Effects of experimentally enhanced flows on fishes of a small Texas (U.S.A.) stream: assessing the...

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Freshwater Biology (1996) 35, 349–362

APPLIED ISSUES

Effects of experimentally enhanced flows on fishes ofa small Texas (U.S.A.) stream: assessing the impact ofinterbasin transfer

W I L L I A M J . M A T T H E W S , * † M A R K S . S C H O R R § A N D M I C H A E L R . M E A D O R ¶University of Oklahoma Biological Station, HC 71 Box 205, Kingston, OK 73439, U.S.A. and *Department of Zoology,University of Oklahoma, Norman, OK 73019, U.S.A.

§Present address: Department of Biology and Environmental Science, University of Tennessee at Chattanooga, Chattanooga,TN 37403, U.S.A.¶Present address: U.S. Geological Survey, Water Resources Division, 3916 Sunset Road, Raleigh, NC 27607, U.S.A.†Author to whom correspondence should be sent

S U M M A R Y

1. Completion of a large interbasin water transfer system in northern Texas (U.S.A.)provided the opportunity to test the effects of pre-planned, experimental increases(µ 330) in flow on the fish fauna of a small, low-gradient, natural stream that wasincluded as part of the conveyance system. Water from Lake Texoma (Red River basin)was pumped via a 16-km pipeline to the headwaters of Sister Grove Creek (Trinity Riverbasin), which then carried the donor water 50 km downstream to Lake Lavon.2. Baseline (pre-transfer) data on the composition of fish assemblages at seven stationson the creek or at its confluence with the receiving reservoir were collected monthly for3 years, and similar data were collected for 2 years during and after trial flows of LakeTexoma water to Sister Grove Creek. We also documented fish abundance at five creekstations immediately before and after three trial flow periods of 10–14 days each insummer and autumn.3. Multivariate analysis of all routine monthly samples over the 5-year pre- and post-transfer period showed moderate changes in the fish fauna of the creek after initiationof the trial flows. Samples taken within a week before and after the artificial high flowsshowed little overall change in abundance of individual fish species, but at somestations the quantitative or qualitative change in composition of the local assemblagewas substantial.4. The trial flows lasted 2 weeks or less. Long-term effects of water transfer on the fishfauna of Sister Grove Creek can only be determined after the conveyance system goesinto normal operation, with periods of artificial flow of longer duration.

Introduction

As water demand in many regions exceeds supplies, to carry water to a recipient system. The ecologicalconsequences of interbasin water transfer throughmanagers have turned to interbasin transfers of water

from source to user localities (Davies, Thoms & natural stream systems remain poorly known. In spiteof potential introduction of exotic taxa or alteration ofMeador, 1992; Meador, 1992). Some, like the Garrison

Diversion Project in the northern U.S.A. and Canada native biota, there have until now been no pre-planned,experimental assessments of the effects of donor water(Davies et al., 1992), plan to use natural stream channels

© 1996 Blackwell Science Ltd 349

350 W.J. Matthews, M.S. Schorr and M.R. Meador

passing through a natural stream to a receiving system.Davies et al. (1992) reviewed water diversion projectsin Africa, Australia and the U.S.A., and emphasizedthat, ‘not one . . . received any form of comprehensiveenvironmental/ecological impact assessment beforeconstruction’. Here we summarize a large-scale experi-ment on effects of interbasin water transfer, thatincluded four trial periods of artificial high flow of10–14 days each, on the fish fauna in a small streamthat will convey water between reservoirs in twodifferent south-western (U.S.A.) river basins. Golladay& Hax (1995) described the effects of one of the trialson the invertebrate meiofauna of this stream.

Fish are important in stream ecosystems (Power,1990; Gelwick & Matthews, 1992). They are used inassessment of stream condition or ‘health’ (Karr, 1991;Karr et al., 1986), and they are prominent and highlyvisible in the public eye. Stream fish assemblagesnaturally vary over time (Grossman, Moyle &Whitaker, 1982; Matthews, Cashner & Gelwick, 1988;Gelwick, 1990; Matthews, 1990). Thus, to assess con-sequences of water transfer to fishes of a carrier stream,it is necessary to have a baseline estimate of thenatural variability in the fauna (Grossman et al., 1990;Matthews, 1990). The kinds of fishes in a stream,and variability of the fauna, may depend largely

Fig. 1 Map of Sister Grove Creek and Lake Lavon, Texas,on schedules of stresses or disturbances (Meador &U.S.A. Arrows indicate location of permanent samplingMatthews, 1992), life histories of organisms or theirstations. Station 4 was abandoned part way through the study,

ability to withstand disturbance (Poff & Ward, 1990), but the original number is retained for continuity with earlierthe size (or discharge) of the stream at a given location publications.(Angermeier & Schlosser, 1989), habitat complexity orheterogeneity (Gorman & Karr, 1978), or chemical (, 500 µS cm–1) conductivity; Lake Lavon has similar

conductivity. In contrast, Lake Texoma has conduc-composition of the water (Matthews, Hough &Robison, 1992). The degree to which water transfer tivity higher than that of most freshwaters, ranging

from about 1000 to 1500 µS cm–1, and reachingchanges physical features or flow schedules of anatural stream should influence its effect on the 2000 µS cm–1 at some depths and/or locations

(Matthews, Hill & Schellhaass, 1985; Matthews & Hill,existing fish fauna. In the present study, three yearsof monthly baseline data on the fishes of a natural 1988). Sister Grove Creek is characterized by seasonal

flow extremes; trial flows were carried out when watercreek were established, then four trials (10–14 dayseach) of water transfer were carried out in the next levels were naturally very low. Therefore, transfer of

Lake Texoma water through Sister Grove Creektwo years. We continued routine monthly samplingof fish assemblages after trial flows began, with addi- resulted in sharply increased flow and increased con-

ductivity.tional sampling of the assemblages immediately beforeand after three of the trial flows. During the first year of study, thirty-four species of

fish were recorded in Sister Grove Creek (Meador,Sister Grove Creek (Fig. 1), in north-central Texas(U.S.A.), will convey water from Lake Texoma Arambula & Hill, 1990). Many of these fish species

are hardy, forming relatively stable local assemblages(Oklahoma–Texas; Red River basin) to Lake Lavon(Texas; Trinity River basin). Sister Grove Creek is a that varied only moderately throughout an entire year,

in spite of environmental conditions varying fromsmall, mostly intermittent stream with relatively low

© 1996 Blackwell Science Ltd, Freshwater Biology, 35, 349–362

Experimental flows and stream fishes 351

extreme flooding to periods of low or no flow (Meador Detail on seasonal discharge is given in Meador &Matthews (1992), and additional information on the& Matthews, 1992).

