1

Sacramento-San Joaquin Delta 

Regional Ecosystem Restoration Implementation Plan

Life History Conceptual Model 

North American Green Sturgeon 

(Acipenser medirostris) 

Prepared by: Joshua A. Israel and A. Pete Klimley, University of California, Davis, 

 jaisrael@ucdavis.edu

Date of Model: December 27, 2008 

Reviewed 
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PREFACE 

This Conceptual Model is part of a suite of conceptual models which collectively 

articulate the current scientific understanding of important aspects of the Sacramento-San 

Joaquin River Delta ecosystem. The conceptual models are designed to aid in the 

identification and evaluation of ecosystem restoration actions in the Delta. These models 

are designed to structure scientific information such that it can be used to inform sound 

public policy. 

The Delta Conceptual Models include both ecosystem element models (including 

process, habitat, and stressor models) and species life history models. The models were 

prepared by teams of experts using common guidance documents developed to promote 

consistency in the format and terminology of the models 

http://www.delta.dfg.ca.gov/erpdeltaplan/science_process.asp . 

The Delta Conceptual Models are qualitative models which describe current 

understanding of how the system works. They are designed and intended to be used by 

experts to identify and evaluate potential restoration actions. They are not quantitative, 

numeric computer models that can be “run” to determine the effects of actions. Rather 

they are designed to facilitate informed discussions regarding expected outcomes 

resulting from restoration actions and the scientific basis for those expectations. The 

structure of many of the Delta Conceptual Models can serve as the basis for future 

development of quantitative models. 

Each of the Delta Conceptual Models has been subject to a rigorous scientific peer review 

process. 

The Delta Conceptual models will be updated and refined over time as new information 

is developed, and/or as the models are used and the need for further refinements or 

clarifications are identified. 
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CONTENTS 

I. Introduction................................................................................................................. 4 

II. Biology (Figure 3, Table 1) ........................................................................................ 4 

A. Distribution (Figure 4, Table 2).............................................................................. 6 

III. Ecology (Figures 5-11) ............................................................................................... 8 

A. Reproduction to embryonic development (Figure 6).............................................. 8 

B. Developing embryo to feeding larvae (Figure 7).................................................... 8 

C. Feeding larvae to juveniles (Figure 8) .................................................................... 9 

D. Juveniles to coastal migrant (Figure 9)................................................................. 10 

E. Maturation of coastal migrants to spawning adults (Figure 10) ........................... 11 

F. Adult spawning migration, spawning, and post-spawning adults (Figure. 11) .... 13 

IV. Stressor by stage and habitat (Table 4 and 5) ........................................................... 14 

A. Entrainment........................................................................................................... 15 

B. Flow operations..................................................................................................... 16 

C. Reservoir operations ............................................................................................. 16 

D. Habitat Loss .......................................................................................................... 17 

E. Water Quality........................................................................................................ 18 

F. Toxics.................................................................................................................... 19

G. Invasives ............................................................................................................... 19 

H. Population ............................................................................................................. 20 

I. Other ..................................................................................................................... 20

V. Future Research ........................................................................................................ 20 

VI. Literature Cited ......................................................................................................... 23

VII. Tables........................................................................................................................ 29 

VIII. Figures....................................................................................................................... 39 
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I. Introduction 

The purpose of this report is to develop a conceptual life history model of North 

American green sturgeon (Acipenser medirostris) and the factors that affect reproduction, 

growth, and survival in the Sacramento and San Joaquin rivers and San Francisco BayDelta. This model can be used to organize, visualize, and evaluate how the complex life 

history of green sturgeon relates to the spatial and temporal variability of riverine and 

estuarine ecosystems and potential consequences of ecosystem restoration and water 

management alternatives. This model is compatible with the suite of environmental and 

species models developed by the Department of Fish and Game Ecosystem Restoration 

Program (ERP) to assess and prioritize proposed restoration actions for the Delta. The 

model has a geographic emphasis on the Sacramento River and Bay-Delta regions, 

though the entire distribution of green sturgeon must be considered when population level 

responses are of concern, due to the unique, highly-migratory life history of this species. 

The conceptual life history model incorporates information from numerous sources 

about green sturgeon, often relying upon life history information from populations 

outside the Southern Distinct Population Segment (DPS) and occasionally considering 

information from the sympatric white sturgeon (A. transmontanus). While surrogate 

information from other North American sturgeon could have been used in the model, the 

distinctive anadromous and ecological characteristics of green sturgeon limited the utility 

of these species’ information. Due to the limits of quantitative information about green 

sturgeon, this model is presented in a qualitative narrative with numerical information 

provided, when available. While it will not provide quantitative limits on species take 

relative to maintaining a stable population size, it could be further developed into a 

population forecasting model since it divides the life history into life history stages, 

transition probabilities, and factors whose affects on reproduction and survival could be 

quantified. 

Life history stage transitions are visualized in a series of life stage submodels 

highlighting the processes and relationships among ecological factors influencing the 

transition between stages (Figures 1 and 2). A complex set of conditions and processes 

are necessary to determine whether an individual fish completes the transition from one 

life stage to the next. Our knowledge of green sturgeon life history remains limited as to 

the relative importance of biotic and abiotic factors critical for maintaining selfsustaining populations of green sturgeon. Thus, the importance, predictability, and 

understanding of each of these linkages are identified in the model. Lastly, a similar 

characterization of independent stressors is undertaken to describe potential factors 

affecting survival during each life history stage in a known geographic region. This 

model is dynamic and not intended to be a final version. As new information becomes 

available, the model should be refined so managers and biologists have the most current 

information available. 

II. Biology (Figure 3, Table 1) 

Green sturgeon (Acipenser medirostris) are long-lived, anadromous fishes, which 

begin their lives in the upper and middle segments of the largest subbasins flowing into 
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the Sacramento River and San Francisco Bay-Delta (Figures 3, 5). Eggs, larvae, and 

juveniles showed distinct tolerances of temperature, dissolved oxygen, light, and salinity 

in experiments (Table 1). Eggs and milt are released in turbulent water above deep, 

complex habitats where they drift and stick onto the substrate. Eggs require constant, cool 

water temperatures and hatched after approximately a week as finless larvae in 

experiments while non-optimal temperatures affected embryonic development in 

experiments (Deng et al. 2002, Linares-Casenave et al. in preparation). Larval sturgeon 

required cool water temperatures and high dissolved oxygen levels while digesting their 

yolk sac prior to feeding on their own (Gisbert et al. 2001, Van Eenennaam et al. 2005). 

Once feeding, larvae initiate a 12-day nocturnal emigration in experiments (Kynard et al. 

2005) and larval metamorphosis is completed after approximately 45 days (63-94mm, 

Deng et al. 2002). Larval and riverine juvenile green sturgeons are bottom-oriented and 

nocturnally active until a few months of age (Kynard et al. 2005). 

Juvenile green sturgeon are tolerant of warmer temperatures, which influences 

growth and behavior (Allen et al. 2006b). High dissolved oxygen levels are required by 

juvenile green sturgeon for respiration and to avoid chronic stress (Lankford et al. 2003, 

Mayfield and Cech 2004). During the day, juveniles selected low light habitats and were 

primarily inactive, while they seemed to forage actively during night in experiments 

(Kynard et al. 2005). Juvenile green sturgeon migrate into seawater portions of natal 

estuaries as early as one and a half years old (75cm TL, Allen and Cech 2007), and 

eventually emigrate to nearshore coastal waters by three years old. Green sturgeon 

returning to the Klamath River grew to 300mm in their first year and 600mm within the 

first 2-3 years of their life (Nakamoto et al. 1995), though the riverine and estuarine 

conditions in this system are distinctly different from the Sacramento River and BayDelta. Subadults are migratory, spending their next 12-16 years foraging in the coastal 

ocean and entering western estuaries during the summer (Moser and Lindley 2007). In 

the ocean, green sturgeon inhabit the coastal shelf out to 100m depth with occasional, 

rapid vertical ascents near or to the surface (Erickson and Hightower 2007). 

Reproductive adults migrate southward back to rivers in late winter and early spring 

to spawn between late March and late July (Benson et al. 2007, Heublein et al in press). 

Younger and smaller adult age classes are dominated by male green sturgeon, while older 

and larger age classes are dominated by females on the Klamath and Rogue rivers, 

presumably due to the earlier maturity and shorter life span of males (Erickson and Webb 

2007, Van Eenennaam et al. 2006). It is presumed age structuring is similar in the 

Southern DPS. Green sturgeon can reach up to 270cm with a maximum age of 60-70 

years old, though fish greater than 200cm are uncommon (Moyle et al. 2002, Skinner 

1962, Emmett et al. 1991). Based on adult spawning behavior and habitat suitable for 

green sturgeon embryo development, it seems likely reproductive females select 

spawning areas with turbulent, high velocities near low velocity resting areas. Green 

sturgeon spawning areas are presumed to be characterized by larger substrates upstream 

of lower gradient reaches, which usually have slower velocities. 

Adults spawn over a short period within a week, and no atretic females (individuals 

undergoing reabsorption of eggs instead of releasing them) have been observed in 

spawning populations, suggesting females spawn regardless of physical conditions in 

spawning habitats. The eggs of a single female are fertilized by the sperm of multiple 
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males. After spawning, adults move downstream into holding habitats in the lower river 

or further into the Delta, returning through the San Francisco Bay to the ocean during late 

fall or winter (Heublein in press). Individuals then migrate northward and return to spawn 

every two to four years (Erickson and Webb 2007, Lindley et al. 2008). Species fecundity 

peaks around 24 years old, when all females in this age cohort have matured 

(Beamesderfer et al. 2007). 

A. Distribution (Figure 4, Table 2) 

Population structure: Green sturgeon range from Ensenada, Mexico to the Bering 

Sea, Alaska (Colway and Stevenson 2007, Moyle 2002). Green sturgeons are currently 

known to spawn in two large California basins- Sacramento and Klamath rivers (Figure 

4). These reproducing populations are genetically distinct and occupy the Southern and 

Northern Distinct Population Segment, respectively (Adams et al. 2002, Israel et al. 

2004). Long term populations trends show adult populations in the less-altered Klamath 

and Rogue rivers are fairly constant with a few hundred spawning adults typically being 

harvested annually by tribal fisheries. The green sturgeon population in the Sacramento 

River is believed to have declined over the last two decades with less than 50 spawning 

green sturgeon being sighted annually in the best spawning habitat along the middle 

section of the Sacramento River (Richard Corwin, Bureau of Reclamation (BOR), Pers. 

