Alaska News

Warming waters pose dangers to Arctic cod, research finds

Arctic waters may not be so friendly in the future to Arctic cod.

A research project being conducted by National Oceanic and Atmospheric Administration scientists has found that even a moderate warming of waters could spell dire consequences for the Arctic cod, a high-fat fish important to the food web. But other fish with lower fat content -- pollock, Pacific cod and saffron cod -- can survive and even thrive in warming waters, the research finds.

The Arctic cod information comes from what is believed to be the first successful spawning and rearing of that fish in captivity, a project underway at NOAA's Alaska Fisheries Science Center laboratory in Newport, Oregon.

The first phase of the study focused on juvenile fish. The second phase, which is still underway, is focusing on the egg and larval stages of the fish.

The captive spawning and growth process allows scientists to experiment with different water temperatures in controlled conditions, said NOAA fisheries biologist Benjamin Laurel, who is conducting the study.

It is also important because it allows scientist to observe a fish "that carries out most of its life -- or used to -- under the ice," Laurel said.

Arctic cod generally swim in waters at about 0 degrees Celsius, or even colder, as saltwater has a lower freezing point than freshwater does. Once water is warmed to 2.5 degrees Celsius or 36.5 degrees Fahrenheit, growth of Arctic cod is stunted compared to that of the other tested species, according to preliminary results


Waters warmed to above 41 degrees Fahrenheit are fatal to Arctic cod eggs, the scientists found.

"It's pretty remarkable for a fish to have such a narrow temperature range," Laurel said.

For Arctic cod, the findings are ominous. With waters off northern Alaska already registering surface temperatures of 57.2 degrees Fahrenheit, and with NOAA predicting future per-decade temperature increases of 0.9 degrees, suitable habitat for the high-fat Arctic cod is expected to shrink.

But other species tested so far -- saffron cod, pollock and Pacific cod -- appear to be not as sensitive to warming water temperatures. Saffron cod, in particular, may be poised to take over much of the Arctic marine territory. Those fish thrive in waters as warm as 68 degrees, according to preliminary results.

Some saffron cod already live in the Arctic year-round, though they are more plentiful in the Gulf of Alaska. If warming occurs as predicted, numbers may increase in the more northern waters. "Here's an animal that's already in the Arctic and poised to take advantage of additional warming," Laurel said.

Arctic cod, with its high fat content, is important to the diet of Arctic marine mammals and predator fish, Laurel said. So warming waters might wind up forcing those animals to switch to lower-fat fish like saffron cod, he said.

There is no commercial harvest of Arctic cod in Alaska or Canada, but it is a species important to commercial fishermen in the Barents Sea.

Saffron cod are caught commercially in Russia. In Northwest Alaska, where they are known as tomcod, they are caught for subsistence use and there is a very small commercial harvest, according to the state Department of Fish and Game.

The study of Arctic cod and the other species will continue, Laurel said.

Meanwhile, another NOAA-led study found that larvae of northern rock fish appear to be resilient to increased levels of acidity in marine waters. Reduced pH levels -- changes to marine chemistry that are occurring in the oceans as they absorb atmospheric carbon dioxide -- did not slow growth of young northern rock fish, according to the study, published in the ICES Journal of Marine Science.

Increasing acidification has been shown to have varying effects on different marine species. Past NOAA research found that higher levels of water acidity slow the growth of juvenile red king crabs and tanner crabs, for example. But pollock, at least in their early life stages, appear to be largely unaffected by incremental increases in water acidity, according to a study by NOAA and Fish and Game scientists.

Yereth Rosen

Yereth Rosen was a reporter for Alaska Dispatch News.