Progress report: Progress report: Biological mechanisms for Hg Biological mechanisms for Hg

accumulation in largemouth bassaccumulation in largemouth bass

Ben GreenfieldBen Greenfield

San Francisco Estuary InstituteSan Francisco Estuary Institute

Fish Mercury Project Fish Mercury Project

2007 Annual Meeting2007 Annual Meeting

Revised presentation to Scientific Review Panel

Largemouth Bass Hg Largemouth Bass Hg ModelingModeling

Committee reviewed Workplan Jan. 2007Committee reviewed Workplan Jan. 2007 Workplan focus:Workplan focus:

1.1. Can biological mechanisms explain spatial Can biological mechanisms explain spatial differences in fish Hg?differences in fish Hg?

2.2. Can biological mechanisms explain variation Can biological mechanisms explain variation among individuals?among individuals?

3.3. What are the seasonal and annual dynamics What are the seasonal and annual dynamics of Hg accumulation?of Hg accumulation?

4.4. What proportion of Hg burden explained by What proportion of Hg burden explained by recent growth?recent growth?

Largemouth Bass Hg Largemouth Bass Hg ModelingModeling

Committee reviewed Workplan Jan. 2007Committee reviewed Workplan Jan. 2007 Workplan focus:Workplan focus:

1.1. Can biological mechanisms explain spatial Can biological mechanisms explain spatial differences in fish Hg?differences in fish Hg?

2.2. Can biological mechanisms explain variation Can biological mechanisms explain variation among individuals?among individuals?

3.3. What are the seasonal and annual dynamics What are the seasonal and annual dynamics of Hg accumulation?of Hg accumulation?

4.4. What proportion of Hg burden explained by What proportion of Hg burden explained by recent growth?recent growth?

Talk outlineTalk outline1.1. Conceptual modelConceptual model

2.2. Selected resultsSelected results Biological drivers of spatial variation in Hg (Questions 1 and 2)Biological drivers of spatial variation in Hg (Questions 1 and 2)

Growth rateGrowth rate Consumption rateConsumption rate

Conceptual model of Hg Conceptual model of Hg uptake into fishuptake into fish

Fish Mercury

Growth

EliminationEgestion

Spawning Loss

ConsumptionPrey Mercury(MeHg)

Multiple Drivers•Bioavailable Hg•Methylation processes•Uptake into lower trophic levels

Fish Mercury

Growth

EliminationEgestion

Spawning Loss

ConsumptionPrey Mercury(MeHg)

Multiple Drivers•Bioavailable Hg•Methylation processes•Uptake into lower trophic levels

General ApproachGeneral Approach

Query the FMP and other datasetsQuery the FMP and other datasets Focus on consumption and growthFocus on consumption and growth Statistical and mechanistic modelingStatistical and mechanistic modeling

Linear and nonlinear modelingLinear and nonlinear modeling Bioenergetics modelBioenergetics model Hg mass balance modelHg mass balance model

Results: growth rateResults: growth rate Hypothesis: Hypothesis: Higher Hg in slower growing Higher Hg in slower growing

fish explains huge variation in fish explains huge variation in largemouth bass Hglargemouth bass Hg Essington and Houser 2003; Simoneau et Essington and Houser 2003; Simoneau et

al. 2005al. 2005 ““Growth dilution”Growth dilution” Evaluate using estimates of growth rate Evaluate using estimates of growth rate

based on scale data (Gary Ichikawa, based on scale data (Gary Ichikawa, CDFG)CDFG)

Statistical and mechanistic modelingStatistical and mechanistic modeling

•Calculate nonlinear growth curve usingAge vs. length data (Von Bertalanffy)

•Use residuals of this growth curve to estimate relative growth rate of individual fish

AmericanRive

Cosumnes/Mok

Delta

FeatherRiver

SacramentoRi

SanJoaquinRi

Watershed

-200

-100

0

100

200

Gro

wth

Re

sid

ual

AmericanRive

Cosumnes/M

okDelta

FeatherRive

r

SacramentoRi

SanJoaquinRi

Watershed

0.5

1.0

1.52.0

Me

rcu

ry (

pp

m)

Regional patterns in growth residuals not associated with Regional patterns in growth residuals not associated with HgHg

