Acipenser transmontanus

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General Information
Common Name: 
White sturgeon
FID: 
AAT01
Status: 

Conservation Status in California: Class 2, Vulnerable (Moyle et al. 2011). The annual recruitment and reproductive success of white sturgeon in California appears to have dropped in recent years.

Life History: 

Life History: White sturgeon primarily live in the estuaries of large rivers but migrate to spawn in fresh water and are capable of long ocean movements between river systems. White sturgeon commonly aggregate in deep, soft-bottomed brackish estuarine habitats, where they move in response to changes in salinity (Kohlhorst et al. 1991). In the lower Columbia River, white sturgeon make seasonal and diel movements (Parsley et al. 2008), moving upstream in the fall and downstream in the spring. They are most active at night when they move into shallower waters to feed. Some individuals express site fidelity by returning to previously occupied sites (Pareley et al. 2008).
In the ocean, some individuals may migrate large distances. White sturgeon tagged in the San Francisco Estuary have been recaptured in the Columbia River estuary (L. Miller 1972 a,b, Kohlhorst et al. 1991). One of these fish was then subsequently recaptured 1,000 km upstream in the Columbia River. Tagged individuals have routinely been detected 1,000 km from the tagging site (Chadwick 1959, Welch et al. 2006). Recently, one white sturgeon tagged in May 2002 in the Klamath River was even tracked to the Fraser River, British Columbia, a distance far greater than 1000 km (Welch et al. 2006). Because this individual spent nearly equal amounts of time in both the Fraser and the Klamath River, it was difficult to determine which was the natal river. However, it is thought that extensive movements are associated with feeding rather than spawning (A. Drauch, UC Davis, pers. comm. 2009).
In estuaries, white sturgeon move into intertidal areas during high tides to feed. Most prey are taken on or near the bottom. Young white sturgeon (~ 20 cm FL) prefer amphipods (Corophium spp.) and opossum shrimp (Neomysis mercedis) (Radtke 1966, Muir et al. 1988, McCabe et al. 1993). The diet becomes more varied as they grow but continues to be dominated by benthic invertebrates such as shrimp, crabs, and clams. Today, most benthic invertebrate prey species in the San Francisco Estuary are nonnative, demonstrating the opportunistic feeding nature of white sturgeon (Moyle 2002). One heavily used prey is the overbite clam, Corbula amurensis, which became very abundant after its invasion into Suisun Bay in the 1980s. However, foraging on the overbite clam may inhibit growth, because at least clams pass through the gastrointestinal tract without being digested, possibly decreasing nutritional intake (Kogut 2008). Fish, especially herring, anchovy, striped bass, starry flounder and smelt, are taken by larger sturgeon. In the San Francisco estuary white sturgeon may feast on Pacific herring eggs (McKechnie and Fenner 1971), much as their Columbia River counterparts do on eulachon eggs (McCabe et al. 1993). In California, the stomach contents of large individuals have also included onions, wheat, Pacific lamprey, crayfish, frogs, salmon, trout, striped bass, carp, pikeminnow, suckers and, in one instance, a cat (Carlander 1969).
In the San Francisco Estuary, young sturgeon reach 18-30 cm by the end of their first year (Kohlhorst et al. 1991). Juvenile white sturgeon also grow rapidly in captivity on artificial diets, consuming 1.5 to 2% of their body weight each day at 18?C (Hung et al. 1989). As they age, growth rates slow so that they reach 102 cm TL by their seventh or eight year. They may ultimately reach 6 m FL. The largest white sturgeon on record weighed 630 kg and was likely more than 100 years old (C. Swift, pers. comm. 1999). Fish of this size were probably the largest freshwater fish in North America (Moyle 2002). The largest white sturgeon in recent years, caught in Oregon, measured 3.2 m FL and was 82 years old (Carlander 1969). In California, the largest white sturgeon on record was from Shasta Reservoir in 1963; it was 2.9 m TL, 225 kg, and at least 67 years old (T. Healy, CDFG, pers. comm. 2001). Today in California, white sturgeon larger than 2 m and older than 27 years are uncommon (Kohlhorst et al. 1980).
Male white sturgeon mature at age 10-12 years (75-105 cm FL), while females mature later at about 12-16 years old (95-135 cm FL) (Kohlhorst et al. 1991, Chapman et al. 1996). However, males mature at age 3-4 years and females at 5 years while in captivity (Wang 1986). Photoperiod and temperature regulate maturation in adult white sturgeon (Doroshov et al. 1997). Prior to spawning adults may move into the lower reaches of rivers during the winter months but later migrate upstream into spawning areas in response to increases in flow (Schaffter 1997 a, b). Spawning initiates in response to high flows from late February to early June (McCabe and Tracy 1994). Only a small percentage of adults will spawn in any given year. In the Columbia River, males spawn every 1-2 years while females spawn every 3-5 years (McCabe and Tracy 1994).
Spawning in the Sacramento River occurs primarily between Knight’s Landing (145 rm) and Colusa (231 rm) (Schaffter 1997 a, b). A few adults occasionally spawn in the Feather and San Joaquin Rivers (Kohlhorst 1976, Kohlhorst et al. 1991). The fecundity of females from the Sacramento River averages 5648 eggs/kilogram body weight so that the one female (1.5 m TL) may contain 200,000 eggs (Chapman et al. 1996). White sturgeon most likely spawn in deep water over gravel riffles or in rocky pools with swift currents. Eggs have been collected from the stream bed at depths of 10 m (Wang 1986). In the Columbia River, white sturgeon spawn over cobble and boulder at depths of 3-23 m and velocities of 0.6-2.4 m/sec (McCabe and Tracy 1994). Adults migrate back to the estuary after spawning.
Eggs (3.5-4.0 mm; in Billard and Lecointre 2001) become adhesive upon fertilization allowing them to stick to stream substrates. Time to hatch is dependant on temperature but larvae generally hatch in 4-12 days (Wang 1986). Larvae are 11 mm at hatch and swim vertically while drifting towards the estuary. Larvae swim horizontally and feed from the bottom once the yolk sac is absorbed in about 7-10 days. Sacramento River white sturgeon larvae upon hatching were found to be photonegative, migrating downstream short distances by swimming near the bottom, seeking cover (Kynard and Parker 2005). Larvae aggregated, swam and foraged near the bottom, with an increasing trend to swim above the bottom. Strong dispersal occurred as early juveniles swam actively downstream. Consequently, Sacramento River white sturgeon are described as having a “two-step downstream dispersal” completed by embryos and early juveniles during both day and night but peaking at night. Juvenile sturgeon use habitats in the upstream less saline portions of the estuaries, suggesting that the ability to osmoregulate increases with age and size (McEnroe and Cech 1987). Osmoregulation efficacy may also be size dependent even between individuals of the same age (Amiri et al. 2009). Consequently, size at time of estuarine entry may be a limiting factor of juvenile survival. In the lower Fraser River, most juvenile white sturgeon use sloughs from June to August (Bennett et al. 2005). Occupied sloughs were more than 5 m deep, turbid and had multidirectional currents, soft sediments, and readily available prey (mysid shrimp, dipteran larvae, fish).
In the San Francisco estuary, the white sturgeon population is dominated by a few strong year classes due to the variability of spawning success from one year to the next. Strong year classes result from years when the estuary experiences high spring outflows (Kohlhorst et al. 1991, Schaffter and Kohlhorst 1999). High spring outflows may quickly move larval sturgeon downstream into suitable rearing areas (Stevens and Miller 1970) or induce more sturgeon adults to spawn (Kohlhorst et al. 1991). In the lower Columbia River, year class strength is correlated to the size and availability of prey at the onset of exogenous feeding (Muir et al. 2000). Amphipods (Corophiidae), copepods, and dipteran larvae and pupae are important prey to larval and young-of-the-year sturgeon. Increased predation on larvae, especially by prickly sculpin, due to habitat alterations (reduction in cover, increased light levels) may be another factor limiting recruitment in some areas (Gadomski and Parsley 2005, Gadomski and Parsley 2005b).

