Aquatic Macrophyte Encroachment in Chinook Salmon Spawning Beds: Lessons Learned from Gravel Enhancement Monitoring in the Lower Mokelumne River, California

Abstract

We studied the effects of colonization of the spawning habitat of Chinook salmon Oncorhynchus tshawytscha by rooted aquatic macrophytes in a regulated central California river. At least seven species of plants invaded four spawning sites below the lowest nonpassable dam during an extended period of relatively low instream flows. The depths associated with aquatic vegetation were similar to those used by spawning salmon. Velocities were significantly lower where plants took root. As plants expanded over riffles, spawning females avoided those areas. We observed significant overall reductions in vegetation after flow events predicted to be of sufficient magnitude to mobilize substrates. However, the proportion of vegetation dislodged did not strongly correlate with the proportion of substrate that we predicted would mobilize. Even so, in areas where vegetation was reduced, use by salmon spawning subsequently increased. While shear stress may be part of the overall predictive equation for macrophyte control at spawning sites, other factors must be studied before a specific management action can be recommended.

Juvenile Chinook salmon,Oncorhynchus tshawytscha,growth and diet in riverine habitat engineered to improve conditions for spawning

“…Consequently, many agencies tasked with restoring populations have attempted to enhance spawning potential by reconfiguring entire channels and/or depositing sediments considered favourable for reproductive adults and incubating eggs (Kondolf et al. 1996; Kondolf 2000; Merz et al. 2008).…”

“…Spawning habitat degradation in natal rivers induced by hydraulic mining, dams and water diversion is believed to be a principle impediment to salmon recovery (Yoshiyama et al 1998(Yoshiyama et al , 2000Zeug et al 2011). Consequently, many agencies tasked with restoring populations have attempted to enhance spawning potential by reconfiguring entire channels and/or depositing sediments considered favourable for reproductive adults and incubating eggs (Kondolf et al 1996;Kondolf 2000;Merz et al 2008). The quality of such engineered habitat for juveniles rearing in their natal rivers remains largely unknown, yet elucidating the effects of large-scale spawning habitat remediation on juvenile salmon rearing conditions is necessary to gauge the value of such management actions holistically, as parr growth rates may influence survival during later life stages (Quinn & Peterson 1996;Moss et al 2005).…”

Aquatic Invasive Species Change Ecosystem Services from the World's Largest Wild Sockeye Salmon Fisheries in Alaska

“…Sudden collapses remain unexplained but have been observed throughout Europe (Simberloff and Gibbons 2004;Mjelde et al 2012). In regulated rivers in its native range, Elodea has been found to encroach on spawning sites of Chinook salmon (Oncorhynchus tshawytscha) (Merz et al 2008).…”

“…The logistic growth model differs from commonly used population models like the Ricker model in how it describes population change at very high population densities (Ricker 1975). In the logistic growth model, growth at very high densities declines more rapidly, an assumption supported by the encroachment effects of Elodea observed on spawning adult salmon (Merz et al 2008). In addition, the limiting environmental conditions of Elodea's encroachment into salmon spawning beds is captured by the harvest limitation (K) in the logistic model but is lacking in an exponential growth model.…”

What are the impacts of flow regime changes on fish productivity in temperate regions? A systematic map protocol

“…For example, Haxton et al [16] found that the relative abundance of lake sturgeon was lower in regulated rivers than in unregulated rivers in Ontario. Low flows resulting from dam construction in California were found to increase the growth of aquatic plants and thereby decrease Chinook salmon spawning habitat availability [17]. Fish abundance, demographic parameters, and diversity were found to consistently decline in response to both increases and decreases in flow magnitude (reviewed in Poff and Zimmerman [13] but also see Webb et al [18]).…”