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A simple device for measuring minimum current velocity to maintain semi-bouyant fish fish eggs in suspension.

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Abstract and Figures

Pelagic broadcast spawning cyprinids are common to Great Plains rivers and streams. This reproductive guild produces non-adhesive semi-buoyant eggs that require sufficient current velocity to remain in suspension during development. Although studies have shown that there may be a minimum velocity needed to keep the eggs in suspension, this velocity has not been estimated directly nor has the influence of physicochemical factors on egg buoyancy been determined. We developed a simple, inexpensive flow chamber that allowed for evaluation of minimum current velocity needed to keep semi-buoyant eggs in suspension at any time frame during egg development. The device described here has the capability of testing the minimum current velocity needed to keep semi-buoyant eggs in suspension at a wide range of physicochemical conditions. We used gellan beads soaked in freshwater for 0, 24, and 48 hrs as egg surrogates and evaluated minimum current velocities necessary to keep them in suspension at different combinations of temperature (20.0 ± 1.0°C, 25.0 ± 1.0° C, and 28.0 ± 1.0° C) and total dissolved solids (TDS; 1,000 ± 300 mg L-1, 3,000 ± 300 mg L-1, and 6,000 ± 300 mg L-1). We found that our methodology generated consistent, repeatable results within treatment groups. Current velocities ranging from 0.001–0.026 needed to keep the gellan beads in suspension were negatively correlated to soak times and TDS and positively correlated with temperature. The flow chamber is a viable approach for evaluating minimum current velocities needed to keep the eggs of pelagic broadcast spawning cyprinids in suspension during development.
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A Simple Device for Measuring the Minimum Current Velocity to Maintain
Semi-Buoyant Fish Eggs in Suspension
U.S. Geological Survey, Oklahoma Cooperative Fish and Wildlife Research Unit, Oklahoma State University, Stillwater, OK
U.S. Geological Survey, Texas Cooperative Fish and Wildlife Research Unit, Texas Tech University, Lubbock, TX 79409, USA
ABSTRACT Pelagic broadcast spawning cyprinids are common to Great Plains rivers and streams. This reproductive guild
though studies have shown that there may be a minimum velocity needed to keep the eggs in suspension, this velocity has not been
at any time frame during egg development. The device described here has the capability of testing the minimum current velocity
needed to keep semi-buoyant eggs in suspension at a wide range of physicochemical conditions. We used gellan beads soaked in
freshwater for 0, 24, and 48 hrs as egg surrogates and evaluated minimum current velocities necessary to keep them in suspension
mg L-1, 3,000 mg L-1, and 6,000 mg L-1). We found that our methodology generated consistent, repeatable results within treatment
groups. Current velocities ranging from 0.001–0.026 needed to keep the gellan beads in suspension were negatively correlated to
current velocities needed to keep the eggs of pelagic broadcast spawning cyprinids in suspension during development.
KEY WORDS minimum current velocity, pelagic broadcast-spawning cyprinids, semi-buoyant eggs, velocity chamber
At least 12 species of Great Plains cyprinids produce non-
adhesive semi-buoyant eggs that are broadcast into the water
column during spawning (Perkin and Gido 2011). This re-
productive strategy presumably allows eggs to complete de-
velopment while avoiding the risk of abrasive damage from
shifting sandy substrates characteristic of Great Plains rivers
and streams (Moore 1944). However, these pelagic broad-
cast-spawning cyprinids are in decline throughout the Great
Plainsandmost are of conservationconcern(Hoagstromet
al. 2011, Perkin and Gido 2011).Anthropogenic modica-
tions of the landscape, fragmentation of rivers through dam
Platania 2007, Durham and Wilde 2009, Hoagstrom et al.
2011, Perkin and Gido 2011).