The purposes of the present study were: stream and on study sites is also in Meador et al.(1990) and Golladay & Hax (1995). Our sites 7 and 61 to test changes in the fish fauna at the scale of the

entire Sister Grove Creek catchment over a total of 52 (headwaters) correspond to sites D1 and D2 of Golla-day & Hax (1995).months (before and after pumping);

2 to test changes in fish assemblages or individual Lake Texoma is a 36 000 ha reservoir of the Red andWashita rivers on the Texas–Oklahoma border. Lakespecies abundances at the scale of 100-m reaches

immediately before and after the pre-planned trial Texoma is markedly stratified in the downlake regionnear the dam from July to September of most yearsflows.(Matthews et al., 1985). Conductivity in Lake Texomais twice or greater than that in Sister Grove Creek. At

Study arealeast seventy-one fish species are known from LakeTexoma (Riggs & Bonn, 1959). In the large, deepSister Grove Creek drains 215 km2 in Grayson and

Collin counties in north Texas (U.S.A.) (Golladay & downlake basin of Lake Texoma near the water with-drawal structure, fewer fish species occur (Matthews,Hax, 1995), in the Texan biotic province (Blair, 1950).

Stream valleys of this region are dominated by alluvial pers. comm.), but some (e.g. Menidia beryllina, Dorosomaspp., and large catfishes of the family Ictaluridae) thatsoils, and support a mesic riparian forest (Blair, 1950).

The region is moist–subhumid (Blair, 1950), with are highly abundant in Lake Texoma are absent inmost of upper and middle Sister Grove Creek. Inextremes of rainfall resulting in major flooding, inter-

spersed by long periods of low or no flow in small addition, numerous native species that are commonin the Red River basin (e.g. Notropis potteri, Hubbs &streams. Sister Grove Creek is 60 km long from its

headwaters near Sherman, Texas, to its confluence with Bonham, 1951; Notropis bairdi, Hubbs & Ortenburger,1929; Macrhybopsis storeriana (Kirtland, 1847);Lake Lavon, a 9000 ha impoundment near McKinney,

Texas. Stream width ranges from µ 3.5 m in the head- Notropis boops, Gilbert, 1884; Hybognathus placitus,Girard, 1856) in or upstream from Lake Texoma arewaters to 7.5 m in the midreaches. Primary substrate is

clay or mud from midreach to downstream; headwater unknown from the Trinity River basin, and thus arepotential candidates for accidental interbasin transfersubstrata are dominated by sand, pebbles and lime-

stone bedrock. Turbidity is moderate to very high. of taxa.This study focused on five fixed collecting stationsThe creek is deeply incised, with earthen banks 2–5 m

high, and 50–100% canopy from riparian forest. The (stations 2–7) on the mainstem of Sister Grove Creek,spaced to provide longitudinal coverage of the catch-lowermost reach of the creek has a defined channel at

low flow, but its extended floodplain (up to 50 m ment, and two stations (stations 0 and 1) in the creek–lake confluence zone (Fig. 1). An original station 4wide) grades into Lake Lavon, forming the Sister

Grove Creek arm of the reservoir (Fig. 1). included in earlier papers was eliminated becauseaccess was impossible on some dates.A U.S. Geological Survey gauging station near mid-

reach records discharge. There have been lengthyperiods without flow in many of the years of record,

Materials and methodsas well as occasional major floods. From 1984 to 1992,Sister Grove Creek had seasonal high discharge (Fig. 2) Field studies—general collectionsfrom late autumn or early winter (November–January)to early summer, with desiccation to low or non- At each site, fish were collected monthly from June

1988 until September 1992 on a total of forty-twoflowing conditions from late summer to autumn(except 1991, when rains produced high flows by dates, with a few months omitted during floods.

Collections were made with a 0.5-cm-mesh seineOctober). During the low flow periods much of theupper creek is intermittent, and the entire creek is (4.25 m 3 1.55 m). A longitudinal reach of about 100 m

was sampled vigorously for µ 45 min at each site,reduced to a series of pools with little interconnectingflow. Pools at most sites were sufficiently deep (1 m following the techniques of Matthews (1986), with

repeated sweeps of the seine through all existingor more) to provide habitat for fishes during drought.



