Spawning tactics of summer chum salmon Oncorhynchus keta in relation to channel complexity and hyporheic exchange

Vertical hydraulic gradient, channel hydraulic, and substratum data were collected at active chum salmon redds to evaluate their influence on redd site selection in the Kwethluk River, a wandering gravel-bedded tributary of Alaska’s Lower Kuskokwim River. Two distinct summer chum salmon spawning tacitcs: primary- and off-channel groups spawning in different hydraulic and thermal environments. Channel hydraulics, ground-surface water exchanges, and bed sediment data were collected throughout the range of topographic conditions at sites occupied and unoccupied by spawners. Analyses of these data showed that redd site selection was incoherent with channel hydraulics and substratum size, when all channel types were considered. Rather, spawning was associated with the exchange of river and groundwater at four spatial scales. In primary channels, chum salmon spawned only in reaches where the regional hydraulic gradient (regional scale) promoted the penetration of river water, or downwelling, into the bed sediments. Within these reaches, primary-channel spawning was influenced by bed topography (fluvial scale) that promoted strong localized downwelling; a logit model, fitted to constituent hydraulics, discriminated between selected and unselected sites with 89 % accuracy. In contrast, spawners in off-channel habitats (flood and spring channels) selected areas of upwelling groundwater, regardless of channel hydraulics and the regional hydraulic gradient. In parafluvial flood channels, spawners selected localized upwelling associated with short groundwater flow paths (parafluvial scale). In spring channels, within the floodplain’s forested riparia (orthofluvial scale), spawners eschewed areas of localized downwelling and uniformly selected upwelling zones feeding these channels. Thus, redd selectivity differentiated two spawning tactics (groups) in this complex channel network where ground and surface water exchange is an important predictor of spawning habitat.     

Brown trout Salmo trutta redd superimposition by spawning Lampetra species in a lowland stream

Reproductive interaction between sympatric lampreys and salmonids was studied. The superimposition of brown trout Salmo trutta redds by spring-spawning river lamprey Lampetra fluviatilis and brook lamprey Lampetra planeri was examined in a small lowland stream of western Lithuania. A high superimposition rate of S. trutta redds by both L. fluviatilis (up to 83%) and L. planeri (up to 48%) was found, when the spawning intensity of Lampetra spp. was high. The occurrence of this phenomenon is the result of the overlap in the spawning habitat preferences at the reach-scale and at the microhabitat scale for the three species. One of the main requirements for Lampetra spp. spawning site selection was the negative streambed slope, an essential trait of the pool-riffle transitional zone. The structure of the salmonid redd created a considerable negative microhabitat slope suitable for Lampetra spp. spawning, which put the redds under a higher susceptibility to be superimposed. The timing of Lampetra spp. spawning overlapped closely with the emergence of S. trutta fry, suggesting a probable ecological effect of superimposition on S. trutta in the pre-emergent and emerging stages.     

Elevated summer temperatures delay spawning and reduce redd construction for resident brook trout (Salvelinus fontinalis)

Redd (nest) surveys for resident brook trout (Salvelinus fontinalis) were conducted annually in a mountain lake in northern New York for 11 years with multiple surveys conducted during the spawning season in eight of those years. Repeated surveys throughout the spawning season allowed us to fit an individually based parametric model and estimate the day of year on which spawning was initiated, reached its midpoint, and ended during each year. Spawning phenology was then assessed relative to (1) mean of maximum daily air temperature and (2) mean of maximum daily water temperature at the lake bottom during summer in each year using a linear model. Elevated temperatures in summer were correlated with a delay in spawning and a reduction in the total number of redds constructed. Increasing the summer mean of maximum daily air temperatures by 1 °C delayed spawning by approximately 1 week and decreased the total number of redds constructed by nearly 65. Lake spawning brook trout select redd sites based on the presence of discharging groundwater that is relatively constant in temperature within and across years, leading to relatively consistent egg incubation times. Therefore, delayed spawning is likely to delay fry emergence, which could influence emergence synchrony with prey items. This work highlights non‐lethal and sub‐lethal effects of elevated summer temperatures on native resident salmonids in aquatic environments with limited thermal refugia.     

