DRAFT

2015 Sturgeon Derby 

Report

Jennifer Sun, April Robinson, Jay Davis, Phil Trowbridge

San Francisco Estuary Institute, Richmond, CA

Robin Stewart

United States Geological Survey, Menlo Park, CA

Vince Palace

Stantec Inc., Winnipeg, MB, Canada

Zachary Jackson

U.S. Fish and Wildlife Service, Lodi, CA 
2

Table of Contents 

Executive Summary.......................................................................................................................................3

Introduction ..................................................................................................................................................4

Methods........................................................................................................................................................6

Field Sample Collection............................................................................................................................6

Laboratory Analysis and Data Quality Assurance ...................................................................................7

Statistical Methods ...................................................................................................................................8

Results and Discussion..................................................................................................................................8

Summary Statistics for Selenium...............................................................................................................8

Comparison with Historical Data.............................................................................................................9

Age, Length, and Tissue Se .....................................................................................................................11

Se Correlations Among Tissues..............................................................................................................11

C, N, and S Isotopes................................................................................................................................11

Se in Fin Rays.........................................................................................................................................12

Se in Otoliths...........................................................................................................................................13

Conclusions.................................................................................................................................................13

Tables and Figures ......................................................................................................................................14

References ..................................................................................................................................................28
3

Executive Summary

The Original Sturgeon Derby (Derby) is an annual fishing derby held in Bay Point, CA that 

presents an opportunity to collect and analyze a variety of tissue samples from angler-harvested 

female white sturgeon (Acipenser transmontanus) for selenium (Se). The collection and analysis 

of these tissues sampled during the 2015 Derby helped to both develop non-lethal sampling 

methods, and better understand the correlation between tissues that can be collected non-lethally 

(muscle plug, fin ray) and those that are of greater toxicological interest (ovary, liver). Otolith 

samples were also collected to inform the development of the fin ray Se microchemical analysis. 

Between January 31 and February 1, 2015, tissue samples were obtained from 8 female white 

sturgeon collected at the Derby and analyzed for Se. The fin rays were also used to estimate age 

of the fish, and the muscle plugs analyzed for C, N, and S isotopes, to provide information about 

recent habitat and foraging behavior.

Se concentrations in muscle plug, liver, and ovary tissue samples were in the upper range of 

concentrations previously measured in San Francisco Bay white sturgeon. Three of the eight 

muscle plug samples showed Se concentrations above the North Bay TMDL tissue target of 11.3 

μg/g dw. Fish age and length were positively correlated, but were not correlated with tissue Se, 

with the exception of a positive relationship between fork length and ovary Se. No clear 

relationship was observed between Se concentrations in muscle plug, liver, ovary, or fin ray 

samples (measured as the maximum or average value in the outer annulus). Isotope data 

suggested the majority of the fish collected had been feeding on invertebrates in Suisun Bay, 

although one may have been piscivorous and several may have been feeding in San Pablo Bay or 

the Delta.

Because of the small sample size and narrow size range of the fish collected at the Derby, these 

preliminary results do not conclusively describe patterns of selenium concentration in white 

sturgeon or relationships between selenium in various sturgeon tissues . Additional data collected 

during the 2016 Derby will help to further evaluate the relationships observed in this data set.
4

Introduction

Selenium is an essential micronutrient that can bioaccumulate and become toxic at 

concentrations just an order of magnitude greater than those required for biological function 

(Baginska 2015). Since 1998, San Francisco Bay has been identified as impaired by selenium 

under the Clean Water Act, having been measured at levels of potential concern in fish and other 

wildlife, including white sturgeon (Acipenser transmontanus). Despite significant selenium load 

reductions from major sources of selenium since 1998, selenium concentrations in wildlife have 

continued to occasionally exceed toxicity thresholds and regulatory guidelines (Presser and 

Luoma 2013, Baginska 2015). 

In order to control and reduce selenium impairment, the San Francisco Bay Regional Water 

Quality Control Board initiated development of a selenium TMDL for North San Francisco Bay

in 2007, and formally adopted the regulation in 2015. The TMDL established a target 

concentration of 11.3 μg/g dw in white sturgeon muscle tissue as the basis for evaluating 

impairment (Baginska 2015). White sturgeon are particularly vulnerable to selenium exposure in 

the Bay because its diet consists primarily of the selenium-rich overbite clam (Potamocorbula

amurensis) (Beckon and Maurer 2008; Stewart et al. 2004). In addition to their benthic feeding 

habits, other high-risk factors for white sturgeon include their longevity (lifespan of over 100 

years), year-round resident status in the Bay-Delta system, and long egg maturation times 

(several years) (Beckon and Maurer 2008). 