Fig. 2 Average monthly discharge forSister Grove Creek (USGS gauge atstation 4) for late 1984–92.

habitat types in pools, and kick samples in any riffles. then gradually reduced by a period of low dischargepumping. Low and high discharge pumping resultedSampling during high water conditions was restricted

to depths of 1.5 m, but even those appeared adequately in stream discharge of about 1–2 m3 s–1 and 3–5 m3 s–1,respectively, with sustained discharge in the head-to represent the diversity of fish present. Fish often

move to the edge of streams during spates (Matthews, waters of the creek slightly above 3 m3 s–1 (Golladay& Hax, 1995). Each trial period included at least 8unpublished data), and we captured substantial num-

bers of individuals and taxa in all periods of sampling days of high discharge pumping with sustained highflows in the creek. The experimental water transfer(Meador & Matthews, 1992). Fish were preserved in

10% formalin, identified in the laboratory, and archived represented a large (µ 30-fold) and locally rapid(Matthews, pers. obs.) increase in flow of Sister Groveat the University of Oklahoma Biological Station.Creek, which typically had discharge in the head-waters , 0.1 m3 s–1 immediately before experimental

Field studies—experimental water transferflows (Golladay & Hax, 1995). Matthews observeddepth of water at one midreach site to increase fromIn addition to routine monthly collections, fish were

collected immediately before and after three trial a few centimetres to more than a metre in a matter ofminutes as initial discharge from pumping arrived atperiods of experimentally enhanced flows (October–

November 1990, July–August 1991, July–August 1992), that location. Peak flows during summer and autumnwater transfers were much higher than mean naturalcreated by pumping water from Lake Texoma to Sister

Grove Creek. For approximately 10 days in summer discharge for Sister Grove Creek in July–August(0.20 m3 s–1) or October–November (0.01 m3 s–1) in theand 14 days in autumn study periods, water was

continuously pumped from the downlake portion of three years before experimental water transfer.Golladay & Hax (1995) showed that one trial flow, withLake Texoma through a 16-km pipeline, and dis-

charged at an outfall (Fig. 1) in the headwaters of current speeds as great as 100 cm s–1, was sufficient totransport large woody debris downstream, and toSister Grove Creek upstream of station 7. Withdrawal

velocities near the intake structure in Lake Texoma remove a large proportion of the invertebrate meio-fauna. Note that in Fig. 2 the trial flows do not appearwere , 13 cm s–1. The intake was screened with 13-

mm-mesh wire screen to prevent entrainment of larger as markedly increased flow, but this is because Fig. 2represents monthly averages, thus high flow for 8–10fishes from Lake Texoma. Depth of the intake pumps

in Lake Texoma ranged from 6 to 11 m; maximum days within an otherwise dry month does not appearvisually striking against the high flows of late winter–lake depth in that area is about 25 m (Matthews

et al., 1985). early spring. However, the trial flows were conductedin late summer and autumn when discharge is historic-Late summer and autumn are normal low flow

periods in Sister Grove Creek. Once started, water ally low in Sister Grove Creek, because the watertransfer system is most likely to be in sustainedtransfer was sustained by high discharge pumping,



operation during seasonal periods of low water levels deviation 5 1.0 (Sneath & Sokal, 1973). The outcomesof DCA and PCA were similar, thus only results fromand high user demand, and the artificial trial dis-

charges were extremely high for that time of year. DCA are presented.Community structure indices (Ludwig & Reynolds,Effects of experimental flows on creek fish assem-

blages were evaluated on a ‘before and after’ basis in 1988), including Jaccard’s index (qualitative), percent-age similarity index (PSI; quantitative) and Shannon–the three periods noted above. There was one addi-

tional period of experimental flow in October 1991, Weiner’s H9 (heterogeneity), were used to comparefish assemblages among samples at individual stationsbut associated fish samples were not made. For each

of the three studied trial flow periods, fish were before and after the three trial flow periods. Matthewset al. (1988) discussed the use of PSI for fish communi-sampled at stations 2, 3, 5, 6 and 7 (Fig. 1), 1–4 days

before onset of pumping and 3–7 days after pumping ties, and its relation to other quantitative communitysimilarity indices. To provide an overview of fishended. Fish at each station were sampled by seining as

above, but all individuals were collected into insulated assemblages at individual stations before and aftertrial flows, DCA was carried out for all thirty before-containers, identified and counted by Matthews, and

released alive near the point of capture. Fish were and-after, site-specific samples (fifteen before pump-ing, fifteen after pumping) on the basis of abundanceheld for less than 10 min, and no mortality was noted.

Measurements of temperature, dissolved oxygen and of nineteen common species. For this DCA, ‘rare’species (5 occurred in fewer than three samples) wereconductivity were made with Yellow Springs Instru-

ments meters at each site before, during and after omitted. For individual taxa, community indices andDCA scores, fixed effects ANOVA models withexperimental pumping, and turbidity samples taken

at those times were analysed on a Hach Model 2100 A ‘station’, ‘ year’, and ‘flow’ (i.e. before and after trialflow) were carried out with the General Linear ModelsTurbidimeter.

Conductivity in the creek averaged , 500 µS cm–1 procedures of SAS (SAS Institute Inc.).prior to water transfer and . 1000 µS cm–1 (maximum1650 µS cm–1) during pumping operations, and

Resultsreturned to normal about 1–2 months after the cessa-tion of pumping. Temperature and dissolved oxygen The fish faunashowed no consistent changes during or after experi-mental water transfer. In forty-two monthly samples at all sites from June

1988 until September 1992, thirty-nine species oftwelve families were collected. The fauna of Sister

Data analysisGrove Creek proper (Table 1) was dominated byminnows (Cyprinidae), sunfishes (Centrarchidae), oneStations were separated into two reaches for analyses:

(i) the stream proper, including stations 2, 3, 5, 6 and Gambusia species (Poeciliidae), and a topminnow(Cyprinodontidae); near the confluence with Lake7; and (ii) station 1 (at the creek mouth) and station 0

on the north shore of Lake Lavon, directly across a Lavon, shads (Clupeidae) were abundant. In creekstations 2–7, the most abundant species were Gambu-small bay from the confluence of the creek (Fig. 1). We

refer to these reaches as ‘creek’ and ‘confluence zone’, sia affinis (mosquitofish), Fundulus notatus (blackstripedtopminnow), Pimephales vigilax (bullhead minnow),respectively.

