Rearing Habitat Research Articles

Reconciling fish and farms: Methods for managing California rice fields as salmon habitat.

Rearing habitat for juvenile Chinook Salmon (Oncorhynchus tshawytscha) in California, the southernmost portion of their range, has drastically declined throughout the past century. Recently, through cooperative agreements with diverse stakeholders, winter-flooded agricultural rice fields in California’s Central Valley have emerged as ecologically functioning floodplain rearing habitat for juvenile Chinook Salmon. From 2013 to 2016, we conducted a series of experiments examining methods to enhance habitat benefits for fall-run Chinook Salmon reared on winter-flooded rice fields in the Yolo Bypass, a modified floodplain managed for flood control, agriculture, and wildlife habitat in the Sacramento River Valley of California. Investigations included studying the effect of 1) post-harvest field substrate; 2) depth refugia; 3) duration of field drainage; and 4) duration of rearing occupancy on in-situ diet, growth and survival of juvenile salmon. Post-harvest substrate treatment had only a small effect on the lower trophic food web and an insignificant effect on growth rates or survival of rearing hatchery-origin, fall-run Chinook Salmon. Similarly, depth refugia, created by trenches dug to various depths, also had an insignificant effect on survival. Rapid field drainage yielded significantly higher survival compared to drainage methods drawn out over longer periods. A mortality of approximately one third was observed in the first week after fish were released in the floodplain. This initial mortality event was followed by high, stable survival rates for the remainder of the 6-week duration of floodplain rearing study. Across years, in-field survival ranged 7.4–61.6% and increased over the course of the experiments. Despite coinciding with the most extreme drought in California’s recorded history, which elevated water temperatures and reduced the regional extent of adjacent flooded habitats which concentrated avian predators, the adaptive research framework enabled incremental improvements in design to increase survival. Zooplankton (fish food) in the winter-flooded rice fields were 53-150x more abundant than those sampled concurrently in the adjacent Sacramento River channel. Correspondingly, observed somatic growth rates of juvenile hatchery-sourced fall-run Chinook Salmon stocked in rice fields were two to five times greater than concurrently and previously observed growth rates in the adjacent Sacramento River. The abundance of food resources and exceptionally high growth rates observed during these experiments illustrate the potential benefits of using existing agricultural infrastructure to approximate the floodplain wetland physical conditions and hydrologic patterns (shallow, long-duration inundation of cool floodplain habitats in mid-winter) under which Chinook Salmon evolved and to which they are adapted.

Assessment of Juvenile Chinook Salmon Rearing Habitat Potential Prior to Species Reintroduction

AbstractSuccessful Pacific salmon reintroduction into rivers where they have been extirpated requires understanding the range of habitats and environmental conditions that currently exist and their ability to support target species. Chinook Salmon Oncorhynchus tshawytscha were extirpated from the San Joaquin River, California, over 60 years ago and are targeted for reintroduction into the system. To assess the remaining habitat along the longitudinal lower San Joaquin River gradient, juvenile Chinook Salmon were reared within an Alluvial Site, a Transitional Site, and two lowland sites (Lowland Cinnamon Slough and Lowland Eastside Bypass) during two rearing periods (early and late). The highest Chinook Salmon growth rates were observed during the early rearing period within the lowland sites when water temperatures were moderate and prey densities were greatest. However, high‐water events precluded a spatial comparison of growth with that of fish reared at the Alluvial and Transitional sites during the early period. In the late rearing period, the lowest and highest growth rates were observed at the Lowland Eastside Bypass (lowest prey abundance) and Lowland Cinnamon Slough (highest prey abundance), respectively. Growth rates at the Alluvial and Transitional sites were intermediate between those at the two lowland sites. Main‐channel (Alluvial and Transitional) growth rates were generally lower than those within the lowland sites, suggesting that main‐channel restoration may require targeted food web enhancement. Our results indicate that lowland floodplain sites can provide quality rearing habitat and growth benefits early in the rearing season. As temperatures increase, salmon can continue to grow if sufficient prey is available. Managers considering measures for improving floodplain access to provide juvenile Chinook Salmon rearing habitat should consider interactions between environmental conditions and prey density—and how these factors vary along the river continuum—to determine when these habitats can provide the greatest growth benefit.

