As we mentioned in the Fall 2017 e-Focus
, Foothill Conservancy contracted with Cramer Fish Sciences
to carry out a fall-run Chinook salmon spawning habitat assessment of the Mokelumne River upstream of Pardee Reservoir. The assessment will enable the Upper Mokelumne River Salmonid Restoration Team we lead to make further determinations regarding reintroducing anadromous (river-hatched, ocean-going) fish to the upper Mokelumne River. The field work for the assessment was completed last fall.
The Mokelumne salmon team is now finalizing the report, which identifies reaches of the river that contain habitat sufficient for Chinook salmon to spawn and juveniles to survive. The study suggests that if fall-run Chinook salmon were introduced above Pardee Reservoir, they would gain access to about 17 miles of historic spawning habitat. Of that, about 13.7 miles were found to have potential to support both adult and juvenile Chinook salmon.
The report evaluates the section of river from Bald Rock Falls above Roaring Camp down to Pardee Reservoir. In general, the scientists concluded that habitat quality increases as the river moves downstream. The reaches above Roaring Camp, while likely to have some small pocket spawning opportunities, are dominated by bedrock outcrops and a lower concentration of the gravel and cobble patches and sizes that salmon prefer for building their nests, called reads. However, as the river moves downstream, the amount of gravel available for spawning increases, with the best habitat found in portions of the Electra and Middle Bar reaches.
In two of the surveyed reaches of the river where habitat was considered marginal-to-poor due to gravel deficiencies and historic degradation from mining and hydropower operations, the study reports that opportunities for restoration or enhancement of spawning and rearing habitat exist.
The study also points out that the reintroduction of salmon to historical habitats on the Mokelumne may have significant cultural, economic and ecological benefits. Salmon attract people for viewing or fishing, which could bring economic benefits from ecotourism. In addition, the scientists claim that reintroduction of salmon to the watershed could provide positive ecosystem-level impacts by restoring marine nutrients to the river and watershed.
As the study says, “Salmon are considered ecosystem engineers because their spawning activities can have profound impacts on everything from sediment distributions, intergravel permeability, and nutrient dynamics, to macroinvertebrate community structure. Salmon carcasses could provide a long-lost source of nutrients, including marine-derived nitrogen, to the upper watershed. In addition, salmon carcasses would also provide a high-calorie food source for local predators and scavengers including otters, bald eagles, and black bears.”
“This is exciting news,” said Watershed Conservation Associate Reuben Childress. “Our team and partners can now use the data and findings in this report to calculate how many fish this segment of the river may be able to support in the future, and where in these reaches there may be restoration opportunities. We may be able to improve fish habitat not only for potentially reintroduced Chinook salmon, but also for the existing salmonid species in the river, such as introduced Kokanee salmon and brown trout, and native rainbow trout.”
We’re excited to see the potential for restoring salmon to the Upper Mokelumne River moving forward, and we look forward to getting our community involved in future efforts to make this happen. We’ll keep you up to date as the project moves ahead, but for any questions, or comments, feel free to give Reuben a call in the office at 209-223-3508, or send him an e-mail.