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Current location: Home > Biological Effects Model > 1° Driver: Susceptibility > 2° Driver: Activity of Fish While in the DWSC |
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Secondary Driver: Activity of Fish While in the Jump down this page to: Steelhead | Chinook Salmon | Delta Smelt | Longfin Smelt | Sacramento Splittail | White Sturgeon | Green Sturgeon | Striped Bass Different species and life stages of fish differ in their tolerance of low DO concentrations, depending on the natural range of DO concentrations the fish species typically encounter in their preferred habitats (Rombaugh 1988; Cech et al. 1990). Species and life stage tolerances reflect adaptations to different environments and differences in metabolic requirements, activity levels, size, and morphology. The early life stages of fish (embryos and larvae) are often more sensitive to low DO concentrations than older life stages (juveniles and adults) of the same species because of their limited ability to detect and avoid low DO concentrations and, in some cases, their higher oxygen requirements. Fish species in the DWSC are migrating to and from spawning grounds. Adult fish are migrating upstream to spawning grounds, and juvenile fish are returning to the ocean (Chinook salmon and steelhead) or to a more suitable rearing area in the Delta (delta smelt, striped bass, and Sacramento splittail). The DWSC is not known to provide spawning or rearing areas for any of the fish species discussed. Migration involves swimming upstream or downstream against or with a current. Physical activity levels are strongly correlated with oxygen requirements. Swimming, the principal physical activity of most fishes, requires substantial amounts of oxygen. The relationship between swimming speed and oxygen consumption depends on a variety of factors (e.g., species’ morphology) but is typically exponential (e.g., Facey and Grossman 1990). Most fishes can endure periods of oxygen demand in excess of oxygen supply (anaerobic respiration; e.g., for burst swimming) but these periods of “oxygen debt” are generally short in duration. For migrating adult fish preparing to spawn, low DO concentrations can contribute to poor spawning success by disrupting spawning activities and limiting the amount of energy available for the production of viable eggs and larvae. The physiological stress and energy demands resulting from exposure of adults to high water temperatures and low oxygen levels can reach levels that affect the amount of energy available for the production of viable eggs and larvae. For example, the exposure of adults to physiologically stressful conditions during egg development can lead to poor egg quality (smaller eggs or eggs containing smaller stores of energy for developing larvae), which is linked to reduced hatching success and larval survival (Coutant 1987). Juvenile fish migrating downstream may experience a reduction in growth. The magnitude of growth effects depends on the severity and duration of exposure to low DO concentrations. Prolonged or repeated exposure to low DO concentrations in laboratory experiments has been shown to reduce growth or developmental rates of fish (Magnusson et al. 1998). Low DO concentrations can reduce the amount of energy available for growth, reducing food conversion efficiency and decreasing food consumption through reductions in activity and loss of appetite (Breitburg 2000; Kramer 1987; Brett 1979; Doudoroff and Shumway 1970). Reduced growth rates of juvenile fishes occur at approximately 2.2 times the oxygen concentration associated with 50% mortality during 24-hour and 96-hour exposures (Breitburg 2000). Jump to "General Effects" discussion under other Secondary Drivers: Steelhead (Oncorhynchus mykiss) Hypothesis: Low DO concentrations can adversely affect the activity levels of steelhead in the DWSC (migrating, feeding) and lead to adverse effects on survival, growth, or reproduction. 1. How does this driver operate? Migrating adults are susceptible to the adverse effects of low DO because of the high metabolic requirements associated with swimming and gonad development, and potential migration delays associated with behavioral avoidance. Juvenile steelhead are susceptible to the adverse effects of low DO concentrations because of the high metabolic requirements of swimming, foraging, and smolt development during their downstream migration to the ocean. 2. Are there critical thresholds associated with this driver? No studies have been conducted to investigate the effects of low DO concentrations on gonad development or migration of adult steelhead. Several studies have demonstrated a reduction in growth rates of juvenile rainbow trout when subjected to DO concentrations below 7 mg/L. JRB Associates (1984 in Karna 2003) found that the median growth rates of rainbow trout were reduced by 25%, 14%, and 7%, respectively, at DO concentrations of 4, 5, and 6 mg/L. 3. How important is this driver? Both adult and juvenile trout are susceptible to the adverse effects of low DO concentrations, but the population effects are unknown. This driver could be important, depending on the timing of adult and juvenile steelhead migration. However, most migration occurs during late fall through spring when DO concentrations are more favorable in the DWSC than in the late summer and early fall. 4. How well is this driver understood? The effects of low DO concentrations on gonad development and migration of adult steelhead or rainbow trout have not been studied. For juvenile fish, some studies have demonstrated reduced growth under hypoxic conditions in the laboratory. However, it is uncertain how these concentrations would affect wild fish. In their natural environment, juveniles may exhibit variable growth responses to low DO depending on their condition, duration of exposure to low DO concentrations, and response to other environmental factors. Jump to "Steelhead" discussion under other Secondary Drivers: Chinook Salmon (Oncorhynchus tshawytscha) Hypothesis: Low DO concentrations can adversely affect the activity levels of adult and juvenile Chinook salmon in the DWSC because of the high metabolic demands of migration, development, and growth. 