The Regional Monitoring Program for Water Quality in San Francisco Bay (the RMP) was 

established in 1993 to provide data and information to inform management decisions for the Bay. 

In 2014, the RMP formed a Selenium Workgroup with the goal of identifying low-cost, nearterm Se monitoring elements to support policy development and decision-making, which now 

includes implementation of the North Bay TMDL. In 2014, the Selenium Workgroup proposed a 

special study to collect a variety of tissue samples from white sturgeon at the 32nd Annual 

Original Sturgeon Derby (Derby) for selenium analysis, in order to address the following 

objectives:

1. Develop methods for non-lethal white sturgeon tissue sample collection and selenium 

analysis, including muscle plug and fin ray sampling techniques; and

2. Evaluate the relationship between tissues that can be monitored non-lethally (muscle plug 

or fin rays) and tissues that are more directly tied to adverse reproductive effects (ovary 

and eggs).

Evaluation of the non-lethal muscle plug monitoring method began during the RMP’s 2009 and 

2014 Status and Trends sampling event, during which 12 paired muscle plug and fillet samples 

were collected per year throughout the San Francisco Bay (data can be accessed at cd3.sfei.org). 

The muscle plug method was further developed during the 2014 and 2015 Sturgeon Muscle Plug 

special studies, during which several muscle plug samples were collected from live white 

sturgeon during annual California Department of Fish and Wildlife sturgeon tagging efforts each 

fall (DuBois and Harris 2015; more information at http://www.dfg.ca.gov/delta/data/sturgeon/ 

bibliography.asp). Additional muscle plug samples collected during the Derby helped to further 
5

increase sample size and improve both the laboratory analysis and interpretation of this type of 

data.

The 2015 Sturgeon Derby also presented the opportunity to evaluate a second non-lethal 

monitoring method using fin ray samples. Dr. Vince Palace and Dr. Norman Halden at the 

University of Manitoba have developed a method for microchemical analysis of Se and other 

trace metals in sturgeon fin rays as an alternative to microchemical analysis in otoliths, which are 

known to be stable tissues that are strong predictors of ovary selenium but cannot be collected 

non-lethally (Reash et al. 2014). Fin rays can be taken as a clip and are easy to collect by nonspecialists, and have been shown to be non-harmful to sturgeon (Collins and Smith 1996). 

Additionally, because fin rays have a regular growth pattern similar to otoliths, concentrations of 

selenium and other elements can be measured in each annual ring and assembled into a time 

series of selenium concentrations. These data can potentially be used to better understand the 

relationship between water, prey, and sturgeon tissue concentrations over time. The Derby also 

presented the opportunity to collect otoliths for a comparison analysis to establish the chemical 

stability of fin ray samples.

In addition to developing non-lethal monitoring methods, the second objective of the Sturgeon 

Derby study was to establish a relationship between tissues that can be monitored non-lethally 

and tissues that are more directly tied to adverse reproductive effects – ovaries or eggs. The 

primary pathway of selenium exposure in white sturgeon is uptake through dietary selenomethionine and maternal transfer to the egg yolk sac, where elevated selenium concentrations 

can cause developmental deformities or mortality (Baginska 2015). In other species, linear or 

log-transformed relationships have been established between muscle plug and ovary 

concentrations (Osmundson and Skorupa, 2011). A similar relationship could also potentially be

established using fin ray Se data. 

The 2015 Sturgeon Derby study was implemented by the RMP, the U.S. Fish and Wildlife 

Service (USFWS), the U.S. Geological Survey (USGS), and Stantec. In addition to addressing 

the objectives previously described, the study was designed to contribute useful information 

relative to key questions identified by the RMP and the Selenium Strategy (Table 1).
6

Table 1. Key Selenium Strategy and RMP management questions addressed by this study

RMP Management Questions addressed

1. Are chemical concentrations in the Estuary at levels of potential concern and 

are associated impacts likely?

b. What potential for impacts on humans and aquatic life exists due to 

contaminants in the Estuary ecosystem?

4. Have the concentrations, masses, and associated impacts of contaminants in the 

Estuary increased or decreased?

b. What are the effects of management actions on the potential for adverse 

impacts on humans and aquatic life due to Bay contamination?

