Abundance of Puget Sound Steelhead near the turn of the 20th century estimated from commercial catch data

Nick GayeskiWild Fish ConservancyMarch 14, 2012

Historical abundance of Puget Sound steelhead, Oncorhynchus mykiss, estimated from catch record data

• Authors: Nick Gayeski, Bill McMillan, Pat Trotter

• Canadian Journal of Fisheries and Aquatic Sciences, vol. 68, pp. 498-510, March 2011

Project Objectives

• Estimate abundance of Puget Sound steelhead based upon:

• Commercial catch data for the year of peak catch – 1895

• Historical data regarding regional development to estimate unreported steelhead catch

• Provide a robust historical baseline of PS steelhead abundance to serve as a reference for recovery so as to

avoid the ‘shifting baseline syndrome’

• Illustrate how quantitative data can be integrated with qualitative (historical) data to estimate historical abundance while fully accounting for the uncertainty of such estimates

Commercial Catch Data: Available for Five Populations

• Nooksack

• Skagit

• Stillaguamish

• Snohomish

• The remaining rivers and streams in Puget Sound

1895 Commercial Catch Data (lbs)

• Nooksack 660,160 lbs.

• Skagit 205,190 lbs.

• Stillaguamish 180,000 lbs.

• Snohomish 401,620 lbs.

• Remaining PS 518,582 lbs.

• TOTAL 1,965,552 lbs.

Methods

1. Start with reported commercial catch in lbs.2. Estimate the weight of steelhead in the catch3. Estimate the unreported catch (tribal, sport,

settlers/agricultural) as a proportion of the reported catch

From 1- 3 , estimate the total numerical catch Estimate the total harvest rate on the 1895 run

represented by the estimated total catchDo this in a way that accounts for all uncertainties

in the estimation procedure

Bayesian Analysis

• The uncertainties are accounted for by employing a Bayesian analysis

• First, we obtain a distribution of the estimated total numerical catch, T:

• T = C*(1+U)/W (eq. 1), where

• C = commercial catch in lbs.

• U = unreported catch (% of reported)

• W = average weight of steelhead (lbs.)

Steelhead weight and unreported catchas a proportion of reported catch

• Weight 7 - 9.5 pounds

• Nooksack 0.10 – 0.30

• Skagit 0.50 – 1.00

• Stillaguamish 0.50 – 1.00

• Snohomish 0.50 – 1.00

• Remaining PS 0.50 – 1.00

Estimation of the Numerical Catch

• Randomly draw a large number of values of U and W (10 million) and

• Apply equation (1) to each.

• Cumulated values in bins of fixed width to build a histogram of T.

Distribution of Total Catch (Snohomish)

Estimation of the Terminal Run

• Place a distribution on harvest rate, R, and on total run size, N and calculate

• P(T|N,R) =(N!/(T!*(N-T)!) *TR*(N-T)(1-R) (eq. 2)

• Equation 2 is calculated for 10 million random values of R and N, and the values of T.

T

N

T

N

T

N

T

N

T

N

Harvest Rate Priors

• Nooksack: uniform(0.6, 0.9)

• Skagit: uniform(0.3, 0.6)

• Stillaguamish: uniform(0.4, 0.7)

• Snohomish: uniform(0.4, 0.7)

• Remaining: uniform(0.4, 0.7)

Terminal Run Size Priors

• Nooksack: uniform(80000, 225000)

• Skagit: uniform(50000, 200000)

• Stillaguamish: uniform(40000, 130000)

• Snohomish: uniform(90000, 290000)

• Remaining: uniform(100000, 370000)

Snohomish Prior and Posterior Distributions of Run Size

Snohomish Posterior and Prior Distributions of Harvest Rate

RESULTS

Total Catch Estimates

• Population Mean Mode SD Cntrl. 90th%-ile

• Nooksack 96800 91300 9700 81700 -- 113500• Skagit 43900 43300 5300 35000 -- 53100• Stilly. 38500 37700 4700 31100 – 46600• Snohomish 85900 83700 10400 69500 -- 104300 • Remaining 110800 109000 13500 89400 – 134500

• TOTAL 375900 365000 43600 306700 – 452000

Total Run Size Estimates

• Population Mean Mode SD Cntrl. 90th%-ile

• Nooksack 132600 127800 20400 101400 – 169000• Skagit 105600 86700 24700 70000 -- 149000• Stilly. 73700 69200 14900 51700 – 100000• Snohomish 164500 153000 33400 114000 -- 224000 • Remaining 212100 185000 43100 148000 – 287700

• TOTAL 688500 621700 136500 485100 – 929700

Harvest Rate Estimates

• Population Mean Mode SD Cntrl. 90th%-ile

• Nooksack 0.74 0.60 0.09 0.61 – 0.88• Skagit 0.43 0.31 0.09 0.31 -- 0.58• Stilly. 0.54 0.42 0.09 0.41 – 0.68• Snohomish 0.54 0.42 0.09 0.41 – 0.68• Remaining 0.54 0.40 0.09 0.41 – 0.68

• Grand Mn. 0.56 0.40 0.09 0.43 – 0.70• Mn (Totals) 0.55 0.59 NA 0.36 – 0.63

Comparison to Current Conditions

• Two methods of comparison

• Compare estimated turn-of-century abundance to NOAA status review estimates for 1980 - 2004 and for 2000 – 2004

• Compare estimates scaled to estimates of lengths of stream accessible to adult winter-run steelhead (fish-per-kilometer)

Current Conditions

Population N, 1980-2004

N, 2000-04 S FKM, All Years

FKM, 5 years

Nooksack* 1600 1600 612 2.6 2.6

Skagit 6993.9 5418.8 982 7.12 5.52

Snohomish 5283 3230.1 926 5.71 3.49

Stillaguamish 1027.7 550.2 445 2.31 1.24

Rest of PS 6673.8 4742.5 4014 1.69 1.18

All of PS 21678 15542 6979 3.1 2.2

Historical Estimates

Population Posterior Mode N Posterior 5th %ile N SK FKM. Mode N FKM, 5%ile N

Nooksack 127800 101400 918 139 110

Skagit 86700 70000 1473 59 48

Snohomish 153000 114000 1389 110 82

Stillaguamish

69200 51700 667.5 104 77

Rest of PS 185000 148000 6021 31 25

All of PS 621700 485100 10469 59.4 46.3

FKM for Recent Average and Estimated Historical Abundance

0

20

40

60

80

100

120

140

160

Nooksack* Skagit Snohomish Stillaguamish "Remainder" Total PS

Population

Fis

h/a

cc

es

sib

le s

tre

am

km

(F

KM

)

1980-2004 2000-2004 1895 Posterior Mode 1895 Posterior 5th Percentile

Fish-Per-Accessible Stream Km for Historic PS and Situk 1952

0

50

100

150

200

250

300

350

Nooksack* Skagit Snohomish Stillaguamish Situk 1952River

Fis

h-p

er-

ac

ce

ss

ible

-str

ea

m k

m (

FK

M)

Posterior Mode Posterior 5th Percentile Situk

CONCLUSIONS

• Current abundance is 1% to 4% of the estimated turn-of-century abundance

• Habitat currently accessible to adult winter-run steelhead is no less than 67% of what was available at the turn of the century

• It is unlikely that habitat loss can explain the majority of this historic decline.

• This may indicate that significant recovery is still in the cards!

• Severe impairment of both ecosystem and autecological function

• Steelhead have lost significant life history and genetic diversity

• Interactions with hatchery fish and loss of salmon abundance in addition to habitat loss and simplification are plausible culprits

Thank You for Your Attention!