update on sparkling lake predators, smelt, and crayfish densities
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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
Adult Smelt Removal
0
50
100
150
200250
300
350
400
450
4/22 4/23 4/24 4/25 4/26 4/27 4/28 4/29 4/30 5/1 5/2 5/3 5/4
Date
Ma
ss
of
Sm
elt
Ca
ug
ht
(kg
) 2003
2002: 375kg : 1800kg
Average Daily Temperature from Sparkling
Lake 3/11 to 6/1 (Courtesy of NTL-LTER)
–Smelt spawn immediately after ice out (Water temp = 4.4 C) (Becker 1983)
0
2
4
6
8
10
12
14
16
90 100 110 120 130
Julian Day
Te
mp
era
ture
2002
2003
Smelt spawning temp
Mortality Sources
• Smelt– Us
• Counting
– Walleye• Bioenergetics
– Smallmouth bass• Bioenergetics
• Crayfish– Katie
• Counting
– Smallmouth bass• Bioenergetics
– Rock bass• Bioenergetics
Smelt and Crayfish Mortality
0
100000
200000
300000
400000
500000
2001 2002 2003
Num
ber
of C
rayf
ish
Rem
oved
Katiesmallmouth bassrock bass
0
100000
200000
300000
400000
2001 2002 2003
Num
ber
of S
mel
t R
emov
ed Us
walleye
smallmouth
Crayfish
Smelt
Size Distributions of Rusty Crayfish in Sparkling Lake
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
10 20 30 40 50 60
Carapace Length (mm)
Pe
rce
nt
of
To
tal S
am
ple
Predators
Ambient
Traps
Smelt and Crayfish Mortality
Crayfish
Smelt
0
100000
200000
300000
400000
2001 2002 2003
Bio
ma
ss o
f Sm
elt
Re
mo
ved
(kg
)
Us
walleye
smallmouth
0
200
400
600
800
1000
2001 2002 2003
Bio
ma
ss
of
Cra
yfi
sh
Re
mo
ve
d (
kg
)
Katiesmallmouth bassrock bass
• 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 mark-
recapture 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 mark-
recapture during summer– SMB: summer mark-recap only
Predator Population Estimates
0
1000
2000
3000
4000
5000
6000
2001 2002 2003
N
rock basssmallmouth basswalleye
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)
Use Crayfish Density as a Proxy
Density of crayfish >10mm actually went up on cobble substrate!!
0
5
10
15
20
25
To
tal
Cra
yfis
h D
ensi
ty
Arrowhead
Birch
Round
Sparkling
Trout
W.Rice
(#/
m2
)
Jul2002
Jul2003
Aug2002
Aug2003
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
No apparent change!!
0
0.05
0.1
0.15
0.2P
erce
nt
of
Sam
ple 2002 July
2003 July
0
0.05
0.1
0.15
0.2
5 10 15 20 25 30 35 40 45
Carapace Length (mm)
Per
cen
t o
f S
amp
le
2002 August
2003 August
Increased Production of Juveniles (July Samples)
0
50
100
150
200
250
2001 2002 2003 2004
Year
Den
sity
(#/
m2) Arrowhead
Birch
Round
Sparkling
Trout
W.Rice
Sparkling had the largest density decrease among lakes sampled
Decreased Juvenile Mortality??
0102030405060708090
100
2001 2002 2003 2004
Year
Per
cen
t Ju
ven
ile
Mo
rtal
ity
Arrowhead
Birch
Round
Sparkling
Trout
W.Rice
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?
Smallmouth bass
Rock bass
0%
20%
40%
60%
80%
100%
2001 2002 2003Year
Per
cen
t o
f D
iet
Dry
Wei
gh
t0%
20%
40%
60%
80%
100%
2001 2002 2003
Per
cen
t o
f D
iet
Dry
Wei
gh
t
Walleye
0%
20%
40%
60%
80%
100%
2001 2002 2003
Year
Per
cen
t o
f D
iet
Dry
W
eig
ht
Smallmouth bass
Walleye
0%
20%
40%
60%
80%
100%
2001 2002 2003P
erce
nt
of
Die
t D
ry W
eig
ht
0%
20%
40%
60%
80%
100%
2001 2002 2003Year
Pe
rce
nt
of
Die
t D
ry
We
igh
t
Smallmouth bass
Walleye
0
0.2
0.4
0.6
0.8
1
smelt mimic shiner other fish
Prey Type
Pe
rce
nt
of
Ide
nti
fie
d F
ish
200120022003
0
0.2
0.4
0.6
0.8
1
smelt mimic shiner other fish
Prey Type
Pe
rce
nt
of
Ide
nti
fie
d F
ish
200120022003
• 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
Relative Body Condition of Sparkling Lake Predators
Year (+1999)
0 1 2 3 4 5Res
idu
als
of
Len
gth
-Wei
gh
t R
egre
ssio
n
-0.04
-0.02
0.00
0.02
0.04
Two-way ANOVA, p < 0.001 Bonferroni post-hoc test for pairwise mean differences
a a b bac b ac ca b b a
smallmouth bassrock basswalleye
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, NTL-LTER
• 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
Good initial production
Macrophytes Decline
Adult Densities Rapidly Increase
YOY predators decline
Cobble substrate
Rapid Establishment
High YOY density
Mucky, weedy substrate
Slow Establishment
Poor initial production
Adult Densities Stay Low
Macrophytes Remain
YOY predators remain high
Low YOY density
???
0
50000
100000
150000
200000
250000
300000
2001 2002 2003
Year
Nu
mb
er o
f C
rayf
ish
Co
nsu
med
rock bass
smallmouth bass
0
50000
100000
150000
200000
250000
300000
2001 2002 2003
Year
Nu
mb
er o
f S
mel
t C
on
sum
ed
smallmouth
walleye
Crayfish Consumption
Smelt Consumption
No Data
Add Predators..
Pre-removal Post-removalwith Stocking