Friend or Foe? Influence of Resident Trout on Steelhead

Production in the Yakima Basin

Ian CourterCramer Fish Sciences

David Child

AcknowledgementsDavid Child, DC Consulting

Jim Hobbs, UC Davis

Chris Frederiksen, YN

Joe Blodget, YN

Dave Fast, YN

Shadia Duery, CFSJay Vaughan, CFS

Tommy Garrison, CFSSteve Cramer, CFS

Funding

Yakima Basin Joint Board

Background

• Use existing data to determine whether resident rainbow trout contribute to the upper Yakima Basin steelhead population

• Construct a steelhead population dynamics model that accounted for conspecific resident rainbow trout

Spawn Timing Resident Spawners Anadromous Spawners

RM

RF

AM

AF

Assortative Mating

Egg ProductionRF RM AF AM

Cross-Ecotype ExchangeResident female

fecundityAnadromous female

fecundity

Model Validation

1992 1994 1996 1998 2000 2002 2004 2006

Ste

elh

ea

d S

pa

wn

er

Ab

un

da

nc

e

0

50

100

150

200

250

300

350Observed Predicted (default parameterization)Predicted (no Rf smolt production)

SAR

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16

Pro

po

rtio

n S

teel

hea

d D

eriv

ed

fro

m R

fxR

m

0.0

0.2

0.4

0.6

0.8

1.0

Photo Credit David Child

Hypotheses

A significant number (≥10%) of resident rainbow trout offspring migrate to the ocean and return as adult steelhead.

Microns

0 500 1000 1500 2000 2500 3000

87S

r : 86

Sr

0.703

0.704

0.705

0.706

0.707

0.708

0.709

Microns

0 500 1000 1500 2000 2500 3000

87S

r : 86

Sr

0.703

0.704

0.705

0.706

0.707

0.708

0.709

0.710

Photo Credit Frank Thrower

Ste

elhe

ad R

esili

ence

Resident A

bundance

Resident C

ontribution Rate

Steelhead Abundance

ConclusionsO. mykiss populations in the Yakima Basin are

partially anadromous, and significant numbers of offspring from resident trout adopt an anadromous life-history.

17% resident maternal origin 30% or more have at least one resident parent

steelhead population viability and recovery is dependent on existence of a robust resident trout cohort, which highlights the importance of jointly managing freshwater and anadromous life-histories as units of the same population.