Selenium Strategy questions addressed

1. What are appropriate thresholds?

2. Are the beneficial uses of San Francisco Bay impaired by selenium?

3. What is the spatial pattern of selenium impairment?

4. How do selenium concentrations and loadings change over time?

Methods

Field Sample Collection

The Derby is an annual angling competition held by the Foundation Sportsman’s Club out of 

McAvoy Harbor in Bay Point, CA. The Derby provides a rare opportunity to collect tissue 

samples from white sturgeon harvested by anglers. The USGS initiated sample collections from 

the derby in 2000/2001(Stewart et al. 2004) and USFWS has collected samples more recently 

over the past several years, and helped facilitate the collection of additional samples for the 

RMP. 

The Derby awards cash prizes to anglers that bring in fish closest to a chosen target length. The 

target size in 2015, chosen randomly from within the legal slot limit of 40-60 inches (101.6-

152.4 cm fork length), was 51 inches (129.5 cm). Fish were permitted to be caught at any time 

between 7:00 am on January 31, 2015 and 1:00 pm on February 1, 2015, and anywhere in the 

San Francisco Estuary. Fish were brought alive to McAvoy Harbor to be measured, and in some 

cases, sacrificed and processed for their tissues.

Tissues were collected from all fish caught, except those that anglers wanted to release alive. A 

total of 27 fish were sampled, including 19 males and 8 females. Tissue samples collected for 

analysis by the RMP included muscle plugs, ovary (in female fish), fin rays, and otoliths. Liver 

samples were collected and analyzed for this study pro-bono by the USGS in Menlo Park. 

Because the RMP was primarily interested in understanding Se impacts on white sturgeon 
7

reproduction, only samples collected from the 8 female sturgeon were analyzed for the RMP. 

The remaining samples were stored for potential future analysis. 

Additional tissue samples were collected by and for collaborating agencies. Blood samples were 

collected for Se analysis by USGS, gut contents for diet analysis by Cramer Fish Sciences, and 

additional ovary samples for histology analysis. USFWS collected a second set of fin ray and 

blood samples for each fish for aging and isotope analysis, as well as a variety of tissues for 

histopathology analyses. Liver and gut samples were not collected from all males, and in several 

cases, otolith, blood plasma, and gut contents could not be collected. A description of all samples 

collected at the Derby, including samples that were archived or analyzed by other agencies, is 

presented in the 2015 Sturgeon Derby Special Study Field Sampling Summary (Robinson and 

Sun, 2015, included in this report as Appendix A).

Once measured for length, fish were killed with a blow to the head by a 4 lb sledge hammer. The 

entire marginal fin ray was removed using a sharp knife, from the point of articulation down to 

the terminal end of the ray as described by Koch et al. 2008.Otoliths were accessed by cutting 

into the skull with a hacksaw. For liver and ovary samples, several small samples were collected 

over the length of the organ and composited for analysis. Muscle plug samples were taken in a 

manner similar to the method used to collect muscle plugs for the RMP 2014 Sturgeon Muscle 

Plug Special Study1(Sun et al., 2016). Two or three muscle plugs were collected from the region 

laterally adjacent to the dorsal fin with a 5 mm diameter biopsy plug, ensuring the collection of 

enough sample mass for selenium and isotope analysis. Following sample collection, otoliths 

and fin rays were dried at room temperature. All other samples were frozen until they were sent 

to various labs for archiving or analysis. A more detailed description of the fish processing and 

sample collection methods is also documented in the 2015 Sturgeon Derby Special Study Field 

Sampling Summary (Appendix A).

Laboratory Analysis and Data Quality Assurance

Se and moisture in muscle plug (skin off), liver, and ovary tissue were analyzed by USGS in one

lab batch – including 1 lab duplicate for each of the 3 tissue types. Three method blanks and 6 

certified reference material (CRM) analyses were also analyzed. Results were reported blank 

corrected. Accuracy was evaluated using CRMs with certified values for selenium, and precision 

was evaluated using duplicate samples and samples collected from other studies. 

C, N, and S isotopes were analyzed by UC Davis in one lab batch, together with the nine samples 

collected for the 2014 Selenium Muscle Plug Study (Sun et al. 2016). One lab replicate was run 

for C and N isotopes, which were analyzed concurrently, but not enough sample mass was 

available to run a lab replicate for S isotopes. QC analyses included four CRMs for C and N

isotopes, 7 laboratory control materials (LCMs) for C and N percent masses, over 30 LCM 

results for C and N isotopes, and 24 LCMs for S isotopes. No method blanks were analyzed.