In response to declining populations of pelagic broadcast-
spawning cyprinids, current research has focused on the min-
imum distance eggs require for drifting in order to complete
tigations have examined transport dynamics at coarse scales
through analysis of patterns of species presence and absence
or recovery of egg surrogates released during the spawning
evaluated the minimum distance required for egg transport
of eight species of pelagic broadcast-spawning Great Plains
cyprinids by determining the minimum stream fragment
length in which populations of these species have persisted
minnow(Hybognathus amarus) and Pecos bluntnose shiner
(Notropis simus pecosensis) suggestthatowvariabilitydue
to channel morphology and complexity may entrain eggs and
shorten the fragment length or reduce water requirements for
Widmer et al. 2012). There has been little attention directly
givento evaluating transportdynamicsthat might inuence
mum current velocity required to keep eggs in suspension)
Recent development of high-resolution models for evalu-
has encouraged the evaluation of velocity and discharge re-
quirements for successful reproduction. In this study, we de-
scribe a simple chamber and method for assessing current ve-
and provide the initial validation of this approach using gellan
The objectives of our study are to describe the creation and
operationforaow chamber that can be used to keepsemi-
buoyant eggs in suspension, while also providing results that
show how this device is capable of obtaining repeatable and
accurate results under different physicochemical conditions.
1 Current Address: Native Fish Lab, Marsh and Associates, LLC, Tempe, AZ 85282, USA
1 Corresponding author email address:
Mueller et al. • Measuring Velocity to Suspend Fish Eggs 85
Design and Construction
ponents: a submersible pump, a riser stem, a ball valve, and
a clear PVC observation and measurement chamber (Fig.
56.8 L min-1at1.7mofheadpressure.Theriserstem,tting,
and control valve included with the pump were connected
with a standard 2.09-cm diameter PVC ball valve. The use
oftwo valves allowed for bothne adjustments and main-
tenance of very low current velocities. Our lowest obtained
velocity was 0.001 m s-1,buttheowchamberhasthecapa-
bilities of lower velocities if needed. We cut a 2.09-cm diam-
eter clear PVC pipe to a length of 120 cm and attached to the
circles around the PVC pipe to delineate a length of 100 cm
centered 10 cm from the top and bottom of the PVC pipe. We
drew smaller hash marks every 1.0 cm on the pipe within this
100-cm length. We used these hash marks to calculate current
velocity by calculating the ratio between the time in seconds
from the bottom of the chamber to the hash mark. Addition-
ally, we used has marks to estimate discharge. We estimated
discharge by multiplying the area of the tube by the average
mately 3.2 kg and could be quickly broken down into two
pieces, making it portable and lightweight.
Prior to placing objects into the column, we closed the
ballvalvetoavoid asuddenjetofwaterwhenthedeviceis
turned on. We then placed the ow chamber into a 37.8-L
plastic tub. Tubs measured approximately 35 cm in depth,
47cmin width, and 47 cm in height, which was sufcient
to keep the pump fully submerged and was wide enough to
catch water as it spilled over the top of the column. We veri-
bob to ensure accurate and consistent measurements in all
We started the pump and opened the ball valve approxi-
mately 3–7% of a full turn to allow the column to slowly
50-cm mark on the pipe then allowed the column to continue
lling while adjusting the ball valve to keep the objects at
over the top of the column, we started a 1-min timer and ob-
served the gellan beads to ensure they remained stationary in
thecolumnwithoutanyadjustmentstotheball valve.If the
gellan beads remained stationary, then we recorded the verti-
cal position of each bead. If the objects had moved within
processuntil theobjectswereable toremainat equilibrium
measure the minimum current velocity needed to keep gellan beads in suspension. B) The clear PVC chamber with circles drawn
regulated at a given temperature and total dissolved solid treatment level. Trials were conducted during October 2012 in laboratory
facilities at Texas Tech University, Lubbock, USA.
