Spawning Habitat

There are two main impacts on spawning habitats that can occur: the elimination of migratory access and degradation of habitat.

Fish obstructions can block access for fish caused by road construction, instream activities, slope destabilization and altered hydrology. Common problems that occur are improper culverting of stream during road construction. Culverts have a smaller cross-sectional area than the natural stream, water flows faster through shallow areas in culverts, which prevents fish moving upstream. Fast moving water also causes erosion and downcutting. This may result in vertical drops at the end of the culvert, making it impossible for fish to travel through it. Culverts can also become blocked due to accumulation of woody debris.

Road construction near streamsides can lead to erosion of road fill material. This can lead to a narrower stream corridor with a steeper gradient and higher velocities that restrict fish passage. Roads also isolate areas that can be overwintering habitat.

Logging along streamsides causes erosion due to unstabilized sediment, which accumulates in streams. Removing vegetation from an area increases volume and the rate of runoff into streams. Fine sediments deposited from erosion fills interstitial space between gravel, which impedes redd construction and can suffocate eggs. This will also displace aquatic invertebrates, an important food source for salmonids. Clearing of riparian vegetation typically results in destabilization of the channel banks, loss of cover and elimination of the primary source of large woody debris, which are crucial for entrapment of spawning gravel.

There are many different considerations when restoring spawning habitat. The primary consideration is the target salmonid species requirements. These include gravel, current flow and water depth. Spawning habitat can be improved or created by cleaning existing gravel, placing new gravel, and/or creating gravel catchment structures. Gravel catchment structures include full and partial-spanning structures such as boulder clusters, weirs (also called sills), grade control measures, and wing deflectors (also called opposed deflectors or groynes). Bank stabilization work is often required prior to starting any spawning bed restoration.

References:

Slaney, P.A. and Zaldokas, D. Eds. 1997. Fish Habitat Rehabilitation Procedures. Watershed Restoration Technical Circular No. 9. Watershed Restoration Program. Ministry of Environment, Lands and Parks. Vancouver, B.C.

The Streamkeepers Handbook: a Practical Guide to Stream and Wetland Care. Module 14. 1995. Community Involvement Division. Salmonid Enhancement Program. Department of Fisheries and Oceans. Vancouver, B.C.

Stream Corridor Restoration. Principles, Processes, and Practices.