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7-2017 Trophic Dynamics of Flathead in the Missouri River Bordering Nebraska Dylan R. Turner University of Nebraska-Lincoln, [email protected]

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This Article is brought to you for free and open access by the Natural Resources, School of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Dissertations & Theses in Natural Resources by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. TROPHIC DYNAMICS OF FLATHEAD CATFISH IN THE MISSOURI RIVER BORDERING NEBRASKA

By Dylan R. Turner

A THESIS

Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science

Major: Natural Resource Sciences

Under the Supervision of Professor Mark A. Pegg Lincoln, Nebraska July, 2017

TROPHIC DYNAMICS OF FLATHEAD CATFISH IN THE MISSOURI RIVER BORDERING NEBRASKA

Dylan R. Turner M.S.

University of Nebraska, 2017

Advisor: Mark A. Pegg

Understanding the trophic dynamics of large, riverine ecosystems is complex and requires knowledge from several inputs and outputs of the ecosystem. Most riverine ecosystems have been altered in some way whether through damming, channelizing, or diverting water. The Missouri River is not immune to these anthropogenic alterations.

The river has dams throughout its middle portion and is channelized from Sioux City,

Iowa to its confluence with the Mississippi River. Flathead Catfish pylodictus olivarius are one of the most ecologically harmful introduced species but little research has looked at the influence native populations of Flathead Catfish have on native prey populations where river modification has occurred. I collected Flathead Catfish diet samples and analyzed potential and realized prey caloric content to answer questions on how this abundant, apex predator influences prey populations within their native range. Flathead Catfish had similar diets among three distinct seasons (spring, summer, fall), selected for three species (Common Carp, Flathead Catfish, and Shovelnose

Sturgeon) and two macroinvertebrate taxa (Ephemeroptera and Plecoptera), and consumed prey resources in similar quantities to introduced populations. The caloric values for prey items varied but selected species did not have highest nor lowest values.

Using our diet indices and consumption rates, I estimated that Flathead Catfish

consumed on average 175.3 ± 2.1 kcals (dry weight) per individual per day, equivalent to around 220.9 kg of biomass consumed by the entire sample population daily. This research will help researchers better understand the trophic dynamics within the

Missouri River ecosystem.

i

ACKNOWLEDGMENTS

I would like to first thank my advisor Dr. Mark Pegg for giving me the opportunity to pursue my passion for fisheries. Whether these opportunities were in the classroom or in the field, they provided me with experiences that have been instrumental in shaping my fisheries career. Furthermore I want to thank Dr. Martin Hamel for helping me throughout my graduate career. You were always being there for me when I needed help, no matter how major or minor the situation may have been. I would also like to thank Dr. Kevin Pope, Dr. Rick Holland, and Gerald Mestl for being on my graduate committee; you have all taught me invaluable lessons that I will use throughout my fisheries career. The experience and skills I have gained have helped me grow as a scientist.

I would also like thank my friends and family who have been there for me throughout my graduate career. Many family members were always there for me helping push me to pursue a career that I am passionate about and giving me motivation to further my education. I want to thank you all for helping me achieve my goals. My parents have always supported me throughout my schooling and no matter how many curve balls life throws at us, I will always be grateful for your love and support. Another person I cannot thank enough for her love and support is my wife

Marissa. Marissa has been extremely supportive throughout my graduate journey and has helped me get through the good and tough times. Your humor, passion, and motivation have always pushed me to achieve and greatly appreciate everything you do for me. ii

I also want to thank everyone at the University of Nebraska – Lincoln that has helped me throughout my graduate career. I thoroughly enjoyed my time at the

University and I am grateful for the amount of support I had in the previous years. I want to specifically thank Jon Spurgeon, Caleb Uerling, Stephen Siddons, Kelly Turek,

Nick Hogberg, and Ryan Ruskamp for helping me with all aspects of this project, from analysis to stomach pumping, I would have not been able to make it this far without each and every one of you. To the several technicians that have endured the hot days, stomach pumping, and several monotonous hours spent with the calorimeter, I thank you all.

