Transcript limnology.wisc.edu

Update on Sparkling Lake
predators, smelt,
and crayfish densities
B.M. Roth, C.L. Hein, S.A. Lischka
T.R. Hrabik, M.J. Vander Zanden, N. Mercado-Silva
J.J. Magnuson, S.R. Carpenter, J.F. Kitchell
Eradication Gameplan: Smelt
• Remove adults during
spawning run with fyke nets
• Increase predation by stocking
walleye (and muskies)
Eradication Gameplan:
Rusty crayfish
• Intensively trap adults
• Increase predation on
juveniles
John Magnuson
Mass of Smelt Caught (kg)
Adult Smelt Removal
450
400
350
300
250
200
150
100
50
0
2003 : 375kg
2002 : 1800kg
4/22 4/23 4/24 4/25 4/26 4/27 4/28 4/29 4/30
Date
5/1
5/2
5/3
5/4
Average Daily Temperature from Sparkling
Lake 3/11 to 6/1
(Courtesy of NTL-LTER)
16
2002
2003
Temperature
14
12
10
8
Smelt spawning temp
6
4
2
0
90
100
110
120
130
Julian Day
–Smelt spawn immediately after ice out (Water temp = 4.4 C) (Becker 1983)
Mortality Sources
• Smelt
– Us
• Counting
– Walleye
• Bioenergetics
– Smallmouth bass
• Bioenergetics
• Crayfish
– Katie
• Counting
– Smallmouth bass
• Bioenergetics
– Rock bass
• Bioenergetics
500000
400000
Katie
smallmouth bass
rock bass
Crayfish
300000
200000
100000
0
2001
2002
400000
2003
Smelt
Number of Smelt Removed
Number of Crayfish Removed
Smelt and Crayfish Mortality
300000
Us
walleye
smallmouth
200000
100000
0
2001
2002
2003
Percent of Total Sample
Size Distributions of Rusty Crayfish in
Sparkling Lake
0.14
Predators
Ambient
Traps
0.12
0.1
0.08
0.06
0.04
0.02
0
10
20
30
40
Carapace Length (mm)
50
60
1000
800
Katie
smallmouth bass
rock bass
Crayfish
600
400
200
0
2001
2002
2003
Smelt
Biomass of Smelt Removed (kg)
Biomass of Crayfish Removed (kg)
Smelt and Crayfish Mortality
400000
300000
Us
walleye
smallmouth
200000
100000
0
2001
2002
2003
• Specific ecosystem responses to:
– Fishery regulation changes
– Exploitation
– Increased predation
Multiple Working Hypotheses
– Fishery regulation changes (Predators)
• Increase in number and size structure
– Exploitation
• Overall decrease in exotic populations/density (crayfish and
smelt)
• Decreased ambient carapace length (crayfish)
• Increased production and/or survivorship of juveniles
(crayfish)
– Increased predation (smelt and crayfish)
• Alternate prey become more prevalent in predator diets
• Implications for predator growth?
Predator Population Estimates
• 2001:
– All three species: Continuous Schnabel markrecapture estimates during summer only
• 2002:
– Walleye: Spring mark, continuous mark-recap during
summer
– RB & SMB: summer mark-recap only
• 2003
– Walleye & RB: Spring mark, continuous markrecapture during summer
– SMB: summer mark-recap only
Predator Population Estimates
6000
5000
rock bass
smallmouth bass
walleye
N
4000
3000
2000
1000
0
2001
2002
2003
Response of Exotics to Exploitation
– Decreased population or density (smelt and
crayfish)
– Decreased ambient carapace length
– Increased production and survivorship of
juveniles
– More macrophytes and snails
• Sampled 6 lakes in 2002 and 2003
– Early July
– Late August
• Variables measured:
– Total crayfish density
• YOY crayfish
• Crayfish >10mm carapace length
– Lengths
• All crayfish >10mm carapace length
2002
2003
All collection done on cobble substrate ONLY (France 1985)
Total Crayfish Density (#/m2)
Use Crayfish Density as a Proxy
25
20
Arrowhead
Birch
Round
Sparkling
Trout
W.Rice
15
10
5
0
Jul
2002
Aug
2002
Jul
2003
Aug
2003
Density of crayfish >10mm actually
went up on cobble substrate!!
