Development of habitat suitability criteria for trout in small streams

We observed 2863 trout in the wild to determine habitat utilization in small streams of the Kings River basin in California's Sierra Nevada mountains. The habitat utilization data were used to develop habitat suitability functions that provide input variables to the instream flow incremental methodology (IFIM) habitat assessment model of the U.S. Fish and Wildlife Service. Observations of habitat utilization of rainbow trout (Salmo gairdneri), brown trout (Salmo trutta), and brook trout (Salvelinus fontinalis) were obtained during the summer months of 1983 and 1984. The observations were made in small streams with discharges ranging from 0.7 m³ s^?1 to 0.03 m³ s^?1. The streams are at elevations of 1250 to 2530 m. Equal effort was applied to observing undisturbed trout in all habitat types. Snorkeling proved to be the most effective method of observation. Individual trout of all species and life stages were most often observed in the lower half of the water column, utilizing low-velocity currents of less than 3.0 cm s^?1. From the depth and velocity utilization data, several forms of habitat suitability functions were developed and evaluated:

• 1 Univariate depth and velocity functions derived from frequency histogram analysis.
• 2 Univariate depth and univariate velocity exponential polynomial models.
• 3 Bivariate depth and velocity exponential polynomial models.

Univariate exponential polynomial models provided the best fit to the data for each species, based on visual comparisons of response surfaces and contour plots, and comparisons of computed sums of squared errors. Bivariate models fitted to the data resulted in greater sums of squared errors than multiplicative aggragation of univariate models, and frequently predicted utilization at zero depth. The habitat suitability functions derived from the univariate exponential polynomial models provided the best input to the IFIM habitat assessment models.     

Evidence of lake trout (Salvelinus namaycush) spawning and spawning habitat use in the Dog River,Lake Superior

Lake trout spawn primarily in lakes, and the few river-spawning populations that were known in Lake Superior were believed to be extirpated. We confirmed spawning by lake trout in the Dog River, Ontario, during 2013–2016 by the collection of and genetic identification of eggs, and we describe spawning meso- and microhabitat use by spawning fish. Between 2013 and 2016, a total of 277 lake trout eggs were collected from 39 of 137 sampling locations in the river. The majority of eggs (220) were collected at the transition between the estuary and the river channel crossing the beach. Lake trout eggs were most often located near the downstream end of pools in areas characterized by rapid changes in depth or slope, coarse substrates, and increased water velocities, where interstitial flows may occur. Depths in wadeable areas where eggs were found averaged 0.9?m (range: 0.4 to 1.3?m) and substrate sizes consisted of large gravel, cobble, and boulder; comparable to spawning characteristics noted in lakes. Water velocities averaged 0.66?m·s^?1 (range: 0.33 to 1.7?m³·s^?1) at mid-depth. This information on spawning habitat could be used to help locate other remnant river-spawning populations and to restore river-spawning lake trout and their habitat in rivers that previously supported lake trout in Lake Superior. The Dog River population offers a unique opportunity to understand the ecology of a river spawning lake trout population.     

A study of physical parameters at the spawning sites of the european grayling (Thymallus thymallus L.)

An investigation of the spawning sites of European grayling, Thymallus thymallus (L.), in two Swedish rivers revealed narrow range in their physical parameters. The bottom substrate was composed of 10–20 per cent sand, 50–70 per cent gravel (<2cm), 20–30 per cent stones (2–10cm), and a few bigger stones (>10cm in diameter). Eggs were found only where the gravel thickness was more than 5 cm. The depth varied between 30–50cm. Mean depth for 22 different spawning sites was 36cm. The water velocity varied between 23–90cm s^?1, average 54 cm s^?1. The temperature at the start of spawning was 3.9°C and at the end it was about 9°C. The results indicate the narrow range in physical parameters at the spawning sites. Small changes in the environment caused by regulation of river flow or water level may disturb the spawning behaviour of grayling and cause a decrease in population size or even extinction.     

