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Ecosystem Considerations 2017 Status of the Gulf of Alaska Marine Ecosystem
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2017
[PDF-7.39 MB]
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Description:The Gulf of Alaska in 2017 remained characterized by warm conditions although conditions have moderated since the extreme heat wave of 2014–2016. The PDO remains in a positive pattern but with lower amplitude. The freshwater runoff into the GOA appears to have been greater than normal during the fall of 2016 and somewhat less than normal in summer 2017, with implications for the baroclinic component of the Alaska Coastal Current. Mesozooplankton biomass measured by the continuous plankton recorder has often shown a largely biennial trend, however biomass remained greater than average in 2014 – 2016. Biomass trends can be influenced by ecosystem conditions and mean size of the community. This suggests that prey availability for planktivorous fish, seabirds, and mammals has been variable recently. The biennial patterns suggests a possible link with biennially varying planktivorous pink salmon abundance which have shown lower than expected marine survival for the 2015 and 2016 outmigration year classes. Copepod community size remained small for the fourth consecutive year. The prevalence of small copepods fits predictions of warm conditions favoring small copepods. This suggests that planktivorous predators may have had to work harder to fill nutritional needs from the numerous, but small, prey items. Bottom trawl survey biomass of motile epifauna was below its long-term mean for the first time since 2001. The increase from 1987 to 2001 was driven by hermit crabs and brittle stars, which continue to dominate the biomass. Octopus catches, which were record high in 2015, declined to a low not seen since 1990. Trends in capelin as sampled by seabirds and groundfish have indicated that capelin were abundant from 2008 to 2013, but declined in during the warm years of 2015–2016. Their apparent abundance coincided with the period of cold water temperatures in the Gulf of Alaska. Preliminary reports suggest that predators were again foraging on capelin in 2017. Fish apex predator biomass during 2017 bottom trawl surveys was at its lowest level in the 30 year time series, and the recent 5 year mean is below the long-term average. The trend is driven primarily by Pacific cod and arrowtooth flounder which were both at the lowest abundance in the survey time series. Pacific halibut and arrowtooth flounder have shown a general decline since their peak survey biomasses in 2003. Pacific cod has continued to decline from a peak survey biomass in 2009. Black-legged kittiwakes had moderate reproductive success in 2017 at the Semedi Islands, in contrast to the complete failure in 2015 for kittiwakes as well as other seabird species. Their reproductive success is typically variable, presumably reflecting foraging conditions prior to the breeding season, during, or both. In general, fish-eating seabirds had less successful reproduction in 2017 than mixed fish and plankton-eating seabird species. Modelled estimates of western Gulf of Alaska Steller sea lion non-pups counts were approaching the long-term in 2016, suggesting conditions had been favorable for sea lions in this area. However, preliminary estimates show a decline in the number of pups from 2015 to 2017 and declines in the number of non-pups in the Cook Inlet, Kodiak, and Semidi area. Human populations in the small (<1500 people) fishing communities in the western Gulf of Alaska have remained stable as a whole since 2000.
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