Diet Composition and Feeding Periodicity of Wild and Hatchery Subyearling Chinook Salmon in Lake Ontario

Diel feeding periodicity, daily ration, and diet composition of wild and hatchery subyearling Chinook salmon Oncorhynchus tshawytscha were examined in Lake Ontario and the Salmon River, New York. The diet of wild riverine salmon was composed mainly of aquatic invertebrates (63.4%), mostly ephemeropterans (25.8%), chiromomids (15.8%), and trichopterans (8.3%). The diet of riverine Chinook was more closely associated with the composition of drift samples rather than bottom samples, suggesting mid-water feeding. In Lake Ontario terrestrial invertebrates were more important in the diet of hatchery Chinook (49.0%) than wild salmon (30.5%) and diet overlap between hatchery and wild salmon was low (0.46%). The diet of both hatchery and wild Chinook salmon was more closely associated with the composition of mid-water invertebrate samples rather than benthic core samples, indicating mid-water and surface feeding. Hatchery Chinook salmon consumed significantly less food (P < 0.05) than wild Chinook salmon in the lake and in the river, and wild salmon from Lake Ontario consumed more food than wild salmon in the Salmon River. Peak feeding of wild Chinook salmon occurred between 1200–1600 hours in Lake Ontario and between 1600–2000 hours in the Salmon River; there was no discernable feeding peak for the hatchery Chinook in Lake Ontario. Hatchery Chinook salmon also had the least diverse diet over the 24-hour sample period. These results suggest that at 7 days post-stocking hatchery Chinook salmon had not yet fully adapted to their new environment.     

Evaluation of δD and δ18O as natural markers of invertebrate source environment and dispersal in the middle Mississippi River‐floodplain ecosystem

Movement of invertebrates among large rivers, tributaries, and floodplain lakes or dispersal of adult aquatic insects from riverine or floodplain habitats may provide important subsidies to food webs in receiving habitats. Intensive sampling at habitat interfaces and artificial labelling are two approaches to assess freshwater invertebrate dispersal, but these are difficult to implement at a landscape scale. Natural chemical tracers have been used to track dispersal of fishes and marine invertebrates, but the potential applicability of stable isotope ratios as natural tracers of invertebrate dispersal in freshwater environments has not been assessed. We evaluated stable hydrogen and oxygen isotopes (δD and δ¹⁸O) as natural markers of source environment and dispersal of macroinvertebrates in the middle Mississippi River, tributaries and floodplain wetlands. Water and invertebrates were collected from 12 sites during 2007–2008. Water δD and δ¹⁸O differed among the river, its tributaries, and floodplain wetlands and were strongly correlated with invertebrate δD and δ¹⁸O. Variability in invertebrate δ¹⁸O rendered it ineffective as an indicator of invertebrate source environment. Mean δD of Mississippi River invertebrates differed from δD of invertebrates from floodplain wetlands; δD distinguished invertebrates from these two environments with >80% accuracy. Neither δD nor δ¹⁸O of aquatic insects changed following emergence from their natal site. Preservation method (ethanol or freezing) did not affect invertebrate δD or δ¹⁸O. Invertebrate δD may be a useful natural tracer of natal environment and dispersal in the Mississippi River‐floodplain ecosystem and other freshwater systems where spatial variation in water δD is present. Copyright © 2010 John Wiley & Sons, Ltd.     

Flow and spawning habitat relationships for Dolly Varden: Understanding habitat–population dynamics in the Canadian Western Arctic

Northern form Dolly Varden (Salvelinus malma malma) have been designated as a species of Special Concern in Canada due to declines in population abundance and potential threats. Concern over detrimental effects of low flows on population abundance prompted research on how variability in discharge regimes influence habitat availability. Habitat suitability indices for prespawning and spawning adult anadromous Dolly Varden from two streams were integrated into a two‐dimensional hydrodynamic habitat model to assess the effect of flow variability on usable habitat. Regional hydrographs were used to identify an ecologically relevant range of flows that provided optimal spawning habitat for these populations and examine the relationship between abundance and discharge. Adults spawned in the tail end of pools at moderate water depths and water velocities, and used pebble‐ to cobble‐sized substrate for building redds; whereas, prespawning adults occupied deeper pools with moderate velocities and used cobble for cover. Model outputs showed that spawning habitat availability was optimized at flow rates between 1.6 and 3.0 m³/s and between 1.0 and 6.0 m³/s in Fish Hole Creek (FHC) and Little Fish Creek, respectively. A positive relationship between flows during the fall spawning period and abundance of the FHC population suggests that higher flows coinciding with optimal habitat availability may have contributed to positive recruitment. To strengthen and refine this habitat–population relationship for Dolly Varden in this area requires investigation of a broader suite of variables associated with environmental regimes and physical habitat in reaches used for spawning.     

