Biotic and abiotic factors related to redband trout occurrence and abundance in desert and montane streams

Redband trout Oncorhynchus mykiss gairdneri in the Columbia River Basin of western North America occupy desert and montane streams with variable habitat conditions. In general, desert streams are lower in gradient and elevation, contain less large substrate and more silt substrate, are less shaded by overhead vegetation, and have higher summer water temperature than montane streams. Consequently, we assessed whether the relationships between biotic and abiotic factors and the occurrence and abundance of redband trout in southwestern Idaho differed between desert and montane streams (<25 m mean width). Increased occurrence of redband trout in desert streams was most strongly related to increased stream shading and decreased amounts of silt substrate, followed by increased amounts of cobble/boulder substrate and absence of piscivorous fish (i.e., smallmouth bass Micropterus dolomieui and northern pikeminnow Ptychocheilus oregonensis ). In montane streams, increased occurrence of redband trout was most strongly related to decreased site elevation and increases in cobble/boulder substrate, followed by decreases in stream gradient and width. Furthermore, occurrence of redband trout decreased in desert streams at mean summer (June–August) water temperature (Temp smr ) >16 °C, whereas for montane streams, occurrence increased at Temp smr >9 °C. Redband trout density in desert streams was most strongly related to higher stream order (i.e., headwater streams), increased stream shading, and increased amounts of cobble/boulder substrate. In montane streams, redband trout density was not well explained by any stream conditions, but stream shading had the strongest positive relationship with density. Redband trout density was negatively related to Temp smr in desert streams, but the relationship was weak for montane streams. That environmental conditions related to the occurrence and abundance of redband trout differ between desert and montane streams is important for fisheries managers who manage these disparate populations occurring in such close proximity to each other.     

Distribution, abundance, and genetic population structure of Wood River sculpin, Cottus leiopomus

The Wood River sculpin Cottus leiopomus is endemic to the Wood River Basin in central Idaho and is a nongame species of concern because of its limited distribution. However, status and genetic population structure, 2 factors often central to the conservation and management of species of concern, have not been assessed for this species. We used backpack electrofishers to survey streams that were small enough (i.e., a priori to contain, possibly contain, or not contain the sculpin, respectively. Native redband trout Oncorhynchus mykiss gairdneri were present at 21 study sites, including 18 of the 20 sites that contained Wood River sculpin. Sixty-one study sites (60%) were dry or had too little water to contain any fish. We estimated that a minimum of 1.36 million Wood River sculpin (≥20 mm total length) currently reside in the basin. The presence of Wood River sculpin was positively associated with stream width:depth ratio and percent cobble/boulder substrate and negatively associated with stream gradient. Mitochondrial DNA haplotype differences were observed between and within the 3 major river subbasins supporting sculpin, with the most striking differences observed between populations in the Camas Creek subbasin and the other 2 subbasins, among which no haplotypes were shared, suggesting relatively long-term isolation. Our results suggest that the Wood River sculpin remains relatively widespread and abundant within its endemic range, despite obvious changes in historical stream connectivity caused by irrigation diversions and other chronic habitat alterations.     

Relationship of diurnal habitat use of native stream fishes of the eastern Great Basin to pPresence of introduced salmonids

Introduced brown trout, Salmo trutta , are common to many streams of western North America. However, the ecological interactions between brown trout and native stream fishes are not well understood, particularly the nature and extent of antipredator responses of native species. We examined the effects of brown trout presence on diurnal habitat use by 2 small native fishes at a mesohabitat scale (e.g., pool, riffle, run, backwater, etc.). Adult and juvenile southern leatherside chub ( Lepidomeda aliciae , formerly Gila copei ) and juvenile mountain sucker ( Catostomus platyrhynchus ) were located in main channel pools in the absence of brown trout, but they were found almost exclusively in backwaters and cutoff pools (i.e., off-channel habitats) in streams where brown trout were abundant. Off-channel habitat appears to provide a refuge for native fishes in streams with abundant brown trout populations. Altered or degraded streams may not include sufficient off-channel refuge habitats to allow coexistence of native species and introduced brown trout.     