Finally I want to thank Nebraska Game and Parks Commission through the Sport

Fish Restoration Fund for providing me with funding and helping me with this project. It has been a pleasure working with each and every member that has helped me out throughout my project. I want to specifically thank Kirk Steffesen, Jared Lorensen, Thad

Huenemann, along with many others that have helped me collect fish species needed for analysis as well as sharing data. Everyone from Nebraska Game and Parks

Commission was extremely helpful throughout this process and I am grateful for the collaborations we have.

iii

Table of Contents

TABLE OF CONTENTS ………………………………………………………………………………………..………iv

LIST OF TABLES………..………………………………………………………...... v

LIST OF FIGURES………………………….………………………………………………………….………………...vi

CHAPTER 1: GENERAL INTRODUCTION AND STUDY OBJECTIVES…….....……….……….……1

LITERATURE CITED…………………………………………....……………..………………………………....……7

CHAPTER 2: CONSUMPTIVE DEMANDS FOR FLATHEAD CATFISH IN THE MISSOURI RIVER

BORDERING NEBRASKA………………………………………………………………………………………………...

ABSTRACT………………………………………...………………………..…………………………………..………..12

INTRODUCTION..……………………………………………..…………………………………….……….………...14

METHODS…………………………………………..………………………………………………….……………..…..18

RESULTS…..……………………………..………………………………………………………………….……………..28

DISCUSSION…………………………………………………………..……………………..……………….…….……31

LITERATURE CITED………………………...... ………………………………..……………………….…..……39

CHAPTER 3: CONCLUSIONS AND MANAGEMENT IMPLICATIONS…..………….…………..…..65

LITERATURE CITED………………………………………………………………………………………..………...... 71

iv

List of Tables

Table 2-1. Orders of prey items in Flathead Catfish stomachs from the Missouri River, 2015. Quantity (Qty) is the numbers of stomachs that had the corresponding prey item present. Proportion is the number of stomachs in which the prey item was present divided by the total number of stomachs (n=463)…………………………………………………………………………………………………………48 Table 2-2. Mean caloric values for potential prey items from the Missouri River, 2015. Shovelnose Sturgeon caloric value was taken from Deslauriers et al. (2016)...49

Table 2-3. Mean calories per gram for orders of macroinvertebrates in the diet of flathead Catfish in the Missouri River, 2015. Plecoptera mean calories were obtained by averaging Oberndorfer and Stewart (1977) and Mcdiffet (1970) values…………………………………………………………………………………………………………..50

Table 2-4: Table 2-4: Caloric consumption ± SE by Flathead Catfish for length groups 100-500mm in 25mm increments for the Missouri River 2015. Average calories consumed ± SE are included for all length groups combined. Average weighted fish and invertebrate caloric values ± SE are included for all fish and invertebrate species found within the diet samples.…………………………………………………………51

v

List of Figures

Figure 2-1. Map of study site on the Missouri River, 2015…………………………………………52

Figure 2-2. A conceptual diagram showing the process to determine the total number of calories consumed within the 20-km sampling site…………..…………………………..53

Figure 2-3. Nonmetric multidimensional scaling plots of diet for Flathead Catfish among seasons in the Missouri River, 2015. Top figure shows all stomach samples. Bottom figure is circled area from Top figure…………………………………….………….54

Figure 2-4. Flathead Catfish condition (relative weight) for all length groups and all seasons. Length groups were split into 25-mm groups……………………….…..……55

Figure 2-5. Flathead Catfish length frequency histogram of all length groups collected. Length groups are split into 25-mm groups………………………………………….……….56

Figure 2-6. Mean (± SE) of relative importance for invertebrate and /crayfish prey items found in Flathead Catfish diets in 2015. Calories consumed per grams dry weight for Flathead Catfish for each 25mm Length group.………………………………..…………………………………………………………………...……57

Figure 2-7. Percent empty stomachs of Flathead Catfish by season. Black bar represents percent of stomachs sampled that contained food items. Gray bar represents percent of stomachs sampled that did not contain food items……………..………58 Figure 2-8. Mean Stomach Fullness of Flathead Catfish by season from Missouri River, 2015……………………………………………………………………………………………………………..59

Figure 2-9. Percent of Occurrence for prey items found in the Flathead Catfish Diets in the Missouri River, 2015……………………………………………………………………………….60

