Habitat Selection of Robust Redhorse Moxostoma Robustum

HABITAT SELECTION OF ROBUST REDHORSE MOXOSTOMA ROBUSTUM :

IMPLICATIONS FOR DEVELOPING SAMPLING PROTOCOLS

DIARRA LEMUEL MOSLEY

(Under the Direction of Cecil A. Jennings)

ABSTRACT

Robust Redhorse, described originally in 1870, went unnoticed until 1991 when they were rediscovered in the lower Oconee River, Georgia. This research evaluated one hypothesis

(habitat use) for explaining the absence of juveniles (30 mm – 410 mm TL) from samples of wild-caught robust redhorse. Two mesocosms were used to determine if juvenile robust redhorse use available habitats proportionately. Pond-reared juveniles were exposed to four, flow-based habitats (eddies = - 0.12 to -0.01 m/s, slow flow = 0.00 to 0.15 m/s, moderate flow = 0.16 to 0.32 m/s, and backwaters). Location data were recorded for each fish, and overall habitat use was evaluated with a Log-Linear Model. In winter, the fish preferred eddies and backwaters. In early spring the fish preferred eddies. Catch of wild juveniles may be improved by sampling eddies and their associated transitional areas.

INDEX WORDS: backwaters, catostomid, eddies, habitat selection, juvenile fish, mesocosm, Moxostoma robustum, Oconee River, robust redhorse

HABITAT SELECTION OF ROBUST REDHORSE MOXOSTOMA ROBUSTUM :

IMPLICATIONS FOR DEVELOPING SAMPLING PROTOCOLS

DIARRA LEMUEL MOSLEY

BSFR, University of Georgia, 1998

A Thesis Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment

of the Requirements for the Degree

MASTER OF SCIENCE

ATHENS, GEORGIA

2006

Diarra Lemuel Mosley

HABITAT SELECTION OF ROBUST REDHORSE MOXOSTOMA ROBUSTUM :

IMPLICATIONS FOR DEVELOPING SAMPLING PROTOCOLS

DIARRA LEMUEL MOSLEY

Major Professor: Cecil A. Jennings

Committee: Mary Freeman Gene Helfman

Electronic Version Approved:

Maureen Grasso Dean of the Graduate School The University of Georgia May 2006

DEDICATION

I dedicate this thesis to everyone who has influenced my life, from members of my immediate family to my favorite street musician and most memorable stranger. Last but not least, I dedicate this thesis to Brenda, my best friend for life!

ACKNOWLEDGEMENTS

Funding for this project was provided by the Georgia Power Company. I would like to acknowledge Jaxk Reeves and his students for assisting me in analyzing my data. I would like to thank Don Dennerline, Rebecca Cull-Peterson, Collin Shea, Steve Zimpfer, John Ruiz, Tom

Reinert, and Jeff Zeigweid for their advice and encouragement. I would like to thank Tavis

McLean for helping me set up my mesocosms. Special thanks to Cecil Jennings for being my academic advisor and mentor. Also, I would like to thank my committee, Mary Freeman and

Gene Helfman for their guidance and support.

TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS...... v

CHAPTER

1 INTRODUCTION ...... 1

Status of robust redhorse ...... 2

Hypothesis of robust redhorse decline ...... 3

2 LITERATURE REVIEW ...... 6

Riverine habitats...... 6

Lower Oconee River habitat...... 6

Effects of Dams ...... 7

Negative implications of Sinclair Dam ...... 8

Habitat use of fishes ...... 9

Habitat use of juvenile suckers...... 10

Habitat selection of juvenile robust redhorse suckers ...... 12

Habitat selection studies...... 12

Use of mesocosms ...... 14

Hypothesis ...... 16

Summary ...... 17

3 METHODS ...... 18

Experimental tanks...... 18

Experimental fish ...... 25

Experimental design ...... 26

Habitat types – flow classes ...... 28

Statistical analysis ...... 29

4 RESULTS ...... 32

Experimental tanks...... 32

Temperature analysis...... 32

Habitat use analysis ...... 32

Fish movement ...... 35

5 DISCUSSION...... 40

Preferred habitat use of juvenile robust redhorse...... 40

Habitats avoided by juvenile robust redhorse ...... 42

Proportional habitat use of juvenile robust redhorse...... 43

Differences in riverine habitats ...... 43

Implications for sampling the Oconee River...... 45

6 CONCLUSION...... 49

LITERATURE CITED ...... 50

vii

CHAPTER 1

INTRODUCTION

Robust redhorse Moxostoma robustum , of the family Catostomidae (suckers), is a benthic riverine fish that can grow to 760 mm total length and 7 kg in weight (Jenkins and Burkhead

1993; Evans 1994). The species was described originally by Edward Cope in 1870 based on specimens collected from the Yadkin River in North Carolina (Jenkins and Burkhead 1993).

Robust redhorse then apparently went unnoticed for 121 years until its rediscovery in 1991 in the

Oconee River, GA by the Georgia Department of Natural Resources (GADNR) (Evans 1994).

The robust redhorse population in the Oconee River seems to consist primarily of large adults

(Evans 1994), as wild juveniles ranging from 30 mm to 410 mm in total length (TL) have not been collected (Evans 1994; Jennings et al. 1996; 1998; 2005). The absence of juveniles in the

Oconee River has been attributed to sampling gear inefficiency, sampling in areas that are not inhabited by juvenile robust redhorse, or an actual low abundance of juvenile robust redhorse.

Therefore, whether the observed population structure results from failed recruitment or an inability to detect juvenile robust redhorse is not clear. As a result, the status of the Oconee

River population and how best to manage it also are unclear.

Robust redhorse is listed as an endangered species in Georgia (Evans 1996), and concerns over possible recruitment failure and eventual extinction of the species led to the formation of the Robust Redhorse Conservation Committee (RRCC) in 1995. The RRCC was formed under a

Memorandum of Understanding between state and federal resource agencies, private industries, and non-governmental conservation organizations of Georgia, South Carolina, and North

Carolina. The goals set by the RRCC were 1) to improve the status of the robust redhorse throughout its former range, 2) identify conservation needs for the robust redhorse and its habitat, and 3) coordinate efforts to address these needs (RRCC 1996). This study aimed to contribute to these goals by investigating the habitat preferences of juvenile robust redhorse.

The ultimate objectives for this work were to better evaluate which of the competing hypotheses best explains the apparent absence of juvenile robust redhorse in samples taken from the Oconee

River and to help guide efforts to restore and conserve the species.

Status of robust redhorse

Historically, robust redhorse occupied medium to large rivers of the Atlantic slope drainages from the Pee Dee River system in North Carolina to the Altamaha River system in

Georgia (Bryant et al. 1996). Presently, wild populations of the species have been found in 1) an

85-km stretch of the Oconee River between Milledgeville and Dublin, Georgia and 2) the

Savannah River in the Fall Line Zone around and below Augusta, Georgia and North Augusta,

South Carolina. A few specimens also have been collected from the Ocmulgee River of Georgia and the Pee Dee River of North Carolina (RRCC 2000). Length-frequency data suggest that the

Oconee and Savannah River populations are made up of mostly larger individuals (Evans 1996;

RRCC 2000).

