Trout Redds Research Articles

Evaluation of alternative approaches to PHABSIM modeling of coastal cutthroat trout spawning habitat

AbstractIn the face of a changing climate and increasing human demand for water, an understanding of habitat preference has become critical for managing wild fish populations and projecting potential changes in habitat and populations. Two approaches to Physical Habitat Simulation (PHABSIM) modeling of coastal cutthroat trout Oncorhynchus clarkii clarkii spawning habitat were compared by modeling a reach, consisting of eight transects covering a pool and upstream and downstream riffles, of a small Puget Sound stream with two sets of habitat variables. The reach contained a cluster of redds 2 years in a row, assumed to be an indication of preferred spawning habitat and was located in the area of maximum spawning in the watershed, based on multiple years of redd surveys. Two PHABSIM instream flow models of the study site, one based on standard microhabitat (depth [D], velocity [V], and substrate [S]) suitabilities and the other based on D, V, and channel unit (CU) suitabilities, were developed and compared for their relative ability to correctly predict coastal cutthroat trout spawning habitat selection at the redd cluster within the PHABSIM study site. One approach was the standard use of habitat suitability criteria (HSC) for D, V, and S to indicate spawning habitat quality. The alternate approach was to replace substrate HSC with CU index HSC that incorporated dominant substrate particle diameter, CU (riffle, deep and shallow pool tail, pool body, deep and shallow pool edge, cascade, waterfall, and terrestrial), where deep and shallow units were based on relative residual depth (RRD), size of CU relative to channel width, and position within CU. Spawning habitat quality was calculated for each transect as weighted usable width with the standard HSC metrics (WUWs) as well as the modified CU index (WUWm). WUWm at the transects bracketing the redd cluster exceeded WUWm at the remaining six transects and was outside the 95% confidence interval for WUWm at the remaining transects. In contrast, WUWs varied less between the redd cluster and the remainder of the transects, suggesting the CU index better reflected spawning habitat quality than substrate. Incorporation of elevation relative to SZF addressed vulnerability to declining flow during incubation. Both models resulted in maximum WUA within the range of discharges that coincided with the majority of fresh cutthroat trout redds in Skookum Creek.

Characterizing the Flow Regime in Brook Trout Incubation Habitats and Implications for Management in a Hydro‐Regulated River

AbstractThe operation of dams, diversions, and power generation facilities unavoidably influence the ecological function of rivers. We evaluated vertical and horizontal hydraulic gradients and subsequent water temperature changes in the hyporheic zone of a spawning area for Brook Trout Salvelinus fontinalis in a managed Lake Superior tributary in Ontario, then conducted a laboratory‐based experiment to show the impact of cold shock during incubation on the timing of larval emergence and survival. Upwelling groundwater was observed at the spawning area during the monitoring period (October 28, 2016, to January 11, 2017); hyporheic water temperatures remained above 3.7°C, whereas ambient river temperature above the substrate fell to 1.5°C until water was released from the upstream control dam. After the release event, water level increased by 0.9 m over the spawning area, and within 24 h, vertical and horizontal flow gradients were reversed in the hyporheic zone; downwelling conditions were observed for 30 h between surface and hyporheic water 1.8 m below substrate, and hyporheic water temperature decreased in unison. Hyporheic temperatures at shallow inshore sites fell below 1°C for more than 53 h. In the laboratory, applying a worst‐case scenario of dam‐induced cold shock on Brook Trout redds using historic monitoring records (i.e., <1.0°C for 40 h), we found no appreciable effect on survival and development timing of incubating Brook Trout eggs compared with a control group. Survival from fertilization to hatching was high for both treatment and control groups (>90%) and lower from fertilization to emergence (55%). Overall, our results suggest that standard winter operating procedures on a Lake Superior tributary had little impact on Brook Trout egg survival and development time to hatching and emergence; however, our findings also suggest that staged winter discharges would lessen the reversal of flow in the hyporheic zone and the magnitude of temperature changes experienced at Brook Trout redds.

