Alaskan & Bering Sea Waters Warm, Threatening Key Fish Stocks & Pushing Invasives North

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The scientists exposed multiple batches of eggs from each species to different temperatures, including those expected under future climate scenarios, Laurel said in an email. They found that hatch success for Arctic and saffron cod occurred within a relatively narrow water-temperature range – from minus 1 degrees Celsius to 5 degrees Celsius (30 to 41 degrees Fahrenheit), the scientists found. Above freezing, at 3.5 degrees Celsius (38.3 degrees Fahrenheit), hatch success for those two species dropped off noticeably, they found.

But for Pacific cod and pollock — considered "boreal" fish species — there was hatch success at much higher temperatures. For Pacific cod, the upper limit was 8 degrees Celsius (46 degrees Fahrenheit) and for pollock it was 12 degrees Celsius (54 degrees Fahrenheit), according to the results. Egg incubation for the Arctic species took about twice as long as for the boreal species, according to the results, and the emerging Arctic larvae were 30 percent to 40 percent larger than the boreal larvae. Arctic cod in particular had much higher fat contents in their eggs than the boreal species — about triple the levels in Pacific cod eggs and more than eight times the levels in pollock eggs, according to the results.

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So far, the team — with members from the U.S. Fish and Wildlife Service and the U.S. Geological Survey as well as UAA — has evaluated 26 possible invasive species, including some that are already in the Bering Sea. So far, she said, the invasive species that ranks as the most dangerous to the Bering Sea system is the European green crab.

The crab has not been spotted in Alaska waters but has been seen as far north as British Columbia, according to the Alaska Department of Fish and Game. Another candidate on the risk list is the sea grape, a sea squirt that looks deceptively "like a cute little gummy bear," Reimer said. It prefers temperatures in the range of 10 to 24 degrees Celsius — and a warmer Bering Sea might become comfortable territory for it. In all, there are about 160 potential invasives that could move into the Bering Sea, Reimer said.

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https://www.adn.com/alaska-news/science/2017/01/30/warming-ocean-waters-off-alaska-bring-widespread-ecological-changes-with-more-expected-in-the-future/