Observations on the structure of brown trout, Salmo trutta Linnaeus, redds

This paper describes the gravel type and structure of brown trout spawning gravels in Teesdale, the flow characteristics of the spawning sites and the size of redds. Factors influencing redd size are investigated and it is concluded that female size is a major factor. Relationships are established between various redd characteristics and the fork length of female fish. The findings are discussed in relation to the existing literature concerning salmonid spawning sites.     

Biological,chemical and physical characteristics of downwelling and upwelling zones in the hyporheic zone of a north-temperate stream

Along a single stream riffle, there is a typical flow pattern in which surface water enters the hyporheic zone in a downwelling zone at the head of the riffle and hyporheic water returns to the stream surface in an upwelling zone at the tail of the riffle. Distinct patterns of physical and chemical conditions in the hyporheic zone are likely to determine patterns of microbial activity and occurrence of hyporheic fauna. Interstitial water and core samples were taken at three depths in the downwelling and upwelling zones of a single riffle in the Speed River, Southern Ontario, Canada. Physical and chemical characteristics of the hyporheic water, bacterial density, protein content, detritus content and faunal composition of the hyporheic sediment were analysed. The downwelling and upwelling zones differed significantly in temperature, pH, redox potential, dissolved oxygen and nitrate with significant positive correlations occurring among the latter three. There were no differences in bacterial density or detritus content between the two zones nor between depths in either zone, but protein content, considered to be a measure of biofilm biomass, was significantly higher in the downwelling zone. Total density of hyporheic fauna and the number of taxa decreased with increasing depth in both upwelling and downwelling zones, and were positively correlated with surface water characteristics (oxygen, temperature and nitrate), sediment protein content and detritus; however, only a weak correlation was found with zone. The composition of taxa differed between the two zones, and faunal distribution was correlated with dissolved oxygen, detritus, protein content and depth.     

Redd superimposition by introduced rainbow trout,oncorhynchus mykiss, on native charrs in a japanese stream

Spawning redd superimposition of introduced, spring-spawning rainbow trout,Oncorhynchus mykiss, on native, fall-spawning Dolly varden,Salvelinus malma, and white-spotted charr,S. leucomaenis, were examined in a small stream in Hokkaido, Japan. The stream reaches in which Dolly Varden and white-sported charr redds were observed in fall 1997 greatly overlapped with the reaches in which rainbow trout redds were recorded in spring 1998. Spawning microhabitats were also similar between trout and the two charr species. Thirteen and 3% of Dolly Varden and white-spotted charr redds, respectively, were superimposed by rainbow trout redds. The eggs or alevins in the disturbed charr redds were potentially damaged because charrs were not likely to have emerged from the redds before the superimposition occurred. In sufficiently great abundance, introduced rainbow trout may negatively impact native charr populations by dislodging the latter’s spawning redds.     

Spatial responses of hyporheic invertebrates to seasonal changes in environmental parameters

1. Spatial relationships between hyporheic invertebrates and subsurface water flow patterns, sediment characteristics, water physicochemical parameters and several possible food sources were compared over three seasons at one site beneath a riffle. Measures of food sources included particulate organic matter (POM), bacterial activity (aerobic respiration, nitrate respiration and mineralisation of organic nitrogen) and microbial abundance. 2. Patterns of water flow changed significantly over the 9‐month study period, from predominantly upwelling beneath the entire riffle in spring, to distinct differentiation between downwelling and upwelling zones in summer and autumn. Water physicochemical parameters changed accordingly, showing gradually weaker correlations with depth and stronger correlations with zone between spring and autumn. 3. Despite these changes, depth remained the strongest predictor of invertebrate richness, density and taxon composition throughout the study period. However, invertebrate distributions were secondarily correlated with water physicochemical parameters, and a minor gradient in invertebrate distributions between downwelling and upwelling zones became stronger from spring to summer. 4. The correlations between invertebrates and physicochemical parameters changed in both magnitude and direction with season. In spring, invertebrates showed a negative correlation with surface water infiltration, whereas in summer and autumn, the correlation was positive. Correlations were strongest in summer, when interstitial dissolved oxygen concentrations were lowest. 5. No relationships were found between hyporheic invertebrates and POM, microbial abundance or activity. This suggests that at this site, proximity to the streambed surface and physicochemical variables are more important than the abundance of food in controlling invertebrate distributions.     

