When Antarctic krill swarm, the semi-transparent shrimp-like crustaceans join together in the millions or trillions, forming dense coral-colored underwater clouds as they swim in sync with one another and traverse frigid ocean currents. Some of these swarms are so large they can be seen from space, extending for miles near the ocean’s surface and hundreds of feet below, attracting predators from land, sea and sky.
Individually, each of these animals is only about two inches long, but collectively they form one of the largest biomasses on the planet. They also fuel the entire food web in the Southern Ocean, which circles Earth’s southernmost continent. “Every single species in Antarctica feeds on krill, or something that feeds on krill,” said Rodolfo Werner, a marine biologist from Argentina who has been studying marine ecosystems in Antarctica for more than 20 years.
But the crustacean’s future, and that of its predators, by extension, are increasingly in jeopardy due to climate change and a growing commercial krill fishery. Rising air and sea temperatures are causing krill’s icy habitat that they rely on for food and shelter to melt, especially in their early life.
Krill larvae feed on algae that grows on the underside of frozen seawater floating near the ocean’s surface. “They graze on the sea ice like cows,” said Werner. But, in the last two years, sea ice coverage in Antarctica has shrunk to historic lows due to rising air and sea temperatures, according to the National Snow and Ice Data Center at the University of Colorado Boulder.
The Antarctic Peninsula, in particular, is warming faster than the global average, according to a scientific study published in Nature Geoscience last fall. According to Ryan Reisinger, a marine biologist and associate professor at the University of Southampton in the United Kingdom who studies whales in the region, the west end of the peninsula is becoming increasingly ice free. “We have less sea ice, both in terms of space and also through the year,” he said. Inevitably, this shift is having an impact on krill populations, he said. “As we get less sea ice, we probably get less Antarctic krill.”
At the same time, less ice is making it easier for commercial fishing vessels to catch krill closer to shore where millions of penguins, seals and whales are vying for their prey, too.
“Because we have less ice near the land, they can get closer inshore, “ said Reisinger. “That’s kind of the way that the fishery is intensifying. They’re fishing closer and longer.” Krill fishing has now become nearly a year-round fishery. It is also the largest fishery in the region and expected to expand.
To help krill and those that eat them adapt to this changing environment, scientists like Reisinger and Werner say it is imperative to set stricter catch limits on krill in certain areas where other animals are feeding, as well as establish a network of marine protected areas in the Southern Ocean. These specially designated areas would prohibit, or limit in some cases, human activity like fishing. They would also have specific conservation and research goals.
But the main international decision-making body responsible for implementing such conservation measures, the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), is failing to do so, scientists and environmental activists say.
“CCAMLR used to have this history of being a great conservation organization,” said Andrea Kavanagh, who directs the Pew Bertarelli Ocean Legacy’s efforts to protect Antarctica’s Southern Ocean. “They are not implementing their conservation mandate whatsoever.”
The commission was formed in 1982 in response to increasing concern over a growing interest in commercial krill fishing, an industry which Russia initiated in the 1960s, hoping to promote krill as an untapped source of healthy protein. Currently, Norway is leading the industry, followed by China. Most of the krill caught are used to make omega-3 supplements for humans and feed for pets and aquaculture, including farm-raised salmon.
Antarctic krill are caught in the Bransfield Strait of the Antarctic Peninsula. Catching and measuring a small number of krill allows scientists to understand the sizes of individuals that make up the swarms. Credit: Ryan Reisinger
Today, the commission is composed of delegates from 26 countries plus the European Union, who are tasked with protecting Antarctica’s marine ecosystems and ensuring that the harvesting of krill or fin fish does not negatively impact them. Delegates have voting rights and full consensus must be reached in order to implement each decision made by the commission.
Over the years the group has achieved several conservation wins, including the establishment of two marine protected areas, or MPAs, in the Southern Ocean. One is the South Orkney Islands Southern Shelf marine protected area, which was established in 2009. It was the first of its kind to be created in waters known as the high seas, which extend beyond any one nation’s national jurisdiction.
The other is the Ross Sea Region MPA, established in 2016 after years of negotiations amongst the commission’s delegates and input from the public, non-governmental organizations and scientists. It is the world’s largest MPA, encompassing an area about three times the size of California. Eighty percent of its waters are closed off to commercial fishing. “That’s been the greatest success in CCAMLR,” Werner said.
Large-scale marine protected areas can provide multiple ecosystem benefits, depending on their design and level of protection. Ones that are fully protected, which prohibit all extractive activities within their bounds, have been proven effective in supporting the growth or maintenance of fish populations and other marine life. “You can think of them as sort of like sanctuaries for these ecosystems,” said Reisinger.
As their populations grow they may become more genetically diverse and consequently more resilient to environmental changes, such as those caused by climate change. Eventually, their populations may grow so much that they spill over beyond the MPA’s boundaries, which can be beneficial to nearby fisheries. But MPAs are not only refuges. They can also serve as important areas of research.
Setting aside areas where human activity is limited can allow scientists to compare how ecosystems are doing within the MPA in comparison to areas that have no restrictions on fishing, for example.
“There are good scientific reasons why you should have areas set aside so that you can see what the impacts of fishing really are,” said Philip Trathan, a marine ecologist who conducted research on Antarctic ecosystems for more than 20 years for the British Antarctic Survey. “If there is no monitoring of an ecosystem and you don’t have any handle on whether populations of whales are going up, or penguins are going down, or any of the indicators of ecosystem health, then, in my view, you should not be fishing,” he said.
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