2012 San Joaquin River Sturgeon Spawning Survey

Final Annual Report

Prepared by:

Zachary J. Jackson1* and Joel P. Van Eenennaam2

1U.S. Fish and Wildlife Service

Stockton Fish and Wildlife Office

850 Guild Avenue, Suite 105

Lodi, California 95240

2University of California-Davis

Department of Animal Science

One Shields Avenue

Davis, California 95616

*Corresponding author: Zachary_Jackson@fws.gov

March 2013
ii

Disclaimer

The mention of trade names or commercial products in this report does not constitute 

endorsement or recommendation for use by the federal government.

Cover Photo: White sturgeon egg sampled from the San Joaquin River on 2 April 2012 using 

artificial substrate samplers. Photo courtesy of University California-Davis using an 

Olympus dissecting microscope and a Nikon DS-U1 digital camera.

The correct citation for this report is:

Jackson, Z. J., and J. P. Van Eenennaam. 2013. 2012 San Joaquin River sturgeon spawning 

survey. Stockton Fish and Wildlife Office, Anadromous Fish Restoration Program, 

U.S. Fish and Wildlife Service, Lodi, California.
iii

Preface

The following is the final report for the U.S. Fish and Wildlife Service’s investigations on

anadromous sturgeon spawning in the San Joaquin River between RK 119 and RK 143, 

funded by the Central Valley Project Improvement Act (CVPIA) Anadromous Fish 

Restoration Program in Fiscal Year 2012. Title 34, Section 3406(b)(1) of the CVPIA, Public 

Law 102-575, requires the Secretary of the Interior to develop within three years of 

enactment and implement a program which makes all reasonable efforts to ensure that, by the 

year 2002, natural production of anadromous fish in Central Valley rivers and streams will be 

sustainable, on a long-term basis, at levels not less than twice the average levels attained 

during the period of 1967-1991. Section 3406(b)(1) also states that "this goal shall not apply 

to the San Joaquin River between Friant Dam and the Mendota Pool."

The purpose of these investigations is to provide scientific information to the Central Valley 

Project Improvement Act Anadromous Fish Restoration Program to assist in developing 

restoration recommendations that will help meet program objectives and achieve its 

anadromous fish doubling goal.
iv

2012 San Joaquin River Sturgeon Spawning Survey

Zachary J. Jackson

U.S. Fish and Wildlife Service, Stockton Fish and Wildlife Office,

850 Guild Avenue, Suite 105, Lodi, California 95240, USA

Joel P. Van Eenennaam

Department of Animal Science, University of California,

One Shields Avenue, Davis, California 95616, USA

Abstract.— Several researchers have suggested that sturgeon (genus Acipenser) may 

spawn occasionally in the San Joaquin River during high-water years. Initial documentation 

of white sturgeon Acipenser transmontanus spawning in the San Joaquin River system 

occurred in 2011 near Grayson, CA (river kilometer 142, rkm, measuring from its confluence 

with the Sacramento River). However, whether sturgeon spawn in the San Joaquin River in 

normal and drier water year types remained unknown. Artificial substrate samplers (i.e., egg 

mats) were deployed at four sites within a 24-km reach of the San Joaquin River from 

Sturgeon Bend (rkm 119) to Grayson Road Bridge (rkm 143) from 16 February to 1 June

2012. During the sample period, 65 white sturgeon eggs were collected among four sites, 45

of which were viable and between developmental stages 4 and 28. Based upon capture 

location, date of capture, water temperature, stage of development, and the assumption that a 

female takes 12–20 hours to release all of her eggs, the eggs likely represent at least six

different females that spawned between 20 March and 14 May 2012. The results of this 

survey confirm that white sturgeon do spawn in the San Joaquin River in both wet- and dryyear conditions and may be an important source of production for the white sturgeon 

population in the Sacramento-San Joaquin river system.
v

Table of Contents

Preface.................................................................................................iii

Abstract.............................................................................................................................. iv

List of Tables ..................................................................................................................... vi

List of Figures................................................................................................................... vii

Introduction..........................................................................................................................1

Study Area ...........................................................................................................................1

Methods................................................................................................................................2

Results..................................................................................................................................3

Discussion............................................................................................................................4

Acknowledgements..............................................................................................................6

Literature Cited ....................................................................................................................8

Tables................................................................................................................................11

Figures................................................................................................................................19
vi

List of Tables

Table Page

1. Location of sites sampled on the San Joaquin River, California, by river kilometer 

(rkm), dates sampled, effort in wetted mat days, and the proportion of effort at 

each site in relation to total effort expended during 2012 egg sampling. A wetted 

mat day is equivalent to one mat set for 24 hours........................................................12

2. Size, collection location, estimated spawn timing, and developmental stage of 

white sturgeon eggs collected on the San Joaquin River, California during 2012 ......13

3. Minimum, maximum, and mean depths of sites sampled with egg mats during 

2012 in the San Joaquin River, California. Sample sites expressed as river 

kilometers (rkm), depths (m) sampled at each site throughout the season, and 

depths (m) of mats that collected white sturgeon eggs................................................16

