In the frigid waters near the South Pole, the Saga Sea trawler is casting its nets for "pink gold."
The Norwegian industrial fishing boat isn't chasing cod, salmon or other fish you might find on a dinner plate. Instead, the trawler is after tons of tiny, bug-like crustaceans known as Antarctic krill, which form the base of Antarctica's food web.
That has caught the eye of conservation groups, which worry that the Saga Sea and other similarly equipped "supertrawlers" are poised to triple or quadruple the annual krill harvest in Antarctica's Southern Ocean.
This little shellfish, which most people probably have never heard of, is in high demand these days. Fish farmers feed the naturally pink krill to farmed salmon, eliminating the need for artificial dyes. Vitamin makers turn fatty krill into fish oil capsules marketed as aids to heart health.
|
| The krill may be "pink gold" to the fishing industry, but it also makes a priceless contribution to the South Pole's complex ecosystem. Photo courtesy of British Antarctic Survey. |
But the tiny marine species' toughest opponent may be climate change. Scientists are just beginning to understand the complex interplay between krill and the sea ice that helps feed and shelter them. But there are already indications that Antarctic warming could spell trouble for the little shellfish and the penguins, sea birds, fish and whales that like to eat them.
One recent study by the British Antarctic Survey found that the number of krill in the Southern Ocean has dropped by about 80 percent since the 1970s. Over the same period, the annual duration of sea ice in the krill's main breeding ground decreased by 30 days.
And in its report released last year, the Intergovernmental Panel on Climate Change echoed those findings, reporting that the decline in the Antarctic krill population is "very likely" a result of changes in sea ice.
The relationship between krill, the ecosystem it supports, the sea ice and rising temperatures is not a simple one.
In one sense, sea ice acts like a floating buffet for the tiny creatures. As the ice melts each spring and summer, it releases iron and other nutrients that fuel the growth of phytoplankton, krill's preferred food source. During periods when a lot of ice melts, the phytoplankton and krill populations balloon.
In the winter, the sea ice provides young krill with a food source -- algae that stick to the undersides of the ice -- and shelter from predators.
"We have this kind of two-step process that links ice and krill," said Marc Mangel, a professor at the University of California-Santa Cruz who studies krill population dynamics. "If we decrease the amount of ice by 10 percent, do we decrease krill production by 10 percent?"
One possibility that Mangel said he is exploring is whether there is a threshold level of sea ice decline below which krill will find it tough to survive.
That is a question with some urgency, given that the Antarctic peninsula, an important krill breeding ground, has warmed by about 2.5 degrees Celsius over the last 50 years. In the past decade, annual ice loss along the peninsula increased by 140 percent, to 60 billion metric tons.
"Changes in ice due to climate change are almost surely going to cause a decrease in krill production," Mangel said, "But we don't know exactly how much."
Christian Reiss, a research fisheries biologist at the National Oceanic and Atmospheric Administration's lab in La Jolla, Calif., said El Niño and La Niña weather patterns also seem to play a role in governing Antarctica's krill, because they can affect phytoplankton populations.
And there is another twist to the krill-climate relationship.
The tiny crustaceans not only depend on sea ice for their livelihood, they also sequester carbon to the tune of 0.2 metric gigatons per year, the equivalent of the annual carbon emissions from 35 million automobiles, according to a British Antarctic Survey study released in 2006. Krill accomplish this mighty feat when they dive deep into the ocean to excrete waste, which sinks to the ocean floor and, presumably, stays there.
With the rise of supertrawlers, which have invigorated the 40-year-old Antarctic krill fishery that operates in a small patch of the Southern Ocean near the peninsula, this form of natural CO2 sequestration could begin to diminish.
The Saga Sea, operated by the Norwegian company Aker BioMarineSciences since 2006, was the first of the new factory fishing vessels to venture into the polar region. Because krill decompose quickly once they are caught, becoming unusable, the Saga Sea holds the shellfish in nets underwater, pumping them to its on-deck processing facility in small batches. That has allowed the vessel and others like it to continuously process krill.
Since the Norwegian ship began operations in 2006, five countries have licensed another six ships to fish for Antarctic krill. And even that number is well below demand. One country, Norway, has turned down five companies seeking licenses this year.
That has caught the attention of conservation groups, who want tougher fishing quotas in place to help Antarctic krill avoid the potentially disastrous combination of increased fishing and a changing environment.
"We realized one boat would have the potential of catching what the entire fleet used to catch in a year," said Gerry Leape, director of the Antarctic Krill Conservation Project. "That, combined with the latest report from the IPCC talking about intense impacts at the poles -- we said, 'These things are coming together.'"
Fisheries managers used to worry about depleting breeding colonies in the small patch of Southern Ocean known as "Area 48," where the commercial krill harvest historically took place. But in the last couple of years, with the rise of the new fishing boats that can catch more krill and cover broader swaths of ocean, "we are now also concerned about actual depletion," Mangel said.
Hanging in the balance are the fish, seals, penguins, whales and seabirds that rely on krill as a major food source.
One study, published in February in Proceedings of the National Academy of Sciences, predicts that if the Southern Ocean warms by 0.47 degrees Fahrenheit, changes in the migratory patterns of fish and declines in the krill population could cause a sharp drop in the number of king penguins -- a species that rebounded from near-extinction over the past century.
Others studies have also drawn strong links between the amount of krill available near Antarctic shores and populations of fur seals and some penguins, Reiss said.
"We see very strong relationships between the productivity cycles of krill and the feeding success and reproductive success of the predators," Reiss said.
Advertisement