Hg vs. growth residuals by watershed; Pearson’s r = Hg vs. growth residuals by watershed; Pearson’s r = 0.02; N = 60.02; N = 6

*

Examine growth residual (G) vs. Hg Examine growth residual (G) vs. Hg accounting for regional differencesaccounting for regional differences

General linear models to look at effect within stationsGeneral linear models to look at effect within stations Square root Hg = f (station, G, length)Square root Hg = f (station, G, length)

G positively associated with HgG positively associated with Hg Positive effect of body size at a given agePositive effect of body size at a given age Mechanism may be higher Hg in larger preyMechanism may be higher Hg in larger prey

G not significant after length accounted forG not significant after length accounted for Growth dilution hypothesis not supportedGrowth dilution hypothesis not supported

Modeling effect of growth rateModeling effect of growth rate

Mechanistic bioenergetic and Hg mass balance model Mechanistic bioenergetic and Hg mass balance model provided by Marc Trudelprovided by Marc Trudel

Ran simulation for growth and Hg uptake from age 2 to 7 Ran simulation for growth and Hg uptake from age 2 to 7 largemouth basslargemouth bass

Calibrated model to Hg data from Frank’s Tract and to Calibrated model to Hg data from Frank’s Tract and to von Bertalanffy growth curvevon Bertalanffy growth curve

Evaluated effect of refitting model to 95% upper and Evaluated effect of refitting model to 95% upper and lower confidence interval growth rates for data setlower confidence interval growth rates for data set Effect on change in Hg over simulation periodEffect on change in Hg over simulation period

Growth changed by separately changing consumption Growth changed by separately changing consumption rate or activity coefficientrate or activity coefficient

Changing growth rate has limited effect Changing growth rate has limited effect on changes to Hg concentrationon changes to Hg concentration

•Modifying growth by changing consumption -less than 5% effect

•Modifying growth by changing activity - about 20% effect

•Direction of effects are consistent with growth dilution

Increased growth

Decreased growth

Effect of growth rate much lower than Effect of growth rate much lower than effect of prey Hgeffect of prey Hg

•Prey Hg changed from silverside at Big Break to silverside at Cosumnes River

•Hypothesis not supported

Higher growth

Lower growth

Decreased growth

Hypothesis: Hypothesis: fish with higher consumption rates will fish with higher consumption rates will have higher tissue Hghave higher tissue Hg

Consumption rates back-calculated using Hg mass Consumption rates back-calculated using Hg mass balance model (Trudel et al. 2000)balance model (Trudel et al. 2000)

Parameter estimates were obtained using local data Parameter estimates were obtained using local data on size, growth, bass Hg, silverside Hg, and on size, growth, bass Hg, silverside Hg, and temperaturetemperature

Fish Mercury(C)

Growth (G)

Elimination (E)

Egestion (1-

Spawning Loss (K)

Consumption (I)Prey Mercury(Cd)

Results: consumption rateResults: consumption rate

0.001

0.01

0.1

1

Franks Cosumnes Vernalis

Station

Hg

(u

g/g

) o

r C

on

su

mp

tio

n (

1/d

)

Tissue Hg Average Consumption (Ages 3-5)

Increased consumption estimate not associated with increased tissue Hg

Consumption rate estimate proportional to Consumption rate estimate proportional to HgHgfishfish/Hg/Hgpreyprey

Model indicates potential mechanism but Model indicates potential mechanism but not an independent assessmentnot an independent assessment

Don’t have access to best prey Hg data yetDon’t have access to best prey Hg data yet

Modeled consumption rate tracks bioaccumulation factor

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

0 5 10 15 20 25

Bioaccumulation Factor

Con

sum

ptio

n (

d-1)

SummarySummary Growth rate differences not responsible for Hg Growth rate differences not responsible for Hg

variationvariation Hg positively associated with size at a given ageHg positively associated with size at a given age Mechanistic model did not explain much variationMechanistic model did not explain much variation

Preliminary consumption rate results don’t Preliminary consumption rate results don’t indicate positive association with Hgindicate positive association with Hg

Preliminary findings consistent with Preliminary findings consistent with interpretation that abiotic and lower-food web interpretation that abiotic and lower-food web processes drive bass Hgprocesses drive bass Hg Hg spatial patterns not driven by fish biologyHg spatial patterns not driven by fish biology

