Murre Die-Off Linked To Warm Water Temperatures
Since late 2013, a large mass of warm water nicknamed “The Blob” has dominated the Gulf of Alaska.
According to new research, these elevated temperatures aren’t confined to the Gulf. Last winter, Kachemak Bay saw a similar pattern of unusually warm water temperatures. Researchers now believe these temperature spikes are linked to last year’s common murre die-off.
The sea can be a vast and mysterious thing, but oceanographers make it their business to understand what’s happening beneath the surface.
Kris Holderied is the director of NOAA’s Kasitsna Bay Laboratory near Homer. She’s part of a team of researchers involved in a long-term ecosystem monitoring project called Gulf Watch Alaska.
Since 2012, Holderied has collected basic information about the water conditions in Kachemak Bay, including salinity, oxygen content and temperature. She says the results from last winter were unusual, to say the least.
“The water temperatures we saw, instead of being in the mid to upper 30s were in the low to mid 40s. Those are temperatures we typically see in June,” said Holderied.
The Kachemak Bay warmup appears to be part of a larger trend. In late 2013, a persistent high-pressure system allowed a huge patch of abnormally warm water to form in the Gulf of Alaska. Three years later, “the Blob” as it's now become known, has yet to dissipate.
Those warm water conditions are thought to be affecting wildlife populations, both in and out of the water.
Researchers now believe last year’s common murre die-off was linked to increasing water temperatures. Volunteers counted about 46,000 dead murres in Alaska last year, but at least half a million may have died.
University of Alaska Fairbanks professor Shannon Atkinson is one of the people trying to understand what caused the die-off.
“The big question is why. What is going on that is resulting in this final disastrous state of birds flying on shore and dying in large numbers?” said Atkinson.
Common murres look like a cross between a loon and small penguin. Most died on shore over the winter, a time they normally would be feeding near the continental shelf.
“The birds that were coming in were way underweight, they were emaciated,” said Atkinson. "The cause of death was pretty much attributed to starvation.”
Now, Atkinson and her colleagues believe they may have identified the reason why the murres starved.
Wintertime trawl surveys conducted by the National Marine Fisheries Service near the continental shelf found that three of the fish species the murres typically eat – pollock, capelin and eulachon – were absent.
“At least in 2015, there were none of them. They had some of the lowest counts, close to zero,” said Atkinson. “So we know that the food wasn’t there and then we saw the birds dying.”
So, how does this relate to warm water temperatures in Alaska?
Fish feed on tiny marine creatures called zooplankton. Cold water tends to favor big, fatty zooplankton species, while warm water promotes the growth of smaller zooplankton, which don’t provide as much energy to the fish.
“That’s why we’ve been calling it the perfect storm. It’s not only that these things are there, but the timing of them and the intensity of them came together in a way that had disastrous effects for these populations,” said Atkinson.
Although the die-off itself has slowed, the effects may be felt for quite some time.
Heather Renner is a biologist with the Alaska National Maritime Wildlife Refuge. She visited common murre colonies during the breeding season last summer.
“What we found was birds not attending the colonies; they were in rafts offshore in the water. Very few laid eggs and of those that did, they did not attend them,” said Renner. “Most were lost to avian predators and I think there was about zero chick production in all the colonies I’m aware of in the Gulf of Alaska.”
Normally about 60 percent of common murres raise a chick.
Renner says the extremely low breeding success last year was likely because the birds entered the breeding season in poor shape.
Time will tell how the large-scale die-off will affect common murres in coastal Alaska. The good news is that over the past several decades, their populations have been increasing in the state.
“Certainly there are going to be changes and I think there will be some species that are able to resilient and some that aren’t,” said Renner.
Renner and her colleagues plan to revisit murre colonies in the Gulf of Alaska this summer.