Smelt Population Estimates
• 2001: 770,000
• 2002: 423,000
• 2003: ???,???
Response of Exotics to Exploitation
– Decreased population
– Decreased ambient carapace length (crayfish)
– Increased production and survivorship of
juveniles (crayfish)
– More macrophytes and snails
Crayfish Size Distribution in
Sparkling Lake
Percent of Sample
0.2
2002 July
0.15
2003 July
0.1
0.05
Percent of Sample
0
0.2
2002 August
0.15
2003 August
0.1
0.05
0
5
10
15
20
25
30
35
40
45
Carapace Length (mm)
No apparent change!!
Increased Production of Juveniles
(July Samples)
Density (#/m2)
250
200
Arrowhead
Birch
Round
Sparkling
Trout
W.Rice
150
100
50
0
2001
2002
2003
Year
Sparkling had the largest density
decrease among lakes sampled
2004
Percent Juvenile Mortality
Decreased Juvenile Mortality??
100
90
80
70
60
50
40
30
20
10
0
2001
Arrowhead
Birch
Round
Sparkling
Trout
W.Rice
2002
2003
2004
Year
YOY mortality was higher in 2002 than in 2003
• Increased predation
– Alternate prey become more prevalent in
predator diets (smelt and crayfish)
– Implications for predator growth?
Rock bass
Percent of Diet Dry Weight
Percent of Diet Dry Weight
Smallmouth bass
100%
80%
60%
40%
20%
0%
2001
2002
2001
2002
Year
2003
100%
80%
60%
40%
20%
0%
2003
Percent of Diet Dry
Weight
Walleye
100%
80%
60%
40%
20%
0%
2001
2002
Year
2003
Percent of Diet Dry Weight
Smallmouth bass
100%
80%
60%
40%
20%
0%
2001
2002
2003
2001
2002
Year
2003
Walleye
Percent of Diet Dry
Weight
100%
80%
60%
40%
20%
0%
Percent of Identified Fish
Smallmouth bass
1
2001
2002
2003
0.8
0.6
0.4
0.2
0
smelt
mimic shiner
other fish
Walleye
Percent of Identified Fish
Prey Type
1
2001
2002
2003
0.8
0.6
0.4
0.2
0
smelt
mimic shiner
Prey Type
other fish
• Increased predation
– Alternate prey become more prevalent in
predator diets (smelt and crayfish)
– Implications for predator growth?
• Residuals of length-weight regression line grouped
by year
Residuals of Length-Weight Regression
Relative Body Condition of
Sparkling Lake Predators
Two-way ANOVA, p < 0.001 Bonferroni post-hoc test for pairwise mean differences
0.04
smallmouth bass
rock bass
walleye
0.02
0.00
-0.02
a
ac
a
a
b
b
b
ac
b
b
c
a
1
2
3
4
-0.04
0
Year (+1999)
5
More to Come..
• How will crayfish densities, growth, and
reproduction respond to continued
exploitation?
• Are smelt going to pull off a year class?
• Will trends continue?
– Predator growth
– Diet shifts
Acknowledgments
• NSF-Biocomplexity, NTLLTER
• Steve Gilbert, WDNR
• Greg Sass, Michele
Woodford, Scott Van
Egeren
• Gretchen Anderson,
Adam Ray, Ellen
Feingold, Andrea Fowler,
Patrick Hermann, Laura
Kessler
Two Regimes
Introduction
Cobble substrate
Mucky, weedy substrate
Rapid Establishment
Slow Establishment
Good initial production
Poor initial production
High YOY density
Low YOY density
Adult Densities Rapidly Increase
Macrophytes Decline
YOY predators decline
Adult Densities Stay Low
Macrophytes Remain
???
YOY predators remain high
Number of Crayfish Consumed
Crayfish
Consumption
300000
250000
rock bass
smallmouth bass
200000
150000
100000
50000
0
Smelt
Consumption
Number of Smelt Consumed
2001
2002
2003
Year
300000
smallmouth
walleye
250000
200000
150000
100000
50000
No Data
0
2001
2002
Year
2003
Add Predators..
Pre-removal
Post-removal
with Stocking