1. How does this driver operate? Migrating adults are susceptible to the adverse effects of low DO concentrations because of the high metabolic requirements and associated oxygen demands of swimming and gonad development during their upstream spawning migrations. Juveniles are susceptible because of the high metabolic requirements of swimming, foraging, and growth during their downstream migration to the ocean. 2. Are there critical thresholds associated with this driver? Migrating Chinook salmon exhibited a delay in migration when water temperatures were greater than 19°C and DO concentrations were less than 5 mg/L in the lower San Joaquin River (Hallock et al. 1970). This likely reflects a behavioral response to low DO concentrations rather than the metabolic effects of low DO concentrations on activity levels. However, an avoidance response suggests that exposure to low DO concentrations encountered in the DWSC can lead to direct effects on spawning success depending on the duration of exposure. In addition, prolonged delays in migration could indirectly affect spawning success by increasing energy expenditures and reducing the amount of energy available for gonad development and spawning. Several studies on juvenile Chinook salmon have demonstrated a reduction in growth rates when DO concentrations dropped below 5 mg/L. Growth rates were reduced 47%, 29%, and 16% at DO concentrations of 3, 4, and 5 mg/L, respectively, and a mean temperature of 15°C (JRB Associates 1984 in Karna 2003). 3. How important is this driver? The effect of low DO concentrations on activity levels may be important because of the potential for relatively large numbers of adult Chinook salmon to encounter low DO concentrations in the DWSC during their upstream migration through the Delta. Avoidance suggests that these concentrations can lead to adverse effects on spawning success depending on the duration of exposure. The potential for reduced growth or other adverse effects on juveniles is low because most migration occurs during the late winter and spring when conditions in the DWSC are more favorable. 4. How well is this driver understood? Few studies have investigated the effect of low DO concentrations on activity of adult and juvenile Chinook salmon. Thresholds for growth effects on juvenile salmon have been identified under controlled conditions in the laboratory and generally occur when DO concentrations are below 5 mg/L (JRB Associates 1984 in Karna 2003). These thresholds serve as general guidelines for evaluating the effects of low DO concentrations on adults and juveniles in their natural environment. Jump to "Chinook Salmon" discussion under other Secondary Drivers: Delta Smelt (Hypomesus transpacificus) Hypothesis: Delta smelt activity levels are higher than normal during periods when they are found in the DWSC, which causes a higher oxygen demand to maintain their metabolic rate. 1. How does this driver operate? The metabolic rate of delta smelt is probably high during the periods when they occur in the DWSC (during migration to and from spawning grounds).
2. Are there critical thresholds associated with this driver? There are important activity level thresholds that determine the oxygen demand of delta smelt in the DWSC, but the oxygen requirements of delta smelt under different activity levels have not been studied. 3. How important is this driver? The importance of delta smelt activity levels in the DWSC to their susceptibility to low DO concentrations is not known. 4. How well is this driver understood? The DO requirements of delta smelt have not been studied directly. The effects of different levels of activity on these DO requirements have not been studied. Jump to "Delta Smelt" discussion under other Secondary Drivers: Longfin Smelt (Spirinchus thaleichthys) Hypothesis: During periods when longfin smelt are found in the DWSC, their activity levels demand more oxygen than that required to maintain their standard metabolic rate. 1. How does this driver operate? Longfin smelt found in the DWSC probably are migrating upstream to spawn or downstream immediately after hatching. During upstream migrations, these fish are developing their gonads in preparation for reproduction. Swimming upstream and developing gonads require significant metabolic activity, and thus these activities are expected to increase oxygen demand. Juvenile fish migrating downstream from the spawning grounds would be in an early stage of development. Growth and development require significant metabolic inputs (and increase oxygen demand). 2. Are there critical thresholds associated with this driver? There are important activity-level thresholds that determine the oxygen demand of longfin smelt found in the DWSC, but the oxygen requirements of these fish under different activity levels have not been studied. 3. How important is this driver? The importance of longfin smelt activity levels in the DWSC to their susceptibility to adverse effects from low DO concentrations is not known. 4. How well is this driver understood? The DO requirements of longfin smelt have been not been studied under controlled laboratory conditions. The effect of different levels of activity on these DO requirements have not been studied; however, any activity (e.g., development of gonads, swimming against a current, larval development of internal organs) in addition to those performed by fish in the laboratory would be expected to increase demand for DO. Jump to "Longfin Smelt" discussion under other Secondary Drivers: Sacramento Splittail (Pogonichthys macrolepidotus) Hypothesis: Sacramento splittail activity levels during periods when they are found in the DWSC create an oxygen demand higher than is required to maintain their standard metabolic rate. 1. How does this driver operate? Sacramento splittail would be most likely to occur in the DWSC during their migrations to and from the spawning grounds. Sacramento splittail gonads develop during their upstream migration. Swimming upstream and developing gonads require significant metabolic activity and are therefore expected to increase oxygen demand. Juvenile fish migrating downstream from the spawning grounds are growing and developing, foraging, and swimming (in general) with the current. Growth and development require significant metabolic inputs (and increase oxygen demand), whereas swimming with the current and benthic foraging require less oxygen than other activities (Gisbert et al. 2001 in Cech and Doroshov 2004). 