Krill feed on phytoplankton and are a critical part of the food web.
AUSCAPE INTERNATIONAL PTY LTD/ALAMY STOCK PHOTO
By Erik Stokstad
Krill, crustaceans smaller than a cigarette, play an outsize role in the ecology of the ocean around Antarctica: Penguins, whales, and other predators feast on vast swarms of the shrimplike animals. Now, researchers have launched a broad international survey of krill’s main habitat in the Scotia Sea—the first in nearly 20 years—to learn whether a growing fishing industry is leaving enough for krill’s natural predators.
The effort, led by the Institute of Marine Research (IMR) in Bergen, Norway, began in earnest last week when Norway’s new polar research vessel Kronprins Haakon sailed from Punta Arenas, Chile, for the Scotia Sea. It and five other vessels will spend nearly 2 months mapping krill abundance across an area about the size of Mexico. Beside gauging population, the project will test tools for cheaper, more frequent surveys that could improve oversight of the fishery. “With a more dynamic management system, we can be more certain that the fishery is not negatively affecting the krill populations or the predators,” says Bjørn Krafft, a marine biologist at IMR who is directing the $5 million Norwegian cruise.
Soviet vessels were the first to ply the Southern Ocean for krill, which was ground into fish meal. By the 1980s, scientists began to worry about the effect on krill-feeding predators. The Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR), a treaty organization established in 1982, set tight limits on fishing, now at 620,000 tons per year. Most fishing stopped after the 1991 collapse of the Soviet Union, but it has been slowly growing again. Norway takes about half the current catch, extracting omega-3 fatty acids for nutritional supplements. “We absolutely need to know whether the catch limit is still precautionary,” says Simeon Hill, an ecologist with the British Antarctic Survey in Cambridge, who is not involved in the project.
CCAMLR organized the previous large krill survey, in 2000. The central finding—about 60 million tons of krill in the Scotia Sea—reassured managers that they had been adequately conservative. But much smaller surveys, conducted annually in a few places, have shown that regional krill populations go through boom and bust cycles, making it harder to gauge the health of the overall stock from a single survey. “We have pieces, but we are missing the big picture,” says marine biologist Rodolfo Werner, an adviser to the Pew Charitable Trusts and the Antarctic and Southern Ocean Coalition, who is based in Bariloche, Argentina.
Casting a wide net
(MAP) A. CUADRA/SCIENCE; (DATA) INSTITUTE OF MARINE RESEARCH
During the survey, vessels will retrace the previous transects, measuring krill swarms with echosounders, a kind of sonar, and confirming the identification with sampling trawls. Some ships will measure oceanographic variables as well, such as temperature, currents, and plankton, to see whether they can be used to predict krill abundance.
IMR will also test remote devices that could gather krill data continuously and more cheaply. The Haakon will deploy moored sensors, as well as wave gliders and a sail-propelled buoy, in order to compare their readings with the net and echosounder data. “This is one of the most beneficial parts of the survey,” says Bettina Meyer, a krill ecophysiologist at the Alfred Wegener Institute in Bremerhaven, Germany.
At the same time, land-based teams from IMR and the Norwegian Polar Institute will track seals, whales, and penguins foraging for krill in the Bransfield Strait, an important feeding ground near the Antarctic Peninsula. Matching their feeding behavior with survey results “has big potential to get a better idea of the interactions between the krill fisheries and the predators,” says So Kawaguchi, a marine ecologist with the Australian Antarctic Division in Kingston.
The survey itself won’t be able to reveal how the overall krill population in the Scotia Sea might have changed since the 2000 survey, given the variability of krill populations over space and time. Finding out what drives population changes will require more research on the seasonal movement of krill, for example, and the impact of climate change. Loss of sea ice, which protects young krill from predators, is expected to reduce their abundance, and rising water temperatures and acidification could also pose serious threats—ones that even the best management plan might
not avert.
Source: Science Mag