Redds of brown trout in the deep channels of a hydroelectric power station

AbstractNatural spawning redds of brown trout were surveyed for the first time in 1−6‐m deep urban channels of a hydroelectric power station (HEP) between two lakes in Finland, by scuba diving and wading. Before damming a century ago, thousands of lake migrating trout spawners ascended through the rapids to upstream spawning areas. Between 2015 and 2018, 11 trout redds were observed at depths of 250−340 cm; these may be the deepest reported in running waters. Nine redds were found at depths of 75−230 cm. The nearest redds were situated only 55 m upstream and 110 m downstream from the HEP inflow and outflow, respectively. Channel substrate and trout redds were dominated by particle size classes 32−64, 64−128, and 16−32 mm. The risk of diving in the area increased due to the high amount of litter on the riverbed. Observations of wild trout parr by local anglers provide evidence that natural spawning produces some fish in the HEP channels.

Hydrogeochemical controls on brook trout spawning habitats in a coastal stream.

Brook trout (Salvelinus fontinalis) spawn in fall and overwintering egg development can benefit from stable, relatively warm temperatures in groundwater-seepage zones. However, eggs are also sensitive to dissolved oxygen concentration, which may be reduced in discharging groundwater (i.e., seepage). We investigated a 2 km reach of the coastal Quashnet River in Cape Cod, Massachusetts, USA, to relate preferred fish spawning habitats to geology, geomorphology, and discharging groundwater geochemistry. Thermal reconnaissance methods were used to locate zones of rapid groundwater discharge, which were predominantly found along the central channel of a wider stream valley section. Pore-water chemistry and temporal vertical groundwater flux were measured at a subset of these zones during field campaigns over several seasons. Seepage zones in open-valley sub-reaches generally showed suboxic conditions and higher dissolved solutes compared to the underlying glacial outwash aquifer. These discharge zones were cross-referenced with preferred brook trout redds and evaluated during 10 years of observation, all of which were associated with discrete alcove features in steep cutbanks, where stream meander bends intersect the glacial valley walls. Seepage in these repeat spawning zones was generally stronger and more variable than in open-valley sites, with higher dissolved oxygen and reduced solute concentrations. The combined evidence indicates that regional groundwater discharge along the broader valley bottom is predominantly suboxic due to the influence of near-stream organic deposits; trout show no obvious preference for these zones when spawning. However, the meander bends that cut into sandy deposits near the valley walls generate strong oxic seepage zones that are utilized routinely for redd construction and the overwintering of trout eggs. Stable water isotopic data support the conclusion that repeat spawning zones are located directly on preferential discharges of more localized groundwater. In similar coastal systems with extensive valley peat deposits, the specific use of groundwater-discharge points by brook trout may be limited to morphologies such as cutbanks, where groundwater flow paths do not encounter substantial buried organic material and remain oxygen-rich.

Fine-Scale Characteristics of Fluvial Bull Trout Redds and Adjacent Sites in Rapid River, Idaho, 1993–2007

From 1993 to 2007, we used single pass, September surveys to locate and measure fluvial bull trout (Salvelinus confluentus) redds in Rapid River, Idaho. Here we describe substrate sizes, redd dimensions, and water depths, velocities, and temperatures within and adjacent to 337 redds. Most (79%) spawning sites had fewer than 20% surface fines (< 2 mm) and mean, annual water depths and velocities ranged from 14.2–23.0 cm and 11.6–30.5 cm s-1, respectively. Mean, annual completed redd total lengths and surface areas averaged from 1.03–1.47 m and 0.37–1.07 m-2, respectively. Pea gravel (2 to < 8 mm) and gravel (8–64 mm) were dominant substrates (> 60%) in redds. Bull trout altered channel water depths and velocities during redd construction; pits averaged 5 cm deeper, leading tailspill edges 1.2 cm shallower, and tailspill crests 6.2 cm shallower than adjacent, undisturbed sites. Conversely, pit velocities averaged 2.1 cm s-1 slower, tailspill edge velocities 2.3 cm s-1 faster, and tailspill crest velocities 10.1 cm s-1 faster than adjacent sites. Mean, annual pit water temperatures ranged from 4.5 to 7.7 °C. Water depths and water velocities over undisturbed sites adjacent to bull trout redds were significantly correlated with water depths and water velocities inside completed redds. Improving our understanding of fluvial bull trout redds will increase the accuracy of redd counts, especially in streams with sympatric, fall spawning salmonids. Data describing fine-scale characteristics of redds and adjacent sites will assist efforts to conserve and restore critical bull trout spawning habitats.