Effects of river flow fluctuations on groundwater discharge through brook trout,Salvelinus fontinalis,spawning and incubation habitats

The effects of short-term fluctuations in river discharge simulating a hydroelectricity peaking regime on the hydrogeological environment of the brook trout's reproductive habitats were examined. Fluctuating river levels altered shallow ( 2.5 m) groundwater pathways, chemistry, and flow potentials within the river bed at spawning and incubation sites. Rising river levels introduced river water into the bank where various degrees of mixing with groundwater occurred. Subsequent recessions of river levels increased the potentials for groundwater flow, particular in an offshore direction. The character of the river water — groundwater interaction appeared to be related to the hydrogeological nature of the river channel and adjacent catchment which varied among sites. The observations suggested hydroelectricity peaking regimes have potential negative impacts on brook trout reproduction.     

Temporal and spatial segregation of spawning in sympatric populations of Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L.

Based on data from Norwegian streams with sympatric populations of Atlantic salmon and brown trout, it is suggested that temporal segregation is the main mechanism segregating Atlantic salmon and brown trout during spawning. Peak spawning of trout was about 15 days earlier than that of salmon. Physical factors, such as water depth, water velocity and distance from the river banks segregate spawning sites of salmon and trout poorly. Gravel sizes of the redds of salmon and trout were significantly different, though with a considerable overlap, and mean egg depth of salmon and trout were 0.18 and 0.12 m, respectively, probably attributable to the different size of spawners of salmon and trout. None of the temporal or spatial parameters analysed segregate spawners of salmon and trout completely. Species determination of eggs and alevins from the redds showed no interspecific superimposition of redds. It is, therefore, concluded that low survival of hybrids after hatching does not explain the low frequency of hybrids observed in sympatric populations of salmon and trout.     

Hyporheic zone hydrology and nitrogen dynamics in relation to the streambed topography of a N-rich stream

The influence of riffle-pool units on hyporheic zone hydrology and nitrogen dynamics was investigated in Brougham Creek, a N-rich agricultural stream in Ontario, Canada. Subsurface hydraulic gradients, differences in background stream and groundwater concentrations of conservative ions, and the movement of a bromide tracer indicated the downwelling of stream water at the head of riffles and upwelling in riffle-pool transitions under base flow conditions. Channel water also flowed laterally into the floodplain at the upstream end of riffles and followed a subsurface concentric flow path for distances of up to 20 m before returning to the stream at the transition from riffles to pools. Differences in observed vs predicted concentrations based on background chloride patterns indicated that the hyporheic zone was a sink for nitrate and a source for ammonium. The removal of nitrate in the streambed was confirmed by the loss of nitrate in relation to co-injected bromide in areas of downwelling stream water in two riffles. Average stream water nitrate-N concentrations of 1.0 mg/L were often depleted to <0.005 mg/L near the sediment-water interface. Consequently, an extensive volume of the hyporheic zone in the streambed and floodplain had a large unused potential for nitrate removal. Conceptual models based mainly on studies of streams with low nutrient concentrations have emphasized the extent of surface-subsurface exchanges and water residence times in the hyporheic zone as important controls on stream nutrient retention. In contrast, we suggest that nitrate retention in N-rich streams is influenced more by the size of surface water storage zones which increase the residence time of channel water in contact with the major sites of rapid nitrate depletion adjacent to the sediment-water interface.     