 

1

In contrast, muscle plugs collected during 2009 and 2014 RMP Status and Trends monitoring were collected using 

8 mm biopsy plugs. During that study, plugs were taken from an arbitrary location on a fillet collected from the 

posterior, dorsal side of each fish.
8

Selenium microchemical analysis was also conducted on 26 fin ray samples by Stantec, 

including samples taken from both male and female fish. A high powered laser ablation mass 

spectrometry technique (laser ablation inductively coupled plasma mass spectrometry or LAICP-MS) enabled the analysis of Se down to the ng/g level from the core of the fin ray 

(representing early life) to the outer edge (representing late life) across each annular growth ring.

Annuli were counted to estimate fish age. The fin rays were then analyzed as laser-ablated tissue 

with an ICP-MS, resulting in multiple selenium measurements per annulus. The resulting data 

were correlated with the growth ring pattern, aggregated, and assembled into a life history time 

series of selenium concentrations. The average and maximum Se concentrations in the outer ring 

of fin rays will be presented in this report. The full results from this analysis will be published by 

Stantec in a separate report and presented in greater detail in the 2016 Sturgeon Derby report. A 

similar method will be used to conduct Se microchemical analyses in otoliths, which yield 

temporal signatures that are known to be chemically stable. The otolith results will then be used 

to evaluate the stability of the Se signature in fin rays.

Statistical Methods

Data analyses were performed using RStudy v0.99.489. The relationship between age and length 

of Sturgeon Derby fish was evaluated using a linear regression model. All other statistics were 

conducted using non-parametric methods. Comparisons of data with previously published studies 

were conducted using non-parametric Mann-Whitney-U tests. Correlations were determined 

using the non-parametric Spearman’s rank correlation test.

Results and Discussion

Tissues were obtained from a total of eight female white sturgeon collected at the Derby. The 

target size was 51 inches (129.5 cm) fork length, and samples were collected from fish ranging 

from 112.7 to 149.2 cm (median = 129.4 cm; mean = 129.1 cm). Estimated ages ranged from 14 

to 20 yr (median = 17 yr, mean = 16.6 yr). Exact sampling locations were not recorded, but 

informal conversations with anglers suggested that the majority of fish were collected in Suisun 

Bay. Field measurements and the results of Se and isotope analyses in muscle plug, ovary, liver, 

and fin ray are presented in Table 2. 

Selenium, C isotopes and N isotopes were analyzed in all eight female fish, but S isotopes were 

only measured in a subset of samples with enough sample mass for analysis. CRM recoveries 

and relative standard deviations met method quality objectives for selenium and isotopes (Ye et 

al. 2015).

Summary Statistics for Selenium

Se concentrations in muscle plugs collected from the eight female fish at the Derby ranged from 

6.2 to 22 μg/g dw, with a median of 8.9 and mean of 11.2 μg/g dw, just below the TMDL target 

of 11.3 μg/g dw. The standard deviation of muscle plug Se concentrations was 1.9 μg/g dw. 

Three of the eight muscle plugs (38%) had Se concentrations above the TMDL target. These 
9

three values (15, 15 and 22) were substantially higher than the remainder of the samples, which 

remained between 5 and 10 μg/g dw. 

Se concentrations in ovaries ranged from 3.5 to 47 μg/g dw, with a median of 17 and mean of 20

μg/g dw. The standard deviation of ovary Se concentrations was relatively high, at 5.1 μg/g dw. 

The distribution was driven by a couple particularly high values (47 and 32 μg/g dw; the next 

highest values were 23 and 17 μg/g dw).

Se concentrations in the liver were higher, ranging from 11 to 74 μg/g dw, with a median of 31 

and mean of 36 μg/g dw. The standard deviation of liver Se concentrations was 6.8 μg/g dw.

Again, the high mean Se concentration was driven in part by one particularly high Se value (74 

μg/g dw) measured in the largest fish. 

One anomalous fish (WHST-27M) accounted for a puzzling combination of the extreme values 

in this small dataset. This individual had the lowest muscle plug Se value measured during this 

study, and was the largest, although not the oldest, fish. This individual also corresponded with 

the highest ovary and liver Se concentrations measured during this study. 