4. Minimum, maximum, and mean hourly water temperatures for each sample site 

for the duration of the study and during the period from estimated spawn timing to 

collection for each white sturgeon egg collection in the San Joaquin River, 

California during 2012.................................................................................................17

5. Minimum, maximum, and mean daily river discharge for each sample site for the 

duration of the study and during the period from estimated spawn timing to 

collection for each white sturgeon egg collection in the San Joaquin River, 

California during 2012.................................................................................................18
vii

List of Figures

Figure Page

1. Location of egg mat sample sites on the San Joaquin River, California between 

Sturgeon Bend (rkm 119) and Grayson Road Bridge (rkm 143).................................20

2. Mean daily discharge (m

3

s

-1

) and mean daily water temperature (°C) observed in 

2012 on the San Joaquin River near rkm 119. The black parallelogram and the 

black circle represent the date when white sturgeon eggs were collected and the 

estimated spawn date, respectively, at rkm 119. Discharge and temperature 

measurements were obtained from the California Data Exchange Center for the 

gauging station near Vernalis, California and thermographs attached to individual 

egg mats, respectively. Horizontal bars indicate upper and lower optimal 

spawning temperatures for white sturgeon (Parsley et al. 1993; McCabe and Tracy 

1994). ...........................................................................................................................21

3. Mean daily discharge (m

3

s

-1

) and mean daily water temperature (°C) observed in 

2012 on the San Joaquin River near rkm 131. The black parallelogram and the 

black circle represent the date when white sturgeon eggs were collected and the 

estimated spawn date, respectively, at rkm 131. Discharge data for rkm 131 were

estimated by subtracting Stanislaus River discharge at Ripon from the discharge 

reported at Vernalis. Discharge and temperature measurements were obtained 

from the California Data Exchange Center and thermographs attached to 

individual egg mats, respectively. Horizontal bars indicate upper and lower 

optimal spawning temperatures for white sturgeon (Parsley et al. 1993; McCabe 

and Tracy 1994). ..........................................................................................................22

4. Mean daily discharge (m

3

s

-1

) and mean daily water temperature (°C) observed in 

2012 on the San Joaquin River near rkm 142. Black parallelograms and black 

circles represent dates when white sturgeon eggs were collected and the estimated 

spawn dates, respectively, at rkm 142. Discharge and temperature measurements 

were obtained from the California Data Exchange Center for the gauging station

near Patterson, California and thermographs attached to individual egg mats, 

respectively. Horizontal bars indicate upper and lower optimal spawning 

temperatures for white sturgeon (Parsley et al. 1993; McCabe and Tracy 1994)........23

5. Mean daily discharge (m

3

s

-1

) and mean daily water temperature (°C) observed in 

2012 on the San Joaquin River near rkm 143. Black parallelograms and black 

circles represent dates when white sturgeon eggs were collected and the estimated 

spawn dates, respectively, at rkm 143. Discharge and temperature measurements 

were obtained from the California Data Exchange Center for the gauging station 

near Patterson, California and thermographs attached to individual egg mats, 

respectively. Horizontal bars indicate upper and lower optimal spawning 

temperatures for white sturgeon (Parsley et al. 1993; McCabe and Tracy 1994)........24
viii

6. White sturgeon egg collection from San Joaquin River in left panel. Right panel 

shows same egg after careful removal of fine sediment..............................................25

7. San Joaquin River mean daily discharge (m

3 s-1

) during the January through June 

period of 1993-2012 at the gauging station near Vernalis, California.........................26
1

2012 San Joaquin River Sturgeon Spawning Survey

Introduction

Two species of sturgeon (genus Acipenser), white sturgeon A. transmontanus and green 

sturgeon A. medirostris, occur in California. Migration and spawning of both white sturgeon 

and green sturgeon in the Sacramento River system has been well documented by direct 

observation, angler catch, and detection of eggs, larvae, and young-of-the-year sturgeon 

(Kohlhorst 1976; Schaffter 1997; Beamesderfer et al. 2004; Poytress et al. 2009, 2010, 2011). 

Several researchers have speculated that sturgeon also spawn within the San Joaquin River 

system occasionally (Kohlhorst 1976; Schaffter 1997; Beamesderfer et al. 2004), such as 

‘when flows and water quality permit’ (Moyle 2002). However, spawning had not been 

confirmed through any direct sampling activities in the San Joaquin River, California until 

recently when fertilized white sturgeon eggs were collected by the U.S. Fish and Wildlife 

Service (USFWS; Gruber et al. 2012). 