Temporal variation in the fish fauna within each Cyprinella lutrensis (red shiner), Lepomis megalotis(longear sunfish) and Lepomis macrochirus (bluegill)reach (separately) was assessed by detrended corres-

pondence analysis (DCA; DECORANA, using all (Table 1). In the confluence zone (stations 1 and 0),the most abundant species were Dorosoma petenensedefaults, Cornell Ecology Programs) and by principal

components analysis of the correlation matrix of (threadfin shad), P. vigilax, Menidia beryllina (inlandsilversides), C. lutrensis, Lepomis humilis (orangespottedspecies abundances (PCA; NTSYS-PC, Exeter

Publishing). For each species, abundance was summed sunfish) and G. affinis. The most common piscivores(comprising . 1% of the total fish collected inacross stations on each sampling date. The DCAs

were carried out on raw data; for PCA, data were the creek and confluence regions combined) wereMicropterus punctulatus (spotted bass), M. salmoides,standardized so that mean 5 0 and standard



Table 1 Numbers of individual fish captured at all stations inSister Grove Creek proper and in the confluence zone fromJune 1988 to September 1992 (in decreasing order of overallabundance)

Fish species Creek Confluenceproper zone

Gambusia affinis (Baird & Girard) 4283 922Pimephales vigilax (Baird & Girard) 1319 3299Dorosoma petenense (Gunther) 9 3345Fundulus notatus (Rafinesque) 3155 73Cyprinella lutrensis (Baird & Girard) 1217 1907Menidia beryllina (Cope) 8 3109Lepomis megalotis (Rafinesque) 615 580Lepomis humilis (Girard) 140 979Lepomis macrochirus Rafinesque 490 529Dorosoma cepedianum (Lesueur) 206 398Pomoxis annularis Rafinesque 185 162Lepomis cyanellus Rafinesque 290 30Ictalurus punctatus (Rafinesque) 44 152Percina macrolepida Stevenson 19 161Micropterus punctulatus (Rafinesque) 72 102Etheostoma gracile (Girard) 98 73Amieurus natalis (Lesueur) 160 5Micropterus salmoides (Lacapede) 44 83Morone chrysops (Rafinesque) 32 50Noturus gyrinus (Mitchill) 42 13Cyprinus carpio Linnaeus 47 5Morone mississippiensis 34 16 Fig. 3 DCA axis 1 and 2 scatterplot of Sister Grove Creek

Jordan & Eigenmann regular monthly fish samples (stations 2–7 pooled withinEthesotoma chlorosomum (Hay) 10 38 dates) across time. Open circles surrounded by dotted line 5

Minytrema melanops (Rafinesque) 46 0 samples before any experimental flows; half-closed circlesNotemigonus crysoleucas (Mitchill) 28 11 surrounded by dashed line 5 samples after one experimentalEtheostoma spectabile (Agassiz) 0 29 flow; closed circles surrounded by solid line 5 samples afterPercina caprodes (Rafinesque) 4 21 two periods of experimental flow.Lepomis microlophus (Gunther) 21 2Lepomis gulosus (Cuvier) 15 6 1990 (first experimental flow) were located throughoutAplodinotus grunniens Rafinesque 7 11

most of a scatterplot (Fig. 3) of DCA axes 1 and 2.Pomoxis nigromaculatus (Lesueur) 7 5Samples made after one or more periods of experi-Campostoma anomalum (Rafinesque) 8 0

Amieurus melas (Rafinesque) 6 2 mental flow were all in the upper left portion of thePimephales promelas Rafinesque 4 1 scatterplot (Fig. 3), indicating less variability in theCarpiodes carpio (Rafinesque) 2 0

fauna after trial flows. Samples made after two orPlyodictis olivaris (Rafinesque) 1 1more trial flow periods (solid circles, Fig. 3) wereIctiobus bubalus (Rafinesque) 0 1

Lepisosteus osseus (Linnaeus) 0 1 displaced most from the centre of the scatterplot.A separate DCA for confluence zone samples (Fig. 4)

included thirty-three species and forty-one samplingdates. The first two axes had eigenvalues of 0.397 andIctalurus punctatus (channel catfish) and Pomoxis annu-

laris (white crappie). 0.199, respectively. The confluence zone showed atemporal pattern (Fig. 4) similar to that of the creekproper. Samples before any artificial flows were scat-

Variation in the fish faunatered widely on axes 1 and 2, whereas samples afterone or more trial flow periods showed less variationFor the creek (stations 2–7 pooled) thirty-five species

comprised . 1% of the total fauna and were included in multivariate space, and samples after two artificialflows were, on average, further from the centre of thein the DCA. The first two axes had eigenvalues of

0.283 and 0.181, respectively. Samples before October scatterplot.



Table 2 Results of ANOVA tests for abundance of fish taxa insamples at ‘creek’ proper stations 2, 3, 5, 6 and 7 (pooled oneach sampling date), in Sister Grove Creek before (n 5 26) vafter (n 5 15) any transfer of Lake Texoma water throughSister Grove Creek

Mean

Fish species Before After F P

Gambusia affinis 82.6 136.9 2.97 0.093Fundulus notatus 69.6 85.0 1.76 0.192Cyprinella lutrensis 25.0 36.1 8.34 0.006Pimephales vigilax 24.2 44.4 5.82 0.021Lepomis macrochirus 11.6 11.7 0.57 0.453Pomoxis annularis 6.7 0.3 7.96 0.007Dorosoma cepedianum 7.3 0.7 2.16 0.150Lepomis megalotis 9.4 24.0 10.63 0.002Lepomis humilis 3.4 3.2 1.76 0.192Lepomis cyanellus 7.0 6.7 0.58 0.452Micropterus punctulatus 2.0 1.2 0.54 0.466Etheostoma gracile 1.7 3.5 0.29 0.592Total of all fish 283.1 360.3 3.54 0.067

Table 3 Results of ANOVA tests for abundance of fish taxa insamples at ‘confluence’ stations (Sister Grove Creek station 1and North Shore Lake Lavon, pooled within each samplingdate) before (n 5 26) v after (n 5 15) the first transfer of LakeTexoma water through Sister Grove CreekFig. 4 DCA axis 1 and 2 scatterplot of Sister Grove Creek–

Lake Lavon regular monthly fish samples in the confluenceMeanzone (stations 0 and 1 pooled within dates) across time.