Trout Redd Locations in Two Streams in the Black Hills, South Dakota, USA

This study examined the spatial and temporal characteristics of brook trout Salvelinus fontinalis and brown trout Salmo trutta redds in two sites from two creeks in the Black Hills of South Dakota, USA. Spawning began in both streams in early October and continued through mid-November. Significant spatial clustering was only observed on both Rapid Creek sites, where-as random redd development was observed in both of the sites on Box Elder Creek. Based on visual observations, brown trout redds were more abundant in Rapid Creek, where-as brook trout redds were more abundant in Box Elder Creek. Differences in redd clustering could be due to species-specific, geological, or hydrological differences between the creeks

Physical laboratory analyses of intergravel flow through brown trout redds (Salmo trutta fario) in response to coarse sand infiltration

AbstractIn the spawning environment of salmonids, the quality of the intergravel flow is an essential abiotic requirement for the survival success of incubated embryos. As one of the most frequently investigated anthropogenic environmental impacts, the enhanced mobilization of fine sediments (&lt;1 mm) and their entry into riverine ecosystems is considered as a major cause for the degradation of a variety of biological processes and habitats, including the spawning habitats of salmonids. In catchments draining crystalline bedrock, however, like the Bohemian Massif in the northern part of Austria, the excessive loading of river channels with coarse sand and fine gravel sediments (D = 1–10 mm) and less cohesive than fines is common as a consequence of altered catchment land use. Here, far less understanding exists of the mechanism and the possible implications of coarse sand infiltration on the functioning of the intergravel flow in salmonid redds. To investigate the intergravel flow hydraulics in response to coarse sand infiltration (D50 = 2 mm) in brown trout spawning redds (Salmo trutta fario) under controlled conditions, a laboratory flume experiment with three infiltration scenarios was conducted: (1) no infiltration; (2) segmental infiltration; and (3) full section infiltration. A more than two times drop in the average intergravel flow velocity was documented from scenario 1 (5.85 cms−1) to scenario 2 (2.53 cms−1) and another clear reduction was seen from scenario 2 (2.53 cms−1) to scenario 3 (1.61 cms−1). Moreover, in scenario 3, a clear reduction of the intergravel flow distance traveled was observed. Based on the findings we conclude that future considerations regarding the sustainable catchment management of salmonid fisheries should include programs to reduce not only the excessive entry of fines, but, in the relevant catchments, also the entry of excessive coarse sand into the riverine ecosystem. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Using Redd Attributes, Fry Density, and Otolith Microchemistry to Distinguish the Presence of Steelhead and Rainbow Trout in the Elwha River Dam Removal Project