Sampling Uncharted Waters: Examining Rearing Habitat of Larval Longfin Smelt (Spirinchus thaleichthys) in the Upper San Francisco Estuary

The southern-most reproducing Longfin Smelt population occurs in the San Francisco Estuary, California, USA. Long-term monitoring of estuarine habitat for this species has generally only considered deep channels, with little known of the role shallow waters play in supporting their early life stage. To address the need for focused research on shallow-water habitat, a targeted study of Longfin Smelt larvae in littoral habitat was conducted to identify potential rearing habitats during 2013 and 2014. Our study objectives were to (1) determine if larval densities vary between littoral habitats (tidal slough vs. open-water shoal), (2) determine how larval densities in littoral habitats vary with physicochemical and biological attributes, (3) determine if larval densities vary between littoral habitats and long-term monitoring channel collections, and (4) determine what factors predict larval rearing distributions from the long-term monitoring channel collections. Larval densities did not vary between littoral habitats but they did vary between years. Water temperature, salinity, and chlorophyll a were found important in predicting larval densities in littoral habitats. Larval densities do not vary between littoral and channel surveys; however, the analysis based on channel data suggests that Longfin Smelt are hatching and rearing in a much broader region and under higher salinities (∼2–12 psu) than previously recognized. Results of this study indicate that conservation efforts should consider how freshwater flow, habitat, climate, and food webs interact as mechanisms that influence Longfin Smelt recruitment in estuarine environments.

Assessing Juvenile Salmon Rearing Habitat and Associated Predation Risk in a Lower Snake River Reservoir

AbstractSubyearling fall Chinook salmon (Oncorhynchus tshawytscha) in the Columbia River basin exhibit a transient rearing strategy and depend on connected shoreline habitats during freshwater rearing. Impoundment has greatly reduced the amount of shallow‐water rearing habitat that is exacerbated by the steep topography of reservoirs. Periodic dredging creates opportunities to strategically place spoils to increase the amount of shallow‐water habitat for subyearlings while at the same time reducing the amount of unsuitable area that is often preferred by predators. We assessed the amount and spatial arrangement of subyearling rearing habitat in Lower Granite Reservoir on the Snake River to guide future habitat improvement efforts. A spatially explicit habitat assessment was conducted using physical habitat data, two‐dimensional hydrodynamic modelling and a statistical habitat model in a geographic information system framework. We used field collections of subyearlings and a common predator [smallmouth bass (Micropterus dolomieu)] to draw inferences about predation risk within specific habitat types. Most of the high‐probability rearing habitat was located in the upper half of the reservoir where gently sloping landforms created low lateral bed slopes and shallow‐water habitats. Only 29% of shorelines were predicted to be suitable (probability >0.5) for subyearlings, and the occurrence of these shorelines decreased in a downstream direction. The remaining, less suitable areas were composed of low‐probability habitats in unmodified (25%) and riprapped shorelines (46%). As expected, most subyearlings were found in high‐probability habitat, while most smallmouth bass were found in low‐probability locations. However, some subyearlings were found in low‐probability habitats, such as riprap, where predation risk could be high. Given their transient rearing strategy and dependence on shoreline habitats, subyearlings could benefit from habitat creation efforts in the lower reservoir where high‐probability habitat is generally lacking. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Juvenile Salmonid Utilization of Floodplain Rearing Habitat After Gravel Augmentation in a Regulated River