Habitat use by subyearling Chinook and coho salmon in Lake Ontario tributaries

The habitat use of subyearling Chinook salmon (Oncorhynchus tshawytscha) and coho salmon (Oncorhynchus kisutch) was examined in three tributaries of Lake Ontario. A total of 1781 habitat observations were made on Chinook salmon (698) and coho salmon (1083). During both spring and fall, subyearling coho salmon used pool habitat with abundant cover. During spring, principal component analysis revealed that water depth was the most important variable governing subyearling Chinook salmon habitat use. Substrate materials used by Chinook salmon in the spring and coho salmon in the fall were significantly smaller than were present on average within the study reaches. When the two species occurred sympatrically during spring they exhibited similar habitat selection. Although the habitat used by coho salmon in Lake Ontario tributaries was consistent with observations of habitat use in their native range, higher water velocities were less important to Chinook salmon than has previously been reported.     

Decay state and inundation history control assemblage structure of log‐dwelling invertebrates in floodplain forests

Fallen timber (logs, large boughs) is recognized as having high ecological significance on forest floors. In floodplain forests, fallen timber potentially has even higher value for supporting biodiversity than upland forests because distinct faunal elements use the timber in the flooded and unflooded conditions. Invertebrates were sampled in logs of the river red gum (Eucalyptus camaldulensis Dehnh.) that had been inundated 1 year earlier and compared with invertebrates in logs that had not been inundated for many years. The invertebrate fauna in river red gum logs was relatively depauperate, probably reflecting the variable, sub‐humid conditions on the floodplain. The abundance and taxon richness of invertebrates was highest in logs with greater structural complexity and heterogeneity due to extensive decay. Recent inundation slightly reduced taxon richness. The succession of log‐dwelling invertebrates was tracked though transitions between terrestrial fauna and aquatic fauna in a spring/summer flood cycle. Transition between the two faunae was rapid. Logs were colonized by aquatic invertebrates within 2 weeks of immersion by floodwaters and recolonized by terrestrial invertebrates within 4 weeks of emersion. This faunal dynamism highlights the need to consider the entire flood cycle in decisions about the management of fallen timber on floodplains for biodiversity. Copyright © 2009 John Wiley & Sons, Ltd.     

Diet complexity of Lake Michigan salmonines: 2015–2016

In Lake Michigan, the unintended introduction of invasive species (e.g., zebra mussel, Dreissena polymorpha; quagga mussel, D. rostriformis bugensis; round goby, Neogobius melanostomus) and reduced nutrient loading has altered nutrient dynamics, system productivity, and community composition over the past two decades. These factors, together with sustained predation pressure, have contributed to declines of several forage fish species, including alewife (Alosa pseudoharengus), which has dominated diets of the five primary salmonine species of Lake Michigan for the last 50 years. Salmonines that have inflexible, less complex diets may struggle if alewife declines continue. We analyzed stomach contents of salmonines collected throughout the main basin of Lake Michigan in 2015 and 2016 to investigate diet composition, diet diversity, and individual variation of alewife lengths consumed. Chinook salmon (Oncorhynchus tshawytscha) almost exclusively consumed alewife and had lower diet diversities compared to the other four species, which consumed relatively high frequencies of round goby (brown trout, Salmo trutta; lake trout, Salvelinus namaycush), aquatic invertebrates (coho salmon, Oncorhynchus kisutch) and terrestrial invertebrates (rainbow trout, Oncorhynchus mykiss) along with alewife. Although clear spatio-temporal feeding patterns existed, much of the variation in diet composition and diet diversity was expressed at the individual level. Salmonine populations consumed the entire size range of alewife that were available, whereas individual stomachs tended to contain a narrow range of alewife sizes. Due to their reliance on alewife, it is likely that Chinook salmon will be more negatively impacted than other salmonine species if alewife abundance continues to decline in Lake Michigan.     

