Bryce Glaser - WDFW

Dan Rawding – WDFW

WanYing Chang - WDFW

OVERVIEWWDFW Steelhead Escapement

Estimation MethodologiesFocus on Redd Surveys

Precision Goals for MonitoringSources of Uncertainty in Redd SurveysExamples of Precision in LCR EstimatesConclusion/Implications

WDFW Steelhead EscapementRedd surveys - the most common method of

estimating escapement used by WDFW.Census Counts - when possible weirs and/or

barriers are used to census steelhead. Mark–Recapture - in other cases weirs, fish

ladders, seining and/or snorkeling are used for mark-recapture programs.

Why Redd Surveys?Tradition Ease of implementation.Relatively inexpensive/Cost Effective.Provide a straight forward estimate of

females.Provide an estimate of spawners, not run size

as from mark-recapture.Other escapement methodologies may be

more difficult.Provide the ability to estimate fine scale

spatial structure if redd locations are GPS’d.

Mark-Recapture

Area-Under-the-Curve

Peak Count Expansion

Redds

Census

Accuracy Cost

Complete

Random

Peak/Supplemental

Method SamplingDesign

Index

Salmon & Steelhead Escapement

×Females / Redd ═

× ═Spawner

Escapement Estimate

Redd Count # of Females

# of FemalesAdults/Female

(Sex Ratio)

Redd Count Expansion

× Fish / Redd

═Spawner

Escapement Estimate

Redd Count

Redd Count Expansion

Redd SurveysCalibrated Survey –

Escapement estimate and sex ratio is obtained from a weir or mark-recapture program.

Females or fish per redd = Estimated #of females or fish/redd estimate.

In years of no trapping or mark-recapture - the redd estimate is expanded by the females per redd estimate and sex ratio or simply by fish per redd to estimate escapement.

Partially Calibrated Survey – Estimate of females per redd and sex ratios, or fish

per redd obtained from another basin is used to expand the redd estimate for the population of concern.

Uncalibrated Survey – professional judgment is used to estimate females

or fish per redd.

AssumptionsCalibrated Redd Surveys

Redds are consistently identified and enumerated.Observer efficiency is incorporated into the females

per redd estimate.

Partially Calibrated Redd SurveysAbove assumptions plus…..Fish or females per redd estimate and observer

efficiency is the same for the source population (calibrated) & the population where applied (partially calibrated surveys).

Spatial distribution of spawning is known. Temporal spawning pattern is known. A statistically valid spatial and temporal study design

is established if survey is not a census.

Precision Goals for MonitoringNOAA’s Draft Guidance for Monitoring Recovery of

Pacific Northwest Salmon and Steelhead (Crawford & Rumsey 2009) CV on average of 15% or less for adult abundance.

Robson & Regier (1964)Research Goal: 95% CI of + 10% of point estimate.Management goal: 95% CI of + 25% of point estimate.

Cousens et al. (1982) 95% CI of + 20% of point estimate – considered to be good.

Sources of UncertaintyFemales/Redd

WDFW standard methodology - Snow Creek data.Sex Ratios

WDFW standard methodology – Assumes 1:1 ratio.Kalama River data

Sampling DesignCensus – Example - Mill, Abernathy, Germany creeksIndex/Supplemental – Examples - Coweeman and

Elochoman rivers.

Generalized random tessellation stratified (GRTS) sampling

Females per Redd

Snow Creek estimate based on calibrated redd surveys compared to the weir count of females from 1977-89.

Mean =0.804, SD = 0.152, CV = 19%Females per redd is constant over the range of escapement.

S n o w C reek S teelh ead , 1977-89

0 .4

0 .9

1 .4

0 1 0 2 0 3 0 4 0 5 0 6 0

N u m b e r o f F e m a le s

Fe

ma

les

pe

r R

ed

d

Slope = 0.001Ho: slope = 0, not rejected p - value = 0.545

Sex RatioWDFW has historically used a 1:1 sex ratio for

expansions (= 2 fish per female).Kalama Winter Steelhead - Fish per female

Kalama Falls Hatchery – operates a fish ladder trap and barrier falls.

Mean fish per female = 1.85 (54% females, 46% males).SD = 0.109, CV = 6%Assume sex ratio is constant regardless of run size.