Gravel augmentation is used in sediment-starved streams to improve salmonid spawning habitat. As gravel is added to river channels, water surface elevations may rise in adjacent areas, activating floodplain habitat at lower flows, and floodplains inundate more frequently, potentially affecting the quantity and quality of juvenile salmonid rearing habitat. We analysed 5 years of juvenile Chinook salmon Oncorhynchus tschawytscha and steelhead Oncorhynchus mykiss data from snorkel surveys before and after gravel augmentation in the Lower American River, a low-gradient, highly regulated alluvial river in California's Central Valley. We measured the quality and quantity of rearing habitat (current velocity and areal extent of inundated riparian vegetation) following gravel placement and tested whether these factors affected juvenile abundance. Gravel augmentation increased floodplain extent by 3.7–19.8%, decreased average flow velocity from 1.6 to 0.3 m s−1 and increased the amount of vegetative cover from 0.3% to 22.6%. Juvenile abundances increased significantly for both species following augmentation. However, the strength of the relationship between abundance and habitat variables was greater for smaller salmonids. These results suggest that, in addition to enhancing salmonid spawning habitat, gravel augmentation can improve rearing habitat where channel incision and/or regulated hydrographs disconnect floodplains from main river channels. Copyright © 2015 John Wiley & Sons, Ltd.

Effectiveness of Instream Wood Treatments to Restore Stream Complexity and Winter Rearing Habitat for Juvenile Coho Salmon

AbstractLarge wood and boulder placement projects have become common in the Pacific Northwest to restore complex stream habitat for juvenile Coho Salmon Oncorhynchus kisutch and other salmonids. We evaluated habitat responses at 91 large wood restoration projects in western Oregon from pretreatment to 1 year and 6 years after treatment. Large logs were arranged in jams without cabling or burial in the bottom or banks of the stream. Projects commonly treated 0.5–1 km of stream, but some extended up to 2.3 km. Significant changes in the amounts of large wood, complex pools, and predicted Coho Salmon rearing capacity were observed within 1 year of treatment. Six years after treatment, the amount of large wood, complex pools, and Coho Salmon rearing capacity remained significantly higher than pretreatment levels by 100, 800, and 32%, respectively, and the surface area of pools and gravel increased significantly over pretreatment levels by 15% and 8%, respectively. However, the amount of large wood decreased in a majority of projects during the 6 years after treatment reflecting net export out of the sites and a lack of recruitment from upstream or local sources. Site‐specific responses in stream habitat were positive overall, but variability among sites suggested independent behavior. Responses of the restoration projects were weakly related to channel size, local lithology, or landscape cover, although retention of large wood was associated with lower gradient and coniferous forest cover. Despite the variability in project behavior, the findings indicate that large wood projects may play a role in maintaining and improving stream complexity and Coho Salmon rearing capacity in coast basins of Oregon, potentially compensating for the lack of natural recruitment of wood to the streams. Attention to location within the stream network and treatment details may improve performance of the restoration actions.

Estuarine Environments as Rearing Habitats for Juvenile Coho Salmon in Contrasting South‐Central Alaska Watersheds

AbstractFor Pacific salmon, estuaries are typically considered transitional staging areas between freshwater and marine environments, but their potential as rearing habitat has only recently been recognized. The objectives of this study were two‐fold: (1) to determine if Coho Salmon Oncorhynchus kisutch were rearing in estuarine habitats, and (2) to characterize and compare the body length, age, condition, and duration and timing of estuarine occupancy of juvenile Coho Salmon between the two contrasting estuaries. We examined use of estuary habitats with analysis of microchemistry and microstructure of sagittal otoliths in two watersheds of south‐central Alaska. Juvenile Coho Salmon were classified as estuary residents or nonresidents (recent estuary immigrants) based on otolith Sr : Ca ratios and counts of daily growth increments on otoliths. The estuaries differed in water source (glacial versus snowmelt hydrographs) and in relative estuarine and watershed area. Juvenile Coho Salmon with evidence of estuary rearing were greater in body length and condition than individuals lacking evidence of estuarine rearing. Coho Salmon captured in the glacial estuary had greater variability in body length and condition, and younger age‐classes predominated the catch compared with the nearby snowmelt‐fed, smaller estuary. Estuary‐rearing fish in the glacial estuary arrived later and remained longer (39 versus 24 d of summer growth) during the summer than did fish using the snowmelt estuary. Finally, we observed definitive patterns of overwintering in estuarine and near shore environments in both estuaries. Evidence of estuary rearing and overwintering with differences in fish traits among contrasting estuary types refute the notion that estuaries function as only staging or transitional habitats in the early life history of Coho Salmon.