Plasma steroid concentrations in relation to the reproductive cycle of cultured male Rhamdia quelen

Seepage water through a lake bottom and the layering of tight and high-permeable layers in the aquifer produce groundwater under greater pressure than the water column of the lake. This results in under-water springs and seepages. When spawning substrata were available, there was a spatial correlation between the degree of groundwater influx and the redd density of brown trout Salmo trutta . In high density spawning areas with > 100 observed redds ha⁻¹, the mean seepage water influx during spring was c . 1200 ml m⁻² min⁻¹ compared to a mean flux of 113 ml m⁻² min⁻¹ in low density spawning areas with 5–10 redds ha⁻¹.     

The Effects of an Environmental Flow Release on Water Quality in the Hyporheic Zone of the Hunter River,Australia

Environmental flow releases have been advocated as a useful rehabilitation strategy for improving river condition but assessments of their success have typically focused on surface water quality and biota. In this study, we investigated the impacts of an environmental flow release on water temperature, conductivity, dissolved oxygen, and nitrate concentrations in surface and subsurface (hyporheic) water at upwelling and downwelling zones in three sites along the Hunter River, New South Wales, Australia. We hypothesised that the flow pulse would ‘flush’ the sediments with oxygenated water, stimulating hyporheic microbial activity and nitrification, enhancing nitrate concentrations over time. Surface and subsurface samples were collected before, 7 days after, and 49 days after an environmental flow release of 5000 Ml for a period of 3 days. No lasting effects on dissolved oxygen or conductivity were evident at most sites although dissolved oxygen declined over time at the downwelling site at Bowmans Crossing. At the downwelling zones at all sites, hyporheic nitrate concentrations declined initially following the release, but then rose or leveled off by Day 49. This initial drop in concentration was attributed to flushing of nitrate from the sediments. At two sites, nitrate concentrations had increased by Day 49 in the upwelling zones while at the third site, it fell significantly, associated with very low dissolved oxygen and likely reductive loss of nitrate. Electrical conductivity data indicate that potential inputs of agriculturally enriched groundwater may contribute to the nitrogen dynamics of the Hunter River. This study highlights the spatial heterogeneity that occurs in the hyporheic zone within and among sites of a regulated river, and emphasises the need for multiple-site surveys and an understanding of groundwater dynamics to assess physicochemical responses of the hyporheic zone to environmental flow releases.     

Brown trout spawning habitat selection preferences and redd characteristics in the Credit River, Ontario

Brown trout Salmo trutta redds in the Credit River, Ontario, were enumerated and assessed for physical, location and cover feature characteristics during the 2002 spawning season. Hydraulic habitats were classified on the basis of channel morphology and availability recorded. Combined use and availability data were used to assess habitat selection preferences and test for significant differences. Significant preferences for upstream pool and riffle habitat were found, but all available habitat types were used to some degree. Non‐preferred habitat redds were significantly larger than those located in preferred habitats and more likely to be found in association with woody debris cover. Larger redds were interpreted as indicative of larger fish. The use of non‐preferred downstream habitats by larger fish was further interpreted in the context of overwinter habitat requirements to reflect possible trade‐offs between reproductive and adult over‐winter survival requirements resulting in the selection of habitat for multiple life‐history functions. Results suggest that redd density alone should not be used to infer critical autumn habitat requirements for brown trout.     

