Movement of Resident Movement of Resident TroutTrout Transplanted Below a Transplanted Below a

Barrier to AnadromyBarrier to Anadromy

Peggy WilzbachPeggy WilzbachMark AshenfelterMark Ashenfelter

USGS California Cooperative Fish Research Unit, USGS California Cooperative Fish Research Unit, Humboldt State UniversityHumboldt State University

Coastal Rainbow Trout (O. mykiss irideus)

Stream-resident form

Steelhead

?=

genetic v. environmental basis of migratory polymorphism poorly understood

Drawings from Behnke 2002

ObjectiveObjective

To determine if resident rainbow trout To determine if resident rainbow trout isolated above a barrier to anadromy will isolated above a barrier to anadromy will exhibit migratory behavior when exhibit migratory behavior when transplanted below the barrier transplanted below the barrier

Experiment Location: Freshwater Creek, CAExperiment Location: Freshwater Creek, CA

5-m waterfall on 5-m waterfall on upper mainstem, 14.5 upper mainstem, 14.5 km from river mouthkm from river mouth

Semi-permanent weir Semi-permanent weir close to mouth allows close to mouth allows escapement to be escapement to be trackedtracked

Watershed-scale full-Watershed-scale full-life cycle monitoring life cycle monitoring (CDFG) increased (CDFG) increased probability of probability of detecting detecting transplanted transplanted individualsindividuals

MethodsMethods

Above-barrier fish (>100 mm FL) captured & PIT-Above-barrier fish (>100 mm FL) captured & PIT-taggedtagged

½ of sample transplanted below falls; ½ were ½ of sample transplanted below falls; ½ were released at point of capturereleased at point of capture Transplant location ~ 10 km from tidewaterTransplant location ~ 10 km from tidewater

Released downstreamReleased downstream Released Released upstreamupstream

Fall 05:Fall 05: 2222 2020Fall 06:Fall 06: 4343 4444

6565 6464

Incomplete design: below-barrier fish not transplanted Incomplete design: below-barrier fish not transplanted above fallsabove falls

Attempts made to re-sight or capture Attempts made to re-sight or capture transplanted individualstransplanted individuals

7 fixed streamwidth antennas, operated yr-7 fixed streamwidth antennas, operated yr-roundround

Mobile PIT tag interrogation system (meter Mobile PIT tag interrogation system (meter marker precision and live or dead data): basin marker precision and live or dead data): basin surveys May – Jun and in Octsurveys May – Jun and in Oct

Downstream migrant traps: Mar - JunDownstream migrant traps: Mar - Jun

Juvenile abundance survey/ night dives: Juvenile abundance survey/ night dives: summersummer

Methods -cont’dMethods -cont’d

tidewater

weir

Downstream migrant trap, & Stream-width fixed antenna-

NFreshwater Creek

(Humboldt Bay)

waterfall

transplant release

Above-barrier populationAbove-barrier population

0

10

20

30

40

50

60

70

80

90

70 90 110 130 150 170 190

Fork length (mm)

# o

f in

div

iduals

Total

Transplanted

Individuals derived from resident rather than anadromous parents - based on Sr/Ca analyses of primordial & freshwater growth regions of otoliths)

population skewed toward older individuals

Size frequency distribution

genotyping of 18 individuals revealed that all showed some degree of introgression with cutthroat trout, with preferential backcrossing to rainbow)

0

1

2

3

4

5

6

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

# Cutthroat trout alleles

# indiv

iduals

Allelic frequency at 11 loci differentiating between rainbow trout &

cutthroat trout

Pure cutthroat trout

Growth rates did not appear to differ Growth rates did not appear to differ between upstream & downstream between upstream & downstream

populationpopulation

2006 2007

p=0.35p = 0.51

Below the barrier:Below the barrier:

Where did the transplants go?Where did the transplants go?

44 of 65 transplanted individuals were re-sighted 44 of 65 transplanted individuals were re-sighted or re-captured over 2 y studyor re-captured over 2 y study

Movement varied considerably among Movement varied considerably among individuals: individuals: 26 remained within 500 m of release location26 remained within 500 m of release location 4 moved upstream (2 moving ~5 km to base of 4 moved upstream (2 moving ~5 km to base of

waterfalls)waterfalls) 9 moved downstream but stayed in freshwater9 moved downstream but stayed in freshwater 1 entered tidewater but returned quickly to freshwater1 entered tidewater but returned quickly to freshwater 4 entered tidewater, with presumed seaward migration4 entered tidewater, with presumed seaward migration

Distance from release point to last known location

tidewater

freshwater

release

Presumed migrant: 185mm FL, 82.13g at Presumed migrant: 185mm FL, 82.13g at releaserelease

At recapture (183 d later, increased 7 mm in At recapture (183 d later, increased 7 mm in length, lost 12 g)length, lost 12 g)

Distance or direction of movement by Distance or direction of movement by transplanted individuals did not vary with transplanted individuals did not vary with fish sizefish size

Individuals that displayed seaward movement ranged in length Individuals that displayed seaward movement ranged in length at transplant from 103mm-185mm (average=132.7mm)at transplant from 103mm-185mm (average=132.7mm)

Largest transplanted individual (226mm) found ~ 6km Largest transplanted individual (226mm) found ~ 6km downstreamdownstream

100

120

140

160

180

200

220

Fork

Length

(m

m )

< 5 km > 5 km

Distance moved from release point

Act of transplantation may have biased movement of transplants, as downstream habitat was “full of fish”

Above-barrier residents enjoyed lower than equilibrium density with removal of transplants

HOWEVER:

6% of tagged, above-barrier individuals were found in below-barrier reaches, presumably washing over the falls

ConclusionConclusion The smoltification of at least some transplanted The smoltification of at least some transplanted

individuals, coupled with above-barrier ‘leakage’ individuals, coupled with above-barrier ‘leakage’ of fish downstream, suggests the potential for of fish downstream, suggests the potential for resident trout to exhibit migratory behavior and resident trout to exhibit migratory behavior and to enter breeding populations of steelhead.to enter breeding populations of steelhead.

Management implications:Management implications: should above barrier populations be included in ESU’s?should above barrier populations be included in ESU’s? Can above-barrier populations be used to help recover Can above-barrier populations be used to help recover

below-barrier populations?below-barrier populations?

YESYES

We thank the California Department of Fish We thank the California Department of Fish and Game, Steelhead Report Card Program and Game, Steelhead Report Card Program

for their support of this workfor their support of this work