Evidence of lake trout (Salvelinus namaycush) spawning and spawning habitat use in the Dog River,Lake Superior

Lake trout spawn primarily in lakes, and the few river-spawning populations that were known in Lake Superior were believed to be extirpated. We confirmed spawning by lake trout in the Dog River, Ontario, during 2013–2016 by the collection of and genetic identification of eggs, and we describe spawning meso- and microhabitat use by spawning fish. Between 2013 and 2016, a total of 277 lake trout eggs were collected from 39 of 137 sampling locations in the river. The majority of eggs (220) were collected at the transition between the estuary and the river channel crossing the beach. Lake trout eggs were most often located near the downstream end of pools in areas characterized by rapid changes in depth or slope, coarse substrates, and increased water velocities, where interstitial flows may occur. Depths in wadeable areas where eggs were found averaged 0.9?m (range: 0.4 to 1.3?m) and substrate sizes consisted of large gravel, cobble, and boulder; comparable to spawning characteristics noted in lakes. Water velocities averaged 0.66?m·s^?1 (range: 0.33 to 1.7?m³·s^?1) at mid-depth. This information on spawning habitat could be used to help locate other remnant river-spawning populations and to restore river-spawning lake trout and their habitat in rivers that previously supported lake trout in Lake Superior. The Dog River population offers a unique opportunity to understand the ecology of a river spawning lake trout population.     

Status and movement of adfluvial brook trout Salvelinus fontinalis at Isle Royale,Michigan, Lake Superior

Adfluvial brook trout Salvelinus fontinalis populations in the Lake Superior basin have suffered declines over the last century due to habitat degradation and exploitation. Natural resources agencies throughout the basin have restored habitat and implemented restrictive angling regulations as tools to protect remnant coaster brook trout populations, but the success of these practices is unknown in some locations. We used electrofishing and passive integrated transponder (PIT) tag movement data from 2008 to 2020 to describe population characteristics, temporal trends, and adfluvial life history of coaster brook trout in Washington Harbor, Isle Royale National Park, Lake Superior after implementation of catch-and-release regulations in 2004. Our results document the presence of an adfluvial coaster brook trout population in Washington Harbor, Isle Royale. Temporal trends indicate that brook trout abundance and distribution in Washington Harbor increased since earlier observations in the late 1990s and early 2000s likely due to enactment of protective regulations, and increased stream flows and water levels observed in recent years in both Washington Creek and Lake Superior, respectively. Annual tag detection of Washington Harbor brook trout in Washington Creek at the antenna arrays varied from 25% in 2009 to 100% in 2011 and 2013, and averaged 60.7% throughout the study. Peak in adfluvial brook trout use of Washington Creek was from August – October with few detections occurring outside of the presumed spawning period. This study provides valuable insight into the population characteristics, movement patterns, and temporal increase in abundance of an adfluvial brook trout population in Lake Superior.     

Importance and seasonal availability of terrestrial invertebrates as prey for juvenile salmonids in floodplain spring brooks of the Kol River (Kamchatka,Russian Federation)

Energy and resource fluxes between terrestrial and aquatic habitats of river flood plains can have reciprocal influences on food webs. Floodplain spring brooks may contain high densities (>1 m⁻²) of juvenile fish even when aquatic food resources appear to be low. A likely explanation is the allochthonous energy subsidy from riparian vegetation (e.g. leaves, invertebrates). To quantify this relationship in a rich salmon river ecosystem, we measured the temporal and spatial flux of terrestrial invertebrate and aquatic food resources in relation to diets of the two most abundant salmonid species in two spring brooks within early (<20 years) and late (>50 years) successional riparia on an expansive coastal flood plain of the Kol River, Kamchatka. Standing crops of benthic invertebrates and density of drifting invertebrates (dry mass) were fairly low (<4 g m⁻² and <1 mg m⁻³, respectively) at both sites, but annual average terrestrial invertebrate input among sites was 22.2 ± 0.1 mg m⁻² day⁻¹. On average 68% of the coho salmon diet was of terrestrial origin, contrasting with 13% for Dolly Varden char at both sites, thus showing resource partitioning. Diet varied temporally and spatially with prey availability. Specifically, larvae of a weevil (Curculionidae) feeding on willow catkins were a dominant diet item for coho in the spring but only at the early successional site; Dolly Varden also ate these weevils but aquatic invertebrates continued to dominate their diets, further demonstrating behavioural segregation. The results show the importance of channel‐floodplain connectivity to management and conservation of salmon rivers. Copyright © 2009 John Wiley & Sons, Ltd.     