Trophic interactions among algal blooms,macroinvertebrates, and brown trout: Implications for trout recovery in a restored river

Positive correlation between trout abundance and dissolved metal concentrations along the Upper Clark Fork River (UCFR; Montana, USA) have forced restoration practitioners to seek underlying causes of reduced fish density beyond heavy metal contamination. Throughout the river, nutrient enrichment and summer algal blooms may be hindering full recovery of trout populations. In this study, we evaluated the community structure and metal body burdens of benthic invertebrates and characterized existing trophic linkages between brown trout and dominant invertebrate taxa before and during summer algal blooms in a downstream reach of the UCFR where fish densities are low (20–30 trout/km), and where metal contamination is relevant but minimal compared with upstream. In spring, estimated invertebrate abundance was 1,727 ± 217 individuals/m² and dominated by Ephemerellidae and Baetidae families. During summer algal bloom, invertebrate abundance increased 15‐fold (20,580 ± 3,510 individuals/m²) mostly due to greater abundance of Chironomidae, Hydropsychidae, and Simulidae. Copper body burdens (130 ± 42 ppm) were higher than any other heavy metal regardless of season, but detectable concentrations of arsenic, cadmium, and lead were also found. A Bayesian mixing model combining metal burdens and stable isotopes showed that in the spring, trout of average size (355 ± 65 g) relied mostly on epibenthic taxa (Ephemerellidae and Hydropsychidae), contrasting with small (<100 g) and large (>400 g) trout relying heavily on Baetidae, a major component of invertebrate drift. Foraging segregation related to trout size did not occur during summer algal blooms, which may reflect increasing influence of benthic algal proliferation or indicate the indiscriminate use of pool habitats as thermal refugia over summer conditions by trout of different ages.     

The influence of fluctuating ramping rates on the food web of boreal rivers

A BACI (before‐after‐control‐impact) sampling design was applied to determine the possible effects of ramping rate (RR) regulation on food webs structure and function in a regulated boreal river. We used carbon and nitrogen stable isotope signatures of primary producers, macroinvertebrates and fish to determine variations in the source of carbon fuelling the food web as well as changes in the food web structure under variable RR flow regime. We hypothesized that unrestricted RR would (1) increase the connectivity between terrestrial and aquatic environments allowing for a higher contribution of terrestrial carbon to support the food web and (2) decrease food web length because of frequent disturbances. Unrestricted RR had little influence on δ¹³C values for the overall food web with most of the differences found between impacted sites compared and control sites, indicating that the proportion of various carbon sources entering the diet of consumers remained unchanged under unrestricted RR. In contrast, significantly higher δ¹⁵N values were measured in impacted sites (invertebrates and fish) and as well as under unrestricted ramping flow regime (invertebrates). Further, unrestricted RR was associated to a significant decrease in the difference between macroinvertebrates and fish δ¹⁵N signatures, equivalent to a reduction of the length of the food web by at least one trophic level. Results from this study indicate that RR should be taken into consideration in the regulation of operating regimes on rivers. Copyright © 2008 John Wiley & Sons, Ltd.     

Trophic ecology of salmonine predators in northern Lake Huron with emphasis on Atlantic salmon (Salmo salar)

Pacific salmon were introduced to the Great Lakes in the 1960s and now support major recreational fishery. Population declines resulting from invasive species have prompted agencies to consider diversifying sport fisheries through stocking. Atlantic salmon are native to Lake Ontario, but a small fishery has developed in northern Lake Huron since the 1990s that appears suited to the Lake Huron food web leading to requests for increased stocking by anglers and consideration by agencies. However, no study has evaluated the trophic ecology of Atlantic salmon in relation to other salmonine predators in northern Lake Huron. In this study, we used stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N), along with mercury (Hg) concentrations to assess resource use, niche overlap, and contaminant accumulation in Atlantic salmon compared to select Lake Huron predators. Atlantic salmon exhibited considerable niche overlap with Chinook and coho salmon but were strongly differentiated from lake trout. In addition, we observed that Atlantic salmon had similar Hg concentrations as coho but were lower than both Chinook salmon and lake trout. Based upon the relationship between fish size, δ¹⁵N, and Hg, Atlantic salmon bioaccumulate Hg similarly to Pacific salmon but likely have lower consumptive demands than Chinook salmon. Continued attention should be placed on understanding how Atlantic salmon fit into the current Lake Huron food web in order to evaluate the long-term efficacy of the Atlantic salmon stocking program.     