Symbols and surrounding polygons are as defined in Fig. 3.Fish species Before After F P

Gambusia affinis 18.4 28.3 1.11 0.298Variation in individual speciesCyprinella lutrensis 49.8 38.3 1.61 0.212

In the creek, mean abundances of twelve species Pimephales vigilax 90.7 56.7 0.01 0.921Menidia beryllina 80.7 62.0 0.60 0.443comprising . 1% of the fish collected were comparedLepomis macrochirus 11.3 14.9 0.40 0.531in all monthly samples before v after the first trial flowsPomoxis annularis 4.6 2.6 0.13 0.721

(October 1990). After trial flows began, abundance of Dorosoma cepedianum 8.9 10.5 0.00 0.999Lepomis megalotis more than doubled, and Cyprinella Lepomis megalotis 10.4 20.0 1.63 0.209

Lepomis humilis 23.6 22.7 2.06 0.159lutrensis and Pimephales vigilax also increased signific-Dorosoma petenense 47.9 136.8 3.84 0.057antly (Table 2). Pomoxis annularis decreased from aMicropterus punctulatus 3.6 0.3 6.12 0.018

mean of 6.7 to 0.3 individuals per collection after trial Percina macrolepida 5.3 1.2 2.07 0.158flows began (Table 2). Other species did not differ Ictalurus punctatus 3.4 3.9 0.93 0.340

Micropterus salmoides 2.9 0.3 1.88 0.178significantly before and after water transfer, althoughTotal of all fish 424.1 438.1 0.37 0.546mean abundance for Gambusia affinis, Fundulus notatus

and Etheostoma gracile increased, and Dorosoma cepedi-anum and Micropterus punctulatus decreased. There juveniles. The mean abundance of Dorosoma petenense

was 47.9 before flows and 136.8 afterward, differingwas no influx of typical ‘lake’ species upstream fromLake Lavon into Sister Grove Creek after trial flows, at P 5 0.057 (Table 3). However, because of the large

number of individual ANOVAs in Table 3, prudentand no observed introduction of species from LakeTexoma or the Red Rivers. alpha control would suggest that P 5 0.057 not be

considered ‘significant’. The other common species inIn the confluence zone (Table 3), mean abundanceof Micropterus punctulatus decreased from 3.6 before the confluence zone showed no significant changes in

abundance after initiation of trial flows.to 0.3 after the onset of experimental flows; most were



Table 4 Numbers of species, numbers of individuals, and Shannon’s diversity index for fish samples, by station, in Sister GroveCreek before and after experimental flow periods, and comparisons of fish assemblages per station before and after pumping byJaccard’s index (presence–absence) and PSI (qualitative)

Species Individuals Shannon’s-H

Jaccard’sYear Site Before After Before After Before After index PSI

1990 2 12 7 162 449 2.185 0.920 0.462 42.63 11 5 146 31 1.676 1.364 0.455 83.35 8 9 190 274 1.697 1.297 0.700 47.46 8 6 74 32 1.499 1.214 0.556 43.57 2 4 198 86 0.169 0.483 0.500 90.1

1991 2 17 16 258 229 1.921 2.067 0.833 59.33 13 9 231 78 1.565 1.527 0.692 83.65 12 9 180 91 2.002 1.944 0.615 60.86 6 10 95 46 0.738 1.756 0.333 42.17 6 6 15 44 1.709 1.440 0.714 39.5

2 12 15 181 267 2.172 2.311 0.588 44.63 12 10 80 42 1.854 1.994 0.692 65.45 10 9 162 108 1.033 1.438 0.583 74.16 10 8 110 156 1.805 1.580 0.800 86.77 7 5 21 14 1.832 1.512 0.200 38.1

Mean 9.7 8.5 140.2 129.8 1.590 1.523 0.581 60.1

Experimental flows: effects at individual stations of study (before any diversion of Lake Texoma waterthrough Sister Grove Creek).

The number of species, number of individuals and Fig. 5 shows the location of all thirty ‘before anddiversity indices at individual stations showed little after’ samples (three ‘before’ and three ‘after’ at eachconsistent difference in samples immediately before of five stations) in a scatterplot of DCA axes 1 and 2.and after artificial flows (Table 4). Jaccard’s index For 1990, four of the ‘after’ (taken within a week after(presence – absence) of qualitative differences in taxa cessation of artificial flow) samples lie within or nearat stations before and after flow trials ranged from the multivariate space occupied by the ‘before’ (1–40.20 to 0.83 per station, with a mean of 0.58 (Table 4). days before artificial flow began) samples, with onlyDifferences often were due to species collected in low station 2 (the most downstream creek site) displacednumbers before but not after experimental flows. A substantially in multivariate space after the trial flow.few species were found at a station after, but not For 1991, four of the five ‘after’ samples lie within thebefore water transfer. In no case was any species multivariate space occupied by samples from beforeabundant at a station before a flow trial flow but trial flow, with station 2 again showing the greatestabsent from the station immediately afterward. displacement relative to its position before the artificial

Quantitatively (Table 4) some stations (e.g. 3 and 7 flow. In 1992 there appeared to have been morein 1990, 3 in 1991 and 6 in 1992) had high similarity displacement of ‘after’ samples relative to ‘before’in structure of fish assemblages immediately before samples in multivariate space. Again, station 2 wasand after trial flows (PSI values ranging 80 to 90.1%), an outlier after the trial flow, and stations 3 and 7 alsobut numerous other stations had PSI , 50% for assem- showed some displacement in multivariate space.blages before and after the flows. Mean PSI for all In spite of more displacement of some stations incomparisons of ‘before and after’ samples was 60.1%, 1992 than in the two previous years, the overallwhich is within the range of natural between-month impression was that the experimental dischargesvariation reported by Meador & Matthews (1992) for resulted in little marked or directionally consistent

change in the fish assemblages immediately after flowsfish assemblages at individual sites for the first year



