A patch of unusually warm Pacific Ocean water off the coast of North America, dubbed “the Blob,” was responsible for a mass die-off of as many as 1.2-milllion common murres as well as countless other species, from small forage fish to baleen whales, researchers have concluded in a recent paper in the journal PLOS ONE.
The Blob started forming in late 2013 and by the summer of 2015 covered more than 4-million square kilometres—that’s roughly the size of the entire European Union. The temperatures within the mass were up to 2 to 3 degrees Celsius higher than normal. While that might sound great for swimming, the impacts on the food chain were devastating.
The biomass of phytoplankton, microscopic marine algae, was down to the lowest levels measured since 1997. “They’re the grazing grass that everything else feeds on,” says John F. Piatt, a research wildlife biologist with the U.S. Geological Survey in Anchorage, Alaska, and lead researcher on the report. “They’re the core food supply for smaller fish.”
Less plankton to graze on had a domino effect up the food chain, all the way to common murres, a member of the auk family found along Canada’s Atlantic and Pacific coastlines.
At the same time, the warmer waters increase the metabolism of cold-blooded fish—from anchovies to Pacific cod—meaning those species needed to eat more to survive, and were generally smaller and leaner. In short, food supplies for common murres were in drastically short supply.
While common murres are highly effective forage feeders—they can fly at speeds of 80 km/hour and have been recorded diving nearly 200 metres below the surface to catch prey—“their Achilles heel is that they have to eat 50 per cent of their body mass every day,” says Piatt.
In 2015 and 2016, tens of thousands of emaciated murre carcasses were found along the Pacific coast from California to Alaska. While die-offs and breeding failures are not unheard of with murres, the report noted that, “the magnitude, duration and spatial extent of this die-off…is unprecedented and astonishing.” Given that only a fraction of dead murres would likely have been found by beachcombing citizen scientists, the researchers extrapolated that anywhere from 500,000 to 1.2-million birds starved to death. That works out to 10 to 20 percent of the Pacific coast population.
Compounding the problem for the species is that between 2015 and 2017, the birds’ birthrate plummeted, with many colonies failing to produce any chicks at all. “They didn’t have the fat stores or knowledge of food supplies around them,” says Piatt. “Unless the food supply is topped up, they don’t breed.”
The warmer water temperatures that caused the Blob were attributed to four factors converging like a rogue wave: a strong El Niño current; warm waters from the Pacific decadal oscillation—an irregular, recurring pattern of warmer or cooler waters; a high-pressure system that was dubbed “the ridiculously resilient ridge” that helped elevate surface water temperatures and; finally, rising ambient temperatures from global warming. Piatt estimates that climate change may have been responsible for about 25 percent of the water temperature increase.
Of concern for cottagers is that on smaller lakes and ponds “the changes can be much quicker and more dramatic,” says Piatt. Regardless of the size of the waterbody, “Species are adapted for a specific water temperature. If the temperature changes too much, you’re going to lose those species.”