AbstractThe removal of impassable dams can affect stream fish communities in many ways, including allowing previously separated anadromous and resident life history types to intermingle. Recolonization of steelheadOncorhynchus mykiss(anadromous Rainbow Trout) into areas that were previously occupied solely by resident conspecifics presents a challenge for monitoring because (1) staging or spawning adults may be difficult to directly observe; and (2) the offspring of the two life history forms are indistinguishable during early life. We evaluated the utility of using redd attributes, fry (age‐0) size, and fry density to distinguish the presence of steelhead and Rainbow Trout in the Elwha River, Washington. Redd area and substrate size differed between forms: steelhead redds were significantly larger and had a greater median substrate particle size than Rainbow Trout redds. Fry density was significantly higher in steelhead spawning reaches than in Rainbow Trout reaches during both survey years (2010 and 2011). Steelhead fry tended to be slightly larger than Rainbow Trout fry but not significantly so in either year. Additionally, otolith microchemical analyses indicated that all fry collected from newly colonized habitat were of steelhead maternal origin, and these fish were intermediate in size to the steelhead and Rainbow Trout fry collected prior to dam removal. Thus, fry size may not effectively differentiate parental origin despite the tendency of anadromous parents to be larger and to spawn earlier than residents. Redd attributes and fry density may be useful for evaluating the spatial distributions and relative abundances of steelhead and Rainbow Trout after dam removal. Our results have implications for other dam removal projects and other monitored species.Received April 13, 2015; accepted July 3, 2015

Multiscale hydrogeomorphic influences on bull trout (Salvelinus confluentus) spawning habitat

We investigated multiscale hydrogeomorphic influences on the distribution and abundance of bull trout (Salvelinus confluentus) spawning in snowmelt-dominated streams of the upper Flathead River basin, northwestern Montana. Within our study reaches, bull trout tended to spawn in the finest available gravel substrates. Analysis of the mobility of these substrates, based on one-dimensional hydraulic modeling and calculation of dimensionless shear stresses, indicated that bed materials in spawning reaches would be mobilized at moderate (i.e., 2-year recurrence interval) high-flow conditions, although the asynchronous timing of the fall–winter egg incubation period and typical late spring – early summer snowmelt high flows in our study area may limit susceptibility to redd scour under current hydrologic regimes. Redd occurrence also tended to be associated with concave-up bedforms (pool tailouts) with downwelling intragravel flows. Streambed temperatures tracked stream water diurnal temperature cycles to a depth of at least 25 cm, averaging 6.1–8.1 °C in different study reaches during the spawning period. Ground water provided thermal moderation of stream water for several high-density spawning reaches. Bull trout redds were more frequent in unconfined alluvial valley reaches (8.5 versus 5.0 redds·km−1 in confined valley reaches), which were strongly influenced by hyporheic and groundwater – stream water exchange. A considerable proportion of redds were patchily distributed in confined valley reaches, however, emphasizing the influence of local physical conditions in supporting bull trout spawning habitat. Moreover, narrowing or “bounding” of these alluvial valley segments did not appear to be important. Our results suggest that geomorphic, thermal, and hydrological factors influence bull trout spawning occurrence at multiple spatial scales.

Artificial steps mitigate the effect of fine sediment on the survival of brown trout embryos in a heavily modified river