The evolution of redd site selection in brook charr in different environments: same cue,same benefit for fitness*

1. Despite the great interest in characterising fish reproductive habitat, the relationship between the selection of a given spawning site and individual fitness has not been experimentally tested. 2. In this study, we used an in situ experimental approach to determine (i) the relative contribution of substrate characteristics as well as hydrological and physicochemical variables to small‐scale redd site selection by brook charr, Salvelinus fontinalis (Mitchill) and (ii) if hatching and emergence success, used as a surrogate of fitness, are improved in selected compared to non‐selected sites in both lake and stream habitats. 3. Our results show that upwelling groundwater flow was always significantly higher in selected than in non‐selected sites in both lake and stream habitats. We found no significant difference in the mean geometric substrate diameter and no consistent differences in substrate composition between selected and non‐selected sites. Oxygen concentration was higher (significantly so in three of four comparisons) and conductivity tended to be lower in selected than in non‐selected sites, while temperature showed no significant or consistent variations. We found a significant positive relationship between the selection of a given spawning habitat and hatching and emergence success in these systems. 4. These results show that the main cue that brook charr use to select their spawning sites is upwelling groundwater in lake and stream habitats, and that active selection of these sites increases individual fitness. This suggests that natural selection acted on the same cues in lentic and lotic environments; this could have been highly adaptive in a species that used both habitats as colonisation routes after the last glaciation.     

Spawning success in Atlantic salmon (Salmo salar L.): a long-term DNA profiling-based study conducted in a natural stream

Spawning success of Atlantic salmon (Salmo salar L.) was investigated, under near-natural conditions, in the Girnock Burn, an 8-km long tributary of the River Dee in Scotland. Employing minisatellite-based DNA profiling, mating outcomes were resolved over three spawning seasons by assigning parentage to progeny samples removed from spawning nests ('redds'). While individual spawning patterns differed markedly, consistent trends were present over the 3 years studied. Multiple spawning was found to be prevalent. More than 50% of anadromous spawners of both sexes contributed to more than one redd. Up to six redds for a single female and seven for a single male were detected. Both sexes ranged extensively. Distance between redds involving the same parent varied from a few metres to > 5 km. Distances > 1 km were common. Both males and females ranged to a similar extent. Range limit was not correlated to fish size. Pairs were not monogamous, both males and females mating with different partners at different sites. Size assortative mating was apparent among 1991 spawners but was not detected for 1992 or 1995. Redd superimposition was found to be common (17-22% of redds over the 3 years), although it was not correlated to the number of anadromous spawners present. High levels of nonanadromous mature parr mating success (40-50% of total progeny sampled) were recorded, and these likely contribute greatly to the effective population size. The relevance of these findings at the individual and population level is discussed, with particular reference to management implications.     

Benthic and hyporheic macroinvertebrate distribution within the heads and tails of riffles during baseflow conditions

The distribution of lotic fauna is widely acknowledged to be patchy reflecting the interaction between biotic and abiotic factors. In an in situ field study, the distribution of benthic and hyporheic invertebrates in the heads (downwelling) and tails (upwelling) of riffles were examined during stable baseflow conditions. Riffle heads were found to contain a greater proportion of interstitial fine sediment than riffle tails. Significant differences in the composition of benthic communities were associated with the amount of fine sediment. Riffle tail habitats supported a greater abundance and diversity of invertebrates sensitive to fine sediment such as EPT taxa. Shredder feeding taxa were more abundant in riffle heads suggesting greater availability of organic matter. In contrast, no significant differences in the hyporheic community were recorded between riffle heads and tails. We hypothesise that clogging of hyporheic interstices with fine sediments may have resulted in the homogenisation of the invertebrate community by limiting faunal movement into the hyporheic zone at both the riffle heads and tails. The results suggest that vertical hydrological exchange significantly influences the distribution of fine sediment and macroinvertebrate communities at the riffle scale.     

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.     