PERSISTING EFFECTS OF RIVER REGULATION ON EMERGENT AQUATIC INSECTS AND TERRESTRIAL INVERTEBRATES IN UPLAND FORESTS

River regulation can alter the structural complexity and natural dynamics of river ecosystems substantially with negative consequences for aquatic insects. However, there have been few studies of regulation effects on the export of emergent insects into terrestrial ecosystems. In northern Scandinavia, we compared emerged aquatic insect and terrestrial invertebrate biomass between four strongly regulated and four free‐flowing rivers using fortnightly measurements at three upland‐forest blocks in each over one summer. The biomass of emerged aquatic insects was significantly lower along regulated rivers than free‐flowing rivers. Biomass in Linyphiidae, Opiliones, Staphylinidae, total Coleoptera, Formicidae and total terrestrial invertebrates was also lower along regulated rivers. Aquatic insect biomass did not explain the entire regulation effect on terrestrial invertebrates but did explain significant variations among Linyphiidae, total Coleoptera, Formicidae and total terrestrial biomass. Variations in Formicidae also explained significant variance among several terrestrial taxa, suggesting some keystone role in this group. Overall, our results suggest that river regulation affects upland‐forest invertebrate communities, with at least some of these effects arising from links between aquatic emergence and terrestrial predators. The data highlight the need to consider areas beyond the riparian zone when assessing the effects of river regulation. Copyright © 2012 John Wiley & Sons, Ltd.     

Food habits of migrating salmonid smolts passing bonneville dam in the Columbia river, 1984

The food habits of migrating juvenile steelhead (Salmo gairdneri), sockeye salmon (Oncorhynchus nerka), coho salmon (O. kisutch), and chinook salmon (O. tshawytscha) were identified from April through August 1984 at Bonneville Dam in the Columbia River. During the spring (April-June), the gammarid amphipods Corophium salmonis and C. spinicorne were the dominant prey for all species. Many insect taxa were also consumed, but in small quantities. Significant diet overlap occurred between all species during the spring due to the importance of Corophium. In summer (July-August), the importance of Corophium declined in the diet of subyearling chinook salmon and was replaced with Daphnia spp. and adult dipterans (primarily chironomids).     

Sources of nitrogen to stream food webs in tributaries of the Red River Valley,Manitoba

Lake Winnipeg has undergone rapid eutrophication over the last several decades with a large portion of the associated nutrient loads delivered via the Red River. Consequently, subcatchments of the Red River Valley (RRV) are priorities for nutrient management, an aim that requires identification of key nutrient sources to stream food webs. We identified the primary sources of nitrogen to food webs of rural streams of the RRV, as well as variation in nitrogen input between spring and summer. We measured δ¹⁵N of particulate organic matter (POM) and collector-gatherer invertebrates collected in spring and summer from 20 subcatchments, which exhibited a range of agricultural intensity and size of municipal wastewater lagoons. δ¹⁵N values of POM and collector-gatherer invertebrates were best predicted by the presence of wastewater treatment lagoons, with δ¹⁵N values increasing with the number of people served by lagoons in spring and summer. When present, wastewater contributed a greater proportion of nitrogen to stream food webs than agricultural sources. Waste sources also had a greater relative contribution to food webs in summer than spring. Despite wastewater lagoons releasing nitrogen in short-term, pulsed discharges, the influence of wastewater on food web nitrogen persisted from the summer release into the following spring. Based on the observed importance of wastewater as a source of nitrogen to stream food webs, we recommend management agencies consider additional actions to reduce nutrient losses from wastewater treatment facilities as well as agricultural lands to more effectively protect aquatic ecosystems.     

