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Trophic and Population Ecology of Introduced Flathead Catfish Pylodictis olivaris in the Tar River, North Carolina
Daniel J. Walker, Jordan Holcomb, Robert Nichols, and Michael M. Gangloff

Southeastern Naturalist, Volume 14, Issue 1 (2015): 9–21

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Southeastern Naturalist 9 D.J. Walker, J. Holcomb, R.Nichols, and M.M. Gangloff 22001155 SOUTHEASTERN NATURALIST Vol1.4 1(41,) :N9–o2. 11 Trophic and Population Ecology of Introduced Flathead Catfish Pylodictis olivaris in the Tar River, North Carolina Daniel J. Walker1,2,*, Jordan Holcomb1,3, Robert Nichols4, and Michael M. Gangloff1 Abstract - Pylodictis olivaris (Flathead Catfish) are large piscivores native to western Gulf of Mexico drainages that have been widely introduced into Atlantic Slope drainages with largely unknown consequences for native lotic faunas. From 2009–2011, we assessed the diet, demography, growth, and spatial distribution of Flathead Catfish in the lower Tar River in east-central North Carolina. We documented current presence of Flathead Catfish using electrofishing at 27 sites in the Tar River and its tributaries Fishing and Sandy creeks and examined diet and growth rates in the lower Tar River population. Stomach contents revealed that Tar River Flathead Catfish are primarily piscivorous but also consumed a diverse range of prey items. Canonical correspondence analysis found that Flathead Catfish ≥500 mm TL appeared to consume centrarchids at greater rates than smaller Flathead Catfish, suggesting a shift to larger prey in larger, older fish. Body-condition analysis found that condition did not change with body size, suggesting that the lower Tar River population has likely not yet over-exploited its resource base. Upstream distribution of Flathead Catfish in the upper Tar River and Fishing Creek, two important refuges for numerous imperiled lotic taxa in this fragmented drainage, appears restricted by two small dams. Our data suggest a need for continued monitoring for natural and human-mediated Flathead Catfish range expansions into sensitive reaches as well as empirical study of possible species-, assemblage-, and ecosystem-level effects of this apex predator on imperiled freshwater biota in the Tar River. Moreover, tabling the removal of some small dams in the Tar Drainage may be a prudent action capable of protecting sensitive taxa, at least in the sh ort-term. Introduction Pylodictis olivaris (Rafinesque) (Flathead Catfish) are native to Gulf of Mexico drainages extending from the Mobile Drainage west to the Rio Grande Drainage. Flathead Catfish are omnivorous with a strongly piscivorous diet (Minckley and Deacon 1959, Pine et al. 2005). This large-bodied (>1.5 m TL) catfish has been widely introduced in the middle and southeastern Atlantic slope drainages (Jackson 1999). Flathead Catfish now occur from the St. Johns River system in Florida north to the Delaware River in New Jersey and Pennsylvania (Brown et al. 2005, Fuller and Neilson 2013). Flathead Catfish introductions coincided with severe and sometimes precipitous native fish declines in several drainages. Thomas (1995) documented a swift 1Appalachian State University, Biology Department, 572 Rivers Street, Boone, NC 28608- 2028. 2University of Tennessee, Forestry Wildlife and Fisheries Department, 274 Ellington Plant Sciences Building, 2431 Joe Johnson Drive, Knoxville, TN 37996-4800. 3Florida Fish and Wildlife Conservation Commission, 7386 NW 71st St. Gainesville, FL, 32653. 4North Carolina Wildlife Resources Commission, Raleigh, NC 27606. *Corresponding author - Manuscript Editor: Nathan Franssen Southeastern Naturalist D.J. Walker, J. Holcomb, R.Nichols, and M.M. Gangloff 2015 Vol. 14, No. 1 10 decline in Lepomis auritus (L.) (Redbreast Sunfish) and Ameiurus spp. (Bullhead Catfish) catch rates in both creel and electrofishing surveys with a simultaneous sharp increase in catch rates of introduced Flathead Catfish in the Altamaha River, GA. Flathead Catfish can affect native fish assemblages through predation and indirectly by competition for other resources (e.g., food, spawning habitat, cover; Baumann and Kwak 2011). These findings raised concerns among fisheries managers and researchers over the impact of introduced Flathead Catfish populations on native fish assemblages (Bringolf et al. 2005). The first documented introduction of Flathead Catfish on the Atlantic slope of North Carolina occurred in 1966, when the North