Comm.). In the Umpqua, Feather, Yuba, and Eel rivers green sturgeon sightings are 

extremely limited and spawning has not been recently recorded. In the San Joaquin and 

South Fork Trinity rivers, the green sturgeon population appears extirpated. 

Eggs, Larvae, Young-of-the-Year: Egg and larval green sturgeon are confined to 

freshwater portions of the Sacramento River mainstem (Table 2). Eggs are incubated in 

immediate proximity to spawning areas between Anderson and Hamilton City due to 

their limited mobility. Modeled temperatures are below 18°C until after the spawning 

season above Colusa (Orlob and King 1997), and temperature loggers demonstrate these 

temperatures are attained as far downstream as the Irvine Finch River Access (Rkm 398) 

until the end of the spawning seasons (P. Klimley, UCD, unpublished data). Eggs have 

been captured upstream of Red Bluff Diversion Dam (RBDD) in the Massacre Flats pool, 

below Red Bluff Diversion Dam, and below the confluence of Antelope Creek between 

April and July (B. Poytress, US Fish and Wildlife, Pers. Comm.). Larval green sturgeons 

disperse from nursery habitats quickly, but then slow their emigration. In the Sacramento 

River, larval and juvenile green sturgeon are encountered in rotary screw traps at Red 

Bluff Diversion Dam between early May and mid-August and in rotary screw traps at the 

Glenn-Colusa Irrigation District pumping plant between early May and October (Adams 

et al. 2002); Table 3). 

On occasion, juvenile green sturgeon older than one year-old are observed in the 

RBDD and GCID rotary screw traps often during winter or early spring. Allen and Cech 

(2007) observed that young-of-the-year green sturgeon could tolerate brackish waters as 

early as three months past hatch in experiments. While little is actually known about the 

distribution of habitat and movement young-of-the-year and riverine juvenile green 

sturgeon, observations suggest that they are distributed in the mainstem below Anderson 

and in fresh and brackish portions of the north and interior Delta. Green sturgeons use 

these areas to forage and rear until they gain the osmoregulatory capacity to tolerate 

higher salinity concentrations. 
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Juveniles: Though green sturgeon are believed to not enter the ocean and reside in 

freshwater and brackish environments for up to three years, juveniles survived in 

seawater as early as the end of their first year (Allen et al. 2006a, Allen et al. 2006b). 

Juveniles use riverine, subtidal, and intertidal habitats along the lower Sacramento River 

and many areas of the Bay-Delta. Juvenile green sturgeon have been captured at Red 

Bluff Diversion Dam and more frequently at the Glenn Colusa Irrigation District’s 

pumping plant indicating potential rearing of more than one age class in the upper and 

middle Sacramento River. There are no records of juveniles from bypasses along the 

lower Sacramento River or its tributaries, including the Feather or Yuba rivers. California 

Department of Fish and Game (CDFG, 2002) reported 61 juvenile and subadult green 

sturgeon (20-112cm) captured during the San Francisco Bay Outflow Study between 

1980-2001, with a majority of individuals captured between April and October. These 

fish were captured in the following locations (CDFG 2002): South San Francisco Bay (3), 

Central San Francisco Bay (6), San Pablo Bay (10), Suisun Bay (21), and the Delta (14). 

Data from the California Department of Fish and Game sturgeon report card found 

anglers captured juvenile green sturgeon between Rio Vista and Chipps Island, 

Sacramento Deepwater Ship Channel, Montezuma Slough, Napa River, Carquinez Strait, 

and Suisun Bay (Gleason et al. 2007). Juvenile green sturgeon were captured during the 

summer in shallow shoals (1-3 m deep) in the lower San Joaquin River (Radtke 1966). 

Juvenile green sturgeon were observed in Clifton Court Forebay between November 

2002 and March 2003 (CDFG 2002). Young-of-the-year juveniles are caught at the state 

and federal fish pumps in the South Delta between March and December. 

Subadults and adults: Coastally migrant subadult green sturgeon tagged by the 

California Department of Fish and Game have been recaptured off Santa Cruz, 

California, in Winchester Bay on the Southern Oregon coast, at the mouth of the 

Columbia River, and in Gray’s Harbor (Chadwich 1959, Miller 1972). Lindley et al. 

(2008) observed fish tagged with individually coded ultrasonic beacons in some of these 

locations also returned to San Francisco Bay, where they were recorded by tag detecting 

monitors. A study of 682 individual green sturgeon used genetic-based mixed stock 

analysis to assess the presence of Sacramento River green sturgeon in western estuaries. 

A majority of samples in collections from the Winchester Bay, OR, Columbia River, WA 

and Willapa Bay, WA were Sacramento River green sturgeon (Israel et al. submitted). A 

significant number of fish collected in Grays Harbor, WA were also of Sacramento River 

origin (Israel et al. submitted). Within coastal migrant and adult collections of fish from 

San Pablo Bay and Suisun Bay, practically all green sturgeon were from the Sacramento 

River, suggesting green sturgeon migrate primarily north of their natal rivers (Lindley et 

al. 2008). 

Within the Bay-Delta, subadults and adults are encountered during California Fish 

and Game surveys during the all seasons. During summer and fall, they are principally 

found in San Pablo, but also in Suisun Bay (Nina Kogut, California Dept. of Fish and 

Game, Pers. Comm.). During the winter and spring, reproductively mature green 

sturgeons enter San Francisco Bay-Delta and migrate up the Sacramento River. 

Ultrasonically-tagged green sturgeon are recorded at detection monitors situated above 

Hamilton City and the vicinity above Red Bluff Diversion Dam during the spring and 

summer (Heublein et al. in press) yet, adult green sturgeon are rarely observed by CDFG 
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in spring fyke net traps near Knight Landing (CDFG 2002). Subadult and adults sturgeon 

are incidentally observed by fishers and biologists in the lower Feather and Yuba rivers in 

the summer, though recent sightings are extremely limited. Subadult and adult green 

sturgeon are rarely observed in monitoring on the Yolo Bypass (Zoltan Matica, 

Department of Water Resources, Pers. Comm.), since this area is rarely inundated and 

connected to the Sacramento River while these fish are in the lower Sacramento River 

area. They have been observed in the South Delta in winter and spring (CDFG 2002), 

with no recent observation of fish residing in the San Joaquin River. 

Spawning: In the Sacramento River, spawning is presumed to occur in the 

mainstem from the confluence of Battle Creek (Rkm 438) to the area upstream of Los 

Molinos. When high outflows are sustained into the early summer, green sturgeon may 

also enter the lower Feather and Yuba rivers. A review of green sturgeon fork length 

from RBDD and GCID (CDFG 2002) suggests that larvae occur in both areas during the 

same period, and thus reproduction likely occurs below RBDD closer to GCID during 

some years. 

III. Ecology (Figures 5-11) 

A. Reproduction to embryonic development (Figure 6) 

Optimal conditions for spawning are presumably found at many locations within the 

upper Sacramento River. Temperatures between 17-18°C are the upper limit of thermal 

optima for green sturgeon embryos, while greater temperatures affected development and 

hatching success (Van Eenennaam et al. 2005). Temperatures greater than 23°C led to 

complete mortality before hatch (Van Eenennaam et al. 2005). Flow relationships for 

white sturgeon have been examined by DFG (Kohlhorst et al. 1991), but not for green 

sturgeon. A flow relationship for green sturgeon is presumed to be similar to white 

sturgeon with greater young-of-year production resulting from greater flows during the 

spawning season between April and July (Kohlhorst et al. 1991). Kohlhorst et al. (1991) 

explored association between white sturgeon year class strength and mean daily 

freshwater outflow from the estuary, mean daily freshwater diversions from the delta, and 

mean daily percent of inflow diverted. Recruitment was significantly positively 

correlated with outflow in all months from April to July, but not mean daily volume of 

diversions. Kohlhorst et al. (1991) also found a recruitment pattern that seemed 

influenced by spawning stock abundance for white sturgeon which matures at about 14 

years of age, and it is likely spawning stock abundance and environmental factors both 

influence recruitment of sturgeon young-of-year. The estimated number of green 

sturgeon contributing to juvenile samples collected at Red Bluff Diversion Dam between 

2002 and 2006 increased with greater flows at Bend Bridge (Israel 2007). This increased 

spawning success may be due to higher flows that increase turbulence in optimal 

spawning habitats, which may increase fertilization rates or may be due to more 

reproductive individuals reaching optimal spawning habitats. 

B. Developing embryo to feeding larvae (Figure 7) 

Water temperature affects the survival of early life stages of green sturgeon. Green 

sturgeon spawning occurs between April and July, which is a period of regulated flows in 

Sacramento and Feather rivers. Water temperatures, which are principally a function of 
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water quantity and air temperature, can fluctuate significantly due to managed releases 

from large reservoirs in both subbasins. Temperature may be a limiting factor for annual 

recruitment, if not enough green sturgeon are able to migrate far enough upstream to 

spawn in areas that permit successful dispersal of eggs and larvae into reaches favorable 

to survival of these life stages. Temperature affects the following critical processes: 1) 

hatching rates, 2) rate and type of embryonic development, and 3) survival (Van 

Eenennaam et al. 2005, Werner et al. 2007). An increased number of embryos developed 

abnormalities between 17.5° and 22°C and the length of hatched embryos decreased at 

these upper temperatures in experiments (Linares-Casenave et al. in preparation). When 

water temperature was experimentally reduced from 26°C after three days to 17°C, a 

significant number of larvae appeared to recover from their deformities in experiments 

(Werner et al. 2007). While green sturgeon may survive incubation at the limits of their 

temperature optimum, reproductive success and young-of-year recruitment are 

presumably negatively impacted when embryos and larvae are exposed to temperatures 

greater than 20°C 

Green sturgeon larvae oxygen consumption increased five-fold while they absorbed 

nutrients in their yolk sacs (Gisbert and Doroshov 2001). Ambient dissolved oxygen 

levels have a significant role in survival of larvae, since fin development is incomplete at 

this stage and they are poor swimmers that cannot move more than a few centimeters 

(Kynard et al. 2005). Green sturgeon remain in habitats with some type of cover until 

they develop into larvae (Kynard et al. 2005). The percent of loss of life among larvae 

exposed to different experimental substrates was significant. Mortality of larvae was 

highest (40%) in cobble substrate compared to sand (11%), slate-rocks (7%), and glass 

(0%) (Nguyen and Crocker 2007). Also in this experiment, the larvae in the flat-surfaced 

treatments had higher specific growth rates. Striped bass, suckers and pikeminnow are 

often observed downstream of spawning green sturgeon at RBDD (J. Israel, Pers. 

