Lower Columbia Steelhead Adult Abundance Monitoring Design – Dam Counts
Spatial Design
Temporal Design
Response Design
Inference Design
Evaluation Thresholds
Spatial Design
The design is a count of steelhead dams in the Clackamas, Sandy and Hood River basins.
Temporal Design
The same sampling took place every year, and continues at the North Fork Dam in the Clackamas River
basin.
Response Design
The proportion of natural-origin fish was obtained by observing fin clips and scanning for coded wire
tags. Clipped fish were not allowed to pass above the dams. The estimate for the Hood River is a
count above Powerdale Dam only. Powerdale Dam was removed in 2009. The estimate for the
Clackamas River population is a count above North Fork Dam only. Fall Creek is not included. The
estimate for the Sandy River population is a count above Marmot Dam only. Marmot Dam was
removed in 2007. Fish were sorted at the dams and all or most of fin-clipped fish were removed.
Unclipped carcasses with coded wire tags (double-index release) were included in the count.
Inference Design
The hatchery proportions observed at North Fork Dam on the Clackamas, Marmot Dam on the Sandy
and Powerdale Dam on the Hood were used as an index of the hatchery proportion for the total
population.
Evaluation Thresholds
Abundance and Productivity Evaluation Thresholds (delisting)
Pass – The observed spawner abundance is > the abundance modeled for delisting at least six times in
any 12-year period and the average observed spawner abundance is > the average modeled abundance
for delisting over that same time period. (12 years was selected because it represents roughly three to
four brood cycles for salmon and steelhead and should thus provide a reasonable snapshot in time of the
trend in status of a population.)
Fail – The observed spawner abundance is > the abundance modeled for delisting less than six times in
any 12-year period or the average observed spawner abundance is < the average modeled abundance
for delisting over that same time period.
Abundance and Productivity Evaluation Thresholds (broad sense recovery)
Pass – The observed spawner abundance is > the abundance modeled for broad sense recovery at least
six times in any 12-year period and the average observed spawner abundance is > the average modeled
abundance for broad sense recovery over that same time period.
Fail – The observed spawner abundance is > the abundance modeled for broad sense recovery less
than six times in any 12-year period or the average observed spawner abundance is < the average
modeled abundance for broad sense recovery over that same time period.
Stock-recruitment curves were developed for each Oregon lower Columbia River population of salmon
and steelhead as a way of determining the abundance and productivity needed to achieve delisting and
broad sense recovery. No recruitment curves were developed for LCR chum due to lack of data.
Because the abundance and productivity derived from these recruitment curves represent the long term
(i.e. 100 year) average, annual benchmarks of abundance and productivity will be developed that will
allow managers to provide more timely assessments of the progress being made to achieving recovery
goals. To do this, in addition to the stock recruitment curves generated for each population, annual
estimates of spawner abundance, harvest of wild fish, age at return, and an index of climate impact are
needed. Because natural fluctuations in climate conditions play such a significant role in the annual
abundance of salmon and steelhead spawners, it is necessary to scale the average abundance targets to
an annual index of climate.
The following illustrates how this information will be used to derive annual benchmarks for abundance
and productivity against which progress towards recovery can be assessed. The example in this case is
for Clackamas winter steelhead.
Step 1- Obtain recruitment parameters for population (Table 1 below).
Step 2 – Determine the age composition of the returning fish.
Step 3 – Obtain total number of spawners (hatchery + wild) for each brood year.
Step 4- Obtain climatic index for each brood year (can be downloaded from this site).
Step 5 – Calculate recruits for each brood year using the following equation based on recruitment curve
for the population.
Step 6 – Calculate recruits after fishery (i.e. spawners) using the fishery impact rates used to determine
the “modeled current” abundance.
Step 7 – Multiply each brood year recruits by recovery scalar to obtain the number of spawners needed
to meet recovery goals given climate conditions for each brood year. The recovery scalar is the amount
that the current survival rate needs to be improved to get the probability of CRT to the threshold for the
risk category targeted for the population. Numbers are calculated as the exp (Ln(Rt)) estimated from Eq.
1. (Table 2 below)
Step 8 – Use the age composition for this population to determine how many of each age fish returned
using the brood year recruits estimated in Step 7.
Step 9 – Take the forecast total and expand it by 20 percent to provide a buffer for the impacts of climate
change.
Step 10 – The number derived in Step 9 is the forecast return if recovery goals have been met. These
annual forecasts can be plotted along with the actual number of spawners observed to track progress
towards recovery.
Table 1. Recruitment model parameters inferred or estimated from data for lower Columbia River
populations of salmon and steelhead with the best matching environmental index and associated time lag
relative to parental brood year.
Table 2. Recovery scalar: the amount that the current survival rate needs to be improved
to attain the threshold for the risk category targeted for the population.