This document summarizes research on the emigration behavior and life history strategies of resident and anadromous rainbow trout/steelhead (Oncorhynchus mykiss) in Scott Creek, California. The key points are: 1) Some O. mykiss remain in the upper watershed and mature as residents, while others migrate to the estuary and ocean as anadromous steelhead. 2) Genetic, physiological, and habitat factors interact to influence the proportion of fish that exhibit resident versus anadromous life histories. 3) The estuary provides important rearing habitat for juvenile O. mykiss and contributes to their growth, but degraded water quality or lack

1. Emigration behavior of resident and
anadromous juvenile O. mykiss:
exploring the interaction among genetics,
physiology and habitat
Sean Hayes, Chad Hanson, Morgan Bond, Devon Pearse,
Andrew Jones, Carlos Garza, Bruce MacFarlane

2. •Small watershed (75km2)
•23km of stream accessible to
anadromous fish
•“native” resident fish above
barriers
•Small hatchery
•Dynamic flow regime
(28m3 s-1 to 0.1m3 s-1)
•Small Estuary (closes
seasonally)
Scott Creek
Map: Rob Schick, NMFS

3. Scott Creek O. mykiss
life history strategies
Ocean
upper watershed estuary/lagoon
Upstream resident
Mature in estuary
(never enter ocean)

4. x
x
x
3 km
Adult
weir
Instream
PIT tag
readers
Scott
Creek
X= barrier
Seine, hook & line, and electrofishing
Smolt
trap

5. Resident populations
“diverged” >100 yrs ago
Big Creek Adults
Weir Adults
Lagoon Juveniles
60
Hatchery Juveniles
Scott Creek Adults
76
Mill Above
Big Creek, Boyer
63
92
Big Creek Above
68
Scott Creek Above
Neighbor-Joining distance tree, with bootstrap values for supported nodes
Do rainbow trout and steelhead differ?

6. x
x
x
?
Proportion of fish assigned to Resident or Anadromous
ancestry by habitat
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Above
Barrier
Upstream Smolt trap Estuary
Anadromou
Resident

7. Genotype distribution in upper
watershed
0.00
0.10
0.20
0.30
0.40
Fork length
Frequency
Resident (n=128)
Anadromous (n=209)

8. Emigration rate
from above
anadromy barrier
• 400 fish PIT
tagged above
• 2.3 % over the falls
• 1.8 % detected at
smolt trap

9. Na+ K+-ATPase Physiology
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
ATPase
activity
0
2
4
6
8
Smolt Trap
Estuary
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
ATPase
activity
0
2
4
6
8
Above Barrier
Upstream
?

10. Upstream samples
0.00
2.00
4.00
6.00
8.00
0 2 4 6 8 10 12
Month
ATPase
Resident
Anadromous
Na+ K+-ATPase Physiology
0
2
4
6
0 2 4 6 8 10 12 14 16
ATPase
Frequency
Resident
Anadromous

11. Why do wild fish migrate at such small sizes?
0
0.04
0.08
0.12
0.16
Fork Length (mm)
Frequency
Typical steelhead smolt size distribution

12. Lagoon- Sand Bar Closed (July-Dec.)
Estuary- Open to Ocean (Jan.-June)
Does estuary serve as nursery habitat?
(Morgan Bond’s thesis)

13. Black lines indicate upper watershed growth
Blue lines indicate migration to estuary and growth
Jan Jul Jan Jul Jan Jul Jan Jul Jan
Fork
Length
(mm)
0
50
100
150
200
250
Mean
5th %
95th %
YOY 1+ 2+ 3+
Is the estuary a nursery?
Ocean
upper watershed estuary/lagoon
85% of returning
adults use estuary
pathway
Size threshold
for ocean
survival

14. What happens when water quality degrades?
3 km
>45% detected moving
Upstream each fall
(probably >90%)

15. Size of recaps at smolt trap in spring
0
2
4
6
8
10
12
14
16
18
20
60 80 100 120 140 160 180 200 220 240 260 280 300
Fork Length
Frequency
Upstream
Estuary (previous summer)

16. A tale of two watersheds
Functional estuary present
No estuary available
Year 1 Year 2 Year 3
Year 1 Year 2 Year 3
(in Central California…)

17. Acknowledgements
Funding
• NMFS
• DFG FRGP
• NURP
• California Sea Grant
Land Owner support
•Big Creek Lumber Company
•The Wilson Family
•Monterey Bay Salmon and Trout Project
•Cal Poly Swanton Ranch
•Lockheed Martin

18. Implications of resident trout studies
• Should residents be counted in steelhead
populations for delisting criteria?
• Residents may become steelhead, but this
probably happens at low frequencies
• Results of resident contribution to
anadromous breeding pending

19. Estuary Environmental Conditions
“Lethal”
levels

20. Influence of genotype on
migration behavior
To sea or not to sea?
Genotype Frequencies
0
0.2
0.4
0.6
0.8
1
Upstream Smolt trap
Frequency
Resident
Anadromous

21. Typical spring downstream migrant (smolt?)
After 5-6 months rearing in estuary
100mm
Steelhead in Scott Creek
85% of returning
adults use estuary
pathway

23. Fork Length (mm) at Trap
Big smolts are less likely to stay
< <150 >150
0
5
10
15
20
25

24. Conclusions
Central Coast steelhead adapt for estuarine use
Steelhead strategies without estuary
• Longer upstream rearing
• Fewer smolts, reduced anadromy?

25. Figure 5. Estimated lagoon yearly population sizes and yearly mean growth rates from 2003-2006 (left y-axis).
The bar graph (right side y-axis) represents mean fork length of fish sampled in the estuary in late fall of each
year, just prior to winter storm season and lagoon opening. Years match points within labeled column. All
data are means ± SE, R2
=0.99. Regression P= 0.005
Estimated Lagoon Population
0 500 1000 1500 2000 2500 3000
SGR
length
as
a
%
per
day
0.2
0.4
0.6
0.8
1.0
2005 2004
2003
2006
Density-dependent Estuary
Growth in Steelhead

26. Implications for Local Rivers
• Larger river- may have more rearing
capacity= larger smolts upstream
• BUT… is there enough water?
• Estuary issues
– Breaching
– Estuary size reduced?
– Enough flow to connect with watershed?

27. Lagoon fish move upstream in the fall and then back
down in spring
Lagoon fish PIT tag reader detections
0
50
100
150
200
250
300
350
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month
Frequency
Upper watershed
Lower watershed
>45% lagoon fish detected moving upstream

28. Escapement ??
Early 20th century spawning
population was 4-10 times larger

29. Why is estuary growth so good?
(Jeff Harding’s diet studies)
Lots of food!
Diet consists of Corophium and Eogammarus sp.

30. But where does food come from?
• Upper watershed growth poor
• Insect diet
• Low flow
• Low light
– low nutrient input into estuary

31. Hypothesis- Nutrient flow from marine derived
nutrients (kelp) enhances productivity
(Alison Collins senior thesis)
Terrestrial Marine
Marine
13C and 15N from Juvenile Steelhead
d13 C (0/00) +/- SD
-26 -24 -22 -20 -18 -16 -14
d
15
N
(0/00)
+/-
SD
6
8
10
12
14
16
Juv. Steelhead - Lagoon
Juv. Steelhead - Above Fall
Adult Steelhead
Coastal Marine Fish

32. Why don’t all fish recruit to the
estuary?