Cooler,bigger; warmer,smaller: Fine-scale thermal heterogeneity maps age class and species distribution in behaviourally thermoregulating salmonids

Behavioural thermoregulation is a survival strategy that occurs in response to an exceedance of thermal stress-inducing thresholds. When salmonids experience exceedance of these thresholds, they seek regions of colder water, known as thermal refuges. During an extreme temperature event of summer 2021 (main stem ~31.5°C) a large aggregation of Atlantic salmon (Salmo salar—all age classes) and brook trout (Salvelinus fontinalis—>20 cm) was observed on the Little Southwest Miramichi River in New Brunswick, Canada. Using a drone-mounted thermal infrared (TIR) sensor, fine-scale TIR imagery of the occupied refuge was acquired. Polarized glasses were worn by an onshore observer to make visual observations. Constructing maps from these data we examined the spatial distribution of fish, and the corresponding temperature of the areas they occupied. Salmonids were found to be distributed by age class and species, with the distribution driven by the mosaic of temperatures in the refuge. Young of the year (YOY), 1+, 2+ and adult Atlantic salmon occupied areas with average temperatures ~30.1, 28.8, 25.7 and 21.9°C, respectively; whilst mature brook trout occupied areas ~21.8°C. Noteworthy is the observation of thermally aggregating young of the year Atlantic salmon, and the range in temperatures they occupied (~8°C). One isolated, shallow, cold water patch (~22°C) exclusively held YOY Atlantic salmon. Our findings highlight the importance of several different thermal characteristics of thermal refuges and their link to salmonid occupancy and can aid the design of ecologically meaningful thermal refuge augmentation/restoration projects.     

A Statistical Model for Managing Water Temperature in Streams with Anthropogenic Influences

Streams in the Pacific Northwest (Oregon, Washington, British Columbia) face rising summer temperatures and increasing anthropogenic influence, with consequences for fish populations. Guidance is needed in small managed watersheds for setting reservoir release rates or for the restriction of water extractions to meet the needs of fish and aquatic ecosystems. Existing environmental flow methods focus on discharge rates and do not typically consider water temperatures, and detailed thermal models are too complex for widespread implementation. We used multiple logistic regression to develop statistical models for estimating the probability of exceeding a salmonid stream temperature threshold of 22 °C as a function of discharge and maximum daily air temperatures. Data required are air temperature, stream temperature and stream discharge over a minimum of one summer. The models are used to make minimum discharge recommendations under varying forecast weather conditions. The method was applied to nine streams in the Pacific Northwest. Minimum recommended discharge generally ranged from 23% to 86% of mean annual discharge and was higher than observed low flows in most streams. Comparison of the new method to existing methods for Fortune Creek in British Columbia indicated that total season discharge volumes could be reduced while meeting thermal requirements. For other streams, it was evident that high water temperatures cannot be managed by increasing discharge, as the discharge required would be greater than natural discharge and higher than achievable by management. The statistical method described in this paper allows for a risk‐based approach to discharge management for fish habitat needs.     

A simplified water temperature model for the Colorado River below Glen Canyon Dam

Glen Canyon Dam, located on the Colorado River in northern Arizona, has affected the physical, biological and cultural resources of the river downstream in Grand Canyon. One of the impacts to the downstream physical environment that has important implications for the aquatic ecosystem is the transformation of the thermal regime from highly variable seasonally to relatively constant year‐round, owing to hypolimnetic releases from the upstream reservoir, Lake Powell. Because of the perceived impacts on the downstream aquatic ecosystem and native fish communities, the Glen Canyon Dam Adaptive Management Program has considered modifications to flow releases and release temperatures designed to increase downstream temperatures. Here, we present a new model of monthly average water temperatures below Glen Canyon Dam designed for first‐order, relatively simple evaluation of various alternative dam operations. The model is based on a simplified heat‐exchange equation, and model parameters are estimated empirically. The model predicts monthly average temperatures at locations up to 421 km downstream from the dam with average absolute errors less than 0.5°C for the dataset considered. The modelling approach used here may also prove useful for other systems, particularly below large dams where release temperatures are substantially out of equilibrium with meteorological conditions. We also present some examples of how the model can be used to evaluate scenarios for the operation of Glen Canyon Dam. Published in 2008 by John Wiley & Sons, Ltd.     

