Snake River White Sturgeon Conservation Plan ... - Idaho Power

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Status and Habitat Use of Snake River White SturgeonIdaho Power Companyexists for passing sturgeon upstream over the height and distance required by conditions in ourstudy reach.2. BEHAVIORAL CHARACTERISTICS OF STURGEON2.1. DistributionWhite sturgeon inhabit the Snake River from its confluence with the Columbia River upstream toShoshone Falls, a historical natural barrier. White sturgeon also inhabit two tributaries of theSnake River—the Salmon and Clearwater rivers (Cochnauer et al. 1985). The species has onlylimited access to its historical habitat because of the development of the hydroelectric system onthe Snake River. The Snake River in Idaho offers a contrast in population status between riversegments with viable, reproducing populations to others with few individuals and no detectablerecruitment. For example, the river segments downstream of both Hells Canyon and Bliss damscontain sizeable populations and show signs of recent reproduction. However, middle sections ofthe Snake River between Swan Falls and Hells Canyon dams, as well as sections upstream ofBliss Dam, contain only small populations and show little or no detectable recruitment (Lukens1981; Cochnauer et al. 1985; Lepla and Chandler 1995a, 1997; Jager et al. 2001; Lepla et al.2001). Many factors contributed to the current status of white sturgeon in the Snake River. Thesefactors include altered habitat, pollution, historical exploitation, and dams. Table 1 representswhat is currently known about the population sizes of resident sturgeon in the reach betweenLower Granite Dam and Shoshone Falls.2.2. Sexual MaturityThe size and age at first maturity for white sturgeon is extremely variable. Male sturgeon in thewild begin to mature around 125 cm as 12 year-olds, while females normally require longerperiods, generally 15 to 32 years (PSMFC 1992). Reproductive periodicities also vary betweensexes; males may reproduce every 2 to 4 years, while females may reproduce at no less than fiveyear intervals (Conte et al. 1988, Chapman et al. 1996, Anders et al. In Press). Spawnperiodicities for white sturgeon may also range up to 11 years (Semakula and Larkin 1968,Simpson and Wallace 1982, Cochnauer 1983). In domestic broodstock, initial egg developmentrequires 2 to 5 years (Binkowski and Doroshov 1985, Conte et al. 1988). Females maycommonly carry 0.1 to 7 million mature eggs depending on fish size and age (Bajkov 1949,Scott and Crossman 1973, Stockley 1981). In general, only a small portion (about 10%) of whitesturgeon populations are reproductive in any given year (S. Doroshov, University of California,Davis, pers. comm. to Apperson and Anders 1990).2.3. SpawningWhite sturgeon are iteroparous, broadcast spawners that depend on free-flowing rivers forsuitable spawning conditions. Spawners broadcast gametes into the water column wherePage 4Hells Canyon Complex
Idaho Power CompanyChapter 4: Conceptual Design for White Sturgeon Passage Facilitiesfertilization occurs before the demersal, adhesive embryos settle to the substrate (Paragamianet al. 2001 and references within). White sturgeon spawn in extremely fast-flowing water, withvelocities exceeding 1.8 m/s considered the most suitable (Parsley et al. 1993, Parsley andBeckman 1994). Researchers have proposed a number of benefits from spawning in fast,turbulent waters. For example, high-velocity flows remove fine sediments from spawning areas,sediments that might otherwise suffocate eggs (Parsley et al. 1993). Also, broadcasting eggs infast, turbulent water may enhance egg viability by dispersing adhesive eggs, thereby preventingclumping and disease. Dispersal probably also reduces egg and larval predation and minimizescompetition among post-larval fish (McCabe and Tracy 1994). In the Snake River, spawnersfitted with radio transmitters (telemetered fish) were commonly associated with turbulent pools,high-velocity runs, and nearby rapids where eggs were collected (Lepla and Chandler 2001).These telemetered fish used a wide range of depths (2–21 m). Upper velocities approached2.72 m/s in some locations (Lepla and Chandler 2001).White sturgeon spawning in the Columbia River Basin occurs during spring months (April–July)when water temperatures are between 10 and 18 °C (Parsley et al. 1993, RL & L EnvironmentalServices 1994), with the peak in spawning occurring when temperatures are typically between13 and 15 °C. Generally, the Snake River reaches have suitable spawning temperatures(10−18 °C) from March through late June, depending on annual spring conditions and thelocation of the reach. Similar to the Columbia River observations, Lepla and Chandler (2001)reported that most spawning in the Snake River occurred when the water temperatures rangedfrom 12 to 16 °C, with mean temperature of 14 °C, which is considered optimal for eggincubation (Wang et al. 1985). The temperature regimes in the Snake River and the temperaturesof the water in which the majority of eggs were collected (12–16 °C) suggest that peak spawningactivity occurs from mid-March to the end of May in the reaches above the HCC and from lateApril to mid-June in the reaches below the HCC (Lepla and Chandler 2001).2.4. IncubationWang et al. (1985) indicated that a water temperature of 14 °C is optimal for egg incubation, eggmortality increases in temperatures of 18 to 20 °C, and water temperatures beyond 20 °C clearlybecome lethal. Although research has not yet established this conclusion, the lower limit atwhich temperatures become lethal to incubating white sturgeon eggs may be similar to the lowerlimit for other sturgeon species, which is near 6 to 8 °C (Wang et al. 1985). Egg incubationusually lasts 7 to 14 days, depending on water temperature (Bajkov 1949, Wang et al. 1985,Conte et al. 1988). Eggs of white sturgeon are vulnerable to predation because adults broadcastthe eggs and provide no parental protection. Research indicates that several species of fish preyon sturgeon eggs, including northern pike minnow, common carp, largescale sucker, and pricklysculpin (Carl 1936, Patton and Rodman 1969, Scott and Crossman 1973, Wydoski and Whitney1979, Kempinger 1988, Miller and Beckman 1993).Embryonic development of white sturgeon eggs collected in the Snake River indicated that mostspawning activity occurred within a temperature range of 12 to 16 °C (mean = 14 °C), which isconsidered to be optimal for egg development. Incubating eggs were commonly associated withturbulent pools and runs with mean column velocities ranging from 0.1 to 2.0 m/s and depths of4 to 19 m. Based on temperature regimes in the Snake River and the timing of most eggHells Canyon Complex Page 5
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