Habitat Requirements: 

Habitat Requirements: White sturgeon adults respond to increases in flow to initiate spawning from late February to early June. Spawning takes place at temperatures ranging from 8 to 19?C, peaking in temperatures around 14?C (McCabe and Tracy 1994). Successful incubation requires stream substrates with minimum amounts of sand and silt because siltation of stream sediments may smother embryos. Recruitment failure in the Nechako River, Canada, was attributed to siltation of main channel sediments after large scale (1,000,000 m3) introduction of fine sediments by upstream stream avulsion (McAdam et al. 2005). The recruitment failure was attributed to egg suffocation and increased predation because larvae lacked interstitial spaces in the substrate in which to hide. Newly hatched embryos preferred substrates from 12 to 22 mm in laboratory tests (Bennett et al. 2007).
The first few months of life are considered to be a critical bottleneck for sustaining populations (Coutant 2004). Successful recruitment also appears to be associated with complex habitats, flooded riparian vegetation (floodplain habitat) and rocky substrates (Coutant 2004). Lack of cover provided by complex riparian habitat downstream of spawning areas decreases recruitment, as do low flows from the time of spawning until the time juveniles outmigrate. Productive spawning areas in the Sacramento River are associated with areas where levees are set back, allowing access to floodplains and backwater habitats (e. g., Wilkins and Butte sloughs) during high spring flows.