Role of estuarine rearing for sockeye salmon in Alaska (USA)

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 481:211-223 (2013) - DOI: https://doi.org/10.3354/meps10190 Role of estuarine rearing for sockeye salmon in Alaska (USA) Ryan K. Simmons1,2,*, Thomas P. Quinn1, Lisa W. Seeb1, Daniel E. Schindler1, Ray Hilborn1 1School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington 98195, USA 2Present address: West Fork Environmental, Inc., Olympia, Washington 98501, USA *Email: ryan@westforkenv.com ABSTRACT: A suite of adaptive traits allows Pacific salmon to exploit diverse habitats during their lives, facilitating their persistence in highly variable and heterogeneous environments. We investigated how juvenile sockeye salmon Oncorhynchus nerka, which typically rear in lakes before migrating rapidly to sea, make use of riverine and estuarine habitats in the Chignik Lake system (Alaska, USA) where lacustrine rearing capacity limits sockeye salmon productivity. Their distribution, growth, and genetic stock composition were examined during June to August, 2007 to 2009. Sockeye salmon inhabited the estuary for up to 3 mo each summer, representing 2 distinct age classes: Age-0 fry and parr, and Age 1+ smolts. The fry and parr grew rapidly in the estuary, attaining sizes comparable to the lake-reared smolts. Smolts also grew in the estuary in all years, although they occupied the estuary for a briefer period in years when they entered at a larger size. Using genetic mixture analyses, fry and parr in the estuary were assigned to a population that spawns in Chignik River immediately upstream of the estuary, whereas the smolts were assigned to 2 genetically distinct population groups associated with separate nursery lakes farther up in the basin. Our findings highlight the role of estuaries for juvenile sockeye salmon in systems with limited freshwater rearing capacity and high salmon density. The persistence of such populations depends in part on preserving a continuum of habitat types, especially in the southern range of the species where a shifting climate and human activities are expected to most greatly impact populations. KEY WORDS: Oncorhynchus nerka · Life history variation · Estuary · Rearing habitat · Juvenile growth · Genetic stock composition · Single nucleotide polymorphism · Climate Full text in pdf format PreviousNextCite this article as: Simmons RK, Quinn TP, Seeb LW, Schindler DE, Hilborn R (2013) Role of estuarine rearing for sockeye salmon in Alaska (USA). Mar Ecol Prog Ser 481:211-223. https://doi.org/10.3354/meps10190 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 481. Online publication date: May 07, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Landscape-Level Assessment of Brood Rearing Habitat for Greater Sage-Grouse in Nevada

Loss of quality brood rearing habitat, resulting in reduced chick growth and poor recruitment, is one mechanism associated with decline of greater sage-grouse (Centrocercus urophasianus) populations. Low chick survival rates are typically attributed to poor-quality brood rearing habitat. Models that delineate suitability of sage-grouse nesting or brood rearing habitat at the landscape scale can provide key insights into the relationship between sage-grouse and the environment, allowing managers to identify and prioritize habitats for protection or restoration. We used Southwest Regional Gap landcover types to identify early and late greater sage-grouse brood rearing in east-central Nevada. We conducted an Ecological Niche Factor Analysis to 1) examine the effect these landcover types and other ecogeographical variables have on sage-grouse selection of brood rearing habitat, and 2) generate landscape-scale suitability maps. We also evaluated if incorporating a fitness component (brood survival) in landscape spatial analyses of habitat quality influenced our assessment of habitat suitability. Because 36% of our 6,500-km2 study area was identified as early brood rearing habitat, we believe this habitat may not be limiting greater sage-grouse populations in east-central Nevada, USA, at least in wet years. We found strong selection for particular landcover types (e.g., higher elevation, moist sites with riparian shrubs or montane sagebrush) during late brood rearing. Late brood rearing habitat on which broods were successfully reared represented only 2.8% of the study area and had a restricted distribution, suggesting the potential that such habitat could limit sage-grouse populations in east-central Nevada.