Observation) and are likely predating upon eggs. Egg predation has not been quantified, 

and its effect on mortality relative to temperature and dissolved oxygen is unknown. 

C. Feeding larvae to juveniles (Figure 8) 

Larvae must quickly switch from feeding on their yolk reserves to the ingestion of 

prey items. This rapid initiation of exogenous feeding by larvae is critical. In 

experiments, larvae deprived of food exhibited a progressive deterioration underway after 

five days of starvation, and necrosis of larvae was observed at 10-15 days of starvation 

(Gisbert and Doroshov 2003). The growth of post-yolk-sac fish (~0.1-10g) to juvenile 

green sturgeon appeared temperature independent when growth was measured between 

19 and 24oC (Allen et al. 2006b). Specific growth rates, wetted weight, and total lengths 

were greater at temperatures >24oC and a cycling temperature of 19-24oC than at a 

constant temperature of 19oC due to increases in food consumption. Thus, is seems 

elevated and cycling temperature do not have adverse effects on juveniles if food is 

abundant and dissolved oxygen is available. Post-migrant larvae and early juveniles 

forage both during day and night with a nocturnal activity peak (Kynard et al. 2005). No 

studies have been undertaken to identify food resources for larval green sturgeon. 

However, larvae and young-of-year of the shovelnose sturgeon feed principally on 

Diptera and Ephemeroptera pupae and larvae (Braaten et al. 2007). 
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Riverine juvenile green sturgeon increased their swimming performance at an 

elevated temperature of 24°C compared to 19°C in experiments. Hence, it is possible that 

these fish can perform at increased activity levels in warmer summer river temperatures. 

Juveniles between 110-181 days past hatch dph were observed to move downstream 

nocturnally until water temperatures decreased to about 8oC (Kynard et al. 2005). 

Juvenile green sturgeon of a mean age of 150 dph, which were saltwater tolerant had a 

decreased swimming performance (Allen et al. 2006a). Among three age groups (100 

dph, 170 dph, 533 dph); when acclimated to saltwater only the youngest fish died at a rate 

of 23%. Juvenile green sturgeon develop critical osmoregulatory capacities between their 

first and second year that permit them to enter saltwater at a size of 75cm and length of 

1.5kg (Allen and Cech 2007). There is no difference in oxygen consumption rates 

between salinity treatments or age groups, indicating the energetic costs of living in a 

particular environment at a particular age were not prohibitively high (Allen and Cech 

2007). In this experiment, oxygen consumption in the lab ranged from 61 to 76 mg O2hr1

kg-1, with a trend of increasing oxygen consumption with body mass. A positive 

correlation existed between swimming performance and small body size and seawater 

intolerance (Allen et al. 2006a). This relationship became negative at sizes larger than 

25cm, once green sturgeon were 100% seawater tolerant. Allen et al. (2006a) 

documented morphological features such as larger relative pectoral fin surface area and 

behavioral features such as rostrum wedging and pectoral fin holding were observed 

suggestive of holding in a riverine environment (Allen et al. 2006a). This adaptation may 

increase the availability of riverine habitats for foraging to young-of-the-year green 

sturgeon. 

D. Juveniles to coastal migrant (Figure 9) 

Our understanding of juvenile habitat is poorly understood. Juvenile green 

sturgeons inhabit the Sacramento River and San Francisco Bay-Delta. In the river, they 

occupy low-light habitats with some rock structure during their first winter. Juveniles 

have been reported to forage at night, while seeking the darkest available habitats during 

the day (Kynard 2005). Juvenile green sturgeon do have morphological and behavioral 

attributes for holding in flowing riverine environments (Allen et al. 2006a). In the 

estuary, it is possible that older juvenile green sturgeon are capable of moving across 

highly variable physical gradients in salinity, temperature, dissolved oxygen as are adults 

in the ocean environment (Kelly et al. 2007, Moser and Lindley 2007). Kaufman et al. 

(2006) found the oxygen binding of green sturgeon juveniles appeared to have low 

temperature sensitivity, which would permit fishes to bind sufficient oxygen with 

increased water temperatures. The oxygen binding and uploading responses of juvenile 

green sturgeon across a range of temperatures between 11° and 24° C suggests they are 

capable of inhabiting slightly hypoxic-environments (e.g., when compared to that of 

rainbow trout) while maintaining moderate aerobic activity (Kaufman et al 2006). These 

experimental data also suggested green sturgeon have a limited ability to handle 

increased environmental CO2. Flow may indirectly influence juvenile foraging and 

survival by modifying the availability of freshwater and low-salinity habitats in the Delta 

and Suisun Bay during green sturgeon’s first year of life. 

Very little is known about the growth and swimming capacity of green sturgeon in 

estuarine and saltwater environments. Larger young-of-the-year and one year-old 

juvenile green sturgeon of 150-851g are found in these environments. Experimental 
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research in freshwater conditions demonstrated green sturgeons can have rapid growth 

rates and high oxygen consumption rates relative to other sturgeon species (Mayfield and 

Cech 2004). Their consumption of food, growth, and food conversion efficiency 

generally increased with temperature between 11°C and 15°C, but stayed constant 

between 15° C and 19° C. Oxygen consumption, activity rate, and ventilatory frequency 

generally increased, while swimming performance decreased with temperatures from 19° 

to 24° C (Mayfield and Cech 2004). Juvenile green sturgeon likely seek areas with 

saturated levels of dissolved oxygen, since temperatures in this non-optimal range are 

likely encountered during the summer and into the early fall in the lower Sacramento 

River and Delta. Green sturgeon bioenergetic performance was optimal between 15° C 

and 19° C, regardless of feeding to food availability. Once juveniles have the capacity to 

live in saltwater, they are believed to spend one to three years in estuaries before making 

an initial ocean migration. These estuarine juveniles are believed to grow as large as 90 

cm based on aging of pectoral fin rays (Nakamoto et al. 1995) and observations of fish at 

the federal and state pumping facilities (CDFG 2002). 

The diet of riverine juvenile green sturgeon is unknown, though they are presumed 

to be generalists and opportunists. They presumably feed upon similar prey as other 

sturgeons. Seasonally abundant drifting and benthic invertebrates have been shown to be 

the major food items of shovelnose and pallid sturgeon on the Missouri River (Wanner et 

al. 2007), lake sturgeon in the St. Lawrence (Nilo et al. 2006), and white sturgeon in the 

lower Columbia (Muir et al. 2000). These seasonally abundant insects included Diptera, 

Ephemeroptera, and Tricopteran pupae and larvae. As sturgeons grow, the begin to feed 

on oligochaetes, amphipods (Corophium sp.), smaller fish, and fish eggs as represented in 

the diets of lake sturgeon (Nilo et al. 2006), pallid sturgeon (Gerrity et al. 2006), and 

white sturgeon (Muir et al. 2000). The diversity of the prey of sturgeons in rivers may be 

an indication of competition with other riverine fish for drifting prey. If this is the case, 

there may be competition for food with other fish present in the Sacramento River such 

as Sacramento suckers, striped bass, and salmonids. When juvenile green sturgeon enter 

the estuary, their diet shifts to larger benthic food items, though they remain generalists 

and opportunists. Mysid shrimp and amphipods (Corophium) were observed to be the 

primary food items in juvenile (<57cm) green sturgeon stomachs (Radtke 1966). 

Available benthic food items have changed during the recent past, and invasive Corbula 

has replaced native mollusks and shrimps. It is possible, this shift has led to dietary 

dilution, increased bioaccumulation of contaminant, and/or reduced growth of green 

sturgeon occupying the estuary, although the importance of this shift is unknown for 

green sturgeon. 

E. Maturation of coastal migrants to spawning adults (Figure 10) 

Subadults and adults inhabit the San Francisco Bay-Delta, Pacific Ocean, and 

estuaries in the Pacific Northwest. Reproductively mature adults migrate up the 

Sacramento River. In San Francisco Bay, coastal migrants were tracked in the San 

Francisco, San Pablo, and Suisun bays (Kelly et al. 2007). In these regions, they 

occupied areas of depths from 0 to >10 meters, where there appeared to be no preference 

for temperature (14.5o to 20.8oC), salinity (8.8 to 32.1 ppt), or dissolved oxygen (7 to 9 

O2 l

-1). Green sturgeon occupied estuaries in Washington State when estuarine water 

temperatures exceeded coastal water temperatures by at least 2oC (Moser and Lindley 

2007). In Willapa Bay, green sturgeon were exposed to rapid tidally influenced 
12

fluctuations in salinity up to 1 PSU h-1and temperature of up to 2o C h-1. They did not 

migrate due to patches of fresh waters or freshets (Moser and Lindley 2007). Subadult 

green sturgeon occupied Willapa Bay when salinity ranged from 24.5-32.2 PSU and San 

Francisco Bay over in a larger range of salinities from 8.8- 32.1 ppt. A majority of 63.4% 

of their summer estuarine movements were non-directional and associated with the 

bottom. These individuals moved slowly with frequently changed direction and swim 

speed (Kelly et al. 2007). Considerable information should become available in the next 

year concerning coastal migrant and adult green sturgeon in the San Francisco Bay-Delta 

as a result of the Central Valley Fish Tagging Consortium’s receiver arrays provides 

detailed temporal and spatial information about the movements of acoustically-tagged 

fish. 

Green sturgeons exhibit a narrow and shallow depth distribution in the ocean. Green 

sturgeon typically swim in depths <100m over the continental shelf (Erickson and 

Hightower 2007). They move in shallower depths during the night than during the day, 

with occasional rapid-vertical ascents to the surface (Erickson and Hightower 2007). 