Next stepsNext steps More extensive mechanistic modelingMore extensive mechanistic modeling

Systematically vary growth, consumption, Systematically vary growth, consumption, temperature, and prey Hg according to temperature, and prey Hg according to observed rangesobserved ranges

Shift focus to temporal dynamics of Hg Shift focus to temporal dynamics of Hg uptake from prey (Questions 3 and 4)uptake from prey (Questions 3 and 4) Dependant on collaboration with UC Davis Dependant on collaboration with UC Davis

team to examine implications of fluctuations in team to examine implications of fluctuations in small fish Hgsmall fish Hg

AcknowledgementsAcknowledgements

Aroon Melwani, John Oram, Jennifer Hunt Aroon Melwani, John Oram, Jennifer Hunt SFEISFEI

Marc Trudel, Department of Fisheries and Marc Trudel, Department of Fisheries and Oceans, CanadaOceans, Canada

Gary Ichikawa, CDFGGary Ichikawa, CDFG

Darell Slotton and Shaun Ayres, UC DavisDarell Slotton and Shaun Ayres, UC Davis

Ancillary materialAncillary material

Potential biological drivers of Potential biological drivers of Hg variationHg variation

Growth rates (growth dilution, starvation Growth rates (growth dilution, starvation concentration)concentration)

Consumption rates Consumption rates Metabolic activityMetabolic activity Fish healthFish health Alternatively, prey Hg (e.g., trophic Alternatively, prey Hg (e.g., trophic

position)position)

Bass Hg does not closely track silverside Hg Bass Hg does not closely track silverside Hg (Grenier et al. 2005 Year 1 Sportfish Report)(Grenier et al. 2005 Year 1 Sportfish Report)

Possibility for mechanisms related to bass growth and Possibility for mechanisms related to bass growth and consumptionconsumption

Ancillary material: Ancillary material: body conditionbody condition

Length vs. mass stations significant in Ancova

2.2 2.3 2.4 2.5 2.6 2.7 2.8Log10(Length)

1

2

3

4Log10(M

ass)

1,11,00,10,0

SJRPOTATO35,SJRVERN36SJR Potato Slough

SJR Vernalis

Overall model R2 = 0.95

General approach: Develop relative body condition using General approach: Develop relative body condition using length weight residualslength weight residuals

Significant differences among sites (ANCOVA using GLM)Significant differences among sites (ANCOVA using GLM)

Results: body conditionResults: body condition Hypothesis:Hypothesis: body condition negatively body condition negatively

associated with [Hg]associated with [Hg] Greenfield et al. 2001; Swanson et al. 2007Greenfield et al. 2001; Swanson et al. 2007

Condition = Residuals of length vs. weight Condition = Residuals of length vs. weight regressionregression

Thinner, leaner fish may be consuming Thinner, leaner fish may be consuming and respiring more to maintain current and respiring more to maintain current body mass.body mass.

““Starvation concentration”Starvation concentration”

No regional patterns in relative body conditions No regional patterns in relative body conditions Hg vs. condition by watershed; Pearson’s r = 0.08; N = 9Hg vs. condition by watershed; Pearson’s r = 0.08; N = 9 Similar results for individual fishes (ancillary materials)Similar results for individual fishes (ancillary materials) Hypothesis not supportedHypothesis not supported

American R

iv

Central D

elt

Cos/Mok R

ive

Eastern Drai

Feather Rive

Northern D

el

Sacramento R

San Joaquin

Western Delt

WATERSHED

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

HG

American R

iv

Central D

elt

Cos/Mok R

ive

Eastern D

rai

Feather Rive

Northern D

el

Sacramento R

San Joaquin

Western D

elt

WATERSHED

-0.2

-0.1

0.0

0.1

CO

ND

ITIO

N

-1.22000E+02

-1.21567E+02

-1.21133E+02

-1.20700E+02

Longitude

37

38

39

40

Latit

ude

-0.2-0.10.00.1

CONDITION

Examine spatial patterns in relative body Examine spatial patterns in relative body conditions - no broad association with Hgconditions - no broad association with Hg