Fig. 5 DCA axis 1 and 2 scatterplot of thirty samples at five Sister Grove Creek stations, taken immediately before or after periodsof experimental flows. Each scatterplot is identical, but for each year the position of samples in multivariate space before(surrounded by dotted line) and after (surrounded by solid line) experimental flow is highlighted. Within each year, numberedsamples correspond to station numbers in Fig. 1, with the letter ‘B’ 5 before flow and ‘A’ 5 after flow.

relative to those present immediately before each trial. any of the eight individual species (Table 5). Cyprinellalutrensis differed with respect to experimental flowsTo compare displacement of stations in multivariate

space after trial flows relative to natural differences at a level of P 5 0.079, and the flow–station interaction(P 5 0.053) was almost significant at a level of 0.05,in fish assemblages of the system, we calculated

Euclidean distance between samples on the scatterplot. suggesting that experimental flows may have influ-enced numbers of this species at some stations butMean distance (in DCA axis units) between fifteen

paired ‘before and after’ samples at individual stations not others. Numbers of species (P 5 0.002), numbersof individuals (P 5 0.006) and DCA axis 1 scores (P 5was 47.3 (SD 33.6), whereas mean distance between

longitudinally adjacent stations before each experi- 0.002) differed significantly among sampling stations(Table 5). Numbers of Fundulus notatus (P 5 0.051) andmental flow was 71.2 (SD 43.9, n 5 12 pairs). Because

the Euclidean distances lack independence (displace- Cyprinella lutrensis (P 5 0.055) nearly differed amongsampling stations at P 5 0.05 (if no Bonferroni adjust-ment of any one sample in multivariate space can

affect distances for two adjacent stations) we made no ment or other alpha control is applied). Species perstation, diversity, DCA axis 1, F. notatus and C. lutrensisstatistical test of means, but use these values to suggest

that differences in assemblages at most stations before all differed among years (P , 0.05).and after experimental flows were not greater thantypical differences between adjacent stations in the

Discussioncreek.

In twelve separate multiway ANOVAs, results of Numerous caveats apply to interpretation of this study.In this, as in any whole ecosystem manipulation,all three periods of experimental flow were combined

to test treatment effects of ‘station’, ‘ year’ and ‘flow’ logistics make replication difficult or impossible, hencepower to detect changes is limited. Changes we(i.e. immediately before v after trial flow for that year)

on four collective properties of the assemblages and detected are probably real, but lack of demonstratedchanges does not rule out more subtle, bioticallyon abundances of the eight most common species.

There was no significant effect of ‘flow’ on numbers important or interesting changes in the system. Ourfindings may not apply to systems other than Sisterof species collected, numbers of individuals, diversity,

the axis 1 score from the DCA analysis (above), or Grove Creek, and plans to use any natural stream



Table 5 Results of ANOVAs for number of species and individuals, assemblage diversity, DCA axis 1 score, and abundance ofcommon individual species in Sister Grove Creek, before and after experimental water transfer. Tabled is F value (above) and Pvalue (below) for each variable

Variable Station Year Flow Station 3 flow Year 3 flow

Species 11.34 6.16 2.30 0.86 0.260.002 0.024 0.168 0.525 0.781

Individuals 8.12 1.48 0.18 2.00 0.960.006 0.284 0.685 0.187 0.423

Shannon index 3.19 5.12 0.24 0.34 1.460.077 0.037 0.637 0.846 0.289

DCA axis 1 score 12.00 30.33 1.67 1.58 0.990.002 0.0002 0.232 0.269 0.414

Gambusia affinis 1.95 0.29 0.00 0.83 1.430.195 0.756 0.950 0.542 0.294

Fundulus notatus 3.81 14.64 2.36 1.43 3.880.051 0.002 0.163 0.308 0.066

Cyprinella lutrensis 3.70 9.39 4.06 3.74 0.010.055 0.008 0.079 0.053 0.986

Pimephales vigilax 2.57 1.41 0.37 0.97 2.060.119 0.299 0.558 0.474 0.191

Ictalurus punctatus 2.46 0.38 0.51 1.11 0.980.130 0.695 0.497 0.416 0.416

Lepomis macrochirus 3.46 1.15 0.71 0.21 0.680.064 0.365 0.423 0.923 0.534

Lepomis megalotis 1.27 0.87 0.22 0.29 0.050.359 0.457 0.652 0.879 0.950

Micropterus salmoides 3.02 2.01 2.63 0.99 0.760.086 0.197 0.143 0.466 0.500

channel as a carrier for water transfer must be evalu- Sister Grove Creek is physically dynamic, withstrong natural fluctuations in discharge, and a complexated locally. In this study, trial flows were provided

in only two seasons of the year, and prolonged high fish fauna adapted for harsh conditions or abruptchanges in environmental conditions (Meador &discharges at other times, e.g. peak reproductive

periods, could have different effects. For example, Matthews, 1992). These physical conditions and char-acteristics of the fish fauna are typical of many smallSchlosser (1985) showed that high flows during

spawning season had negative effects on recruitment streams in the south-western United States, and SisterGrove Creek has a fish fauna comparable to that ofof stream fishes. Additionally, there could be inter-

actions between temperature and flow: fish might many other small streams in the south-west (Meador& Matthews, 1992; Matthews et al., 1988; Matthewsresist downstream displacement in summer more than

in winter, if lower temperatures reduce swimming & Gelwick, 1990). However, this introduces anothercaveat: fish in low gradient, small south-westerncapacity. Finally, we emphasize that these trial flows

lasted no longer than 2 weeks. Longer periods of streams may already represent a tolerant subset of thepotential regional fauna (Matthews, 1987), which hassustained high flow may have more potential to

modify habitat through increased bank erosion, down- successfully passed through a ‘physiological screen’(Smith & Powell, 1971). Results of this study shouldcutting, or removal of woody debris, with cumulative

effects on fish assemblages. With these caveats consid- therefore not be extrapolated to stream systems con-taining less tolerant fish species.ered, the pre-planned aspect of the trial flows made