Green sturgeon migrate northward into Canadian waters during the fall, moving faster 

with a maximum rate of >45km day-1 during the spring (Lindley et al. 2008). There is an 

over-wintering aggregation site north of Vancouver Island and south of Cape Spencer, 

AK. Beamesderfer et al. (2007) modeled green sturgeon annual ocean survival to be 87% 

with natural mortality rate of 8%, and harvest mortality rate of 5%, and recent analyses 

(Lindley et al. 2008) of acoustically tagged recaptures in the ocean indicate survival is 

83%, which is close to the proposed theoretical estimate. 

Little is known about the prey of subadult and adult green sturgeon. They are 

presumed to be similar to other anadromous sturgeons and be secondary consumers and 

opportunistic predators of macrocrustaceans and bivalves in bay, subtidal, and intertidal 

habitats. Radtke (1966) identified Corophium sp. (amphipods) and Neomysis sp. 

(Opossum shrimp) in green sturgeon stomachs from the Delta. Stomaches of green 

sturgeon in San Pablo Bay contained the greatest variety of food items including 

Corophium sp., Photis californica (amphipod), Cragon franciscorum (Bay shrimp), 

Macoma sp. (clam), Synidotea laticauda (isopod), and unidentified crab and fish (Ganssle 

1966). The stomachs of green sturgeon in Suisun Bay included Corophium sp., C. 

franciscorum, Neomysis sp., and annelid worms (Ganssle 1966). Shallow pits in intertidal 

areas are indicative of digging and predation by green sturgeon on burrowing shrimp 

such as Neotrypaea sp and Upogebia pugettensis in Willapa Bay, WA (Dumbauld et al. 

2008). In Willapa Bay, WA, the coastal migrant and adult green sturgeon seemed to 

forage on macrocrustaceans (Neotrypaea sp., U. pugettensis, and Crangon sp.), bivalves, 

and benthic fishes. 

Reproductively mature green sturgeons migrate into rivers prepared to spawn. 

Female green sturgeon presumably hold their eggs in an advanced stage of ovarian 

maturation until optimal water temperatures and the presence of males stimulate 

spawning. There have not been any observations of atresia in any riverine-captured fish 

on the Klamath or Rogue rivers (Van Eenennaam et al. 2006, Webb and Erickson 2007), 

suggesting cool water temperatures below 15° C limits egg degeneration and reabsorption 

through their spawning migration in these coastal rivers. Similar conditions are 

presumably optimal in the Sacramento River and tributaries for green sturgeon spawning 
13

migration. On the Rogue River, 95% of the females and 88% of the males appeared to be 

reproductively active or had recently spawned during the period of April to July (Webb 

and Erickson 2007). In this study, vitellogenic females and pre-meiotic males, both nonreproductive adult developmental stages, were observed in freshwater during the spring 

(Webb and Erickson 2007). Female and male green sturgeon captured during the fall in 

the Rogue River showed signs of gonadal tissue repair with 29% and 44% pre-meiotic, 

respectively, and this indicated they had already initiated their next gametogenic cycle 

(Webb and Erickson 2007). 

F. Adult spawning migration, spawning, and post-spawning adults 

(Figure. 11) 

Adult green sturgeon are presumed to migrate directly to spawning areas, though 

they may aggregate temporarily in the upper Delta during the spring or summer in an 

effort to migrate during the same period upstream to spawning areas or convene with 

outmigrating post-spawners. These staging behaviors have been observed in anadromous 

lake sturgeon on the St. Lawrence River (Hatin et al. 2002), and movement data on green 

sturgeon may demonstrate synchrony in spawning migration or outmigration. Green 

sturgeon carrying individually coded ultrasonic beacons entered the Golden Gate as early 

as February and as late as May and moved up the river to spawn (Heublein et al. in 

press). The tagged fish moved upstream rapidly to spawning areas. On the Sacramento 

River, adult green sturgeon were detected at Knights Landing in March and April, 

slightly earlier than spawning fishes in Northern DPS rivers. At the height of green 

sturgeon migration, which is typically reached during the period of early May 1 and late 

July, green sturgeon are most frequently found aggregating in isolated spots between 

Glenn-Colusa Irrigation District’s site (GCID, Rkm331) upstream to Cow Creek at Rkm 

451. Adult green sturgeon were present during late spring from Patterson riffle at Rkm 

374 to immediately below the Red Bluff Diversion Dam at Rkm 391 frequently since 

1981 (Brown (2007). Adult fish carrying ultrasonic beacons started their up-migration 

later than March, their upstream movement being impeded by the Red Bluff Diversion 

Dam (Heublein et al. in press). The apparent propensity for subadult and adult green 

sturgeon to aggregate in isolated freshwater habitats (S. Lindley, NOAA-Fisheries, Pers. 

Comm.; R. Corwin, Pers. Comm.) is similar to behavior observed in a resident population 

of lake sturgeon (Borkholder et al. 2002). While this behavior facilitates spawning, it is 

unclear for how long green sturgeon may aggregate and the reasons for this behavior later 

in the summer and fall seasons. 

Very little information is known about adult green sturgeon habitats in the 

Sacramento River. Our understanding for green sturgeon riverine habitats is primarily 

based on the preferences of other sturgeon species and observations of bank substrate. 

Green sturgeon likely evolved a reproductive strategy to spawn in rapidly-flowing small 

rivers with their spawning grounds situated quite close to the river mouth (Artyukhin and 

Andronov 1990). Adult green sturgeon held in habitats greater than five meters depth in 

reaches characterized by small elevation gradients or off-channel coves of the rivers north 

of the Sacramento River (Benson et al. 2007, Erickson et al. 2002). Habitats like this are 

common on the Sacramento River, though it is unclear what physical or biological 

properties in deep pools favor green sturgeon occupancy. 
14

Green sturgeon spawn in fast moving, turbulent waters in river reaches 

characterized by steep discontinuities in the channel slope and coarse cobble (Moyle 

2002). These reaches often exist within canyons in the Klamath and Rogue rivers or 

reaches containing volcanic substrates in the Sacramento River. These habitats were 

situated primarily above Keswick Dam (Rkm 483), but now exist between Battle Creek 

and Red Bluff Diversion Dam such as at China Rapids and Iron Canyon. Green sturgeon 

eggs are highly adhesive (Van Eenennaam et al. 2008), indicating that their adhesiveness 

limits their movement downstream from spawning areas. Although spawning habitats 

may exist as far downstream as Glenn Colusa Irrigation District’s diversion site, adults 

may need to swim farther up the river to ensure survival of eggs and larvae in suitable 

downstream reaches It is possible the temperature in the downstream reach may constrain 

the realized area available as larval nursery and juvenile foraging. 

Once adult green sturgeons have spawned they appear to reside in rivers for up to 

six months until autumn or winter. This type of behavior has been observed in all 

spawning populations. On the Sacramento River, the area around Glenn-Colusa Irrigation 

District’s diversion at 331 Rkm appears to be frequently occupied by green sturgeon as 

early as mid-June until early December (Heublein 2006), although sampling has not 

focused earlier than mid-June. On the Rogue River, green sturgeon restrict their 

movements to deep water, >5m in reaches separated by abrupt elevation changes or offchannel coves where the flows are slow (Erickson et al. 2002). Green sturgeon in the 

Klamath River were observed to spend the summer in a single location ranging from 44 

to 199 days, although one individual was detected in multiple holding pools, staying for a 

minimum of one month at each pool (Benson et al. 2007). In the Klamath River, features 

such as rapids, outcrops of bedrock, and large boulders in the middle of the channel were 

frequently found in holding pools. Adult green sturgeon resided in freshwater over the 

summer, though a limited number of adult green sturgeon left in the late spring following 

spawning, although this may have been a response to tagging and handling stress (Benson 

et al. 2007). Green sturgeon used cues like increased flows and temperatures decreases 

below 10oC associated with rainstorms to initiate their outmigration. On the Klamath 

River, green sturgeon outmigrated between 6.6-49.3 km day-1and exited as late as 

December (Benson et al. 2007). In the lower Rogue River, the average swimming speed 

for two individuals ranged from 3.6-11.2 km day-1 (Erickson and Webb 2007) 

IV. Stressor by stage and habitat (Table 4 and 5) 

Green sturgeons are long lived, and thus face environmental and anthropocentric 

stressors that may affect the probability that they reach reproductive maturity. Males are 

observed to reproduce as early as 14 years old, while females grow older prior to 

maturing as early as 16 years old (Van Eenennaam et al. 2005). Both males and females 

occupy all types of aquatic environments- freshwater, estuarine, and marine. Numerous 

environmental factors potentially limit green sturgeon survival during the earliest stages 

of their life cycle while in freshwater. This period is called the “critical age” in fishes due 

to its relevance in survival and recruitment of individuals into the adult population 

(Hardy and Litvak 2004). Recruitment failure of the earliest life history stages may be a 

significant bottleneck for other North American acipenserids such as Pallid sturgeon and 

the white sturgeon in Upper Columbia and Kootenai rivers, the populations of which 
15

have numerous reproductive adults, but few recently surviving wild juveniles (Duke et al. 

1999, Hildebrand et al. 1999, Korman and Walters 2001) .

There are many potential limiting factors during this early life period. They are 

the following: 1) warm water temperatures, 2) insufficient flows, 3) decreased dissolved 

oxygen, 4) lack of rearing habitat, and 5) increased predation. Water is released from 

Shasta Dam to maintain daily temperatures below 18o C downstream to a temperature 

compliance point, which in 2007 was maintained at Jellys Ferry and Balls Ferry to 

facilitate the incubation of eggs of spawning winter-run Chinook. This maintenance of 

cool water temperatures benefits green sturgeon spawning upstream of Red Bluff 

Diversion Dam. Temperature records from acoustic telemetry receivers along the 

mainstem have not been analyzed, but may provide data for assessing whether 

temperatures are limiting survival of embryos, larvae or juveniles downstream of RBDD. 

Once larvae grow into juveniles, their survival may be limited by lack of habitat, 

insufficient food, and possibly contaminants. Juveniles are fairly tolerant of variable 

temperature and dissolved oxygen, and are likely mobile enough to select favorable 

habitats (see Ecology sections). It is possible that juveniles can also be entrained in water 

diversions for farmland irrigation, although their benthic behavior likely limits this 

impact, and this is not well understood. 

