Coast Steelhead Adult Abundance Monitoring Design
Spatial Design
Temporal Design
Response Design
Inference Design
Evaluation Thresholds
References
Spatial Design
The design is similar to that created for Oregon coast coho (Stevens, 2002). A GIS coverage of streams
was used as a frame for the population. The coverage was based on USGS 1:24,000 topographic maps,
modified by ODFW to correspond to the target population of streams for each population. The goal was
to provide annual estimates for each of the assessment units with a 95% confidence interval of +30%.
To do this, a minimum of 30 sites or 30% (whichever comes first) of the available spawning habitat for
was sampled in each of the assessment units.
Inference is made for Independent Populations prior to 2008, and for Strata from 2008- present. . Click
here to see the current spawner assessment units monitored by.ODFW’s Oregon Adult Salmonid
Inventory and Sampling (OASIS) project (ODFW monitors only the portions in Oregon). Generalized
Random Tessellation Stratified designs (GRTS) achieve a spatially-balanced random point distribution
(Stevens, 1997; Stevens & Olsen, 1999; Stevens & Olsen, 2003; Stevens and Olsen, 2004) and this
approach was used.
Temporal Design
A rotating panel design was used to accommodate the need for repeat visits while continuing to expand
the scope of the sample every year. Sets of panels are visited on different cycles. The design consists of
40 panels, with one panel defining sites visited every year, 3 panels defining sites visited on a 3-year
cycle, 9 panels defining sites visited on a 9-year cycle, and 27 panels defining sites visited on a 27-year
cycle. An equal number of sites were allotted to each panel. Due to reduction in funding, all sites
conducted Since 2008 are from the annual panel exclusively.
Response Design
Spawning ground surveys are conducted from January through May. Visits at a site are conducted at
least once every 14 days throughout the course of the spawning survey season. Surveyors either walk
upstream or boat downstream, depending of the size of the stream being surveyed. On average, sample
sites are roughly 1 mile long. The exact length of samples sites is determined by proximity to landmarks
(such as bridge crossings and tributary junctions).The surveyors count redds, live and dead fish (by
species and fin-mark), and sample carcasses for gender, length (mm MEPS), scales, fin clips and tags.
For a full description of the field methods used to conduct the spawning surveys click here.
Analytical procedures to calculate metrics:
Because adult steelhead spawners are not reliably observable in spawning ground surveys, redd counts
are used as a proxy for adult abundance. (Susac, 1998). Steelhead can be found spawning in streams
over a period of several months. Because it is too costly and impractical to conduct daily counts of the
number of steelhead redds deposited at all randomly selected spawning survey sites during this
extended time period, it is necessary to employ statistical techniques to expand periodic counts (i.e.
those conducted once every 14 days or less throughout the spawning season) to an estimate of the total
number of redds deposited at the site.
Individual sites are assessed for quality of data according to methods developed by Stevens (2002) and
Susac and Jacobs (1998). Sites that pass QA/QC tests are expressed using an indicator variable Spt to
represent sites within population area p or strata t that were successfully surveyed. This indicator variable
expression is given as:
{
I(Spt) =
1, if (Spt) meets criteria within population p and stratum t;
0, otherwise.
The response (R), which is the number of redds per mile observed at each successful site over the entire
season within the population areas (Spt) is calculated using rates of positive fin mark observations from
both recovered carcasses and live adult observations to adjust response for hatchery and wild fish. The
following equation was used to adjust response from each site for hatchery fish (Hankin 1982) for
population area (Spt),
Rw = R * (w/w+h)
where, Rw = response from wild, R = response from site, w = wild fish observed within population area Spt
and, h = hatchery fish observed within population area Spt.
Inference Design
Expansion of observations to areas not surveyed is performed by weighting each site to represent a
fraction of the total available miles of habitat. The response from each site is then multiplied by this
weight to determine redd abundance over the frame. Weight is calculated using the formula:
W = m / ∑ I (Spt)
where W = weight, m = total spawning habitat stream miles in population area Spt. Steelhead redd
abundance for a population area (Spt) is then calculated as follows:
X = ∑ R* W
where, X = steelhead redd abundance, R = response for each site, and W = weight. Similarly, the
response variable for wild fish (RW) was used to determine redd abundance from wild steelhead.
Furthermore, this redd abundance estimate is converted from redds to adults using the equation
N = 1.0379X +42
where, N = number of adult spawners, and X = redd abundance.
Refer to http://epa.gov/nheerl/arm/analysispages/software.htm) to calculate population abundance
estimates and confidence intervals.
Evaluation Thresholds
There are currently no established abundance goals for Oregon Coast Steelhead abundance.
References
Beidler, W.M., and T.E. Nickelson. (1980). An evaluation of the Oregon Department of Fish and Wildlife standard
spawning survey system for coho salmon. Oregon Department of Fish and Wildlife, Information Reports
(Fish) 80-9, Portland.
Hankin, D. 1982. Estimating escapement of Pacific salmon: marking practices to discriminate wild and hatchery
fish. Transactions of the American Fisheries Society, 111:286-298.
Perrin, C.J., and J.R. Irvine. (1990). A review of survey life estimates as they apply to the area-under-the-curve
method for estimating the spawning escapement of pacific salmon. Canadian Technical Report of
Fisheries and Aquatic Sciences 1733.
Stevens, D.L., Jr. (1997). .Variable density grid-based sampling designs for continuous spatial populations’.
Environmetrics 8: 167-195.
Stevens, D.L. (2002). Sampling design and statistical analysis methods for integrated biological and physical
monitoring of Oregon streams. OPSW-ODFW-2002-07, Oregon Department of Fish and Wildlife,
Portland, Oregon.
Stevens, Jr., D. L. and A. R. Olsen. (1999). .Spatially Restricted Surveys Over Time for Aquatic Resources.
Journal of Agricultural, Biological, and Environmental Statistics 4:415-428.
Stevens, Jr., D. L. and A. R. Olsen. (2004). .Spatially Balanced Sampling of Natural Resources. Journal of the
American Statistical Association 99:262-278.
Stevens, Jr. D.L., and N.S. Urquhart. (2000). Response Designs and Support Regions in Sampling Continuous
Domains. Environmetrics 11:13-41.
Stevens, Jr., D.L., and A. R. Olsen. (2003). Variance Estimation for Spatially Balanced Samples of Environmental
Resources. Environmetrics 14:593-610.
Susac, G. and S. Jacobs. (1998). Evaluation of Spawning Ground Surveys for Indexing the
Abundance of Adult Winter Steelhead in Oregon Coastal Basins. Annual Progress
Report, Oregon Department of Fish and Wildlife, Portland, Oregon.
Willis, R.A. (1954). The length of time that silver salmon spent before death on spawning grounds at Spring Creek,
Wilson River in 1951-52. Fish Commission of Oregon Research Briefs 5:27-31.