Impact of Pacific Heat Wave Lingers in Gulf of Alaska

A marine heat wave that hit coastal waters from California to Alaska from 2014 to 2016 is still impacting the Gulf of Alaska, leaving fisheries’ researchers uncertain about whether the ecosystem will ever revert to pre-heat wave conditions.

Their concerns are summarized in a new NOAA Fisheries study released in mid-March that offers a comprehensive and quantitative look at initial and lingering effects of the eastern Pacific Ocean heat wave.

“As of 2019, the Gulf of Alaska ecosystem had yet to recover from the effects of this major heat wave,” said Rob Suryan, program manager for the Alaska Fisheries Science Center and lead author on this study.

From 2012 to 2016 the percentage of global ocean experiencing strong or severe heat waves rose from 30% to nearly 70%. Researchers have also documented increases of disturbance to marine ecosystems, biodiversity and ecosystem services associated with marine heat waves.

NOAA Fisheries said that it hopes to resume its assessment of this ecosystem in 2021, since it was unable to conduct several key research surveys in 2020 because of restrictions imposed prevent the spread of the global novel coronavirus pandemic.

Understanding how marine ecosystems respond to cyclical, linear or random environmental change or their additive effects is an important challenge in marine ecology and resource management. The report notes that it is critical for scientists to be able to understand and predict species responses, to help resource managers manage commercial, subsistence and recreational fisheries and protect marine mammal species in Alaska.

What needs to be done next is to identify the mechanisms that cause species abundance fluctuations, Suryan said.

“For instance, understanding what forage fish and zooplankton species do well or poorly when water temperatures are warmer is critical for understanding how the marine mammals, seabirds and commercial fish stocks that feed on them will fare in this same environment,” he explained.

It was found that about half of the ecosystem indicators showed an abrupt change during, and a prolonged response after, the heat wave ended. NOAA Fisheries staff who prepare annual ecosystem status reports for fisheries resource managers, even in 2020, found that some Gulf indicators had yet to recover.

Researchers said species with primarily negative responses to the heat wave included forage fish, adult groundfish, pinnipeds and commercial fish, especially Pacific cod and sockeye salmon.