Benthic community structure in two adjacent streams in Yellowstone National Park five years after the 1988 wildfires

Physical characteristics, benthic macroinvertebrates, and periphyton assemblages in two adjacent headwater streams in Yellowstone National Park were evaluated five years after the 1988 wildfires. The catchment of one stream was burned by wildfire (burned stream) while the other catchment was unburned (unburned stream). Physical measures revealed channel alteration in the burned stream relative to the unburned stream Periphyton biomass was lower in the burned than the unburned stream (29.2 vs. 50.5 g/m 2 AFDM, respectively), further demonstrating the unstable physical conditions of that system. Kendall's coefficient of concordance (an index of similarity) between diatom assemblages was 0.22, indicating distinct assemblage composition between streams. Navicula permitis Hust. was the most abundant diatom in the burned stream while Hannaea arcus (Ehr.) Patr. was dominant in the unburned stream. Macroinvertebrate taxa richness, density, and biomass were all greater in the unburned stream, although Chironomidae was the most abundant taxon in both streams. Results suggest the removal of terrestrial/riparian vegetation by wildfire can directly influence benthic assemblages by altering the inherent disturbance regime of the physical habitat templet.     

Geographic patterns of ground-dwelling arthropods across an ecoregional transition in the North American Southwest

We examined the biogeographic patterns of ground-dwelling arthropod communities across a heterogeneous semiarid region of the Southern Rio Grande Rift Valley of New Mexico. Our 3 sites included portions of 5 ecoregions, with the middle site a transition area where all ecoregions converged. We addressed the following 3 questions: (1) Do the species assemblage patterns for ground arthropods across habitats and sites conform to recognized ecoregions? (2) Are arthropod assemblages in distinct vegetation-defined habitats within an ecoregion more similar to each other or to assemblages in similar vegetation-defined habitats in other ecoregions? (3) Is there a detectable edge effect with increased arthropod diversity in the area of converging ecoregions? We encountered 442 target arthropod species from pitfall traps operating continuously for 7 years over a series of different habitats at each of the 3 sites. We examined geographic distributions of spider and cricket/grasshopper species in detail, and they showed affinities for different ecoregions, respectively. Each habitat within a study site supported a unique overall arthropod assemblage; nevertheless, different habitats at the same site were more similar to each other than they were to similar habitats at other sites. Overall arthropod species richness was greatest in the area where all 5 ecoregions converged. Arthropod species and their geographic distributions are poorly known relative to vascular plants and vertebrate animals. Findings from this research indicate that ecoregional classification is a useful tool for understanding biogeographic patterns among arthropods.     

Effects of livestock grazing exlosure on aquatic macroinvertebrates in a montane stream, New Mexico

Aquatic macroinvertebrate populations inhabiting reaches of a stream within areas excluded from livestock grazing for a decade were markedly different from those in grazed areas when density, biomass, biotic condition indices, and mean chi square indices of the two populations were compared. Increased densities and biomasses of more tolerant forms of macroinvertebrates were observed in grazed reaches. Because pretreatment data were not available, differences in macroinvertebrate populations and relative tolerances of taxa in grazed and ungrazed areas could be as easily attributed to linear changes in stream habitat as to removal of domestic livestock. Results of this study have implications for the design of future research on the effects of livestock grazing on stream environments and biota: (1) baseline/pretreatment information is prerequisite, and (2) the study should take a watershed (ecosystem) approach.     