Figure 2-10. Figure 2-10: Chesson’s alpha diet selectivity index (dots) for prey items (fish) found within the Flathead Catfish diets in the Missouri River 2015. The line located at 0.1 is the random feeding threshold line where an alpha value over 0.1 indicates positive prey selection. Alpha values below 0.1 represents random feeding. Relative abundance of each prey item (bars) are represented on the right y-axis. Shovelnose Sturgeon were not sampled equally (*)..………………….61 Figure 2-11. Chesson’s alpha diet selectivity index (dots) for prey items (macroinvertebrates) found within the Flathead Catfish diets. The line located at 0.14 is the random feeding line. Species with an alpha value ≥ 0.14 indicates positive prey selection. Alpha values ≤ 0.14 represents random feeding. Relative abundance of each prey item (bars) are represented on the right y- axis…………………………………………………………………………………………………………….….62

vi

Figure 2-12. Diel feeding chronology of Flathead Catfish in the 20-km sampling site in the Missouri River in September 2015 as determined from changes in stomach fullness (mean fullness ± SE). Stomach fullness was determined from a 12-hour sampling period……………………………………………………………………………………..……..63

Figure 2-13. Diel feeding chronology of Flathead Catfish in the 20-km sampling site in the Missouri River in October 2015 as determined from changes in stomach fullness (mean fullness ± SE). Stomach fullness (N = 10) was determined from a 12-hour sampling period……………………………………………………………………………….64

1

CHAPTER 1

GENERAL INTRODUCTION

Trophic dynamics can provide information regarding the complex interactions among species at different trophic levels. These interactions occur across habitat types

(i.e., terrestrial and aquatic) and are complex by nature (Lindeman 1942; Mann 1969).

Researchers have been trying to understand trophic interactions for decades, to better understand ecosystem function. Gaining knowledge of trophic interactions is important because the influence each trophic level has on the other, above or below, determines ecosystem health (Wetzel 1995; Polis et al. 1997), yet understanding these interactions is multifaceted. Anthropogenic influences to aquatic ecosystems have occurred worldwide and add complexity to trophic interactions because most have been altered from their original state. It is vital that researchers better understand how these trophic dynamics within altered ecosystems are affecting the energy flow in the ecosystem

(Power et al. 1996).

Predation is an important driver of community structure in aquatic ecosystems

(Power 1990) and can exert top-down pressure to influence prey abundance (Vanni and

Layne 1997). Through predation, predators provide a means of checks and balances that, if not in place, could change the biological makeup of a system (e.g., altering food- web dynamics). Predation in aquatic ecosystems has been extensively studied, with many studies focusing on predation by introduced species and their effect on native fish communities through predator-prey interactions (Thomas 1993, Kwak et. al. 2006, Fugi 2 et al. 2008). However, there are other factors that can influence predation including habitat alterations. Habitat alteration is thought to influence predator-prey interactions within riverine ecosystems by concentrating or diluting interactions (e.g., occurrence of contact between species; Ryer 1988). For example, habitat alteration may benefit certain predator species leading to an increase in their abundance. Such shifts in abundance may influence trophic interactions throughout the food web.

Rivers worldwide have been altered to meet a suite of human needs often resulting in shifts in community structure of in these systems (Nilsson et al. 2005;

Poff et al. 1997). These shifts in community structure may alter the energy base and how energy is transferred between trophic levels (Nilsson and berggren 2000), whether from temperature changes resulting from hypolimnetic releases from a dam, a warm- water reservoir where a cool-water stream previously existed, or a number of other changes (Mims and Olden 2013). For instance, introduction of non-native fishes has negatively influenced native fish assemblages through resource competition and predation (Ogutu-Ohwayo 1990; Crowl et al. 1992; Brown et al. 2005; Albins and Hixon

2008; Sharpe et al. 2017). Other possible outcomes include an increase in competition for food resources and encroachment of predators that can exert stress on the existing food web (Garvey et al. 1994; Spurgeon et al. 2014).