Development and evaluation of bioenergetic-based habitat suitability criteria for trout

We constructed energetic models of habitat use for 82–322 g rainbow trout (Oncorhynchus mykiss) in a large regulated river, and 8–28 g Colorado River cutthroat trout (O. clarki pleuriticus) in a small headwater stream, to determine if observed summer habitat use by these species could be attributed to net energy acquisition, and to develop habitat suitability criteria based on net energy gain. Metabolic models of energy expenditure were derived from literature sources, but measurements of energy availability were site-specific. From the energy models, we assigned a suitability value of 1.0 to the entire range of velocities where positive net energy gains were predicted, and a suitability value of zero to velocities where negative net energy gains were predicted. Predicted net energy gain velocities were compared with observed velocities used by each species. For rainbow trout, the energetic model predicted energetically profitable velocities ranging from 5 to 45 cm s⁻¹. Predicted velocities were similar to velocities used by rainbow trout. This indicated that rainbow trout, as a group, were using energetically profitable stream locations, but some rainbow trout used non-profitable velocities. For Colorado River cutthroat trout, the energetic model predicted energetically profitable velocities ranging from 5 to 45 cm s⁻¹; however, Colorado River cutthroat trout used significantly lower velocities than predicted. The dissimilarity between velocities predicted and used by Colorado River cutthroat trout may be attributed to their inability to utilize energetically profitable velocities available in the stream because of depth restrictions The results suggest that the predictive abilities of energetic models vary between streams because of differences in depth and velocity availability. © 1997 John Wiley & Sons, Ltd.     

A Comparison of Lake Trout Spawning,Fry Emergence,and Habitat Use in Lakes Michigan,Huron, and Champlain

Restoration of self-sustaining populations of lake trout is underway in all of the Great Lakes and Lake Champlain, but restoration has only been achieved in Lake Superior and in Parry Sound, Lake Huron. We evaluated progress toward restoration by comparing spawning habitat availability, spawner abundance, egg and fry density, and egg survival in Parry Sound in Lake Huron, in Lake Michigan, and in Lake Champlain in 2000–2003. Divers surveyed and assessed abundance of spawners at 5 to 15 sites in each lake. Spawning adults were sampled using standardized gill nets, eggs were sampled using egg bags, and fry were sampled using emergent fry traps and egg bags left on spawning reefs overwinter. Spawning habitat was abundant in each lake. Adult lake trout abundance was low in Lake Michigan and Parry Sound, and very high at one site in Lake Champlain. Egg deposition was lowest in Lake Michigan (0.4–154.5 eggs•m⁻², median = 1.7), intermediate in Parry Sound (39–1,027 eggs•m⁻², median = 278), and highest in Lake Champlain (0.001–9,623 eggs•m⁻², median = 652). Fry collections in fry traps followed the same trend: no fry in Lake Michigan, 0.005–0.06 fry•trap⁻¹ day⁻¹ in Parry Sound, and 0.08–3.6 fry•trap⁻¹ in Lake Champlain. Egg survival to hatch in overwinter egg bags was similar in Lake Michigan (7.6%) and Parry Sound (2.3–8.9%) in 2001–02, and varied in Lake Champlain (0.4–1.1% in 2001–02, and 1.8–18.2 in 2002–03). Lake trout restoration appears unlikely in northern Lake Michigan at current adult densities, and failure of restoration in Lake Champlain suggests that there are sources of high mortality that occur after fry emergence.     

Effects of river regulation on the structure of a fast-growing brown trout (Salmo trutta L.) population

During the last 70 years, the Norwegian lake Mjøsa and its inflowing rivers have been subjected to serious changes due to hydroelectric power development. Regulation of the main inlet river, Gudbrandsdalslagen, started in 1919. The river power station at the Hunder fall was completed in 1964. This resulted in a reduction of winter water flow below the Hunder dam from approximately 26m³s^?1 to 2m³s^?1, which affected the most important spawning area of the fast-growing population of brown trout, Salmo trutta L. The population was investigated in detail in 1907, 1909, 1961, and 1985, and river growth, smolt age, and growth in Lake Mjøsa are compared. Only wild fish were included in the study. The main pattern throughout this period shows an increased river growth rate before smoltification and reduced smolt age. The average smolt age dropped from 4.7 years in 1909 to 4.1 years in 1985, and at the same time smolt size decreased from 26.8 cm to 25.1 cm. Considering the major changes in abiotic factors in the river spawning section, the changes in age structure and growth of brown trout smolt are comparatively small. In Lake Mjøsa, increased productivity due to input of nutrients has obviously favoured forage fish such as smelt (Osmerus eperlanus (L.)) and vendace (Coregonus albula (L.)). The growth rate of brown trout in the lake has improved from 1909 to 1961 and 1985, followed by a reduced spawning age. However, due to increased human exploitation the average length of ascending fish (approximately 68 cm) and condition factor ( K = 1.14–1.16) have altered little.     

