Progress report: Biological mechanisms for Hg accumulation in largemouth bass Ben Greenfield San Francisco Estuary Institute Fish Mercury Project 2007 Annual Meeting Revised presentation to Scientific Review Panel

Largemouth Bass Hg Modeling Committee reviewed Workplan Jan Committee reviewed Workplan Jan Workplan focus: Workplan focus: 1.Can biological mechanisms explain spatial differences in fish Hg? 2.Can biological mechanisms explain variation among individuals? 3.What are the seasonal and annual dynamics of Hg accumulation? 4.What proportion of Hg burden explained by recent growth?

Largemouth Bass Hg Modeling Committee reviewed Workplan Jan Committee reviewed Workplan Jan Workplan focus: Workplan focus: 1.Can biological mechanisms explain spatial differences in fish Hg? 2.Can biological mechanisms explain variation among individuals? 3.What are the seasonal and annual dynamics of Hg accumulation? 4.What proportion of Hg burden explained by recent growth?

Talk outline 1.Conceptual model 2.Selected results Biological drivers of spatial variation in Hg (Questions 1 and 2) Biological drivers of spatial variation in Hg (Questions 1 and 2) Growth rate Growth rate Consumption rate Consumption rate

Conceptual model of Hg uptake into fish Fish Mercury Growth Elimination Egestion Spawning Loss Consumption Prey Mercury (MeHg) Multiple Drivers Bioavailable Hg Methylation processes Uptake into lower trophic levels

Fish Mercury Growth Elimination Egestion Spawning Loss Consumption Prey Mercury (MeHg) Multiple Drivers Bioavailable Hg Methylation processes Uptake into lower trophic levels

General Approach Query the FMP and other datasets Query the FMP and other datasets Focus on consumption and growth Focus on consumption and growth Statistical and mechanistic modeling Statistical and mechanistic modeling Linear and nonlinear modeling Linear and nonlinear modeling Bioenergetics model Bioenergetics model Hg mass balance model Hg mass balance model

Results: growth rate Hypothesis: Higher Hg in slower growing fish explains huge variation in largemouth bass Hg Hypothesis: Higher Hg in slower growing fish explains huge variation in largemouth bass Hg Essington and Houser 2003; Simoneau et al Essington and Houser 2003; Simoneau et al “Growth dilution” “Growth dilution” Evaluate using estimates of growth rate based on scale data (Gary Ichikawa, CDFG) Evaluate using estimates of growth rate based on scale data (Gary Ichikawa, CDFG) Statistical and mechanistic modeling Statistical and mechanistic modeling

Calculate nonlinear growth curve using Age vs. length data (Von Bertalanffy) Use residuals of this growth curve to estimate relative growth rate of individual fish

Regional patterns in growth residuals not associated with Hg Regional patterns in growth residuals not associated with Hg Hg vs. growth residuals by watershed; Pearson’s r = 0.02; N = 6 Hg vs. growth residuals by watershed; Pearson’s r = 0.02; N = 6 *

Examine growth residual (G) vs. Hg accounting for regional differences General linear models to look at effect within stations General 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 Hg G positively associated with Hg Positive effect of body size at a given age Positive effect of body size at a given age Mechanism may be higher Hg in larger prey Mechanism may be higher Hg in larger prey G not significant after length accounted for G not significant after length accounted for Growth dilution hypothesis not supported Growth dilution hypothesis not supported

Modeling effect of growth rate Mechanistic bioenergetic and Hg mass balance model provided by Marc Trudel Mechanistic bioenergetic and Hg mass balance model provided by Marc Trudel Ran simulation for growth and Hg uptake from age 2 to 7 largemouth bass Ran simulation for growth and Hg uptake from age 2 to 7 largemouth bass Calibrated model to Hg data from Frank’s Tract and to von Bertalanffy growth curve Calibrated model to Hg data from Frank’s Tract and to von Bertalanffy growth curve Evaluated effect of refitting model to 95% upper and lower confidence interval growth rates for data set Evaluated effect of refitting model to 95% upper and lower confidence interval growth rates for data set Effect on change in Hg over simulation period Effect on change in Hg over simulation period Growth changed by separately changing consumption rate or activity coefficient Growth changed by separately changing consumption rate or activity coefficient

Changing growth rate has limited effect on 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 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: fish with higher consumption rates will have higher tissue Hg Hypothesis: fish with higher consumption rates will have higher tissue Hg Consumption rates back-calculated using Hg mass balance model (Trudel et al. 2000) Consumption rates back-calculated using Hg mass balance model (Trudel et al. 2000) Parameter estimates were obtained using local data on size, growth, bass Hg, silverside Hg, and temperature Parameter estimates were obtained using local data on size, growth, bass Hg, silverside Hg, and temperature Fish Mercury (C) Growth (G) Elimination (E) Egestion (1-  Spawning Loss (K) Consumption (I) Prey Mercury (Cd) Results: consumption rate

Increased consumption estimate not associated with increased tissue Hg

Consumption rate estimate proportional to Consumption rate estimate proportional to Hg fish /Hg prey Model indicates potential mechanism but not an independent assessment Model indicates potential mechanism but not an independent assessment Don’t have access to best prey Hg data yet Don’t have access to best prey Hg data yet Modeled consumption rate tracks bioaccumulation factor