The Missouri River is one such altered river system. The Missouri River originates at the confluence of the Jefferson and Madison Rivers in Montana, and flows 3,734 km to its confluence with the Mississippi River near Saint Louis, Missouri. From 1927 to 3

1969, the United States Army Corps of Engineers modified the Missouri River from Sioux

City, Iowa to Kansas City, Missouri from a slow, meandering, silt-laden river with islands, sandbars, and side channels into a fast, deep, and less turbid main channel (Schneiders

1996). The river was also straightened, thus shortening the river by about 200 km. The channelization of the Missouri River also changed the available habitat and largely eliminated access to the historical floodplain (Morris et al. 1968; Whitely and Campbell

1974). The narrowed banks, deeper channel, and increased flow created a much different environment than that in which native fish had evolved. Additionally, the introduction of several non-native fishes such as Common Carp Cyprinus carpio, Grass

Carp Ctenopharyngodon idella, Bighead carp Hypophthalmichthys nobilis, and Silver

Carp Hypophthalmichthys molitrix, have likely increased competition for certain resources within the river and has further stressed native fish communities (Koehn

2004).

Alteration of river systems has led to declines of native fishes (Vitousek et al.

1997; Yoon et al. 2016; Steffensen et al. 2014), but some native species may be able to take advantage of the change in habitat availability to increase their abundance or expand their range. If the species that benefits most from such alterations is an apex predator, top-down pressure may be exerted on the ecosystem leading to increased consumption of native prey species and ultimately changing the energy demands within the system. The Missouri River is home to many predatory species such as the Pallid

Sturgeon Scaphirhynchus albus, Channel Catfish Ictalurus Punctatus, Blue Catfish

Ictalurus furcatus, and Flathead Catfish Pylodictis olivaris. Flathead Catfish are often 4 considered an apex predator where they exist (Pine III et al. 2005). Channelization, revetment, and use of wing dams within the Missouri River has likely created additional habitat suitable for juvenile and adult Flathead Catfish (Sandheinrich and Atchison

1986), yet little is known about how Flathead Catfish influence prey throughout the river. Few studies have investigated pressures exerted by Flathead Catfish on the overall fish community through predation within their native range, and even fewer have studied predation by Flathead Catfish within large, altered rivers like the Missouri River

(Hogberg 2014).

Flathead Catfish are native to much of central North America, stretching from the Rio Grande River to the lower Great Lakes Region, including the Mississippi River and Missouri River drainages (Jackson 1999). Flathead Catfish have also been introduced throughout much of the United States of America. Flathead Catfish are known to exhibit fast growth rates and adults can reach large sizes with individuals reported > 900 mm total length (TL) attaining weights > 45 kg (Jenkins and Burkhead

1994; Jackson 1999). Their aggressive behavior and ability to consume large prey items has attributed to the decline of prey species when Flathead Catfish are introduced

(Guier et al. 1984; Brown 2005; Pine et al. 2005). Presumably, when Flathead Catfish remain the most abundant apex predator, there is an increased threat to other species via predation. Within the Missouri River, extensive habitat alteration has led to a presumed increase in abundance of Flathead Catfish compared to pre-alteration conditions, particularly within the channelized segments of the Missouri River (UNL unpublished data). This potential increase in relative abundance indicates that Flathead 5

Catfish are thriving in the channelized habitat of the Missouri River, likely due to the presence of channel-forming structures (wing dikes and rock revetment) which are preferred habitats in most populations. If the relative abundance of Flathead Catfish continues to remain at their current levels throughout the Missouri River bordering

Nebraska, prey and other sport fishes will continue to be subjected to a gauntlet of predation that could be influencing population and community level dynamics. For example, Flathead Catfish have been observed consuming Pallid Sturgeon

Scaphirhynchus albus, a federally listed endangered species, in the Missouri River bordering Nebraska (Steffensen et al. 2015). Therefore, it is important to gain a better understanding of the available energy in prey items, as well as what current energetic consumption and relative influence Flathead Catfish may have on sport and prey fishes at their current abundances.

Objectives

The goal of my research is to determine the energetic consumption by Flathead

Catfish within the Missouri River. Understanding the energetic consumption for

Flathead Catfish will help fisheries managers better understand how they are influencing other native predator and prey populations within the Missouri River. For example, the greater abundance of Flathead Catfish compared to other predators in the

Missouri River could be detrimental to prey species and increase competition for limited calorically dense food items. Such a finding could lead to future management decisions that increase Flathead Catfish harvest. 6

To better understand the energetic consumption of Flathead Catfish, my specific objectives for this project were to 1) determine diet composition of Flathead Catfish, 2) determine diet selectivity and mean stomach fullness of Flathead Catfish by season, 3) quantify energetic input from several potential and realized prey fishes within the

Missouri River, and 4) determine Flathead Catfish caloric demands by calculating daily ration and prey caloric values (Figure 2-1; Table 4). These objectives will help give resource managers a better understanding of what role Flathead Catfish play in the

Missouri River and the potential influence they can have on other fish species within the

Missouri River.

