Beamer, E.M., Jackey, W.T., Marks, D., Teel, D., Kuligowski, D. and Henderson, R., 2013. Juvenile Chinook Salmon Rearing in Small Non-natal Streams Draining into the Whidbey Basin. Skagit River System Cooperative, La Conner, WA. pp. 74.

We electrofished 63 small coastal streams draining into the Whidbey basin for juvenile Chinook salmon presence. The small streams sampled ranged in watershed size from 3 to 1,862 hectares and had channel slopes ranging between <1% to 38% for the electrofished reaches. Bankfull channel width of the electrofished stream reaches ranged from 0.8 to 6.9 meters.
In 32 of the 63 streams we found juvenile Chinook salmon present on at least one of the 474 sampling event days over the six year study period (2008 – 2013) in which we caught a total of 1,879 juvenile Chinook salmon. Juvenile Chinook salmon presence rates ranged from 0% to 100%, depending on stream. Most juvenile Chinook salmon were caught in the months of January through May each year. Juvenile Chinook salmon body size found in the small streams was similar to or larger than juvenile Chinook salmon body size found in adjacent nearshore habitat from January through April. After April, juvenile Chinook salmon were larger in nearshore areas than in small streams. While in small streams, individual juvenile Chinook salmon reared an average of 38.5 days and grew 0.23 mm/day.
Statistical analysis suggests that four factors influence whether juvenile Chinook salmon are present within Whidbey Basin small streams: 1) distance to nearest Chinook salmon bearing river, 2) stream channel slope, 3) watershed area, and 4) presence and condition of culverts at the mouth of a stream. Streams further from Chinook salmon bearing rivers and with steeper channel slopes had lower juvenile Chinook salmon presence rates. A minimum watershed size of approximately 45 hectares with channel slopes less than 6.5% may be necessary before juvenile Chinook salmon potential exists. We found culverts at stream mouths likely cause upstream migration problems for small fish such as Chinook salmon fry.
Streams of the size in this study are often not considered salmon habitat because many flow seasonally and do not provide habitat for spawning salmon. However, we found that numerous small streams entering the Whidbey Basin do provide rearing habitat for fry migrant Chinook salmon originating from the three nearby rivers (Skagit, Snohomish, and Stillaguamish). These same small streams are not well mapped and may be subject to inadequate protection as fish habitat. Better mapping of small streams and a predictive model for juvenile Chinook salmon potential would help managers better protect this unique habitat type.