The members of the older age classes principally face anthropocentric threats to 

their survival in estuarine and marine environments. Once within the estuary, juveniles 

might accumulate pollutants such as methyl-mercury and pyrethroids, whose uptake is 

enhanced by the benthic feeding orientation of green sturgeon. Pyrethroids also may limit 

the availability of prey for young green sturgeon due to their effect of very low dosages 

on zooplankton and bottom-dwelling organisms. The size of the populations of subadults 

and adults have been potentially limited by human fisheries and barriers to spawning 

areas which may prevent them from racing the most optimal spawning habitats. Harvest 

can cause abrupt declines in green sturgeon adult abundance. Even an amount as small as 

10% additional mortality over the green sturgeon’s life-span can reduce population 

abundance by 50% and adult abundance by 90% (Beamesderfer et al. 2007). An 

additional simulated increase in mortality of 20% over natural mortality resulted in no 

green sturgeon surviving to adulthood. These forms of mortality could include human 

and nonhuman sources of direct mortality, and are not well quantified for the Southern 

DPS. Of greater concern, might be even much smaller additional mortality rates’ 

influence on green sturgeon’s reproductive potential. Additional rates of only 2-3% 

annual mortality over green sturgeon’s life cycle reduced egg production to levels making 

sturgeon stocks extremely susceptible to overfishing (Beamesderfer et al. 2007). 

A. Entrainment 

Entrainment, or loss of life due to water pump, canal, or dam operations can be a 

problem for almost every life stage of green sturgeon- larvae, juveniles, subadults, and 

adults. While managers do not understand the impact of entrainment on green sturgeon in 

the Sacramento River, its effects may be predictable based on knowledge of behavior of 

the various life stages and past capture records from various water operation facilities. 

Larvae and juveniles may be trapped and killed at riverine and estuarine pumps located 

on the bottom when they are operated at night, since these life stages are benthic and are 

nocturnally active, presumably coming into shallower areas to feed. Juvenile green 
16

sturgeon have been entrained at the GCID diversion site and state and federal pumping 

facilities (CDFG 2002). Juvenile green sturgeon are entrained regularly at the Tracy and 

Banks Pumping Plants. While green sturgeon are vulnerable to impingement or 

entrainment at screened diversions when they are less than 30 mm in length, screening 

criteria for Delta smelt (0.1 fps) and juvenile salmon (0.33fps) were protective to juvenile 

green sturgeon (>30mm) in experiments (Swanson et al. 2004). It is possible subadult 

and adult green sturgeon are also affected by entrainment at the state and federal pumping 

facilities in the Delta because a small number of adult-sized fish were collected from 

Clifton Court Forebay in 1992-1993, and a 1.6 m green sturgeon was collected at the fish 

salvage facility in 2003 (Brent Bridges, BOR, Pers. Comm.). Adult green sturgeon are 

also killed as they are caught in the small space, through which water passes very rapidly, 

between the bottom and the moveable dam gates on Red Bluff Diversion Dam. This may 

significantly reduce the number of adults in the Sacramento River returning to the sea 

after spawning (Richard Corwin, Pers. Comm.). The overall impact of entrainment of fish 

populations is typically unknown (Moyle and Israel 2005), however there is enough 

descriptive information to predict where green sturgeon may be entrained. 

B. Flow operations 

Southern DPS green sturgeon likely spawned in the Sacramento, Feather, and San 

Joaquin rivers, judged upon the characteristics of the local habitats (Adams et al. 2007). 

Historic flows in these rivers during the upstream migration period occurring from March 

through July included increasing flows during winter rainstorms and spring melting of the 

snowpack. These flow increases enabled green sturgeon to migrate into the upper 

portions of these rivers with reaches characterized by high velocity flows and coarse river 

bed surfaces. Current flow management may inhibit the return of green sturgeon to the 

Sacramento River and Bay-Delta estuary by restricting seasonal flow necessary as cues 

for spawning and misdirection of juveniles during their outmigration. If similar to white 

sturgeon (Kohlhorst et al. 1991), seasonal flows during the April to June spawning 

migration for green sturgeon may also be correlated with juvenile green sturgeon 

recruitment. Flows also influence turbidity, dissolve oxygen, and temperature, and these 

all affect biological processed during green sturgeon’s “critical period”. 

Although the effect of operations Delta Cross Channel are not known, they are open 

when juvenile and post-spawn green sturgeon are outmigrating through the lower 

Sacramento River headed to the Delta. This periodicity suggests that juvenile and postspawn green sturgeon likely are redirected by these operations, which may delay 

migrations, expose fish to adverse conditions, or influence growth and survival. 

C. Reservoir operations 

In the upper Sacramento River, the flow volume and temperature of the river are 

dependent on water releases from Shasta and Keswick dams. Until the reservoirs are full 

in the late spring, the rate of water release is lower than naturally occurs, increasing only 

slightly during rains and rapid melting of the snows in the surrounding Trinity and 

Cascade mountains. The flows are generally 200 m3

/s in the spring, reaching 1,500 m3/s 

during rainstorms (Brown 2007). Under these conditions, adult green sturgeon may move 

upstream and spawn in deep pools in the mainstem of the Sacramento River. Late in 

spring (usually on May 15), a series of gates are closed at the Red Bluff Diversion Dam, 

permitting water to form a temporary reservoir and then flow into irrigation canals 
17

leading to farmlands. Flows from May through September range from 280-425 m3

/s 

(Brown 2007). Large aggregations of green sturgeon have been observed in the pool 

below the diversion dam during May and June after the gates are closed (Richard Corwin, 

Pers. Comm.). It is unknown whether a high proportion of the late migrating green 

sturgeons that are forced to stay below the dam to spawn, move downstream to spawn, or 

possibly enter other large tributaries such as the Feather River. Based on preliminary 

results in 2008, it is possible that reservoir operations, which control temperature and 

flow, may actually lengthen the spawning period of green sturgeon in the area 

immediately downstream of RBDD (Israel et al., unpublished data). 

Increased water flows presumably enhance spawning efficiency for green sturgeon. 

The flow of water on the Sacramento, Feather, and Yuba rivers is controlled by dams, 

and the flows can be predicted with high reliability. Thus, water managers can directly 

influence the successful production of larvae and juveniles. Outflow to the San Francisco 

Bay-Delta between April and July is significantly correlated with white sturgeon year 

class strength (Kohlhorst et al. 1991), and a similar relationship is presumed to exist with 

green sturgeon. Daily discharge at known green sturgeon spawning locations were similar 

to the estimated minimum necessary for strong age classes of white sturgeon on the 

Sacramento River (19,988 cfs, Neuman et al. 2007). On the Feather and Yuba rivers this 

volume of flow was not observed between 1996 and 2006. Additional study is necessary 

to understand how year class strength is correlated with flow rate. Increased water 

temperature decreases survival and increases mortality during gastrulation and yolk sac 

digestion. It is possible that river water temperature also influences spawning site 

selection although this has not been examined. Turbidity may increase the rate of 

fertilization of eggs (Van Eenennaam et al. 2008). 

D. Habitat Loss 

Managers do not know the historic spatial and temporal distribution of green 

sturgeon in the San Francisco Bay Delta. Assessments of historic habitat changes are 

based on our perception of what constitute optimal spawning, rearing, and foraging 

habitats. Dams on the Feather, Yuba, and San Joaquin rivers have changed the flow rate 

and period of temperatures favorable to green sturgeon embryo and larval survival, thus 

limiting recruitment on these systems. Dams and water conveyance structures (i.e., 

Themalito Outlet) have been built on these tributaries and their operation block passage 

by adult green sturgeon to preferred spawning habitats upstream of them. National 

Marine Fisheries Service (NMFS 2006) identified numerous potential adult migration 

barriers including RBDD, Sacramento Deep Water Ship Channel locks, Fremont Weir, 

Sutter Bypass, and the Delta Cross Channel Gates on the Sacramento River and Shanghai 

Bend and Sunset Pumps on the Feather River. In the Central Valley, approximately 4.6% 

of the total river kilometers have spawning habitat characteristics similar to where 

Northern DPS green sturgeon spawn (Neuman et al. 2007). Only 12% of this habitat is 

currently occupied. Of the 88% that is unoccupied (approx. 4000 kms) Neuman et al. 

(2007) found 44.2% is currently inaccessible due to dams. 

Modification of the riverscape has resulted in loss of spawning habitat, rearing 

habitat, and increased barriers to migration. Larvae, juveniles, and adults life history 

stages are all benthic in orientation and all require deep habitats for dispersal, holding, 

and spawning. Successful fertilization and survival of embryos seems to require 
18

spawning habitats reflecting specific water quality and quantity parameters, which have 

been negatively impacted by construction of dams and channelization of the river. 

Riparian habitats provide allochthonous contributions to the river food web that indirectly 

support juvenile prey items. It is possible that modifications in temperature regime 

controlled by the Shasta Dam temperature control device may benefit green sturgeon 

spawning above Red Bluff Diversion Dam, but more research is necessary to understand 

the impacts of temperature on the distribution and success of green sturgeon spawning. 

Channelization of the estuary has likely negative impacted the amount of subtidal 

and intertidal habitat available for green sturgeon foraging. These habitats have been lost 

along San Pablo and Suisun bays, where subadult and adult green sturgeon are commonly 

found. These estuarine habitats are likely important for growth during the juvenile, 

coastal migrant, and adults life stages. Invasive plant species in the estuary have likely 

impacted the quantity of shallow habitat available to coastal migrant and adult green 

sturgeon, and alterations of the food web due to invasive species have also likely shifted 

green sturgeon estuarine diet. Managers understand and the predictability of the impact of 

invasive species on green sturgeon is low and primarily based on observations of other 

species and ecology theory. 

It is unknown if floodplains were a commonly used habitat by juvenile green 

sturgeon, though they may have served as migration corridors for adults. Since 1934, the 

Yolo bypass has been flooded and available for juvenile habitat before January in only 16 

years (22% of the record). It is flooded into June once every fifty years, thus not typically 

available to larvae or riverine juveniles outmigrating to the estuary. Since 1934, the Yolo 

Bypass has been inundated after April in only 8 years (11% of the record), thus it is 

presumably a minor migration barrier for adults in a small number of years. It is possible 

subadult and adult fish use the drain, Cache Slough, and other perennially wetted portions 

of the bypass more frequently, but without inundation the Yolo bypass is not connected 

to the Sacramento River. 