7

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gracilis), Plains (Hybognathus placitus), Western Silvery Minnow (H.

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12

CHAPTER 2

DIET ANALYSIS AND CONSUMPTIVE DEMAND FOR FLATHEAD CATFISH IN THE LOWER

CHANNELIZED MISSOURI RIVER

Abstract

Most riverine ecosystems have been altered in some way, whether that is through damming, channelizing, or diverting water. Studies on trophic dynamics within altered aquatic ecosystems have mainly focused on negative trophic cascades in response to physical changes to the system and introduction of non-native species.

However, little is known about how a native apex predator may exert top-down pressure on a community when it has flourished under altered riverine conditions.

Flathead Catfish are the native apex predator within the Missouri River ecosystem and to better understand the influence Flathead Catfish have on energetic demand of lower trophic levels, I wanted to determine diet composition and similarity among seasons, stomach fullness through seasons, diet selectivity of Flathead Catfish, the caloric values of potential and realized prey items, and the daily consumption of prey items. A total of

784 Flathead Catfish were sampled, of which 463 fish had food items present. A total of

25 orders of vertebrate and invertebrate prey items were identified. Flathead Catfish had similar diet items within their diets through all three seasons (Global R=0.03) and mean stomach fullness was not different among seasons (p-value=0.2544). The diet selectivity index showed that Flathead Catfish were actively selecting three fish species including: Common Carp, Flathead Catfish, and Shovelnose Sturgeon and two 13 macroinvertebrate species including: Ephemeroptera and Plecoptera. Flathead Catfish had a 24 hr daily ration of 7.34 percent body weight per day. Furthermore, average calories consumed for an individual Flathead Catfish was about 175 ± 2.1 kcals (dry weight) per day. The estimation of total calories consumed by an individual and a sample population will begin to help fisheries managers better understand the influence

Flathead Catfish have on lower trophic levels.

14

Introduction

Many non-native predators have been introduced throughout North America by intentional or unintentional releases. Where predator introductions have occurred, the invasion has usually gone unchecked and has altered the trophic dynamics of the ecosystem through competition with native predators and increased predation on native prey species (Byers 2002; Ruzycki et al. 2003; Whitfield et al. 2002; Sih et al.

2010). The ability of a non-native species to alter trophic dynamics within the ecosystem can reduce native predator and prey populations to a point of eradication (Vitousek et al. 1997). One of the most ecologically harmful aquatic species when introduced outside of its native range is the Flathead Catfish Pylodictus olivaris (Fuller et al. 1999).

Flathead Catfish are known to be apex predators in both native and non-native populations, having the ability to grow to large sizes, often have obligate piscivorous feeding strategies, and have a large gape (Jenkins and Burkhead 1994; Jackson 1999).

These attributes allow Flathead Catfish to consume a wide variety of food resources

(Jenkins and Burkhead 1994; Jackson 1999). Flathead Catfish are most frequently found near stones, rip-rap, riffles, and submerged vegetation (Daughtry and Sutton 2005).

Due to their consumptive abilities and variety of preferred habitat, there have been several studies that have documented invasions of Flathead Catfish and their influence on native fish populations (Guier et al. 1984; Brown et al. 2005). Fewer studies have evaluated Flathead Catfish predation on fish communities within their native range and even fewer studies have looked at the impacts Flathead Catfish have in modified habitats within their native range. 15

Habitat alterations in both lentic and lotic freshwater ecosystems have played a major role in the change of natural trophic dynamics (Power et al. 1996; Pringle et al.

2000). For example, habitat modification can increase or decrease suitable habitat for native fishes. Many studies have shown the decline of native species because of habitat alterations including channelizing, damming, and reducing floodplain access (Pringle et al. 2000). Other native species have shown the ability to adapt to these new habitats and flourish in these environments. New habitat formed from anthropogenic alterations may allow some predators to expand their historic range, potentially increase their abundances as well. Flathead Catfish are one such species within the

Missouri River that may have increased in abundance following substantial river modification. These predators may have the ability to capitalize on alterations and exploit organisms that reside within these ecosystems (Franssen 2011).