Hyporheic invertebrate community composition in streams of varying salinity in south‐western Australia: diversity peaks at intermediate thresholds

Many streams of southwestern Australia have become secondarily saline through land clearance and other human activities in their catchments. Elevated salinities impact on aquatic biota and ecological processes of surface streams but little is known of the effects on the diversity and community composition of hyporheic (subsurface) invertebrates occupying the saturated sediments where surface and groundwaters exchange. We hypothesized that biodiversity of hyporheic invertebrates would decline with increasing salinity, especially where saline groundwater upwelled into the surface stream. We also predicted changes in community composition associated with salinity and direction of vertical hydrological exchange. Water and hyporheic invertebrates were sampled from downwelling and upwelling zones of 13 streams in southwestern Australia ranging in median surface water salinity from 0.27 to 17.86 g L⁻¹. Overall, taxa richness of hyporheic invertebrates was uncorrelated with salinity but, surprisingly, correlated positively with the salinity of upwelling water. However, when the sites were divided into ‘fresh’ (<3 g L⁻¹) and ‘mesosaline’ (>3 g L⁻¹) groups, this relationship became non‐significant. Instead, taxa richness and total abundance were correlated positively with salinity of downwelling water in fresh sites and negatively in mesosaline sites, resulting in a peak in richness at intermediate salinities. Community composition was unrelated to direction of hydrological exchange but was strongly associated with hyporheic salinity. Hyporheic assemblages of ‘fresh’ rivers were typified by harpacticoid copepods and candoniid ostracods, whereas the amphipod Austrochiltonia and several dipteran groups were more common below ‘mesosaline’ rivers. Although many hyporheic taxa collected in this study apparently have broad tolerances to salinity, secondary salinization due to human activities potentially changed community composition, possibly altering rates of ecological processes such as organic matter breakdown occurring within the sediments of streams undergoing salinization. Copyright © 2007 John Wiley & Sons, Ltd.     

Optimal sampling designs for estimating salmonid run abundances from video recordings at a fishway on the Bois Brule River,Wisconsin, a tributary to Lake Superior

Using a simulation program and video census data (2004–2018) from the Bois Brule River fishway, Wisconsin, USA, we compared alternative sampling designs to estimate spawning run abundances of steelhead, coho salmon, Chinook salmon, and brown trout. We evaluated two types of two-stage sampling designs, comprising varying numbers of days sampled within a year (1st stage samples) and varying numbers of hours sampled within a day (2nd stage samples). While days were sampled using stratified random sampling under both types of sampling designs, hours were sampled using uniform (1/24) or non-uniform (proportional to hourly runs) selection probabilities under the first and second types of sampling designs, respectively. Number of days sampled within a year, comprising three strata, varied from 30 to 200 days in 10-day increments, and number of hours sampled within a day varied from 2 to 24 h in 2-hour increments. Spawning run sizes of the salmonids could be estimated with a relative root mean square error (RMSE) of less than 10% on average by employing a two-stage sampling design with samples of 100 days·yr⁻¹ and 8 hrs·day⁻¹, i.e., 800 hrs·yr⁻¹; by contrast, full census involved reviewing 250 days·yr⁻¹ and 24 hrs·day⁻¹, i.e., 6000 hrs·yr⁻¹, of video. Sampling more days (>100) resulted in greater reductions in estimation error than sampling more hours (>8). Non-uniform (vs. uniform) selection probabilities for hours sampled slightly reduced error of estimates. Our results underscore that optimal sampling designs could ensure a considerable reduction in survey resources while maintaining relatively low error in estimation of salmonid abundances.     