Information regarding sturgeon distribution in the San Joaquin River was limited to anecdotal 

reports and California Department of Fish and Wildlife (CDFW) sturgeon report card data 

(Gleason et al. 2008; DuBois et al. 2009, 2010, 2011, 2012). Information regarding sturgeon 

habitat use and movements throughout the San Joaquin River is lacking, but critical to 

improve management and protection of these species. Angler fishing report cards (Gleason 

et al. 2008; DuBois et al. 2009, 2010, 2011, 2012) document a small sturgeon fishery in the 

reach of the San Joaquin River upstream of Stockton, California (river kilometer, hereafter 

rkm, 64; Figure 1). Since implementation of the Sturgeon Report Card in 2007, anglers have 

reported catching 169 white sturgeon and 6 green sturgeon on the San Joaquin River 

upstream from Stockton (Gleason et al. 2008; DuBois et al. 2009, 2010, 2011, 2012). Of the 

reported fish, 108 (64%) white and 5 (83%) green sturgeon were caught between Stockton 

and the Highway 140 bridge (rkm 202). The remaining 61 (36%) white and 1 (17%) green 

sturgeon were caught upstream of the Highway 140 bridge. Reports indicated anglers 

concentrate in two areas known locally as Sturgeon Bend (rkm 119) and Laird Park (rkm

143; H. Rutherford, CDFW warden, personal communication). Additionally, anglers and 

game wardens indicate that sturgeon caught during March and April commonly expel milt or 

eggs during handling, indicating that spawning could be occurring nearby. 

The primary focus of this study was to determine if sturgeon are spawning in the San Joaquin 

River in various water-year types by collecting fertilized sturgeon eggs on artificial substrate 

samplers. Understanding the spatial and temporal distribution of sturgeon in the San Joaquin 

River is vital for the management and recovery of these important species. Further, 

understanding the physical characteristics of the areas being used by sturgeon will help 

identify future restoration actions.

Study Area

The San Joaquin River originates from the central Sierra Nevada and drains parts of the 

Sierra Nevada and Diablo ranges. It flows through 531 km of the state, first west towards the 

floor of the Central Valley of California, then north towards the Sacramento-San Joaquin 

Delta, eventually reaching the Pacific Ocean. Friant Dam (rkm 431), constructed in 1942,
2

forms a complete barrier to upstream anadromous fish passage. Downstream of Friant Dam, 

the river encounters increasingly greater anthropogenic influence through water diversions 

and habitat alteration. Sampling occurred at four locations in a 24-km reach of the San 

Joaquin River from Sturgeon Bend (rkm 119) to Grayson Road Bridge (rkm 143) in 

Stanislaus County, CA (Figure 1).

Methods

Sturgeon eggs were sampled by deploying artificial substrate samplers (i.e., egg mats) in 

close proximity to presumed spawning areas based on hydraulic conditions, side-scan sonar

images, and angler and warden observations. Egg mats were constructed from two 89 x 65-

cm rectangular sections of furnace filter material secured back to back within a welded steel 

framework (McCabe and Beckman 1990; Schaffter 1997; Poytress et al. 2009). The 

orientation of the furnace filter material allowed either side of the egg mat to collect eggs. 

Egg mats were held in position by a 2.0-kg anchor attached to the upstream end of the egg 

mat with two 76-cm lengths of 9.5-mm diameter braided polypropylene rope. A labeled float 

was attached to the downstream end of each egg mat with a 9.5-mm diameter braided 

polypropylene rope. Float line length varied between egg mats, depending on water depth 

and velocity. Mats were predominantly deployed in areas of accelerating velocities (i.e., 

areas flanking deepest portions of pools) and were set in pairs. Sampling occurred from 16 

February to 1 June 2012.

Environmental and sample effort data were collected during both the setting and retrieval of 

egg mats. Environmental data consisted of depth, GPS coordinates, temperature, turbidity, 

river discharge, and weather condition. Depth (m) and GPS coordinates were recorded 

directly above each egg mat with a Lowrance depth finder (Model StructureScan HDS 10-

m). Hourly water temperature was monitored at each egg mat with a temperature logger

(Model Stowaway Tidbit). Turbidity (nephelometric turbidity units, NTUs) was measured 

with a Hach turbidimeter (Model 2100P). All discharge data were obtained through the 

California Data Exchange Center. Discharge data for rkm 119 were obtained from the 

gauging station located near Vernalis, CA. Discharge data for rkm 131 were estimated by 

subtracting Stanislaus River discharge at Ripon, CA from the discharge reported at Vernalis. 

Discharge data for rkm 142 and 143 were obtained from the gauging station located near 

Patterson, CA. Sample effort data consisted of the date and time individual egg mats were 

set and retrieved.

Egg mat sampling consisted of visual inspection, generally twice per week, throughout the 

sample period. Egg mats were retrieved from the river after initial deployment, placed on the 

deck of a boat in a custom-made egg mat carrier, and initially inspected on both sides by at 

least two field crew members. After initial inspection, egg mats were rinsed with water to 

remove debris and sediment and then re-inspected. Rinse water and debris were filtered by a 

removable 3.2-mm mesh net placed within the egg mat carrier below each egg mat to capture 

any dislodged eggs. After the second egg mat inspection and inspection of the mesh nets, the

mats were redeployed. 
3

All eggs removed from the egg mats were counted and identified to species in the field with

an egg key (Reyes et al. 2007; Wang 2010; Reyes 2011). All suspected sturgeon eggs and 

unidentified eggs were placed into vials of 95% ethyl alcohol (EtOH) for laboratory 

identification and further analysis. Suspected sturgeon eggs were sent to the University of 

California-Davis (UCD) for species confirmation, photography, measurement of egg 

diameter, and determination of developmental stage (Dettlaff et al. 1993). Egg length and 

width were measured (± 0.001 mm) with an Olympus dissecting microscope with a camera 

lucida and a Nikon Microplan II digital image analyzing tablet. Representative photographs 

were taken with a Nikon DS-U1 digital camera connected to the microscope.