Comparison with Historical Data

Tissue Se concentrations measured during the Derby were in the upper range of those measured 

previously in white sturgeon in San Francisco Bay (Figure 1). The muscle plug Se concentrations

measured during the Derby (8.9 μg/g dw, range= 6.2-22 μg/g dw; n=8) were significantly greater

than the plug and fillet concentrations measured in female sturgeon in RMP Status and Trends 

monitoring (plugs: median 5.3 μg/g dw, range 2.6-7.5 μg/g dw, n=11 measured in 2009 and 

2014, p=0.0003; fillets: median 4.7 μg/g dw, range 1.8-12 μg/g dw, n=22 measured 1997-2014, 

p=0.001). Se concentrations in Derby plugs were also significantly greater than those measured 

in female muscle fillets reported by Linares-Casenave et al. (median 5.4 μg/g dw; range 2.6 – 19 

μg/g dw; fish collected in 2003-2005; p=0.01), and in the upper range of plug Se measured 

during the RMP’s 2014 Muscle Plug study (median 4.4 μg/g dw; range 1.8-25 μg/g dw; n=8; 

p=0.06) (Sun et al. 2016). 

Ovary and liver tissue Se concentrations measured during the 2015 Derby were similarly 

relatively high compared to previous studies (Figure 1). Ovary Se concentrations measured in

Derby study (median 16.9 μg/g dw; range 3.5-47 μg/g dw; n=8) were significantly greater than 

those reported by Linares-Casenave et al. (median 3.2 μg/g dw; range 1.1-46.7 μg/g dw; n=29; 

p=0.03), and higher but not significantly different from samples collected during the RMP’s 

2014 Status and Trends monitoring event (median 7.3 μg/g dw; range 4.3-7.4 μg/g dw; n=3; 

p=0.19), largely due to the small sample size of the latter dataset. Liver Se concentrations 

(median 31 μg/g dw; range 11-74 μg/g; n=9) were even more elevated compared to 

concentrations previously reported in female sturgeon by Linares-Casenave et al. (median 7.9 

μg/g dw; range 4.7 – 34 μg/g dw; n=24; p=0.0004) and measured in female sturgeon collected by 

the RMP in 2009 (median 7.2 μg/g dw; range 4.5-16 μg/g dw; n=7; p=0.001).
10

Two factors may be contributing to the high Se concentrations observed in this study relative to 

previous studies. First, the relatively high Se concentrations measured during this study may

have been influenced by elevated Se concentrations in P. amurensis, the primary prey item of 

white sturgeon in the North Bay, in recent years due to low river flows during the drought 

(Stewart, unpublished data). Both muscle plug and liver concentrations measured during this 

study were more similar to Se concentrations measured by Stewart et al. (2004) in fish collected 

in January, after a period of low river flows. Second, the timing of sample collection, and its 

impact on fish reproductive status, may also have contributed to the observed Se concentrations. 

Female white sturgeon in San Francisco Bay spawn every two or more years in the spring, 

typically between late February are early May, with peak activity occurring in March and April

(Kohlhorst 1976). Selenium can substitute for sulfur in proteins of the egg yolk precursor 

vitellogenin, causing selenium to accumulate in the liver and ovaries prior to spawning (Linville 

2006). Increased production of vitellogenin and egg yolk proteins in the liver and ovary of prespawning white sturgeon could be contributing to elevated Se concentrations measured in these

tissues. This effect was observed in a study published by Linares-Casenave and others in 2015, 

in which significantly higher Se levels were measured in the muscle, liver, and gonads of 

vitellogenic compared to pre-vitellogenic female white sturgeon (Student’s t-test; muscle: 

p=0.02; ovary: p=0.0008; liver: p=0.0003; n=18 pre-vitellogenic, 8 vitellogenic females). The 

authors of this study postulated that dietary changes prior to spawning could be contributing to 

elevated Se in tissues as well.

Sturgeon sampled between April and August during RMP Status and Trends monitoring, or 

between August and October as part of the 2014 Selenium in Sturgeon Muscle Plugs study, 

would not be expected to be producing vitellogenin. However, some females collected in late 

January and early February during this Derby could be expected to have begun vitellogenin 

production. Ovary and muscle plug Se measured during the Derby were more similar to the 

distribution of Se previously reported by Linares-Casenave et al. (2005) for vitellogenic females

(muscle: median 9.5 μg/g dw; ovary: median 20.6 μg/g dw; n=8). Ovary Se concentrations in 

Derby fish were significantly higher than those reported by Linares-Casenave et al. in previtellogenic females (p=0.001), but not in vitellogenic females (p=0.72). Similarly, muscle plug 

Se concentrations in Derby fish were significantly higher than those in the pre-vitellogenic 

females (p=0.0001), but not vitellogenic females (p=0.07). Liver Se concentrations measured 

during the Derby were significantly higher than both the pre-vitellogenic and vitellogenic 

females measured by Linares-Casenave et al (2015).

