Member Highlight: Ecosystem Cascades Affecting Salmon

2017-08-07T11:50:02+00:00 August 7, 2017|
A common murre about to feed its chick an anchovy or sardine at the Farallon Islands rookery, July 2017. (Credit: Point Blue Conservation Science)

(Click to enlarge) A common murre about to feed its chick an anchovy or sardine at the Farallon Islands rookery, July 2017. (Credit: Point Blue Conservation Science)

Interpreting relationships between species and their environments is crucial to inform ecosystem-based management (EBM), a priority for NOAA Fisheries. EBM recognizes the diverse interactions within an ecosystem — including human impacts — so NOAA Fisheries can consider resource tradeoffs that help protect and sustain productive ecosystems and the services they provide.

(From Science Daily) — In the coastal ocean of California — seabird predators, forage fish on which they feed, and the survival of salmon out-migrating to sea are each of particular interest, and an improved understanding of their interactions could in turn improve the management of the ocean ecosystem.

For example, in the California Current, understanding the interactions between predator seabirds, forage fish in the coastal ocean and out-migrating salmon from San Francisco Bay could improve the understanding of salmon early survival in the ocean and a measure of the possible strength of the year class return.

In the Gulf of the Farallones, new research by scientists from NOAA Fisheries’ Southwest Fisheries Science Center, Point Blue Conservation Science, H.T. Harvey and Associates, University of California Santa Cruz, U.S. Geological Survey and the U.S. Fish and Wildlife Service found that the common murre, a small ocean seabird, can make a difference in the number of salmon that survive to return as adults. This is especially true when ocean conditions cause the murres to feed primarily on salmon and anchovy. The research has been published online in the Journal of Marine Systems, and will be included in the journal’s October print issue.

Large colonies of more than 500,000 common murres nest throughout the Gulf of the Farallones, offshore of San Francisco. In typical years, with nutrient-rich water welling up from the depths, the murres prey primarily on young rockfish around their offshore breeding sites.

When ocean conditions change, and the upwelling falters, young rockfish that are the typical prey for the murres become scarce. Then the murres switch, feeding instead on adult northern anchovies found closer to shore. That’s a problem for the young salmon entering the ocean at these near-shore locations, because the murres eat them too.

The finding documents one of the first examples of what biologists call “bottom-up” influences — changes at the base of the food web — causing “top-down” effects on West Coast salmon, such as an increase in predation by a species higher in the chain, in this case the common murres.

“This is the first example we’ve found involving salmon where bottom-up drivers are causing top-down impacts,” said NOAA Fisheries research biologist Brian Wells, lead author of the research. “The lack of upwelling affects salmon in a top-down way.”

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