Estimates of date and time of fertilization (i.e., spawn timing) were based on an average 

water temperature for the time period between egg collections, estimated egg developmental 

stage, and rates of embryonic development established for white sturgeon (Wang et al. 1985, 

1987). 

Results

Cumulative egg mat sampling totaled 670.9 wetted mat days (wmd; one mat set for 24 hours) 

between four sample sites (Table 1). Eighty-two percent (552.3 of 670.9 wmd) of the total

sampling effort was expended approximately evenly across three sample sites downstream of

Laird Park (rkm 119, rkm 131, and rkm 142). Mats were added at the rkm 143 site during 

the sixth week of sampling due to observations of sturgeon in the area, which accounted for 

17.7% of total effort (118.5 wmd).

Sixty-five white sturgeon eggs were collected among four sampling sites between 20 March 

and 14 May 2012 and transferred to UCD for analysis. Twenty eggs (31%) were not viable, 

many of which were covered in fungus. It could not be determined if these were fertilized 

eggs that died during embryogenesis or were un-fertilized eggs (Table 2). Forty-five eggs 

(69%) were viable and determined to be in various stages of post-fertilized embryonic 

development (Table 2; Dettlaff et al. 1993). 

Egg mats were deployed at river depths ranging from 0.4–9.3 m ( = 3.8 m; Table 3). Egg 

samples were collected from mats deployed at depths ranging from 1.6–9.1 m with a mean 

depth of 3.8 m. San Joaquin River water temperatures recorded during the study are 

summarized in Table 4. Daily average water temperatures ranged from 12.8–19.4 °C ( = 

16.3 °C) at the lowest site (rkm 119; Figure 2), 13.1–24.9 °C ( = 18.7 °C) at rkm 131

(Figure 3), 13.4–24.8 °C ( = 19.2 °C) at rkm 142 (Figure 4), and 16.1–24.7 °C ( = 20.8 °C) 

at rkm 143 (Figure 5) during the sample period. The 19 April egg collections at rkm 142, 

and the 10 May collections at the rkm 142 and 143 sites, included the highest recorded 

hourly water temperatures during the period from estimated spawn timing until collection, 

ranging from 18.2–20.9 °C, 19.7–23.2 °C , and 19.7–23.0 °C, respectively (Table 4). San 

Joaquin River discharge ranged from 35.0–125.1 m

3 s-1

( = 63.0 m

3 s-1

) at rkm 119 (Figure 

2), 20.0–80.5 m

3 s-1

( = 35.2 m

3 s-1

) at rkm 131 (Figure 3), and 12.7–43.0 m

3 s-1

( = 21.6 m

3

s

-1

) at the upper sites (rkm 142 and 143; Figures 4 and 5) throughout the sample period 

(Table 5). Turbidity grab samples ranged from 9.3–68.3 nephelometric turbidity units (NTU) 
4

among sites during the sample period and from 19.0–63.9 NTU among sites on days when 

eggs were collected.

 

Minimum and maximum egg diameter were measured in the lab on 88% (n = 57) of egg 

samples after carefully removing attached debris. Lab measurements were not taken on eggs 

that had become covered in fungus (n = 8), making accurate measurements of size 

impossible. The mean maximum diameter (as the eggs are slightly oblong in shape) was 

3.54 mm ± 0.10 (ranging 3.35–3.76 mm), and mean minimum diameter was 3.40 mm ± 0.11 

(ranging 3.11–3.62 mm).

Discussion

During 2012, egg mat sampling identified white sturgeon spawning at four locations 

extending over 24 km of the San Joaquin River. Eggs were collected at rkm 119, 131, 142, 

and 143 on one, one, four, and two occasions, respectively (Table 2), representing at least six 

distinct spawning events. On two occasions, eggs were collected at successive sampling sites 

on the same day. Whether or not the eggs collected on 2 April and 10 May 2012 at both the 

rkm 142 and 143 sites at similar stages of embryogenesis were from the same female or 

different females cannot be concluded. Given the time over which a female spawns (12–20 

hours; J. P. Van Eenennaam, unpublished) and the proximity of the sites, it is possible that a 

single female spawned at both sites. However, future genetic analyses may be able to 

confirm whether the sampled eggs were from a single female or from multiple females. 

Optimal spawning temperatures for white sturgeon have been reported to be 10–18°C in the 

Columbia River (Parsley et al. 1993; McCabe and Tracy 1994). Kohlhorst (1976) reported 

the optimal spring spawning temperature for white sturgeon to be 14–16°C in the Sacramento 

River. Optimal temperatures for development and survival of white sturgeon embryos are 

reported to be 14–17°C, with hatching rates decreasing at 20°C and complete arrest of 

embryonic development at 23°C in laboratory experiments (Wang et al. 1985). Although 

some of the days during the one-week spawning and embryo incubation period had elevated 

water temperatures above what has been reported as optimal, there were no obvious signs of 

deformities at the stages of embryonic development observed in any viable eggs that were 

collected. However, it is at later stages of embryogenesis and post-hatch larvae when 

obvious problems have been observed that were related to elevated incubation temperature in 

green sturgeon embryos (e.g., substantial shortening of the embryo body, decrease in percent 

dry weight, lordosis, kyphosis, edema; Van Eenennaam et. al. 2005). Fertilization and early 

cleavage stages did not appear to be affected by temperature in the majority of the eggs, as 

abnormal cleavage could lead to gastrulation arrest and, consequently, mortality before 

neurulation (Sytina and Shagaeva 1987). Sytina and Shagaeva (1987) also reported the 

complete block of egg cleavage at temperatures outside the spawning range (e.g., ≥ 28°C) in 

stellate sturgeon A. stellatus.