Landscape‐Level Assessment of Brood Rearing Habitat for Greater Sage‐Grouse in Nevada

Abstract: Loss of quality brood rearing habitat, resulting in reduced chick growth and poor recruitment, is one mechanism associated with decline of greater sage‐grouse (Centrocercus urophasianus) populations. Low chick survival rates are typically attributed to poor‐quality brood rearing habitat. Models that delineate suitability of sage‐grouse nesting or brood rearing habitat at the landscape scale can provide key insights into the relationship between sage‐grouse and the environment, allowing managers to identify and prioritize habitats for protection or restoration. We used Southwest Regional Gap landcover types to identify early and late greater sage‐grouse brood rearing in east‐central Nevada. We conducted an Ecological Niche Factor Analysis to 1) examine the effect these landcover types and other ecogeographical variables have on sage‐grouse selection of brood rearing habitat, and 2) generate landscape‐scale suitability maps. We also evaluated if incorporating a fitness component (brood survival) in landscape spatial analyses of habitat quality influenced our assessment of habitat suitability. Because 36% of our 6,500‐km2 study area was identified as early brood rearing habitat, we believe this habitat may not be limiting greater sage‐grouse populations in east‐central Nevada, USA, at least in wet years. We found strong selection for particular landcover types (e.g., higher elevation, moist sites with riparian shrubs or montane sagebrush) during late brood rearing. Late brood rearing habitat on which broods were successfully reared represented only 2.8% of the study area and had a restricted distribution, suggesting the potential that such habitat could limit sage‐grouse populations in east‐central Nevada.

Quantifying Flow-Dependent Changes in Subyearling Fall Chinook Salmon Rearing Habitat Using Two-Dimensional Spatially Explicit Modeling

Abstract We used an analysis based on a geographic information system (GIS) to determine the amount of rearing habitat and stranding area for subyearling fall chinook salmon Oncorhynchus tshawytscha in the Hanford Reach of the Columbia River at steady-state flows ranging from 1,416 to 11,328 m3/s. High-resolution river channel bathymetry was used in conjunction with a two-dimensional hydrodynamic model to estimate water velocities, depths, and lateral slopes throughout our 33-km study area. To relate the probability of fish presence in nearshore habitats to measures of physical habitat, we developed a logistic regression model from point electrofishing data. We only considered variables that were compatible with a GIS and therefore excluded other variables known to be important to juvenile salmonids. Water velocity and lateral slope were the only two variables included in our final model. The amount of available rearing habitat generally decreased as flow increased, with the greatest decreases occurring b...

A Comparative Assessment of a Natural and Created Estuarine Slough as Rearing Habitat for Juvenile Chinook and Coho Salmon

Short-term otolith growth rates, residence times, and forage of two species of juvenile salmon (Oncorhynchus spp.) were compared in a created and natural estuarine slough on the Chehalis River in Washington to assess the functional equivalency of the created slough in providing suitable rearing habitat. Otolith microstructure, mark-recapture data, and forage of sub-yearling chinook, O. tshawytscha, and coho, O. kisutch, residing in both sloughs during the spring of 1991 and 1992 served as indicators of rearing habitat quality. No significant differences in the number or width of coho daily otolith increments were detected between the sloughs. Juvenile chinook residence and emigration times were also comparable. Aquatic and terrestrial insects composed the majority of all chinook and coho diets; however, the order of importance of main prey items did differ between sloughs, and salmon in the created slough had emptier stomachs, possibly because of reduced prey availability and/or foraging efficiency.

