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Study Details How Timing Of Phytoplankton Blooms off Alaska, B.C. Tied To Salmon Productivity
Posted on Friday, February 06, 2015 (PST)

The timing of spring phytoplankton blooms in southern Alaska and coastal British Columbia has been correlated to the productivity of pink salmon in a recent study.

 

The study sought to connect biological conditions in the ocean, specifically phytoplankton, when juvenile salmon arrive, with the productivity, defined as adults produced per spawner, of 27 stocks of returning adult pink salmon. Due to the similarity of the migration and where the fish feed in the water column when in saltwater, the researchers believe the findings very likely apply to sockeye salmon, with a weaker link to chum salmon, as well.

 

However, the correlation between the timing of the spring bloom and the productivity of the salmon is opposite depending on the location of where the bloom occurs along an east-west line that splits southeast Alaska and the sea off British Columbia.

 

“Our study provides evidence that an earlier spring bloom is associated with higher productivity for pink salmon stocks in Alaska and lower productivity for British Columbia stocks,” said Michael Malick, a PhD candidate in the School of Resource Management at Simon Fraser University in Vancouver, British Columbia.

 

Conversely, the productivity for the southern stocks off British Columbia is strongest when the bloom is later, the study says. It is widely thought that the first year a juvenile salmon is in the ocean is a critical period that has a strong influence on salmon abundance when they return to spawn as adults.

 

So the timing of this spring bloom in the ocean helps to explain the variability in returns of the salmon to their native streams to spawn, according to the study.

 

“Linking phytoplankton phenology to salmon productivity along a north/south gradient in the Northeast Pacific Ocean,” was published online Jan. 7, 2015, in the Canadian Journal of Fisheries and Aquatic Sciences (http://www.nrcresearchpress.com/doi/abs/10.1139/cjfas-2014-0298#.VNQKrp3F9qU).

 

Along with Malick, authors are Randall Peterman, professor emeritus, and Sean Cox, associate professor, both in the School of Resource Management at Simon Fraser University; and Franz Mueter, associate professor, School of Fisheries and Ocean Sciences, University of Alaska Fairbanks.

 

While salmon of any type don’t feed directly on phytoplankton when they enter the ocean, the spring bloom represents the base of the marine food chain and is an important driver of groups higher on the food chain, such as zooplankton, which pink and other species of salmon do feed on in the coastal environment, Malick said.

 

“For several reasons we discuss in the paper, it is likely that our results are transferable to chum and sockeye salmon, which tend to have similar diets and similar responses to changes in ocean conditions as pink salmon,” he said. “It’s not clear how our results would transfer to chinook and coho salmon though, which tend to have different diets (they tend to eat more fish) compared to pink salmon in coastal environments.”

 

The spring bloom in the coastal Northeast Pacific Ocean is driven by both large-scale climate patterns and regional and local-scale physical environmental conditions, the study says.

 

For example, the bloom in the Gulf of Alaska is “correlated with the onset of water column stability” and that is partly controlled by the strength of the Aleutian low pressure system. But the bloom is also driven by local conditions, such as sea surface temperature and sea surface salinity, in addition to being the result of freshwater runoff in the spring.

 

In this area, an earlier spring bloom is generally a more intense bloom and the timing and phytoplankton biomass “are strongly correlated with yield and productivity of certain marine populations,” the study says.

 

The early bloom in the northern area tends to happen in warmer, wetter years associated with the Aleutian low, higher zooplankton mass and increased salmon productivity.

 

While an earlier spring bloom is also associated with water column stability in the south, the stability is driven by thermal warming and reduced upwelling-favorable winds, also associated with the Aleutian low, the study says. However, these conditions are also associated “with increased predator abundances, reduced zooplankton biomass, and decreased salmon productivity,” the study says.

 

Changes to the spring bloom timing caused by natural climate variability or by climate change could potentially cause latitudinal shifts in salmon productivity, according to the study.

 

“It is generally recognized that a warming climate will lead to an earlier onset of spring conditions, including earlier timing of peak zooplankton biomass and outmigration of pink salmon,” the study says. If the two aren’t in sync, then it could lead to a northward latitudinal shift in pink salmon productivity.

 

Malick added that the timing of the spring bloom has been shown to be sensitive to changes in climate in some areas. That combined with the study results “suggests that climate change could have important implications for Pacific salmon if a warming climate causes systematic shifts in the timing of the spring bloom.”

 

“A major result of this research is that the timing of ecological events, such as the spring bloom, [is] important when trying to understand variability in Pacific salmon returns. While this outcome is unlikely to have a direct influence on the current management of wild Pacific salmon, it may have relevance for salmon hatchery management where release timing can be altered,” Malick said. “However, our focus in this study was on wild salmon, which limits our ability to provide recommendations for hatchery practices.”

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