fisheries management to remediate mercury contamination in sport fish colorado parks and wildlife 26...
TRANSCRIPT
Fisheries Management to Remediate
Mercury Contamination in Sport Fish
Colorado Parks and Wildlife26 September 2013
Hg 80200.59
Dr. Jesse M. Lepak
No advisory
0.3 – 0.5 ppm
Advisory
Data pending
QF (egestion)
C(consumption)
QG
QS
(standard)
QU (excretion)
QR (respiration/metabolism)
QA
(active) QH
(SDA)
(Growth)
+ +
Wisconsin Fish Bioenergetics Model 3.0 (Hanson et al. 1997)
Bioenergetics
Original Hg content + (Consumption * Prey Hg * α) - elimination
Daily predator Hg concentration =
Predator weight
Bioenergetics
0.00
0.25
0.50
0.75
1.00
0 1000 2000 3000 4000 5000 6000
Example: Brush Hollow Reservoir
Immature walleye
Female walleyeMale walleye
Walleye weight (g)
Wal
leye
Hg
(ppm
)
Simulate management to reduce ♂♂ mercury?
• Establish male “baseline” model;• Double and half weight gain at age (changes in
density due to harvest);• Switch to rainbow trout diet and double
growth;• Increase system productivity (bloom or
biomass dilution: lower prey Hg, WI);• Decrease water level fluctuation (decreased
methylation rates: lower prey Hg, SD).
0
0.25
0.5
0.75
1
Walleye age (years)
3 4 5 6 7 8 9 10 11 12
Wal
leye
Hg
(ppm
)Baseline conditions
Walleye age (years)
Wal
leye
Hg
(ppm
)
0
0.25
0.5
0.75
1
Altered growth
CurrentDouble weight gain at ageHalf weight gain at age
3 4 5 6 7 8 9 10 11 12
0
0.25
0.5
0.75
1
Walleye age (years)
Wal
leye
Hg
(ppm
)RBT diet and doubling weight gain at age
3 4 5 6 7 8 9 10 11 12
0
0.25
0.5
0.75
1
Walleye age (years)
Wal
leye
Hg
(ppm
)Increasing system productivity
3 4 5 6 7 8 9 10 11 12
0
0.25
0.5
0.75
1
Walleye age (years)
Wal
leye
Hg
(ppm
)Decreased water level fluctuation
3 4 5 6 7 8 9 10 11 12
Summary• Female walleye had lower than expected Hg
due to RBT consumption (growth dilution);• Simulating increased walleye growth alone
decreased Hg, but not below 0.5 ppm;• Simulations with reduced prey Hg showed the
largest reductions in walleye Hg;• These are only simulations, results may vary
(e.g., methylation increase with productivity);• Simulated responses mid-life span rapidly
reached equilibrium.
Walleye age (years)
Wal
leye
Hg
(ppm
)Mid-life span simulation (gizzard shad diet)
3 4 5 6 7 8 9 10 11 12
0
0.25
0.5
0.75
1
• We tested a whole-lake management action experimentally;
• 25 ha College Lake, dense, slow growing northern pike population (crayfish diet);
• Provided rainbow trout as higher quality forage to quantify growth dilution;
• Repeated measures on individuals (2 months; 30 fish and 1 year; 15 fish);
• A pond component (~40 days) was conducted to verify results.
Do responses really happen this quickly?
College
Lake
N
Rainbow trout stocking
N
25 ha
0.1 ha each
Length, gastric lavage (diet), weightLength, gastric lavage (diet), weight
BiopsyBiopsy Release into College Lake or pondsRelease into College Lake or ponds
50:50 denture 50:50 denture cream/neosporincream/neosporin
Floy Floy TagTag
Initial sampling
• ~1 kg of RBT per pike (27,000, 150 mm);Stocking and recapture
0%
25%
50%
75%
100%
Initial capture
Initialrecapture
Unfed Increasedforage
Recapture(2010)
Die
t com
posi
tion
(% w
et b
iom
ass)
Sample period/treatment
Cray
fish
Oth
er fi
sh Rain
bow
trou
t
Nor
ther
n cr
icke
t fro
gs
Other inverts Warbler
n = 254 n = 30 n = 12 n = 8 n = 15
▼ ▼
At pond draining: 1 RBT remainedNorthern pike diet response
Ponds
Δ w
eigh
t (%
)
Total length (mm)
-10
0
10
20
30
40
400 450 500 550 600 650 700 750 800
Northern pike weight change at length
-50
-25
0
25
50
-50 -25 0 25 50
Δ T-
Hg
conc
entr
ation
(%)
Δ weight (%)
College LakeExperimental ponds
Northern pike Hg response
0
1000
2000
3000
4000
5000
400 500 600 700 800
T-H
g co
ncen
trati
on (p
pm)
Total length (inches)
Pre-manipulationPost-manipulation
• 50% of the pike exceeded advisory levels before; We removed 35% of those from the advisory.
1.25
1.00
0.75
0.50
0.25
0.00 400 500 600 700 800
Northern pike Hg response
T-H
g po
st-m
anip
ulati
on (p
pm)
T-Hg pre-manipulation (ppm)
Recapture (2010) 1:1 line
One year later…
1.25
1.0
0.75
0.50
0.25
0.00.0 0.25 0.50 0.75 1.0 1.25
Implications
• Providing quality (low Hg, high calorie) prey has potential to reduce sport fish Hg rapidly;
• More cost effective and ecologically “safe” to manage for prey species already present or increase productivity/decrease methylation;
• Even if low Hg, high quality prey are present, individual sport fish may have elevated Hg;
• The general patterns observed were present across the landscape in Colorado.
No advisory
0.3 – 0.5 ppm
Advisory
Data pending
N,PN,P
0
0.25
0.5
0.75
1
-20 0 20 40 60 80 100 120 140
Chlorophyll a (mg/L)
Prob
abili
ty o
f an
advi
sory
Given that you caught a piscivore….
PCA (unitless)
Prob
abili
ty o
f an
advi
sory
0
0.25
0.5
0.75
1
-4 -2 0 2 4 6
PCA including chlorophyll a, secchi depth and total phosphorus
Given that you caught a piscivore….
Conclusions
• Food web structure (from productivity to predators) is extremely important;
• Food web structure can change rapidly through management and stochasticity;
• Caution, there are reasons why some of these actions may increase bioaccumulation (e.g., increasing productivity);
• Implications for monitoring and potentially remediating mercury contamination in sport fish.
Thank you
Hg 80200.59