The spatial arrangement of Neritina virginea (Gastropoda: Neritidae) during upstream migration in a split‐channel reach

This paper relates differences in flow hydraulics between a main channel (MC) and a side channel (SC) of a river to patterns of upstream migration by Neritina virginea (Neritidae: Gastropoda), a dominant diadromous snail in streams of Puerto Rico (Greater Antilles). Near‐bed water velocity, snail density and shell size were measured on a weekly basis between August and December 2000 along cross‐sections in a main channel (MC) and an adjacent channel (SC) under a bridge crossing of the Río Mameyes of Northeastern Puerto Rico. Near‐bed velocity and water depth were used to compute Reynolds (Re) and Froude (Fr) numbers, and to classify flows within each channel. During base flow conditions (<2 m³ s⁻¹), flow was chaotic and supercritical (Fr > 1) in the MC, and non‐chaotic and subcritical (Fr < 1) in the SC. Higher mean densities (>100 ind m⁻²) of relatively small snails (mean ± s.d., 6.3 ± 2.8 mm) were consistently recorded in the MC. Conversely, the SC had lower mean densities (<20 ind m⁻²) and significantly larger snails (7.6 ± 2.4 mm). Within the MC, migratory groups preferred near‐bed velocities > 0.8 m s⁻¹. Within the SC, they preferred the channel thalweg and depths > 30 cm. The spatial arrangement that was observed between and within the channels may be related to food resources, predation pressure or biomechanics. Characteristics of preferred upstream migration pathways of N. virginea must be accounted when building road crossings in coastal streams with diadromous fauna. Published in 2007 by John Wiley & Sons, Ltd.     

The effect of wood and temperature on juvenile coho salmon winter movement,growth, density and survival in side‐channels

In British Columbia, side‐channels have been built to compensate for lost salmonid habitat. Most are structurally simple with little in‐stream wood; however, they support high densities of juvenile coho salmon. We longitudinally divided in halves the top 100 m of two dead‐end artificial side‐channels, one side‐channel with low winter water temperatures (surface‐fed) and one with relatively higher water temperatures (groundwater‐fed), closed the downstream end of each side‐channel with two‐way traps, and treated only one half of each channel with bundles of wood. Trapped fish were marked daily and coho salmon movement, growth and smolt output were monitored for two years. Wood addition increased juvenile coho winter carrying capacity and spring smolt output only in the ‘colder’ surface‐fed side‐channel. In contrast, in the groundwater‐fed side‐channel, with relatively higher water temperatures, the wood treatment slightly reduced the channel's carrying capacity and the spring output of coho salmon smolts. Copyright © 2003 John Wiley & Sons, Ltd.     

ABUNDANCE AND BODY CONDITION OF SCULPIN (COTTUS SPP.) IN A SMALL FOREST STREAM FOLLOWING RECOLONIZATION BY JUVENILE COHO SALMON ONCORHYNCHUS KISUTCH

Recolonization by native species following reintroduction can affect resident species through a variety of processes. We examined the effects of natural recolonization by coho salmon Oncorhynchus kisutch on sculpin (Cottus rhotus and Cottus gulosus), small benthic fishes, in a small forest stream in Western Washington, USA. Provision fish passage around a small dam allowed coho access to habitat, which had been inaccessible for over 100 years. We found that density (g m^?2 and number m^?2) was unchanged, and body condition (the slope of the relationship between length and weight) of sculpin tended to increase from before relative to a 5‐year period following recolonization. The proportion of sculpin comprising the total fish assemblage decreased after coho colonization relative to before but remained stable for a 5‐year period after coho reintroduction, whereas coho density increased over fivefold. Additionally, we used Akaike's information criteria to evaluate the relative importance of physical and biological variables to predict sculpin density in pool habitats during the initial coho recolonization period. Physical microhabitat variables had little support for predicting sculpin density, whereas there was a significant support for stream temperature; cutthroat trout (Oncorhynchus clarkii) density and year were the most important predictors of sculpin density. Coho density was not significant in any model. Our results indicate coho introduction and subsequent recolonization have to date had minimal individual or population level effects on sculpin, therefore demonstrating that species reintroductions into their native range can have no measurable effect on resident organisms. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

Effects of land‐cover transitions on emerging aquatic insects and environmental characteristics of headwater streams in an agricultural catchment

