Seabird Die-offs in Alaska

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By Alaska Science Center July 22, 2024

Marine Heatwaves

A Global Issue

Beginning in 2015, large numbers of dead seabirds have been appearing on beaches in most marine areas of Alaska. Although seabird die-offs are known to occur sporadically (e.g. 1970, 1989, 1993, 1997/1998, and 2004) in Alaska, these recent die-offs have been distinguished from past events by their increased frequency, duration, geographic extent, and number of different species involved.

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Recent die-offs

Common Murre on the water in Kachemak Bay, Alaska — Common Murre (Credit: Sarah Schoen, U.S. Geological Survey)

The first large die-off occurred from spring of 2015 to spring of 2016 when about 47,000 Common Murres (Uria aalge), an abundant and important subsistence seabird species in Alaska, were discovered dying or dead on beaches and lakes across Alaska. The die-off was centered in the Gulf of Alaska but stretched all the way from southern California to the southeast Bering Sea. Total mortality was estimated to range from 0.5-1.2 million birds, marking the largest die-off of seabirds ever recorded in the Pacific Ocean.

Multiple die-off events of smaller magnitude have also occurred in Alaska since 2016, primarily in the Bering and Chukchi seas, including die-offs of Tufted (Fratercula cirrhata) and Horned (Fratercula corniculata) puffin, Thick-billed Murre (Uria lomvia), Crested Auklet (Aethia cristatella), Northern Fulmar (Fulmarus glacialis), and a few other species. For example, in summer 2019 over 8,500 Short-tailed Shearwater (Puffinus tenuirostris) were discovered dead in the Bering and Chukchi seas.

What is USGS doing about seabird die-offs?

Researchers at the USGS Alaska Science Center have been working in collaboration with many partner agencies, non-governmental organizations, universities and rehabilitation centers to investigate seabird die-offs. We conduct surveys to investigate the distribution and magnitude of die-off events, and we examine carcasses to determine the possible cause(s) of death. We are also trying to understand the potential role of harmful algal bloom toxins and are monitoring forage fish populations to better understand the availability and quality of seabird prey. Additionally, we study the effects of the die-offs on seabird reproduction and population size.

Short-tailed Shearwater carcasses on beach in Bristol Bay, Alaska — Emaciated Short-tailed Shearwater carcasses littered the beaches of Bristol Bay during the summer of 2019.

(Credit: Sarah Schoen, U.S. Geological Survey)

Why do seabird die-offs occur?

Most seabird die-offs occur when birds are not able to find, catch and eat enough food to keep up with their high energetic demands. Examination of carcasses following die-offs usually indicate that most birds have died of starvation. Die-offs often occur during the winter, when it is colder and requires more food to maintain body condition, and frequently follow storms, which can push birds away from their prey and make it harder to forage. Changes in prey availability owing to overfishing or competition for prey with other bird, mammal and fish predators can also result in die-offs. Other factors that can lead to die-offs include poisoning by harmful algal bloom neurotoxins and oil spills.

Are die-offs associated with marine heatwaves?

Marine heatwaves are characterized by unusually warm water that can extend over large areas of the ocean and last for long periods of time. Seabird die-offs have occurred at the same time as marine heatwaves in the North Pacific and Bering and Chukchi seas.

What happened to seabird prey during the North Pacific marine heatwave in 2014-2016?

The North Pacific marine heatwave in 2014-2016 was the longest marine heatwave documented at the time, with high sea surface temperatures recorded through multiple winters. During this period of unusual ocean warming, the availability and quality of prey resources decreased abruptly. For example, the occurrence of key forage fish species including Pacific capelin and Pacific sand lance declined in seabird diets. By summer of 2016 the energy content of Pacific sand lance was reduced by 89% compared to 2012-2013 when waters were cooler. Lower prey availability and lower prey quality likely explain why the majority of die-off seabirds starved during 2015-2016. It also appears likely that warm ocean temperatures increased the metabolic rates of large predatory fish like Pacific cod and walleye pollock, leading to a large increase in their consumption of prey also eaten by seabirds.