2 cm
86 The Prairie Naturalist•45(2):December2013
during the 1-min test. Once this step was complete, we un-
pluggedthepumpand nofurtheradjustmentsweremade to
the valves for the remainder of the trial. If there was a need to
stem from the pump and turned them upside down over a dip
net. After the water was drained out of the pipe, we repeated
thepreviouslydescribed lling procedure and recorded the
Experimental Design
Weusedredgellan beads (TechnologyFlavors and Fra-
grancesInc.,Amityville,NewYork,USA) totesttheinu-
ence of water temperature and TDS on the minimum veloci-
ties required to keep egg surrogates in suspension. Originally
used in food and drinks, studies have shown these beads have
asimilarshape and specic gravity(SG)assomesh eggs
and do not change physically with the addition of salinity
beads are packaged in a preservative solution that can affect
theirSG. Reinertetal. (2004)soakedgellan beadsinwater
for 0, 24, and 48 hrs and found that SG was negatively cor-
related with soak time, presumably due to the absorption of
water. Therefore, the gellan beads were soaked in water for
For each soak time treatment group, we ran trials at three
different water temperatures: 20.0 ±1.0°C,25.0±1.0°C,
and 28.0 ±1.0° C.Thetemperature of thewaterwas main-
tained by the addition of one or more 50-W submersible heat-
soak time and temperature combination, there were also three
different TDS treatment levels: 1,000 mg L-1, 3,000 mg L-1
and 6,000 mg L-1. Total dissolved solid treatment levels were
established through the addition of the appropriate amount of
Instant Ocean seawater mix (Spectrum Brands, Cincinnati,
Ohio, USA). We determined the treatment levels based upon
values observed in the Canadian River during the spawning
season of pelagic broadcast-spawning cyprinids native to the
temperature × TDS treatment group. We placed three gellan
beads from each soak time × temperature × TDS treatment
groupinthe appropriate ow chamberandconductedthree
replicate trials per treatment group using the procedure de-
scribedabove. Weperformedpoweranalyses(Zar 1999) to
determine the appropriate number of trials per temperature,
TDS,soaktime treatment group.Themajority of thebeads
the column and in these cases we used a mean vertical posi-
tion for our velocity calculations. There were a few instances
(Table1) where one of the three beads would become sta-
an additional trial in these cases to ensure this was a result
of physical or SG differences that were found among gel-
lanbeads (Reinertetal.2004).Trialswhere thebeadswere
ed from analysis as visual examination indicated these beads
were damaged or otherwise deformed.
Weusedanalysisof covariance(ANCOVA)toevaluate
the effects of soak time, temperature, and TDS on the mini-
mum current velocity necessary to keep the gellan beads in
suspension with soak time as a covariate and temperature and
TDS as independent variables. We used Dunnett’s multiple
comparison procedure as a post-hoc test to evaluate differ-
ences among treatment groups. We performed all analyses
using SAS 9.2 (SAS Institute, Inc., Cary, North Carolina,
Our methodology generated consistent, repeatable results
of variation of the mean minimum current velocities for each
treatmentgroupdidnotcorrelatewithsoaktime(r = 0.02, P
=0.93),temperature(r = 0.22, P=0.28),orTDS(r = 0.30,
mum current velocity among treatment groups was approx-
imately 0.002 m s-1 based upon a post-hoc power analysis
(Zar1999).Asexpected,soak timehadaninuence on the
minimum current velocity necessary to keep gellan beads in
soaked in water prior to testing required lower current ve-
locities to remain in suspension than those that received no
Overall, soak time, TDS, and the interaction between
soak time and temperature explained approximately 83%
of the variation in current velocity required to keep gellan
beads in suspension. There was an inverse relationship be-
tween TDS and current velocity that was independent of soak
time and temperature (F1,83 = 23.08, P < 0.05). However,
temperature interacted with the three soak times differently,
of temperature and soak time exhibited a positive relation-
shiptominimumcurrentvelocity(β1 =0.0004,t1=3.18,P<
0.05), while the interaction of the other two soak times with
temperaturedidnotproduceaneffect(24hrs:β1 =−0.004,t1
=–1.65,P =0.10;48hrs:β1=−0.003,t1=–1.85,P =0.07).