Three stocked populations of robust redhorse exist in the Broad River, SC and the Broad and Ogeechee rivers of Georgia. Thirty-four thousand phase I (yearling) and phase II (age 1+) robust redhorse have been stocked in the Ogeechee River, Georgia between 1997 and 2002.

Forty thousand phase I and phase II robust redhorse have been stocked in the Broad River, GA

-2- between 1995 and 1998 (RRCC 2002). An additional 18,000 phase I robust redhorse have been stocked in the Broad River, SC in 2004 and 2005 (F. Sessions – SC DNR 2005 pers. comm.).

Structure and sizes of these populations are unknown (RRCC 2002).

Hypotheses of robust redhorse decline

Cope’s (1870) description of catches of this sucker during spawning runs in the Yadkin

River, (“Cart loads have … often been caught at once…”) suggests that robust redhorse once were abundant. Evans (1994) surmised that robust redhorse were as abundant in the Oconee

River as in the Yadkin River, and as with populations in the Yadkin River, have since declined.

Sedimentation caused by agricultural practices, deterioration of habitat caused by dams, and predation by introduced predators are believed to have contributed to the decline of robust redhorse and are perceived as potential threats to the survival of the Oconee River population

(Evans 1994). All known remaining wild populations of robust redhorse exist in rivers that are influenced by hydropower dams (RRCC 1998).

Many hypotheses have been proposed to explain the potential recruitment failure of

Oconee River robust redhorse. Evans (1994) wondered if the population was biologically senescent because most of the fish collected were greater than 20 years old. This notion was soon dispelled, however, because robust redhorse adults were observed spawning, and viable eggs and larvae of robust redhorse were collected in the wild (Jennings et al. 1996; 1998).

Furthermore, some recruitment to the adult population was documented recently (Jennings et al.

2000). Predation by flathead catfish Pylodictis olivaris , an invasive predator that was introduced in the early 1980s, also was expected to limit recruitment of robust redhorse at the juvenile stage

-3-

(Evans 1994). However, limited investigations of stomach contents from flathead catfish captured in the Oconee River did not reveal any robust redhorse remains (e.g., molariform gill arches) (Jennings et al. 2005; personal observation). The hydro-peaking operation of Sinclair

Dam was hypothesized to displace larval robust redhorse downstream and reduce the abundance of low-velocity rearing habitats for larval and juvenile robust redhorse in the Oconee River.

Habitat modeling suggests that low velocity habitats occur in the Oconee River near spawning areas; however, low velocity habitats are dynamic during dam discharge and the ability of larval robust redhorse to find these areas is unknown (Ruetz and Jennings 2000). Furthermore, excessive sedimentation in spawning gravel sites can severely limit the emergence of larval robust redhorse (Dilts 1999).

Still, members of the RRCC are baffled by the absence of juvenile robust redhorse in samples. In a reintroduction effort to establish a self-sustaining population of robust redhorse, nearly 40,000 phase I and phase II hatchery-reared robust redhorse were coded-wire tagged and released in the Broad River of Georgia between 1995 and 1998. The introduced fish ranged from 20 mm to 100 mm TL. Upstream and downstream monitoring efforts were initiated within two weeks after the initial stocking in 1995 and continued on an annual basis. The stocked robust redhorse were not collected until 1999, when four individuals ranging from 404 to 420 mm TL were captured in Clark Hill Reservoir approximately 100 to 140 km from the initial release site (Dennerline and Jennings 2000). Inexplicably, stocked robust redhorse < 385 mm

TL or four years of age have not been captured in the Broad River (Freeman et al 2002). What proportion of fish stocked in the Broad River have survived is unknown, but healthy robust redhorse 385 mm TL or greater and 4+ years in age are captured continuously in Clark Hill Lake,

-4-

GA, down-river from the release sites (C. Jennings - USGS, unpublished data). The capture site on Clarks Hills Lake is an average of 101 km from all release sites of the hatchery-reared fish

(Freeman et al. 2002). Why the fish were not sampled for four years after their release is unknown and raises questions about 1) whether the sampling methods were capable of sampling robust redhorse less than 385 mm TL, and 2) whether all habitats were sampled sufficiently enough to detect juvenile robust redhorse.

Given the lack of knowledge about habitat use by juvenile robust redhorse, the goals of this investigation were to gain an understanding of how juvenile robust redhorse use available habitat and to make inferences about where and how to sample them in the wild. Therefore, two experimental mesocosms were used to investigate the behavioral patterns of pond-reared juvenile robust redhorse in relation to meanders, straight-channels, backwaters, and their corresponding flows. The objective of this study was to determine if pond-reared juvenile robust redhorse use these habitats in proportion to their availability. After satisfying the objective of the study, I attempted to interpret the available length-frequency data for wild robust redhorse in the Oconee

River.

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CHAPTER 2

LITERATURE REVIEW

Riverine habitats

Third-order or higher streams are considered rivers and are defined by their magnitude

(Vannote et al. 1980). Geomorphic features such as sediment size and heterogeneity as well as channel and floodplain morphology define the physical habitat of a river; these features are created and maintained by a wide range of flows. The morphology of a river is formed by the constant erosion and deposition of sediment (Vannote et al. 1980). The main river and its connecting channels represent the lotic (flowing water) part of the river-floodplain system; oxbow lakes, abandoned channels, and backwaters represent the lentic (still water) portion.

Depending on the position of the river channel and channel dynamics, habitats may be ephemeral or stable over decades or centuries (Kellerhals and Church 1989).

Lower Oconee River habitat

The lower Oconee River of central Georgia is a low-gradient, highly sinuous, sand- bedded river located in the southeastern region of the United States (U.S.). The main-channel habitats of the river are comprised of meanders and straight-channels. Though not as abundant, off-channel habitats such as tributaries, backwaters, and oxbows are also present (Ligon et al.

1995). These habitats potentially provide juvenile robust redhorse with several habitat types for various activities (e.g., foraging, resting, predator avoidance). Off-channel habitats can be

-6- reduced or lost by the elimination of high flows (Poff et al. 1997). The scarcity of off-channel habitats in the Oconee River may reflect the geomorphic changes the river has undergone since the construction of Sinclair Dam in 1953 (Ligon et al. 1995).

Effects of dams

Dams modify river flow by capturing low and high flows for irrigation and municipal water needs, electrical power generation, flood control, maintenance of recreational reservoir levels, and navigation. Such human modifications of the flow regime change the natural hydrograph, alter habitat dynamics, and create new conditions to which the native biota may be poorly adapted (Poff et al. 1997).

Frequently, dams are implicated as causes of population decline and extirpation of some freshwater fishes (Allan and Flecker 1993). Taylor et al. (2001) examined changes in the

Kinkaid Creek fish community before and after the construction of Kinkaid Dam and concluded that the impoundment created habitat more favorable to some species and less suitable to others.

As a result, six fish species became locally extinct. Other studies downstream of dams have documented either little change in overall fish species richness (Travnichek and Maceina 1994), substantial reductions in richness (Kapasa and Cowx 1991), or large shifts in dominant species within assemblages (Erman 1973; Martinez et al. 1994). Studies of southeastern mid-, and large- size rivers suggest that species diversity, including redhorse species, decreases downriver from dams (Travnichek and Maceina 1994; Freeman et al. 2001).