Carolina Wildlife Resources Commission (NCWRC) released 11 mature individuals into the Cape Fear River, subsequently establishing a viable population of Flathead Catfish (Guier et al. 1984). In North Carolina, introduced populations of Flathead Catfish are established in Coastal Plain and Piedmont reaches of the Neuse, Cape Fear, Tar, Pee Dee, and Catawba rivers (Fuller and Neilson 2013, Kwak et al. 2006). Recent research on the Cape Fear population of Flathead Catfish assessed diet, prey selectivity, feeding chronology, and hypothesized possible impacts of Flathead Catfishes on the native fish community (Baumann and Kwak 2011, Pine et al. 2005). Those studies determined that the Flathead Catfishes of the Cape Fear River were opportunistic generalists, and that an ontogenetic dietary shift occurred at 300 mm TL, whereby larger individuals fed significantly more on larger prey, especially clupeids and centrarchids. Additionally, Flathead Catfish did not prey on imperiled species found in the Cape Fear River (Baumann and Kwak 2011). Although these studies did not show a correlation between increasing Flathead Catfish numbers and declining native fish populations, stomach-content analysis and diet-selectivity calculations suggested potential impacts on native fishes, especially sunfishe s. The Tar River Drainage is the northernmost watershed occurring entirely within North Carolina (Fig. 1; Philips 1989). The Tar River drainage supports populations of rare and imperiled aquatic species recognized at both the state and federal level including Noturus furiosus (Jordan and Meek) (Carolina Madtom), Ambloplites cavifrons (Cope) (Roanoke Bass), Elliptio steinstansana (Johnson and Clarke) (Tar Spinymussel), Alasmidonta heterodon (Lea) (Dwarf Wedgemussel), and Orconectes carolinensis (Cooper and Cooper) (North Carolina Spiny Crayfish) , as well as numerous endemic species (Clamp 1999, USFWS 2012). Additionally, the Tar River supports a population of anadromous Alosa sapidissima (Wilson) (American Shad) and other important food and game fishes that may be negatively affected by Flathead Catfish (Layher and Boles 1980, Menhinick 1991) . Specific dates of introduction of Flathead Catfish into the Tar River are not clear, although it was known to be introduced in the Roanoke-Chowan drainage by the 1980s (Hocutt and Wiley 1986). The establishment of Flathead Catfish in the Tar River is suspected to have occurred in the 1990s (Homan 2010). However, no prior studies have assessed ecological effects of Flathead Catfish in the Tar River drainage. The North Carolina Wildlife Resources Commission began conducting catfish-specific surveys of the lower Tar River in 2006, and documented increasing Southeastern Naturalist 11 D.J. Walker, J. Holcomb, R.Nichols, and M.M. Gangloff 2015 Vol. 14, No. 1 Flathead Catfish catch rates and simultaneous decreases of Ameiurus catus (L.) (White Catfish) catch rates (NCWRC 2009). Between 2006 and 2008, the relative abundance of Flathead Catfish increased from 14% to 56% of all catfish captured in the Tar River, whereas White Catfish abundance dropped from 53% to 32% of the catfish sampled in the Tar River during the same time period. Additionally, the largest Flathead Catfish reported by the NCWRC from the Tar River weighed ~23 kg at age 9 y. The objectives of our study were to (1) document locations where Flathead Catfish were collected in the Tar River Drainage, (2) investigate age and growth relationships, and (3) determine diet and describe feeding habits to assess potential Flathead Catfish impacts on Tar River ecosystems. These data will establish baseline presence and population growth-rate parameters as well as provide a means for assessing the condition factor and nutritive status of Flathead Catfish in the Tar River. Furthermore, quantifying the condition factor of Flathead Catfish will allow us to make inferences about the effects of potential resource scarcity on these fish. Materials and Methods Presence surveys The occurrence of Flathead Catfishes in the upper Tar River was documented as part of an ongoing study of the impacts of small dams on North Carolina fish assemblages (Fig. 1). We conducted surveys in 27 wadeable reaches of the Tar River, Sandy Creek, and Fishing Creek using a Smith-Root 12B backpack electroshocker (Smith-Root Inc., Vancouver, WA). In sections of reaches too deep to use the backpack electroshocker, we surveyed with 3.7-m-wide by 1.8-m-deep seines with 4.8-mm2 mesh. Each reach was approximately 150 m in length. Three