Increasing the availability and spatial variation of spawning habitats through ascending baseflows

Precipitation in fall and winter is important to recharge aquifers in Northern California and the Pacific Northwestern United States, causing the baseflow in rivers ascend during the time when Chinook salmon (Oncorhynchus tshawytscha) construct redds. Herein, we evaluate the availability of spawning habitats under a constant streamflow common in regulated rivers against ascending baseflows patterned from free‐flowing rivers. A binomial logistic regression model was applied to predict the suitability of redd locations based on physical characteristics. Next, two‐dimensional hydrodynamic habitat models were developed at two locations representing a broad range of channel forms common in large rivers. Hydrodynamic and habitat models were leveraged together to simulate the quality, amount, and spatial distribution of spawning habitat at a series of individual flow rates, as well as the combined effect of those flow rates through a spawning season with ascending baseflows. Ascending baseflows increased the abundance of spawning habitat over individual streamflows at a site where the river channel is confined by levee‐like features. However, improvements were greater at an unconfined site that facilitated lateral connectivity and greater expansion of wetted channel area as streamflows increased. Ascending baseflows provided spatial separation in preferred habitats over a spawning season, which may reduce the risk of superimposition among runs or among species. Ascending baseflows provided a benefit across the range of hydrologic regimes in a 100‐year gauge record ranging from 20% to 122% improvements in habitat area over low streamflows that are currently used to manage for spawning habitat. Although replicating natural flow regimes in managed systems can be impossible or impractical, these results demonstrate that incorporating elements of the natural flow regime like ascending baseflows can benefit the restoration and conservation of riverine species.     

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.     

Effect of dam removal on habitat use by spawning Atlantic salmon

By impeding migration and degrading habitat downstream, dam construction has caused population declines in many migratory fish populations. As part of the landlocked Atlantic salmon (Salmo salar) restoration program in Lake Champlain, the Willsboro Dam was removed from the Boquet River, NY in 2015 providing an opportunity to study the effects of dam removal on spawning habitat quality and availability. Spawning habitat surveys were conducted downstream of the dam site in 2014, 2016 and 2017, and in historical spawning grounds upstream in 2016 and 2017. The habitat used was characterized by measuring depth, water velocity, and substrate size at each redd. Mean habitat use did not differ between upstream and downstream sites for any variables in 2016 and only differed for depth in 2017. However, the variance in depth and substrate used for spawning were lower at the upstream site in 2016, likely due to an abundance of habitat. In the downstream site, the mean and variance in depth at redds decreased after dam removal as did the variance in substrate size, increasing the habitat suitability of redds. When compared to literature data, habitat used upstream of the former dam was of medium quality in both 2016 and 2017, and improved downstream from low to medium quality in both column velocity and substrate size after dam removal. This study illustrates that positive shifts in the quality of habitat used can occur rapidly following dam removal by allowing access to suitable spawning habitat upstream and improving habitat downstream.     