While reproductive stage was not identified for the 2015 Derby Study, 7 of the 8 females 

sampled were within the age range at which female white sturgeon typically mature (15 to 32 

years). Histology analysis of ovaries collected during the 2016 Sturgeon Derby special study will 

allow a direct evaluation of the impact of sturgeon maturity on muscle and ovary Se 

concentrations.
11

Age, Length, and Tissue Se

Similar to other studies, a significant positive correlation was observed between age and fork 

length in the 8 Derby sturgeon (p=0.04, R

2=0.46) (Figure 2). However, when comparing age and 

fork length to tissue Se concentrations (Figure 3), a significant positive relationship was 

observed only between fork length and ovary Se, based on a non-parametric rank correlation test

(Spearman’s rank correlation, rho=0.80, p=0.02). No significant relationship between age or fork 

length and muscle plug Se was detected within this size range. In contrast, Linares-Casenave et 

al. (2015) found a significant positive relationship between (1) Se in muscle and fish age, and (2) 

liver Se and fish length, based on a comparison of concentrations measured in fish separated into 

three size classes ranging from 53 to 170 cm (age 4 - 28). All fish collected during the Derby fell 

within a much narrower size and age range (112.7 – 149.2 cm fork length; 12 – 20 yrs), making 

it more difficult to assess the relationship between these characteristics and measured Se

concentrations (Figure 3). The small sample size of this data set also makes detection of 

correlations more difficult. Se and histology data from a different size range of fish collected 

during the 2016 Derby will increase the sample size and allow for further evaluation of the 

relationships reported by Linares-Casenave et al. 

Se Correlations Among Tissues

Based on the small number of samples analyzed in this study, no apparent positive or negative 

relationship among the tissues sampled was observable (Figure 4). The absence of a clear 

relationship may be related to the small sample size. Poor correlation was also observed between 

these tissues in female sturgeon measured by Linares-Casenave et al. (2015) (Figure 5). In this

study, as was previously described, these high Se concentrations largely corresponded with 

vitellogenic females sampled prior to the spawning season. It is possible that in the pre-spawning 

season, when Se concentrations are high, the rate of Se incorporation into the liver and ovary is

more strongly influenced by variable factors such as recent foraging location and temporal 

proximity to spawning. Additional data collected from fish of a different size and age range

during the 2016 Sturgeon Derby, together with data on reproductive maturity, will hopefully help 

clarify relationships of Se concentrations in these tissues.

C, N, and S Isotopes

C, N, and S isotopes values were measured in a subset of the muscle plug samples with enough 

sample mass for analysis (Table 2, Figures 6-9), and may provide information about habitat use 

and foraging. The measured isotope values generally fell within the range of values previously 

observed in white sturgeon collected in the North Bay (Stewart et al. 2004). δ

15N values ranged 

from 14.6 to 17.9‰, suggesting mixed foraging patterns, similar to what was observed in the 

2014 Muscle Plug study (Sun et al. 2016). Fish with lower δ15N values were likely foraging more 

on invertebrates, while fish with higher δ15N were likely more piscivorous. However, the 

measured δ15N values in fish collected both during the 2014 Muscle Plug study and the 2015 
12

Derby study suggest that the majority of fish are feeding on P. amurensis. No clear trend of 

muscle Se relative to δ

15N is apparent in the preliminary dataset (Figures 6 and 7). 

δ

13 C values ranged from -21.7 to -28.8 ‰, which is similarly consistent with expected values for 

sturgeon caught in North San Francisco Bay and the Delta, based on recently collected δ13C 

values measured in P. amurensis (Robin Stewart, personal communication). In contrast with fish 

caught in Suisun Bay during the fall 2014 Sturgeon Muscle Plug study, the generally lower δ13C 

values in the Derby fish may reflect a seasonal shift in P. amurensis δ

13C values or a shift to

foraging closer to the Delta. Across both studies, the highest muscle plug Se concentrations 

were measured in fish collected between -23.0 and -26.7‰ δ

13C (Figures 6 and 7). This 

corresponds with δ

13 C values for clams in Suisun Bay, where selenium concentrations in P. 

amurensis are highest (Stewart 2013).

