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Research focuses on importance of first year for Salmon


August 19, 2013

Juvenile salmon“Spatial diversity” in the first year of life can protect an entire salmon species from the effects of large-scale forces such as climate change and the operation of hydroelectric dams, according to a new NOAA Fisheries research article published last week.

The researchers liken species’ prospects to that of financial investment portfolios, which balance risk.

“Managers understand that div-ersity is important for maintaining healthy fish populations, but they need to know where to focus their efforts,” said Jim Thorson, a NOAA fisheries biologist and lead author of the study.

“Understanding what life stage conveys that stabilizing ‘portfolio effect’ is the golden ticket. In this case, it’s the parr stage.” Parr are juvenile salmon living in freshwater streams during their first year of life.

Contributing to the article, “Spatial variation buffers temporal fluctuations in early juvenile survival for an endangered Pacific salmon,” were Mark D. Scheuerell and Eric R. Buhle,, also of NOAA’s Northwest Fisheries Science Center in Seattle, and Timothy Copeland of the Idaho Department of Fish and Game.

The findings are reported in a study published online Wednesday in the Journal of Animal Ecology, a peer-reviewed scientific journal. Up until now, other high-profile studies of the portfolio effect in Pacific salmon have all focused exclusively on adult abundance. There had been no evidence of a similar effect in salmon survival during early freshwater life stages such as eggs and parr.

“In addition to refining our understanding of the portfolio effect, this work helps scientists better understand and predict survival in various stages in the life of a salmon,” according to the researchers.

In the study, scientists from NOAA Fisheries and Idaho Department of Fish and Game used a new set of information on the parr life stage, culled from 25 years of data from 15 different Snake River spring/summer chinook populations in central Idaho. The Snake River spring/summer chinook stock is listed as threatened under the federal Endangered Species Act.

Combining these new data with novel mathematical models led the researchers to conclude that the likelihood that a young salmon would survive during its first year depended in large part on where it was. Juveniles in some streams did better than their cousins in different streams.

And not only did winners and losers vary from place to place, but from year to year. This variability – some salmon survive and some do not – actually helps protect the overall population from large forces like climate change and hydropower operations that affect them all.

“We conclude that spatial variation decreases interannual changes in overall juvenile production, which suggests that conservation and restoration of spatial diversity will improve population persistence for this metapopulation,” the study abstract says.

“However, the exact magnitude of spatial buffering depends upon demographic parameters such as adult survival that may vary among populations and is proposed as an area of future research using hierarchical life cycle models. We recommend that future sampling of this metapopulation employ a repeated-measure sampling design to improve estimation of early juvenile carrying capacity.”

“This study represents a sea change for understanding salmon life cycles,” Thorson said. “Our analysis is based on more realistic data for populations during the first year of life and a state-of-the-art model. Now, we have vastly improved our ability to see how this group of salmon responds to changes in its environment over time.”

Life-cycle models are used extensively by scientists to address a broad range of questions related to Pacific salmon listed under the ESA, such as how harvest policies, habitat restoration and climate change affect population sizes and risks of extinction. Many of these models rely on data from other regions, or even other species, because more specific information simply isn’t available.

Such information gaps can prevent an accurate assessment of natural and human-caused factors affecting the survival of juvenile salmon.

The data collection efforts conducted as part of this study were funded by the Bonneville Power Administration.

Image above: “Spatial diversity” could be very important to the lives of juvenile salmon.


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