Sculpins and Crayfish in Lake Trout Spawning Areas in Lake Ontario: Estimates of Abundance and Egg Predation on Lake Trout Eggs

Crayfish (Orconectes spp.) and sculpins (Cottus spp.) were collected at eight lake trout spawning reefs in Lake Ontario to assess abundance and potential to consume lake trout eggs. Abundance of crayfish ranged from a high of 9.5/m² in eastern Lake Ontario to 0/m² in western Lake Ontario where the absence or near absence at four reefs sampled was attributed to cold water upwelling. Sculpin abundance ranged from 4.2 to 50.1/m². Mean daily egg consumption (eggs/stomach) for sculpins 50 to 75 mm in length, ranged from 0 to 0.9 but differences among reefs were not significant. At one reef, significantly more eggs (2.5 eggs/stomach) were consumed by large sculpins (> 75 mm) than by small (44–49 mm) sculpins (0.2 eggs/stomach). Estimated egg consumption (eggs/stomach/m²) for sculpins > 43 mm for the eight reefs for the period between estimated date of peak lake trout spawning and a standardized 30-d period post spawning, ranged from 0 to 496 eggs/m² consumed or from 0 to 54% of estimated egg abundance. No lake trout eggs were found in crayfish stomachs, because of their mode of feeding. Estimated egg consumption by crayfish was indirectly estimated from a relationship developed between carapace length and egg consumption using published literature and experimental work. Using this procedure, estimated egg consumption by crayfish for a standardized 30-d period after the date of peak spawning ranged from 0 to 65 eggs/m² consumed, or from 0 to 82% of potential egg abundance for the eight reefs. At low egg abundance (< 100/m²), the density of crayfish and sculpin observed in Lake Ontario could result in sufficient egg consumption to cause almost 100% mortality of lake trout eggs. At higher egg abundance, however, mortality due to crayfish and sculpins appears to be relatively low. Deposition was sufficiently low at 5 of 8 sites to suggest the possible importance of sculpin and crayfish predation on lake trout recruitment failure in Lake Ontario.     

Modelling changes in trout habitat following stream restoration

Stream restoration was implemented on the Upper Arkansas River near Leadville, Colorado, to improve brown trout (Salmo trutta) populations. Metals pollution and channel disturbance associated with historic mining, land use, and water development degraded aquatic and riparian habitat. Changes in instream habitat quality following restoration were investigated with a before–after–control–impact study design. Baseline, as‐built, and effectiveness surveys were conducted in 2013, 2014, and 2016, respectively. Two‐dimensional hydrodynamic modelling with River2D was used to estimate weighted usable area (WUA) for adult, juvenile, fry, and spawning brown trout across a range of flows. WUA was calculated from habitat suitability curves for velocity, depth, and channel substrate. Foraging positions (FP) and habitat heterogeneity were also evaluated as indices of habitat quality. All results were analysed with analysis of variance. At impact sites, WUA increased by 12.2% from 2013 to 2014 but decreased by 10.2% from 2014 to 2016, whereas FP increased by 24.8% from 2013 to 2014 but decreased by 26.1% from 2014 to 2016. Spawning habitat increased 53.3% from 2014 to 2016 at impact sites. The 15.4% increase in depth variability from 2013 to 2016 indicates that habitat heterogeneity was enhanced at impact sites. No changes in WUA, FP, or habitat heterogeneity were observed at control sites. Although changes in WUA and FP suggest that initial habitat improvements were not sustained, increased spawning habitat and depth heterogeneity suggest otherwise. Our results highlight the value of monitoring strategies that utilize multiple lines of evidence to evaluate restoration effectiveness, inform adaptive management, and improve restoration practices.     