δ

34 S values ranged from 12.4 to 17.9‰, consistent with foraging in the fresh and brackish 

waters of the Bay. The highest liver and ovary values were observed in sturgeon with widely 

varying stable isotope values.

Se in Fin Rays

Preliminary data on fin ray analyses were presented by Dr. Palace at the SETAC North America 

conference in November 2015 (Palace, 2015). Multiple selenium measurements can be made 

across a single annular ring of the fin ray, resulting in multiple measurements representative of 

sturgeon tissue Se for any given year. The average and maximum Se concentrations measured in 

the outermost annular ring for each fish are presented in Table 2. 

Additional analysis of the data planned by Dr. Palace, using different summation and averaging 

methods, will further probe the relationship between fin ray and muscle tissues, and the potential 

use of fin rays to non-lethally monitor Se in sturgeon. Some initial observations are:

 The maximum Se concentrations measured in fin ray tissue deposited in the most recent 

year ranged from approximately 0.2 to 0.8 μg/g, with the highest and lowest values 

observed in males. The average across all fish (male and female) of the maximum Se

concentration measured in the outermost annular fin ray ring has remained stable for the 

past 6 years at just below 0.5 μg/g. 

 Initial analyses show widely varying temporal patterns in the fin ray Se concentrations of 

the 8 female fish. Time series of the maximum annual Se concentrations show either 

increasing or decreasing trends in different fish in recent years, and longer time series 

over the lifespan of each fish reveal a similar level of variation in both trends and level of 

stability in Se concentration.

 Initial analyses have not indicated a significant correlation between fin ray and tissue Se

concentrations (Figure 10). The maximum and average Se concentrations as measured in 

the outer fin ray annulus of each fish, composed of the most recently deposited tissue, 

showed poor correlation with Se muscle plug concentrations.

Additional fin ray data will be collected at the 2016 Sturgeon Derby. The combined dataset from 

2015 and 2016 will be analyzed and presented in the 2016 Derby report. 
13

Se in Otoliths

Microchemical analyses will be conducted on the 2015 Derby otoliths, together with the otoliths 

that will be collected at the 2016 Sturgeon Derby in February 2016. A comparison of otolith and 

fin ray results will help evaluate the stability of Se concentrations in fin ray annuli and inform 

the interpretation of the fin ray data. Analysis of the combined 2015 and 2016 dataset will be 

included in the 2016 Derby Report.

Conclusions

The muscle plug, ovary, and liver Se concentrations measured in this study were in the upper 

range of previously measured values. The relatively high Se concentrations observed during this 

study may be influenced by the select characteristics of the Derby fish, which were only females 

collected shortly before spawning season, following low flows, in a region known to have high 

prey Se concentrations. The isotope data suggest that although some fish collected during the 

Derby appeared to have been foraging into the Delta and possibly San Pablo Bay, the fish with 

the highest selenium concentrations were feeding largely on P. amurensis in Suisun Bay, where 

clam selenium concentrations are highest. 

The poor correlations among Se concentrations in different tissues suggest that, at least within 

the narrow size range of fish collected during the Derby, muscle plug Se concentrations are not 

closely reflecting Se concentrations in the ovary and liver, and may not be reflective of Se

toxicity impacts being experienced by these fish and their offspring. However, the sample size 

for this study was too small to draw conclusions. This hypothesis will be tested more rigorously 

after additional data are collected in the 2016 Derby.

The low sample size and relatively narrow length and age range of fish caught during the Derby

are likely contributing to the poor correlation observed between Se in various tissues, and 

between either length or age and tissue Se. In contrast with previous studies, only fork length and 

ovary Se were significantly correlated. Additional data from a different size range of fish, as well 

as reproductive maturity data, collected during the 2016 Sturgeon Derby will be valuable in 

further evaluating these relationships. Otolith analysis will also contribute to the full evaluation 

of fin ray Se microchemistry as a reliable method to analyze Se bioaccumulation and predict Se 

concentrations in other tissues. Collection of these additional samples is planned for February 6-

7, 2016, and the results of this study will be published in late 2016.
14

Tables and Figures

Table 2. 2015 Sturgeon Derby Study: field measurements, selenium and isotope results in female fish.

