Warmer than average sea surface temperatures are expected to persist in the Gulf of Alaska through the spring of 2020 as a neutral Nino, exacerbating ecosystem conditions in the western Gulf still reeling from the extreme marine heatwave of 2014-2016.
An ecosystem status report released by NOAA Fisheries on Jan. 30 said sea surface temperature projections from the National Multi-Model Ensemble from NOAA’s Climate Prediction Center are for continued warm patterns such as those seen in 2019, but at a reduced magnitude.
The report documents how continued warm ocean temperatures are affecting the Gulf’s marine ecosystem and commercial fish stock productivity, with elevated ecosystem concerns documented for Pacific cod and arrowtooth flounder in the Gulf. Pacific cod stock levels were low enough to automatically result in a closure of a directed commercial fishery in 2020 while for arrowtooth flounder, already low fishing pressure on this stock did not warrant further catch reductions.
Pollock in the western Gulf may be experiencing more limitations in prey than those in the eastern Gulf, the report said. Further supporting evidence of below average foraging conditions is the poor condition or skinniness of Pacific Ocean perch, which have similar diets to pollock.
Federal fisheries biologists said precautionary measures were already incorporated into setting catch levels to address uncertainties for remaining stocks. The Alaska-wide sablefish stock assessment also documented elevated ecosystem concerns, prompting a 57 percent reduction in the biological catch level.
The extreme marine heatwave of 2014-2016, known also as “The Blob” was followed by a return of more typical temperatures in 2017 and 2018, but then in September of 2018 sea surface temperatures in the western Gulf shelf area crossed a temperature threshold and became a marine heatwave and that status remains, NOAA biologists said.
Sea level pressure patterns from late 2018 through the summer of 2019 brought high pressure over the Gulf, suppressing storms and contributing to development of warm sea surface temperatures similar to those of the “Blob” heatwave, particularly in summer months. Biologists noted that while the total number of days in heatwave status in 2019 was similar to that of 2015 there was proportionally more heat this past summer. That heat extended into the water column, especially in the western Gulf.
The coastal Gulf also had warmer than normal air temperatures and lower than usual precipitation, prompting drought conditions that normally have summer rain.
The ecosystem meanwhile is responding to the current heatwave in different ways.
During the winters of 2014-2015 and 2015-2016, warm temperatures impacted predators such as Pacific cod and murres. Then in the winter of 2018-2019, which was not quite as warm, ecosystem impacts may have been less severe, researchers said.
It is also possible, they said, that given declines in the Pacific cod and murre populations that the ecosystem structure may have changed since 2014 and 2016, resulting in different ecosystem impacts of elevated sea temperatures, including marine fisheries food sources.
In its 2019 Eastern Gulf of Alaska report card fisheries biologists made several observations, including that human populations in fishing communities in the eastern Gulf have remained stable since 2000, with minimal decadal changes. There were no significant population changes within large communities between 2010 and 2018.
The report also noted that total zooplankton density Icy Strait in 2019 was slightly below average and represented a slight decline from 2017 and 2018k suggesting about average foraging conditions for planktivorous fish, seabirds and mammals and an improvement relative to the below-average densities of 2013 to 2016. The overall copepod communities size also remained low, due to below average abundance of large copepods.
The western Gulf report card for 2019 flagged lower biomass of some and more in others, and that human populations in fishing communities in the western Gulf have increased since 1990, largely in urban areas.