E. Water Quality 

Water quality is likely a limiting factor during early life history stages of green 

sturgeon. Green sturgeons have a high rate of oxygen consumption and require high 

levels of dissolved oxygen to avoid stress (Gisbert et al. 2001, Lankford et al. 2003, 

Mayfield and Cech 2004). Eggs, embryos and larvae require higher levels of dissolved 

oxygen than juvenile green sturgeon, although growth does not seem to be controlled by 

dissolved oxygen. It is possible that low levels of dissolved oxygen results in chronic 

stress in young green sturgeon (Lankford et al. 2003), which forage in subtidal and 

intertidal Delta habitats and the Stockton Deep Water Ship Channel. However, there is 

high uncertainty and no knowledge about the presence of these conditions in particular 

habitats. Salinity can affect green sturgeon, although the predictability of this stressor is 

also limited. Peer-reviewed research has provided a clearer understanding of this 

stressor’s effect and indicates the juvenile population of green sturgeon is physiologically 

heterogeneous. Thus, some juvenile green sturgeon are adapted to entering seawater 

earlier than others, who may be subjected to reduced foraging and survival in more saline 

environments (Allen and Cech 2007). Once in estuarine and seawater environments, 

seawater-tolerant green sturgeons seem to not be limited by the physical properties of the 

water due to their high mobility within these environments. Climate change will affect 
19

water quality and quantity, and may influence egg incubation, larval and juvenile growth 

rates, and spawning migration periodicity. While green sturgeon spawning persists in a 

reach of the Sacramento River with potentially cold waters regulated via the Shasta Dam 

temperature control device, the management utility of this tool with a changing climate is 

uncertain. 

F. Toxics 

Green sturgeons are long-lived fish which presumably forage annually in 

estuaries. Other anadromous sturgeon have been found to be as sensitive as salmonids to 

most contaminants, and green sturgeon should be presumed to be affected by water 

quality (Dwyer et al 2005). Estuarine food webs are often impacted by contaminants due 

to intensive modification of flows, sediment routing, and historic human influences. 

Manager’s understanding of whether green sturgeons suffer from bioaccumulation of 

contaminants is limited. Green sturgeon do not spend as much time in estuaries as white 

sturgeon, but the effect of bioaccumulation of contaminants have been studies on this 

species in San Francisco Bay-Delta. Similar to white sturgeon, green sturgeons’ growth, 

fecundity, and egg size are likely negatively affected by contaminants which persist for a 

long time in the environment like selenium and mercury (Linville 2006), Robert 

Kaufman, UCD, Pers. Comm.). Early life history stages may also be impacted, and 

Linville (2006) observed larvae to have increase skeletal deformities and mortality 

associated with maternal effects of selenium exposure. Increasing uptake of Lselenomethionine in juvenile green sturgeon results in an increase in mortality in fish fed 

80mg Se/kg after only two weeks. Smaller quantities of 20mg/kg decreases feeding 

efficiency, and >20mg/kg reduced growth rates after four weeks (Lee et al. 2008a). 

Methylmercury in sediments was highest in the Central Bay between 2002 and 

2006, though shallower parts of San Pablo Bay and Suisun Bay also contained levels 

greater than 0.2 ppb (SFEI 2007). The amount methylmercury resulting in the death of 

juvenile green sturgeon lies between 20 to 40mg/kg, with greater consumption increasing 

mortality significantly (Lee et al. 2008b). Pollutants like endrocrine disruptors and 

pyrethroids, may also have effects on juvenile green sturgeon. Intersexual changes 

characterized by the formation of ovaries in males have been observed in shovelnose 

sturgeon and have been potentially linked to endocrine-disrupting organochlorine 

chemicals (Harshbarger et al. 2000). If green sturgeons are similar to other sturgeon, it 

would seem likely that pyrethroids accumulated in the tissues of members of the benthos 

even at extremely low level may affect ecological fitness by reducing growth, increasing 

disease, and producing abnormal swimming (Inge Werner, UC Davis, Pers. Comm.). 

This may impact juvenile green sturgeon more so than subadults or adults, due to their 

relative size. While multiple toxicants persist in the San Francisco Bay-Delta, the nearand long-term independent and synergistic effects of these chemicals on green sturgeon 

are unknown. 

G. Invasives 

Colonization of invasive species has negatively impacted the native Bay-Delta fish 

community. These species have likely impacted green sturgeon through changes in the 

food web by either increasing availability of new benthic species to their possible food 

resources or reducing native food resources. It is unknown whether these invasions by 
20

exotic bivalves, shrimp, and amphipods have led to dietary dilution, if they are inedible, 

or increased foraging opportunities for the generalist green sturgeon. 

H. Population 

Green sturgeons are long lived, and thus the cumulative effects of the stressors 

described above may have a major influence on the probability of them reaching 

reproductive maturity. Males may reproduce as early as 14 years old, while females grow 

older prior to maturing as early as 16 years old (Van Eenennaam et al. 2005). While 

younger age classes may be missing from the population’s demography, it is possible that 

this lack of recruits is not observable until subadults are observed as bycatch in white 

sturgeon sports and commercial fisheries. Green sturgeon have traditionally been 

harvested as bycatch in commercial fisheries. The states of Washington, Oregon, and 

California eliminated legal sportsfishing and commercial bycatch of green sturgeon 

between 2006 and 2008. While uncommon, green sturgeon are still captured in Pacific 

Northwest and Sacramento River sports fisheries. On the Sacramento River, sturgeon 

fishing occurs farther upstream than white sturgeons typically migrate for spawning. In 

2008, guides and private fishers were observed angling with rod and reel at “sturgeon 

hotspots” occupied principally by green sturgeon upstream of Tehama Bridge. These 

fishers viewed sturgeon fishing in these “hotspots” as catch and release fishing (J. Israel, 

Pers. Observation). The retention of green sturgeon is no longer allowed in California or 

the Pacific coast, except in tribal fisheries on the Klamath River (Adams et al. 2007). 

Chronic stress (i.e.: chasing, confinement, or depth reduction) has been observed to 

influence the bioenergetics of green sturgeon, though it did not influence their swimming 

performance (Lankford et al. 2005). Thus, fisher handling of green sturgeon is likely to 

have a minimal effect on survival. Poaching for sturgeon seems to be a threat in the 

Sacramento River, and green sturgeon may be illegally harvested in these operations. 

Manager’s understanding for the effect of fishing-associated mortality on green sturgeon 

is low and the predictability of this stressor is little. 

There is no hatchery for green sturgeon. Van Eenennaam et al. (2008) details 

protocols for spawning green sturgeon for use in conservation aquaculture. These 

protocols combined with a Hatchery and Genetic Management Plan for monitoring 

artificial propagation and its influence on the natural population should be formalized 

between regulatory and involved agencies and organizations prior to release of 

propagated fishes into the wild. 

I. Other 

Disease: It is unknown whether disease is a stressor in green sturgeon. Ongoing 

research in Lake Sturgeon is examining whether egg and larval densities influence 

disease transmission. No studies have evaluated disease transmission, the types of 

diseases potentially affecting green sturgeon, or their impact on green sturgeon 

population viability. NMFS (2006) stated there was not enough information to determine 

if disease played a role in the decline of Southern DPS green sturgeon. 

V. Future Research 

One conclusion of the NMFS Biological Review Team assessing the status of green 

sturgeon was that “it is essential that immediate efforts be undertaken to implement 
21

population monitoring for this [Southern] DPS using methods that directly assess 

population status” (NMFS 2003). Thus, these suggestions aim to focus on life history 

stages and processes critical to persistence of the species, which in green sturgeon are 

principally earlier in the life history. Although laboratory studies have yielded much 

information on the physiological needs of the species, field studies have yet to be 

completed applying this information to identifying adult spawning, larval survival, 

juvenile rearing, and juvenile smoltification. Information is necessary about the life 

history diversity, abundance, population growth rate, and riverscape structure 

(periodicity) of Sacramento River green sturgeon. Outside of the Sacramento River and 

San Francisco Bay-Delta, this same type of information is necessary for other spawning 

populations on the Klamath and Rogue rivers. 

 

Developing flow and temperature recommendations for the middle Sacramento 

River during the spawning migration, spawning, and downstream larval transport stages 

of green sturgeon’s life history are necessary for ensuring recruitment of green sturgeon 

in the long term. Water temperature data below Red Bluff Diversion Dam to Hamilton 

City should be collected with additional CDEC temperature stations installed to evaluate 

temperatures during April to October when eggs, larvae, juveniles, and adults are in this 

reach. 

Parallel genetic studies and/or sonar (i.e. DIDSON) studies should be focused on 

estimating abundance of green sturgeon spawners in the Sacramento River. This will 

provide important information for determining the abundance of adult green sturgeon 

annually in the Sacramento River. These efforts should be advanced collaboratively and 

in a modeling framework so long-term data can be informative enough to improve 

estimates of green sturgeon abundance in the Sacramento River and Bay-Delta. 

 

Managers should develop research and monitoring to estimate the riverine larval 

and juvenile populations for a period of time reflecting the potential variation in physical 

and biological processes influencing recruitment. These results will give managers an 

idea for the effect of management on critical habitats, influence of adult demography on 

recruitment dynamics, and the actual production of green sturgeon in younger cohorts. 

Estimates derived from these types of studies may be a good indication for spawning and 

abundance, which are not negatively influenced by the impact of entrainment, operations, 

and harvest. If estimates of young riverine fish are known, then adaptive research 

evaluating the impacts of anthropocentric stressors on older life history stages will allow 

managers to assess the actual effects of these anthropocentric stressors. Currently, 

abundance derived from harvest or operational entrainment data does not allow managers 

to determine if these impacts are causing declines in abundance or just reflect the natural 

production of spawning adults. 

The distribution of spawning adults as well as a characterization of their spawning 

habitat within the Sacramento River should be completed. This will provide insight into 

the density of spawning adults and influence spawning aggregation have to the juvenile 

population, the rates of egg and larval mortality, and the potential loss of this spawning 

habitat by flow and temperature modification in the system. In 2008, UCD, BOR, and 

FWS initiated tracking green sturgeon as they move within the upper mainstem and 

collected eggs at spawning sites. Additional funding is necessary to adequately monitor 
22

spawning movements and increased egg and larval collection sites along the Sacramento 

riverscape to evaluate green sturgeon habitat relationships. 

