A new study suggests a marine heatwave may have caused about 1 million north Pacific seabirds to die.
A cooperative effort between federal agencies and university researchers revealed that nearly 62,000 dead or dying seabirds washed ashore onto Alaska and West Coast beaches between the summer of 2015 and spring of 2016. But carcass recovery suggests this was a fraction of the roughly 1 million birds that died during this time period.
Rising temperatures between 2014 and 2016 created a large mass of unusual warm seawater, known as the Blob, which in turn reduced food supplies for seabirds and fish.
Lead researcher and study co-author Julia Parrish said the number of birds that are estimated to have died is alarming.
“In 2015, we started to see larger-than-normal numbers of these birds wash ashore as carcasses ... In places along the West Coast, and definitely in the Gulf of Alaska, that got so intense that there were literally thousands of these birds per kilometer of beach,” Parrish said. “That’s so many that if you were walking along, you’d literally be almost knee-deep in carcasses at the tideline.”
Parrish, along with her colleagues and researchers, analyzed data from the dead birds from wildlife rehabilitation centers, citizen beach surveys, community reports, and studies were conducted by universities, private organizations and government entities to better understand the massive die-off.
The analysis was published Wednesday in the scientific journal PLOS One. It found that the common murres were dying from starvation due to warmer ocean temperatures affecting plankton, the tiny aquatic organisms that are a big part of the ocean’s food chain. Plankton-feeding species include the fish that are eaten by common murres. According to Parrish, these seabirds mirror salmon in terms of their diet. Anything a salmon eats, these birds will dive in the ocean and eat as well.
On Jan. 1-2, 2016, 6,540 common murre carcasses were found washed ashore near Whitter, Alaska, translating into about 8,000 bodies per mile of shoreline — one of the highest beaching rates recorded during the mass mortality event.
David B. Irons
“The death of all of these murres suggests to us that those large fish were also having a hard time and the reason why we know about the murres is, a dead bird floats but a fish sinks,” Parrish said.
According to U.S Geological Survey Research Wildlife Biologist John Piatt, forage fish scarcity was the most likely cause of the die-off and breeding failures at colonies in 2015-2017.
“No other factor was found that could explain the magnitude or spatial extent of these events," Piatt said.
Nearly 2,000 common murres were found washed ashore along the Oregon Coast. The biggest impact was in Alaska, where nearly three-quarters of dead murres were found.
Piatt said common murres were failing to reproduce during this time as well. Nearly two-thirds of the dead murres were adults.
"With heatwave impacts on their food supplies from below and above in the food chain, murres were caught in an 'ecothermic vise' and populations were severely impacted for years. In plain language, there was a run on the grocery stores at the same time that the quality and quantity of food delivered to the stores was reduced, and many consumers starved,” U.S. Geological Survey Research Wildlife Biologist John Piatt said.
A recently published study said the world's oceans were warmer in 2019 than any other time in recorded human history.
Parrish said the massive amounts of carcasses washed ashore is an indicator of a huge change in the ecosystem.
Further research could explore the potential for future warming to cause similar die-off events.
“That’s why we can use a change in carcasses floating to shore as an indicator of something bad. In this case, a very large in terms of space and long-lasting in terms of years, shift in the marine ecosystem associated with a warming ocean,” Parrish said.