Habitat for Salmonids

Habitat for Salmonids

Coho salmon (Oncorhynchus kisutch) populations are estimated to be at less than 1% of their historic population size within California. Additionally Steelhead (Oncorhynchus mykiss) are listed as threatened by the Endangered Species Act (ESA). However, significant populations have been shown to be residing in the Golden Gate National Recreation Area (GOGA) and Point Reyes National Seashore (PORE). Due to this, these areas act as a stronghold against regional extinction. Therefore, there is a significant need for surveying and monitoring of these populations in these areas in order to protect and restore areas that salmonids may reside in since available habitat remains a limiting factor for species diversity. 

Recording Habitat Units

One crucial aspect of the Coho and Steelhead Monitoring Program (CSMP)’s basinwide approach within the San Francisco Bay Area Network (SFAN)’s Inventory and Monitoring program is identifying and establishing suitable habitats for salmonids through habitat surveying. Also known as habitat typing, these surveys utilize a metric stadia rod and measuring tape to break up habitat units based on the topography, cover, and overall composition of the area. The main types of habitat units are riffles, flatwaters, backwaters, scour pools, and mid channel pools. Riffles are the shallower, faster moving sections of a stream with rocks breaking up the water surface. Often, riffles are found at the top and bottom of pools and act as a form of transportation for aquatic organisms. Flatwaters are classified by relatively deep water (< 0.3m) with water flowing downstream in a uniform manner. Backwaters are areas similar to side channels except they only connect to the mainstream once, rather than twice. Additionally, backwaters are orientated as a countercurrent to the mainstream and can be visually described as the “thumb” of the stream. Backwaters may act as a refuge for aquatic organisms from predation or temperature changes. Scour pools are deeper areas where the stream runs against bedrock walls. These pools often have significant woody debris that make up the deepest portion of the pool. Mid channel pools are deep areas that run along the streambed with minimal scour along the thalweg with most of the pool covering over ⅔ of the channel. At each pool we measure the crest depth and maximum depth, using the difference to determine residual pool depth–an important measure of the geomorphic component of salmonid habitat. Another important characteristic recorded is the size and quantity of woody debris in the water within the habitat unit. Such debris ranges from 10cm to > 50cm, with different classifications at each increment including large woody debris and small woody debris jams. It is widely agreed upon that suitable salmonid habitat involves deep pools connected by riffles with large woody debris (20cm to > 50cm) within the water that salmonids can use for habitat, refuge, and rearing. 

Example of a Flatwater
Lunch on Pine Gulch
Large Woody Debris

Such an immense amount of data can be overwhelming and difficult to inventory. Nonetheless, with proper categorization followed by physical sampling such as electrofishing and snorkeling census counts, CSMP is able to illustrate the watershed as a whole. Furthermore, the data collected is used to determine O. kisutch and O. mykiss densities while also identifying habitat constraints on these threatened populations. .

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