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Current location: Home > Biological Effects Model > Adverse Effects > Reduced Spawning Success |
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Adverse Effect: Reduced Spawning Success Jump down this page to: Steelhead | Chinook Salmon | Delta Smelt | Longfin Smelt | Sacramento Splittail | White Sturgeon | Green Sturgeon | Striped Bass 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 DO concentrations 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 larva survival (Coutant 1987). Avoidance behavior or reduced activity levels in response to hypoxia also can influence spawning success by disrupting activities such as courtship, nest building, nest guarding, and parental care (Kramer 1987). Jump to "General Effects" discussion under other adverse effects: Steelhead (Oncorhynchus mykiss) Hypothesis: Low DO concentrations contribute to poor spawning success by disrupting spawning activities and limiting the amount of energy available for the production of viable eggs. 1. What is the mechanism causing this adverse effect? Low DO concentrations can reduce spawning success by limiting the amount of metabolic energy available for migration and gonad development or creating a barrier or impediment to upstream migration. Avoidance of low DO concentrations or prolonged delays in migration could adversely affect spawning success by increasing energy expenditures (depleting reserves available for gonad development and spawning) or increasing the exposure of adults to other stressful conditions (e.g., high water temperatures). 2. Are there critical thresholds associated with this adverse effect? No studies of the effects of low DO concentrations on steelhead spawning success were found. 3. How important is this mechanism? The potential for adverse effects on significant numbers of adult steelhead is low because most adults migrate through the Delta in the late fall to early spring when DO concentrations frequently exceed the regulatory minimum. 4. How well is this mechanism understood? Suitable water temperatures have been reported for adult migration and holding (Exposure to High Water Temperatures), but critical temperature and DO thresholds for egg viability in migrating adults have not been identified. Jump to "Steelhead" discussion under other adverse effects: Chinook Salmon (Oncorhynchus tshawytscha) Hypothesis: Low DO concentrations can contribute to poor spawning success by disrupting migration and limiting the amount of energy available for the production of viable eggs. 1. What is the mechanism causing this adverse effect? Low DO concentrations can reduce spawning success my limiting the amount of metabolic energy available for migration and gonad development or creating a barrier or impediment to upstream migration. Avoidance or prolonged delays in migration could adversely affect spawning success by increasing energy expenditures and reducing the amount of energy available for gonad development and spawning. 2. Are there critical thresholds associated with this adverse effect? Hallock et al. (1970) found evidence that Chinook salmon delayed migration up the San Joaquin River until DO concentrations in the DWSC increased to 5 mg/L. In the Willamette River, a water temperature of 22.4°C and a minimum DO concentration of 3.3 mg/L caused spring-run Chinook salmon to stop migrating (Alabaster 1988 in McCullough 1999). 3. How important is this mechanism? This mechanism may be important because of the potential for overlap in the timing of upstream migration of adult Chinook salmon and the occurrence of low DO concentrations in the DWSC. The ability of adults to access other rivers may permit successful spawning but would reduce the number of adults that spawn in the San Joaquin River system. 4. How well is this mechanism understood? Suitable water temperatures have been reported for adult migration and holding (Exposure to High Water Temperatures) but critical temperature and DO thresholds for egg viability have not been identified. Jump to "Chinook Salmon" discussion under other adverse effects: Delta Smelt (Hypomesus transpacificus) Hypothesis: Delta smelt exposed to DO concentrations below the regulatory minimum have reduced spawning success. 1. What is the mechanism causing this adverse effect? The existence of low DO concentrations in the DWSC may restrict delta smelt migrations to and from spawning habitats in the San Joaquin River (Swanson pers. comm.); this restriction could cause decreased spawning success among delta smelt that encounter low DO concentrations. 2. Are there critical thresholds associated with this adverse effect? Delta smelt may have a threshold of detection for low DO concentrations. Neither the incipient limiting threshold nor a low DO–detection threshold that might impede migrations has been determined for delta smelt. 3. How important is this mechanism? The extent and importance of delta smelt failing to reach spawning territories upstream of the DWSC as a result of low DO concentrations are not known. It is not known how delays (or prevention) of spawning migrations caused by low DO concentrations in the DWSC affect delta smelt populations because we do not know the:
