Mitigating the impacts of stream and lake regulation in the flathead river catchment,Montana, USA: An ecosystem perspective

1. Seventy-two per cent of the Flathead River catchment (22 241 km²) is federally designated and protected as wilderness or national park. Thus, the catchment remains one of the more pristine areas of its size in the temperate latitudes of the world. 2. Discharge in the downstream reaches of the river system outside the protected areas is regulated by three dams for flood control and hydropower production. These dams have blocked natural migration of native fish from Flathead Lake (496 km²) and isolated populations in sub-catchments. Temperature and erratic flow fluctuations have altered phenologies of river zoobenthos and fish, and in dam tailwaters aquatic biodiversity is drastically reduced in comparison to unregulated segments. 3. Ecological problems caused by changing water quality conditions, altered land-use patterns and introductions of non-native biota are interactive with the impacts of stream and lake level regulation, thereby emphasizing the complexity of this river–lake ecosystem. 4. Mitigation of the effects of regulation is compromised by differing management priorities and regulatory mandates of County, State, Tribal, and Federal agencies responsible for natural resource management within the catchment. Moreover, economic and ecological interests outside the Flathead influence the way flows are regulated within the catchment. 5. The most pervasive influences of stream and lake regulation can be ameliorated by retrofitting the hypolimnial release dam with a selective depth outlet structure to allow temperature control, and by controlling changes in flow rates to create a more natural hydrograph in the tailwaters of the large dams. Allowing fish passage by construction of fish ladders is problematic because upstream passage will commingle native species that were isolated upstream by construction of the dams with non-native species that were introduced subsequently below the dams. Cascading food web interactions elicited by invasions of non-native biota may offset any advantage to native stocks gained by passage and/or augmentation with hatchery stocks. 6. Mitigation must be adaptive in the sense that unanticipated effects and interactions with other management objectives can be documented and alternative action can be implemented. 7. This case history of the effects of stream and lake level regulation, and the approaches to management reviewed in this paper, should serve as a lesson in river conservation.     

Effects of hot dry summers on the loss of Atlantic salmon, Salmo salar, from estuaries in South West England

Salmon, Salmo salar L., were radio tagged in four estuaries in South West England. At medium to high summer flows, most salmon entering the river did so within 10 days of tagging. Lower flows were associated with an increased tendency for fish to remain in tidal water for a protracted period, and for those delayed fish to fail to enter the river. The delay was correlated with low freshwater flow, but it was concluded that high water temperature, and in some situations low dissolved oxygen, were likely to be the major influences. The causes of failure to enter the river by the delayed fish include lethally low levels of oxygen in some situations, but a major factor may be missed physiological opportunity. Implications in terms of water resource management, fisheries management and climate change are discussed.     

Salinity and geomorphology drive long‐term changes to local and regional fish assemblage attributes in the lower Pecos River,Texas

River systems throughout arid regions worldwide have been heavily impacted by human activities, resulting in long‐term ecological consequences. The lower Pecos River in the Trans‐Pecos region of Texas is no exception, having undergone anthropogenic changes that include decreased flow, elevated salinity, species loss and species invasion. We compared historical and contemporary fish assemblage attributes from the Pecos River at local (site‐specific) and regional (Trans‐Pecos region) scales across a 24‐year time period. Fish assemblage data were collected in October 1987 and 2011, by seining at 15 sites spanning 430 km of the river in Texas. Additionally, we examined contemporary environmental conditions to determine species–environment relationships. We found that fish assemblages were significantly different between time periods, likely due to increased salinisation in the upper half of the study region. Decreased species richness, species replacement and increases in euryhaline species were documented in the upstream sites. Freshwater springs lower the salinity and maintain flows in the downstream reach, allowing for maintenance of the native fish fauna. Careful management of regional aquifers, irrigation practices and petroleum waste water will be necessary for protecting biodiversity and environmental flows in the lower Pecos River.     

The effects of short-term regulation releases from an impoundment on downstream fish fauna

Abstract. The short-term ecological effects of a simulated large-scale regulation release (360 10⁶1d^-1), over a 5-day period, from an impoundment into the Afon Vyrnwy were investigated. A dramatic increase in the density and biomass of the fish fauna occurred at the time of the release. Elevated discharge rate was considered the primary factor responsible for the enhancement of the fauna. This increase in density and biomass of the fish fauna was suggested as being the result of fish displaced by tru-released water moving upstream to regain station after the flow had abated. Implications of these observations in the design of operating guidelines for use at regulating reservoirs are discussed.     

Nitrogen loading alters seagrass ecosystem structure and support of higher trophic levels

• 1. Anthropogenic‐derived nutrient inputs to coastal environments have increased dramatically worldwide in the latter half of the 20th century and are altering coastal ecosystems. We evaluated the effects of nitrogen loading on changes in macrophyte community structure and the associated fauna of a north temperate estuary. We found that a shift in primary producers from eelgrass to macroalgae in response to increased nutrient loading alters habitat physical and chemical structure and food webs. As nitrogen load increased we found increased macroalgal biomass, decreased eelgrass shoot density and biomass, decreased fish and decapod abundance and biomass, and decreased fish diversity.
• 2. The central importance of macroalgae in altering eelgrass ecosystem support of higher trophic levels is evident in the response of the ecosystem when this component was manipulated. Removal of macroalgae increased eelgrass abundance and water column and benthic boundary layer O₂ concentrations. These changes in the physical and chemical structure of the ecosystem with lower macroalgal biomass resulted in higher fish and decapod abundance and biomass.
• 3. Both a ¹⁵N tracer experiment and the growth of fishes indicated that little of the macroalgal production was immediately transferred to secondary consumers. δ¹⁵N values indicated that the most abundant fishes were not using a grazing food web based on macroalgae. Fish tended to grow better and have a greater survivorship in eelgrass compared to macroalgal habitats.
• 4. Watershed‐derived nutrient loading has caused increased macroalgal biomass and degradation and loss of eelgrass habitat, thus reducing the capacity of estuaries to support nekton.