Ourresultsdemonstratethat theowchamberdescribed
in this paper can be used to estimate minimum current ve-
locities required to keep semi-buoyant eggs in suspension
at any time during egg development and to provide the data
temporal scales. The results of our study are consistent with
Mueller et al. • Measuring Velocity to Suspend Fish Eggs 87
gellan bead behavior as predicted by basic physics and work
conductedbyReinertetal.(2004).An increase inTDSre-
sults in an increase in the density of the water medium, which
would increase the buoyancy of the gellan beads and thus
reduce minimum current velocity necessary to keep them in
suspension. Additionally, soaking the beads in water reduced
theirspecic gravityasthey absorbedwaterand resultedin
lower current velocities needed to keep them in suspension.
However, it seemed that the density of water inside and out-
sidethe gellanbeadswereinuenced similarlybytempera-
ture, resulting in relatively minor effect of temperature we
observed on minimum current velocity.
physicochemicalconditions such as, temperature and TDS;
however, the chamber may over simplify stream conditions.
For example, minimum current velocities obtained using this
device may be relative as the chamber only measures hori-
zontal rather than vertical movement. Furthermore, current
velocity in a stream is not the only factor that is keeping these
eggs in suspension. Turbulence created by interacting with
channel features and ripples created by sand bed features may
cause the velocity to be pushed in more of a quasi-vertical
motion rather than simple horizontal as in a pipe with lami-
Table1.Numberoftrials(n)persoaktime,temperature,andtotaldissolvedsolid(TDS)treatmentgroupwiththemean(± SD) and
range of minimum current velocities necessary to keep gellan beads in suspension. Trials were conducted during October 2012 in
laboratory facilities at Texas Tech University, Lubbock, USA.
Soaktime(hrs) Temperature(°C) TDS(mgL-1)n
Mean current velocity
020 1,000 40.017 ± 0.006
3,000 30.015 ± 0.005
6,000 30.015 ± 0.005
25 1,000 40.017 ± 0.006
3,000 30.018 ± 0.001
6,000 30.013 ± 0.006
28 1,000 30.026 ± 0.003
3,000 30.021 ± 0.009
6,000 30.016 ± 0.007
24 20 1,000 30.006 ± 0.001
3,000 30.005 ± 0.001
6,000 30.002 ± 0.001
25 1,000 50.005 ± 0.002
3,000 30.002 ± 0.000
6,000 30.001 ± 0.001
28 1,000 30.003 ± 0.001
3,000 30.001 ± 0.001
6,000 30.001 ± 0.001
48 20 1,000 30.007 ± 0.001
3,000 30.006 ± 0.001
6,000 40.003 ± 0.001
25 1,000 40.004 ± 0.003
3,000 30.001 ± 0.000
6,000 30.001 ± 0.001
28 1,000 30.005 ± 0.003
3,000 30.001 ± 0.000
6,000 40.001 ± 0.000
88 The Prairie Naturalist•45(2):December2013
Figure2.The effect oftemperatureand total dissolvedsolids (TDS) on the minimum currentvelocityrequiredtokeepgellan
beadssoaked0-hrs(A),24-hrs(B),and48-h rs(C)insuspension.TrialswereconductedduringOctober2012inlaboratoryfacili-
ties at Texas Tech University, Lubbock, USA.
Mueller et al. • Measuring Velocity to Suspend Fish Eggs 89
chamber calculates uplift velocity. Regardless, this device
may be appropriate for questions related to magnitudes of
differences when talking about stream velocity.
Past studies have demonstrated the importance of dis-
charge for pelagic broadcast-spawning shes in freshwater
systems(Reinert et al.2004,Medleyet al.2007);however,
there remains a lack of knowledge on the interactions be-
tween semi-buoyant eggs, the physicochemical environment,
and the ow dynamics within a river channel. Researchers
using this chamber can obtain both estimates of the mini-
mum current velocity needed to keep semi-buoyant eggs in
suspension and how physicochemical conditions inuence
this velocity. Understanding how changes in physicochemi-
cal conditions affect egg buoyancy may provide insight for
determining the fragment length necessary for successful re-
production, especially as streams become increasingly frag-
mented due to the creation of dams and impoundments.