Summary Understanding the factors that determine successful salmonid embryo incubation in the many structurally modified river systems of the Northern Hemisphere is crucial for maintaining healthy salmonid populations. In this context, the joint impact of fine sediment accumulation together with anthropogenic river modifications on salmonid embryo survival has been rarely investigated. We investigated brown trout embryo survival to hatch (STH) together with ten physicochemical, hydraulic and morphological parameters in artificial brown trout redds in a heavily modified stream (i.e. channelized, artificial log steps) in central Switzerland. We were interested to understand whether (i) STH is more sensitive to the timing and duration of low oxygen rather than a mean oxygen concentration, (ii) STH was negatively affected by increased fine sediment deposition decreasing redd gravel permeability, (iii) higher water levels, causing fine sediment resuspension, benefit STH, (iv) STH was negatively affected by organic content in the redds and especially (v) hydraulic gradients related to redd scale bed‐form and/or the artificial step structure benefit embryo STH, and hence could mitigate the negative impact of fine sediment and/or organic content. Up to 50%, brown trout embryos survived with interstitial oxygen exceeding 3 mg L−1. Embryos endured up to 6 days ≤ 1 mg L−1 but were more sensitive to oxygen depletion close to hatch. Therefore, timing and duration of low oxygen were important for embryo STH, and hence, oxygen dynamics need to be considered when assessing in redd conditions for salmonid STH. Partial least squares regression identified the horizontal hydraulic gradient, Fredle index, distance to artificial log steps upstream and amount of accumulated fine sediment as influential predictors for embryo STH. The water level above the redd and total organic carbon content in the redd were not influential. Among the identified influential predictors, 70.9% of the variation in STH could be explained by a logistic regression model containing redd distance to the next upstream step (26.4%, P = 0.004), Fredle index (27.2%, P = 0.003) and horizontal hydraulic gradient (10.1%, P = 0.04). In the logistic regression, the amount of accumulated fine sediment (P = 0.75), field seasons (P = 0.93) and field sites (P = 0.66) was non‐significant. In summary, brown trout STH was sensitive to redd gravel permeability, which was measured as Fredle index and affected by fine sediment deposition. At the same time, hydraulic gradients related to artificial log steps, which enhanced hyporheic exchange, benefited embryo STH, and hence mitigated fine sediment impact. This result can be probably transferred to other surface water‐dominated river systems with good hyporheic water quality. To what extent it can be transferred to river systems with other hydraulic boundary conditions remains to be evaluated. Altogether, our results clearly indicate that the impact of fine sediment on salmonid incubation success needs to be understood in the hydrological and morphological context of the particular river system.

Impact of Reservoir Elevation during the Spawning Season on the Distribution of Bull Trout Redds

AbstractAdfluvial Bull Trout Salvelinus confluentus reside in Chester Morse Lake (CML), a major reservoir in the City of Seattle water supply system on the central west slope of the Cascade mountain range, Washington. Annual surveys over a 12‐year period (2000–2011) were used to investigate the spatial distribution of adfluvial Bull Trout redds in river systems of CML relative to reservoir elevation. Because reservoir elevations were lower in the spawning season than during the incubation period, some redds placed in river reaches near the reservoir were vulnerable to cumulative effects from impending inundation as reservoir levels increased and as fine sediments settled across gravel substrates. Higher average elevation of CML during the peak period of spawning caused significantly lower percentages of Bull Trout redds in lowermost river reaches, where fluctuating water levels could adversely affect incubating eggs (R 2 = 0.73). Annually, the proportion of redds distributed within habitat reaches where inundation, as indicated by mean CML elevation during the incubation period, could affect them, varied from 1% to 18%. However, a greater proportion of annual Bull Trout redds (10–68%) fell within the maximum reservoir elevation during the incubation period. These results suggest that maintaining moderate reservoir elevations during the spawning season and holding the reservoir near this elevation through the incubation period can lower the effect on incubating Bull Trout redds. The implications for water level management to benefit adfluvial Bull Trout derived from this data set could also be applicable in similar systems, especially where knowledge of temporal and spatial distribution of salmonid spawning is available.Received November 13, 2012; accepted June 17, 2013

Fall synchrony between leaf color change and brook trout spawning in the Laurentides Wildlife Reserve (Québec, Canada) as potential environmental integrators

Fall biological processes are driven by a combination of environmental factors, with cumulative effects over the length of the growing season, which are currently difficult to model. This study evaluated if leaf color change in fall (i.e., leaf yellowing) and brook trout spawning could be two biological processes that are synchronized at a regional scale and if leaf yellowing could be used to determine the peak of spawning activity of this species. To this end, we surveyed 551 brook trout redds and examined 193 digital images of forest trees in the Laurentides Wildlife Reserve (Québec, Canada) over the fall season. Results showed that leaf yellowing and brook trout spawning were synchronized, providing one of the first examples of temporal matching between freshwater and terrestrial biological processes at the regional scale. Considering the difficulty of monitoring the phenology of freshwater fish spawning at high spatial and temporal resolution, terrestrial integrators of environmental conditions, such as leaf color change, may prove to be promising predictors of spawning activity in the management of fish populations.