Sampling DesignCensus

Entire spawning area is surveyedIndex/Supplemental

Indices in mainstem and tributaries are surveyed.At peak spawning time in index, a supplemental

survey occurs in the remainder of the spawning area.Test for differences in % redds visible in tributaries

vs. mainstem at the time of supplemental survey.Supplemental survey counts are expanded based on

% redds visible in index areas.Generalized random tessellation stratified (GRTS)

Spatially balanced designs (EMAP)

Mill, Abernathy and Germany Creeks 2008

Name Mill Abernathy Germany MAGEsc 34 223 228 485

SD(esc) 6.8 44.2 45.1 96.1CV(esc) 20% 20% 20% 20%L95%CI 21 136 139 296U95%CI 47 310 316 673

• Sampling design is census: CV= 0• Uncertainty from Females/Redd and Sex Ratio

• CV = 20%; equivalent to 95% CI + 40%

Index/Supplemental –Coweeman River

Index/Supplemental –Coweeman River

Sampling Design – Index/Supplemental: CV = 17%Uncertainty from sampling design, females/redd and

sex ratio: CV=26%; 95% CI + 51%Escapement Estimate: 63114% of the redds were in index surveys86% of redds were in supplemental surveysTest for differences in mainstem vs. trib. indices.

separate timing expansion for tributaries and mainstem was necessary (Chi-square test, p=0.013)

• Sampling Design – Index/Supplemental: CV = 5%

• Uncertainty from sampling design, females/redd and sex ratio: CV=20%; 95% CI + 40%

• Escapement Estimate: 286

• 42% of the redds were in index surveys

• 58% of redds were in supplemental surveys

• Test for differences in mainstem vs. trib. indices.

• no difference (Chi-square test p=0.97)

• single timing expansion.

General random tessellation stratified (GRTS) designs

Used extensively in OregonAdvantage – provides unbiased estimate

ODFW Targeted Sampling Rate to achieve CV ≤ 15%Hypothetical Example:

ODFW Targeted Sampling: CV = 15%WDFW Females per Redd: CV = 19%WDFW (Kalama) Sex Ratio: CV = 6%

Escapement CV= 24%, 95% CI + 49%

Precision Comparison

Sampling Design

Census MAG

Index/Supp.

Coweeman

Index/Supp.

ElochomanGRTS

CV 20% 26% 20% 24%

95% CI + 40% + 51% + 40% + 49%

SummaryRedd surveys are inexpensive, but also

imprecise compared to other methods.Largest source of variation in redd based

escapement estimates is from females or fish per redd estimates.

Smallest source of variation is from sex ratios.CV for spatial sampling designs depends on

effort.Escapement CV ranges from 20% for a census,

to ~25% for GRTS and index/supplemental designs.

SummaryIf redd surveys are to be used to

estimate escapement, WDFW needs additional calibrated studies to better estimate females or fish per redd.

If redd based escapement estimates are not able to meet established ESA, Research and/or management precision goals for key populations, then alternate escapement methods should be considered.Mark-recapture or weirs for selected

steelhead populationsPossibly the use of imaging sonar for

steelhead.

AcknowledgementsFunding for LCR surveys:

NOAA via Mitchell Act fundsWashington State Salmon Recovery Funding

BoardThom Johnson & Randy Cooper - Snow Cr.

data.Cameron Sharpe and Kalama Research

Team -Kalama R. data.Biologists and technicians that conducted

redd surveys.

Literature CitedCousens, N.B.F., G.A. Thomas, C.G. Swann, and M.C. Healy. 1982. A

review of salmon escapement estimation techniques. Canadian Technical Report of Fisheries and Aquatic Sciences. 1108.

Crawford, B. A. and S. Rumsey. 2009 (Draft). Guidance for monitoring recovery of Pacific Northwest salmon and steelhead listed under the Federal Endangered Species Act (Idaho, Oregon, and Washington). NOAA’s National Marine Fisheries Service – Northwest Region, Portland, OR.

Robson, D.S., and H.A. Regier. 1964. Sample size in Petersen mark-recapture experiments. Transactions of the American Fisheries Society 93: 215-226.