One may question whether the percent of non-viable eggs (31%) could be related to the 

elevated temperatures; however, some of these non-viable eggs were found early in the 

spawning season when temperatures were closer to optimal. A number of factors other than 
5

temperature may be causing or contributing to mortality of embryos, including sampling 

related damage and contaminants. 

Several of the viable eggs were almost completely covered in sand particles which were 

carefully removed by gently scraping the egg with fine needle forceps until the stage of 

development could be discerned (Figure 6). Kock et al. (2006) suggest that sediment cover 

may be an important early life stage mortality factor in rivers where white sturgeon spawn 

over fine substrates. Eggs completely buried in shifting sand would likely die from lack of 

oxygen. Efforts to accurately characterize the substrate types present in the known spawning 

areas have been initiated, but are not complete. Regardless, the river bed within the sampling 

area is dominated by sand and silt substrates. However, if the eggs are attached to cobble or 

other types of large substrate and become coated in silt or sand as the jelly coat forms, they 

will likely remain viable as long as they are exposed to sufficient water flow. The degree of 

jelly coat formation on fertilized sturgeon eggs is not fully understood, but recent work has 

documented variations among species (Van Eenennaam et al. 2012).

California Department of Fish and Wildlife Sturgeon Report Card data indicate six green 

sturgeon and 169 white sturgeon were reported by anglers in the last five years within the 

San Joaquin River upstream of Stockton, five of which were caught in March and April 

(Gleason et al. 2008; DuBois et al. 2009, 2010, 2011, 2012). Although the data indicate the 

presence of a limited number of green sturgeon, it is possible that some fish go unreported

(e.g., poaching; Beamesderfer et al. 2004) or are misidentified as white sturgeon. It remains 

unknown how and to what extent green sturgeon use the San Joaquin River. However, the 

reported presence of green sturgeon in the San Joaquin River coincides with the spawning

migration period of the Southern Distinct Population Segment of green sturgeon within the 

Sacramento River (Poytress et al. 2009, 2010, 2011). Although there is a temporal overlap in 

spawn timing between white and green sturgeon (Kohlhorst 1976; Poytress et al. 2009), no 

documentation exists where these two sturgeon species spawn in close proximity to each 

other. Turbidity may be driving the separation of spawning locations. Generally, green 

sturgeon spawn in areas where turbidity is less than 10 NTU (Poytress et al. 2009, 2010,

2011). Conversely, white sturgeon spawn in areas that are generally turbid in nature ( = 42 

NTU; Perrin et al. 2003). Because of elevated turbidity levels in the San Joaquin River, we

hypothesize that green sturgeon on a spawning run within the San Joaquin River system may 

be seeking less turbid water upstream of the sampled area in the mainstem or within one of 

the tributaries where turbidity is lower. Therefore, focusing future egg sampling efforts 

between rkm 119 and rkm 143 may limit the ability to detect spawning green sturgeon in the 

San Joaquin River. 

In addition to egg sampling, larval sampling with a benthic D-net has been accepted as an 

effective method to document the spawn timing of sturgeon species (Kohlhorst 1976). 

Although larval samples will not provide information on specific spawning locations, 

methods from Dettlaff et al. (1993) can be used to estimate spawn timing. Larval captures 

could help determine if there were deformities at hatch, but many deformed larvae would 

likely be unable to “swim-up” and thus captures would be expected to be rare. Larval 

captures would confirm the presence or absence of normal swim-up larvae during the periods 

of elevated water temperatures. The bridge abutments at the Airport Way (rkm 116) and 
6

Grayson Road (rkm 143) crossings provide an ideal tie-off location for larval D-net sampling 

of known white sturgeon spawning locations at rkm 119, 131, 142, and 143. Larval sampling 

at these two locations would provide the opportunity for detection of larval green sturgeon 

dispersing from speculated spawning locations within the Stanislaus, Tuolumne, Merced, or 

upper San Joaquin rivers. Furthermore, without documentation of larval white sturgeon in 

the San Joaquin River upstream of the Delta, it is unknown if spawning events within the San 

Joaquin River are a source of larval production for the Sacramento-San Joaquin white 

sturgeon population. 