Dams block up-river migration of fish (Erman 1973; Allan and Flecker 1993; Taylor et al. 2001), restrict the transport of all but the finest sediments down-river (Ligon et al. 1995; Poff

-7- et al. 1997), and alter down river habitats (Travnichek and Maceina 1994; Freeman et al. 1997;

Poff et al. 1997). Understanding how dams impede the migration of fish up-river and the transport of sediment down-river is simple, but the alteration of habitat is not as simple to comprehend. A case study of Sinclair Dam highlights this phenomenon.

Negative Implications of Sinclair Dam

Sinclair Dam impounds the Oconee River to form Lake Sinclair in Milledgville, Georgia.

The dam is primarily used as a hydroelectric-peaking facility. Peaking hydropower results in extreme fluctuations in discharge, velocity, and available habitat (Stanford et al. 1996). Since the construction of Sinclair Dam, the bed of the Oconee River downstream of the dam has been lowered, and its channel has been incised because the dam restricted the transport of most sediment (Ligon et al. 1995). Now, a much larger magnitude of flow is necessary to inundate the floodplain (off-channel habitats). As a result, the duration and timing of and availability to off- channel habitats that several species (possibly robust redhorse) may rely on for survival have been reduced (Ligon et al. 1995).

Prior to 1997, Sinclair Dam was operated year round under a hydro-peaking regimen

(during evenings at peak demands). Under this regimen, flows fluctuated unnaturally on a daily and seasonal basis (Ligon et al 1995). In efforts to promote habitat stability during the robust redhorse spawning season, negotiations among Georgia Power Company and state, and federal regulatory agencies (see Hendricks 1998) led to approval of modifications in the operational regimen designed to increase minimum flows throughout the year. The new operational regimen also were expected to increase the stability of flows throughout the year and run-of-the-river

-8- flows during May to allow for spawning and early rearing of robust redhorse and anadromous fishes (Hendricks 1998).

Habitat use of fishes

Habitat preference and use by fish change with life stages, seasons, diel periods, and specific conditions. These changes in habitat use usually are associated with physiological preferences (Bowman 1970; Buynak and Mohr 1979; Matheney and Rabeni 1995; Bevelhimer

1996; Dahl and Greenberg 1996; Elliott and Leggett 1996; Thurow 1997), food availability

(Houde and Schekter 1980; Papoulias and Minckley 1990; Allouche and Gaudin 2001), or predator avoidance (Werner et al. 1983; Houde 1987; Schlosser 1988; Litvak and Leggett 1992;

Wahle and Steneck 1992; Houde 1994; Mori et al. 1994; Rooker et al. 1997b; Widdicombe and

Austen 1999; Warren et al. 2000; Brown et al. 2001). In many circumstances, fish respond to one or more of these factors when selecting habitat. For example, red drum Sciaenops ocellatus begin their lives in estuaries and reside there as juveniles for up to four years before moving offshore to adult habitats (Rooker et al. 1997a). The productivity and abundance of structure in the estuary provide young red drum with food for fast growth and protection from predators

(Rooker et al. 1997a). Northern hogsuckers Hypentelium nigricans use slow deep water in winter and fast shallow water and large substrate through warm seasons (Matheney and Rabeni

1995). Although food is less abundant and the fish’s metabolism decreases during winter, slow deep habitats allow the hogsucker to conserve energy. During the warm seasons, food and predators are more abundant, and shallow, fast habitats provide better feeding opportunities and predator avoidance (Matheney and Rabeni 1995). Diel changes of habitat have been observed

-9- for hornyhead chub Nocomis bigutattus, which use deep, structurally complex pools during the day and shallow habitats at night. Even though food densities are higher in shallow habitats, deep pools offer hornyhead chub protection from predators during the day and they move to the shallows to feed at night (Schlosser 1988). Under specific conditions such as flash floods, common carp Cyprinus carpio and white sucker Catostomus commersoni move from main- channel habitat to off-channel habitat (backwaters) to escape increasing turbidity, increasing water velocities, and decreasing temperatures (Brown et al. 2001).

Habitat use by juvenile suckers

Habitat use by juvenile suckers has not been well documented. However, the few available studies suggest that many juveniles of medium- to large-bodied riverine suckers use different types of main-channel habitats such as shallow river margins, riffles and runs, and pools

(Smith 1979; Trautman 1981; Jenkins and Burkhead 1993). More interestingly, most of the redhorse species such as shorthead redhorse M. macrolepidotum , black redhorse M. duquesnei , golden redhorse M. erythrurum , river redhorse M. carinatum , and silver redhorse M. anisurum use backwater habitats (Jenkins and Burkhead 1993).

Backwaters provide young suckers with optimal conditions for survival (Kott et al. 1979;

Werner et al. 1983; Parker and McKee 1984; Martin 1986; Houde 1987; Tyus 1987; Marsh and

Langhorst 1988; Papoulias and Minckley 1990; Mueller et al. 1993; Modde 1996; Modde et al.

1996; Mueller et al. 2003). Backwaters provide various types of structure such as woody debris, aquatic grasses, and other macrophyte flora that juvenile suckers may use as protection from predators. Backwaters usually are warmer and more productive than the main-channel habitats.

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As a result, young suckers find more feeding opportunities there (Schlosser. 1988; Papoulias and

Minckley 1990; Jenkins and Burkhead 1993; Modde 1996). The biggest difference between backwater habitats and main-channel habitats, meanders and straight-channels is water velocity.

Low water velocities allow young juvenile suckers to use more of their energy for feeding rather than maintaining position in high velocity currents, which leads to faster growth (Parker 1989;

Modde et al. 1996).

The use of backwater habitats depends on their presence, persistence, and suitability (Poff et al. 1997). Along the Colorado River, dams and irrigation together have changed the timing, frequency, and duration of off-channel habitats that are used by young razorback Xyrauchen texanus and flannelmouth suckers Catostomus lattipinnis (Valdez et al. 2001; Gurtin et al. 2003).

Furthermore, predation by nonnative fishes is thought to make off-channel habitats in the

Colorado River unsuitable, especially if the habitat lacks structure (Minckley 1983; Weiss et al.

1998; Modde et al. 2001b). Similar restraints have been proposed for copper redhorse M. hubbsi in the Richelieu River in Canada (Mongeau et al. 1992), black redhorse M. duquesnei in the

Wisconsin River in Wisconsin (Fago and Hauber 1993), greater redhorse M. valenciennesi in the

Grand River in Canada (Bunt and Cooke 2001), and the warner sucker C. warneresis in the

Warner Basin in Oregon (Kennedy and Vinyard 1997).

Habitat selection of juvenile robust redhorse suckers

Larval robust redhorse are collected annually (between early May to late June) drifting in the main channel of the lower Oconee River via push-nets, in shallow reaches near gravel bars

(inside reaches of meander habitat) via seines, and in light traps set in slack waters along the

-11- river margin (Jennings et al. 1996;1998). Generally, adult robust redhorse are collected in meanders containing woody debris and gravel bottom substrates (Evans 1998). Habitat use data for wild juvenile robust redhorse ranging from 30 mm to 410 mm TL are non-existent.