Heat exchanges and temperatures within a salmon spawning stream in the Cairngorms,Scotland: seasonal and sub‐seasonal dynamics

Stream temperatures are often used to predict salmonid embryo development; but there are very few medium‐term studies of the heat exchanges determining water column and bed temperatures. Furthermore, no research exists on the energy balance for sub‐arctic Scottish rivers. This paper reports results of a hydrometeorological study of a Cairngorm stream (Girnock burn, northeast Scotland) over the salmon spawning–hatch season (late October 2001 to mid‐April 2002) that aims: (1) to characterize seasonal and sub‐seasonal stream energy budget and thermal dynamics; and (2) to explain these variations with respect to meteorological and hydrological factors. In terms of average energy flux contributions, sensible heat (38.7%), the bed heat flux (37.0%) and friction at the stream bed and banks (24.3%) are heat sources, while latent heat (73.1%) and net radiation (26.9%) are heat sinks. All energy losses and 38.7% of heat gains occur at the air–water interface; and 61.3% of energy gains (including friction) take place at the water–channel bed interface. Typically, temperatures increase (+1.97°C) and show dampening of thermal response from the water column to depth in the stream bed. The most salient findings include: (1) the stream bed (atmosphere) is the dominant energy source (sink) for heating (cooling) channel water, which may be attributed to inferred heat advection by groundwater up‐welling into the bed of this upland stream; (2) sensible heat is the primary atmospheric energy source due to limited net radiation; (3) friction at the stream bed and banks is an important heat source. Energy budget terms and temperatures exhibit (sub‐)seasonal changes in response to meteorological and hydrological conditions; a schematic diagram is presented to summarize these results. This paper clearly illustrates the need for further medium‐ to long‐term empirical stream energy balance research to characterize heat flux dynamics and, thus, understand and predict water temperature variations over time‐scales of relevance to biological studies. Copyright © 2004 John Wiley & Sons, Ltd.     

Estimating flow rates to optimize winter habitat for centrarchid fish in Mississippi River (USA) backwaters

The backwaters of large rivers provide winter refuge for many riverine fish, but they often exhibit low dissolved oxygen levels due to high biological oxygen demand and low flows. Introducing water from the main channel can increase oxygen levels in backwaters, but can also increase current velocity and reduce temperature during winter, which may reduce habitat suitability for fish. In 1993, culverts were installed to introduce flow to the Finger Lakes, a system of six backwater lakes on the Mississippi River, about 160 km downstream from Minneapolis, Minnesota. The goal was to improve habitat for bluegills and black crappies during winter by providing dissolved oxygen concentrations >3 mg/L, current velocities <1 cm/s, and temperatures >1°C. To achieve these conditions, we used data on lake volume and oxygen demand to estimate the minimum flow required to maintain 3 mg/L of dissolved oxygen in each lake. Estimated flows ranged from 0.02 to 0.14 m³/s among lakes. Data gathered in winter 1994 after the culverts were opened, indicated that the estimated flows met habitat goals, but that thermal stratification and lake morphometry can reduce the volume of optimal habitat created. This article is a U.S. Government publication and is in the public domain in the United States.     

