Fisheries Management to Remediate Mercury Contamination in Sport Fish Colorado Parks and Wildlife 26 September 2013 Hg 80 200.59 Dr. Jesse M. Lepak.

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