Effects of fish farm effluents on egg-to-fry development and survival of brown trout in artificial redds

Egg-to-fry development and survival of brown trout Salmo trutta were compared in two rivers of the Pyrenean piedmont, the Nive d'Arnéguy, with few human activities, and the Nive des Aldudes, with many anthropogenic activities including 11 fish farms and two sewage treatment plants (STPs). Survival was estimated between spawning (early December) and emergence time (early March) by means of capsules, 7 cm³ in volume, filled with green eggs then inserted into the gravel of artificial redds at spawning sites. In the Nive des Aldudes, three sets of conditions were studied: a fish farm near the springs, a fish farm and an STP in a village, and a series of fish farms and an STP in a village. In each situation, two artificial redds were created upstream and two others downstream from the fish farms. In the Nive d'Arnéguy, four sites were equipped: each of the two downstream sites with two artificial redds, and the two upstream sites with one redd. Substratum characteristics (proportion of fine particles) and the quality of surface and interstitial water (oxygen content, ammonia and nitrite nitrogen) were periodically measured. There was no redd substratum difference between sites upstream and downstream of fish farms. Survival to fry emergence was higher in the Nive d'Arnéguy (63·5%) than in the Nive des Aldudes (47·7%). In this latter river, the nitrogen released from the STPs was 0·5% that from fish farms. Fish farming impaired survival close to fish farm effluents (31·6%), as compared to survival upstream (63·6%), and induced a development delay during the yolk-sac fry stage. These differences were mainly linked to a drop in the dissolved oxygen content in interstitial water induced by the nitrogen flow in surface and interstitial waters.     

Responses of Hyporheic Meiofauna to Habitat Manipulation

Interactions between interstitial meiofauna and physicochemical parameters of the hyporheic zone were examined via an in situ experiment on the Speed River, Ontario. The manipulation comprised reversing upwelling and downwelling zones at the riffle scale, and was maintained for 1 month. Significant differences in physicochemical parameters were detected between zones and between treatments (control vs. manipulated). Depth-related variables, such as sediment particle size, were most important in structuring the hyporheic community during pre- and post-manipulation phases. Flow reversal was largely successful, with more significant changes occurring in the original downwelling zone. For example, change from downwelling to upwelling resulted in decreased larval chironomid dominance but an increase in the numbers of oligochaetes, nematodes, mites, and copepods. However, under field conditions, it was difficult to keep other variables, such as water temperature, constant and some of these may have contributed to the changes seen in the meiofauna.     

Responses of hyporheic invertebrate assemblages to large-scale variation in flow permanence and surface–subsurface exchange

1. Flow permanence (the proportion of time that flowing water is present) strongly influences benthic invertebrate assemblages in ephemeral and intermittent river reaches. Effects of varying flow permanence on hyporheic invertebrate assemblages are not well understood, and have not previously been studied at large spatial scales. 2. We used a 52‐km long flow‐permanence gradient in the alluvial Selwyn River, New Zealand to assess hyporheic assemblage responses to variation in flow permanence and surface–subsurface exchange. The Selwyn mainstem consists of perennial and temporary reaches embedded in longer downwelling (losing) and upwelling (gaining) sections. 3. We predicted that hyporheic invertebrate diversity, density and assemblage stability would increase with increasing flow permanence. We further predicted that assemblage structure would be influenced by the relative contribution of downwelling and upwelling water at the reach‐scale. 4. Hyporheic invertebrates were collected at 15 river cross‐sections over a 13‐month period. As predicted, hyporheic taxon richness, density and assemblage stability varied directly with flow permanence. The distribution of taxa along the flow permanence gradient appeared to be related to desiccation resistance. However, it is possible that proximity to colonist sources also contributed to distribution patterns. 5. Taxon richness was significantly higher at sites in the gaining section compared with the losing section. Sites with high flow permanence in the gaining and losing sections supported distinct hyporheic assemblages, characterised by amphipods and isopods in the gaining section, and ostracods, Hydra sp. and the mayfly Deleatidium spp. in the losing section. 6. Results of the study suggest an expansion of the scope of the Hyporheic Corridor Concept to include large hyporheic flowpaths associated with unbounded alluvial plains rivers. Hyporheic assemblages in alluvial rivers are strongly influenced by large‐scale flow permanence gradients, large‐scale surface water–groundwater exchange, and their interactions.