4. How well is this mechanism understood? This adverse effect is not well understood because no studies of the effect of low DO concentrations on delta smelt migration rates or spawning success 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 have reduced spawning success. 1. What is the mechanism causing this adverse effect? The presence of low DO concentrations in the DWSC may prevent or restrict migrating longfin smelt access to spawning habitats in the San Joaquin River; this could decrease spawning success among longfin smelt that encounter low DO concentrations. 2. Are there critical thresholds associated with this adverse effect? Longfin smelt may have a threshold of detection for low DO. Neither the incipient limiting threshold nor a low DO–detection threshold that might impede migrations has been determined for longfin smelt. 3. How important is this mechanism? The impact on individual longfin smelt or on their population of delays (or prevention) of spawning migrations related to low DO concentrations in the DWSC is unknown. This impact is not likely to be large because the number of longfin smelt that use habitats in and above the DWSC for spawning is currently very small. 4. How well is this mechanism understood? No studies of the effect of low DO concentrations on longfin smelt migration rates or spawning success 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 have reduced spawning success. 1. What is the mechanism causing this adverse effect? The existence of low DO concentrations in the DWSC may restrict migrating Sacramento splittail access to spawning habitats in the San Joaquin River; this restriction could decrease spawning success among Sacramento splittail that encounter low DO concentrations. Although, Sacramento splittail are tolerant of low DO concentrations (Young and Cech 1996), these fish may detect and choose to avoid low DO concentrations if they have other available alternatives. No studies on Sacramento splittail detection and avoidance of low DO concentrations have been published. 2. Are there critical thresholds associated with this adverse effect? Sacramento splittail may have a threshold of detection for low DO concentrations. Neither, the incipient limiting threshold nor a low DO–detection threshold that might impede migrations has been determined for this species. 3. How important is this mechanism? The effect on Sacramento splittail population of delays (or prevention) of spawning migrations related to low DO concentrations in the DWSC is unknown. This effect is not likely to be large because Sacramento splittail are not likely to delay spawning migrations until DO concentrations are well below the regulatory minimum. Thus, the occurrence of low-DO events that might cause delayed migrations among Sacramento splittail is probably infrequent. Most fish in the Delta move upstream to spawning grounds at periods of high flow (some are hard-wired to a particular time of year when high flow should occur (e.g., salmon, sturgeon), but others (e.g., splittail) probably wait for the flow. So, when there are no high flows (and DO concentrations are typically lower), no migration occurs. 4. How well is this mechanism understood? No studies on the effect of low DO concentrations on Sacramento splittail migration rates or spawning success 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 have reduced spawning success. 1. What is the mechanism causing this adverse effect? No studies on the effect of low DO concentrations on white sturgeon spawning success have been published. However, their overall sensitivity and behavioral response to low DO concentrations suggest that white sturgeon that encounter low DO concentrations on their spawning migrations may experience delays in reaching their spawning grounds. Delayed spawning migration may cause fish to miss spawning opportunities. Delayed migration also exposes adults to increased risk of mortality prior to spawning. 2. Are there critical thresholds associated with this adverse effect? White sturgeon may have a threshold of detection for low DO. Neither the incipient limiting threshold nor a low DO–detection threshold that might impede migrations has been determined for white sturgeon. 3. How important is this mechanism? The impact on white sturgeon populations of delay (or prevention) of spawning migrations related to low DO concentrations in the DWSC is unknown because also unknown are the:
These fish are long-lived and iteroparous spawners; thus, difficulty reaching spawning grounds in a given year may result in an end to the spawning migration for that year. If individuals forgo spawning in a given year (e.g., because of inaccessibility of spawning habitat caused by low DO concentrations in the DWSC), they have the opportunity to spawn in a future spawning season if they can survive during the intervening nonspawning period. 4. How well is this mechanism understood? No studies of the effect of low DO concentrations on white sturgeon migration rates or spawning success have been published. 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 statutory minimum have reduced spawning success. 1. What is the mechanism causing this adverse effect? Adequate DO concentrations are required to ensure successful migration of adult striped bass to spawning habitats and suitable conditions for spawning, incubation, and juvenile rearing. 2. Are there critical thresholds associated with this adverse effect? Critical thresholds for striped bass spawning success have been studied.
3. How important is this mechanism? This adverse effect may not be important because most striped bass spawning occurs below the DWSC in most years. In addition, conditions in the DWSC during April and May are adequate to support adult striped bass. 4. How well is this mechanism understood? An understanding of the effect of low DO concentrations on striped bass spawning success is limited largely by the lack of data on how much spawning habitat is used in and above the DWSC and to what extent this habitat contributes to the overall striped bass population. Jump to "Striped Bass" discussion under other adverse effects: |