Sample 

ID

Sample 

Date

Fork 

Length 

(cm)

Age

(yr)

Muscle Plug Ovary Liver Muscle Plug Fin Ray

Sample 

Weight 

(mg dw)

% 

Moisture

Selenium 

(μg/g

dw)

Selenium 

(μg/g

dw)

Selenium 

(μg/g

dw)

d13C 

Isotope

(‰)

d15N 

Isotope

(‰)

d34S 

Isotope

(‰)

Max

Selenium

(μg/g)

Average

Selenium

(μg/g)

WHST03M1/31/2015 124.5 16 64.5 53.8 7.0 4.6 30 -27.9 16.8 17.5 0.53 0.32

WHST06M1/31/2015 124.1 14 35.1 71.4 22 17 29 -26.7 16.5 17.2 0.47 0.28

WHST08M1/31/2015 131.9 17 15.5 74.0 15 32 11 -23.0 16.6 14.7 0.60 0.28

WHST09M1/31/2015 131.4 17 36.3 75.8 15 16 48 -25.3 17.0 17.2 0.40 0.27

WHST10M1/31/2015 112.7 12 31.4 74.4 9.5 3.5 22 -27.2 15.0 12.4 0.54 0.40

WHST15M1/31/2015 127.3 20 16.7 80.1 7.5 17 31 -26.0 15.4 14.0 0.45 0.30

WHST17M2/1/2015 131.4 18 38.0 79.1 8.3 23 45 -21.7 17.9 16.9 0.37 0.26

WHST27M2/1/2015 149.2 19 35.0 57.6 6.2 47 74 -28.8 14.6 15.1 0.51 0.29

Average 129.1 16.6 11 20 36 -25.8 16.2 15.6 0.48 0.30

Median 129.4 17.0 8.9 17 31 -26.4 16.5 16.0 0.49 0.29

Standard Error 3.6 0.9 1.9 5.1 6.8 0.9 0.4 0.7 0.03 0.02
15

Figure 1. Muscle plug, ovary, and liver selenium concentrations measured in San Francisco Bay 

white sturgeon during the 2015 Sturgeon Derby and previous studies. The previous studies from 

which data are included on these graphs are: Linares-Casenave et al. (2015), 2014 Muscle Plug 

(RMP 2014 Sturgeon Muscle Plug Special Study), RMP S&T (muscle fillets or plugs collected 

during RMP Status and Trends sport fish monitoring, 1997-2014 or 2009-2014, respectively). 

The white bars show the median concentration for each set of samples, and points represent 

measurements of individual fish. Points are colored by sex and maturity, where data are available 

(M = male, U = unknown sex, F = female of unknown maturity, F preVTG = pre-vitellogenic 

female, F VTG = vitellogenic female).

Jan/Feb Year-Round Sept-Oct April-Aug April-Aug

Jan/Feb Year-Round April-Aug 

Jan/Feb Year-Round April-Aug 
16

Figure 2. Relationship between fish age and fork length in eight female fish caught during the 

Derby.
17

Figure 3. Relationship between selenium concentration in muscle plug, ovary, and liver tissue

and fish age or length.
18

Figure 4. Relationships between selenium concentrations in muscle, ovary, and liver tissue

collected from female sturgeon at the 2015 Sturgeon Derby.
19

Figure 5. Relationships between selenium concentrations in muscle, ovary and liver tissue in 

female sturgeon, as reported in Linares-Casenave et al., 2015.
20

Figure 6. Relationship between muscle plug selenium and C, N, and S isotopes in white sturgeon 

muscle plugs collected during the 2014 Muscle Plug study and 2015 Sturgeon Derby study. The 

d34S value for 0924-01 was considered dubious by the analytical laboratory.
21
22

Figure 7. Muscle plug selenium concentration compared with C and N isotopes in white

sturgeon collected during the 2014 Selenium in Muscle Plugs study and 2015 Sturgeon Derby 

study. Each point represents an individual fish. Points are labeled by muscle plug selenium 

concentration (μg/g dw).
23

Figure 8. Relationship between ovary selenium and C, N, and S isotopes in white sturgeon ovary 

samples collected during the 2015 Sturgeon Derby study. 
24
25

Figure 9. Relationship between liver selenium and C, N, and S isotopes in white sturgeon liver 

samples collected during the 2015 Sturgeon Derby study. 
26
27

Figure 10. Relationship between the maximum and average selenium concentration measured in 

the outer fin ray annulus, and muscle plug, ovary, and liver concentrations.
28

References

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