Habitat Availability / Quality

Alluvial riparian corridors have been mapped for several streams in Santa Cruz County. This is important for assessing how habitat conditions may be potentially impacting salmonid production.

Importance to Salmonids

While specific habitat requirements differ throughout the salmonid life cycle, a diversity of habitat types is required for all stages. Streams composed of a variety of habitats, such as pools, riffles, and flat water, provide productive salmonid spawning and rearing habitat. In-stream structural elements are required to create microhabitats and maintain hydrologic and geomorphic complexity. Large and small woody debris, root wads, undercut banks, boulders, overhanging terrestrial vegetation, aquatic vegetation, and bedrock ledges provide shelter from predators, territorial niches, foraging areas, and resting habitat. These structural elements also create heterogeneous stream flow, increased pool development, and enhanced gravel retention. For example, when large woody debris (LWD) creates a channel obstruction by resting mostly perpendicular to the flow, plunge pools may be created. Pools are created when the stream passes over the LWD and drops into the stream bed below, scouring out a depression (Flosi et. al 1998) and by loss of bank stability and complexity due to a variety of land use practices. LWD presence is critical to creating habitat diversity, cover, pools, and to collecting and retaining sediment.

Habitat complexity creates productive invertebrate habitat by providing nutrients, trapping nutrient inputs, and providing suitable substrates. Development and maintenance of habitat diversity and in-stream structural elements in unconfined alluvial reaches requires mature streamside vegetation. Access to suitable habitat may vary seasonally, and migration patterns often enable salmonids fish to reach spawning or rearing ground that may be inaccessible for part of the year. Access to upstream habitat may be cut off during summer months, but this higher elevation habitat can provide excellent rearing habitat that will be reconnected the following winter. Human-made barriers inhibiting migration during any season can limit access to these important habitats (see Migration Corridors below).

Human Impacts

To increase land use and protect property, stream modifications have been implemented in many watersheds – resulting in the construction of dams and levees, the straightening of stream courses, and clearing of native vegetation to increase drainage rates and prevent organic material from blocking bridges and culverts. Land and road development also results in stream modification with governmental and private landowners armoring stream banks to confine channels and control erosion. This type of infrastructure protection and flood control is evident along the San Lorenzo River in downtown Santa Cruz. The modification of in-stream flows may also have a significant effect upon habitat availability and quality – both in terms of access to habitat and the formation of in-stream geomorphic features such as pools. The loss of channel complexity, cover, bank stability, and presence of pools has adversely affected spawning and rearing habitat. Channel condition and complexity have been dramatically altered through most of the watershed by channelization, loss of LWD, and associated pools.

Reference

Flosi, G., S. Downie, J. Hopelain, M. Bird, R. Coey, and B. Collins. 1998. "California Salmonid Stream Restoration Manual. Third Edition." State of California Resources Agency, California Department of Fish and Game, Inland Fisheries Division. 495 pp. View on-line source.

Local Reference

Lassettre, N., and M. Kondolf. 2000. Process-Based Woody Material Management at the Basin Scale: Soquel Creek, CA. In Proceedings of the Conference on Restoration and Management of Coast Redwood Forests: Jackson Demonstration State Forest, edited by W. H. Russel and C. Winslow.

General References

California Department of Fish and Game (CDFG). 2002. "Status Review of California Coho Salmon North of San Francisco." Report to the California Fish and Game Commission. 336 pp. View on-line document.

Lassettre, N.S. 1999. "Annotated Bibliography on the Ecology, Management, and Physical Effects of Large Woody Debris (LWD) in Stream Ecosystems." Department of Landscape Architecture and Environmental Planning, University of California, Berkeley. Prepared for the California Department of Forestry. View on-line source.

Opperman, J.J. 2002. Anadromous Fish Habitat in California's Mediterranean-Climate Watersheds: Influences of Riparian Vegetation, Instream Large Woody Debris, and Watershed-scale Land Use. PhD Dissertation, University of California, Berkeley.

Back to top