Habitat selection studies

Habitat selection studies are useful because they have the potential to provide knowledge of what habitats fish use, when they use them, and why. Selection studies of fish(es) may be conducted for different life stages, seasons, diel patterns, or specific conditions. These studies can be conducted under natural or controlled conditions, in the field or in an experimental setting, and usually are designed to be analyzed statistically (Bowman 1970; Schlosser 1988;

Wahle and Steneck 1992; Matheney and Rabeni 1995; Bevelhimer 1996; Widdicombe and

Austen 1999; Allouche and Gaudin 2001). The various types of studies may differ in the observation methods and types of data collected. All selection experiments have disadvantages and advantages; some results may be predictable and others are unanticipated.

The duration of a habitat selection experiment depends on its objectives. Some habitat selection studies may last several years (Martinez et al. 1994; Mueller et al. 2000; Gilliam and

Fraser 2001), and others may last only a few minutes (Wahle and Steneck 1992). Field studies designed to investigate seasonal patterns of habitat use are considered long-term studies. In such studies, observations of fish can be made using active sampling (e.g., electrofishing or seining), passive sampling, (e.g., trammel, gill, or hoop nets), or by surveillance (e.g., visual, video, or telemetry). For example, Matheney and Rabeni (1995) used radio telemetry to track 25 northern hogsuckers for one year to evaluate seasonal movement and habitat use. In contrast, situational

-12- studies about specific habitat conditions may only last a few minutes. This type of study is often carried out in controlled, artificial settings (Wahle and Steneck 1992; Bevelhimer 1996; Jordan and Willis 2001; Levin and Hay 2003). For example, substratum preference and use for

American lobster Homarus americanus were tested under no-threat and threat conditions in small 20-gallon aquaria. Each trial only lasted five minutes, and observations were made visually by the researcher (Wahle and Steneck 1992).

There are obvious advantages and disadvantages to both of these approaches.

Advantages of long-term studies are that the habitat data are exact because they were collected in the field, and the longevity potentially allows natural behavioral patterns (e.g., feeding, habitat selection, spawning) to be recognized. However, the disadvantages of long-term studies are the amount of time required (fish may be lost, fished out, or die), the associated cost, the inability to control sources of error, the complexity of the habitats, and the potential weather constraints.

The major advantages of short-term studies are the researcher’s ability to replicate and manipulate the treatments and the better ability to control sources of error because they can be carried out in an artificial environment under controlled conditions. For example, Wahle and

Steneck (1992) reported 20 replicates of their selection study and were able to manipulate a high- risk environment for the test lobster by tethering them and adding predators to the tank. The specific shortcoming of this study was the micro-scale of the replicated habitats because the available space and conditions in the wild were greatly under-represented.

A balance of the advantages and disadvantages of long-term and short-term habitat selection studies can be met by using an approach that is intermediate to long- and short-term studies. A two-month study was conducted in an artificial outdoor stream (mesocosm) to

-13- investigate the effects of avian predation threat, water flow, and cover on the habitat use of chub

Leuciscus cephalus (Allouche and Gaudin 2001). The duration of the study was long enough to collect sufficient amounts of data, yet short enough to limit financial and mortality costs.

Furthermore, the artificial stream (mesocosm) was stationed outside under natural conditions, which created a system that experienced seasonal photoperiod and temperatures (Allouche and

Gaudin 2001).

Use of mesocosms

A mesocosm is a medium scale representation of a system (Martin 2001). In common fisheries usage, a 10-gallon aquarium housing bluegill would be referred to as a microcosm, a

1000-gallon tank housing bluegill as a mesocosm, and a farm pond with bluegill as a macrocosm. The mesocosm in this study is a 2670-l tank constructed as a medium scale representation of the lower Oconee River.

Experiments conducted in mesocosms have several potential advantages over microcosm experiments (Hickey et al. 1999). First, the relatively large volume is a better approximation of the space available in the wild, thereby providing the potential to reconstruct and simulate habitat types that are representative of field conditions (Litvak and Leggett 1992; Elliott and Leggett

1996). For example, the mesocosm used by Allouche and Gaudin (2001) simulated 6 riffle-pool type habitats and periodically displayed a model cormorant above the mesocosm to simulate harassment by avian predators. Second, mesocosms are suitable for long-term experiments

(Purcell et al. 1997). Widdicombe and Austen (1999) observed the effects of bioturbation on the diversity and structure of a macrobenthic community continuously for 20 weeks. Finally,

-14- mesocosms accommodate animals that are too large to manipulate in microcosms. Adult (249-

299 mm TL) smallmouth bass Micropterus dolomieu were used in a tank study that examined habitat selection based on temperature, food, and physical structure (Bevelhimer 1996). The value of mesocosm research comes from the reproduction of suitable habitats in which juvenile robust redhorse were able to behave and function as naturally as possible.

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HYPOTHESIS

I hypothesized that hatchery-reared juvenile robust redhorse would not use each habitat type in proportion to its availability. Based on the literature, I think that backwater habitat provides more food and protection for juvenile robust redhorse than meanders and straight- channels. If robust redhorse evolved in river systems with extensive floodplains, then the innate behavior of these fish may result in their use of backwater habitats. Only limited effort has been expended to sample such habitats during previous attempts to monitor the wild robust redhorse population. If this hypothesis is correct, it may explain the apparent absence of juvenile robust redhorse. If my hypothesis is not correct, gear-inefficiency or low abundance is likely the reason why juvenile robust have not been collected in the wild.

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SUMMARY

The fate of the imperiled robust redhorse depends on the ability to identify limiting factors to their survival and the willingness to make appropriate management decisions.

Establishing how habitat type influences the early life history of robust redhorse is of fundamental importance in understanding their ecology and ultimately restoring native populations. The data I collected were needed to evaluate among competing hypotheses about fate of the robust redhorse population in the Oconee River. If pond-reared juvenile robust redhorse and wild-produced juvenile robust redhorse have similar behavioral patterns, researchers and managers should be able to sample juvenile robust redhorse in their natural habitat, assuming that the current sampling gear are adequate. Finding juvenile robust redhorse in the wild will 1) strengthen statistical estimates of the Oconee River population, 2) assist biologists in determining if the population is declining or self-sustaining, and 3) help inform managers about how best to conserve and restore this imperiled species.

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CHAPTER 3

METHODS

Experimental tanks

The experiment was conducted in two identical mesocosms that simulated the lower

Oconee River. The mesocosms were 4.87 m long, 1.22 m wide, 0.67 m high, and included three habitat types. On either end of the tanks there were parabolic-shaped constructions made of polyurethane-plastic that simulated meander habitat. Behind these structures was the simulated backwater habitat, and there was simulated straight-channel habitat within the tank (Figure 1).