replicates of four mesohabitats (run, riffle, pool, and bank) were sampled for approximately 100 s each (at least 1200 s/reach). If a new species was detected on the last replicate Figure 1. Map of Tar River watershed study sites in North Carolina showing the locations of dietary study site (square), fish community survey site locations (open circles), sites where Flathead Catfish were detected (filled circles), and dams (crosse s). Southeastern Naturalist D.J. Walker, J. Holcomb, R.Nichols, and M.M. Gangloff 2015 Vol. 14, No. 1 12 of a given mesohabitat, that mesohabitat was sampled for an additional 50 s or until no new species were detected. In addition to electro-fishing, one sampling period (3 nights) was conducted at the NC Highway 42 crossing of the Tar River using conventional (hook-and-line) and set-line angling. Stomach-content analysis We collected Flathead Catfish from the lower Tar River in Greenville, Pitt County, NC, between August and October 2010 (Fig. 1) using a Smith-Root 7.5 GPP boat-mounted electrofisher emitting low-frequency, pulsed DC (15 pulse, 240–340 volts, 1–1.5 amps). We captured 20 individuals during two morning sampling efforts specifically targeting Flathead Catfish that covered approximately 2 river km, whereas the remainder of specimens were collected opportunistically during NCWRC sampling efforts in autumn 2010 (ntotal = 71). All fish sampled were euthanized with a lethal (>500 ppm) dosage of tricainemesylate (MS-222). We stored all fish collected after 25 August 2010 in freezers prior to processing. We assigned fish-identification numbers and recorded their mass (g) and total length (TL in mm). Body condition, a relative measure of the physical fitness of members of a population, was calculated by log-transforming and plotting weight-at-length data using Studentized residual scores as an index of body condition (Jako b et al. 1996). Methods for stomach-content analysis were adapted from Hyslop (1980). In the field, we made a ventral incision in each fish from the vent to the breast and attached cable ties around the base of the esophagus and beginning of the intestinal tract to contain the contents of the stomach, which was then excised from the rest of the digestive tract. Stomachs were then placed in labeled Whirl-Paks (Nasco Inc., Fort Atkinson, WI) and preserved in 10% formalin for transport back to the lab. We injected the largest stomachs with formalin to ensure preservation. In the lab, stomachs were soaked in water to remove excess formalin, and then patted dry before being weighed whole. We opened stomachs with an incision along the longest axis of the organ and collected and weighed separately any contents. Stomach fullness (Ft), an indicator of feeding intensity, was calculated as a percentage of total mass using the equation put forth by Hyslop (1980) : Ft = [(Wt. (wet) of stomach contents)/(Wt. (wet) of fish)] * 100 We then identified stomach contents to the lowest feasible taxon. We were unable to conclusively identify much of the gut-content material because of delays between collection and processing as well as damage to the contents due to the strong pharyngeal jaws of Flathead Catfish. Bones, scales, and exoskeletons were grouped together as unidentifiable fish or invertebrate parts, respectively. Plant and inorganic materials were classified as detritus. Otolith analysis Otolith analysis has been verified as an accurate means of estimating the age of Flathead Catfish (Nash and Irwin 1999). We removed lapilli otoliths in the field via a dorsal incision through the supraoccipital bone (Long and Stewart 2010). When possible, both lapilli otoliths were removed so that we could read them Southeastern Naturalist 13 D.J. Walker, J. Holcomb, R.Nichols, and M.M. Gangloff 2015 Vol. 14, No. 1 independently to increase the accuracy of age estimations. We then packaged otoliths in labeled vials for transport back to the lab. In the lab, otoliths were prepared for reading following Buckmeier et al. (2002). We processed otoliths individually and independently of fish-size data. First, otoliths were soaked in 95% ethanol to withdraw moisture and aid in removal of any remaining tissue. We then placed dried otoliths directly on a hotplate at 300 °C until they changed to a golden brown color (typically ≤5 min). Preparing otoliths in this manner increased annuli visibility and contrast to the bone matrix. Annuli are formed each spring, so the number of annuli corresponds to the age of the fish in years (Buckmeier et al. 2002). We