An Evaluation of Redd Counts as a Measure of Bull Trout Population Size and Trend

AbstractThe use of redd counts to monitor abundance and trend of bull trout Salvelinus confluentus has been clouded by uncertainties concerning measurement error, life history variation, and correspondence of redd counts to adult population size. We compared census redd counts with population estimates of mature females for a migratory fluvial population of bull trout (primarily ≥ 300 mm fork length) and for a population of small (&lt;200 mm), likely resident, bull trout. We also compared the measurement error of the experienced surveyors who conducted the redd counts to that of a group of inexperienced surveyors. Although the regression of redd counts on adult females for the migratory population was statistically significant, a large proportion of the variation in the relationship was unexplained (r 2 = 0.47). Despite that variation, redd counts accurately reflected a greater than 50% decline in the population over 10 years; however, 5‐year trends in redd counts could be misleading. Power analysis parameterized by using the variation in the number of females per redd and measurement error of experienced surveyors indicated that minimum declines of 44–56% or increases of 78–118% over 10–15 years would be necessary for detection using traditional statistical criteria. Geometric mean abundance of migratory adults derived from redd counts and adults‐per‐redd values from the present study and published averages were similar to measured adult numbers in most cases. For both migratory and resident populations, redd counts by experienced surveyors were substantially more accurate and precise than those by inexperienced surveyors. Counts of migratory bull trout redds were more accurate and precise than counts of resident bull trout redds, which were significantly smaller and consistently underestimated. Thus, bull trout redd counts can be used to estimate abundance levels and to detect substantial longer‐term changes in abundance, particularly for migratory populations. However, the reliability of the counts depends on the skill of the surveyors.Received April 4, 2011; accepted August 8, 2011

A high‐resolution hydrodynamic investigation of brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) redds

AbstractHigh‐resolution velocity measurements were taken over a series of redds on a gravel‐bed stream using a Pulse Coherent Acoustic Doppler Profiler (PCADP) to quantify the hydrodynamics of brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) redds. On redds studied, over 4500 velocity measurements per redd were acquired per day to quantify the flow velocity, flow depth and related fluid mechanics metrics of Reynolds numbers, Froude numbers and turbulent kinetic energy per unit area. Results showed that velocity and Froude numbers varied widely at the redd scale, but consistently showed higher velocities and Froude numbers over the tailspill regions relative to the surrounding study limits. Results of Reynolds numbers calculations showed no apparent correlations to spawning location preference and redd structure. Turbulent kinetic energy per unit area consistently demonstrated a strong correlation with redd locations. The metric maintained low values (i.e. unidirectional flow with little turbulence) where all redds and attempted redds were observed. The study also demonstrates that a number of hydraulic metrics and several spatial scales will likely be necessary to understand any inherent relationship between river hydraulics and redd placement. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Potential negative impacts of introduced rainbow trout on endangered Sakhalin taimen through redd disturbance in an agricultural stream, eastern Hokkaido

Nomoto K, Omiya H, Sugimoto T, Akiba K, Edo K, Higashi S. Potential negative impacts of introduced rainbow trout on endangered Sakhalin taimen through redd disturbance in an agricultural stream, eastern Hokkaido. Ecology of Freshwater Fish 2010: 19: 116–126. © 2009 John Wiley &amp; Sons A/SAbstract – Sakhalin taimen (Hucho perryi) populations have decreased in Hokkaido, northernmost Japan, primarily because of overexploitation and habitat degradation. Here we document another threat to this species, that of spawning redd superimposition by artificially introduced rainbow trout (Oncorhynchus mykiss). Sakhalin taimen and rainbow trout are the only spring‐spawning salmonid species in Hokkaido. In 2006–2008, spawning activities of both these species were observed in a Hokkaido stream, and it was determined that their spawning periods overlapped during mid‐late April. They also spawned at similar water velocities, depths and substrate compositions. Although female Sakhalin taimen were larger than female rainbow trout, their egg burial depths were nearly identical. During the observation period, rainbow trout redds were approximately five times more abundant than Sakhalin taimen redds, and about 30% of the observed Sakhalin taimen redds were superimposed by rainbow trout redds. The high degree of spatial and temporal overlap in spawning, the similar egg burial depths of both species, and the high proportion of superimposed redds suggest that the introduced rainbow trout impact the endangered Sakhalin taimen in Hokkaido, and possibly, in other areas where the two species occur together.