These three habitat types are characteristic of habitats in the lower Oconee River. The mesocosms were situated under a pole barn adjacent to Whitehall Fish Laboratory and were exposed to ambient temperatures, artificial light (four 100-watt incandescent light bulbs), and some natural light. The mesocosms were equipped with eight viewing windows, 25.4 cm by 25.4 cm, made of one-way glass so that the researcher could see the fish but the fish couldn’t see him.

There were three windows on either side of the mesocosm for viewing the straight-channel and meander habitats, and one window on either end of the tank to view the backwater habitat

(Figure 2). Gravel of the same type and size (2-36 mm) found in the Oconee River was used as substrate in both mesocosms. Water, free of chlorine and fluoride, was recirculated in a bioball- filter-system for all tanks used in the study.

Water flow was generated by two Minn Kota  18-kg thrust trolling motors positioned at opposite corners on either end of the mesocosm. A grid made of yarn, with mostly 135.5 cm 2

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Figure 1 a. Aerial view of the mesocosm with the backwater habitat, upper right-hand corner, behind the parabolic-shaped polyurethane construction (outlined in green). b. Aerial view of the mesocosm with the main-channel habitats, straight-channel (yellow) and meander-bends (red).

-19-

Figure 2 a. Six viewing windows, made of one-way glass, for observing the straight-channels and meanders. b. Viewing window, made of one-way glass, for observing the backwater habitat (upper-right hand corner).

-20- cells, superimposes the mesocosm (Figure 3) and was used as a location reference for recording observations (Porter and Church 1987). Current velocity maps for both mesocosms were constructed by taking water velocity readings with a Marsh-McBurney 2000 ® flow meter at surface, middle of the water column, and just above the substrate within each cell of the superimposed grid (Figure 4). Robust redhorse are benthic fish and the benthic flows in mesocosm 1 ranged from –12 cm/s to 30 cm/s and averaged 7 cm/s. The benthic flows in mesocosm 2 ranged from –11 cm/s to 32 cm/s and averaged 6 cm/s (Microsoft Excel 2000). The resultant flow vectors and current velocities in the tanks were similar to these same factors in the lower Oconee River (T. Rassmussen – University of Georgia, personal communication). Two viewing platforms were constructed 2.7 meters above each tank and were used to make observations of the fish. Each platform was accessed by climbing the ladder permanently affixed to it (Figure 5). Fish did not respond to the presence of the observer.

Two additional tanks were used as holding tanks for the test fish. The holding tanks and the experimental mesocosms were both located under the same pole barn. One of the holding tanks was used as the acclimation tank and the other as the receiving tank. The study fish were placed in the acclimation tanks upon arrival from Richmond Hill Fish Hatchery. A trolling motor, positioned in one corner of the acclimation tank, was used to produce water flow. All fish were acclimated to flowing water for at least 6 weeks before being used in the experimental mesocosms. Fish that had been used in a trial were transported to the receiving tank.

-21-

Figure 3. Mesocosm with gravel substrate and superimposed yarn grid.

-22-

Figure 4. Map of average velocities at the surface, mid-depth (60% depth), and the benthic layer of the mesocosms. The velocity values are measured in cm/s.

-23-

platforms

Figure 5. Platforms built over the mesocosm for making observations. The platforms were accessed by ladders attached to them.

-24-

Experimental fish

The fish in this experiment were progeny of Oconee River brood stock, 2003 year-class, and were pond-reared at the Richmond Hill Fish Hatchery. The fish were removed from the pond via a seine net and placed in a raceway at the hatchery one day prior to their transportation to facilities at the University of Georgia. The fish were transported from Richmond Hill Fish

Hatchery to Whitehall Fish Lab on October 26, 2004. The fish ranged from 94 mm to 142 mm total length and from 6.3 g to 27.5 g in weight. One potential drawback of using pond-reared fish is that they were never exposed to flowing water and may not behave the same as a wild robust redhorse in the mesocosm. Therefore, all of the hatchery-reared fished were placed in the acclimation tank and allowed to acclimate in flowing water for at least six weeks prior to the beginning of the experiment. Two weeks of acclimation time is probably sufficient because the hatchery-reared fish are first generation captive fish and their phenotypes or genotypes are not likely to change (Rhodes and Quinn 1998; Deverill et al. 1999; Larsen and Pedersen 2002; Teel et al. 2003; Weber and Fausch 2003). Longer acclimation times have been suggested for second generation captive fish because the phenotypes and/or genotypes of these fish may be altered

(Jonsson et al. 2003; Metcalfe et al. 2003; Petersson and Jarvi 2003; Miyazaki et al. 2004).

Water used in the tanks was treated with un-iodized salt (NaCl); Melafix, an anti- bacterial solution; and Pimafix, an anti-fungal solution to prevent pathogen outbreaks. Salt was used at 3 lbs per 100 gallons and both melafix and pimafix were used at 2.2 parts per thousand

(ppt).

-25-

Unique tags were surgically attached to each fish so that the fish could be observed individually in the mesocosms. All tags were 7 cm long and made of the combination of two different colored yarns. Prior to the attachment of the tags, the fish were anaesthetized with tricaine methane sulfonate (MS-222) at 80 ppm. Each fish was then measured, weighed, and the tag was surgically attached with a small suture under the skin near the first dorsal spine (Figure

6). After the fish was measured, weighed, and the tag was attached, the fish was placed in a bath of malachite green and formalin solution (by East Riding Koi Co.) for 20 minutes before being placed in the mesocosm to kill any pathogens on the fish’s body (Piper et al. 1982). The fish were acclimated to the mesocosm for two days prior to the beginning of each trial. During the trials, fish in the mesocosms were fed frozen bloodworms daily at 1% of their body weight

(Allouche and Gaudin 2001). In an effort to prevent biases of habitat selection because of food availability, the appropriate amount of bloodworms was thawed in water, and about half of the bloodworms were poured in the center of each of the straight-channels, in both mesocosms.

Flow of the water distributed the bloodworms proportionately around the tanks. To further prevent biases of habitat selection because of food availability, the fish were fed after the last observational period every day during each trial. At only 1% of their body weight, food did not accumulate in the tanks (personal observation 2004-2005).

Experimental design

This study was designed to investigate if juvenile robust redhorse used a variety of habitats, based on water velocity and channel morphology, in proportion to their availability.

-26-

suture yarn tag

Figure 6. The yarn (tag) is tied to the suture thread and the suture is placed under the skin near the first dorsal spine. The first arrow points to the suture that connects the tag to the fish, and the second arrow points to the tag made of two different colors of yarn.

-27-

The experiment was conducted in four 10-day trials, with eight pond-reared, juvenile robust redhorse used per trial, per mesocosm. Therefore, one trial consisted of 10 days, two mesocosms, and 16 fish. Trial 1 began December 12, 2004 and ended December 21, 2004. Trial

2 began January 11, 2005 and ended January 20, 2005. Trial 3 began February 15, 2005 and ended February 24, 2005. Trial 4 began March 9, 2005 and ended March 18, 2005. Fish locations in the tank were determined via aerial observations. Fish were observed and their locations in the tank were recorded during the first 10 minutes of each hour between 0800 and

1700 hours each day for all trials. In all trials, water temperature in the tanks and ambient temperature were also recorded every hour between 0800 and 1700 hours.