Spawning ecology of finespotted Snake River cutthroat trout in spring streams of the Salt River valley, Wyoming

We studied spawning ecology of cutthroat trout ( Oncorhynchus clarki ) in streams that originate as springs along the Salt River, a Snake River tributary in western Wyoming. We assessed (1) relative numbers of upstream-migrant and resident adults present during the spawning period in spring streams, (2) influence of habitat modification on use of spring streams for spawning, and (3) habitat features used for spawning in spring streams. Four spring streams were studied, 2 with substantial modification to enhance trout habitat and 2 with little or no modification. Modifications consisted primarily of constructing alternating pools and gravel-cobble riffles. Only a small portion of adult fish in spring streams during the spawning period had migrated upstream from the Salt River between March and the middle of June. Larger numbers of adult fish and more redds were observed in the 2 modified streams compared with the 2 streams with little or no modification. Most spawning occurred on constructed riffles with small gravel and over a narrow range of depths and velocities. Cutthroat trout, rainbow trout ( Oncorhynchus mykiss ), and their hybrids were observed in 1 stream with habitat modifications, indicating that measures to halt invasion by rainbow trout, as well as habitat improvement, are needed to preserve this native trout within the Salt River valley.     

Species composition and habitat associations of benthic algal assemblages in headwater streams of the Sierra Nevada, California

Despite their trophic importance and potential importance as bioindicators of stream condition, benthic algae have not been well studied in California. In particular there are few studies from small streams in the Sierra Nevada. The objective of this study was to determine the standing crop of chlorophyll- a and benthic algal species assemblages present in the small 1st- and 2nd-order streams of the Kings River Experimental Watersheds (KREW, watersheds of Bull, Providence, Duff, and Teakettle Creeks) and determine the associations of these measures with stream habitat. We collected samples of benthic algae from rock substrata in September 2002 (7 sites) and 2005 (the same 7 sites plus 5 additional sites). Habitat and water-quality data were collected concurrently. Chlorophyll- a values ranged from 0.2 to 3.2 mg ? m –2 . Chlorophyll- a in the Bull Creek watershed was generally lower than in the other watersheds. Benthic algal assemblages were dominated by diatoms and cyanobacteria. We collected 79 taxa of diatoms in 2002 and 126 taxa in 2005. Diatom taxa richness in individual samples ranged from 15 to 47. Nonmetric multidimensional scaling analysis of arcsine square-root transformed proportional abundances of diatoms identified 3 groups of sites. Bull Creek sites were generally different from other sites (group 1), and the sites from Bull Creek were different in 2002 (group 2) and 2005 (group 3). Five taxa appeared to be particularly important in distinguishing groups: Achnanthidium minutissimum , Cocconeis placentula , Eunotia incise , Eunotia pectinalis var. minor , and Planothidium lanceolatum . Elevation, water temperature, pH, specific conductance, and canopy were habitat variables correlated with the differences in diatom assemblages among sites. Our results provide a valuable baseline for future studies of benthic algae in Sierra Nevada headwater streams and will be particularly important in understanding the effects of different forest restoration management strategies being tested in the KREW project.     

Functional characteristics of wilderness streams twenty years following wildfire

We compared functional attributes of streams draining catchments burned by wildfire 20 years previously to those of streams in unburned catchments. Long-term analyses of channel profiles indicated most channel change occurred within the first 10 years after fire with little subsequent change the following 10 years. Much of the standing dead timber had fallen, and its effect on stream morphology was directly related to stream size, with important ramifications for future years as decay progresses. The volume of wood in the active channel was 5X higher in a 3rdorder burn stream than in other burn or reference streams, but > 80% of this wood was still bridging the stream. Retention of leaves was strongly associated with channel morphology and location of debris dams. Sediment respiration was significantly greater (1.7X) in streams of burned catchments, resulting from greater amounts of loosely attached organic matter in the sediments of these streams. In concordance with respiration results, coefficients of exchange (k ex ) were almost 5X higher in burn streams than in reference streams, although estimates of transient storage were similar between stream types. We expect the input of large woody debris to increase in the next 10 years in fire-impacted streams as bridging trees collapse into the stream, thereby enhancing channel complexity and habitat heterogeneity, instream metabolism and retention, and consequently stream function. The results emphasize the importance of landscape history, such as large-scale wildfires, on present patterns and processes in stream ecosystems.     

