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Adverse Effect: Reduced Swimming Performance Jump down this page to: Steelhead | Chinook Salmon | Delta Smelt | Longfin Smelt | Sacramento Splittail | White Sturgeon | Green Sturgeon | Striped Bass All fishes have an incipient limiting threshold for DO, below which they experience a decline in the ability to perform certain activities and functions, such as swimming. When low DO concentrations limit the swimming performance of fish, they also limit their ability to feed, avoid predators, and negotiate swift currents. Laboratory studies of a number of species have demonstrated the presence of a threshold oxygen concentration below which maximum cruising or sustained swimming speeds are reduced. This threshold generally coincides with the oxygen concentration that begins to limit the rate of oxygen uptake (incipient limiting level). The effect of DO concentrations on burst swimming speeds has not been measured. Although burst speeds are achieved largely through anaerobic metabolism, low ambient concentrations of DO may lead to fatigue and restrict the frequency of repeated swimming bursts needed to capture prey or escape predators (Kramer 1987; Beamish 1978). Jump to "General Effects" discussion under other adverse effects: Steelhead (Oncorhynchus mykiss) Hypothesis: Steelhead exposed to DO concentrations below the regulatory minimum exhibit reduced swimming performance. 1. What is the mechanism causing this adverse effect? Increased swimming speeds require more oxygen to meet the metabolic demands of exercising aerobic (red) muscle cells (Moyle and Cech 2000). If DO concentrations are not sufficient to sustain the increased metabolic demands of rapid swimming, maximum swimming velocity is reduced (Fry 1971). Fish exhibit sustained, prolonged, and burst swimming speeds depending on the swimming demands for a particular activity (Beamish 1978).
Many studies have examined the relationship between DO concentrations and sustained swimming performance. In salmonids, swimming performance is depressed at 6.5–7.0 mg/L over a wide range of temperatures (Davis et al. 1963 in Hicks 2000). 2. Are there critical thresholds associated with this adverse effect? Reductions in swimming performance of juvenile steelhead have been observed at DO concentrations of 9 mg/L and lower (Davis 1975 in Hicks 2000), as shown in the table below.
3. How important is this mechanism? The potential for population-level effects associated with reduced swimming speed increases with severity and duration of exposure to low DO concentrations and the number of fish exposed to such conditions. Compared to resident fish, migratory fish such as steelhead are less likely to experience significant population-level effects because of their limited exposure to low DO concentrations in the DWSC. 4. How well is this mechanism understood? A decrease in swimming performance (i.e., speed) can affect a fish’s ability to capture prey, avoid predators, and migrate upstream against heavy currents. While the negative effects of low DO concentrations have been demonstrated under laboratory conditions, application to wild fish is problematic because of the complex linkages of swimming performance and other mechanisms to growth, survival, and reproductive success. Jump to "Steelhead" discussion under other adverse effects: Chinook Salmon (Oncorhynchus tshawytscha) Hypothesis: Chinook salmon exposed to DO concentrations below the regulatory minimum exhibit reduced swimming performance. 1. What is the mechanism causing this adverse effect? Fish exhibit sustained, prolonged, and burst swimming speeds, depending on the swimming demands for a particular activity (Beamish 1978).
Most studies have examined the relationship between DO concentrations and sustained swimming performance. In salmonids, swimming performance is depressed at 6.5–7.0 mg/L over a wide range of temperatures (Davis et al. 1963 in Hicks 2000). 2. Are there critical thresholds associated with this adverse effect? Chinook salmon juveniles tested at DO concentrations from 7 mg/L to 3 mg/L exhibited reductions in swimming speeds from 10% to 38%, respectively (Davis et al. 1963 in Hicks 2000). 3. How important is this mechanism? The potential for population-level effects associated with reduced swimming speed increases with severity and duration of exposure to low DO concentrations and increases in the number of fish exposed to such conditions. Compared to resident fish, migratory fish such as Chinook salmon are less likely to experience significant population-level effects because of their limited exposure to low DO in the DWSC. Adults are able to move away from low DO concentrations into more favorable areas such as the Sacramento and Mokelumne Rivers. Juvenile fish typically migrate downstream when DO conditions are more favorable. 4. How well is this mechanism understood? A decrease in swimming performance (i.e., speed) can affect a fish’s ability to capture prey, avoid predators, and migrate upstream against heavy currents. The critical thresholds are defined through laboratory research, and application to wild fish is problematic because of the complex relationships between swimming performance and biological performance (growth, survival, and reproductive success). Jump to "Chinook Salmon" discussion under other adverse effects: Delta Smelt (Hypomesus transpacificus) Hypothesis: On average, delta smelt exposed to DO concentrations below the regulatory minimumexperience reduced swimming performance. 1. What is the mechanism causing this adverse effect? No studies on the effect of low DO concentrations (below the regulatory minimum) on swimming performance have been published, but it is likely that low DO concentrations impair the swimming performance of delta smelt. Swanson et al. (1998) studied delta smelt swimming ability under lab conditions and found that, at best, delta smelt are moderately good swimmers for their size and that individuals vary greatly in their swimming performance. Swimming performance most likely would be reduced under DO concentrations less than those found in the laboratory. 2. Are there critical thresholds associated with this adverse effect? The incipient limiting threshold for delta smelt has not been determined. 3. How important is this mechanism? The extent and importance of impaired swimming ability of delta smelt as a result of exposure to low DO concentrations are not known. 