Mesohabitat use by brown trout (Salmo trutta) in a small groundwater‐dominated stream

Groundwater‐dominated streams have particular flow regimes that commonly support populations of trout. Meso‐ and micro‐habitat surveys were carried out on a reach of the river Tern that drains a Triassic sandstone aquifer in the English West Midlands, to investigate brown trout (Salmo trutta) habitat use with varying flows. Mesohabitats were mapped over a range of summer and autumn flows and coupled with direct underwater observation (snorkelling) of fish locations together with point measurements of velocity and depth. The number of habitat types recorded was low and dominated by glides, runs, and backwaters. Brown trout showed a strong association with glides and runs with adults being more associated with runs and parr with glides. General habitat use curves showed brown trout to favour depths between 0.30 and 0.40 m and velocities below 0.40 m s^?1. A clear preference was shown for sand and gravel bed materials. However, the differentiation of hydraulic habitats was weak and there was no trend in mesohabitats or change in trout use of mesohabitats with discharge. The study raises limitations of the mesohabitat survey approach when linking fish ecology, flow and physical habitat in small streams with low flow variability and low habitat diversity. In these situations, other factors (especially cover features) appear to strongly influence brown trout distribution. Copyright © 2010 John Wiley & Sons, Ltd.     

Migratory salmonid redd habitat characteristics in the Salmon River,New York

Non-native migratory salmonids ascend tributaries to spawn in all the Great Lakes. In Lake Ontario, these species include Chinook salmon (Oncorhynchus tshawytscha), coho salmon (O. kisutch), steelhead (O. mykiss), and brown trout (Salmo trutta). Although successful natural reproduction has been documented for many of these species, little research has been conducted on their spawning habitat. We examined the spawning habitat of these four species in the Salmon River, New York. Differences in fish size among the species were significantly correlated with spawning site selection. In the Salmon River, the larger species spawned in deeper areas with larger size substrate and made the largest redds. Discriminant function analysis correctly classified redds by species 64–100% of the time. The size of substrate materials below Lighthouse Hill Dam is within the preferred ranges for spawning for these four species indicating that river armoring has not negatively impacted salmonid production. Intra-specific and inter-specific competition for spawning sites may influence redd site selection for smaller salmonids and could be an impediment for Atlantic salmon (S. salar) restoration.     

Evidence of spawning by lake trout Salvelinus namaycush on substrates at the base of large boulders in northern Lake Huron

Identification of lake trout spawning sites has focused on cobble substrates associated with bathymetric relief (e.g., ‘contour’ or ‘slope’ along reefs), but this ‘model’ may be narrow in scope. Previous telemetry work conducted near Drummond Island, USA, Lake Huron, identified egg presence in substrates at the base of large boulders (>1 m diameter); however, the extent of this phenomenon was unknown. Telemetry data paired with multi-beam bathymetry identified a 0.63 km² area used by lake trout characterized by low bathymetric relief and numerous (~269) large boulders (>1 m diameter) with small-diameter substrates at their bases. Diver surveys revealed egg presence at all 40 boulders surveyed, exclusively associated with clean gravel-cobble (0.6–42 cm) substrates in undercut areas beneath overhanging edges of boulders and in narrow spaces between adjacent boulders. Egg presence was not associated with boulder or substrate physical characteristics which highlighted the possible importance of interstitial currents. Successful incubation in these habitats was inferred by capture of free embryos and post-embryos the following spring using traps and an electrofishing ROV although at lower densities than at popular spawning habitats nearby (1–3 km away). Free embryos and post-embryos were also caught where eggs were not observed the previous fall including unexpectedly on top of boulders which suggested that post-hatch stages may move more than previously thought. Extensive use of boulder-associated habitats for spawning, egg incubation, and early growth suggested this undescribed habitat type may provide an unanticipated contribution to total available lake trout spawning habitat and recruitment in the Great Lakes.     

Salmonid habitat modelling studies and their contribution to the development of an ecologically acceptable release policy for Kielder Reservoir,North‐east England