Evaluation of Steelhead Passage Flows Using Hydraulic Modeling on an Unregulated Coastal California River

Passage and habitat connectivity flows for steelhead Oncorhynchus mykiss through depth sensitive natural, low gradient, critical riffle sites were investigated in the unregulated Big Sur River, California. The River2D two‐dimensional hydraulic habitat model, along with quantitative passage metrics and species‐specific and lifestage‐specific depth criteria, were used to evaluate and compare predicted fish passage flows with flows derived by a traditional empirical critical riffle fish passage method. Passage flows were also compared with historical unimpaired natural hydrology patterns to assess the frequency and duration of suitable passage flows under the naturally variable flow regimes characteristic of Central California coastal rivers. A strong relationship (r² = 0.93) was observed between flows predicted by hydraulic modeling and flows identified by the empirical critical riffle method. River2D provided validation that the flows derived using the traditional critical riffle methodology provided for contiguous passable pathways of suitable hydraulic (depth and velocity) conditions through complex cobble‐dominated riffle sites. Furthermore, steelhead passage flows were spatially and temporally consistent between lagoon and upstream riffles for adults, and were generally indicative of a river system in equilibrium with a naturally variable flow regime and associated intact ecological processes. An analysis of 25 years of continuous flow data indicated sufficient flows for upstream passage by young‐of‐year and juvenile steelhead were produced between 37% and 100% and between 1% and 95% of the time, respectively. September and October are the most challenging months for natural flows to meet young‐of‐year and juvenile passage and habitat connectivity flows. Careful consideration of seasonal and interannual flow variability dynamics, therefore, are critical components of an effective flow management strategy for the maintenance and protection of passage and habitat connectivity flows between lagoon and upriver habitats. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.     

MODELLING CHANGES IN SALMON HABITAT ASSOCIATED WITH RIVER CHANNEL RESTORATION AND FLOW‐INDUCED CHANNEL ALTERATIONS

The River2D two‐dimensional hydraulic and habitat model was used to simulate fall‐run Chinook salmon (Oncorhynchus tschawytscha) spawning and fry and juvenile rearing habitat of the first phase of a stream channel restoration project on Clear Creek, California. Habitat was simulated for a range of stream flows: (1) before restoration; (2) based on the restoration design; (3) immediately after restoration; and (4) after one and two large flow events. Hydraulic and structural data were collected for three sites before restoration, and prerestoration habitat was simulated. Habitat simulated for these sites was extrapolated to the prerestoration area based on habitat mapping. The topographical plan for the restoration was used to simulate the anticipated habitat after restoration. Although the restoration increased spawning habitat, it was less successful for rearing habitat. Channel changes associated with high‐flow events did not entirely negate the benefits of the restoration project. The results of this study point out the need for models that can simulate the changes in channel topography associated with high‐flow events, which could then be used to simulate habitat over time. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

Exploring Particle Density Effects on Partial Mobility of Steelhead Spawning Gravels

Yellowbank Creek is a small stream in coastal central California being assessed for salmonid habitat limiting factors and restoration potential. Yellowbank flows through low‐density marine mudstone bedrock, which is the gravel source for the stream. To assess the potential effects of the low‐density substrate on spawning gravels, a tracer stone study comparing the incipient motion of low‐density mudstone particles and typical density granitic particles was used to populate a logistic regression particle entrainment model. A model comparison approach was used to test the strength of the model. Results demonstrate partial mobility of both mudstone and granitic particles under boundary shear conditions ranging from 6.9 to 42.2 N m^‐2. The modelling results quantify the strong negative correlation between particle entrainment and particle density. Mudstone gravel was three times more likely to be entrained than granitic gravel, within the context of the experimental conditions. The effect of density difference on partial mobility was greater in smaller grain size fractions. This work has implications for salmonid spawning success in atypical geologic settings and may assist in prioritization of restoration efforts. Copyright © 2013 John Wiley & Sons, Ltd.     

Flushing flow recommendations for maintenance of salmonid spawning gravels in a steep,regulated stream

A study was conducted to develop flushing flow recommendations for maintaining the quantity of salmonid spawning gravels in the North Fork of the Feather River, a regulated stream in California, U.S.A. This required the development of a technique which would prescribe flows to remove sediments from the gravels without removing the gravels themselves, which are in finite supply in the river. Field studies involved the use of a ‘two-point-are’ procedure which allowed depth, velocity, and substrate measurements to be concentrated over spawning gravels at each site. Measurements were repeated at each site at three different flows ranging from 1.7 to 11.3 m³ s^?1. The local velocity and depth measurements were used to evaluate hydraulic conditions within areas containing spawning gravels. Four flow levels were derived which would provide varying degrees of sediment transport and flushing; (1) surficial flushing of gravels; (2) mobilization of gravels; (3) surficial flushing of cobbles; and (4) mobilization of cobbles. Results of the study indicated a flushing flow of 56.6 m³ s^?1 occurring as a planned release or natural flow for from 1–3 days would be sufficient to transport sediment from spawning gravels. This flow was intermediate to levels which maximize surficial gravel flushing and levels which maximize surficial cobble flushing.     

Response of fish assemblages to restoration of rapids habitat in a Great Lakes connecting channel

Rapids habitats are critical spawning and nursery grounds for multiple Laurentian Great Lakes fishes of ecological importance such as lake sturgeon, walleye, and salmonids. However, river modifications have destroyed important rapids habitat in connecting channels by modifying flow profiles and removing large quantities of cobble and gravel that are preferred spawning substrates of several fish species. The conversion of rapids habitat to slow moving waters has altered fish assemblages and decreased the spawning success of lithophilic species. The St. Marys River is a Great Lakes connecting channel in which the majority of rapids habitat has been lost. However, rapids habitat was restored at the Little Rapids in 2016 to recover important spawning habitat in this river. During the restoration, flow and substrate were recovered to rapids habitat. We sampled the fish community (pre- and post-restoration), focusing on age-0 fishes in order to characterize the response of the fish assemblage to the restoration, particularly for species of importance (e.g. lake whitefish, walleye, Atlantic salmon). Following restoration, we observed a 40% increase in age-0 fish catch per unit effort, increased presence of rare species, and a shift in assemblage structure of age-0 fishes (higher relative abundance of Salmonidae, Cottidae, and Gasterosteidae). We also observed a “transition” period in 2017, in which the assemblage was markedly different from the pre- and post-restoration assemblages and was dominated by Catostomidae. Responses from target species were mixed, with increased Atlantic salmon abundance, first documented presence of walleye and no presence of lake sturgeon or Coregoninae.     

Effects of channel restabilization on habitat diversity,twentymile creek,mississippi

Twentymile Creek, a sand-bed stream draining a 450 km² catchment in northeast Mississippi, was channelized prior to 1910, in 1938, and in 1966. Straightening and enlargement in 1966 was followed by channel instability—rapid bed degradation (2-4 m) and cross-section enlargement by 1.4 to 2.7 times. Grade control structures (GCS) (weirs with stoneprotected stilling basins) and various types of streambank protection were constructed along the channel in the early 1980s to restore stability. Other investigators have suggested that habitat recovery in incised, channelized streams is facilitated by construction of GCS because they create stable scour holes and promote natural formation of a low-flow channel flanked by vegetated berms. Effects of restabilization of Twentymile Creek on aquatic habitats were assessed in four ways. The fraction of the bank line covered by woody vegetation was mapped from aerial photographs taken in 1981 and 1985; physical habitat (depth, velocity, substrate, and cover) and fishes were sampled at base flow; and the existence and size of a low-flow channel was ascertained from cross-section surveys taken in 1980 and 1989. Woody vegetation, physical aquatic habitat, and fishes were also sampled from Mubby-Chiwapa Creek, a similar-sized unstable channel with no GCS. Physical habitat variables and fishes were sampled concurrently at five stations on Twentymile Creek, and four stations on Mubby-Chiwapa. Four of the five Twentymile stations were either above or below a GCS. Bank-line woody vegetation cover increased 8 per cent between 1981 and 1985 along Twentymile Creek but was stable along Mubby-Chiwapa. Reaches above and below GCS were deeper with slower current velocities than elsewhere. Mean Shannon diversity indices based on physical data were similar for both streams, but were 58 per cent higher for stations immediately above and below GCS than for other stations. Since construction of the GCS and bank protection measures, longitudinal berms have formed within the enlarged Twentymile Creek channel, creating a low-flow channel. Low-flow channel capacity was equivalent to a mean daily discharge equalled or exceeded 30 per cent of the time, and was considerably lower than the effective discharge. Differences in aquatic habitat diversity among the stations sampled were primarily due to the scour holes below the GCS and the low-flow channel. Thirty-nine fish species were collected from Twentymile Creek, but only 22 from Mubby-Chiwapa. Fourteen species were collected exclusively at GCS. Principal component analyses of the abundance of the eight numerically dominant fish species indicated similar faunas at most stations, but Twentymile Creek GCS stations were faunistically distinct. Abundance of several of the numerically dominant species was positively influenced by greater depths and lower velocities found near Twentymile GCS. The mean fish diversity index for Twentymile Creek was 29 per cent higher than for Mubby-Chiwapa, and fish diversity was positively correlated with substrate diversity and mean depth.     

Application of a 2D hydrodynamic model to design of reach‐scale spawning gravel replenishment on the Mokelumne River,California

In‐stream chinook salmon (Oncorhynchus tschawytscha) spawning habitat in California's Central Valley has been degraded by minimal gravel recruitment due to river impoundment and historic gravel extraction. In a recent project marking a new direction for spawning habitat rehabilitation, 2450 m³ of gravel and several boulders were used to craft bars and chutes. To improve the design of future projects, a test was carried out in which a commercial modelling package was used to design and evaluate alternative gravel configurations in relation to the actual pre‐ and post‐project configurations. Tested scenarios included alternate bars, central braid, a combination of alternate bars and a braid, and a flat riffle with uniformly spaced boulders. All runs were compared for their spawning habitat value and for susceptibility to erosion. The flat riffle scenario produced the most total, high, and medium quality habitat, but would yield little habitat under flows deviating from the design discharge. Bar and braid scenarios were highly gravel efficient, with nearly 1 m² of habitat per 1 m³ of gravel added, and yielded large contiguous high quality habitat patches that were superior to the actual design. At near bankfull flow, negligible sediment entrainment was predicted for any scenario. Copyright © 2004 John Wiley & Sons, Ltd.     

Juvenile masu salmon in a regulated river

We examined the relationship between the physical environment and habitat use of juvenile masu salmon, Oncorhynchus masou, in the Nobori River in Hokkaido, Japan to provide a perspective for the conservation of fish habitat in regulated streams. The study was undertaken during the autumn and winter, with an emphasis on the hierarchy of three spatial scales: microhabitat, channel‐unit and reach scales. The microhabitat‐scale analysis indicated juvenile masu salmon preferred a midstream habitat type, with a greater depth (Avg. ± SD: 35.4 ± 14.2 cm) and high (43.4 ± 23.1 cm s^?1) and uniform current velocities during the autumn, and a channel margin habitat type with a moderate current (about 20 cm s^?1) and submerged cover during winter. In addition, different cover types have different roles in determining juvenile salmon distributions during winter. Grass cover had extremely high carrying capacities, whereas coarse substrate cover provided winter habitat for larger juvenile salmon. Channel‐unit scale analyses showed that abundance of juvenile salmon tended to be higher in pools than runs in the autumn through winter. Reach‐scale analysis showed that abundance and mean body length of juvenile salmon significantly differed between differently regulated reaches during winter, associated with the dominant cover type in each reach. This study demonstrated that the habitat conditions determining juvenile masu salmon distribution differ according to the season and scale of analysis. Therefore, for conservation of fish communities, it is important to evaluate and conserve or create fish habitats in regulated reaches, with a focus on the hierarchy of spatial scales and seasonal differences. Copyright © 2007 John Wiley & Sons, Ltd.     

Determining habitat limitations of Maumee River walleye production to western Lake Erie fish stocks: documenting a spawning ground barrier

Tributaries provide spawning habitat for three of four major sub-stocks of Lake Erie walleye (Sander vitreus). Despite anthropogenic degradation and the extirpation of other potamodromous species, the Maumee River, Ohio, USA continues to support one of the largest fish migrations in the Laurentian Great Lakes. To determine if spawning habitat availability and quality could limit production of Maumee River walleye, two habitat suitability models were created for the lower 51 km of the Maumee River and the distribution and numbers of walleye eggs deposited in a 25 km stretch of river were assessed. Walleye eggs were collected using a diaphragm pump at 7 and 10 sites from March/April to May 2014 and 2015. The habitat suitability models showed that <3% of the river yielded ‘good’ walleye spawning habitat and 11–38% yielded ‘moderate’ walleye spawning habitat, depending on the model. However, a large set of rapids at river kilometer 28 and more than five river kilometers of less suitable habitat separated areas of ‘good’ habitat. The rapids may present a migratory barrier for many spawning walleye, as modeled water velocities exceed maximum estimated walleye swim speeds 71–100% of days during pre-spawn migration and spawning during the study period. In both study years, there was a sharp decline in mean egg numbers from spawning sites downstream of the rapids (439.7 eggs/2 min tow ± 990.6 SD) to upstream sites (5.9 eggs/2 min tow ± 19.4 SD). Physical barriers like rapids may reduce spawning habitat connectivity and could limit walleye production in the Maumee River.     

A MODEL INCORPORATING DISTURBANCE AND RECOVERY PROCESSES IN BENTHIC INVERTEBRATE HABITAT—FLOW TIME SERIES

We describe and demonstrate a model (Benthic Invertebrate Time Series Habitat Simulation) for calculating the effect of changes to flow regimes on benthic invertebrate habitat and population dynamics. The following inputs are required: a hydrograph (discharge time series), habitat–discharge relationship, disturbance–discharge relationship, wetted width–discharge relationship and a recolonization time series. Habitat–discharge, disturbance–discharge and wetted width–discharge relationships are common outputs from instream hydraulic habitat models (e.g. Physical Habitat Simulation, River Hydraulic Habitat Simulation and River2D). Hydraulic habitat models calculate a combined habitat suitability index from physical habitat suitability curves for water depth, velocity and substrate composition and weight this by area to give a weighted usable area (WUA). Because conventional invertebrate habitat suitability curves are based on density estimates, the combined habitat suitability index can be treated as an index of density and WUA treated as an index of potential relative abundance (at the reach scale) in the absence of disturbance due to flow variation (flooding and drying) and biotic processes. Our approach begins with WUA and calculates realizable suitable habitat (i.e. relative abundance) by taking into account the resetting of benthic invertebrate densities by floods and drying and recovery (or accrual) rates and times. The approach is intended mainly to compare the relative amounts of productive invertebrate habitat sustained by natural and modified flow regimes, but it also has the potential for investigating the influence of flow variation on invertebrate population dynamics. We anticipate that the model will be particularly useful for assessing effects of changes in flow regimes caused by diversions, abstractions or water storage on annual benthic invertebrate productivity. Copyright © 2013 John Wiley & Sons, Ltd.     

Physical and biological evolution of constructed reefs – long-term assessment and lessons learned

Artificial reefs are widely used to restore lost or damaged habitat, particularly spawning habitat. However, reefs are often designed without consideration for testing design features and constructed without clear objectives or a long-term assessment plan to evaluate changes in reef characteristics. To mitigate for degradation of lake trout spawning habitat in Thunder Bay, Lake Huron, we constructed 29 cobble reefs in 2010–11. Reef design incorporated height, orientation, and size as replicated factors. In addition to assessment of reef use by lake trout, we evaluated the biotic and abiotic changes in the reefs over five years post-construction and compared them to two adjacent degraded reefs and a semi-natural reef. Each reef was mapped annually by side-scan sonar to examine changes in the physical structure, such as slumping. Divers surveyed a subset of the reefs each year, and sampled substrate to quantify benthic macroinvertebrates, including zebra mussels. Algal colonization and round gobies were evaluated qualitatively. Temperature, dissolved oxygen, and sediment accumulation were measured over the winter at the vertical center and base of two reefs each year. Little physical change or sedimentation occurred. Qualitative abundance of coregonine eggs, presence of other fishes, and colonization by algae and macroinvertebrates increased throughout the monitoring period, indicating that the reefs have long-term value for a diversity of species.     