‘before and after’ comparisons possible, with sampling Diversion of Lake Texoma water through SisterGrove Creek in summer and autumn resulted in abrupttightly coupled to onset and cessation of water transfer,

providing a unique opportunity to assess effects of increases in discharge, well above average naturalflows for those months, and in at least a doubling ofabruptly elevated flow or introduction of water of

different quality on a fish fauna. conductivity of water in the stream. Although the



artificial high flows in Sister Grove Creek were brief ated control, the DCAs do not prove that water transfercaused changes in faunal structure, but the DCAs doin ecological time, they probably represented an

unusually long period of sustained high flow. Dis- show a pattern of progressive changes over time thatshould be monitored in the long term.charge in small south-western (U.S.A.) streams typic-

ally increases rapidly after storms, then rapidly In addition to whole fish assemblages or biodiversityof systems, managers are concerned with the well-declines. Additionally, unlike natural rainfall flood

events, these artificial flows were not confounded being of individual fish species. Analysis of varianceof abundance of individual species showed significantby other factors such as surface runoff, changes in

meteorology, or influx of allochthonous terrestrial mat- increases in abundance of two minnow and one cen-trarchid species, and a decrease in one centrarchid inerials (nutrients, litter, invertebrates), that typically

accompany rainfall events and can alter the behaviour the creek proper after water transfer began. All otherspecies exhibited only non-significant changes inof fishes.

Most observed changes in individual taxa were in abundance. Specific life history adaptations of mostof these species are poorly known, but in general thespecies of low abundance, and no species that was

abundant in any year was absent in any another. We species exhibiting increases after water transfer weretypical of streams with harsh physical conditionsfound no influx of typical ‘lake’ species into Sister

Grove Creek from Lake Lavon, and no species (Matthews, 1987; Matthews & Gelwick, 1990). How-ever, no common pattern of ecological traits, e.g.restricted to the Red River–Lake Texoma system

appeared in Sister Grove Creek during the period of trophic group or reproductive mode, characterizes thespecies that increased or decreased. In the confluenceour study.

The DCAs provided a comprehensive overview of zone, one centrarchid decreased in abundance (mostlyas juveniles), and one forage species, a clupeid, almostmonthly variation in the fauna of the Sister Grove

Creek system. Pooling samples for all sites in the creek trebled in abundance.Fish assemblages in individual 100 m stream reachesor in the confluence zone on a given date could mask

some changes in local assemblages. However, from are naturally more variable than the fish fauna of awhole catchment (Matthews, Harvey & Power, 1994),the perspective of asking ‘did the fish fauna of the

catchment change?’, it seems appropriate to sum all as fishes move up and down stream, or as microhabit-ats within short reaches change with time. Undersamples for a given date. For example, a decrease in

a species at one site hypothetically could be offset by natural conditions, therefore, some degree of changein the fish assemblage is expected (Grossman et al.,an increase at another site, with no net change in the

total fish in the system. Biologically, it seems that for 1982). In evaluating changes with respect to experi-mental water transfer, we were most interested ina small catchment it should be the total fish fauna

that is of most concern, rather than the details of detecting changes in species across all stations, astested by the main effect of ‘flow’ in the ANOVAs,composition of the assemblage in a given 100 m reach.

For both the creek proper and the confluence zone and viewing individual stations as replicates. In theANOVAs only one of twelve species or collectivewith Lake Lavon, regular monthly samples collected

after one or more periods of experimental water properties showed the main effect of ‘flow’ as nearlysignificant (P , 0.10), and two of twelve showed mar-transfer were within the ranges of DCA axis scores

for samples before any water transfer, but there was ginally significant interactions (P 5 0.05 and 0.06) offlow with station or year. To summarize the ANOVAs,evidence of displacement of samples in multivariate

space over time. Because DCA accounts for a large few individual species or collective properties of thelocal assemblages showed detectable changes afteramount of variation on the first axis, it is important

to note in Figs 3 and 4 that this displacement is evident trial flows, although the low power nature of thedesign makes it premature to rule out the existence ofalong axis 1. Further, the sample dates after onset of

water transfers were located in a markedly limited undetected, subtle effects.Assemblages at some individual stations differedportion of the total multivariate space in the DCA

scatterplots, reflecting overall lessening of variation in markedly before and after experimental flows.Jaccard’s index and PSI values comparing compositionthe fish fauna after water transfer began. Because this

large, ecosystem-level experiment has no unmanipul- of fish assemblages at individual stations before and



after each experimental water transfer varied widely, tolerance of these fishes (Chipman, 1959; Matthews &Hill, 1977). Indeed, increased salinity to concentrationswith ten of thirty possible cases lower than 0.50

(Jaccard’s) or 50% (PSI). Sites near the confluence we observed in Sister Grove Creek may actually bebeneficial physiologically to many freshwater fishesprobably changed less in water level in response to

pumping than did creek sites located upstream in the (Peterson & Meador, 1994). Other water quality para-meters we measured (temperature, oxygen, turbidity)catchment, but there appeared to be more fine silt at

the most downstream site in the creek proper (Station were not altered in any substantial way by the experi-mental water transfers.2) by late in our period of study (Matthews, pers.

obs.). This lowermost creek station exhibited some of Examination of long-term discharge records forSister Grove Creek indicate that in most years (particu-the largest changes in community similarity before

and after trial flows (Table 4). However, there was larly during the spring) there are sustained periods ofdischarge substantially greater than the dischargesno consistent pattern of greater changes in the fish

assemblages of headwaters v lower mainstream after attributable to conveyance of water from Lake Texomathrough the creek to Lake Lavon. Our studies do nottrial flows (Table 4).