MAGNITUDE,FREQUENCY AND DURATION OF INSTREAM FLOWS TO STIMULATE AND FACILITATE CATADROMOUS FISH MIGRATIONS: AUSTRALIAN BASS (MACQUARIA NOVEMACULEATA PERCIFORMES,PERCICHTHYIDAE)

The migratory response and behaviour of catadromous Australian bass with regard to hourly mean river flows and water temperatures was assessed over 15 months. Fish movement was assessed using a 75‐km passive acoustic telemetry array in the regulated Shoalhaven River below Tallowa Dam, NSW, Australia. The majority (62%) of downstream pre‐spawning migrations from freshwater to estuarine habitats were stimulated by a series of flow pulses from April to September, but a proportion of fish (38%) commenced downstream migrations under regulated baseflow conditions after a sustained decrease in water temperature to below 15°C in late autumn. Equal numbers of fish undertook post‐spawning upstream return migrations during flow pulses and during regulated baseflow conditions, with regulated baseflow migrants exhibiting a preference for dusk–dawn passage through freshwater pool–riffle sequences. The median magnitude of flow pulses at the time of commencement of downstream and upstream freshwater migrations by Australian bass was not large, equivalent to natural (in the absence of river regulation) flows equalled or exceeded for 56% and 48% of time, respectively. There was no evidence for increased numbers of migrants with increasing flow pulse magnitude, with individual fish ignoring some flow pulses but responding to subsequent events. In regulated rivers, the release of more frequent flow pulses with peak magnitudes approximating the natural 50th flow duration percentile may be more effective in stimulating greater numbers of Australian bass to undertake pre‐spawning and post‐spawning migrations between freshwater and estuarine habitats than the release of a single, larger event. The propensity of Australian bass to also undertake spawning migrations under regulated baseflow conditions emphasizes the need for provision of baseflow regimes in regulated rivers that can facilitate migrations by large bodied fishes. Copyright © 2011 John Wiley & Sons, Ltd.     

Mitigation of cold‐water thermal pollution downstream of a large dam with the use of a novel thermal curtain

Hypolimnial releases from dams during periods of thermal stratification modify the downstream riverine thermal regime by decreasing water temperature and reducing natural diel thermal variability. This cold‐water thermal pollution in rivers can persist for hundreds of kilometres downstream of dams and impact important ecological processes such as fish spawning. To mitigate this problem, a first‐of‐its‐kind thermal curtain was fitted to the large bottom release Burrendong Dam on the Macquarie River, Australia. The thermal curtain acts by directing warmer, near‐surface epilimnial water to the low‐level hypolimnial offtake. This study aimed to test the efficacy of the thermal curtain by measuring temperatures before and after the curtains installation, quantifying the magnitude and extent of cold‐water thermal pollution along the Macquarie River downstream of Burrendong Dam. Epilimnial releases with use of the curtain increased diel temperature ranges and the mean monthly water temperature below the dam. Epilimnial releases with use of the curtain increased diel temperature ranges from 0.9°C to 2.5°C and reduced the difference between the mean monthly water temperature of an upstream control and a downstream site by up to 3.5°C. A comparison of the monthly temperature means along the river, indicated that thermal recovery, whereby temperatures returned to within the natural range of upstream temperatures occurred 45 km downstream of the dam during summer when the thermal curtain was deployed, compared with approximately 200 km prior to deployment of the curtain. Our study suggests that the use of thermal curtains can reduce cold‐water thermal pollution and improve ecological outcomes for river ecosystems downstream of dams.     

The effect of Keepit Dam on the temperature regime of the Namoi River,Australia

Modifications to water temperature caused by the release of hypolimnetic water from thermally stratified reservoirs pose a major threat to the aquatic biota of lowland rivers in Australia's Murray–Darling basin. Keepit Dam is earmarked as one of several deep‐release structures in the basin causing ecologically significant temperature modification over a large length of river. This study utilized discrete and continuously monitored historical water temperature data from stream gauging stations, together with reservoir thermal profile data, to assess the impacts of Keepit Dam on the thermal regime of the Namoi River. Modifications to selected components of the river's annual temperature cycle were quantified in relation to a pre‐dam temperature regime estimated from statistical models incorporating catchment, hydrological and sample attributes. Keepit Dam has modified the thermal regime of the Namoi River. The effect was greatest immediately downstream from the dam where the annual maximum daily temperature was approximately 5.0 °C lower and occurred three weeks later than the pre‐dam condition. This change was sufficient to disrupt thermal spawning cues for selected Australian native fish species. The magnitude of disturbance progressively diminished with distance from the dam. Key aspects of the river's annual temperature cycle were largely restored to the pre‐dam condition within 100 river km downstream from the dam, which is closer than previous estimates. However, there was marked inter‐annual variation in the magnitude of thermal modification and ecological impact as a result of year to year changes in tributary flow and reservoir behaviour. Copyright © 2002 John Wiley & Sons, Ltd.     