One of the most highly altered river systems in the United States of America is the Missouri River (Morris et al. 1968; Schneiders 1996). The downstream most 1200 km have been channelized through the construction of armored banks and armored wing dykes that have created much different habitat from historical conditions (e.g., increased water velocity and consistent discharge; Schneiders 1996; Pegg et al. 2003).

Much of the channel has been narrowed and access to the floodplain is limited to only extreme, high-flow events (Morris et al. 1968; Whitely and Campbell 1974). This limited access to the floodplain has likely caused a shift in how energy moved through the food web within the Missouri River. Ultimately, the resulting change in habitat, among other stressors, has led to declines of several native species, including large predators and 16 their predominant prey (e.g., and chubs) that reside in the historic Missouri

River (Steffenson et al. 2014).

Alterations to river ecosystems have changed food and energy pathways from what occured naturally within the environment (Gibson et al. 2005). Alongside river alterations, increased predation can further exert pressure on the food and energy demands within the ecosystem. Flathead Catfish are an apex predator in the Missouri

River and have likely exploited the alterations of the Missouri River. Due to the implementation of wing dams and armored banks to the channelized Missouri River, preferential habitat for Flathead Catfish has likely increased, potentially changing food and energy demands where demand are present. Recent years have pointed to a high population of Flathead Catfish, whereas other native large bodied predators have been declining (e.g., Pallid Sturgeon and Channel Catfish; Steffenson et al. 2014). The high abundance of Flathead Catfish and likely increased food/energy demand can potentially be changing the historic makeup of the Missouri River food web. Changes to the historic food web of the Missouri River can potentially create more issues from pre alterations, such as increased competition for limited food resources, loss of prey items, etc., that can fundamentally change the community dynamics within the Missouri River.

Apex predators are known to consume large numbers of prey items (Feeney et al. 2012) that can affect abundances of prey items available to other native predators within the ecosystem thus influencing trophic dynamics. Understanding the nutritional benefit that prey items contribute to large predators provides a clear perspective on trophic dynamics and energy flow within ecosystems (Cheryl and Ridux 1992). Many 17 food resource studies have estimated energy availability within an ecosystem by looking at caloric values of potential prey items available to predators (Wanless 2005).

Successfully managing a native predator fishery within a highly altered riverine ecosystem is difficult and it would be useful to understand the amount of energy (e.g., food resources) available to the predators along with the prey importance to predators.

One way to determine prey importance is by understanding the caloric benefit to the predator (Polis 1981; Eggelton and Schramm 2004).

Native apex predators within highly altered ecosystems tend to decline when subjected to drastic habitat alterations (Stefferud et al. 2011). However, little research has been conducted to evaluate native predators that have the ability to capitalize on anthropogenic alterations within a riverine ecosystem. Native predators that can adapt to alterations can cause new challenges to fisheries managers because the increase in abundance is not a typical response to aquatic alterations. The adaptation to newly created habitat could have important implications for sportfish management as well as ecosystem function.

I examined what role Flathead Catfish are having towards the energy flow within the Missouri River. Energy flow within the Missouri River has implications to native predator and prey species and their management. This study is assuming the consumption represents energetic need for Flathead Catfish. This assumption is based on the idea that if condition is good and recruitment does not appear to be an issue, than the population is thriving and consuming the resources they need. Identifying the food items these apex predators are consuming and the amount of food resources 18 consumed is important to understand what is available to them in the system as well as what potential impacts they may have on other native fish species. My specific objectives were to 1) determine diet composition of Flathead Catfish, 2) determine diet selectivity and mean stomach fullness of Flathead Catfish by season, 3) quantify energetic input from several potential and realized prey fishes within the Missouri River, and 4) determine Flathead Catfish energetic demand by using daily ration estimates and prey caloric values within a reach of the channelized Missouri River in Nebraska.

Methods

Sampling area

The Missouri River is channelized from Sioux City, Iowa downstream to the confluence of the Mississippi River. The channelized portion of river bordering

Nebraska consists of armored outside banks and armored wing dykes on the inside banks that helps maintain a uniform, deep, fast flowing channel. I sampled a 20-km

(810-830 rkm, Figure 2-1) reach as my specific site because abundances of Flathead

Catfish were greater in that location than other areas of the river.

