs about 600 million tonnes.”
Whales breathing near several krill trawlers in the Southern Ocean. CREDIT: Ralph Lee Hopkins.
Back-of-the-envelope calculations
Sovca is also a co-author on this latest study that calculates the overlap between the krill that whales need to eat to survive and what humans fishers are catching.
“We multiplied how much whales eat by how many whales there are now, and were before whaling,” Savoca explains. “We then compared those numbers to the estimated amount of krill in the southern ocean, focusing specifically on the SW Atlantic sector.”
The southwest Atlantic sector of the Southern Ocean is important because it is the region where most of the krill in this area is found.
According to their results, the current krill biomass can’t support both the expanding krill fishery and the recovery of the whale populations to their pre-whaling size. The calculations highlight a burgeoning conflict between humans and wildlife at the bottom of the Earth.
Savoca is surprised “that we allow industrial super trawlers to drag their nets through pods of feeding whales. Imagine if that were happening off the coast of the US or Europe, there would be an uproar!”
[Related: How do blue whales find food? They check the weather.]
They also saw that both the whales are specifically targeting dense swarms of krill. Other predators including penguins and seals do not go after swarms in this manner. This means that the trawling vessels and the whales occupy the same spots.
“They are bound to compete directly for krill unless there are guardrails in place to prevent it,” Savoca says.
The Association of Responsible Krill Harvesting Companies (ARK) says that it abides by catch limits and fishing in designated areas. They also monitor and report vessel activity use of marine mammal exclusion devices including rigid or flexible grids on their fishing gear. However, four humpback whales were entangled in one of Aker BioMarine’s nets in 2021 and 2022.A 2022 study did find that krill fishing in the Antarctic has a low bycatch rate.
Avoiding further conflict
In October, the Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR) will meet in Hobart, Australia. Savoca hopes that some of their recommendations can be presented during this annual meeting. They recommend including whale populations and prey requirements when calculating catch limits every year.
“As whale populations rebound, it is now essential that CCAMLR includes recovered (humpback whales) and recovering (blue and fin) whales as monitoring species,” the authors write in the study. “CCAMLR and the IWC [International Whaling Commission] should work together to quantify and include whale prey requirements in any updated krill harvesting regulations.”
Savoca and his team also call for increasing monitoring of krill and larvae hotspots, use the United Nations’ High Seas Treaty as a framework for keeping individual parties accountable, and including more voices from the Global South. These countries do not receive as many financial benefits from luxury tourism and fisheries, and are more impacted by the degraded Southern Ocean.
“Most people I have spoken to about this didn’t even know we fished for krill in the Antarctic, and awareness is so important,” says Savoca. “Beyond that, knowing that there are very few regulations to protect wildlife from fishing, and knowing that we can do better [is important]. With common sense regulations we can have our krill and the whales (and penguins and seals, etc) can have it too.”
Source : Popular Science