2. Are there critical thresholds associated with this driver? There are important activity level thresholds that determine the oxygen demand of Sacramento splittail found in the DWSC, but the oxygen requirements of these fish under various activity levels have not been studied. 3. How important is this driver? The importance of Sacramento splittail activity levels to their susceptibility to low DO concentrations in the DWSC is not known. 4. How well is this driver understood? The effects of different concentrations and kinds of activity on the DO requirements of Sacramento splittail have been not been studied under controlled, laboratory conditions. Any activity (e.g., development of gonads, swimming against a current, larval development of internal organs) in addition to those performed by fish in the laboratory would be expected to increase their demand for DO. Jump to "Sacramento Splittail" discussion under other Secondary Drivers: White Sturgeon (Acipenser transmontanus) Hypothesis: White sturgeon activity levels during periods when they are found in the DWSC create an oxygen demand higher than that required to maintain their standard metabolic rate. 1. How does this driver operate? Adult white sturgeon found in the DWSC are probably migrating upstream to spawn; larval, juvenile, or subadult sturgeon in this area could be migrating to rearing areas in the lower Delta or estuary or (less likely) foraging after migration in the slow-moving waters of the eastern Delta. During upstream migrations, these fish may be developing their gonads in preparation for reproduction. Swimming upstream and developing gonads require significant metabolic activity, and thus these activities are expected to increase oxygen demand. Juvenile fish migrating downstream from the spawning grounds would be in an early stage of development. White sturgeon grow very quickly in their early (freshwater) life stages (Moyle 2002) and, presumably, this early rapid growth is important to their survival in later life stages. Growth and development require significant metabolic inputs (and increase oxygen demand), and low DO concentrations are known to significantly reduce white sturgeon growth rates over exposure periods of approximately 10 days (Cech et al. 1984; Cech and Crocker 2002). 2. Are there critical thresholds associated with this driver? There are important activity level thresholds that determine the oxygen demand of white sturgeon found in the DWSC, but the oxygen requirements of these fish under various activity levels have not been studied. 3. How important is this driver? The importance of low DO as a driver of white sturgeon activity levels and associated adverse effects is not known. 4. How well is this driver understood? The DO requirements of white sturgeon have been well studied under controlled laboratory conditions (Cech et al. 1984; Cech and Doroshov 2004). The effect of different levels of activity on these DO requirements has not been studied; however, any activity (e.g., development of gonads, swimming, larval development) in addition to those performed by fish in the laboratory would be expected to increase demand for DO. Jump to "White Sturgeon" discussion under other Secondary Drivers: Green Sturgeon (Acipenser medirostris) Although little species-specific information is available for green sturgeon, it is likely that information for white sturgeon is generally applicable to green sturgeon. Jump to "Green Sturgeon" discussion under other Secondary Drivers: Striped Bass (Morone saxatilis) Hypothesis: While in the DWSC, striped bass have elevated activity levels, which cause an increased oxygen demand to maintain their metabolic rate. 1. How does this driver operate? The metabolic rate of striped bass is likely elevated during the times when they occur in the DWSC (i.e., during migrations to and from their spawning grounds) for two reasons.
2. Are there critical thresholds associated with this driver? The specific DO requirements of eggs, larvae, and migrating striped bass would likely fall into the optimal habitat criteria range above 5 mg/L, based on the literature referenced above. DO concentrations below this threshold may cause negative impacts, especially when combined with the increased metabolic demands of migration and early development. Based on the findings of Breitburg (2002) and Kramer (1987), the EPA reported that negative effects on juvenile striped bass feeding and growth occur at DO concentrations below 4 mg/L (U.S. Environmental Protection Agency 2003). 3. How important is this driver? The importance of striped bass activity levels in the DWSC in determining their sensitivity to low DO concentrations is unknown. In general, adult striped bass are likely to migrate through the DWSC during spring, when DO concentrations are suitable to sustain the increased metabolism associated with migration. Juvenile striped bass, however, may be exposed to DO concentrations near or below 5 mg/L for significant periods while they move through the DWSC in the summer and early fall. 4. How well is this driver understood? Based on an extensive literature review and research, the EPA established 5 mg/L as a minimum criterion for Chesapeake Bay to protect early life stages of striped bass (U.S. Environmental Protection Agency 2003). Jump to "Striped Bass" discussion under other Secondary Drivers: |