Post on 20-Jan-2016
Riparian Management and Fish Productivity
Peggy Wilzbach and Ken CumminsUSGS CA Cooperative Fish Research UnitHumboldt State University
Habitat isn’t enough. Fish need food!
• Many streams with pristine habitat support low production of salmonid fishes
• Some of the most productive streams have suboptimal habitat (but abundant food)
The greatest salmonid production is realized in hatchery channels!
Options for increasing salmonid production?
• Direct addition of food organisms (not realistic over long-term)
• Nutrient or organic matter enrichment
• Increasing autotrophic production
Case study: Effects of riparian canopy opening and salmon carcass addition on the abundance and growth of resident salmonids
Wilzbach, M.A. et al. 2005. Can. J. Fish. Aquat. Sci. 62: 1-10.
buffer
Experimental Design
Tectah
Tarup
Pac
ific
Oce
an
Pac
ific
Oce
an SF Rowdy
Little Mill
Peacock
Savoy
0 5 10 15
kilometers
N
Lower Smith River Lower Klamath River
Savoy Creek: closed canopy
Tarup Ck– Open Section
Time of day (h)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
µm
ol•s
-1•m
-2
0
50
100
150
200
250
300
350
Closed Open
Incident Radiation: Savoy Ck, July 6, 2003
Stream temperature did not differ between cut and uncut reaches in these coastal streams
Total Salmonid Biomass
Treatment effects:
riparian
date
(but not carcasses)
June 2002
-4
-2
0
2
4
6
8October 2002
UncutCut
June 2003
Carcass treatment
None Added
Ch
ang
e in
bio
mas
s af
ter
man
ipu
lati
on
(g l
m- 2
)
-4
-2
0
2
4
6
8October 2003
None Added
Specific Growth Rates
Significant treatment effects: riparian, date, riparian* carcass
None Added
Sp
ecif
ic g
row
th r
ate
(%l
day
-1)
0.0
0.1
0.2
0.3
0.4
0.5
Uncut Riparian Cut Riparian
overwinter 2002
Carcass treatment
None Added
oversummer 2002 overwinter 2003
None Added
Conclusions:
• Increased light was more effective than carcass addition in enhancing salmonid productivity of study sites
• Carcass enhancement may fail to increase salmonid production in settings where light is limiting or other factors prevent its successful use
• Selective trimming of riparian alder should be evaluated as a management tool for enhancing salmonid production
Can the food-generating capacity of a stream be readily assessed?
Across broad spatial scales, highly productive streams are associated with:
• moderate temperatures, groundwater inputs
• relatively low vegetative canopy coverage
• hard waters, relatively high concentrations of inorganic nutrients
• Within regions, need to directly measure prey availability
• Macroinvertebrate drift more accurately reflects prey availability than does the benthos
• The ratio of behavioral to accidental drifters may provide a good index of prey availability during low flow conditions
Behavioral drifter: predictably available on a diel basis
Accidental drifter: without predictable pattern of drift entry; “windfall” diet items
-0.1 0.0 0.1 0.2 0.3 0.4
0
10
20
30
40
50
60P
erce
nt
of
dri
ft m
ass
fro
m b
ehav
iora
l d
rift
ers
(AS
IN S
QR
T)
Specific growth rate of salmonids (% · day-1)
R2 = 0.42
Summer
-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6
0
10
20
30
40
50
60
70
Per
cen
t o
f T
erre
stri
al I
nve
rteb
rate
s in
Dri
ft
(A
SIN
SQ
RT
)
Specific growth rate of salmonids (%· day-1)
R2 = 0.62
In our study, % of terrestrial inverts was negatively related to fish growth
to establish the amount, spatial pattern of light gain, and riparian composition needed to optimize local food supplies - without sacrificing beneficial functions of riparian vegetation or cumulating temperature loadings downstream.
Research needs: