Upstream Movement Of Fish Research Articles

Population recovery of a migratory anadromous fish in a small forest stream following restoration of longitudinal connectivity

Restoration of movement corridors is a key management action used to address threats to migratory and other mobile species. Yet, we lack restoration effectiveness studies that allow for species to reestablish naturally (i.e. without supplementation) following habitat reconnection that capture all phases (dispersal, growth, and regulation) of recovery, and that takes an ecosystems approach. We investigated the natural recovery of migratory anadromous Coho salmon following habitat reconnection across a 5‐km section of Rock Creek, a forested tributary of the Cedar River, Washington, United States, 3 km upstream of Landsburg Dam. The dam blocked upstream fish movement for 102 years until the completion of a fish ladder in 2003. We also evaluated the response of non‐migratory trout, which are closely related to Coho salmon. Juvenile Coho salmon natal to the Cedar River dispersed into Rock Creek for rearing until spawning there in 2007. After restoration, juvenile Coho salmon density (fish/m2) increased 18‐fold, approaching an asymptote (i.e. regulation phase) a decade later. Coho salmon recovery in Rock Creek was spatially variable, however, slowing with distance from the site of restoration. Trout density was also higher after restoration relative to before, likely due to several mechanisms, including increased capacity resulting from the reestablishment of marine organic matter subsidies delivered by spawning anadromous fish. Our study demonstrates that migratory species can recover naturally after the restoration of habitat connectivity and associated movement corridors. Furthermore, our results suggest that such actions can also benefit nontarget species by reestablishing key ecosystem links driven by the target species.

A perched culvert and natural obstructions limit fish dispersal in an intermittent prairie stream

Poorly constructed road crossings block upstream movement of fish into stream reaches that provide critical habitat or connect isolated populations. Although removing these barriers is often a conservation priority, quantifying fish passage following removal has not been well studied, particularly in intermittent streams. In this study, we sought to understand how barriers influence the dispersal of fishes in intermittent prairie streams. We used passive integrated transponder tags and antenna stations to quantify fish movement of 3 prairie-stream fishes (Central Stoneroller Campostoma anomalum [Rafinesque, 1820], Southern Redbelly Dace Chrosomus erythrogaster [Rafinesque, 1820], and Creek Chub Semotilis atromaculatus [Mitchill, 1818]) through a road crossing in an intermittent prairie stream for 3 y before and 3 y after removing a perched culvert. We verified that no upstream fish movement occurred through the culvert, despite large aggregations of tagged fish in the intermittent reach below the culvert. In contrast, tagged individuals of all 3 species were detected above the road crossing in each of the 3 y following removal. We also tracked the recovery of these species, plus the Orangethroat Darter Etheostoma spectabile (Agassiz, 1854), following a severe drought in 2018 in 2 spring-fed tributary reaches, 1 without a downstream barrier and 1 with the removed downstream culvert. Surveys of the tributary reaches showed rapid recovery of fish densities following drought in the tributary without a downstream barrier. However, recovery at the site above the removed culvert appeared to be limited by a natural waterfall. Our observations suggest barrier removal allowed access to spawning habitat within the intermittent reach immediately upstream of the site, but other obstacles or shear distance to perennial spring-fed tributary reaches also limited recolonization following severe drought. Increased connectivity between perennial and intermittent reaches in prairie streams likely benefits fishes by increasing their resilience following disturbance and providing habitat during critical life stages.

An ecologically dispatch strategy using environmental flows for a cascade multi-sluice system: A case study of the Yongjiang River Basin, China

The construction of estuary sluice has profound and adverse biological consequences through its effect on the hydrodynamic process and salinity gradient. Environmental flow plays an essential role in the conservation of the ecological environment, but its calculation methods remain biased towards the traditional single-target fish species. Consequently, these flows ignore the ecological requirements of different biological communities and therefore disregard the long-term perspective of the riverine and estuarine ecosystem. Actually, we found that once the sluice was built, the available habitat throughout the river would show a degradation by 81.55% for fish that produce floating eggs and 14.25% for fish that produce sticky eggs. In addition, changes in the distribution of salinity in estuaries and coastal waters caused by the closure of sluice indicated that the habitats of fish living in low-salinity areas would disappear. This study proposes an ecologically oriented multi-sluice system operation strategy that integrates the demands of fish with different living habits on environmental flow into the joint operation of a multi-sluice system to maintain different ecological functions throughout the Yongjiang River basin. The spawning habits of fish in the study area were investigated, and the differences in their adaptability to various hydrological factors were summarized. MIKE 21 model and PHABSIM were used to ascertain the environmental flow through the data of velocity, water depth, and salinity. Model predictions of the effective habitat were supplemented by the optimum selection, and the discharge of the Fenghua River was suggested to be 105 m3/s. Likewise, the survival salinity requirements revealed that the discharge of Yongjiang sluice should reach 250–300 m3/s. Results were used to design the joint ecological scheduling schemes, with the aiming of ensuring that the flow velocity of the entire migration channel can meet the requirements of facilitating the upstream movement of fish whilst keeping eggs floating. In the Considering the upstream ability of fish, the tidal law of the estuary and the planned discarded water of estuary sluice, it is suggested that during the spawning time, seven consecutive days of the ebb tide should be selected to carry out the joint operation of Fenghua, Yaojiang and Yongjiang River, and the flow constraint factors are 105, 100 and 250 m3/s, respectively.

Experimental and numerical studies on deflector configuration in straight flood channel for heterogeneous flow enhancement and fish habitat improvements

For ecological restoration of concrete flood channels, installing current deflectors is a straightforward, cost-effective, and efficient approach with minimal maintenance. It is important to find the appropriate arrangement, orientation, number, protrusion length, width, and spacing of deflectors to achieve an effective flow pattern. In this research, indoor flume experiments were carried out to identify the flow conditions and fish trajectories in the absence and presence of deflectors. Deflectors were found to enhance the flow heterogeneity and benefit the upstream movement of fish in the floodway. To further optimize the design, a 2D numerical simulation was conducted to predict the effectiveness of different deflector configurations. The results showed that compared with aligned deflectors or solid triangles, staggered deflectors and central islands were more suitable for the creation of non-uniform flows and pool areas. The optimum orientation of deflectors was perpendicular to the flow. A set of four deflectors with appropriate intervals along the channel was highly recommended. It was found that the ideal contraction ratio (α= deflector length / channel width) was between 25% and 50% to protect the river bank and bed from erosion. As the width of the deflector had less effect on the flow pattern, the narrowest deflector with a ratio (β) between deflector width and channel width of approximately 17%, was found to be preferable considering the construction cost. The ratio (γ) between deflector spacing and channel width was proposed to be set from 1.67 to 2.5 for flow concentration and sinuosity generation.

Stairs pipe culverts: flow simulations and implications for the passage of European and Neotropical fishes

Culvert fishways can improve upstream fish passage in brooks and have been studied in relation to North American and Australian species. Research focusing on fish species from other world regions and, in parallel, effect of baffles on flow turbulence is rare. In this paper we present computational fluid dynamics of a sloped baffle culvert, called “stairs pipe”. We aimed at evaluating if: (1) the flow met the requirements of Neotropical and European species; (2) the flow turbulence was acceptable for fish passage; (3) the flow limited fish movements. The average flow velocities for 5% slope and discharge rates of 5–13 L/s were lower than the prolonged speeds of three Neotropical species, namely, piau (Leporinus reinhardti), mandi (Pimelodus maculatus), and lambari (Piabarchus stramineus) and higher than the sustainable speeds of three European species, namely, dace (Leuciscus leuciscus), barbel (Barbus barbus), and brown trout (Salmo trutta). The turbulence flow characteristics i.e. levels of turbulence kinetic energy were similar to those produced by comparable culverts but higher than those in a fish ladder. The water jet created by baffles at an angle of 30° can limit fish movements, restraining them from jumping. The stairs pipe might improve upstream fish movement in different regions of world; nevertheless, further experimental research should concern the use of different swimming modes in the culvert flow.

Spatial covariation of fish population vital rates in a stream network

Animal populations are spatially structured in heterogeneous landscapes, in which local patches with differing vital rates are connected by dispersal of individuals to varying degrees. Although there is evidence that vital rates differ among local populations, much less is understood about how vital rates covary among local patches in spatially heterogeneous landscapes. In this study, we conducted a nine‐year annual mark–recapture survey to characterize spatial covariation of survival and growth for two Japanese native salmonids, white‐spotted charr Salvelinus leucomaenis japonicus and red‐spotted masu salmon Oncorhynchus masou ishikawae, in a headwater stream network composed of distinctly different tributary and mainstem habitats. Spatial structure of survival and growth differed by species and age class, but results provided support for negative covariation between vital rates, where survival was higher in the tributary habitat but growth was higher in the mainstem habitat. Thus, neither habitat was apparently more important than the other, and local habitats with complementary vital rates may make this spatially structured population less vulnerable to environmental change (i.e. portfolio effect). Despite the spatial structure of vital rates and possibilities that fish can exploit spatially distributed resources, movement of fish was limited due partly to a series of low‐head dams that prevented upstream movement of fish in the study area. This study shows that spatial structure of vital rates can be complex and depend on species and age class, and this knowledge is likely paramount to elucidating dynamics of spatially structured populations.

A potential engineering solution to facilitate upstream movement of fish in mountain rivers with weirs: Southern Carpathians, the Azuga River

An important aspect in the restoration of longitudinal connectivity in rivers and streams is the implementation of fish migration systems at the upstream of the functional hydraulic structures (weirs, drop structures or river sills). The diversity of these existing structures as well as the different locations of these weirs within the river, watershed and riparian zone challenge the design engineers to find new holistic solutions for fish migration systems. The Azuga River study area requires a new synergistic fish migration design system. Being a mountain area, rapid increase in water level is quite frequent, especially after heavy or prolonged rainfalls and during spring snow melt. Therefore, it is necessary to design a specific system for fish migration to meet this locations requirements. Due to the characteristics in this location of the Azuga river, the classic fish migration systems would not be functional. The indigenous/mountain trout is considered as the target species in this paper. Although this is a good swimming species, the use of classical systems could, due to exhaustion, prevent and/or reduce the movement of fish upstream of the two weirs (also known as river sills). This new, comprehensive solution, presented in this paper includes: (i) the restoration and stabilization works of the right bank in the weir study area by using biotechnical measures and (ii) the upstream migration system itself - for supporting the migration of fish on the Azuga River.

Use of Cylindrical Bristle Clusters as a novel multispecies fish pass to facilitate upstream movement at gauging weirs

Globally, gauging weirs are commonly installed in rivers to monitor flows. They have widespread negative impacts on the upstream movement of fish due to the barriers created by the unfavourable hydraulic conditions on the downstream face. There is a need to develop simple low-cost solutions to enhance multi-species fish passage, while not impacting the ability of these structures to gauge flow or increasing their potential to accumulate debris. This study investigated the use of an array of Cylindrical Bristle Clusters (CBCs), mounted on the downstream face of Crump weirs, to improve upstream passage of multiple species of fish while maintaining gauging accuracy. The simplicity and modularity of the design helps improve cost effectiveness and ease of installation. Laboratory tests with roach (Rutilus rutilus) showed that the passage efficiency of a Crump weir was increased from 0% (control) to ≈30% when retrofitted with CBCs. Swim path analysis indicated fish utilised low velocity zones in the wake of clusters to facilitate passage. Time taken to pass the weir and length of the swim path were greatest under the highest cluster density, where manoeuvrability was most constrained. Following these promising experimental results, the fish pass efficiency of a weir retrofitted with a staggered array of CBCs, was evaluated in the field. Upstream passage of a number of non-salmonid fish, including chub (Squalius cephalus) and roach, was monitored using Passive Integrated Transponder telemetry at a 7 m long, 1.2 m wide, Crump weir with a 1:5 downstream slope. Overall passage efficiency, considering all species, increased from 2% to 14% when the fish pass was installed, and for chub from 0 to 52%. Debris accumulation was minimal during the test period. Assessment of the impact of a variety of CBC array densities on gauging was also undertaken. As predicted using theory, there was no effect on gauging when arrays were placed downstream of the point at which flow regime changes from sub- to supercritical. This study highlights the potential for a staggered array of CBCs to improve the upstream passage of multiple species of fish at gauging weirs, common barriers to fish migration throughout the world, without affecting the accuracy of flow gauging.

Effects of interlocked carpet ramps on upstream movement of brown trout Salmo trutta in an upland stream

This paper assesses the extent to which Interlocked Carpet Block Ramps (ICBRs) impede the upstream movement of brown trout Salmon trutta (L. 1758). It presents model simulations of hydraulic conditions across an ICBR of the type used widely for energy dissipation in high gradient rivers. Model simulations were related to published hydraulic suitability criteria for upstream movement of fish to assess the usability of individual routes, connectivity between routes and whether routes were available to allow upstream passage across the whole ramp. Results suggest that connected routes were available at most of the simulated discharges. Nevertheless, higher and lower discharges appeared to impose constraints, due to swimming ability and minimum useable water depths, respectively. Precise patterns of hydraulic suitability and connectivity of potential routes at different discharges varied appreciably between simulations using the different hydraulic criteria.

Measuring 30 years of improvements to aquatic connectivity in the Greater Toronto Area

Instream barriers (e.g. dams, weirs and road crossings) fragment aquatic habitat and prevent the upstream movement of fish, impairing the ability of fishes to complete critical life stages, access critical habitat and for dispersal among local populations. Mitigation efforts have improved aquatic connectivity to some degree, but it has been challenging to quantify the overall improvement in connectivity without long-term and costly field assessments. The development of spatially explicit habitat connectivity indices make it possible to evaluate current stream connectivity, and quantify the improvement prior mitigation projects have had on connectivity. We combined a list of instream barrier mitigation projects completed in five watersheds in the Toronto (Ontario, Canada) area from 1987–2016 (mitigated barriers) and a previously established inventory of all known instream barriers in 2016 (current barriers). The cumulative improvement to connectivity was measured for potadromous (remain in tributaries) and diadromous (move between tributaries and lake) fish species using the dendritic connectivity index. Aquatic connectivity improved for diadromous species between 0 and 14.5% and for potadromous species between 0.1 and 4.4% in the five studied watersheds. Some variation in improvement among the watersheds can likely be attributed to differences in mitigation strategies among the watersheds and a historical emphasis on mitigating instream barriers to benefit migratory salmonid species.

Possibilities of fish passage through the block ramp: Model-based estimation of permeability

Block ramps offer an opportunity to combine hydrotechnical structures with fish passages. The primary study objective was to evaluate the effectiveness of a block ramp for upstream fish movement in a mountain stream. Geodetic measurements of the bottom surface and water level were taken for three cross-sections. The description of the geometric and hydrodynamic parameters of the block ramp was supplemented with information on the width and length of crevices between boulders. Measurements of the geometric and hydrodynamic parameters of the block ramp were performed at 76 measurement sites, at three different types of discharge. Ichthyological data were collected in the analyzed stream. Measurements covered among others total length, width, and height of caught fish. Salmonid, cottid, balitorid, and cyprinid fish were studied. The determination of the main effects of the geometric and hydrodynamic parameters of the block ramp on the possibilities of use by target fish species employed generalized linear models (GLMs). The study shows that the block ramp cannot provide longitudinal connectivity and migration of fish occurring in the mountain stream. According to estimates, the block ramp did not meet the permeability expectations. The reason for low usefulness of the ramp for fish is particularly excessively strong water current. The stream concentration constituted an unsurmountable velocity barrier for fish moving upstream for each of the analyzed discharges. The developed model suggests that some crevices in the side zones of the ramp could be parts of the migration corridor, but only for small and medium-sized fish. At medium and high water stages, movement of fish in crevices was difficult due to fast water current, and at low and very low discharges, some crevices lost their permeability, and could become ecological traps for fish. The necessity of estimation of ramp permeability during pre-construction phase was emphasized.

Fishway with two entrance branches: Understanding its performance for potamodromous Mediterranean barbels

AbstractMany fish passes have been built across the world in recent years. This study analyses the performance of a modified type of pool and weir fishway with two access branches, using passive integrated transponder telemetry. A circum‐Mediterranean barbel, Luciobarbus bocagei (Steindachner, 1864), was chosen as the target species. Both hydraulic values (flow and volumetric energy dissipation) and biological parameters (attraction, entrance and passage success) were measured in the fishway, these being related to the environmental variables affecting upstream fish movement. Flow discharge, water temperature and atmospheric pressure were important for fish entering the fishway. There was no preference between path routes, even though the main discharge was concentrated in the turbine channel. This type of fishway design could be an alternative for the conservation of fish populations where multiple fish approach options are possible.

Potential barriers to upstream fish passage caused by anthropogenic river modifications: A computer modeling study of emerald shiners (Notropis atherinoides) in the upper Niagara River

Anthropogenic modifications at the head of the Niagara River attributed to land reclamation and the installation of vertical, bulkhead seawalls have altered the river channel, leading to increased water velocities and reduced availability of aquatic habitat. As a result of the increased velocities in the channel, concerns have been raised that the habitat connectivity of the emerald shiner (Notropis atherinoides), a key forage species for sportfish and threatened avian species, has been reduced between Lake Erie and the upper Niagara River. In this study, the influence of water velocity stressors on emerald shiner movement was assessed by identifying potential hydrodynamic barriers to upstream fish movement using a combination of depth-averaged velocities simulated in a 2-D hydrodynamic model and field measurements collected with a current meter. Results indicate that high velocities (in excess of 2.0ms−1) immediately downstream of the Peace Bridge, an international road crossing between Buffalo, NY, USA and Fort Erie, Ontario, Canada, restrict potential emerald shiner movement to within close proximity of either shoreline. Along both shorelines, several additional threats to successful upstream passage exist, the largest of which are located along vertical bulkhead seawalls. The extent of the identified potential barriers fluctuates slightly with water level, but the locations remain consistent. Finally, of the potential barriers identified using the model, the field measurements indicate the seawall along Broderick Park, along the U.S. shoreline, is the most substantial impediment to upstream movement, as velocities within several shiner body-lengths of the shoreline remain between 0.83 and 1.18ms−1 for nearly 200m. The results of this study, in conjunction with empirical estimates of passage success, swimming tests on shiners native to the Niagara River, and additional field measurements will help determine if remediation work is warranted to facilitate upstream passage at the identified impediments.

Population connectivity and genetic structure of burbot (Lota lota) populations in the Wind River Basin, Wyoming

Burbot (Lota lota) occur in the Wind River Basin in central Wyoming, USA, at the southwestern extreme of the species’ native range in North America. The most stable and successful of these populations occur in six glacially carved mountain lakes on three different tributary streams and one large main stem impoundment (Boysen Reservoir) downstream from the tributary populations. Burbot are rarely found in connecting streams and rivers, which are relatively small and high gradient, with a variety of potential barriers to upstream movement of fish. We used high-throughput genomic sequence data for 11,197 SNPs to characterize the genetic diversity, population structure, and connectivity among burbot populations on the Wind River system. Fish from Boysen Reservoir and lower basin tributary populations were genetically differentiated from those in the upper basin tributary populations. In addition, fish within the same tributary streams fell within the same genetic clusters, suggesting there is movement of fish between lakes on the same tributaries but that populations within each tributary system are isolated and genetically distinct from other populations. Observed genetic differentiation corresponded to natural and anthropogenic barriers, highlighting the importance of barriers to fish population connectivity and gene flow in human-altered linked lake-stream habitats.

Constraints upon the response of fish and crayfish to environmental flow releases in a regulated headwater stream network.

In dry climate zones, headwater streams are often regulated for water extraction causing intermittency in perennial streams and prolonged drying in intermittent streams. Regulation thereby reduces aquatic habitat downstream of weirs that also form barriers to migration by stream fauna. Environmental flow releases may restore streamflow in rivers, but are rarely applied to headwaters. We sampled fish and crayfish in four regulated headwater streams before and after the release of summer-autumn environmental flows, and in four nearby unregulated streams, to determine whether their abundances increased in response to flow releases. Historical data of fish and crayfish occurrence spanning a 30 year period was compared with contemporary data (electrofishing surveys, Victoria Range, Australia; summer 2008 to summer 2010) to assess the longer–term effects of regulation and drought. Although fish were recorded in regulated streams before 1996, they were not recorded in the present study upstream or downstream of weirs despite recent flow releases. Crayfish (Geocharax sp. nov. 1) remained in the regulated streams throughout the study, but did not become more abundant in response to flow releases. In contrast, native fish (Gadopsis marmoratus, Galaxias oliros, Galaxias maculatus) and crayfish remained present in unregulated streams, despite prolonged drought conditions during 2006–2010, and the assemblages of each of these streams remained essentially unchanged over the 30 year period. Flow release volumes may have been too small or have operated for an insufficient time to allow fish to recolonise regulated streams. Barriers to dispersal may also be preventing recolonisation. Indefinite continuation of annual flow releases, that prevent the unnatural cessation of flow caused by weirs, may eventually facilitate upstream movement of fish and crayfish in regulated channels; but other human–made dispersal barriers downstream need to be identified and ameliorated, to allow native fish to fulfil their life cycles in these headwater streams.

Assessing the Effects of Historical Exposure to Endocrine-Active Compounds on Reproductive Health and Genetic Diversity in Walleye, a Native Apex Predator, in a Large Riverine System

In this combined field and laboratory study, we assessed whether populations of native walleye in the Upper Mississippi River experienced altered genetic diversity correlated with exposure to estrogenic endocrine-active compounds (EACs). We collected fin-clips for genetic analysis from almost 600 walleye (13 sites) and subsampled 377 of these fish (6 sites) for blood and reproductive organs. Finally, we caged male fathead minnows at 5 sampling sites to confirm the presence of estrogenic EACs. Our findings indicate that male walleye in four river segments produced measurable concentrations of plasma vitellogenin (an egg-yolk protein and, when expressed in male fish, a biomarker of acute estrogenic exposure), a finding consistent with the presence of estrogenic EACs and consistent with published historical data for at least three of these study sites (Grand Rapids, St. Paul, and Lake City on Lake Pepin). Patterns of vitellogenin induction were consistent for native walleye and caged fathead minnows. No widespread occurrence of histopathological changes, such as intersex was found compared with published reports of intersex at the furthest downstream study site. To assess possible effects of estrogenic exposure on the genetic diversity of walleye populations at the study sites, we DNA-fingerprinted individual fish using 10 microsatellite loci. Genetic differences were observed between populations; however, these differences were consistent with geographic distance between populations, with the largest observed difference in genetic diversity found between fish upstream and downstream of St. Anthony Falls (and/or Lock and Dam 1 of the Mississippi River), traditionally a historical barrier to upstream fish movement. Although the persistent occurrence of endocrine disruption in wild fish populations is troubling, we did not detect degradation of reproductive organs in individual walleye or alteration in genetic diversity of walleye populations.

Evidence of a Year-Round Resident Population of Lake Sturgeon in the Kettle River, Minnesota, Based on Radiotelemetry and Tagging

We used radiotelemetry to study the movement of lake sturgeon Acipenser fulvescens in the Kettle River of east-central Minnesota. Our objectives were to determine whether the tracked fish were seasonal or year-round residents of the river and to determine their seasonal movements, responses to changes in discharge, and activity centers. We were also interested in the response of these fish to the removal of a hydroelectric dam that had blocked upstream movement of fish for 87 years. Eight fish received transmitter implants and were tracked for about 7 months, from October 1994 through May 1995. Three tagged fish were not identified or located thereafter, but the remaining five were tracked weekly from April 1995 to September 1996. Lake sturgeon did not move upstream of the former hydroelectric dam or downstream of the Kettle River's confluence with the St. Croix River but rather remained within this 20-mi reach, despite the absence of physical barriers at either end. We found that sturgeon movement was highly correlated with change in discharge, with upstream movements occurring during periods of rising discharge and downstream movements during falling discharge. Lake sturgeon used activity centers, with approximately 80% of the weekly daytime observations falling within four activity centers. Using mark–recapture techniques, we also documented that the lake sturgeon population in the Kettle River is small, and it appeared to mix very little with adjacent populations. We believe that if this population does mix with other nearby populations, mixing probably occurs on a time scale of years rather than weeks or months.

Differences in an ensemble of streamside salamanders (Plethodontidae) above and below a barrier to brook trout

AbstractI examined the species composition, relative abundances, and size distributions of an ensemble of streamside salamanders in two contiguous sections of an Appalachian headwater stream: one containing brook trout and one that was trout free. The two stream sections were separated by a natural waterfall that formed a permanent barrier to the upstream movement of fish. The two stream sections differed in the overall abundance of salamanders, the relative abundance of the six species present, and the size-distribution of the salamander ensemble. These results suggest that brook trout have an effect on the structure of co-occurring ensembles of salamanders, and that the continued coexistence of stream salamanders with brook trout does not indicate lack of strong ecological interactions.

Dispersal, Boundary Processes, and Trophic‐Level Interactions in Streams Adjacent to Beaver Ponds

I combined long—term (10 yr) descriptive and short—term experimental studies in a headwater stream in northern Minnesota to assess: (1) the effect of annual variation in stream discharge and spatial proximity of beaver (Castor canadensis) ponds on lotic fish abundance and (2) the subsequent influence of discharge and fish predation on lotic invertebrate colonization. Considerable annual variation in fish density occurred in the stream over the 10—yr period, particularly in pool habitats. Increased fish density was associated with increased stream discharge and creation of beaver ponds downstream from the study site. Wiegert traps used to monitor directional (upstream vs. downstream) fish movement during the last 4 yr of the study indicated annual changes in fish density were associated with the amount of fish dispersal occurring along the stream segment. Downstream fish movement, out of an upstream beaver pond occurred primarily during periods of elevated stream discharge. Upstream movement, out of a downstream beaver pond, occurred over a broader range of discharge conditions. A controlled, "slpit—stream," experiment examining the effect of very low vs. elevated discharge on upstream fish movement indicated, however, that upstream movement of fish out of beaver ponds was also reduced by very low discharge conditions. Movement data for individual fish species revealed considerable variation among the taxa in the tendency for downstream vs. upstream movement, due to variation in the morphology of upstream vs. downstream beaver ponds and its subsequent effects on the composition of fish dispersing from these source areas. Most fish movement occurred over relatively brief time periods, suggesting life history and developmental processes were critical in influencing the timing of dispersal. Size structure of fishes captured in the stream indicated predominantly older age classes (>age I) of fish where dispersing along the stream. However, based on the occurrence of age O individuals only 1 of 12 species, the creek chub Semotilus atromaculatus), routinely reproduced in the stream. Experiments conducted in an artificial stream located below one of the beaver ponds indicated discharge and fish predation have potentially strong and interactive effects on invertebrate colonization in stream ecosystems. Differences in colonization of riffles and pools under low vs. elevated discharge and fish vs. no—fish treatments suggested, however, that the interactive effect of these factors on invertebrate colonization was variable over even small spatial scales. Elevated discharge increased invertebrate colonization in riffles but decreased invertebrate colonization in pools. Contrary to intuitive expectations, fish predation reduced invertebrate colonization more under elevated than low discharge conditions, particularly in pool habitats. Taken together, these results: (1) beaver ponds act as reproductive "sources" for fish on the landscape, while adjacent stream environments act as potential reproductive "sinks," (2) large—scale spatial relationships between beaver ponds and streams, along with the influence of discharge on the permeability of the boundaries between these habitats, are critical in controlling fish dispersal between ponds and streams and the subsequent abundance and composition of fish in lotic ecosystems, and (3) fish predation and discharge have potentially cascading effects on invertebrate colonization in lotic ecosystems.

The lake sturgeon, Acipenser fulvescens, in the Menominee River, Wisconsin-Michigan

The Menominee River is the boundary between the Upper Peninsula of Michigan and northeastern Wisconsin. It contains one of the few fishable lake sturgeon populations remaining in either state. Two sections of the river harbor naturally reproducing sturgeon stocks. Dams at either end of these sections curtail upstream movement of fish; however, some sturgeon move downstream over the dams. Surveys conducted in 1969 and 1970 and again in 1978 and 1979 intensively studied the sturgeons in a 42 km stretch of the river. Mark and recapture estimates of the number of sturgeon longer than 25 cm in this section ranged from 1884 to 2865. The number of fish longer than 107 cm ranged from 185 to 243. An estimate of 2834 sturgeon between 25 and 165 cm was made on a different 34 km stretch in 1979. Censuses on the hook and line fishery in 1969 and 1970 estimated sturgeon harvests of 59 and 48 fish, respectively. In 1974, the size limit was raised from 107 to 127 cm. Harvests of these larger fish were estimated at 19 and 41 in 1981 and 1982, respectively. Some other characteristics of the sturgeons and the fishery on the Menominee are also included.