Cattle Trampling of Simulated Bull Trout Redds

AbstractListing of the bull trout Salvelinus confluentus under the Endangered Species Act and concerns over livestock stepping on bull trout redds have led many U.S. Department of Agriculture Forest Service managers to remove livestock from bull trout spawning areas once spawning begins. While this policy has extensive ramifications for livestock producers who graze their cattle on national forests, a lack of data precludes evaluation of the benefit of livestock removal to bull trout populations. To fill this information gap, we assessed the probability that cattle would step on simulated bull trout redds in grazing allotments within the Little Lost River drainage in Idaho. Bull trout redds were simulated using clusters of clay shooting targets. Simulated redds were placed in streams within three grazing pastures where bull trout have historically spawned or currently spawn. During the 14–21‐d grazing period, 15–83% of the simulated redds were affected by trampling. When the control period was standardized to the same time period as the treatment, cattle were found to be responsible for affecting 12–78% of simulated redds and breaking 6–49% of the clay targets. Impacts were higher in pastures where cattle stocking intensity was higher, but impacts were also determined by site conditions adjacent to the simulated redds.

Impact of Didymosphenia geminata on hyporheic conditions in trout redds: reason for concern?

Didymosphenia geminata (Lyngbye) Schmidt (commonly called didymo) is an invasive diatom and of concern to fisheries managers in North America and more recently New Zealand. Didymo grows in thick mats in several river systems on the South Island of New Zealand, often smothering entire river beds. Salmonid eggs, deposited in gravel nests (redds), depend on constant water exchange across the riverbed to provide oxygen-rich water for development. Thick didymo mats might restrict the flow of oxygen-rich water into spawning gravels, resulting in increased egg mortality and reduced trout recruitment. The present study measured hyporheic hydraulic conditions in trout redds with varying didymo cover in the Clutha River catchment, South Island, New Zealand. Didymo cover had no significant effects on several hydraulic variables (flow into the substrate, hydraulic conductivity and hyporheic oxygen concentration). However, there was a significant difference in the potential surface water–groundwater exchange between sites, suggesting some effect of didymo on hydraulic conditions. Considering the limited number of replicates, the impact of didymo on trout redds in the Clutha River cannot be excluded. The present study highlights the need for further research on the possible effects of didymo on important surface water–groundwater exchange processes.

Increasing experimental approaches in stream trout research – 1987–2006

Abstract – This review of stream trout research literature for the 1987–2006 period covered &gt;1300 papers dealing with 22 relevant topics, when compared with &lt;400 papers on 18 topics in the previous one (1967–1986). The percentage of experimental approaches here quantified for both research reviews was 18% in the 1967–1976 period, increased to 21% in 1977–1986, to 39% in 1987–1996, and up to 43% in 1997–2006. Particular journals in the recent two decadal period published high percentages of experimental papers (The Journal of Animal Ecology and Canadian Journal of Fisheries and Aquatic Sciences; 62.9% and 62.4%, respectively), others, intermediate percentages (Nordic Journal of Fisheries Research, Transactions of the American Fisheries Society, North American Journal of Fisheries Management and Ecology of Freshwater Fish: 44.1%, 42.4%, 40.5%, and 35.6%, respectively); the remainder covered ≤33%. Research papers on stream ‘trouts’ published over the last two decades were classified into 22 subject areas for nine major journals separately and combined for 55 other journals. Subject areas dealing with the biology and ecology of trout redds, egg development, alevin emergence and onto fry and parr were the most heavily reported in nine major journals, as well as in all other journals combined. Habitat characteristics and cover use by trout were the next. Atlantic salmon and brown trout were the species with highest publication coverage in nearly all subject areas, with low coverage for all salvelinid (charr) species except brook charr. Research on Atlantic salmon in the UK used experimental approaches in nearly 60% of publications and in mid to high 30% for those on Atlantic salmon and brown trout in Scandinavian countries. Consideration is given to future research needs for stream trouts.