mounted otoliths to individual microscope slides using Crystalbond 509 thermoplastic adhesive (Crystalbond; Buehler, Lake Bluff, IL) perpendicular to the slide, and with the posterior end of the otolith in contact with the glass. After the adhesive had set, otoliths were sectioned by grinding the anterior end down with a table-mounted power sander, and then wet-polished by hand under a dissecting microscope with 600-grit sandpaper until the annuli could be seen radiating from the nucleus of the otolith. Two independent readers counted annuli outward from the nucleus. Any differences in observed age were resolved by re-examining the otol iths together. Statistical analysis Lengths of the Flathead Catfish (mm TL) were plotted against their masses (g) after we linearized the data using a LOG10 transformation. We fit a linear regression to the data and used Studentized residual scores as an index of body condition (Jakob et al. 1996, Sutton et al. 2000). The residual scores provide a relative measure of body condition for each individual, and standardizing the residuals by dividing each by its error allows for direct comparison of body condition across size classes. To identify outliers, we established a threshold of ±2.5 Studentized residual score. We assessed growth rates by plotting the length of each fish against its age determined through otolith analysis and then produced a von Bertalanffy growth curve using Fisheries Analysis and Management Software (FAMS v. 1.0; American Fisheries Society, Bethesda, MD). To assess ontogenetic diet shifts, we created a matrix comprised of the presence–absence data of the diet contents and stomach fullness of the Flathead Catfish collected with stomach contents (n = 36). Canonical correspondence analysis (CCA; PC-ORD v. 4, MjM Software, Gleneden Beach, OR) was conducted to identify relationships among total length, stomach fullness, and the presence of stomach contents identified from Flathead Catfish. Stomach fullness characterized the horizontal axis, and total length characterized the vertical axis. We further investigated ontogenetic diet shift by comparing total length of Flathead Catfish individuals to their stomach fullness. These analyses were used to establish a length threshold delineating a potential ontogenetic diet shift. Results Presence surveys Flathead Catfish were found at 4 of 27 sites in the upper and mid-reaches of the mainstem Tar River and its tributaries (Fig. 1). We found Flathead Catfish in the Tar Southeastern Naturalist D.J. Walker, J. Holcomb, R.Nichols, and M.M. Gangloff 2015 Vol. 14, No. 1 14 River several km upstream of the partially breached Webb’s Mill Dam near Spring Hope, NC. These records are the first Flathead Catfish detected upstream of that dam. Flathead Catfish were not detected in the Tar River upstream of Louisburg, where a small dam may be serving as a barrier, or in Fishing Creek upstream of Bellamy’s Mill Dam (Fig. 1). Growth analysis Linear regression of LOG10(mass) by LOG10(TL) revealed a strongly linear relationship between mass and length (R2 = 0.99, df = 1, F = 11945.1, P < 0.001; Fig. 2). The Studentized residual scores calculated from this regression (mean= 0.004, SD = 1.0171) indicated only 2 fish with outlying body condition. Both fish had greater than expected body condition (Studentized residual= 2.759 and 3.001, respectively). Flathead Catfish ages ranged from less than 1 to 8 years old. The mean age was 3.15 y, the approximate age of sexual maturity in Flathead Catfish (Minckley and Deacon 1959). The mean TL (mm) calculated for each age class (n = 54; Fig. 3) was entered into the FAMS von Bertalanffy growth-function solver. An optimal solution was found after 20 iterations: R2 = 0.91, P = 0.0003, Linf = 3561.95, K = 0, t0 = -1.124. Stomach-content analysis The majority of stomach contents analyzed were categorized as fish or fish remnants, and these items comprised >60% of stomach contents (Table 1). The CCA results demonstrated a trend toward greater piscivory in larger fish, as the smaller Flathead Catfish (less than 500 mm TL) were associated with Cyprinid and unidentifiable invertebrate prey items (Fig. 4A). Flathead Catfish ≥500 mm TL exhibited a shift towards fuller stomachs and were associated with centrarchid and ictalurid prey types (Fig. 4B). Centrarchids were the most frequently identified fish, which adult (≥500 mm TL) Flathead Catfish appeared to consume at an elevated rate compared Figure 2. Relationship between LOG10- transformed Flathead Catfish length and weight in the Tar River. Southeastern Naturalist 15 D.J. Walker, J. Holcomb, R.Nichols, and M.M. Gangloff 2015 Vol. 14, No. 1 to sub-adults. Additionally, adult Flathead Catfish consumed more ictalurid catfish than sub-adults. Other items detected in Flathead Catfish stomachs include crayfishes (Cambaridae), bivalves (Corbicula fluminea (O.F. Müller) [Asian Clam]), and both organic and inorganic detritus (i.e., bark, leaves, and gravel). Stomach fullness ranged from 0 to 6.2% of body mass. Mean stomach fullness (for fishes with prey in their stomachs) was 0.9%. Discussion Flathead Catfish populations are robust in the lower Tar River downstream of Webb’s Mill Dam near Spring Hope, NC. Multiple size classes (including 2 individuals weighing 15.7 and 16.5 kg, respectively) were found approximately 600 m Figure 3. Mean length-atage for Flathead Catfish in the lower Tar River, NC. Error bars display ± 1 SE. Solved Von Bertalanffy growth function: Lt = 3561.952(1-e-0.036(t- (-1.124)). Figure 4 (following page). (A). Canonical correspondence analysis of total length, stomach fullness (Ft), and stomach contents. Centrarchid and ictalurid prey items correspond with greater stomach fullness, and a shift from Cyprinid and invertebrate prey items to larger prey types appears to occur at 500 mm TL (median TL = 476 mm). (B). Stomach fullness of Flathead Catfish at total length. Table 1. The percent occurrence of prey items identified from the stomach s of Flathead Catfish. % occurrence Prey Catfish less than 500 mm TL Catfisth ≥500 mm TL Total Centrarchidae 4.76 19.36 13.46 Ictaluridae 0.00 9.68 5.77 Cyprinidae 9.52 0.00 3.85 Cambaridae 4.76 6.45 5.77 Corbiculidae 4.76 3.23 3.85 Identified fish 14.29 16.13 15.39 Unidentified fish 42.86 38.71 40.39 Unidentified invertebrate 14.29 3.23 7.69 Detritus 19.05 19.36 19.23 Southeastern Naturalist D.J. Walker, J. Holcomb, R.Nichols, and M.M. Gangloff 2015 Vol. 14, No. 1 16 Southeastern Naturalist 17 D.J. Walker, J. Holcomb, R.Nichols, and M.M. Gangloff 2015 Vol. 14, No. 1 downstream of the Spring Hope dam. It is likely Flathead Catfish occur throughout the Lower Tar River and its major tributaries from Webb’s Mill Dam downstream to the Albemarle Sound Estuary. Because of the large unsampled reach between our study sites upstream of Webb’s Mill Dam, it is difficult to speculate how far upstream Flathead Catfish have extended their range in the Tar River. It is likely that a lowhead dam just upstream of Louisburg, NC, is the upstream-most barrier to Flathead Catfish range expansion in the Tar River. However, we have not sampled the Tar River near the Louisburg Dam, so the upstream distribution of Flathead Catfish in the Tar remains unresolved. Surveys also failed to detect Flathead Catfish at 7 sites upstream and 2 sites downstream of Bellamy’s Mill Dam in Fishing Creek. Bellamy’s Mill Dam, completed ca. 1859, is the first major barrier in the Fishing Creek sub-drainage. Because the confluence of Fishing Creek and the Tar River is downstream of Rocky Mount Mill Pond (the first major barrier to possible Flathead Catfish upstream distribution on the Tar River) and Flathead Catfish were detected well downstream of this structure, it seems likely that they also occur in lower Fishing Creek. However, we only sampled 2 sites downstream from Bellamy’s Mill in Fishing Creek. We did not detect Flathead Catfish at 3 sites in Sandy Creek including 2 sites downstream from Laurel Mill Dam, the first anthropogenic barrier in the Swift Creek sub-drainage. The prevalence of beaver dams in Sandy and Swift creeks, combined with a lack of habitat and forage, may limit Flathead Catfish distribution in this lower Tar River sub-drainage. The results of the diet and population analyses are consistent with those of other studies of invasive Flathead Catfish populations in Atlantic Slope drainages. Flathead Catfish in the Tar River are strongly piscivorous but also consume a diverse range of prey items, as was found in previous studies of other populations (Baumann and Kwak 2011, Minckley and Deacon 1959, Pine et al. 2005). The trend in our analysis of the stomach contents indicates that large, older fish were more likely to have consumed centrarchids. Larger fish also consumed ictalurids (most probably Ictalurus punctatus (Rafinesque) [Channel Catfish] and Ameirus spp. [bullhead catfish]) at elevated rates, again consistent with an ontogenetic diet shift found in previous studies of other populations, though the results of our CCA suggest that the ontogenetic