Average daily discharge in the San Joaquin River in early 2011 was two to three times higher 

than the mean daily discharge for water years 1993 to 2012 (Figure 7). As speculated by 

researchers (e.g., Kohlhorst 1976; Schaffter 1997; Moyle 2002; Beamesderfer et al. 2004), 

river discharge levels of this magnitude may have triggered white sturgeon to enter and 

spawn within the San Joaquin River in 2011. River discharge levels in 2012 were generally 

half or less than the 20-year average. However, documentation of at least six distinct 

spawning events during 2012 show that spawning also occurs in dry years and may occur 

annually. There was a general trend of collecting eggs around short-duration peaks in river 

discharge during the 2012 sampling season (Figures 2, 3, 4, and 5). Spring pulses of 

discharge from the Merced and Tuolumne rivers in late April and early May intended to 

increase survival of emigrating salmonids preceded collection of white sturgeon eggs at all 

four sampling locations. Water temperatures at most sampling sites had been over 18°C and 

increasing for several weeks, yet a late peak in spawning activity occurred around the time 

that short-duration increases in discharge from the tributaries arrived at the sampling 

locations. This suggests the possibility that there were a number of white sturgeon holding in 

the lower San Joaquin River that responded to the change in environmental conditions (e.g., 

river discharge, temperature) to initiate spawning. 

Additional sturgeon egg and larval sampling, in conjunction with acoustic tracking of adults, 

should be continued throughout a variety of water year types to better understand the spatial 

and temporal distribution and habitat preferences of white sturgeon in the San Joaquin River. 

Continued study of the response of white sturgeon to changes in river discharge and 

temperature may be important for informing fishery and water management decisions. 

Understanding the effects of water management in a regulated system like the San Joaquin 

River may result in increased spawning activity, spawning success, and recruitment of white 

sturgeon. Additionally, a better understanding of white sturgeon distribution and use and the 

potential to encounter various life-history stages of green sturgeon within this system may 

enhance the understanding and ability to manage for both species.

Acknowledgements

This project was funded by the Anadromous Fish Restoration Program under the authority of 

the Central Valley Project Improvement Act (P.L. 102-575). Bill Powell, Tim Matt, Ron 

Smith, Patrick Hapgood, Steve Tsao, Dave Dominguez, Jonathan Thompson, and Kes Benn 

assisted in the field. Alexandra Fitzgerald assisted with table and figure development. Bill 

Poytress, Zoltan Matica, Michelle Workman, Nina Kogut, Josh Gruber, Alexandra 
7

Fitzgerald, Paul Cadrett, Ramon Martin, and Donnie Ratcliff provided comments that 

improved this report.
8

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data report. California Department of Fish and Game, Stockton, California.

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data report. California Department of Fish and Game, Stockton, California.

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California.

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11

Tables
12

Table 1.—Location of sites sampled on the San Joaquin River, California, by river kilometer

(rkm), dates sampled, effort in wetted mat days, and the proportion of effort at each site in 

relation to total effort expended during 2012 egg sampling. A wetted mat day is equivalent 

to one mat set for 24 hours. 

Sample site (rkm) Sample dates Wetted mat days % Effort

119 16 Feb – 1 Jun 188.6 28.1%

131 16 Feb – 1 Jun 181.7 27.1%

142 16 Feb – 1 Jun 182.0 27.1%

143 22 Mar – 1 Jun 118.5 17.7%

Total Effort 16 Feb – 1 Jun 670.9 100.0%
13

Table 2.—Size, collection location, estimated spawn timing, and developmental stage of white sturgeon eggs collected on the San Joaquin 

River, California during 2012.

Sample 

date

Location 

(rkm)

Egg diameter (mm) Spawning Developmental 

Min Max Date Hours stage Comments

22 Mar 142 3.368 3.468 - - - not viable

22 Mar 142 3.433 3.512 - - - not viable

22 Mar 142 3.302 3.370 21 Mar 0035 18 blastopore closure

22 Mar 142 3.522 3.543 - - - marbled, not viable

22 Mar 142 3.349 3.402 - - - marbled, not viable

22 Mar 142 3.435 3.641 20 Mar 1835 19 early neurulation

22 Mar 142 3.359 3.414 - - - marbled, not viable

22 Mar 142 - - - - - crushed, appears not viable

22 Mar 142 3.490 3.490 - - - marbled, not viable

22 Mar 142 3.263 3.720 - - - oblong shaped, early neurulation

22 Mar 142 3.416 3.567 - - - marbled, not viable

22 Mar 142 3.177 3.422 20 Mar 1835 19 early neurulation

22 Mar 142 3.226 3.615 20 Mar 1835 19 early neurulation

22 Mar 142 3.198 3.584 20 Mar 1835 19 early neurulation

22 Mar 142 3.303 3.598 20 Mar 1835 19 early neurulation

22 Mar 142 3.461 3.573 20 Mar 1835 19 early neurulation

22 Mar 142 3.602 3.691 20 Mar 1835 19 early neurulation

22 Mar 142 3.356 3.731 - - - oblong, not viable

22 Mar 142 - - - - - collapsed/crushed

22 Mar 142 3.259 3.426 - - -

22 Mar 142 3.302 3.611 20 Mar 1835 19 early neurulation

22 Mar 142 3.573 3.602 20 Mar 1835 19 early neurulation

22 Mar 142 3.365 3.546 20 Mar 1835 19 early neurulation

22 Mar 142 3.415 3.581 20 Mar 1835 19 early neurulation

22 Mar 142 3.491 3.759 - - - marbled, not viable

22 Mar 142 3.370 3.552 20 Mar 1835 19 early neurulation

2 Apr a3.575 3.591 31 Mar am 22 initial separation of tail region

2 Apr a- - - - - fungus covered, not viable

2 Apr a3.335 3.346 31 Mar am 22 initial separation of tail region
14

Table 2. —Continued (See page 14 for heading).