White Sturgeon Spawning and Rearing Habitat in the Lower Columbia River

Abstract Estimates of spawning habitat for white sturgeons Acipenser transmontanus in the tailraces of the four dams on the lower 470 km of the Columbia River were obtained by using the Physical Habitat Simulation System of the U.S. Fish and Wildlife Service's Instream Flow Incremental Methodology to identify areas with suitable water depths, water velocities, and substrates. Rearing habitat throughout the lower Columbia River was assessed by using a geographic information system to identify areas with suitable water depths and substrates. The lowering of spring and summer river discharges from hydropower system operation reduces the availability of spawning habitat for white sturgeons. The four dam tailraces in the study area differ in the amount and quality of spawning habitat available at various discharges; the differences are due to channel morphology. The three impoundments and the free-flowing Columbia River downstream from Bonneville Dam provide extensive areas that are physically suitable for rea...

Estimating Coho Salmon Rearing Habitat and Smolt Production Losses in a Large River Basin, and Implications for Habitat Restoration

To develop a habitat restoration strategy for the 8,270-km2 Skagit River basin, we estimated changes in smolt production of coho salmon Oncorhynchus kisutch since European settlement began in the basin, based on changes in summer and winter rearing habitat areas. We assessed changes in coho salmon smolt production by habitat type and by cause of habitat alteration. We estimated that the coho salmon smolt production capacity of summer habitats in the Skagit River basin has been reduced from 1.28 million smolts to 0.98 million smolts (–24%) and that the production capacity of winter habitats has been reduced from 1.77 million to 1.17 million smolts (–34%). The largest proportion of summer non-main-stem habitat losses has occurred in side-channel sloughs (41%), followed by losses in small tributaries (31%) and distributary sloughs (29%). The largest loss of winter habitats has occurred in side-channel sloughs (52%), followed by losses in distributary sloughs (37%) and small tributaries (11%). By type of impact, hydromodification (diking, ditching, dredging) associated with agricultural and urban lands accounts for 73% of summer habitat losses and 91% of winter habitat losses. Blocking culverts on small tributaries account for 13% of the decrease in summer habitat and 6% of the decrease in winter habitat. Forestry activities account for 9% of summer habitat losses and 3% of winter habitat losses. Limitations of the analysis and implications for developing a habitat restoration strategy are discussed.

Interactions Between Greater Snow Geese and Their Rearing Habitat

For herbivores, food quality is a major component of habitat quality. However, food quality is complex to assess because it must integrate not only the availability of nutrients but also their digestibility and the requirements of the animal. To evaluate the quality of food and to determine the feeding constraints faced by young herbivores, we compared two brood—rearing habitats used by the Greater Snow Goose (Chen caerulescens atlantica) in the High Arctic using three levels of investigating. The first was based on a quantitative and qualitative analysis of the plants; the second was behavioral, and compared the feeding effort of human—imprinted goslings; and the third was physiological and compared food selection and plant nutrient metabolizability by the goslings. The two habitats grazed by goslings were a sedge meadow (dominated by Carex aquatilis and Dupontia fisheri) and a grass meadow (dominated by Dupontia fisheri and Eriophorum spp.). Plant biomass was higher in the sedge than in the grass meadow. Plant quality declined during the summer but Eriophorum spp. had a significantly higher nitrogen and lower fiber content than the other two species at all times. However, when combining data on quality and relative abundance, the overall plant quality was similar in both meadows. Goslings spent more time feeding and had a higher pecking rate in the grass than in the sedge meadow. Comparison of diet quality to overall plant quality indicated a higher nitrogen and lower fiber content of the diet in the grass meadow but not in the sedge meadow, probably because goslings fed selectively on Eriophorum in the former habitat. Apparent metabolizability of organic matter and nitrogen, and nitrogen assimilation efficiency by goslings, were lower in the sedge than in the grass meadow at some periods. However, goslings did not compensate by an increased rate of food intake when their nitrogen intake was low which suggests that they had reached their gastrointestinal capacity. Under some circumstances, food quality is therefore more important than food abundance for herbivores. We show that integration of our three levels of investigation (plant food, animal behavior, and physiology) is essential to fully evaluate habitat quality for an herbivore.