Longitude

37

38

39

40

La

titu

de

0.00.10.20.30.40.50.60.70.8

HG

Condition Hg

Delta San Joaquin

Sacram

ento

Delta San Joaquin

Sacram

ento

Body condition vs. Hg among individual Body condition vs. Hg among individual fish within a sitefish within a site

Approach:Approach: Generate body condition estimates for each Generate body condition estimates for each

individual largemouth bass (N = 498)individual largemouth bass (N = 498) Generate estimates of Hg variation within Generate estimates of Hg variation within

sitessites Residuals from ANOVA of Hg vs. site Residuals from ANOVA of Hg vs. site

No relationship between condition and Hg No relationship between condition and Hg (linear regression p > 0.5)(linear regression p > 0.5)

Body condition not associated with HgBody condition not associated with Hg

Ancillary material: Ancillary material: growth rategrowth rate

1 3 5 7 9AGE

150

240

330

420

510

600

LE

NG

TH

Feather RiveDeltaCosumnes/Mok

WATERSHED

Cosumnes/MokelumneFeather RiverDelta

Graphical analysis of growth rate differences in 3 regions

Statistical output of growth residual Statistical output of growth residual analysisanalysis

Parameters Final R2Is growth residual

significant?Station 0.41Station, G, interaction 0.55 Yes Station, length, interaction 0.75Length 0.19Length, G 0.19 No

G positively associated with HgG positively associated with Hg Results indicate a positive effect of body size at a given ageResults indicate a positive effect of body size at a given age

Length vs. Hg stronger than G vs. HgLength vs. Hg stronger than G vs. Hg Growth residual not significant after length accounted forGrowth residual not significant after length accounted for

Mechanism may be higher Hg in larger preyMechanism may be higher Hg in larger prey Hypothesis not supportedHypothesis not supported

Example plots of growth residuals vs. Hg Example plots of growth residuals vs. Hg at individual stationsat individual stations

-100 -50 0 50 100Growth Residual

0.24

0.36

0.48

0.60M

erc

ury

(u

g/g

we

t)

-50 0 50 100Growth Residual

0.30

0.45

0.60

0.75

0.90

Me

rcu

ry (

ug

/g w

et)

Sacramento River At River Mile 44

Camanche Reservoir

•At some stations (e.g., Sacramento River at River Mile 44), growth residual was positively related to Hg•This is not consistent with the growth dilution hypothesis•At many stations (e.g., Camanche Reservoir), there was not apparent relationship between growth residual and Hg

Ancillary material: Ancillary material: consumption rateconsumption rate

Hg mass balance modelHg mass balance model

Trudel, M., Tremblay, A., Schetagne, R., Rasmussen, J.B., Trudel, M., Tremblay, A., Schetagne, R., Rasmussen, J.B., 2000. Estimating food consumption rates of fish using a mercury 2000. Estimating food consumption rates of fish using a mercury mass balance model. Canadian Journal of Fisheries and mass balance model. Canadian Journal of Fisheries and Aquatic Sciences 57, 414-428.Aquatic Sciences 57, 414-428.

Fish Mercury(C)

Growth (G)

Elimination (E)

Egestion (1-

Spawning Loss (K)

Consumption (I)Prey Mercury(Cd)

Consumption Rate Estimates

0

0.01

0.02

0.03

0.04

2 3 4 5 6 7 8

Age

Con

sum

ptio

n (1

/d)

Franks

Cosumnes

Vernalis

What proportion of Hg burden can What proportion of Hg burden can be explained by recent growth?be explained by recent growth?

Hypothesis: Hypothesis: majority of Hg burden due to majority of Hg burden due to recent growthrecent growth

Preliminary estimates based on empirical Preliminary estimates based on empirical datadata Burden = body mass * Hg concentrationBurden = body mass * Hg concentration Estimated representative body mass at a Estimated representative body mass at a

given age using length at age model and given age using length at age model and length-mass regressionlength-mass regression

Calculated Hg concentration at given ageCalculated Hg concentration at given age

SJ RiverAt Vernalis

CosumnesRiver

FranksTract

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0-2 yr3 yr4 yr5 yr

•60 to 80% Hg due to past 2 yr of growthHypothesis supported

Back up images of excel objects Back up images of excel objects

-20%

-15%

-10%

-5%

0%

5%

10%

15%

20%

25%

Consumption Activity exponent