Sample 

date

Location 

(rkm)

Egg diameter (mm) Spawning

Min Max Date Hours Spawning Comments

2 Apr a- - - - - fungus covered, not viable

2 Apr a3.345 3.385 31 Mar am 22 initial separation of tail region

2 Apr a3.390 3.599 31 Mar am 22 initial separation of tail region

2 Apr a3.397 3.516 - - - some fungus, not viable

2 Apr a3.614 3.614 31 Mar am 22 initial separation of tail region

19 Apr 142 - - - - - collapsed/crushed sturgeon egg

19 Apr 142 3.472 3.478 18 Apr 0313 22 late-neurulation

19 Apr 142 3.113 3.449 18 Apr 0313 22 late-neurulation

19 Apr 142 3.437 3.476 18 Apr 0313 22 late-neurulation

19 Apr 142 3.345 3.453 - - - marbled, not viable

10 May 142 3.432 3.708 8 May 1911 26 initial separation of tail region

10 May 142 3.472 3.531 8 May 1911 26 initial separation of tail region

10 May 142 3.366 3.691 8 May 1911 26 initial separation of tail region

10 May 143 - - - - - fungus covered, not viable

10 May 143 3.443 3.575 8 May 1317 28 separated tail and straight cardiac tube

10 May 143 3.302 3.435 8 May 1317 28 separated tail and straight cardiac tube

10 May 143 - - - - - fungus covered, not viable

10 May 143 3.539 3.598 8 May 1317 28 separated tail and straight cardiac tube

10 May 143 3.354 3.368 - - - marbled, not viable

10 May 143 3.509 3.617 8 May 1317 28 separated tail and straight cardiac tube

10 May 143 3.388 3.495 8 May 1317 28 separated tail and straight cardiac tube

10 May 143 3.615 3.673 8 May 1317 28 separated tail and straight cardiac tube

10 May 143 3.567 3.612 8 May 1317 28 separated tail and straight cardiac tube

10 May 143 3.330 3.526 8 May 1317 28 separated tail and straight cardiac tube

10 May 143 3.579 3.616 8 May 1317 28 separated tail and straight cardiac tube

10 May 143 - - - - - fungus covered, not viable

14 May 131 3.365 3.545 13 May 0612 18 blastopore closure

14 May 131 3.416 3.586 13 May 0612 18 blastopore closure

14 May 131 3.536 3.711 13 May 0612 18 blastopore closure
15

Table 2. —Continued (See page 14 for heading).

Sample 

date

Location 

(rkm)

Egg diameter (mm) Spawning

Min Max Date Hours Spawning Comments

14 May 131 3.402 3.456 13 May 0612 18 blastopore closure

14 May 131 3.363 3.590 13 May 0612 18 blastopore closure

14 May 119 3.292 3.500 13 May 1540 14 Gastrulation

14 May 119 3.289 3.369 14 May 0040 14 Gastrulation

14 May 119 3.303 3.472 14 May 0040 14 Gastrulation

14 May 119 3.402 3.476 14 May 0040 14 Gastrulation

14 May 119 3.473 3.474 14 May 0740 4 2-cell

*Spawning date and time was estimated by back-calculation based on the developmental stage of embryogenesis (Dettlaff et al. 1993), developmental rates of white 

sturgeon (Deng et al. 2002), and daily water temperatures recorded on temperature loggers attached to the egg mats on the San Joaquin River.

a

Eggs were collected at both the rkm 142 and 143 sites on 2 April, 2012. However, due to lost datasheets, it is impossible to tell which eggs and how many were collected 

at each site.
16

Table 3.— Minimum, maximum, and mean depths of sites sampled with egg mats during 

2012 in the San Joaquin River, California. Sample sites expressed as river kilometers (rkm), 

depths (m) sampled at each site throughout the season, and depths (m) of mats that collected 

white sturgeon eggs.

Sample depths (m) White sturgeon egg sample depths (m)

Sample site (rkm) Min Max Mean Min Max Mean

119 1.0 9.3 5.4 5.8 9.1 7.1

131 0.5 9.1 4.6 4.2 5.2 4.7

142 1.1 4.1 2.8 1.6 3.8 2.7

143 0.4 2.1 1.4 1.6 1.6 1.6

All sites 0.4 9.3 3.8 1.6 9.1 3.8
17

Table 4.— Minimum, maximum, and mean hourly water temperatures for each sample site 

for the duration of the study and during the period from estimated spawn timing to collection

for each white sturgeon egg collection in the San Joaquin River, California during 2012.