Funding was provided by the U.S. Fish and Wildlife
Service Great Plains Landscape Conservation Cooperative.
B. Durham and two anonymous reviewers provided com-
ments and suggestions to improve this manuscript. Cooper-
ating agencies for the Texas Cooperative Fish and Wildlife
Research Unit are the U.S. Geological Survey, Texas Tech
University, Texas Parks and Wildlife, and the Wildlife Man-
agement Institute. Cooperating agencies for the Oklahoma
Cooperative Fish and Wildlife Research Unit are the U.S.
Geological Survey, Oklahoma State University, Oklahoma
Department of Wildlife Conservation and the Wildlife Man-
descriptive purposes only and does not imply endorsement
by the U.S. Government.
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fragmentationimperilpelagic-spawning riverine shes.
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Submitted 9 January 2013. Accepted 10 July 2013. Associate
Editor was Melissa Wuellner.
... In these species the eggs become suspended in the water column when experiencing flow. By remaining in the water column, these pelagic eggs benefit from exposure to well-oxygenated water, while avoiding abrasive damage from coarse substrates (Mueller et al., 2013). ...
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Truncated distributions of pelagophilic fishes have been observed across the Great Plains of North America, with water use and landscape fragmentation implicated as contributing factors. Developing conservation strategies for these species is hindered by the existence of multiple competing flow regime hypotheses related to species persistence. Our primary study objective was to compare the predicted distributions of one pelagophil, the Arkansas River Shiner Notropis girardi, constructed using different flow regime metrics. Further, we investigated different approaches for improving temporal transferability of the species distribution model (SDM). We compared four hypotheses: mean annual flow (a baseline), the 75th percentile of daily flow, the number of zero-flow days, and the number of days above 55th percentile flows, to examine the relative importance of flows during the spawning period. Building on an earlier SDM, we added covariates that quantified wells in each catchment, point source discharges, and non-native species presence to a structured variable framework. We assessed the effects on model transferability and fit by reducing multicollinearity using Spearman’s rank correlations, variance inflation factors, and principal component analysis, as well as altering the regularization coefficient (β) within MaxEnt. The 75th percentile of daily flow was the most important flow metric related to structuring the species distribution. The number of wells and point source discharges were also highly ranked. At the default level of β, model transferability was improved using all methods to reduce collinearity; however, at higher levels of β, the correlation method performed best. Using β = 5 provided the best model transferability, while retaining the majority of variables that contributed 95% to the model. This study provides a workflow for improving model transferability and also presents water-management options that may be considered to improve the conservation status of pelagophils.
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Surface push nets have been employed in the Savannah River estuary (SRE) to monitor striped bass Morone saxatilis spawning activity since the 1960s, but most intensively since the mid-1980s. These methods provide relative catch-per-unit-effort data for comparing station-to-station and year-to-year changes in egg abundance but do not provide total annual production estimates. To quantify the sampling efficiency of our gear, we investigated the use of gellan beads as striped bass egg surrogates. Gellan beads were comparable to striped bass eggs in size and specific gravity, and are appropriate surrogates for efficiency trials. In 1999 and 2000, we released known quantities of gellan beads to evaluate the efficiency of our egg sampling gear. Efficiency ranged from 1 bead per 11,300 at large (0.009%) to about 1 bead per 300,000 at large (0.0003%), depending on release and recapture locations. The use of egg surrogates was an effective and informative technique for evaluating our standardized egg sampling gear and may be similarly useful for other systems and other species with semibuoyant pelagic eggs. Additionally, the use of egg surrogates uncovered previously unsuspected biases in sampling efficiency because of differences in channel morphology and hydrology within the SRE.
