Steelhead Pigmentation Study David Casterson Soquel High School

Steelhead (Oncorhyncus mykiss) were observed and counted by snorkeling in Big Creek during August of each sample year beginning in August, 2000. Age class (young of year, 1-year-olds, and 2+-year-olds) and color form ("normal" and "light"; see photos) were recorded for each individual in each pool (see data file for details).

"Light" color form. (photo: D. Casterson, Aug. 2002)	"Normal" color form. This form seemed to increase in frequency in the last few years, while the light form declined.

The year class data and repeated sample data (Table 1) suggest a trend toward increasing frequesncy of the "normal" color form and a decline in the "light" form. This is most evident in the "2000" year class, and in the "all years" trend between 1998 and 2002. External factors which might alter the stream environment over that time period include declining flow rates and/or the Kirk Complex wildfire which greatly increased sediment load and water color in the winter of 2000. The data are also available in an excel file.