Clackamas & Sandy River Spawning Surveys
Spring Chinook spawning surveys in the Sandy Basin consist of carcass recovery and redd counts. These surveys are designed to be a complete census of the primary spawning areas in the upper Sandy Basin. Conducting surveys in the mainstem Sandy River is problematic because of limited visibility from glacial meltwater. Therefore, the Sandy River has been surveyed with less intensity and consistency through the years and is dependent on water clarity. Following the removal of Marmot Dam in 2007, we have begun to include the Little Sandy River in our survey area. Surveys in the upper Sandy Basin have been conducted in 1996–1999 and 2002–present.
Data collected from carcasses include pre-spawning mortality (based on females), hatchery : wild composition (based on presence or absence of fin clips or thermal marks in otoliths), and age composition and freshwater life history in wild fish (based on analysis of scales). Redd counts have been used to estimate spawner escapement and run size, as well as spawning distribution.
General protocols are to survey all spawning areas in the upper Sandy Basin on a 7–10 day cycle, with increased effort during peak spawning to insure weekly coverage of the primary spawning areas that have accounted for 80–90% of all redds in the upper Sandy Basin (Salmon and Zigzag rivers, and Still Creek). All redds are counted in each survey, and because the same people are counting redds they are able to track the progression of spawning and can distinguish new spawning activity in areas that become heavily used and often result in construction of multiple redds in a gravel patch.
Redd coordinates are recorded with a GPS connected to a personal digital assistant (PDA) and tallied. Comments are recorded on the PDA to help interpret data at the end of the season. Redd counts are summarized by sections that have been used since 1996. In 2012, we have split the lower sections of the Salmon and Zigzag rivers based on the location of weirs to facilitate additional analyses.
Spawning distribution within and between subbasins is estimated from redd counts. We have also used a simple linear regression of redds and the old Marmot Dam counts to then estimate run size from redd counts in the years following removal of the dam.
All carcasses with identifiable adipose fins or adipose fin clips are processed. Fish are cut open to verify sex, and retention of eggs in females is used to determine spawning success (pre-spawning mortality). All fin clipped fish are scanned for a coded wire tag (CWT) with a hand-held wand, and we collect the snout and biological data (fork length, sex, spawning success) from those that have a tag. Tails are cut on the tagged and untagged fish and carcasses are returned to the stream channel.
We collect otoliths from all carcasses with an intact adipose fin (and those with questionable fin clips) that will later be sent to an otolith lab in Washington to identify whether or not an induced thermal mark is present (unclipped hatchery fish). We also collect scales and tissue samples from all unclipped fish. Otoliths and tissues are put in individually numbered vials, and scales are put in numbered waterproof envelopes. Data are recorded on envelopes and entered into PDA including cross-reference to the otolith and tissue vial number. Other biological information includes fork length (cm), sex, spawning success, and location. Tails are cut and carcasses are returned to the stream channel.
All data on carcasses is recorded on a PDA and uploaded daily. Data checks are conducted in-season and immediately at the end of the season to identify and correct data entry errors or to verify any questionable data. Data are summarized by section, and in 2012 a new section break at the weirs was added.
Composition of the spawning population is estimated by section, subbasin, and upper Sandy Basin using finclips initially, and then the combination of finclips and thermally marked otoliths in unclipped fish following results of the otolith analysis. Pre-spawning mortality is estimated from the rate of egg retention in female carcasses.
Tissue samples are being stored for possible genetic studies of spring and fall Chinook composition if funding becomes available. These samples may also provide the basis of future studies on the rate and magnitude of genetic change in a population where hatchery fish are successfully excluded from the population.