Water velocities were measured before and after each trial to determine if flows remained consistent within and between trials (Allouche and Gaudin 2001). The first trial began on

December 12, 2004 and the last trial ended March 18, 2005.

Habitat types - flow classes

Based on the available literature for flow classification in riverine environs (Jowett and

Richardson 1994; Pert and Erman 1994; Beechie et al. 2005) and using the range of velocities that were present in each mesocosm, four benthic flow classes were constructed to analyze habitat use of the test fish. The four flow classes are identical in terms of flow value for each mesocosm. Flow class 1 (-12 - -1 cm/s) corresponds to eddies, flow class 2 (0 – 15 cm/s) represents slow flows, flow class 3 (16 – 32 cm/s) signifies moderate flows, and flow class 4 pertains to backwaters. Fast flows ( ≥ 45 cm/s) were not available in either of the mesocosms.

All flow classes represent the benthic layer in the mesocosms. The amount of each flow class

-28- was similar between the two mesocosms (Figure 7).

Statistical analyses

Flow and temperature data were tested for normality with the Shapiro-Wilkes test (SAS

1999) and for constant variance with the F-Max test (Sokal and Rholf 1995). If data were not normal or if the variances were not constant, then the data were transformed. After transformation if the data still were not normal or the variances not constant then a non- parametric test was used to analyzed those data. An α = 0.05 was used to evaluate the significance of all statistical tests.

A frequency table of the flows, one for each mesocosm, was created from the flow data collected. The range, mode, and mean of the flows were also determined for each mesocosm

(Microsoft Excel 2000). A t-test was used to evaluate if flow distribution in mesocosm 1 and mesocosm 2 were the same (SAS 1999).

An analysis of variance (ANOVA) was used to evaluate the mean temperatures among trials to determine if there were any differences. A Waller-Duncan mean separation test was conducted on the mean temperatures of the four trials to partition any similarities and/or differences among the temperatures (SAS 1999).

Ten location observations were recorded for each fish each day. Consequently, the locations of the fish were not independent from one hour to the next. Therefore, the modal location reference for each fish within a day was found. Thus, instead of having 10 location observations, per fish, per day, there was one location observation, per fish, per day. The modal

-29-

Flow Class Availability

40 tank 1 tank 2 30 percent of availability of percent

0 class 1 class 2 class 3 class 4 flow class

Figure 7. Flow class availability for mesocosm 1 and 2.

-30- location was used for each fish by day to make analyses on the habitat use of the fish throughout the trials (J. Reeves – Statistics Department, University of GA, - 2005 pers. comm.). For each trial and mesocosm, a potential of 80 data points were used for the habitat use analysis. A Log-

Linear Model analysis was used to evaluate the habitat use data, specifically to determine if the fish used habitats differently between mesocosms, seasons, flow class, and all combinations of the three (SAS 8.2 1999). A post hoc Log-Linear Model analysis (with flow classes of interest removed) was used to determine if the preference of eddies, the avoidance of moderate flows, or both contributed to the significance of the model. Average fish movement (i.e., number of changes in location) versus water temperature was determined. The Kruskal Wallis test was used to compare the average movements among trials (SAS 8.2 1999). A t-test was run on the before and after trial sub-sample data to determine if the flow distributions remained the same within and between trials.

-31-

CHAPTER 4

RESULTS

Experimental tanks

Mean flows in the two experimental mesocosms were significantly different, p = 0.0033, primarily, because mesocosm 2 has more cells with negative flows than mesocosm 1. There were 30 times as many cells in mesocosm 2 that had flows ranging from -7 to -4 cm/s than in mesocosm 1 (Figure 8).

Temperature analyses

The mean water temperatures (Figure 9) were significantly different among trials ( p <

0.0001; SAS 1999). The Waller-Duncan mean separation test grouped the mean temperatures for trials 2-4 together and separated the mean temperature of trial 1 (SAS 1999). Trial 1, hereafter, is referred to as ‘winter’ and trials 2-4 are referred to as ‘early spring’.

Habitat use analysis

The results of the Log-Linear Model analysis indicated that the fish did not use habitats differently between tanks ( p =0.97) nor seasons ( p =0.54). Therefore, the habitat data were analyzed for both tanks and seasons simultaneously. Furthermore, as expected, the fish did not use the flow classes in proportion to their availability ( p <0.001). The preference for eddies and the avoidance of moderate flows contributed to the significance of the model. Even though fish

-32-

Frequency mesocosm 1

20 occurence

0 0 0.1 0.2 -0.1 0.02 0.04 0.06 0.08 0.12 0.14 0.16 0.18 0.22 0.24 0.26 -0.12 -0.08 -0.06 -0.04 -0.02 More flow (m/s)

Frequency mesocosm 2

occurence 20

0 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 0.22 0.24 0.26 0.28 0.30 0.32 -0.12 -0.10 -0.08 -0.06 -0.04 -0.02 flow (m/s)

Figure 8. Frequency histogram of flows in mesocosm 1 (top graph). Frequency histogram of flows in mesocosm 2 (bottom graph).

-33-

Average temp by Trial

10.4

10 9.2

8.6

6 temperature (Celcius) temperature 4 3.6

0 T1(winter) T2(early spring) T3(early spring) T4(early spring) trial

Figure 9. Average temperature for each trial used to determine habitat use of juvenile robust redhorse in an experimental mesocosm. The bars represent standard deviation.

-34- habitat use was not affected by season, fish movement can differ seasonally. Therefore, the habitat use results were partitioned into winter and early spring (Table 1). During the winter the fish showed a preference for eddies and backwaters and avoided slow to moderate flows

(p<0.001) based on the proportion of their availability (Figure 10). During the early spring the fish showed a preference for eddies, avoided the moderate flows, and used slow flows and backwaters in proportion to their availability ( p<0.001) (Figure 11).

Fish movement

Results from the Kruskal-Wallis test for mean movements per trial indicate that there was not a significant difference in fish movement among the trials. However, generally, fish did move more as temperatures increased (Figure 12). The test fish were never observed using the water column. During trial 1, two fish died prematurely and were not replaced.

-35-

Table 1. Habitat use of test fish in the winter and early spring.

Habitat type Winter Early spring eddies + + slow flows - 0 moderate flows - - backwaters + 0

‘+’ = preferred, ‘-‘ = avoided, ‘0’ = proportionate use of habitat

-36-

Winter Habitat Selection

expected 30 observed number ofobservations number 20

0 (-.11 - -.01) (0.0 - 0.15) (0.16 - 0.32) BW1&2 flow classes

Figure 10. Use of flow classes by juvenile robust redhorse in mesocosm during winter 2004. The blue bar is the expected number of observations and the red is the observed number of observations. The test fish did not use each flow class proportionately ( p<0.001).

-37-

Early Spring Habitat Selection

expected 30 observed number of observations of number 20

0 (-.11 - -.01) (0.0 - 0.15) (0.16 - 0.32) BW1&2 flow class

Figure 11. Use of flow classes by juvenile robust redhorse during early spring 2005. The test fish did not use each flow class proportionately ( p<0.001).