 

Little is known about green sturgeon food selection and foraging behavior making 

the predictability of where preferred food is available low. As green sturgeon move into 

the estuary and marine environments, food resources are not well understood. If native 

food sources have declined due to invasive species occupying their habitat or pollutants 

reducing available food, finding sufficient food may be problematic for juvenile green 

sturgeon. There is a need to investigate further the effects of selenium and other 

contaminants on green sturgeon and to find ways to reduce sources. Recent evidence 

indicates adult white sturgeon may be accumulating selenium in concentrations 

detrimental to reproduction, presumably by consuming the introduced overbite clam 

(Linville 2006). 

The California Department of Fish and Game should invigorate their tagging efforts 

for green sturgeon in the Bay-Delta as an annual survey. CDFG should consider using 

acoustic telemetry and continuing PIT tag marking studies to track migrations, determine 

fidelity to spawning areas, monitor survival of fish salvaged at the pumping plants, and to 

locate important feeding and spawning areas. These data can be integrated into a 

hydrodynamic model of the watershed and estuary to determine if changes in flow regime 

affect movements of green sturgeon between spawning and rearing areas. 

The State Water Project and Central Valley Project pumping plants in the south 

Delta capture green sturgeon in all life history stages. However, not known is what 

proportion of captured fish die as a result of capture. Does loss of life increase due to an 

increase in predation on fish drawn towards the plants? Does the contact with the screens 

harm individuals? To avoid future construction of conveyance facilities (i.e., pumping 

stations) to become stressors, research is necessary to develop screening criteria for green 

sturgeon larvae, juveniles, and adults. Additionally, given the limited opportunity for 

capturing green sturgeon, better coordination between salvage facilities and researchers 

may provide fish for field-based research. Scientists at UC Davis are currently obtaining 

juvenile sturgeon for their telemetric studies from these pump salvage facilities. 

Support should be provided for priority research guided by the Interagency 

Ecological Program Sturgeon Work Team. This conceptual model should indicate that 

much is already known about the basic biology of green sturgeon from laboratory studies 

and can serve as the basis for developing hypotheses for testing in field studies. The next 

research step should be to discern the importance of this biology on population viability 

within the watershed. A systematically applied research program attempting to study the 

critical periods and habitats of green sturgeon in riverine and estuarine environments will 

provide managers with information on the actual utilization, status, and abundance of 

different life history stages of green sturgeon in the Sacramento River. Once these field 

observations are completed, our larger and more comprehensive understanding for the 

basic ecology of the species will permit the development of a population viability model, 

which could prioritize the above-mentioned risks to the population and guide 

management decisions. 
23

VI. Literature Cited 

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and Size at Maturity of Green Sturgeon, Acipenser medirostris, in the Rogue River, 

Oregon Environmental Biology of Fishes 79: 255-268. 

Erickson, D.L., North, J.A., Hightower, J.E., Weber, J., and Lauck, L. 2002. Movement 

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USA. . Journal of Applied Ichthyology 18: 565-569. 
25

Ganssle, D. 1966. Fishes and decapods of San Pablo and Suisun bays. In Ecological 

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Gerrity, P.C., Guy, C.S., and Gardner, W.M. 2006. Juvenile pallid sturgeon are 

piscovorous: a call for conserving native cyprinids. Transactions of the American 

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Gisbert, E., Cech, J.J., and Doroshov, S.I. 2001. Routine metabolism of larval green 

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growth, and survival of shortnose sturgeon, Acipenser brevirostrum, and Atlantic 

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145-154. 

Harshbarger, J.C., Coffey, M.J., and Young, M.Y. 2000. Intersexes in Mississippi River 

shovelnose sturgeon samples below Saint Louis, Missouri, USA. Marine Environmental 

Research 50: 247-250. 

Hatin, D., Fortin, R., and Caron, F. 2002. Movement and aggregation areas of adult 

Atlantic sturgeon (Acipenser oxyrinchus) in the St. Lawrence River estuary, Quebec, 

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precautionary monitoring and population monitoring Ph.D., Department of Animal 

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29

VII. Tables 

Table 1. Green sturgeon life stage by biological measures. The abbreviation UNK is used where preferences are 

Habitat

(life stage )

Upper/Middle Rivers

Egg/embryo/ larvae

Upper/Middle Rivers

Endogenously feeding 

larvae

3 Middle/Lower rivers

Young-of-year Juveniles

4 Delta/ Bay 

Juveniles

5 Ocean/Delta/Bay

Coastal Migrants

6 Delta/Bay 

Spawning Adult

7 River

Spawning Adult

8 River /Delta

Post-spawn

Ocean/Delta

Mature Adult all year 15 years - max. age 19-73 kg7 152-2437 UNK seawater 

14 years - 

max. age

7

19-73 

kg7 152-2437 UNK freshwater- seawater 

UNK UKNUNK

9

Oxygen 

range

Turbid

range

Tail Length 

(cm)

Weight 

(g) Age (dph)

May- January

~August - 

~March 16-99 dph

~0.1- 

105

1 April-July < 10 dph1 <~0.11 <1.31

Periodicity Temperature (optimal) °C Salinity range

<27 (15-19)5

90-152 UNK

freshwaterseawater 60-90 UKN 

5

<27 (15-19)5 freshwater

freshwater

all year UKNall year >100dph- 1.5 years UKN

UNK

152-2437 19-73 kg7 UNK

UNK

UKN

UNK

UNK

freshwaterseawaterfreshwaterseawater

freshwater

20-605

March- July 14 years - 

max. age

7

19-73 

kg7 152-2437

1.5- 13 years 

February- July 14 years - 

max. age

7 UKN

2

UNK UKNUNK

April - 

October 8-15 dph1 <~0.11 1.3- 201 11-23 (<17)2

UKN

>60% air 

saturation3 UKN

11-23 (<17)2 freshwater

>60% air 

saturation3 UKN

UKN

1. Deng et al. 2002. 2. Van Eenennaam et al 2005. 3. Gisbert et al 2001. 4. Van Eenennaam et al 2001. 5. Allen et al. 2006a. 7. Lindley et al 2008

2006.
30

Table 2. Green sturgeon life stage periodicity. 

Egg/Embryo/LarvaeSighting locationRBDD GCID JuvenileSighting locationRiver (GCID)Delta Suisun Bay North Bay Coastal migrantSighting locationCoastal ocean Western Estuaries Spawning/Postspawning/Mature adultSighting locationSacramento River  RBDD North Delta South Delta West Delta Suisun Bay North Bay 

Jan Feb Mar April May Jun Jul Aug Sep Oct Nov Jan Feb Mar April May Jun Jul Aug Sep Oct Nov Jan Feb Mar April May Jun Jul Aug Sep Oct Nov Jan Feb Mar April May Jun Jul Aug Sep Oct Nov 
31

Table 3. Green sturgeon larvae and juveniles observed at rotary screw traps at Glenn Colusa Irrigation District (GCID) and Red Bluff Diversion Dam (RBDD) between 1996 and 2008. Identification of enumerated fishes are assumed to be green sturgeon. 

 GCID RBDD 

1996 337 410 1997 237 354 1998 0 302 1999 291 78 2000 35 - 2001 34 - 2002 9 35 2003 9 359 2004 6 264 2005 32 271 2006 6 193 2007 1 19 2008 0 0 
32

Table 4. Green sturgeon life stage stressor matrix. 

A B C 

Habitat

(life stage )

Upper/Middle Rivers

Egg/embryo/ larvae/ 

Endogenously feeding 

larvae

Middle/Lower rivers

Juveniles

Delta/Bay

Juveniles

Ocean/Delta/BayCoastal Migrants

Delta/Bay

Spawning Adult

River

Spawning Adult

8 River/ Delta 

Post-spawn

Ocean/Delta/Bay

Mature Adult

affects migration 

pathways

affects migration 

pathways

direct mortality direct mortality

affects migration 

pathways RBDD: direct mortality

RBDD: direct mortality affects spawning habitat selection

direct mortality & 

salvage

direct mortality & 

salvage

direct mortality & 

salvage

affects 

g

affects 

Entrainment: 

Power Plant

Entrainment: 

SWP/CVP

Flow Operations: 

Delta Cross Channel

Reservoir 

Operations: Altered 

seasonal flows

Flow Operations: S. 

Delta Operable 

Gates

Flow Operations: 

Barriers

Habi

Prey A

6 affects migration pathways affects migration pathways3 GCID: direct mortality & salvage Volume of flow influences tranport and dispersal affects migration pathways

1 & 2 RBDD: direct mortality & salvage

Entrainment: Small 

Ag.

affects migration 

pathways

Volume of flow 

influences tranport and 

dispersal

affects 

g

9

affects migration 

pathways 5 affects migration pathways affects migration pathways affects 

gro

salvage

affects migration 

pathways

affects post-spawning 

migration affects 

47

affects migration 

pathways

affects spawning 

migration
33

Table 4 continued. Green sturgeon life stage stressor matrix. 

D continued E 

Habitat

(life stage )

Upper/Middle Rivers

Egg/embryo/ larvae/ 

Endogenously feeding 

larvae

Middle/Lower rivers

Juveniles

Delta/Bay

Juveniles

Ocean/Delta/Bay

Coastal Migrants

Delta/Bay

Spawning Adult

River

Spawning Adult

8 River/ Delta 

Post-spawn

Ocean/Delta/Bay

Mature Adult

affects stress 

response

affects stress 

response

affects holding 

habitat selection

affects spawning 

habitat selection

affects spawning 

habitat selection

affects survival by 

altering movement 

W. Quality: 

Turbidity

W. quality

Salinity 

Distributio

W. Quality: Temperature Habitat Loss: Migration

affects stress 

response

W. Quality: Diss. 

Oxy.

Habitat Loss: 

Foraging

affects fertilization, 

survival, and growth 

rates

affects survival, 

development, and 

growth rates

affects survival and 

growth

affects survival and 

growth

affects stress 

response

affects survival and 

growth

affects spawning habitat selection

affect post-spawn 

recovery

affects holding 

habitat selection

affects survival and 

growth

9

affects surviva

growth

1 & 2

affects foraging

34567

affects fertilization 

and predation rates

affects surviva

growth
34

Table 4 continued. Green sturgeon life stage stressor matrix. 