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Impoundments, diversion dams, and stream dewatering have created a mosaic of large river fragments throughout the Great Plains of central North America. Coincident with these habitat changes are massive declines in the distribution and abundance of Great Plains fishes belonging to the “pelagic-spawning” reproductive guild. We analyzed longitudinal fragment lengths (measured in river kilometers, rkm) and literature accounts of population status for eight species from this guild across 60 fragments to derive thresholds in stream length associated with extirpations. Fragment length predicted population status (F2,21 = 30.14, P < 0.01), with lengths averaging 136 ± 21 rkm for extirpated, 226 ± 69 rkm for declining, and 458 ± 137 for stable populations. Fragment length explained 71% of reported extirpations and estimated thresholds in fragment length explained 67% of variation in population persistence. Our findings provide insight into appropriate spatial scales for conducting riverscape conservation approaches that address the hierarchical effects of fragmentation on stream-dwelling fishes.
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We studied daily growth-increment formation In the otoliths of early life history stages of Sharpnose Shiner, Notropis oxyrhynchus, and Smalleye Shiner, Notropis buccula, In the Brazos River, Texas to investigate the influence of streamflow and intermittency on the production of young. Both species successfully produced offspring throughout a four- to five-month period. Successful reproduction occurred over a longer period In 2004 than in 2003. The results of our study revealed that recruitment by N. oxyrhynchus and N. buccula populations In the Brazos River, Texas are related to streamflow In two principal ways. First, the greatest proportion of young-of-year produced during the reproductive season is associated with elevated streamflow events. Second, no young-of-year are successfully produced during periods of intermittency when the river Is not flowing. Our results suggest that the focus of conservation efforts, which to date have primarily concentrated on creating proper streamflow conditions for spawning, should also be focused toward ensuring proper conditions for survival of ova and young larvae.
We quantified the availability and utilization of habitat types by eight small-bodied cyprinid fish species, including the federally threatened Pecos bluntnose shiner Notropis simus pecosensis, in the Pecos River, New Mexico. The Pecos River is a medium-sized, sand-bed river with a highly variable hydrograph and some reaches characterized by historic and recent periods of flow intermittency. Fish habitat was described in four reaches at flows of 0.05–2.29 m/s by means of a simultaneous, coordinated program of channel topographic surveys, mesohabitat mapping, fish sampling, and measurement of microhabitat and chemical parameters. We determined that fish habitat in this sand-bed river was effectively described at the mesohabitat scale. Furthermore, mesohabitats were visually distinguishable and separable by means of hydraulic and geomorphic parameters and the relationship between flow and depth, velocity, and velocity : depth ratios. The eight cyprinid species in the Pecos River primarily used four mesohabitat types that were consistently available at the full range of flows examined, including perpendicular and parallel plunges, backwaters, and slackwaters. In winter, five species (red shiner Cyprinella lutrensis, plains killifish Fundulus zebrinus, plains minnow Hybognathus placitus, Arkansas River shiner N. girardi, and sand shiner N. stramineus) shifted to backwaters, where water temperatures were relatively warmer than those of the main channel. Runs, flats, and riffles were generally the most available mesohabitat types, but their availability changed with flow; only four species (red shiner, plains killifish, speckled chub Macrhybopsis aestivalis, and sand shiner) selected these types, and they did so infrequently in summer. The Pecos bluntnose shiner was a habitat specialist that selected primarily rare plunge pools at sandbar faces, whereas species such as the red shiner were habitat generalists that used a variety of mesohabitat types. We found that a range of base flows sustained the preferred habitats of the eight cyprinid species and that no single flow maximized this preferred habitat because of a scaling effect of flow on sand bedforms.