1. Kielder Reservoir regulates the Rivers North Tyne and Tyne. It provides a regular supply of water for downstream users, supports abstractions for a major water transfer scheme and provides hydroelectric power (HEP). Kielder's release regime typically alternates between a 1.3 m³ s⁻¹ compensation flow and 10–15 m³ s⁻¹ HEP releases of between 3 and 7 days in duration. Occasionally releases of up to 30 m³ s⁻¹ are made for the purpose of encouraging fish runs, for recreational events or to help in water quality management. The impacts of this release regime on Atlantic salmon (Salmo salar) and brown trout (S. trutta) habitat at four sites on the North Tyne are assessed and alternative regimes, designed to minimize impacts, are presented. 2. There is no evidence that the compensation flow results in extreme loss of instream habitat. A discharge of 1.3 m³ s⁻¹ ensures that water is maintained over most of the channel area at sites representative of upper, middle and lower sections of the North Tyne. This discharge lies above breaks in slope of respective site discharge versus wetted area curves; thus, disproportionate increases in discharge would be needed to increase wetted area. Simulations using the Physical Habitat Simulation System (PHABSIM) suggest that the compensation flow provides between 50% and 90% of the maximum possible weighted usable area (WUA) for juvenile (0+) salmonids. 3. During HEP releases, juvenile salmonid habitat (WUA) apparently falls to between 20 and 40% of site maxima. Newly emerged juvenile fish (March and April) are most affected by HEP releases because they are relatively small (25 mm in length) and water temperatures are relatively low at this time of year. During March and April, critical near‐bed displacement velocities for newly emerged fish may be exceeded across large parts (80%) of sites up to 8 km downstream from Kielder Reservoir; fish would either be displaced downstream or forced to relocate to flow refuge areas. 4. The availability of Atlantic salmon spawning habitat (WUA) at a key site is limited by the compensation flow; 1.3 m³ s⁻¹ provides approximately one third of the habitat available at the optimum discharge (4 m³ s⁻¹). At this site, a discharge of approximately 2 m³ s⁻¹ is needed to ensure most of the bed is inundated by water. Regulation has reduced the duration of flows exceeding 2 m³ s⁻¹ from 90 to 60% of the spawning season. 5. Simulations suggest that when discharge drops from 30 m³ s⁻¹ to the compensation flow, up to 60% of the optimum spawning habitat available at the former discharge may be left stranded (dry). This could potentially lead to egg or alevin mortality. 6. PHABSIM simulations suggest that increasing the compensation flow to 4 m³ s⁻¹ during the spawning period (November and December) is likely to increase the availability of suitable spawning habitat. Also, increasing the compensation flow to 2 m³ s⁻¹ during the incubation period (January through March) would minimize redd stranding. Reductions in the number of HEP releases in March and April would limit the extent to which newly emerged fish are exposed to velocities that potentially displace them. Such changes to the Kielder release regime may have implications for water resource management. While it is important that the biological instream flow requirements of the North Tyne are incorporated into the Kielder operating policy, these should be integrated along with the need for channel maintenance flows, downstream water supply abstractions and HEP generation, as well as for transfers of water to other catchments. Copyright © 2000 John Wiley & Sons, Ltd.     

Movement and summer habitat of brown trout (Salmo trutta) below a pulsed discharge hydroelectric generating station

Radiotelemetry was used to investigate detailed movement and summer habitat of brown trout Salmo trutta (size range 157–488 mm TL, n=18) in the Kananaskis River, Alberta. Flows in the Kananaskis River respond to pulsed daily discharge from an upstream hydroelectric generating facility (range 0.15–25 m³ s⁻¹). Wetted area available for brown trout doubled during periods of high flow. Fluctuating river levels did not appear to influence the degree to which brown trout moved within the study site. However, there was evidence that brown trout used cover and pools more as discharge increased. During high flow conditions, brown trout used similar depths (63 cm), and significantly lower surface water velocities than during low flow conditions. Brown trout also moved closer to shore into interstitial spaces among woody debris and root complexes during high flow. Pool habitats were used most often compared with all other habitat types combined. Pools with large woody debris accounted for 75% of all habitat observations. Woody debris was used more often than all other cover types. Results of the study indicate that the effects of river regulation on brown trout appear to have been moderated by woody debris in pools and along river banks, which provided refuge from high water velocities during periods of high flow. Copyright © 1999 John Wiley & Sons, Ltd.     

Predation on Lake Trout Eggs and Fry: a Modeling Approach

A general model was developed to examine the effects of multiple predators on survival of eggs and fry of lake trout, Salvelinus namaycush, associated with spawning reefs. Three kinds of predation were simulated: epibenthic egg predators consuming eggs on the substrate surface during spawning, interstitial egg predators that can move in rocky substrate and consume incubating eggs, and fry predators. Also simulated was the effect of water temperature on predation rates. The model predicted that interstitial predation on eggs accounted for most (76 to 81%) of the predation on early life history stages of lake trout; epibenthic egg predation (12 to 19%) and fry predation (0 to 12%) had less effect on lake trout survival. Initial predation conditions chosen for the model were: epibenthic egg predation peaked at 2 eggs/m²/d over 30 d, interstitial egg predation at 2 eggs/m²/d over 180 d, and fry predation at 1 fry/m²/d over 60 d. With a starting egg density of 100 eggs/m² and initial predation conditions, no lake trout were estimated to survive to swim-up. At egg densities of 250 eggs/m², 36% of the lake trout survived. At the highest egg densities examined, 500 to 1,000 eggs/m², estimated survival increased to about 70 to 80%. Simulated survival rates of lake trout decreased dramatically as predation rate increased but were not as sensitive to increases in the duration of predation.     

