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 Knights 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).