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: