Around 62,000 common murres were washed up on the coast of the Pacific Ocean between 2013 and 2016, but up to a million birds are thought to have died.
Scientists said that warmer sea waters, known as the 'blob', led to a shortage of the fish for the birds to feed on.
New findings published in the scientific journal PLOS One, suggest that the birds most likely starved to death due to a 1,000 mile area of warmer water that affected the north-eastern Pacific between 2013 and 2016.
The higher water temperatures affected food supply for the birds. Diminishing supplies of plankton led both to a drop in the population of the smaller fish eaten by the birds and increased competition from other predators.
"Imagine panicking about any emergency and everyone rushing to the supermarkets to stock up, and at the same time, delivery trucks stop supplying to shops as frequently," explains Julia Parrish, a researcher at the University of Washington and one of the authors of the report.
"Beyond the sea wave, what happened was a squeeze on the ecosystem: fewer forage fish, more small prey and a sharp increase in competition with other large predators like Pacific cod,” she continued.
The common murre is a bird that usually spends a substantial part of its life at sea, only moving to the coast during the breeding season. Normally you will see hundreds and even thousands of couples gathering along the coastline during the mating period. Unfortunately the views along the coast between California and Alaska in 2015-2016 were altogether different. Around 62,000 murre carcasses were found, tens of thousands more than in previous years. Scientists say that the actual number dead is likely to be around one million as only a small number of birds that die at sea are normally washed ashore.
There are now also concerns that this devastation is likely to be repeated, as scientists warn of a new ‘blob’ forming.
"The case of the common murre was unprecedented in magnitude," explains John Piatt, a research biologist at the Alaska Science Center. "It is surprising, alarming, a red flag warning of the tremendous impact that sustained oceanic warming over time can have on the marine ecosystem".
2019 saw ocean temperatures reach record heights. Using climate projection models, specialists are already warning that sea-level heat waves will be forty times more frequent by the end of the century than they are now. These changes are a direct result of climate change.
Julia Parrish concluded, "As well as the massive mortality of species as emblematic as the puffin, these scenarios show us that ocean warming will totally change the ecosystems, and the environment in which sea birds will have to survive within will be very different moving forward."
Reference: Piatt et al 2020. Extreme mortality and reproductive failure of common murres resulting from the northeast Pacific marine heatwave of 2014-2016. PLOS ONE doi.org/10.1371/journal.pone.0226087.