An experimental assessment of the effectiveness of gravel cleaning operations in improving hyporheic water quality in potential salmonid spawning areas

Dissolved oxygen (DO) conditions within the hyporheic zone were investigated in a gravel stream (River Sieg) in North Rhine Westphalia, Germany, populated in the spawning season by recurring migratory fish species, like Atlantic salmon (Salmo salar L.) and sea trout (Salmo trutta trutta L.). The gravel bed was cleaned at three sites in an area of approximately 150 m² to a depth of 50 cm, reducing the quantity of grains <2 mm to below 0.2%. DO concentrations in cleaned and uncleaned sediments were monitored in situ at 10, 20 and 30 cm sediment depth from the end of November 2001 to the end of April 2002. DO showed only minor fluctuations at the cleaned sites and steadily decreased at all uncleaned sites over time. Fine sediment accumulation over 5 months in the cleaned sites was comparable to the proportion of material within the bed prior to the experimental cleaning and probably influenced the DO concentrations of the hyporheic water. Decreasing DO concentrations at all sites coincided with increasing water temperatures towards the end of the study period. The cleaning operation significantly improved the conditions of DO in the hyporheic zone of the three study sites. Copyright © 2008 John Wiley & Sons, Ltd.     

Relationship between lake trout spawning,embryonic survival,and currents: A case of bet hedging in the face of environmental stochasticity?

Lake trout, Salvelinus namaycush, spawning in the Great Lakes occurs primarily on cobble substrate at relatively shallow water depths that can experience strong water currents. Strong currents may limit embryonic survival by damaging or displacing eggs, but may also reduce the accumulation of fine material and limit foraging by potential egg predators. To better understand the importance of currents, we evaluated the role of currents in spawning habitat selection, egg density and survival, and egg predator density at a spawning reef in Lake Champlain (USA). Most spawning occurred one week after the largest storm event associated with the strongest currents and greatest upwelling. Highest spawning activity was associated with a relatively shallow part of the reef that had the highest current velocity and greatest potential for egg displacement. Within the interstices, the survival of naturally deposited eggs was unrelated to the concurrent loss of artificial eggs. We propose that the reproductive strategy of spawning on shallow areas of a reef that have the highest current velocity and high potential for egg loss represents a type of bet hedging to optimize survival of those embryos that remain within interstices. This strategy may have evolved in response to environmental stochasticity that resulted in higher egg survival.     

HYDRAULIC GEOMETRY AND LONGITUDINAL PATTERNS OF HABITAT QUANTITY AND QUALITY FOR RAINBOW TROUT (Oncorhynchus mykiss)

We developed predictions of habitat quantity and quality for three life stages of rainbow trout, Oncorhynchus mykiss, across a range of stream sizes characterized by mean annual discharge of 1 to 50 m³ s^?1. The physical habitat template was created by nesting a reach‐scale two‐dimensional hydrodynamic model (River2D) within a downstream hydraulic geometry system using published coefficients for low‐gradient and high‐gradient watersheds. This provided both longitudinal and transverse estimates of depth and velocity profiles that, when combined with habitat suitability curves for the life stages, resulted in predictions of habitat quantity (weighted usable area) and habitat quality (the proportion of the stream profile that provided useable habitat) for rainbow trout along the stream continuum. Habitat quantity increased asymptotically for all life history stages but increased more rapidly in the low‐gradient watershed. Habitat quality decreased non‐linearly for young‐of‐the‐year and peaked at intermediate stream sizes for juveniles in both low‐gradient and high‐gradient watersheds. Adult habitat quality peaked in the high‐gradient watershed but increased asymptotically in the low‐gradient watershed, presumably due to lower mean velocities at larger stream sizes. Incorporation of transverse variation in depth and velocity in our physical habitat template provides a more realistic representation of habitat quantity and quality than do earlier assessments based on simple modal estimates of depth and velocity. Copyright © 2013 John Wiley & Sons, Ltd.     