Streams and their adjacent riparian zones are increasingly viewed as interdependent systems linked by reciprocal exchanges of energy, organisms, and materials. We assessed potential associations between the emerging aquatic insect flux and transitions between agricultural land and forest fragments to better understand these stream‐riparian linkages in managed landscapes. We sampled stream environmental conditions and emerging insects at 28 sites distributed along three streams flowing through agriculture‐forest‐agriculture transitions in central Ohio, USA, in the summer of 2012. Ephemeroptera and Trichoptera (ET) taxa had higher flux densities in forests (mean and 95% CI: 0.3 insects m^?2 d^?1 [0.1, 0.8]) compared to agriculture (mean and 95% CI: 0 insect m^?2 d^?1 [0, 0.1]; p = .004), and ET taxa were found in 67% of forested sites compared to only 15% of agricultural sites. In contrast, Dolichopodidae were more strongly associated with agricultural land (mean and 95% CI: 0.6 insect m^?2 d^?1 [0.3 to 1.2]) than forests (mean and 95% CI: 0.1 insects m^?2 d^?1 [0.1, 0.2]; p = .002). Although Chironomidae were the most numerically abundant, ET taxa were among the larger bodied insects and comprised >30% of the total biomass flux, illustrating the importance of taxonomic traits in mediating flux dynamics. Mechanisms driving emerging insect flux were related to substrate grain‐size distribution, channel width, and nutrient concentrations. Overall, our results demonstrate that small forest fragments are strongly related to the aquatic‐to‐terrestrial insect flux and thus have important implications for terrestrial biodiversity and food webs in agricultural landscapes.     

Ecology of an estuarine mysid shrimp in the Columbia River (USA)

The estuarine mysid, Neomysis mercedis, has colonized John Day and other run‐of‐the‐river Reservoirs of the Columbia River, over 400 km from the estuary. In John Day Reservoir N. mercedis numbers peaked (2 m^?3) in August in areas near the dam in association with lower water velocity and softer bottom than at the upstream sampling sites. Neomysis broods were primarily released in late spring and early fall. Gut content analysis showed that Neomysis feeds mostly on cladoceran zooplankton and rotifers in John Day Reservoir. Diel vertical migration was documented, with daytime distribution restricted to the bottom and preferentially to the soft‐textured sediments in the deepest areas. Common pelagic fishes in the reservoir, especially juvenile American shad (Alosa sapidissima) and chinook salmon (Oncorhynchus tshawytscha), are daytime zooplankton feeders that cannot prey on Neomysis owing to mysid diel vertical migration. Thus, Neomysis has become an important food web component in John Day Reservoir. We also collected N. mercedis further upstream in Lower Granite Reservoir, where another estuarine crustacean, Corophium salmonis, also is reported, underscoring the need to better understand the role of these estuarine invertebrates in the trophic ecology of the Columbia River. Copyright © 2006 John Wiley & Sons, Ltd.     

Rehabilitation of bedrock stream channels: the effects of boulder weir placement on aquatic habitat and biota

The placement of boulder weirs is a popular method to improve fish habitat, though little is known about the effectiveness of these structures at increasing fish and biota abundance. We examined the effectiveness of boulder weir placement by comparing physical habitat, chemical and biotic metrics in 13 paired treatment (boulder weir placement) and control reaches in seven southwest Oregon watersheds in the summer of 2002 and 2003. Pool area, the number of boulders, total large woody debris (LWD) and LWD forming pools were all significantly higher in treatment than control reaches (p < 0.05). No differences in water chemistry (total N, total P, dissolved organic carbon) or macroinvertebrate metrics (richness, total abundance, benthic index of biotic integrity etc.) were detected. Abundance of juvenile coho salmon (Oncorhynchus kisutch) and trout (O. mykiss and O. clarki) were higher in treatment than control reaches (p < 0.05), while dace (Rhinichthys spp.; p < 0.09) were more abundant in control reaches and no significant difference was detected for young‐of‐year trout (p > 0.20). Both coho salmon and trout response to boulder weir placement were positively correlated with difference in pool area; p < 0.10), while dace and young‐of‐year trout response to boulder weir placement were negatively correlated with difference in LWD (p < 0.05). The placement of boulder weirs appears to be an effective technique for increasing local abundance of species that prefer pools (juvenile coho and trout >100 mm). Based on our results and previous studies on bedrock and incised channels, we suggest that the placement of boulder structures is a useful first step in attempting to restore these types of stream channels. Published in 2006 by John Wiley & Sons, Ltd.