Short-term effects of wildfire on montane stream ecosystems in the southern Rocky Mountains: one and two years post-burn

The frequency and intensity of wildfire in the western United States has increased over the last century, creating a heterogeneous mosaic of landscapes in various stages of recovery. The 2002 Hayman Fire was one of the largest wildfires in Colorado history and was unprecedented for its speed and intensity, with over 50%–70% of the burn area classified as moderate to high severity where much of the canopy crown was consumed. We evaluated the short-term impact of the Hayman Fire on ecological properties in montane stream ecosystems in the summers of 2003 and 2004, one and two years post-fire. Fire significantly altered surface temperature, dissolved oxygen concentration, and the chemical composition of stream water, including concentrations of nitrate, phosphate, and mineral salts. However, fire did not have significant impacts on stream conductivity, pH, or total concentrations of cations or anions during our study period. Streams in the burn area contained fewer benthic macroinvertebrate taxa compared to unburned streams during the year after fire and contained lower invertebrate densities and biomass compared to reference streams 2 years post-fire. Average C:N ratio of the benthic macroinvertebrate community was significantly and negatively related to stream nitrate concentration, possibly due to a shift in community composition or invertebrate nitrogen acquisition in fire-affected streams.     

Influence of fine sediment on macroinvertebrate colonization of surface and hyporheic stream substrates

Colonization of macroinvertebrates was assessed in a stream impacted by inputs of fine sediments. Colonization was examined at the stream surface and within the hyporheos with Whitlock-Vibert (W-V) boxes. Hyporheic areas accumulated much greater amounts of all size categories of sediment. No significant difference was observed in the amounts of organic matter accumulated at either depth. Only 150-μm sediment had significant effects on macroinvertebrate total numbers and number of taxa. Total numbers of invertebrates at 30 cm were only 20% of those at the surface. Canonical Correspondence of Analysis indicated that the strongest influence on macroinvertebrates colonizing W-V boxes at the surface was stream size and secondarily fine sediments. Within the hyporheos, abundance of fine sediment was the dominant influence on macroinvertebrate assemblages. Impacts of sedimentation on hyporheic environments can have significant and persistent impacts on streams.     

Secondary production estimates of benthic insects in three cold desert streams

We studied aquatic insect production in three cold desert streams in southeastern Washington. The size-Frequency (SF) and P/B methods were used to assess production, which is expressed by taxon, functional group, and trophic level. Dipterans (midges and black flies) were the most productive taxa, accounting for 40-70% of the total insect production. Production by collectors and detritivores was the greatest of all functional groups and trophic levels, respectively, in all study streams. Insects with rapid development times and multiple cohorts are very important in cold desert streams; they were major contributors to the total insect production. Total insect production rates in our study streams (14-23 g DW·m -2 ·yr -1 ) were greater than those found in Deep Creek, Idaho (1.2 g DW·m -2 ·yr -1 ), the only other cold desert stream for which production data are available. Our values also were generally greater than published data for most cold/mesic (3-27 g DW·m -2 ·yr -1 ) and humid/mesic (3-25 g DW·m -2 ·yr -1 ) streams, but lower than in Sonoran Desert Streams (>120 g DW·m -2 ·yr -1 ) or New Zealand streams (～40 g DW·m -2 ·yr -1 ). Our data support the contention of others that production, rather than density or biomass, is the most accurate and meaningful way to assess the role of these organisms in lotic ecosystems.     

Present effects of past wildfires on leaf litter breakdown in stream ecosystems

We investigated the present effects from a 10-year-old wildfire on leaf litter breakdown rates in 3 headwater streams in central Idaho. These systems experienced a massive debris flow one year after the fire. Based on soil instability and burn patterns, we identified 3 stream conditions: unburned, burned only, and burned/scoured. We placed leaf bags containing willow leaves ( Salix sp.) in each stream type and removed bags at various time intervals until all bags were collected 100 days after their introduction. Leaf material was dried and weighed, and decay rate coefficients were calculated. Macroinvertebrates colonizing the bags were enumerated and identified, and selected taxa were placed into trophic groups. We found that the unburned stream had the fastest leaf litter breakdown rate, the lowest level of incident light reaching the stream, and the largest amount of benthic organic matter. The burned/scoured stream was nearly opposite in all respects. Numbers of 2 detritivore invertebrate taxa, Serratella tibialis and Zapada oregonensis, were highest in the unburned stream but lowest in the burned/scoured stream. A third taxon, Baetis sp., showed the opposite relationship. Presence of predatory invertebrates did not affect detritivore abundance or leaf decay rate in the bags. Our research suggests that recovery response variables of some stream systems may not have returned to prefire levels even a decade after the initial wildfire. In this study, the recovery of our streams appears to be connected to the return of the riparian zone, though fire-induced debris flows may slow or alter final recovery of the stream system.     