The influence of riparian shade on lowland stream water temperatures in southern England and their viability for brown trout

Suitable thermal conditions in streams are necessary for fish and predictions of future climate changes infer that water temperatures may regularly exceed tolerable ranges for key species. Riparian woodland is considered as a possible management tool for moderating future thermal conditions in streams for the benefit of fish communities. The spatial and temporal variation of stream water temperature was therefore investigated over 3 years in lowland rivers in the New Forest (southern England) to establish the suitability of the thermal regime for fish in relation to riparian shade in a warm water system. Riparian shade was found to have a marked influence on stream water temperature, particularly in terms of moderating diel temperature variation and limiting the number of days per year that maximum temperatures exceeded published thermal thresholds for brown trout. Expansion of riparian woodland offers potential to prevent water temperature exceeding incipient lethal limits for brown trout and other fish species. A relatively low level of shade (20–40%) was found to be effective in keeping summer temperatures below the incipient lethal limit for brown trout, but ca. 80% shade generally prevented water temperatures exceeding the range reported for optimum growth of brown trout. Higher levels of shade are likely to be necessary to protect temperature‐sensitive species from climate warming. © Crown copyright 2010.     

Juvenile coho salmon behavioural characteristics in Klamath river summer thermal refugia

During the summer in the main‐stem Klamath River, juvenile salmonids respond positively to cooler tributary temperatures by congregating in large schools at the mouths of these tributaries, referred to as thermal refugia. The purpose of this paper is to summarize results from coho salmon (Oncorhynchus kisutch) thermal refugia studies conducted since 2006 in the Klamath River. Results showed that juvenile coho salmon started using thermal refugia when the Klamath River main‐stem temperature approached approximately 19 °C. The majority of the juvenile coho salmon within the studied thermal refugia were found in the slower velocity habitat associated with cover. Juvenile coho salmon counts in the studied thermal refugia dramatically decreased at temperatures >22–23 °C, suggesting that this approximates their upper thermal tolerance level. Although some juvenile coho salmon were very mobile, others chose, until smoltification, to rear in the mouths and lower reaches of non‐natal tributaries where thermal refugia occurred, apparently because of suitable habitat conditions. Information gained from these investigations will improve our knowledge of the life history of coho salmon in the Klamath River drainage and how they use the main‐stem river. Copyright © 2010 John Wiley & Sons, Ltd.     

Modelling the impact and potential mitigation of cold water pollution on Murray cod populations downstream of Hume Dam,Australia

A one‐dimensional hydrodynamic reservoir model is coupled with a stochastic fish population model to examine the impacts of cold water pollution (CWP) on the Australian freshwater fish, Murray cod, downstream of Hume Dam, Australia. Mitigation of CWP through the introduction of selective withdrawal capabilities to access near‐surface water is predicted to increase discharge temperatures during the crucial spring‐early summer post‐spawning period by 4–6°C for normal operating conditions, that is, a full reservoir in early spring. No improvement in discharge temperature was predicted for drought conditions characterized by relatively low storage levels in early spring. The predicted temperature increase using selective withdrawal increased the predicted average minimum female population abundance by 30–300% depending on the assumed spawning behaviour. Increased discharge temperatures appear to be achievable and are expected to reduce the stress currently impacting Murray cod populations due to CWP during crucial post‐spawning periods. This provides evidence that mitigation of this problem may assist in rehabilitating Murray cod populations in the Murray River downstream of Hume Dam. Copyright © 2007 John Wiley & Sons, Ltd.     