Spawning and Rearing Habitat Use by White Sturgeons in the Columbia River Downstream from McNary Dam

Spawning and rearing habitats used by white sturgeons Acipenser transmontanus were described from water temperature, depth, and velocity measurements and substrate types present at sites where eggs, larvae, young-of-the-year, and juveniles (ages 1–7) were collected. Spawning and egg incubation occurred in the swiftest water available (mean water column velocity, 0.8–2.8 m/s), which was within 8 km downstream from each of the four main-stem Columbia River dams in our study area. Substrates where spawning occurred were mainly cobble, boulder, and bedrock. Yolk-sac larvae were transported by the river currents from spawning areas into deeper areas with lower water velocities and finer substrates. Young-of-the-year white sturgeons were found at depths of 9–57 m, at mean water column velocities of 0.6 m/s and less, and over substrates of hard clay, mud and silt, sand, gravel, and cobble. Juvenile fish were found at depths of 2–58 m, at mean water column velocities of 1.2 m/s and less, and over substrates of hard clay, mud and silt, sand, gravel, cobble, boulder, and bedrock.

Effectiveness of Selected Stream Improvement Techniques to Create Suitable Summer and Winter Rearing Habitat for Juvenile Coho Salmon (Oncorhynchus kisutch) in Oregon Coastal Streams

We examined the use of constructed pools by juvenile coho salmon (Oncorhynchus kisutch) during summer and winter. Log, gabion, and rock structures placed across the full stream width provided good summer habitat but poor winter habitat for juvenile coho salmon. Rearing densities in constructed habitats during summer and winter were generally similar to those in natural habitats of the same type, except that constructed dammed pools supported lower densities during winter than natural dammed pools. The addition of brush bundles to pools created by full-stream-width structures increased the density of juvenile coho salmon in dammed pools during winter, but not in plunge pools. We concluded that the development of off-channel habitat has the greatest potential to increase production of wild coho salmon smolts in Oregon coastal streams.

Changes in Salmon Spawning and Rearing Habitat from Increased Delivery of Fine Sediment to the South Fork Salmon River, Idaho

Levels of surface and subsurface fine sediment (<4.75 mm in diameter) were measured annually from 1965 to 1985 in spawning and rearing areas for chinook salmon Oncorhynchus tschawytscha and steelhead O. mykiss (formerly Salmo gairdneri) in the South Fork Salmon River, Idaho. Between 1950 and 1965, logging and road construction, in combination with large storm events of 1964 and 1965, resulted in the delivery of increased amounts of fine sediments to the South Fork Salmon River. Surface and subsurface fine sediment levels peaked at 46% of the surface area in 1966 and 48% of the volume in 1969, respectively. A logging moratorium initiated in 1965, coupled with natural recovery and watershed rehabilitation, led to significant decreases in the amounts of fine sediments delivered to and stored in the South Fork Salmon River; this reduction led to a limited resumption of logging operations within the watershed in 1978. By 1985, surface and subsurface sediment levels in chinook salmon spawning areas averaged 19.7% of the surface area and 25.4% of the volume, respectively. However, additional recovery to prelogging fine sediment levels is probably contingent on both further watershed recovery and the occurrence of flood flows capable of transporting material downstream. An equilibrium between incoming sediment from the watershed and outgoing sediment from the river appears to have been reached under flow regimes that have occurred since 1975.