shift occurs around 500 mm TL in the Tar River population and not 300 mm TL as reported from the Cape Fear River population of Flathead Catfish (Baumann and Kwak 2011). This finding may have important trophic and economic consequences for Tar River ecosystems and fisheries because both centrarchids and ictalurids are important mesopredators and game fishes as well as endangered freshwater-mussel hosts in most Atlantic Slope lotic ecosystems (Michaletz and Dillard 1999). Cape Fear River Flathead Catfish were strongly piscivorous, but prey selection was generally random and did not target naive (i.e., not co-evolved) fishes (Pine et al. 2005). Although few studies have shown a demonstrable downward trend in mesopredatory and game fishes in systems recently invaded by Flathead Catfish, Thomas (1995) documented population shifts within Altamaha River, GA, native mesopredatory guilds coincident with Southeastern Naturalist D.J. Walker, J. Holcomb, R.Nichols, and M.M. Gangloff 2015 Vol. 14, No. 1 18 the establishment of Flathead Catfish. A similar decline in native mesopredator catch was also documented in earlier catfish surveys of the Tar River (NCWRC 2009). Dietary trends may reflect ontogenetic diet shifts linked to a gape threshold, above which it is easier for adult Flathead Catfish to consume larger and betterdefended prey. This prey base of larger fish, in turn, may eventually allow more rapid increases in weight with age and lead to growth estimates similar to other studies conducted on older Flathead Catfish populations (Jackson 1999, Minckley and Deacon 1959). Alternately, the stomach-fullness data could be driven by gastric evacuation rates or feeding chronology of the Flathead Catfish i n the Tar River. Our data also indicate Tar River Flathead Catfish were younger (max age 8 y) on average compared to other North Carolina Atlantic Slope populations (e.g., maximum age in Neuse River = 14 y, in Cape Fear River = 17 y, and in Lumber River = 12 y; Kwak et al. 2006) as well as other southeastern coastal plain rivers (e.g., maximum age in Satilla River = 10 y and in Ocmulgee River = 16 y; Sakaris et al. 2006), suggesting that this is a relatively young population. However, the NCWRC (2009) study of Flathead Catfish in the Lower Tar River from 2006–2008 documented a 9-year-old Flathead Catfish. While that fish was older than the fish encountered in this study, it is still younger than the published maximum ages of Flathead Catfish in other drainages. Both studies of ages of Flathead Catfish in the Tar River relied on boat electrofishing, so the discrepancies in maximum age encountered may be attributable to differences in sampling effort. In this study, 51 of the 71 Flathead Catfish were collected as by-catch during fall sampling for other species, whereas the 9-year-old Flathead Catfish was collected during a multi-year catfish-specific sampling effort. During the two morning sampling efforts of boat electrofishing specifically targeting Flathead Catfish conducted during the collection period of this study, we made anecdotal observations of the effectiveness of electrofishing on Flathead Catfish. It appeared that the larger, and presumably older, fish were less responsive to the electricity and may be underrepresented in electrofishing surveys. Sakaris et al. (2006) found that introduced populations of Flathead Catfish in Georgia grew at substantially increased rates relative to native populations. If the Tar River Flathead Catfish populations are relatively young, as both the NCWRC age report and our age data suggest, the effects they exert on the native fish communities (and on the Tar River ecosystem in general) could increase over time if the population grows in age, size classes, and number of fish. As more Flathead Catfish in the Tar River population mature and surpass our observed 500-mm-TL ontogenetic length threshold, reductions in the prey base of large fish (Ictaluridae and Centrarchidae) may become more apparent. Concurrently, increases in the number of juvenile Flathead Catfish (less than 500 mm) may significantly impair benthic communities and lower trophic levels (benthic macroinverterbrates, Cambaridae). Our residual score data did not identify any fish with significantly lowered body condition. Across life-history stages, Flathead Catfish in the lower Tar River generally exhibit average or improved body condition. This finding may indicate Southeastern Naturalist 19 D.J. Walker, J. Holcomb, R.Nichols, and M.M. Gangloff 2015 Vol. 14, No. 1 that