Dynamics of river fish populations in response to hydrological conditions: a simulation study

Increasing multi‐sectoral demands on water resources have led to water abstraction and transfer activities, and the construction of dams and embankments that have significantly altered the flood regimes of rivers throughout the world resulting in the loss of fish production and biodiversity. The current emphasis on sustainable development and biodiversity conservation is leading efforts to mitigate these impacts by means of interventions such as the release of artificial floods downstream of dams and the manipulation of water levels within impounded floodplains. Whilst much work has been done to determine the hydrological requirements for the maintenance of salmonid populations, few equivalent studies are available from which to develop criteria for the management of hydrological regimes for fishes and fisheries in large floodplain–river systems such as the Mekong. The population dynamics of fish in such rivers are believed to respond to hydrological conditions in a density‐dependent manner. An age‐structured population dynamics model incorporating sub‐models describing density‐dependent growth, mortality and recruitment was used to explore how hydrological conditions within a theoretical floodplain–river system affect the dynamics of a common floodplain–river fish species. Graphical summaries of the response of exploitable biomass to a range of different drawdown rates, dry and flood season areas and volumes, and flood season durations are presented under five different model assumptions concerning density‐dependent processes. Optimal flooding patterns are also described for the model species and theoretical river system. The patterns of predictions that emerge from the simulations provide guidelines for managing or manipulating hydrological conditions in river systems for both fixed and variable volume hydrological scenarios. As a general rule of thumb, exploitable biomass is maximized by minimizing the rate of drawdown and maximizing the flood duration and flood and dry season areas or volumes. However, experiences from dam and other hydraulic engineering projects suggest that these predictions should be treated with caution until we better understand the influence of hydrology on spawning behaviour, system primary production, and critical habitat availability. Copyright © 2004 John Wiley & Sons, Ltd.     

Annual Variation in Larval Fish Assemblages in a Heavily Regulated River During Differing Hydrological Conditions

One of the most severe anthropogenic impacts on river systems worldwide has been alterations to the natural flow regime. Understanding biological responses to altered flow regimes is critical to effectively rehabilitate aquatic ecosystems. This study investigated changes in the larval fish assemblages during varying hydrological conditions over 5 years in the lower River Murray, in south‐eastern Australia. Larval fish were sampled during spring/summer during three distinct hydrological periods: under a within‐channel flow pulse and a water level raising (2005); during a drought with very low flows and stable water levels (2006, 2007 and 2008); and during an overbank flow (2010). Data were analysed for annual, spatial and seasonal variations, and correlations were examined between changes in larval assemblages and environmental variables. Hydrology was a key driver in inter‐annual variation in larval fish assemblages. High abundances of small‐bodied to medium‐bodied native species were recorded under low flows, while for other species, abundance was more strongly correlated to temperature, representing seasonal variation. Two large‐bodied species were only recorded during the within‐channel flow pulse and overbank flow conditions, and significant increases in larval abundances were recorded during overbank flow conditions. We suggest groupings based on species response to hydrology (low‐flow to medium‐flow spawners, high‐flow spawners or seasonal spawners). This study suggests that a range of conditions (low flows and overbank flows) are required to maintain a diverse and abundant native fish fauna in the lower River Murray. Copyright © 2015 John Wiley & Sons, Ltd.     

Gastrulation and hatch as critical thermal windows for salmonid embryo development

Climate change and impoundment increase river temperatures, shifting the bioclimatic envelope in which freshwater biota have evolved and increasing salmonid egg mortality. To mitigate this, conservation flows from reservoirs are often implemented to maintain favourable water temperatures downstream from impoundments throughout salmonid embryo development. However, as water to maintain conservation flows becomes scarcer, there is a need to understand the requirements of salmonid embryos and balance these with anthropogenic demands. This study combines a laboratory-based and a modelling approach to test the effect of different temperatures on the survival from fertilisation to hatch of a model salmonid species. Further, the effect of dropping temperatures from high to optimal conditions at hatch—a perceived period of greater sensitivity to high temperatures—is tested. The study shows embryo mortality increases with temperature and is greatest during gastrulation and hatch. Also, embryos that experienced high temperatures during gastrulation had high mortality rates at hatch, even when hatch conditions were optimal. This indicates sublethal developmental abnormalities caused by high temperatures during gastrulation increase mortality at hatch. Therefore, to maintain high rates of salmonid embryo survival, cold water resources from reservoirs ideally will target both gastrulation and hatch developmental stages.     