Seasonal trends and colonization patterns of macroinvertebrate assemblages in two streams with contrasting flow regimes

Patterns of colonization by macroinvertebrates were examined in two streams that differ in flow regime: a snowmelt system and a mesic groundwater system. Experiments were conducted during spring runoff, summer baseflow, and winter baseflow using artificial substrata. Colonization patterns reflected seasonal changes in benthic macroinvertebrate assemblages and life histories in each stream. The density and biomass of benthic organisms were approximately 3X greater in winter than in either spring or summer for both streams. Similarly, colonization was greater in winter than in spring or summer for both streams. In spring, colonization patterns were different between streams, with colonization being imperceptible in the snowmelt stream. Macroinvertebrate abundance fluctuated during the summer colonization experiment at both sites, resulting from a complex interplay among population emergence, recruitment, and/or movement. Assemblages in the snowmelt system primarily comprised mobile or ruderal taxa, such as Beatis tricaudatus and Chironomidae, whereas relatively sessile taxa, such as Glossoma nigrior , were predominant in the mesic groundwater system. Seasonal patterns of colonization differed among stream types primarily because of the profound interplay of flow regime and temperature on benthic community structure and organism life history.     

Redband trout response to hypoxia in a natural environment

Redband trout ( Oncorhynchus mykiss gairdneri ) were observed approximately every 2 weeks in an intermittent southwest Idaho stream between August and December 1991. Instantaneous daytime dissolved oxygen concentration and water temperature declined from 4.0 to Rhinichthys osculus ) were also present in each pool until drying. The response of these fish to such extreme habitat conditions is probably a primary factor accounting for their distribution within arid landscapes.     

Species-environment relationships among filter-feeding caddisflies (Trichoptera: Hydropsychidae) in Rocky Mountain streams

Species-environment relationships were determined for filter-feeding macroinvertebrates from 55 Rocky Mountain stream sites to establish species distribution patterns. Species abundance and 20 environmental variables were measured at each site with species-environment relationship determined using canonical correspondence analysis and stepwise multiple regression. Results suggest that the distribution of several taxa was strongly related to upstream-downstream environmental gradients. Arctopsyche grandis abundance increased with stream size (width and depth) and decreased with increasing turbulence (Reynolds number). Brachycentrus abundance also increased with stream size (depth). Hydropsyche abundance increased with increasing baseflow. Parapsyche elsis abundance also increased with stream size (depth). Hydropsyche abundance increased with increasing baseflow. Parapsyche elsis abundance demonstrated negative correlation with depth, Froude number, and conductivity. Taxa followed previously reported patterns, partitioning habitat according to stream size. Arctopsyche grandis , Brachycentrus , and Hydropsyche were found in larger (3rd- to 6th order) streams, while Parapsyche elsis was observed in small headwater (1st- and 2nd- order) streams. Other filter-feeding taxa such as Simulium, Pisidium and ostracods exhibited little or no apparent habitat partitioning among stream sites.     