Summary Growth rate differences not responsible for Hg variation Growth rate differences not responsible for Hg variation Hg positively associated with size at a given age Hg positively associated with size at a given age Mechanistic model did not explain much variation Mechanistic model did not explain much variation Preliminary consumption rate results don’t indicate positive association with Hg Preliminary consumption rate results don’t indicate positive association with Hg Preliminary findings consistent with interpretation that abiotic and lower-food web processes drive bass Hg Preliminary findings consistent with interpretation that abiotic and lower-food web processes drive bass Hg Hg spatial patterns not driven by fish biology Hg spatial patterns not driven by fish biology

Next steps More extensive mechanistic modeling More extensive mechanistic modeling Systematically vary growth, consumption, temperature, and prey Hg according to observed ranges Systematically vary growth, consumption, temperature, and prey Hg according to observed ranges Shift focus to temporal dynamics of Hg uptake from prey (Questions 3 and 4) Shift focus to temporal dynamics of Hg uptake from prey (Questions 3 and 4) Dependant on collaboration with UC Davis team to examine implications of fluctuations in small fish Hg Dependant on collaboration with UC Davis team to examine implications of fluctuations in small fish Hg

Acknowledgements Aroon Melwani, John Oram, Jennifer Hunt SFEI Marc Trudel, Department of Fisheries and Oceans, Canada Gary Ichikawa, CDFG Darell Slotton and Shaun Ayres, UC Davis

Ancillary material

Potential biological drivers of Hg variation Growth rates (growth dilution, starvation concentration) Growth rates (growth dilution, starvation concentration) Consumption rates Consumption rates Metabolic activity Metabolic activity Fish health Fish health Alternatively, prey Hg (e.g., trophic position) Alternatively, prey Hg (e.g., trophic position)

Bass Hg does not closely track silverside Hg Bass Hg does not closely track silverside Hg (Grenier et al Year 1 Sportfish Report) Possibility for mechanisms related to bass growth and consumption Possibility for mechanisms related to bass growth and consumption

Ancillary material: body condition

SJR Potato Slough SJR Vernalis Overall model R 2 = 0.95 General approach: Develop relative body condition using length weight residuals General approach: Develop relative body condition using length weight residuals Significant differences among sites (ANCOVA using GLM) Significant differences among sites (ANCOVA using GLM)

Results: body condition Hypothesis: body condition negatively associated with [Hg] Hypothesis: body condition negatively associated with [Hg] Greenfield et al. 2001; Swanson et al Greenfield et al. 2001; Swanson et al Condition = Residuals of length vs. weight regression Condition = Residuals of length vs. weight regression Thinner, leaner fish may be consuming and respiring more to maintain current body mass. Thinner, leaner fish may be consuming and respiring more to maintain current 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 = 9 Hg 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 supported Hypothesis not supported

Examine spatial patterns in relative body conditions - no broad association with Hg Examine spatial patterns in relative body conditions - no broad association with Hg Condition Hg Delta San Joaquin Sacramento Delta San Joaquin Sacramento

Body condition vs. Hg among individual fish within a site Approach: Approach: Generate body condition estimates for each individual largemouth bass (N = 498) Generate body condition estimates for each individual largemouth bass (N = 498) Generate estimates of Hg variation within sites Generate estimates of Hg variation within sites Residuals from ANOVA of Hg vs. site Residuals from ANOVA of Hg vs. site No relationship between condition and Hg (linear regression p > 0.5) No relationship between condition and Hg (linear regression p > 0.5) Body condition not associated with Hg Body condition not associated with Hg

Ancillary material: growth rate

Cosumnes/Mokelumne Feather River Delta Graphical analysis of growth rate differences in 3 regions

Statistical output of growth residual analysis G positively associated with Hg G positively associated with Hg Results indicate a positive effect of body size at a given age Results indicate a positive effect of body size at a given age Length vs. Hg stronger than G vs. Hg Length vs. Hg stronger than G vs. Hg Growth residual not significant after length accounted for Growth residual not significant after length accounted for Mechanism may be higher Hg in larger prey Mechanism may be higher Hg in larger prey Hypothesis not supported Hypothesis not supported

Example plots of growth residuals vs. Hg at individual stations 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: consumption rate

Hg mass balance model Trudel, M., Tremblay, A., Schetagne, R., Rasmussen, J.B., Estimating food consumption rates of fish using a mercury mass balance model. Canadian Journal of Fisheries and Aquatic Sciences 57, Trudel, M., Tremblay, A., Schetagne, R., Rasmussen, J.B., Estimating food consumption rates of fish using a mercury mass balance model. Canadian Journal of Fisheries and Aquatic Sciences 57, Fish Mercury (C) Growth (G) Elimination (E) Egestion (1-  Spawning Loss (K) Consumption (I) Prey Mercury (Cd)

What proportion of Hg burden can be explained by recent growth? Hypothesis: majority of Hg burden due to recent growth Hypothesis: majority of Hg burden due to recent growth Preliminary estimates based on empirical data Preliminary estimates based on empirical data Burden = body mass * Hg concentration Burden = body mass * Hg concentration Estimated representative body mass at a given age using length at age model and length-mass regression Estimated representative body mass at a given age using length at age model and length-mass regression Calculated Hg concentration at given age Calculated Hg concentration at given age

SJ River At Vernalis Cosumnes River Franks Tract 60 to 80% Hg due to past 2 yr of growth Hypothesis supported

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