4. How well is this mechanism understood? The mechanism causing this adverse effect is not well understood because no studies on the effect of low DO concentrations on delta smelt swimming ability have been published. Jump to "Delta Smelt" discussion under other adverse effects: Longfin Smelt (Spirinchus thaleichthys) Hypothesis: Longfin smelt exposed to DO concentrations below the regulatory minimum experience reduced swimming performance. 1. What is the mechanism causing this adverse effect? No studies on longfin smelt swimming performance or the effect of low DO on swimming performance have been published. 2. Are there critical thresholds associated with this adverse effect? The incipient limiting threshold for longfin smelt has not been determined. 3. How important is this mechanism? The extent and importance of impaired swimming ability of longfin smelt attributable to exposure to low DO concentrations are not known. 4. How well is this mechanism understood? No studies on the effect of low DO on longfin smelt swimming ability have been published. Jump to "Longfin Smelt" discussion under other adverse effects: Sacramento Splittail (Pogonichthys macrolepidotus) Hypothesis: Sacramento splittail exposed to DO concentrations near the regulatory minimum do not experience reduced swimming performance. 1. What is the mechanism causing this adverse effect? Young and Cech (1996) displayed critical swimming velocities between approximately 20 cm/s (for small fish) and 65 cm/s (for large fish). No studies of the effect of DO on swimming performance have been published. However, given their tolerance for extremely low DO concentrations, it is likely that Sacramento splittail do not display negative effects of exposure to low DO concentrations until they are well below 5 mg/L. 2. Are there critical thresholds associated with this adverse effect? The incipient limiting threshold for Sacramento splittail has not been determined; however, given that their incipient lethal threshold is so low, it is likely that their incipient lethal threshold is well below the regulatory minimum. However, DO concentrations in the DWSC periodically drop well below the regulatory minimum, and at those times, Sacramento splittail could experience adverse effects. 3. How important is this mechanism? The extent and importance of impaired swimming ability of Sacramento splittail as a result of exposure to low DO concentrations are not known. 4. How well is this mechanism understood? No studies on the effect of low DO concentrations on Sacramento splittail swimming ability have been published. Jump to "Sacramento Splittail" discussion under other adverse effects: White Sturgeon (Acipenser transmontanus) Hypothesis: White sturgeon exposed to DO concentrations below the regulatory minimum experience reduced swimming performance. 1. What is the mechanism causing this adverse effect? White sturgeon reduce swimming activity under hypoxic conditions (58% saturation [4.7–5.7 mg/L]) (Cech et al. 1984). Studies of other sturgeon species have not revealed a similar decrease in activity (Cech and Doroshov 2004). Reduced swimming activity attributable to low DO concentrations in the DWSC could impair the upstream migration of adults preparing to spawn in the San Joaquin River or its tributaries. Reduced swimming activity also could prevent or delay outmigrating juvenile sturgeon from accessing areas of the Delta with higher oxygen and food concentrations than those found in the DWSC. Delayed juvenile migration through the DWSC also would extend the period of exposure to low DO concentrations and compound the effects of that exposure (e.g., reduced growth rate and exposure to predators). 2. Are there critical thresholds associated with this adverse effect? The incipient limiting threshold for white sturgeon has not been determined, but it is apparently above 58% saturation (4.7–5.7 mg/L), the level at which Cech et al. (1984) found significant declines in swimming activity among white sturgeon. 3. How important is this mechanism? The extent and importance of impaired swimming ability of white sturgeon attributable to exposure to low DO concentrations are not known. 4. How well is this mechanism understood? Whereas Cech et al. (1984) documented reduced swimming activity (voluntary) during exposure to low DO, there have been no studies on the swimming ability of white sturgeon under low DO concentrations. The tendency to reduce swimming and other behaviors suggests that white sturgeon reduce their oxygen demands when exposed to low DO concentrations by minimizing their nonessential behaviors. Jump to "White Sturgeon" discussion under other adverse effects: 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 adverse effects: Striped Bass (Morone saxatilis) Hypothesis: Striped bass exposed to DO concentrations below the regulatory minimum exhibit reduced swimming performance. 1. What is the mechanism causing this adverse effect? Oxygen is required to maintain all aerobic metabolic processes, which are the dominant energetic pathways in fishes. Increased swimming speeds require more oxygen to meet the metabolic demands of exercising aerobic (red) muscle cells (Moyle and Cech 2000). If DO concentrations are not sufficient to sustain the increased metabolic demands of rapid swimming, maximum swimming velocity is reduced (Fry 1971). 2. Are there critical thresholds associated with this adverse effect? Most fish exhibit a threshold DO concentration below which swimming performance is reduced (Beamish 1978). At this time, the critical swimming velocities of striped bass in relation to DO concentrations are unknown. 3. How important is this mechanism?
The importance of this mechanism is unknown but would depend on the numbers of striped bass that are exposed to limiting levels, the duration of exposure, and the ultimate effects of reduced swimming performance on survival and recruitment. 4. How well is this mechanism understood? The general effects of reduced oxygen availability on swimming performance are well understood (Fry 1971, Beamish 1978). Specific critical swimming velocities are also well documented for many species (Beamish 1978), but a value specific to adult striped bass is unknown currently. Jump to "Striped Bass" discussion under other adverse effects: |
DO concentrations in the DWSC may reach levels that adversely affect the swimming performance of striped bass. Given current understanding of DO dynamics in the DWSC (see figure at right) and the fact that most striped bass spawn below the DWSC, this adverse effect may have little impact on overall striped bass populations. Until more information is known about spawning habitat use above the DWSC and the timing and abundance of juveniles and adults in the DWSC, the potential impact of reduced swimming performance on striped bass populations will remain uncertain.