Distribution: 

Distribution: White sturgeon can be found in salt water from the Gulf of Alaska south to Ensenada, Mexico. However, spawning only occurs in a few large rivers from the Sacramento-San Joaquin system northward. Self-sustaining spawning populations are currently only known in the Fraser (British Columbia), Columbia (Washington), and Sacramento Rivers. Landlocked populations also occur above major dams in the Columbia River (McCabe and Tracy 1994). California sturgeon are caught in small numbers in the Columbia River region and at least one white sturgeon tagged in the Klamath River spent extensive time in the Fraser River (Welch et al. 2006).
In California, white sturgeon spawn primarily in the Sacramento (to Keswick Dam) and Feather Rivers (to Oroville Dam facilities) but adults may spawn also in the San Joaquin River when water quality and flow conditions are favorable (Shaffter 1997a, b). The lower Pit River likely was an important spawning area prior to the construction of Shasta Dam in the 1940s (T. Healey, CDFG, pers. comm. 2001). Shasta Dam trapped young sturgeon behind it, establishing a landlocked population that sustained itself and a small fishery. However, subsequent dams on the Pit River blocked access to spawning areas preventing ongoing reproduction of this population (T. Healey, CDFG, pers. comm. 2001). Long-lived individuals and fish from stocking attempts in the 1980s are still occasionally caught in Shasta Lake. Historically, small runs also occurred in the Russian, Klamath and Trinity Rivers.
Aquaculture facilities now cultivate white sturgeon in California with some young sold in the aquarium trade, perhaps facilitating more introductions. White sturgeon planted in reservoirs in southern California (C. Swift, pers. comm., 1999) and the San Francisco region are occasionally caught by anglers (e. g., a 21 kg individual caught in Lafayette Reservoir, Contra Costa County)

GIS Mapping Interpretation and HUC Anomalies: Several occupied HUC12s in the Sacramento basin intersect Shasta (Churn Creek, HUC12 ID 180201540304) or Lassen (Deer and Salt Creeks HUC12 IDs 180201570206 & 180201560601) National Forests. These intersections are artifacts of HUC shape and do not denote white sturgeon occurrence on these forests.

Abundance Trends: 

Trends in Abundance: As a result of variable year class success, the number of adults in the San Francisco estuary varies from year to year. CDFG estimates of adult (> 1 m TL) numbers varied from 11,000 in 1954 to 115,000 in 1967 (Kohlhorst et al. 1991). Adult numbers subsequently decreased to 74,000 in 1979, then increased to 128,000 by 1984, decreased again to 60,000 in 1990, peaked at 144,000 in 1998, and declined to a 50 year low of 10,000 in 2005 (Schaffter and Kohlhorst 1999, CDFG 2006). Fewer than 2,000 female white sturgeon were expected to migrate into the Sacramento-San Joaquin in 2006. Catch of large individuals kept by anglers (CPUE) show a decreasing trend in numbers from 1980 (~ 850) to 2007 (~ 520) in the San Francisco Estuary (M. Gingras, CDFG, pers. comm. 2009). Overall, the limited information on trends in adult and juvenile white sturgeon suggests that white sturgeon abundance is declining.
Trends of year class indices (YCI), based on the number of age 0 and age 1 juveniles, suggest recruitment has decreased significantly, with virtually no recruitment for 12 of the 29 years (1980-2008) of record (Figure 1). Recruitment was very low (combined YCI

Description: 

Description: White sturgeon adults have wide rounded snouts, with four barbels in a row on the underside, closer to the tip of the snout than to the mouth (Moyle 2002). Their mouths are highly protrusible and lack teeth. Their bodies have 5 widely separated rows of bony plates (scutes). Scute counts per row are: 11-14 (dorsal row), 38-48 (two lateral rows) and 9-12 (bottom rows). Four to eight scutes are also found between the pelvic and anal fin. They lack the large scutes behind the dorsal and anal fins found in green sturgeon. However, small remnant scutes (fulcra) may be present. The dorsal fin has one spine followed by 44-48 rays. The anal fin has 28-31 rays. The first gill arch has 34-36 gill rakers. Body coloration is gray brown on the dorsal surface above the lateral scutes, while the ventral surface is white and fins are gray. Their viscera are black. Dispersing juveniles tend to be darker than dispersing free embryos (Kynard and Parker 2005). Juveniles less than one year old can be distinguished from green sturgeon because they have more dorsal fin rays (greater than 42 vs. 35-40), lateral scutes (35 vs. 30 or less) and gill rakers on the first arch (23 or more vs. 15-19). Live mature males and females can be differentiated by the shape of their urogenital opening; a male opening is shaped like a “Y” while a female opening is shaped like an “O” (Vecsei et al. 2003).