Macroinvertebrate richness is lower in high-elevation lakes vs nearby streams: evidence from Grand Teton National Park,Wyoming

Mountain ecosystems will be strongly impacted by climate change, yet little is known of extant biodiversity in high-elevation lakes, particularly in North America. In this study, we sampled the littoral zone of six alpine and subalpine lakes in Grand Teton National Park (GRTE), Wyoming, to characterise invertebrate diversity and environmental variation in these climate change-threatened ecosystems. Overall, we collected 19 aquatic invertebrate taxa, and found that each lake harboured a unique assemblage of invertebrates despite close geographic proximity in some instances (e.g. less than 5 km). The results of this study complement previous efforts focused on macroinvertebrate diversity of streams in the Teton Range, highlighting much lower diversity in montane lakes vs nearby streams. Taken together, the two studies establish an important baseline understanding of mountain freshwater biodiversity in GRTE. With rapidly changing hydrologic inputs to mountain lakes driven primarily by the recession of alpine glaciers, these results may help target aquatic invertebrates to monitor as climate change affects the region. Moreover, these data clarify habitat factors, both biotic and abiotic, that influence high-elevation lake assemblages of the Teton Range.     

Winter macroinvertebrate communities in two montane Wyoming streams

Macroinvertebrate communities were examined on 4 winter dates over a 4-yr period in 2 high-altitude Rocky Mountain streams to document overwintering assemblages potentially experiencing spring acid pulses. Taxa richness values were comparable to other published lists for alpine and montane stream systems despite the fact that most literature reflected summer collections. Mean benthic density ranged from 1406 to 19,734 organisms/m 2 , and drift rates ranged from 0 to 1740 organisms/100 m 3 . Benthic collections showed higher taxa richness than drift collections while the Ephemeroptera and Plecoptera occurred in greater proportions in drift than in benthos. The Nemouridae (Plecoptera), Ephemerellidae and Heptageniidae (Ephemeroptera), Chironomidae (Diptera), and Hydracarina were the numerically dominant taxa in benthic collections. Grazer/scrapers and shredder/detritivores were always the numerically dominant functional feeding groups at all sites, composing 60-90% of the benthos. Predators, constituting approximately 15% of the community, occurred in the same relative proportion at all sites on all dates. Winter macroinvertebrate communities in these low-order, montane streams exhibit high taxonomic richness and benthic densities as great as lower-elevation mountain streams in the West.     

A habitat suitability model for pygmy rabbits ( Brachylagus iIdahoensis ) in southeastern Idaho

A habitat suitability model was developed for pygmy rabbit ( Brachylagus idahoensis ) habitat on the Idaho National Engineering and Environmental Laboratory (INEEL) in southeastern Idaho. Suitable pygmy rabbit areas were characterized by greater cover and density of total shrubs and big sagebrush ( Artemisia tridentata ), as well as greater forb cover. Soil texture also played an important role in distinguishing suitable pygmy rabbit areas from nonuse sites. Principal components analysis (PCA) of several vegetation variables and soil texture was used to develop a habitat suitability model for pygmy rabbit habitat. This model, which can be used to successfully distinguish between pygmy rabbit use and nonuse areas on the INEEL, has the potential for use throughout the pygmy rabbits range.     

Density and biomass of redband trout relative to stream shading and temperature in southwestern Idaho

Density and biomass of redband trout ( Oncorhynchus mykiss gairdneri ) relative to stream temperature were examined in headwater reaches of Big Jacks and Little Jacks Creeks in southwestern Idaho. Stream shading was greater (mean of 80% versus 46%) and solar insolation was lower (mean of 7.9 versus 15.1 mJ · m -2 · day -1 ) in Little Jacks Creek ( P P ≤ 0.07) but increased more rapidly and to higher levels (24° - 26° C) in Big Jacks Creek. Daily maximum water temperatures (23 km downstream of headwater springs) during July 1996 were lower in Little Jacks Creek (ranged from 18° to 22° C) than in Big Jacks Creek (20.2° to 26° C, P P -2 and 25.0 g · m -2 ) compared to Big Jacks Creek (0.3 fish · m -2 and 8.9 g · m -2 , P = 0.01). Trout density was negatively correlated with increases in water temperature ( P = 0.03) and solar insolation ( P = 0.09) in both streams. Trout biomass increased with stream shading and was negatively correlated with solar insolation ( P < 0.1). Warmer water temperatures in Big Jacks Creek were likely due to historical summerlong livestock grazing, which drastically reduced riparian shading.