-38-

Fish Movement

400

350

300

250

200 number ofmoves number

150

100

0 (0 - 2.5) (2.6 - 4.5) (4.6 - 6.5) (6.6 - 8.5) (8.6 - 10.5) (10.6 - 12.5) (12.6 - 14.5) (14.6 - 16.5) tempearture class ( oC)

Figure 12. The number of moves by juvenile robust redhorse within a temperature class during winter 2004 and early spring 2005.

-39-

CHAPTER 5

DISCUSSION

Habitat preference and use by fish change with life stages, seasons, diel patterns, and specific conditions. In this study, I ascertained how juvenile robust redhorse used a variety of flows in experimental mesocosms without the influence of food availability or predator presence.

Furthermore, results of the study suggested that habitat use of juvenile robust redhorse was influenced by flow and some seasonal component(s) (e.g., temperature, photoperiod).

Habitat use by juvenile and adult suckers or juvenile and adults of taxa with small maximum body size similar to juvenile robust redhorse may overlap (Schlosser 1987; Brown and

Moyle 1991). For example, small fishes, including juveniles of large taxa, in a warm-water

Illinois stream used riffles and runs whereas the larger fish used pools (Schlosser 1987).

Therefore, juvenile robust redhorse habitat use may be similar to the habitat use of like-sized riverine fishes, whether they are adults of small taxa or juveniles of large taxa.

Preferred habitat use of juvenile robust redhorse

In this study, pond-reared juvenile robust redhorse showed a preference for eddies and backwaters during winter and eddies alone during early spring. This pattern of habitat use is similar to patterns observed for other suckers and riverine fishes in the wild. Although data on winter habitat use by juvenile robust redhorse are unavailable, available data on habitat use during fall suggest juvenile robust redhorse use slow, deep pools. Recently released,

-40- pond-reared juvenile robust redhorse may have selected deeper, slow moving water in the Broad

River, GA in October of 1997 (Freeman et al. 2002). Deep pools often contain large eddies along their sides (Brown et al. 2001); however, whether the deep pools in the Broad River contained eddies was not determined. Adult northern hogsuckers use slow deep pools that are flanked by eddies during winter (Matheney and Rabeni 1995). Juvenile blue suckers Cycleptus elogatus also used slow deep pools during the spring, as did juvenile flannelmouth suckers

Catostomus latipinnis in the summer (Childs et al. 1998). In the Current River, Missouri, adult northern hog suckers used rocky rapids and riffles in addition to eddies during the winter

(Minckley 1963). Juvenile blue suckers and flannelmouth suckers’ use of eddies near deep- water pools in the Little Colorado River, Arizona during the spring and summer was hypothesized as a trade-off between foraging efficiency and predation risk (Childs et al. 1998).

Other riverine fishes such as juvenile rainbow trout Oncorhynchus mykiss (Simpkins et al. 2000) and rainbow darter Etheostoma caeruleum (Harding et al. 1998) used eddies adjacent to fast flows. Rainbow darters were suspected to use eddies because food became entrapped in the eddying current, which made the habitat more profitable than other available habitats (Harding et al. 1998).

Many riverine fishes use backwater habitats during high discharge in the winter (Brown et al. 2001; Modde et al. 2001a; Gurtin et al. 2003). For example, white suckers use backwaters during high-flow events and runs when discharge and water levels are low in the Grand River of

Ontario during the winter (Brown et al. 2001). Off-channel habitats may provide some juveniles and small-bodied adults refuge from high flows or predators (Tschaplinski and Hartman 1983;

Brown and Hartman 1988; Harvey et al. 1999). Likewise juvenile robust redhorse may use

-41- backwaters during high discharge as a velocity shelter or for predator avoidance; however, water levels in the lower Oconee River are usually too low to inundate floodplains and backwater habitats during winter. Therefore, wild juvenile robust redhorse in the Oconee River are likely to be found in eddy habitats.

Habitats avoided by juvenile robust redhorse

Many riverine fish species prefer low velocity habitats and avoid flows exceeding 0.15 m/s during the winter and early spring (Mueller et al. 2000; Hesthagen and Heggenes 2003;

Schwartz and Herricks 2005). In the present study, test fish avoided moderate flows during both winter and early spring. Similarly, larval and juvenile robust redhorse experienced higher survival and growth when exposed to low-velocity water flows versus high-velocity water flows

(Weyers et al. 2003). Several studies have shown that fishes use low velocity habitats to conserve energy during the winter and early spring (Cunjak and Power 1986; Chisholm et al.

1987; Baltz et al. 1991; Brown and Mackay 1995; Harvey et al. 1999; Solazzi et al. 2000).

Juvenile cutthroat trout used low velocity areas along the stream margin during flood conditions in winter in a northern California stream, probably to conserve energy (Harvey et al. 1999). In contrast, juvenile rainbow trout and juvenile Sacramento suckers Catostomus occidentalis increased their use of high-velocity riffles in the presence of squawfish Ptychocheilus grandis

(Brown and Moyle 1991). In this study, the slow flow-class was avoided during winter conditions. Since both eddies and slow flows are low-velocity habitats, the mechanism(s) for the preference of eddies over slow flows cannot be determined, and whether fish found slow-flow habitat to have been less profitable than eddies because of food availability is unknown.

-42-

Proportional habitat use of juvenile robust redhorse

During the winter, the test fish rarely moved during the observational period. In the spring, the test fish used backwaters and slow flows in proportion to their availability. During the early spring study, the test fish were often observed swimming around the mesocosms in the main channel and backwaters. Usually, one or two of the eight fish (per mesocosm) would remain in the same location throughout a 10-hour daily observational period, whereas the other six or seven would switch locations several times during the 10-hour period. The fish that moved switched among locations from eddies, backwaters, and slow flows. In my study, the proportional use of backwaters and slow flows during early spring may have resulted from increases of fish movement because of the increase of water temperatures (Hasan and Quasim

1961) and more than likely reflected their physiological preference of low-velocity habitats.

Differences in riverine habitats

Rivers contain a variety of low-velocity habitats, such as backwaters, eddies, and boundary areas between water-sediment interface (slow flows), and fish use of these areas may be influenced by differences among the habitats. Eddies and slow flows both exist in the main channel and often are adjacent to each other (Kellerhals and Church 1989; Jowett and

Richardson 1994; Heggenes et al. 1996; Chan et al. 1997). The primary differences between the two are the direction of their currents and food availability. Eddies flow opposite to the flow in the main channel, and slow flows travel in the direction of the flow in the main channel (Harding et al. 1998). Slow-flow habitats provide low water velocities that fish may use to conserve energy (Hasan and Quasim 1961; Chan et al. 1997; Thurow 1997; Beechie et al. 2005). Eddies

-43- provide low water velocities and also are areas of deposition for solid materials, including food; therefore, fish may use eddies both for foraging (Lehane et al. 2002; Beechie et al. 2005) and as a refuge from strong currents (Harding et al. 1998; Schwartz and Herricks 2005). Food in eddies may result in increased feeding opportunities for fish. In the experimental mesocosms eddies were always adjacent to slow flows.