Associations of watershed vegetation and environmental variables with fish and crayfish assemblages in headwater streams of the Pedernales River,Texas

Intermittent headwater streams serve important functions for humans and wildlife in semi‐arid rangelands. Increases in ashe juniper coverage in central Texas over recent decades are believed to have negatively impacted stream flows. Few studies have examined relationships between aquatic species and environmental factors in these systems as well as the influence of juniper coverage on assemblage structure. During summer 2003 and spring 2004, we examined species–environment relationships to infer potential effects of juniper cover on aquatic ecology relative to local‐scale and watershed‐scale environmental variables. Fish and crayfish species assemblages and physicochemical variables were investigated in spring‐fed headwater tributaries of the Pedernales River, Texas. Fish abundance was much higher in summer 2003, whereas crayfish abundance was higher in spring 2004. Fish species richness was lower during spring 2004, possibly due to below average precipitation during spring 2004 that reduced deep‐water refugia. Higher abundance of crayfish in spring 2004 samples was probably due to their ability to survive low‐flow conditions, and a release from fish predation pressure. Fish assemblage structure was more strongly associated with local abiotic factors during spring 2004 when flow was reduced, whereas structure during summer 2003 samples suggested a relatively greater influence of predation. In general, juniper cover was weakly associated with fish and crayfish assemblages, although it tended to be positively associated with relatively high‐quality habitat for sensitive taxa (flowing runs with coarse substrate; deep, connected pools). We suggest that intermediate levels of juniper cover in the region provide indirect benefits to aquatic organisms. However, short‐term, local environmental factors appear to have a much greater influence than watershed vegetation on fish and crayfish assemblages in these intermittent streams. Copyright © 2007 John Wiley & Sons, Ltd.     

RELATIONSHIPS BETWEEN RIVER DISCHARGE AND ABUNDANCE OF AGE 0 REDHORSES (MOXOSTOMA SPP.) IN THE OCONEE RIVER,GEORGIA, USA,WITH IMPLICATIONS FOR ROBUST REDHORSE

Robust redhorse (Moxostoma robustum) and notchlip redhorse (M. collapsum) are two species of redhorses that reside in the lower Oconee River, Georgia. Robust redhorse is listed as a state endangered species in Georgia and North Carolina, and attempts to investigate factors affecting its reproductive success have met with limited success. Therefore, catch of robust redhorse young were combined with catch of notchlip redhorse to increase sample size. These congeners with similar spawning repertoire were assumed to respond similarly to environmental conditions. River discharge during spawning and rearing seasons may affect abundance of both redhorses in the lower Oconee River. An information‐theoretic approach was used to evaluate the relative support of models relating abundance of age 0 redhorses to monthly discharge statistics that represented magnitude, timing, duration, variability and frequency of river discharge events for April through June 1995–2006. The best‐approximating model indicated a negative relationship between the abundance of redhorses and mean maximum river discharge and the number of high pulses during June as well as a positive relationship with intermediate duration of low flows during April–June. This model is 9.6 times more plausible than the next best‐fitting model, which revealed a negative relationship between the abundance of redhorses and mean maximum river discharge during May and the number of high pulses during June as well as a positive relationship between abundance and intermediate duration of low flows during April–June. Management implications from the results indicate low‐stable flows for at least a 2‐week period during spawning and rearing may increase reproductive success of robust and notchlip redhorses. Copyright © 2012 John Wiley & Sons, Ltd.