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Scientists breed Arctic fish as they study ocean warming

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ANCHORAGE, Alaska (AP) — A silvery fish that represents an important link in the Arctic food chain has been successfully grown in laboratory conditions, giving federal researchers a tool to learn more about the key but vulnerable species.

Arctic cod are found in North American waters and as far south as the Bering Sea, but they are far more abundant in the Chukchi and Beaufort seas, said Benjamin Laurel, a fisheries research biologist with the National Oceanic and Atmospheric Administration.

Arctic cod are difficult to study because they spend so much time under sea ice. To breed them in lab conditions, scientists collected young cod off the north coast of Alaska and flew them to a lab in Oregon.

The fish are vulnerable when water temperatures warm.

At 32 degrees, Arctic cod have a relatively high growth rate, Laurel said. At 35.5 degrees, Arctic cod are "rapidly outpaced" by other Bering Sea species such as walleye pollock and Pacific cod.

Arctic cod eggs also are vulnerable. A temperature of 41 degrees is lethal, he said.

Scientists want to know how Arctic cod will respond to warming ocean temperatures. NOAA scientists estimate sea surface temperature in the Chukchi is warming at 1.8 degrees per decade.

"The concern is, if the Arctic cod are not there, what happens to the ecosystem, or what happens if they're replaced by something?" Laurel said.

Arctic cod have the richest fat content of any cod species and serve as a key middle link in a relatively short Arctic food chain, he said. They feed on plankton and become prey for ringed seals, the main diet of polar bears.

They also are an important food source for seabirds, narwhals and beluga whales.

Arctic cod can grow to nearly 12 inches in four to five years. They're found at all depths, Laurel said, and appear to seek out pockets of the coldest water.

"They're pretty widely spread, and they seem to be tuned in to their preferred temperature," he said.

There is no North American commercial fishery for Arctic cod.

Scientists collected young fish from the Beaufort Sea for three summers starting in 2012. They loaded the cod into small, breathable bags and flew them to the Alaska Fisheries Science Center laboratory in Newport, Oregon. The lab is set up to chill natural seawater from the Pacific.

Initial studies focused on growth of juvenile Arctic cod in response to temperature and food availability.

Scientists followed usual protocols for breeding cold-water fish but were unsuccessful the first year, Laurel said.

"They're really, really temperature-sensitive as you might imagine, but even more so than we thought," he said.

They tried again and successfully hatched Arctic cod in colder temperatures. A second set of studies has targeted the effects of temperature and food availability on eggs and larva.

Scientists will perform comparative studies on walleye pollock, Pacific cod and saffron cod to see which is most likely to thrive under varying temperatures.

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