Fish Collection

Flathead Catfish were sampled using a 15 Hz, 3-4 amp pulsed DC electric field produced by a boat-mounted generator and Smith-Root 5.0 GPP pulsator during May-

October 2015. When applicable, a chase boat was used and positioned approximately

20-m downstream from the electrofishing boat to collect fish drifting downstream.

Electrofishing time varied based on catch, but fish were not held in the live well for 19 more than 30 min to reduce side effects from electrofishing (e.g., regurgitation). I measured Flathead Catfish to the nearest millimeter and weighed to the nearest gram.

Stomach content removal

I removed stomach contents from Flathead Catfish using pulsed gastric lavage methods (Foster 1977; Kamler and Pope 2001). A water pump and hose assembly forced water into the stomach of a Flathead Catfish ≥ 300 mm to induce regurgitation.

The stomach was massaged to help dislodge any food items while pumping water. I held the fish at a 45-degree angle above a 600-µm sieve and an 8-L pail to collect stomach contents during lavage (Foster 1977). A 500-ml wash bottle, rather than water pump, was used to lavage the stomachs from fish ≤ 300 mm to prevent the stomach from rupturing. A clear acrylic tube was placed down the throat to determine if food items were still present. Following the lavage procedure, stomach samples were placed in whirl-packs and preserved with 10% buffered formalin solution for later examination in the laboratory. However, any stomach samples that contained sturgeon species were preserved in ethanol for genetic analysis to document and determine if they were Pallid

Sturgeon.

A dissecting microscope was used to identify prey items from each preserved stomach sample. Macroinvertebrates were enumerated, weighed to the nearest gram, and identified to the lowest taxonomic level. Fish items that I collected in the diets were identified to the lowest taxonomic level possible and measured (mm), weighed 20

(grams), and counted. Prey items that were unidentifiable were classified as unidentified.

I collected five additional Flathead Catfish per 100 mm length group to verify complete removal of stomach contents through the lavage process in the field. The additional Flathead Catfish were processed in the same manner as above, but were then euthanized and entire stomachs removed. The stomachs were then analyzed in the lab to determine if all contents had been removed from the lavage process.

Diet Analysis

I assessed several aspects of Flathead Catfish diets to gain a more complete understanding of how they are interacting with other organisms from a predator-prey perspective. First, I used a multivariate approach to evaluate seasonal diets of Flathead

Catfish. I used a Bray-Curtis similarity matrix following fourth-root transformation of diet count data to perform an analysis of similarity (ANOSIM) to test for diet overlap of

Flathead Catfish among the three seasons. Analysis of similarity tests use randomization techniques to determine the average of all ranked dissimilarities among and within groups (Sampson et al. 2009) and produces a Global R value, where closer to zero represents a more similar diet and closer to one a more dissimilar diet. I used a multidimensional scaling plot to visualize the diets between seasons. All tests were performed in Primer-E version 6 (Clarke and Gorely 2006).

Second, I evaluated aspects of Flathead Catfish diet as it relates to condition, size distribution, proportion of empty stomachs, mean stomach fullness, and diet selectivity. 21

To better assess initial condition, size distribution, and ontogenetic shift in diets

(insectivory to piscivory), I looked at relative weight, length frequency, and an index of relative importance of diet items. Length-frequency histograms were used to better understand what size groups were most abundant in the sample population (Murphy and Willis 1996). Flathead catfish condition was described using a standard weight equation (Anderson 1980; Anderson and Neuman 1996; Bister et al. 2000) to generate relative weights. Relative weights that are near 100 suggest a healthy population. I used a modified index of relative importance to determine the ontogenetic shift in diet of Flathead Catfish. The original IRI is calculated as follows:

퐼푅퐼 = (푁푖) + (푉푖)×푂푖

where Ni is the percent by number of prey item i within a stomach, Vi is the percent by volume of prey item i within a stomach, and Oi is the frequency with which prey item i occurs within a given length group. Here, I substituted percent volume for percent mass because mass was more precise for smaller prey items. Volume and mass are often used interchangeably in diet analyses (Garvey and Chipps 2012). Crayfish were grouped with the vertebrate samples because of the handling process of crayfish and fish are likely similar (Hoyle and Keast 1987).

