New research reveals ecosystem cascades affecting salmon

August 1, 2017, NOAA Headquarters
Common murres flying with forage fish (likely anchovy) in their mouths near their breeding ground on the Farallon Islands off San Francisco. 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.

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.

The murre colony on the Farallon Islands off the California Coast, as viewed from a research study blind atop Shubrick Point, July 2017. Credit: Point Blue Conservation Science

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 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."

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

The new research shows that salmon survival drops sharply in the years when lead the murres to prey on anchovy and salmon. Even in years when the murres are preying on anchovy, salmon comprise less than 10 percent of the diet of the murres; but the impact can be a significant factor in the survival of salmon. The research concludes that predation by the seabirds can make a difference in the number of salmon that survive to return as adults.

The salmon affected are primarily fall-run Chinook, which are the primary species supporting salmon fisheries off the California Coast. The research helps reveal the complex relationships between species and their environment, which in turn helps NOAA Fisheries anticipate and respond to changes that affect fish, birds and people.

For example, the murres preyed heavily on anchovy and salmon in 2005, which likely contributed to the collapse of the California salmon fishery in 2007 and 2008, the researchers found. Congress appropriated $170 million in disaster relief for fishermen affected by the collapse.

NOAA Fisheries managers can use the details to make better decisions about how best to protect and manage marine species.

"Understanding the dynamics behind these connections can help us anticipate impacts to , which are very important both economically and environmentally," said John Field, a research fisheries biologist at the SWFSC in Santa Cruz. "That can help fisheries managers make smart and informed decisions about how to manage these species into the future."

Explore further: Anomalous ocean conditions in 2015 may bode poorly for juvenile Chinook salmon survival

More information: Brian K. Wells et al, Environmental conditions and prey-switching by a seabird predator impact juvenile salmon survival, Journal of Marine Systems (2017). DOI: 10.1016/j.jmarsys.2017.05.008

Related Stories

Salmon fishing season at risk in Calif.

March 13, 2008

U.S. officials are considering canceling the 2008 salmon fishing season in California and Oregon because of a dramatic decline in salmon population.

Recommended for you

A world of parasites

May 25, 2018

Alex Betts, Craig MacLean and Kayla King from the Department of Zoology, shed light on their recent research published in Science, which addressed the impact that parasite communities have on evolutionary change and diversity.

Bumblebees confused by iridescent colors

May 25, 2018

Iridescence is a form of structural colour which uses regular repeating nanostructures to reflect light at slightly different angles, causing a colour-change effect.

A better B1 building block

May 25, 2018

Humans aren't the only earth-bound organisms that need to take their vitamins. Thiamine – commonly known as vitamin B1 – is vital to the survival of most every living thing on earth. But the average bacterium or plant ...

Plant symbioses—fragile partnerships

May 25, 2018

All plants require an adequate supply of inorganic nutrients, such as fixed nitrogen (usually in the form of ammonia or nitrate), for growth. A special group of flowering plants thus depends on close symbiotic relationships ...


Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Aug 02, 2017
I find this article very interesting since I am a commercial fisherman. I am curious as to how it was determined that the Common Murre was eating salmon smolts. I believe it can happen but have a hard time believing Murres are responsible for the collapse of our salmon populations to any measurable extent. Can you please reveal your data source or provide a link to the research.

Thank You.
not rated yet Aug 02, 2017
edso, here is a PDF of the Abstract, http://www.scienc...a%3Dihub It comes down to the fact that generally Murres feed farther to sea and tend to eat upwelling rockfish, when seasons are bad for the rockfish, the murres feed on anchovies and smelt instead, and get a percentage of salmon smolt, this was found by comparing stomach contents and watching what parent murres were feding their young. While the percentage was only up to as much as 10% of their feed being salmon smolt, it is still a very heavy toll on the outgoing run.

I am in WA State, and enjoy salmon fishing myself, and I can see how this can affect localized populations, in this case the runs from the San Francisco Bay or the Russian River runs, where the San Francisco runs are impacted more easily by close-feeding birds and areas where, like the Russian River, there is not a huge area that is drained, and so there are not that many smolt to begin with, comparatively,
1 / 5 (1) Aug 04, 2017
Hatchery practices that pollute salmon runs with aversive (DON'T BREED HERE, WOW, IT IS WAY TOO CROWDED!) pheromones are responsible for poor predator avoidance behaviors as well as run abandonment. Shutting all hatcheries down entirely to allow natural processes to revive is the only way to recovery, since hatchery management is too intransigent and stupid to change their crazy, destructive practices.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.