both juvenile and adult Flathead Catfish in the lower Tar River are not currently over-exploiting their prey base, or that current prey-consumption rates of Flathead Catfish have not depleted the prey base. The lower Tar River in the study reach had abundant habitat for all flathead life-history stages (i.e., vegetated shallows for juveniles and sub-adults, and structure near deeper water for larger adults; Minckley and Deacon 1959). If over-exploitation were occurring, we would expect to see decreased condition-index scores at some life-history stage. Moreover, Flathead Catfish growth rates in the lower Tar River population are somewhat higher than those reported from other Atlantic Slope drainages (Kwak et al. 2006, Sakaris et al. 2006). Our study is the first to examine life-history attributes of Flathead Catfishes in the Tar River. We found that Tar River Flathead Catfish consume a range of prey items including fishes, mollusks, and crayfish, consistent with other studies of the diet of invasive Flathead Catfish populations. Because there were few changes in condition with age, we believe that the Tar River Flathead Catfish population has not exceeded its carrying capacity, and given the relatively young ages found among sampled individuals, this population appears to be robust. This finding is alarming because Flathead Catfish have already been correlated with a decrease in the native ictalurid catch rate in the Tar River, and appear to have negatively affected centrarchid and ictalurid populations in other systems. Further, imperiled centrarchids and ictalurids in the Tar River basin (Roanoke Bass and Carolina Madtom) may be at increased risk of local extirpations due to Flathead Catfish. Given their broadly generalist feeding tendencies across their life history, Flathead Catfish are not only a potential threat to sensitive lotic taxa, but aquatic communities as a whole in the Tar River and its tributaries. In their analysis of 762 animal extinctions, Clavero and Garcia-Berthou (2005) found that invasive species were the second-leading cause of extinction among North American fishes. The importance of understanding the trophic and management implications of introduced Flathead Catfish in the Tar River drainage and along the Atlantic Slope cannot be overstated. These data are critical to managers tasked with creating effective policies to protect native species and ecosystems from large, invasive game fishes. The popularity of Flathead Catfish as a food fish further complicates the issue. In public meetings, citizens have demanded that the state of North Carolina introduce Flathead Catfish to other drainages, threatening to do so themselves if the state agencies refuse (B. Tracy, NC Department of Environment and Natural Resources Division of Water Quality, Raleigh, NC, pers. comm.). The tradeoff between managing endemic species and sport fish highlights one of the key difficulties facing aquatic resource conservation in the Tar River and across the globe. Although the majority of scientific evidence suggests that introduced Flathead Catfish may have widespread and potentially dramatic effects on naïve ecosystems, unauthorized introductions by sportsmen appear likely to continue to expand this species’ range. Targeted education and substantial penalties need to be included in management strategies designed to conserve the Tar River Drainage ecosystem and its imperiled species. Southeastern Naturalist D.J. Walker, J. Holcomb, R.Nichols, and M.M. Gangloff 2015 Vol. 14, No. 1 20 Acknowledgments We would like to acknowledge the invaluable technical and logistical assistance from the North Carolina Wildlife Resources Commission. Financial support for this research came from a grant to M.M. Gangloff from the North Carolina Department of Environment and Natural Resources Albemarle-Pamlico National Estuarine Program and a grant to D.J. Walker from the North Carolina Association of Environmental Professionals. Members of the Aquatic Conservation Research Lab at Appalachian State University assisted with fieldwork and provided helpful comments on earlier drafts of this ma nuscript. Literature Cited Baumann, J.R., and T.J. Kwak. 2011. Trophic relations of introduced Flathead Catfish in an Atlantic River. Transactions of the American Fisheries Society 140:1120–1134. Bringolf, R.B., T.J. Kwak, W.G. Cope, and M.S. Larimore. 2005. Salinity tolerance of Flathead Catfish: Implications for dispersal of introduced populations. 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