Copyright © 2002 John Wiley & Sons, Ltd.     

引大济湟总干渠工程对大通河水生生态环境的影响及对策

本文研究了青海省引大济湟调水总干渠工程建设对大通河干流中上游水生生态环境的影响及鱼类保护措施。现场捕获鱼类9种,采集浮游植物26种,浮游动物10种,底栖动物14种,水生维管束植物4种,分析了鱼类区系组成、种群结构及生境习性等,结合工程建设造成的水文情势变化、阻隔、生境条件变化等对鱼类产生的影响,提出生态放水、修建过鱼道、人工增殖放流等措施,切实保护鱼类资源和生态环境。     

Impact of fish and pearl farming on the benthic environments in Gokasho Bay: Evaluation from seasonal fluctuations of the macrobenthos

ABSTRACT: In order to clarify the influence of mariculture on the benthic fauna, samples of the macrobenthos were collected from Gokasho Bay, where intensive fish culture and pearl oyster culture have been carried out. Monthly samples collected from the fish farm and pearl farm sites during June 1995 to July 1996 revealed that the community structure of the two sites showed distinct differences with seasonal fluctuations. At the fish farm site, azoic conditions were found from July to November; after December, the diversity increased markedly through successive recruitments of small-sized species such as the polychaetes Capitella sp. and Pseudopolydora paucibranchiata , and the amphipods Aoroides spp.; macrofaunal density, biomass and species richness peaked from March to April. At the pearl farm site, a higher diversity, including larger-sized species, and no clear seasonal fluctuations in abundance was found, and the community structure was similar to that at the control site. These results show the large impact by fish farming on the macrofauna, whereas pearl farming causes less effect on the benthic fauna. It is suggested that the difference in the level of organic input between the two sites results in the differences in the dissolved oxygen content of the bottom water, sulfide content of the sediments and, subsequently, the macrobenthic assemblages.     

The influence of hydrology on the recruitment of brown trout in an Alpine river,the Ybbs River,Austria

Abstract – We monitored yearly recruitment (1997–2008) of brown trout (Salmo trutta) in a fourth‐order Austrian Alpine river. The relative proportion of recruits to adult fish varied strongly among years (5.6–66.4%). These proportions were strongly correlated with specific flow patterns. High flows before and during the spawning period were positively correlated with recruitment, whereas high flows during incubation and emergence were negatively correlated with recruitment success. Unsteady flow modelling supported a causal hypothesis for these relationships in demonstrating that discharges > 30 m³·s^?1 resulted in substantial sediment motion (erosion and deposition) in suitable spawning areas within the study stretch.     

Effects of irrigation pumps on riverine fish

Abstract  The total number and condition of fish extracted via high and low flow irrigation pumps was assessed over a 2-year period in the Namoi River, Australia. A combination of boat electric fishing and fyke netting was used for 10 weeks during the peak irrigation period to determine species and size classes susceptible to entrainment during water abstraction. Over 2300 fish passed through the pump outlets over the study period, with many individuals (7.5% of total) both killed and injured. The maximum number of fish entrained in a single day was 232. Mortality was significantly higher from the high volume pump site, but only large (>200 mm long) or small (<50 mm long) fish were killed. Medium-sized fish (50–200 mm long) largely survived the abstraction process; although 70 were injured (3% of total), only one was killed (0.07%). The Electric fishing surveys showed that only four species were present in storage dams, suggesting that survival through the pump systems may be size and species specific. Fish that survived the water abstraction process had no opportunities to return to the main river system and were effectively classified as lost from the main river population. The development of suitable mitigation measures, including operational changes and screening, are suggested as mechanisms to prevent extraction and minimise any adverse impacts arising from irrigation development.     

Life history plasticity: migration ceased in response to environmental change?

Fish often migrate between habitats, and by that, fitness is improved. We estimated population parameters and studied possible migration of brown trout Salmo trutta between a Norwegian river and a tributary under two different regulated water flow regimes. In the 1970s, the main stem had high winter flows and reduced summer flows. Since 1981, the river has reduced minimum flow regime: 2.5 m³·s^?1 in winter and 6 m³·s^?1 in summer; the tributary has a natural flow regime. The growth of trout in the main stem was reduced from 1975 to 2013, with significantly lower mean lengths in all age groups. In the tributary, a similar reduction was observed in juvenile fish (age‐0 and age‐1). Mean length (mm) was unchanged in ≥age‐2 fish, while body length variation among fish ≥age‐4 was greatly reduced. The condition factor (Fulton's K) declined in both main stem and tributary. While it appears that sexual maturation was delayed in the tributary, the difference was not significant. In the 1970s, juveniles from the tributary migrated into the main stem to feed and grow, before returning to the tributary to spawn. PIT tagging of fish in the tributary in 2012 and subsequent surveys for recapture (in 2012 and 2013) indicated residency among fish in the tributary and no migration into the main stem. Thus, the migratory behaviour appears adaptive, and reduced habitat quality in terms of food and shelter due to reduced flow appears to have removed the growth benefit previously associated with the migration.