Temporal and spatial variation in quality of hyporheic water in one unregulated and two regulated boreal rivers

AbstractThis study describes the temporal and spatial variations in hyporheic water quality in three boreal rivers, the River Tobyälven, an unregulated river, the river Mangälven, a regulated river with a minimum discharge requirement and the river Järperudsälven, a regulated river without any minimum discharge requirements. A total of 43 permanent piezometers were used to measure dissolved oxygen (DO), temperature, electrical conductivity, pH, NO and NH in the hyporheic water at 150 mm and 300 mm depth, at monthly intervals from October 2001 to October 2002. Another seven piezometers were installed in brown trout redds and monitored during the incubation period, from December 2001 to April 2002. In the river Tobyälven, temporal patterns in hyporheic water chemistry correlated to variations in surface water chemistry and discharge. In the river Järperudsälven, the hyporheic water chemistry did not correlate to discharge or surface water chemistry. In the river Mangälven, the water chemistry was dominated by releases from a large upstream lake, and there were weak correlations between surface water chemistry and hyporheic water chemistry at some sites. The incubation conditions for brown trout eggs were most favourable in the unregulated river, characterized by high DO levels that remained high throughout the incubation period. In the river Järperudsälven the DO levels were variable during spawning, and then gradually declined to critically low levels during incubation, whereas in the river Mangälven the DO conditions were intermediate and stable. Thus we observed a stronger coupling between surface water conditions and hyporheic conditions, i.e. vertical connectivity, in the unregulated river than in the regulated river with minimum flow requirements, which in turn was stronger than in the river without minimum flow requirements. Copyright © 2007 John Wiley &amp; Sons, Ltd.

SAMPLING VARIABILITY AND ESTIMATES OF DENSITY DEPENDENCE: A COMPOSITE-LIKELIHOOD APPROACH

It is well known that sampling variability, if not properly taken into account, affects various ecologically important analyses. Statistical inference for stochastic population dynamics models is difficult when, in addition to the process error, there is also sampling error. The standard maximum-likelihood approach suffers from large computational burden. In this paper, I discuss an application of the composite-likelihood method for estimation of the parameters of the Gompertz model in the presence of sampling variability. The main advantage of the method of composite likelihood is that it reduces the computational burden substantially with little loss of statistical efficiency. Missing observations are a common problem with many ecological time series. The method of composite likelihood can accommodate missing observations in a straightforward fashion. Environmental conditions also affect the parameters of stochastic population dynamics models. This method is shown to handle such nonstationary population dynamics processes as well. Many ecological time series are short, and statistical inferences based on such short time series tend to be less precise. However, spatial replications of short time series provide an opportunity to increase the effective sample size. Application of likelihood-based methods for spatial time-series data for population dynamics models is computationally prohibitive. The method of composite likelihood is shown to have significantly less computational burden, making it possible to analyze large spatial time-series data. After discussing the methodology in general terms, I illustrate its use by analyzing a time series of counts of American Redstart (Setophaga ruticilla) from the Breeding Bird Survey data, San Joaquin kit fox (Vulpes macrotis mutica) population abundance data, and spatial time series of Bull trout (Salvelinus confluentus) redds count data.