Evaluation of energy expenditure in adult spring Chinook salmon migrating upstream in the Columbia River Basin: an assessment based on sequential proximate analysis

The upstream migration of adult anadromous salmonids in the Columbia River Basin (CRB) has been dramatically altered and fish may be experiencing energetically costly delays at dams. To explore this notion, we estimated the energetic costs of migration and reproduction of Yakima River‐bound spring Chinook salmon Oncorhynchus tshawytscha using a sequential analysis of their proximate composition (i.e., percent water, fat, protein, and ash). Tissues (muscle, viscera, and gonad) were sampled from fish near the start of their migration (Bonneville Dam), at a mid point (Roza Dam, 510 km upstream from Bonneville Dam) and from fresh carcasses on the spawning grounds (about 100 km above Roza Dam). At Bonneville Dam, the energy reserves of these fish were remarkably high, primarily due to the high percentage of fat in the muscle (18–20%; energy content over 11 kJ g^?1). The median travel time for fish from Bonneville to Roza Dam was 27 d and ranged from 18 to 42 d. Fish lost from 6 to 17% of their energy density in muscle, depending on travel time. On average, fish taking a relatively long time for migration between dams used from 5 to 8% more energy from the muscle than faster fish. From the time they passed Bonneville Dam to death, these fish, depending on gender, used 95–99% of their muscle and 73–86% of their visceral lipid stores. Also, both sexes used about 32% of their muscular and very little of their visceral protein stores. However, we were unable to relate energy use and reproductive success to migration history. Our results suggest a possible influence of the CRB hydroelectric system on adult salmonid energetics. Published in 2006 by John Wiley & Sons, Ltd.     

Effects of selective water withdrawal schemes on thermal stratification in Kouris Dam in Cyprus

Thermal stratification and its seasonal variations in Kouris Dam in Cyprus were simulated, and the impact of five different water withdrawal schemes was studied, using the 2‐D, laterally averaged CE‐QUAL‐W2 reservoir model. Based on the model simulations, it was found that the thermal stratification of the reservoir is significant for most of the year. Most importantly, a complete mixing of the water column, triggered by seasonal variations in meteorological conditions, occurs in late‐January. Predicted thermal stratification and water temperature profiles in the reservoir are noticeably affected by water withdrawal schemes. It was found that deep‐water withdrawals tend to facilitate heat transfer in the water column and deepen the water mixing layer (epilimnion), especially from September to the following January. These study results suggest that it is prudent for Kouris Dam to integrate selective water withdrawal schemes into reservoir management by using the water withdrawal effects on thermal stratification for different water quality management strategies.     

SEASONAL PATTERNS OF RIVER CONNECTIVITY AND SALTWATER INTRUSION IN TIDAL FRESHWATER FORESTED WETLANDS

Hydrology can be difficult to interpret in tidal freshwater forested wetlands because of several influencing factors including river discharge, tidal stage, local precipitation, evapotranspiration, groundwater and prevailing winds. River discharge and tidal stage are considered the primary factors affecting these wetlands and both vary on a seasonal basis and have potential implications for wetland saltwater intrusion. We examined the hydrologic patterns of tidal freshwater swamps along the lower reach (20 km) of the Apalachicola River system in northwest Florida, USA. Water level recorders were installed in five wetlands along this reach and recorded ground and surface water levels at 15‐min intervals from December 2006 to April 2009 (non‐continuously). Seasonal trends related to flooding frequency and duration were compared to long term (2000–2008) records of creek and river salinities measured in the tidal freshwater forested zone. Tidal freshwater swamps tended to maintain a narrow water level range (often ±20 cm of the ground surface) except during high river flows (>680 cms or 24 000 cfs) when levels increased 1 to 2 m above ground and dampened tidal effects. All tidal forested wetlands had the highest mean water levels and most days tidally pulsed during the Jul–Oct season which coincided with peak river/creek salinities and low river‐flows associated with drought conditions. We explored the implications for the timing of salt water intrusion in these swamps and potential changes related to sea level rise and water management in the Apalachicola River drainage basin. Copyright © 2011 John Wiley & Sons, Ltd.     