Sample hourly 

temperatures (oC)

Spawn timing to 

collection hourly 

temperatures (oC)

Sample site 

(rkm)

Sample 

date Min Max Mean Min Max Mean

119 14 May 11.7 20.4 16.2 17.2 18.6 17.8

131 14 May 12.0 26.6 18.7 17.0 19.0 18.1

142 22 Mar 12.1 26.8 19.3 14.2 16.6 15.7

142 19 Apr 12.1 26.8 19.3 18.2 20.9 19.5

142 10 May 12.1 26.8 19.3 19.7 23.2 21.3

143a10 May 14.7 26.3 20.8 19.7 23.0 21.3

b

2 Apr 12.1 26.8 19.3 15.8 18.6 17.4

All sites 12.0 26.8 18.8 14.2 16.6 18.1

a

Sample hourly temperatures for rkm 143 were based on data from 9 April-29 May 2012.

bEggs were collected at both the rkm 142 and 143 sites on 2 April, 2012. However, due to lost datasheets, it is 

impossible to tell which eggs and how many were collected at each site. Spawn timing to collection hourly 

temperatures were calculated with temperature data gathered at rkm 142 due to an incomplete sample range at 

rkm 143. 
18

Table 5.—Minimum, maximum, and mean daily river discharge for each sample site for the 

duration of the study and during the period from estimated spawn timing to collection for 

each white sturgeon egg collection in the San Joaquin River, California during 2012.

Sample discharge (m3s

-1

)

Spawn timing to collection 

discharge (m3s

-1

)

Sample site (rkm) Sample date Min Max Mean Min Max Mean

119 14 May 35.0 125.1 63.0 124.1 125.1 124.6

131 14 May 20.0 80.5 35.2 80.5 80.5 80.5

142 22 Mar 12.7 43.0 21.6 34.2 35.8 34.9

142 19 Apr 12.7 43.0 21.6 25.5 31.4 28.5

142 10 May 12.7 43.0 21.6 30.3 34.7 32.9

143 10 May 12.7 43.0 21.6 30.3 34.7 32.9

a

2 Apr 12.7 43.0 21.6 19.6 20.5 20.2

All sites 12.7 125.1 35.3 19.6 125.1 50.6

aEggs were collected at both the rkm 142 and 143 sites on 2 April, 2012. However, due to lost datasheets, it is 

impossible to tell which eggs and how many were collected at each site.
19

Figures
20

Figure 1.—Location of egg mat sample sites on the San Joaquin River, California between 

Sturgeon Bend (rkm 119) and Grayson Road Bridge (rkm 143). 

^ Sample Sites

Rivers 

Major Roads

Important Local Road

Local Connecting Road

Major Road Less Important than a Freeway

Other Major Road

Secondary Road
21

Figure 2.—Mean daily discharge (m

3

s

-1

) and water temperature (°C) observed in 2012 on the San Joaquin River near rkm 119. 

The black parallelogram and the black circle represent the date when white sturgeon eggs were collected and the estimated spawn 

date, respectively, at rkm 119. Discharge and temperature measurements were obtained from the California Data Exchange Center 

for the gauging station near Vernalis, California and thermographs attached to individual egg mats, respectively. Horizontal bars 

indicate upper and lower optimal spawning temperatures for white sturgeon (Parsley et al. 1993; McCabe and Tracy 1994).
22

Figure 3.— Mean daily discharge (m

3

s

-1

) and water temperature (°C) observed in 2012 on the San Joaquin River near rkm 131. 

The black parallelogram and the black circle represent the date when white sturgeon eggs were collected and the estimated spawn 

date, respectively, at rkm 131. Discharge data for rkm 131 were estimated by subtracting Stanislaus River discharge at Ripon 

from the discharge reported at Vernalis. Discharge and temperature measurements were obtained from the California Data 

Exchange Center and thermographs attached to individual egg mats, respectively. Horizontal bars indicate upper and lower 

optimal spawning temperatures for white sturgeon (Parsley et al. 1993; McCabe and Tracy 1994).
23

Figure 4.—Mean daily discharge (m

3

s

-1

) and water temperature (°C) observed in 2012 on the San Joaquin River near rkm 142. 

Black parallelograms and black circles represent dates when white sturgeon eggs were collected and the estimated spawn dates, 

respectively, at rkm 142. Discharge and temperature measurements were obtained from the California Data Exchange Center for 

the gauging station near Patterson, California and thermographs attached to individual egg mats, respectively. Horizontal bars 

indicate upper and lower optimal spawning temperatures for white sturgeon (Parsley et al. 1993; McCabe and Tracy 1994).
24

Figure 5.—Mean daily discharge (m

3

s

-1

) and water temperature (°C) observed in 2012 on the San Joaquin River near rkm 143. 

Black parallelograms and black circles represent dates when white sturgeon eggs were collected and the estimated spawn dates, 

respectively, at rkm 143. Discharge and temperature measurements were obtained from the California Data Exchange Center for 

the gauging station near Patterson, California and thermographs attached to individual egg mats, respectively. Horizontal bars 

indicate upper and lower optimal spawning temperatures for white sturgeon (Parsley et al. 1993; McCabe and Tracy 1994).
25

Figure 6.—White sturgeon egg collection from San Joaquin River in left panel. Right panel shows same egg after careful removal 

of fine sediment.
26

Figure 7.— San Joaquin River mean daily discharge (m

3 s-1

) during the January through June period of 1993-2012 at the gauging 

station near Vernalis, California.