Chinook salmon spawning surveys in deep waters of a large,regulated river

In 1986 research divers surveyed and mapped deep-water spawning redds of fall chinook salmon (Oncorhynchus tshawytscha) in selected sites within an impounded segment of the main-stem Columbia River, Washington State, U.S.A. In velocities over 3m s^?1 and depths up to 11 m, two divers riding a manoeuvrable sled made cross-current transects communicating observations of substrate materials and deep-water spawning sites. Surface personnel tracked the position of the sled with a laser locating system that logged the information into data storage. Subsequently, the computerized data were translated into overlaying maps depicting location of redds, substrate materials, and depth contours. Deep-water spawning (>3m) occurred at most survey sites in velocities between 0.6 and 0.8m s^?1. The average depth of spawning was 6.5 m, and the maximum was 9.1 m-deeper than the depth redds can normally be detected by aerial observation (3–4 m). Deep-water spawning ranged from none to substantial in areas of near identical physical characteristics. A method for estimating abundance and density of deep-water redds, based upon the data collected with this mapping technique, is presented. This study combined with current limited information concerning deep-water spawning suggests that up to 80 per cent of the escapement of fall chinook salmon in this reach may spawn in deep water.     

RESTORATION OF SPAWNING HABITATS OF BROWN TROUT (SALMO TRUTTA) IN A REGULATED CHALK STREAM

Gravel bed spawning grounds are essential for the reproduction of salmonids. Such spawning grounds have been severely degraded in many rivers of the world because of river regulation and erosive land use. To reduce its effects on salmonid reproduction rates, river managers have been restoring spawning grounds. However, measures of effectiveness are lacking for the restored spawning sites of brown trout (Salmo trutta). In this study, two methods were used to restore gravel bed spawning grounds in the Moosach River, a chalk stream in Southern Germany: the addition of gravel and the cleaning of colmated gravel. Seven test sites were monitored in the years 2004 to 2008, focussing on sediment conditions. Furthermore, brown trout egg survival and changes in the brown trout population structure were observed. Both gravel addition and gravel cleaning proved to be suitable for creating spawning grounds for brown trout. Brown trout reproduced successfully at all test sites. The relative number of young‐of‐the‐year brown trout increased clearly after the restoration. Sediment on the test sites colmated during the 4 years of the study. In the first 2 years, highly suitable conditions were maintained, with a potential egg survival of more than 50%. Afterwards, the sites offered moderate conditions, indicating an egg survival of less than 50%. Conditions unsuitable for reproduction were expected to be reached 5 to 6 years after restoration. Copyright © 2011 John Wiley & Sons, Ltd.     

Migratory patterns and return to the catch site of adult brown trout (Salmo trutta L.) in a regulated river

The spawning migration and local homing of adult brown trout was analysed using radio telemetry in a regulated river in central Norway. Twenty‐eight large (37–64 cm) brown trout (Salmo trutta L.) were tracked before, during and after spawning in the River Nea, a watercourse with several obstructions, including an outlet tunnel from a power station and a regulated stretch (26 km) with 45 weirs. Two major patterns of spawning migration were found: (1) about half (n = 16; 57%) of the trout moved very little and remained in the deeper pools of the river from June until November; (2) about half (n = 12; 43%) of the trout migrated relatively long distances (12.5–28 km) up the river prior to the spawning period where they stayed in the outlets of small tributaries, or in rapids on the main river during the spawning period. We assume that these trout belong to a population of lake‐run migratory trout using the River Nea for spawning. There was no significant difference in body length of migratory and stationary brown trout and no significant difference in total distance moved by migratory males (30.5 km, n = 6) and females (20.5 km, n = 6, p > 0.05). Among migratory trout, we found no correlation between body length and migrated distance. Of the 12 migratory trout, nine undertook fast upward migration in periods of high water flow (> 100 m³/s). They passed the outlet tunnel from the power station and negotiated two to 35 weirs before reaching their main reproduction areas. Three trout crossed several weirs when the discharge was low (10–40 m³/s). When there was low discharge, fish remained at the outlet tunnel for up to four weeks and showed a high level of activity. Postspawning downstream migration started between 25 September and 25 October. Most migratory trout (n = 9) wintered in pools on the lower part of the river or in weir basins; only two trout descended to the lake (Selbusjøen) in late autumn. Copyright © 2004 John Wiley & Sons, Ltd.