PORTLAND, OR – The Pacific Northwest Waterways Association today released a review of scientific literature which the group says confirms that data is lacking to confirm the delayed mortality effects of the Lower Snake River dams on fish listed on the Endangered Species List. Delayed mortality is the scientific hypothesis that proponents of dam breaching rely upon to justify the removal of the four dams, PNWA says. However, as demonstrated in the report authored by fisheries scientists at Mount Hood Environmental, significant questions remain about the concept’s mechanism and magnitude.
PNWA Executive Director Heather Stebbings says they want the region to truly understand the science on this matter, and where the gaps in information might be.
MHE reportedly examined hundreds of scientific papers produced over a 30-year period and ultimately concluded that evidence supporting delayed mortality is contradictory and inconclusive.
“While there is some evidence to support the idea that the Federal Columbia River Power System projects could influence ocean survival, there is also a significant body of literature suggesting that the observed effects are caused by other explanatory variables, such as fish size, distance traveled, and ocean conditions,” PNWA says.
“Snake River salmon and steelhead abundance depends on many factors,” according to Ian Courter, senior scientist with MHE, “including tributary and estuary habitat conditions, predation, fisheries, and mainstem hydropower dams. We found that delayed mortality may be occurring, but mechanisms are not well-defined, and the magnitude is unknown. Future research should focus on these two key uncertainties to determine whether removal of the LSRD would significantly increase adult fish returns.”
Looking across all of the data, MHE identified three pathways that merit further investigation to address the possible effects of delayed mortality: examining Snake River salmonids for nonlethal injuries when they arrive at the Columbia River estuary to model the potential effect of stress and injury from dam passage; analyzing when juvenile Snake River salmon and steelhead arrive at the estuary; and understanding what relationship may exist between estuary conditions and fish survival in the ocean, PNWA says.
Stebbins adds that after 30 years of research, there are many significant questions that remain unanswered regarding the theory of delayed mortality, and they can’t ask policymakers to make catastrophic decisions such as dam breaching without having all of the information.
For the full literature review, click here.