Backwaters are off-channel habitats that, like eddies and slow flow habitats, also provide fish with an abundant food supply and refuge from fast flowing water. Backwaters provide: 1) velocity refuge for young fish (Parker 1989; Modde et al. 1996; Tyus et al. 2000), 2) warmer water than the water in the main channel (Schlosser. 1988; Papoulias and Minckley 1990;

Jenkins and Burkhead 1993; Modde 1996), 3) a richer source of food than in the main channel

(Schlosser. 1988; Papoulias and Minckley 1990; Jenkins and Burkhead 1993; Modde 1996), and

4) more shelter and structure to young fish for protection from predators than are available in the main channel (Schlosser 1988; Parker 1989; Modde et al. 1996). Current velocity in the backwater areas was non-existent; however, there also were non-flowing areas in the main channel. Most of the time, test fish were observed in close proximity to the walls, crevices, and tight spots within the mesocosm. The backwater areas had all three features and were four times as small as the open main channel. In fact, the test fish showed preference for the backwater with the stand-pipe (more structure) compared to the backwater without the stand-pipe (less structure).

Fish affinity to structure (e.g., woody debris, boulders, stream edge) has been well documented in other studies (Wahle and Steneck 1992; Allouche and Gaudin 2001; Martin

2001), and predation has been hypothesized as the evolutionary process reinforcing this behavior

-44-

(Johns and Mann 1987). Why the test fish used areas close to the walls in my study cannot be determined. Furthermore, any apparent affinity to structure does not explain the test fish’s overall preference for eddies. Though the mechanisms for habitat use cannot be determined, the test fish in this study may have selected habitats based on some combination of flow and structure.

Implications for sampling the Oconee River

Most sampling effort for juvenile robust redhorse has been focused around middle to outside portions of meanders and around sandbars, with minimal efforts being placed in backwaters (Jennings et al. 1998; Jennings et al. 2005). Boat electrofishers (Evans 1999; RRCC

2000), gill nets (Jennings et al. 2005), and hoop nets (Jennings et al. 2004) have been used to sample juvenile robust redhorse around meander habitat (moderate to fast flows), and seines have been used to sample around sandbars (Jennings et al. 1998; RRCC 2000; Jennings et al.

2004). Few attempts have been made with backpack electrofishers to collect juvenile robust redhorse in backwaters (RRCC 2000; Freeman et al. 2002). All attempts have been unsuccessful in collecting wild juvenile robust redhorse from the Oconee River or elsewhere. However, different gear types in various habitats have been used to sample other juvenile suckers (Table

2), though none have proven to be efficient because only a few individuals have been caught.

The results of this study support the hypothesis that the absence of juvenile robust redhorse in catch data may be related to sampling in the wrong habitats. However, the gear inefficiency and actual abundance hypotheses also need to be evaluated. Furthermore, scarcity of juvenile

-45-

Table 2. Juvenile catostomids that have been collected, the habitats collected in, the gear used, and the name of collectors.

Species Habitat Gear Citation C. Jennings personal comm. RRCC 2000 Cull 2005

near sandbars seine Carpoides cyprinus C. Jennings personal comm. backwaters backpack electro

main channel boat electrofisher Minytrema melanops near sandbars seine

slack-water tribs backpack electro

outside meanders boat electrofisher Jennings et al. 1998; Moxostoma collapsum 2005

-46- suckers have been reported for others species with healthy adult populations (Beal 1967; Hand and Jackson 2003; Morey and Berry 2003).

Juveniles of many suckers, including robust redhorse, have been difficult to collect (Beal

1967; Hand and Jackson 2003; Morey and Berry 2003). Sampling for blue suckers, a federally- listed “Species of Concern” (Williams et al. 1989), in two different regions of the United States failed to capture juveniles (Hand and Jackson 2003; Morey and Berry 2003). Out of 4,093 overnight hoop net sets over 10 years, only 264 adult and no juvenile blue suckers were collected from randomly selected 1-km stream reaches of the upper Yazoo River (Hand and Jackson

2003). Electrofishing and hoop nets used to sample moderate to swift flows and inside bends

(which include eddies) for blue suckers in the James River and Big Sioux River, during summer caught 74 adult blue suckers in the James River and 28 adults in the Big Sioux River; however, juveniles were not collected in either river (Morey and Berry 2003). Fish behavior and gear bias were suggested to be the main factors that affected the inability to sample juvenile blue suckers

(Beal 1967). The habitat (high current velocity) that juvenile blue suckers are suspected to use was also determined to be difficult to sample (Moss et al. 1983). Juveniles are uncommon in samples from healthy populations of other suckers such as notchlip redhorses M. callapsum and spotted suckers Minytrema melanops . In October of 1997, 300 pond-reared robust redhorse fingerlings were released into Hannah Creek, a tributary of the Broad River, GA, and sampled with a backpack electro-fisher. Only 29 of the 300 fingerlings were recaptured within 24 hours of their release (Freeman et al. 2002). Therefore, the absence of wild juvenile robust redhorse in capture data may reflect their behavior and the difficulty of sampling all possible habitats.

The results from this study suggest that eddies should be sampled more intensely during

-47- winter and early spring and backwaters, when present, should also be sampled during the winter.

Eddies exist near the downstream-end of sandbars, in the transitional zone of two meanders in the lower Oconee River (personal observation). Eddies in the transitional zone of meanders are typically deeper areas of deposition (Allan 2001), making eddies difficult to seine and impossible to backpack electrofish; however, these areas could be sampled with boat electrofishers (R.

Jenkins - Roanoke College, personal communication; C. Jennings - USGS, personal communication; personal observation). Sandbars are sampled yearly with seines; however, the mesh size (1.59 mm) for the seines are designed for larval fish and are too small to efficiently collect juvenile robust redhorse. Seines of adequate mesh size, such as 8.50 mm or 6.35 mm, should be used when seining for juvenile robust redhorse (Jenkins and Burkhead 1993).

Backwaters can be sampled with backpack shockers, barge electrofishers, or seine.

-48-

CHAPTER 6

CONCLUSION

The results of this study suggest that juvenile robust redhorse are likely to be found in eddies and backwaters in the winter and eddies and slow flows during early spring. This hypothesis is supported by one of the world’s leading specialists on the ecology and life history of catostomids (R. Jenkins - Roanoke College, personal communication). Habitats implicated to be prime habitats for these juvenile robust redhorse are the type of habitats that wild juvenile robust redhorse are likely to use, but are often over-looked or under-sampled by researchers (R.

Jenkins - Roanoke College, personal communication). Of the four different habitat types in the mesocosms, the test fish in this study showed an overall preference for eddies, the habitat type least abundant, and a secondary preference for backwaters, the second least abundant habitat type. Ironically, little if any sampling effort has been concentrated in eddies and backwaters, which also are two of the least abundant habitat types in the lower Oconee River. Therefore, the current catch data may reflect biases in the current sampling regimen in regards to the type of habitat that is sampled and the time of year that sampling occurs for juvenile robust redhorse.

Sampling in the wrong habitats for juvenile robust redhorse is likely the reason why these fish have not been collected in the wild. Once wild juvenile robust redhorse are collected in the

Oconee River, it will improve our ability to make inferences about the status of the population and how best to manage it.

-49-

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