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Factors Limiting Salmonid Production
The sustainability of salmonid populations in the Russian River watershed depends upon a variety of factors, including habitat conditions. During each life stage, an individual salmonid encounters a series of environmental factors that provide suitable, less-than-desirable, or unusable habitat. Essential habitat requirements are known as "limiting factors." Limiting factors are defined as environmental conditions that, if at sub-optimal levels, will prevent an organism from reaching its full biotic potential (Lincoln et al. 1998).
Large woody debris creates habitat complexity. The pool in the foreground and a riffle in the
background were caused by the large wood in the center of the image.
Limiting factors for anadromous salmonids include water temperature, gravel substrate, water quality, migration corridors, habitat availability, and estuarine conditions. Each salmonid species has different requirements and tolerances with respect to each factor, but generally, clean, cold water, moderately sized gravel, low turbidity, migration access, and the presence of instream large woody debris are necessary for sustainable populations
Moderately sized gravel and clean, cold water provide optimal
conditions for spawning for this coho.
In the Russian River watershed, human impacts including development and the introduction of exotic invasive species have changed stream ecosystems, resulting in less than optimal conditions for salmonids. Instream gravel mining removes gravel and changes substrate features. Timber harvest can cause temperature increases, sedimentation and a dearth of large woody debris. Urban, suburban, and rural development have resulted in water withdrawals, stream channelization, habitat removal and decreased water quality. Agricultural development may increase turbidity and remove riparian habitat. Additionally, dams for flood control and water storage have impeded migration passage. Now that the impacts of these and other activities are understood, efforts are underway to minimize their negative effects on salmonid populations and to ameliorate the legacy left over from past practices.
Today, erosion control measures that prevent sediment from
reaching creeks and streams are routinely implemented during public works and
other development projects.
Lincoln, R., G. Boxshall, and P. Clark. 1998. A Dictionary of Ecology, Evolution, and Systematics. Second Edition. Cambridge, UK: Cambridge University Press.
