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Biological Monitoring

What we do

Snorkel surveys

Snorkel surveys help to determine the abundance and distribution of fish in local streams.  Most RCD surveys focus on juvenile steelhead and salmon; however, we also collect data on other species when possible.  Snorkel surveys are a non-harmful method for accurately determining how many fish are within a given reach of stream, their preferred habitat associations, and their distribution within the stream system. 

Estimating juvenile salmonid abundance and distribution, both within a stream and at a watershed scale, provides important information on population trends and serves to focus restoration activities where they are most needed. Not all streams within a watershed provide equal habitat for salmonids.  At the stream level, some reaches may be critically important while other areas may serve only as migration routes or be too steep to provide habitat.

 

The Friends of the Napa River coordinated a snorkel survey of much of the Napa River watershed in 2001 and 2002. 

 

Methods

We generally follow the Hankin-Reeves methodology, which is based on partitioning a stream into a series of habitat units and randomly sampling each habitat type at regular intervals. 

• Three habitat classes are established within the study reach: riffles, pools, and glides.  Riffles are areas of deposition formed during high flows, pools are areas of stream scour during high flows, and glides are areas which are neither riffles nor pools. 
• All habitat units must be longer than the stream is wide and must be separated by a distinct hydraulic break. 
• The length and width of every snorkeled habitat unit is measured or estimated.
• Two biologists walk upstream and snorkel dive habitat units as they are encountered: every 5th pool, every 8th glide, and every 10th riffle. 
• Observations are recorded on waterproof notepads.
• Surveys continue upstream until fish are no longer observed, the stream goes dry, a barrier to spawning migration is reached, or landowner access runs out.
• Fish density is estimated from measurements of habitat area and fish counts
• Steelhead densities can be extrapolated to the reach or stream scale where habitat data are available.

Snorkel Surveys

• Suisun Creek Predatory Fish Species Inventory and Juvenile Steelhead Distribution Study - 2008
• Central Napa River Watershed Project - 2005 (Streams surveyed: Bale Slough, Bell Creek, Canon Creek, Napa River, Rector Creek, and Soda Creek)
• Water for Fish and Farms Project – 2007, 2008 - York Creek, Carneros Creek, Redwood Creek
• Napa River Salmon Monitoring Project – 2006, 2007, 2008 – Napa River