The impact of cold water releases on the critical period of post‐spawning survival and its implications for Murray cod (Maccullochella peelii peelii): a case study of the Mitta Mitta River,southeastern Australia

The effects of cold water releases, as a by‐product of storing irrigation water in large dams, has been a source of great concern for its impact on native freshwater fish for some time. The Mitta Mitta River, northeast Victoria, is impacted by altered thermal regimes downstream of the fourth largest dam in Australia, Dartmouth dam, with some daily temperatures 10–12°C below normal. Murray cod (Maccullochella peelii peelii) were endemic to the Mitta Mitta River; however, resident Murray cod have not been found in this river since 1992. The response of eggs and hatched larvae from Murray cod to different temperature gradients of water were measured and the post‐spawning survival recorded. As a case study, post‐spawning survival was then inferred from flow data for each year of operation of Dartmouth Dam, recorded since first operation in 1978, and included in a stochastic population model to explore the impact of the altered (historical) thermal regime on population viability. Experimental results revealed no egg and larval survival below 13°C and predicted historical temperature regimes point to more than 15 years of low temperatures in the Mitta Mitta River. Population modelling indicates that the impact of cold water releases on post‐spawning survival is a significant threatening process to the viability of a Murray cod population. Additionally, we consider changes to the thermal regime to explore how the thermal impact of large dams may be minimized on downstream fish populations through incrementally increasing the temperature of the releases. The modelled Murray cod population responds to minor increases in the thermal regime; however, threats are not completely removed until an increase of at least 5–6°C. Copyright © 2005 John Wiley & Sons, Ltd.     

Benthic Response to Flow Alteration in a New Mexico Arid Mountain Stream

Past and current pressure on streams and rivers for consumptive use requires the development of tools and decision‐making processes for water managers to minimize impacts on ecological function. This paper examines the utility of modeling benthic biomass in relation to benthic macroinvertebrate (BMI) community attributes for water resource management scenarios in the Cliff‐Gila Valley of the Gila River, New Mexico, USA. The river benthos biomass model (RivBio) was used in conjunction with hydraulic modeling to predict growth and decline of benthic biomass. BMI community attributes were compared along gradients of hydrologic impact (successive existing diversions) in the Cliff Gila Valley and were compared to community attributes in similar regional streams. Benthic biomass was minimally affected by proposed diversions at flows above 4.25 cms (150 cfs), but was severely reduced downstream because of existing diversions during lower flow periods. Riffle habitat was disproportionately affected during extreme low and interrupted flow, which may have resulted in BMI communities shifted towards multi‐habitat generalists that can persist in lentic conditions. Flow augmentation from proposed diversions and storage would greatly mitigate these existing biomass losses by providing consistent base flow and lotic conditions in riffle habitat. Both benthic biomass and BMI community endpoints were useful when comparing water management scenarios. Copyright © 2016 John Wiley & Sons, Ltd.     

Water quality changes and effects on fish populations in the hanjiang river,china, following hydroelectric dam construction

Since its completion in 1973 the Danjiangkou Dam has markedly changed downstream flows, water levels, temperatures, sediment loads and other water quality characteristics in downstream reaches of the Hanjiang River. There have been changes in the growth, spawning behaviour and overwintering condition of local fish populations, in the composition and abundance of food organisms and in the composition of the commercial fish catch. Despite the changed environment and the absence of a fish pass, fish populations are still able to grow and spawn under the new regime. Where conditions are like those of the Hanjiang River, dams may not necessarily have calamitous consequences for fishery production.