The Pecos River between Sumner Dam and Brantley Reservoir (320 km), New Mexico, contains populations of several pelagic-spawning cyprinid fish species, including the federally threatened Pecos bluntnose shiner (Notropis simus pecosensis). Females of this reproductive guild release semi-buoyant eggs that are fertilized and drift, incubate, and hatch on increased flows associated with spring runoff, summer rainstorms, or irrigation releases from Sumner Reservoir. We used artificial eggs (beads) to estimate transport and retention of natural eggs during an irrigation release in five reaches of the Pecos River occupied by bluntnose shiner. Bead retention was highest (1.7–4.5%/km) in the broad complex reaches of upper critical habitat and the quality section (upper 200 km), and bead retention was lowest (0.6%/km) in the narrow, deep, channelized reach of lower critical habitat (60 km). Only 10% of beads were transported more than 50 km from their release location in the reach with highest retention. Modeled spawning events in all five reaches showed highest egg retention of 35% in the reach that also had the highest density of adult Pecos bluntnose shiner (37 km from Cortez Gasline to Acme). The model predicted that during an irrigation release, about 90% of bluntnose shiner eggs produced during a natural spawning event are retained in the upper 250 km of occupied habitat, with only 10% passing downstream into unsuitable habitat or into Brantley Reservoir. We conclude that retention of drifting eggs is greatest during high flows when flood wave attenuation and channel storage are greatest and in broad complex channel reaches, which coincide with existing population centers.
Long-distance drift of eggs and larvae has been identified as a possible cause of downstream displacement and poor recruitment of the endangered Rio Grande silvery minnow (Hybognathus amarus; silvery minnow). Seven experiments were conducted using artificial eggs to estimate silvery minnow egg drift and retention in the Albuquerque and Isleta reaches of the regulated Middle Rio Grande, New Mexico, USA over a range of flows during expected spawning times. Bead retention varied by reach, discharge, and shape of the hydrograph. Highest retention (6.9 and 9.7% per km in the Albuquerque and Isleta reaches, respectively) occurred on the ascending limb of a high flow in areas where there was substantial floodplain inundation. Retention was maximized at different flows in each reach (97 and 140 m3/s, respectively), possibly associated with reach-specific floodplain inundation thresholds. Lowest retention in each reach (2.1 and 1.7%, respectively) occurred on the descending limb of low and high flows, respectively. Of the silvery minnow eggs produced in the combined Albuquerque and Isleta reaches in 2005, 8–14% are predicted to have been retained in the Albuquerque Reach (67 km) and 49–83% in the Isleta Reach (86 km) based on the distribution of adult fish and measured bead retention rates. Although silvery minnow propagules are capable of drifting long distances, our study suggests that considerable retention occurs in the Middle Rio Grande. Habitat restoration to increase channel habitat complexity, and flow management to promote floodplain inundation should help to retain a greater proportion of propagules in upstream reaches. Copyright © 2010 John Wiley & Sons, Ltd.
Rehabilitation of the Middle Rio Grande (MRG) in central New Mexico has become necessary because of changes in morphology resulting from the installation of dams, and because of habitat restoration considerations for the endangered Rio Grande silvery minnow (Hybognathus amarus). Bendway weirs are erosion control and channel-stabilization structures placed transverse to the channel flow that have been increasingly used to prevent river migration while simultaneously enhancing aquatic habitat. Plans for rehabilitation along the MRG include the use of bendway weirs; however, past projects using these structures have relied on field experience and engineering judgment rather than specific design guidelines. A physical model of a reach of the MRG was constructed to develop empirical design equations for eddy velocities in bendway weir fields. Data from physical model simulations were used to develop two empirical expressions for predicting eddy velocities behind bendway weirs, along with two expressions for predicting velocities at the toe of installed weirs. These equations relate the velocity found after bendway weir installation to weir design characteristics and pre-weir channel conditions. A designer can use the described approach to predict velocities in eddies and velocities at the toe of bendway weirs using only weir design variables and pre-weir channel conditions, and thus avoid some of the uncertainty with weir design that previously existed. Copyright © 2009 John Wiley & Sons, Ltd.