SOURCE: Seattle Times
DATE: November 3, 2019
SNIP: [A]s climate change warms the die-offs of seabirds and marine mammals have been on the rise. The grim tally includes a nearly fivefold increase in ice-seal carcasses spotted on shore, strandings of emaciated gray whales, and near the St. Lawrence Island village of Savoonga, a discouraging spectacle: auklets abandoning seaside nests as their chicks succumb to hunger.
The animal die-offs offer the world a stark example of the perils of rising ocean temperatures, which already are upending parts of the Bering Sea ecosystem as climate change — driven by greenhouse-gas pollution from fossil fuels — unfolds in Alaska at a breakneck pace. For the past two years, the winter ice has largely disappeared, and this fall, ice formation in some of the northern waters has been at historic lows.
Federal and university scientists are trying to better understand why some birds and marine mammals have been unable to find enough food, and whether toxic algae blooms — increasing as the water warms — could have contributed or caused some of the die-offs.
The struggles of Alaska’s seabirds grabbed scientists’ attention in 2015, when hundreds of thousands of dead and dying common murres washed ashore along state’s south-central coast during a period of unusually warm water temperatures.
That Alaska seabird die-off was thought to be the biggest on record and could be devastating if repeated, according to a National Park Service publication. It was followed by a series of other die-offs.
Scientists have sent more than 220 seabird carcasses found along different parts of Alaska’s shoreline to a U.S. Geological Survey (USGS) laboratory in Madison, Wisconsin, for necropsies.
More than 80% of the birds were found to have died from a lack of food, according to Robert Dusek, a government biologist in Madison.
Why can’t the seabirds find a meal?
In some areas, the answer may be simple: a food shortage.
Many of these seabirds eat tiny shrimplike creatures such as krill and copepods, whose numbers — according to federal marine surveys — have declined as the water off Alaska has warmed.
Others, such as the murres, dine on small fish such as smelt, which in the northern Bering Sea have suffered a 98% population drop in eight years, according to federal surveys. And as seabirds search for these fish, they may face increased competition for their prime food sources from Pacific cod and pollock that — as the winter ice has faded — migrated here from waters farther south.
The seabird’s difficulties finding food were on painful display this summer near Savoonga, a St. Lawrence Island village in the northern Bering Sea, where a poster on the wall in the local tribal building urges people to not eat birds found dead along the beaches, to handle them with gloves and to report those locations to scientists in Nome or Anchorage.
As the winter ice has faded — and waters have warmed — seal deaths also have been on the rise.
During the past two years, 282 seal carcasses have been spotted on the northern Alaska’s shoreline, and a lack of food appeared to play a role in one major die-off Sheffield investigated.
In June 2018, she tallied 45 carcasses of bearded, ringed and spotted seals on a half-mile stretch near the village of Wales, north of Nome on the Seward Peninsula.
These were all ice seals, which during the winter and spring months depend on the frozen sea to help them find food, bear their young and escape predators. They were mostly pups and young adults, and during this summer season they should have been foraging for small fish and other marine life in coastal waters.
Toxic algae may have played a role in the deaths of 39 walruses that in the summer of 2017 washed up on the shores of Northwest Alaska. Analysis found moderate levels of saxitoxin in samples taken from some decaying bodies.
Algae toxins may be involved in some of the bird die-offs.
So far, the USGS scientists have looked for traces of saxitoxin in more than 100 dead Alaska seabirds. More than 30% tested positive, including many that were determined to have died from starvation.
This finding raises the possibility that some birds are disoriented and weakened by ingesting the toxins to the point where they can’t forage for food.