G H 

Habitat 

(life stage) 

Invasives: 

Competition 

Invasives: 

Predation 

Population: 

Allee effect 

Population: 

Hybridization 

Population: 

Harvest 

Population: 

Disease 

Upper/Middle 

Rivers 

1 & 2 Egg/embryo/ 

larvae/ 

Endogenously 

feeding larvae 

affects survival affects survival affects survival 

Middle/Lower 

3 rivers 

Juveniles 

affects growth affects survival affects survival 

Delta/Bay 4 

Juveniles 

affects growth affects survival 

Ocean/Delta/Bay 5 

Coastal Migrants 

direct mortality 

Delta/Bay 6 

Spawning Adult 

direct mortality 

River 

7 

Spawning Adult 

affects finding 

mates direct mortality 

8 River/ Delta 

Post-spawn 

direct mortality 

Ocean/Delta/Bay 9 

Mature Adult 

direct mortality 
35

Table 5. Green sturgeon life stage stressor matrix with importance, understanding, and predictability sco

A B C D 

Habitat 

(life stage) 

Entrainment 

Small Ag. 

Entrainment 

Power Plant 

Entrainment 

SWP/CVP 

Flow 

Ops: 

Delta 

Cross 

Channel 

Flow 

Ops: 

Barriers 

Reservoir 

Ops: 

Altered 

seasonal 

flows 

Habitat 

Loss: Prey 

Availability 

Ha

L

Spa

I = 4 I = 3 

U = 2 U = 2 

1 

Upper/Middle Rivers 

Egg/Embryo/ 

Larvae/Feeding larvae P = 3 P = 3 

I = 2 I = 2 I = 2 I = 2 

Middle/Lower rivers 3 U = 1 U = 1 U = 2 U = 1 

Juveniles P = 2 P = 2 P = 3 P = 1 

I = 2 I = 1 I = 2 I = 2 I = 2 

Delta /Bay U = 2 U = 1 U = 3 U = 1 U = 1 

4 Juveniles P = 2 P = 1 P = 3 P = 2 P = 1 

I = 2 I = 2 I = 2 Delta U = 1 U = 1 U = 1 5 Coastal Migrants P = 1 P = 2 P = 1 

I = 2 I = 3 Delta/Bay 6 U = 1 U = 2 

Spawning Adult P = 2 P = 2 

I = 4 I = 3 I 

River U = 2 U = 2 U 

7 Spawning Adult P = 2 P = 3 P 

I = 2 I = 1 I = 1 I = 2 I = 2 I = 2 

River/Delta U = 2 U = 1 U = 1 U = 1 U = 1 U = 2 8 Post-spawn P = 2 P = 1 P = 1 P = 2 P = 2 P = 3 

Ocean/Delta/Bay 9 Mature Adult 
36

Table 5 continued. Green sturgeon life stage stressor matrix with importance, understanding, and predictabili

D 

continued E F 

Habitat 

(life stage) 

Habitat 

Loss: 

Migration 

Habitat 

Loss: 

Foraging 

W. Quality: 

Temperature

W. 

Quality: 

Diss. Oxy. 

W. 

Quality: 

Turbidity 

W. quality: 

Salinity 

Distribution

Toxics: 

Heavy 

Metals 

I = 3 I = 3 I = 3 

U = 3 U = 3 U = 1 1 

Upper/Middle Rivers 

Egg/Embryo/ Larvae/ 

Feeding larvae P = 3 P = 2 P = 1 

I = 2 I = 3 I = 2 I = 2 I = 3 

Middle/Lower rivers 3 U = 1 U = 3 U = 2 U = 1 U = 1 

Juveniles P = 2 P = 3 P = 2 P = 1 P = 2 

I = 2 I = 2 I = 2 I = 2 I = 3 I = 2 

Delta /Bay U = 1 U = 1 U = 2 U = 2 U = 1 U = 2 

4 Juveniles P = 1 P = 1 P = 2 P = 2 P = 2 P = 2 

I = 2 

Delta U = 2 

5 Coastal Migrants P = 2 

I = 2 

Delta/Bay 6 U = 1 

Spawning Adult P = 2 

I = 3 I = 3 I = 2 

River U = 1 U = 1 U = 1 7 Spawning Adult P = 3 P = 3 P = 1 

I = 2 I = 2 I = 2 I = 2 

River/Delta U = 1 U = 1 U = 1 U = 1 

8 Post-spawn P = 1 P = 3 P = 3 P = 2 

I = 2 I = 2 I = 2 

Ocean/Delta/Bay U = 1 U = 1 U = 1 

9 Mature Adult P = 1 P = 1 P = 2 
37

Table 5 continued. Green sturgeon life stage stressor matrix with importance, understanding, and predictabili

G H I 

Habitat 

(life stage) 

Invasives: 

Competition

Invasives: 

Predation 

Population: 

Allee effect 

Population: 

Hybridization 

Population: 

Harvest 

Population: 

Disease Oth

I = 2 I = 1 I = 2 I = 

U = 1 U = 1 U = 1 U = 

1 

Upper/Middle 

Rivers 

Egg/Embryo/ 

Larvae/ Feeding 

larvae P =1 P =1 P = 1 P = 

Middle/Lower I = 2 I = 2 I = 2 I = 

3 rivers U = 1 U = 1 U = 1 U = 

Juveniles P =1 P =1 P = 1 P = 

I = 2 I = 2 I = 

Delta /Bay U = 1 U = 1 U = 

4 Juveniles P =1 P =1 P = 

I = 3 I = 

Delta U = 2 U = 

5 Coastal Migrants P = 3 P = 

I = 2 I = 

Delta/Bay 6 U = 2 U = 

Spawning Adult P = 3 P = 

I = 2 I = 3 I = 

River U = 1 U = 2 U = 

7 Spawning Adult P = 1 P = 3 P = 

I = 2 I = 

River/Delta U = 2 U = 

8 Post-spawn P = 3 P = 

I = 3 I = 

Ocean/Delta/Bay U =3 U = 

9 Mature Adult P = 3 P = 
38

Explanation of importance, understanding and predictability. 

4 = High importance: expected sustained major population level effect, e.g., the outcome addresses 

a key limiting factor, or contributes substantially to a species population’s natural productivity, 

abundance, spatial distribution and/or diversity (both genetic and life history diversity) or has a 

landscape scale habitat effect, including habitat quality, spatial configuration and/or dynamics. 

3 = Medium importance: expected sustained minor population effect or effect on large area or 

multiple patches of habitat 

2 = Low importance: expected sustained effect limited to small fraction of population, addresses 

productivity and diversity in a minor way, or limited spatial or temporal habitat effects 

1 = Minimal or no importance: Conceptual model indicates little or no effect 

4 = High predictability: Understanding is high and nature of outcome is largely unconstrained by variability in ecosystem dynamics, 

other external factors, or is expected to confer benefits under conditions or times when model indicates greatest importance. 

3 = Medium predictability: Understanding is high but nature of outcome is dependent on other highly variable ecosystem processes 

or uncertain external factors. 

OR 

Understanding is medium and nature of outcome is largely unconstrained by variability in ecosystem dynamics or other external 

factors 

2 = Low predictability: Understanding is medium and nature of outcome is greatly dependent on highly variable ecosystem 

processes or other external factors 

OR 

Understanding is low and nature of outcome is largely unconstrained by variability in ecosystem dynamics or other external factors 

1 = Little or no predictability: Understanding is lacking 

OR 

Understanding is low and nature of outcome is greatly dependent on highly variable ecosystem processes or other external factors 

4 = High understanding: Understanding is based on peer-reviewed studies from within system and scientific reasoning supported 

by most experts within system. 

3 = Medium understanding: Understanding based on peer-reviewed studies from outside the system and corroborated by non peerreviewed studies within the system. 

2 = Low understanding: Understanding based on non peer-reviewed research within system or elsewhere. 

1 = Little or no understanding: Lack of understanding. Scientific basis unknown or not widely accepted 
39

VIII. Figures 

Figure 1. Conceptual model of Acipenser medirostris life history 

(modified from Wildhaber et al. 2007). 
40

Ecological attributes

Toxic

Disease

Habitat

availability

Prey

availability

Contributor to direct mortality 

Rate-affecting process affecting 

survival, growth, and development

Biotic ecological attribute affecting 

survival, growth, and development

Abiotic ecological attribute affecting 

survival, growth, and development

Competition

Reproduction

Nutrients

Food Web

Temperature

Dissolved

Oxy

Salinity

Sediment

Channel

Morphology

Hydraulic

habitats

Non‐native

fishes

Native

fishes

Other than

fishes

Population

of origin

Con‐

specifics Light

Dredging

Entrainment

Boat traffic

Harvest

Human

Activity

Non‐Human

Predation

Reservoir

operations

Channel

engineering

Non‐native

fishes

Native fishes

Other than

fishes

Diversion

operations

Management attributes

Figure 2. Symbols and labels used in submodels of the Acipenser 

medirostris conceptual model (modified from Wildhaber et al. 2007). 
41

. 

Figure 3. Green sturgeon life history biology diagram from Beamesderfer et al (2007) 
42

. 

Figure 4. Green sturgeon habitats and distribution from Beamesderfer et al. (2007) 
43

Figure 5. Life history ecology diagram. Spawning green sturgeon adults (SpA) enter 

the river in the spring to spawn and outmigrate as post-spawners (PoA). Eggs (E) are 

broadcast spawned and mature into larvae (L), enter the estuary at juveniles (J), then 

migrate into coastal ocean habitats as subadults (Sub). Black line represents 2006 daily 

average flow at Vernalis (waterdata.usgs.gov). Temperature data are 2006 data from 

Bend Bridge, GCID, Bethel Island, Port Chicago, and Martinez (cdec.water.gov). 
44

Figure 6. Submodel for the transition from spawning adult with viable gametes to 

developing embryo stage in the Acipenser medirostris life history conceptual model. 
45

Figure 7. Submodel for the transition from developing embryo to larval stage of 

exogenous feeding in the Acipenser medirostris life history conceptual model. 
46

Figure 8. Submodel for the transition from larval stage of exogenous feeding to 

juvenile stage in the Acipenser medirostris life history conceptual model. 
47

Figure 9. Submodel for the transition from juvenile stage to coastal migrant in the 

Acipenser medirostris life history conceptual model. 
48

Figure 10. Submodel for the transition from coastal migrant to spawning adult 

with viable gametes in the Acipenser medirostris life history conceptual model. 
49

Figure 11. Submodel for the transition from spawning adult with viable gametes to Mature 

Adult stage in the Acipenser medirostris life history conceptual model.