DURHAM, N.C. – A recent paper by a Nicholas School PhD candidate examining dams’ impacts on endangered spring-run Chinook salmon in the rivers of California’s Central Valley could serve as a cautionary tale to policymakers, scientists and resource managers currently embroiled in a debate about the construction of new dams in the region.  

The paper, “Directed Connectivity Among Fish Populations in a Riverine Network,” was published in the September 3 online issue of Journal of Applied Ecology.  

It uses analytical techniques from network science to study the relative importance of individual populations of salmon within the valley and to examine how the addition of large water-storage dams blocked access to habitat and fragmented these populations over time, says Robert S. Schick, a doctoral candidate in the University Program in Ecology.

Schick wrote the paper with Steven T. Lindley of the National Oceanic and Atmospheric Administration’s Southwest Fisheries Science Center in Santa Cruz, Calif.

The paper has become topical thanks to a recent $9 billion bond proposal by Calif. Gov. Arnold Schwarzenegger to construct two new dams and expand a third in the environmentally fragile Sacramento-San Joaquin River Delta.

Schwarzenegger believes the new dams could help alleviate water-shortage problems associated with frequent droughts in the region. Some money from the bond would be used to pay for conservation improvements such as increased seasonal river flows to aid Delta smelt, salmon and other species of fish that live in the delta area or swim upriver to spawn. 

After first establishing the historical structure in the San Joaquin and Sacramento River systems, Schick and Lindley studied the progressive impact of dams on spatial connectivity among Chinook populations. In addition, they established the spatial structure of the current extant populations in the Central Valley.

“We were able to document reduced spatial and demographic connectivity between salmon populations in the rivers as a result of the dams, and we identified several populations that had become vulnerable to, and dependent upon, production in fish hatcheries,” Schick says.

In addition to identifying problems linked to the dam, their network analysis identified potential solutions.

“By highlighting the demographic impact of individual populations, network science allowed us to propose a recovery pathway for spring-run Chinook salmon in the Central Valley,” Schick notes. “This pathway highlights dams whose removal would have the greatest positive impact on the species.”

The methods he and Lindley employed to do their analysis can be applied broadly across taxa and systems, he adds, and would be useful tools for scientists, policymakers and environmental managers in California who want a better understanding of the structure and function of impaired ecosystems.

“We feel our work documents the harmful role of dams on spring-run Chinook salmon and can be used as a cautionary tale,” he says.