To what degree should artificial 2 week episodes of yet show any major changes in the overall fish faunaof Sister Grove Creek as a result of three periods ofhigh, sustained flow and altered water chemistry

influence fishes in Sister Grove Creek? Fish popula- water transfer, each lasting not more than 2 weeks.The key to continued long-term success of fish speciestions in this system experience natural floods, as well

as periods of low flow, high temperature and oxygen in Sister Grove Creek is probably the availability ofappropriate habitat. If the transfer of water is sustainedstress (Matthews, 1987; Meador & Matthews, 1992).

Matthews et al. (1994) documented relatively minor over long periods of time, both habitat for spawning(e.g. nesting substrates) and suitable physical structurechanges in distribution of fishes among individual

pools in Brier Creek, Oklahoma, in a major flood in for use as day-to-day habitat by fishes should bemonitored. Over time, the stream channel shouldsummer. During floods, larval fishes are flushed from

stream segments (Harvey, 1987), but we have repeat- adjust morphologically to any increased flows. If,however, sustained flows result in scouring of theedly observed that juveniles and adults find low flow

refugia near stream banks (in eddies, etc.) during creek channel, input of more mud or silt, export ofwoody debris and its associated invertebrate biotafloods, where they persist until the water level drops.

Lancaster & Hildrew (1993) similarly showed in a (Golladay & Hax, 1985), fish species dependent onsuch habitats could decrease. Furthermore, full-scaledetailed assessment of flow that some areas of streams

afforded hydraulic refugia for invertebrates, and sug- operation of the water transfer system will enhancethe likelihood that some fish species not now knowngested that such refugia in spates can be important to

the entire aquatic community. Although little is actu- from the Trinity River basin will be introduced fromLake Texoma–Red River, thus monitoring species com-ally known about behaviour of stream fish during

spates, adults and juveniles apparently are restricted position in Sister Grove Creek will remain important.Within the time frame of this study, effects appearedfrom use of much of their natural habitat (Matthews,

unpublished data), thus they may be only poorly to be relatively minor for the fish fauna as a whole.However, Sister Grove Creek will require long-termadapted for longer periods of high flow.

Water transfer through Sister Grove Creek resulted evaluation of fish (and other fauna) responses if watertransfer is sustained. As interbasin transfers of waterin a marked rise in conductivity. However, much of

the specific conductance in Lake Texoma water is due become more widespread, effects on natural streamsmust be predicted or evaluated on a case-by-caseto sodium chloride salinity (because of Permian salt

deposits in the upper Red River basin, where conduc- basis. Although experimental flow trials are not apanacea for detecting or ameliorating all potentialtivity of the main river approximates that of ocean

water; Echelle, Echelle & Hill, 1972). Thus, the approxi- ecological consequences to a system, we recommendthem as a logical procedure, and one that should bemate doubling of conductivity in Sister Grove Creek

by addition of Lake Texoma water made the creek standard protocol in any implementation of interbasinwater transfer. Unfortunately, it is not possible tomore saline. Doubling of salinity, although dramatic

in a relative sense, was well within the limits of produce large experimental flows until the requisite



Gelwick F.P. & Matthews W.J. (1992) Effects of anphysical plant (pumps, diversions etc.) is already inalgivorous minnow on temperate stream ecosystemplace; thus, experimental trials like ours are, for now,properties. Ecology, 73, 1630–1645.most useful in assisting water managers to ‘fine tune’

Golladay S.W. & Hax C.L. (1995) Effects of an engineeredtransfer schedules or other protocols to minimizeflow disturbance on meiofauna in a north Texas prairieimpacts in donor, carrier or recipient systems after astream. Journal of the North American Benthological

system has been built.Society, 14, 404–413.

Gorman O.T. & Karr J.R. (1978) Habitat structure andstream fish communities. Ecology, 3, 507–515.

Acknowledgments Grossman G.D., Dowd J.R. & Crawford M. (1990)Assemblage stability in stream fishes: a review.

We thank a large number of people for assistance in Environmental Management, 14, 661–671.the field on Sister Grove Creek, particularly Frank Grossman G.D., Moyle P.B. & Whitaker J.O. Jr (1982)McCormick, Brian Gambill, Nicole Witt, Maria Miller, Stochasticity in structural and functional characteristicsFran Gelwick, Steve Cantrell and Jeff Stewart, and of an Indiana stream fish assemblage: a test of

community theory. American Naturalist, 126, 275–285.Loren Hill for assistance in study site selection. WeHarvey B.C. (1987) Susceptibility of young-of-the-yearthank Patti Cantrell and Barbara Ward for data man-

fishes to downstream displacement by flooding.agement, Pam Farris for word processing, CoralTransactions of the American Fisheries Society, 116, 851–McCallister for figures, and Phil Lienesch and Fran855.Gelwick for reviews of the manuscript or discussions.

Karr J.R. (1991) Biotic integrity: a long-neglected aspectSteve Golladay and Carolyn Hax provided helpfulof water resource management. Ecological Applications,

discussions on effects of flow on aquatic biota. We1, 66–85.

thank the North Texas Municipal Water District, par- Karr J.R., Fausch K.D., Angermeier P.L., Yant P.R. &ticularly Mr Dolan McKnight, for coordination and Schlosser I.J. (1986) Assessing biological integrity ininformation regarding experimental flows. This study running waters: a method and its rationale. Illinoiswas funded by the North Texas Municipal Water Natural History Survey, 5, 1–28. Champaign, Illinois.District, Wylie, Texas. Lancaster J. & Hildrew A.G. (1993) Characterizing in-

stream flow refugia. Canadian Journal of Fisheries andAquatic Sciences, 50, 1663–1675.

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Meador M.R. & Matthews W.J. (1992) Spatial and(Manuscript accepted 6 November 1995)temporal patterns in fish assemblage structure of an


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