riparian management and fish productivity peggy wilzbach and ken cummins usgs ca cooperative fish...

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: