Beach Surveys Show the Link Between Marine Heatwaves and Seabird Die-offs

The National Park Service works with the Coastal Observation and Seabird Survey Team (COASST) volunteers to document dead seabirds along the coast.

NPS/Stacia Backensto

More evidence shows the connection between marine heatwaves and seabird die-offs. This recent study, a multi-partner effort led by the University of Washington, used more than 90,000 surveys of 106 seabirds on more than 1,000 beaches conducted by the Coastal Observation and Seabird Survey Team (COASST). The study harnessed massive amounts of data from citizen science spanning the coast of California to northern Alaska.

Measuring the magnitude and timing of mortality events from 1993-2021, the authors were able to identify a change in the rate and magnitude of events related to marine heatwaves. Previously, massive seabird die-offs that likely exceeded 250,000 birds occurred about once a decade. But between 2014 and 2019, five events occurred at this magnitude and were linked to persistently warmer waters of the northeast Pacific Ocean.

The proximal causes of mortality for the seabirds varied, but were all related to marine heatwave conditions. Some species were impacted more than others, with murres, puffins, auklets, and shearwaters experiencing greater mortality than other species.

This is important because marine heatwaves, linked to climate change, are becoming more frequent and extensive.

For more information, see: Marine heatwaves caused mass seabird die-offs, beach surveys show, Hannah Hickey, UW News, July 6, 2023

Beach surveys were conducted by thousands of coastal residents and undergraduate interns in collaboration with the University of Washington, the Coastal Observation and Seabird Survey Team (COASST), the Aleut Community of St. Paul in Alaska; the U.S. Fish and Wildlife Service; Bird Studies Canada; the U.S. National Park Service; Moss Landing Marine Laboratories; the National Oceanic and Atmospheric Administration, Greater Farallones National Marine Sanctuary; and the Greater Farallones Association.

Marine bird mass mortality events as an indicator of the impacts of ocean warming

Abstract

The frequency and severity of marine heatwaves (MHWs), an emergent property of global warming, has led to large-scale disruptions to marine ecosystems. As upper trophic species, marine birds reflect shifts in trophic structure and stability; therefore, a sharp increase in marine bird mortality is a clear signal of ecosystem impact. In this study, we analyzed 29 yr (1993–2021) of beached bird monitoring data (~90 000 surveys) to identify marine bird mortality events throughout the Northeast Pacific and Alaska, USA, and examined linkages to ocean?climate variability. Mortality events were documented throughout the study period, but massive events (>500 km in extent, >10 carcasses km^–1) occurred infrequently (n = 5), with an unprecedented sequence from 2014?2019. Event characteristics, including encounter rate (carcasses km^–1), duration, and spatial extent, were positively related to prior-year averaged sea surface temperature anomaly, with event magnitude (product of encounter rate, extent, and duration) displaying a step-like transition, increasing 5-fold between +0°C and +1°C above baseline (1981–2010) temperatures. Mortality events occurred more frequently following MHWs, and a common sequence of mortality events (at 1–6 and 10–16 mo after heatwave onset) was observed in the California Current large marine ecosystem following 3 prolonged MHW events. Following the second wave of mortality at 10–16 mo after MHW onset, a consistent 16 mo period of depressed carcass encounter rates ensued. Given continued global warming, our results point to more frequent large-scale mortality events and the potential for a new lower carrying capacity for marine birds in the Northeast Pacific.

Jones, T., J. K. Parrish, J. Lindsey, C. Wright, H. K. Burgess, J. Dolliver, L. Divine, R. Kaler, D. Bradley, G. Sorenson, R. Torrenta, S. Backensto, H. Coletti, J. T. Harvey, H. M. Nevins, E. Donnelly-Greenan, D. L. Sherer, J. Roletto, and K. Lindquist. 2023. Marine bird mass mortality events as an indicator of the impacts of ocean warming. Marine Ecology Progress Series: HEATav8.