Salmon Tipping Points: Data

Biometric analysis of historic Prince Williams Sound salmon populations over time.
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Ocean acidification has been identified as a stressor for aquatic species globally, including in the Northeast Pacific Ocean. Recent experimental work has shown negative effects of acidification on the growth and behavior of coho and pink salmon. Understanding the impacts of ocean acidification on the productivity of wild salmon populations, and how it interacts with other stressors such as climate change and increased competition due to hatchery supplementation, is critical for anticipating future population responses and for improving salmon management.

The Research Question

Is population productivity of pink salmon, measured as the number of recruits per spawner, affected by ocean acidification, climate warming, and competition with other salmon?

What We Did

We studied the combined effects of changes in ocean conditions and salmon abundances on the productivity of wild pink salmon in Prince William Sound (PWS), Alaska. We used 60 years of spawner escapements and harvest data to understand whether wild pink salmon productivity has been associated with changes in ocean acidification, temperature, competition among pink salmon, and interspecific competition with other species of Pacific salmon.

What We Found

  • Large-scale hatchery production negatively affects the productivity of wild pink salmon populations, likely via competition between wild and hatchery-reared juveniles in nearshore marine habitats.
  • Data show effects of climate and species competition on salmon populations. For example, the 1988/89 regime shift in the North Pacific Ocean was associated with changing temperature-productivity and spawner-productivity relationships.
  • Climate driven regime shifts affect the two broodlines differently, both in terms of recruitment and productivity
  • Negative effects of ocean acidification are not yet detectable in wild PWS pink salmon, although this result was based on a relatively short time series (1980-2013) of model-derived ocean acidification proxies.
  • Recruitment variation can be so large that it may obscure the effects of climate driven regime change

Why It Matters

Understanding the effects of ocean acidification, one of the major stressors of global change to aquatic species, is critical for projecting potential future impacts on salmon, and our results suggest that such population level impacts are not yet detectable. Our findings also highlight that the benefit of higher wild escapements for producing greater recruitment of wild pink salmon diminishes with increasing releases of hatchery fish. Collectively, these results can help improve salmon management and forecasts of population responses to global change.

Avenues for Future Work

Future work should extend regional ocean biogeochemical models to reconstruct historical ocean conditions prior to the 1980s and reevaluate potential influences of ocean acidification on pink salmon productivity using time series that extend further back in time and include recent years.

Publications

Non-stationary and interactive effects of climate and competition on pink salmon productivity. https://onlinelibrary.wiley.com/doi/full/10.1111/gcb.16049

Principle Investigators

Jan Ohlberger, University of Washington

Our Partners

Sponsors of the Salmon Tipping Points Project