Percent empty stomach (PES) is a commonly used metric to understand when a fish species has the highest proportion of food items present in their stomachs. Percent empty stomach was calculated for each season as:

NumE PES = x 100, NumT 22 where NumE is the number of catfish with empty stomachs and NumT is the total number of catfish sampled. Empty stomachs were determined by having no prey items present post-gastric lavage.

Mean stomach fullness (MSF) was used to determine the mean proportion of food found within the stomachs for each season. To determine mean stomach fullness I estimated the maximum stomach capacity by each length group using Kamler and Pope

(2001). Mean stomach fullness was calculated as:

1 P Vij MSFi = ∑j=i x 100, p Cj where P is the number of fish with food in their stomach, j is the individual fish, i is the prey type, Vi is the volume (ml), and Cj is stomach capacity of fish j. I used the stomach capacity equation for Flathead Catfish developed by Hogberg and Pegg (2016) and

Gosch et al. (2009) to quantify C as:

퐶 = 7.0 푋 10−7(푇퐿)2.9726 where TL equals total length.

Frequency of occurrence (Oi) is the probability that a specific prey species was present in the stomach, and was calculated for each season. Frequency of occurrence is calculated as follows:

Ji Oi = x 100, P 23

where Ji is the number of stomachs containing prey items, i and P are the total number of fish containing prey items in their stomach. Fish with empty stomachs were not included in this analysis.

Finally, I used Chesson’s (1978) selectivity index (α) to determine if certain prey items were actively chosen or eaten at random. Chesson’s (α) is calculated for individual prey items:

푟 푖⁄ 푝푖 ∝푖= 푟 , ∑푚 푗⁄ 푗=1 푝푗

where ri is the percent of a prey item in the diet, pi is the percent of that prey available in the system, and rj and pj are those values for all prey taxa. The index ranges between

0 and 1, with random feeding occurring at 1/m, where m is the number of prey taxa available in the system. Prey items (α) below the random feeding line show no selection whereas prey items (α) above the random feeding line show positive selection. I determined Pi using abundance data consequently collected by Nebraska Game and

Parks Commission in the same general river reach from June-August 2015. Multiple gear types were used (e.g., mini fyke nets, trammel nets, electrofishing, and otter trawls) to determine fish species populations. Not all gear types sampled each species equally but, we used several gear types to help reduce gear bias. Macroinvertebrate abundance estimates were taken from Hay et al. (2008).

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Caloric analysis

Potential prey items used for caloric content analysis were collected by staff from Nebraska Game and Parks Commission in early August through late September

2015. Fish were kept on ice until returning to the laboratory where the samples were frozen until analyzed. Each Individual fish was measured to the nearest mm and weighed to the nearest hundredth of a gram. I began to estimate caloric density by removing all contents of each fish’s stomach and intestinal tract to remove any food items that may potentially lead to inaccuracies due to diet items being present in the gut. Each fish ≥ 50 g was coarsely cut into manageable pieces, ground using a 1 horsepower commercial electric grinder, then homogenized for 3 minutes using a handheld electric blender in a stainless steel bowl. A 50 g sample was then weighed and placed on an aluminum drying tin to dry for 96 hours in a 60 degree Celsius oven. Fish ≤

50 g were dried whole (without gut contents) for 96 hours in a 60 degree Celsius oven because of the potential loss of material in the wet grinding process. The dried samples were removed and further ground using a fine coffee grinder to a consistent texture.

Dried fish samples were analyzed using a Parr 1241 adibatic oxygen calorimeter

(Eggleton and Schramm 2004). Each fish that had more than 3 g dried mass was divided evenly three ways and had two, 1-g samples run in the calorimeter. If the fish had less than 3 g dried mass an equal amount of sample was divided evenly three ways and two subsamples were processed. The third subsample for fish over and under three grams was only analyzed if the caloric values from the first two samples differed by more than

10%. For example, if a fish dry weight was 1.50 g, then two 0.50 g samples were 25 analyzed in the calorimeter. If the two samples varied by more than 10% of the gross calories per gram then the third sample was run. To address potential error from the ignition fuse and sulfur build up after combustion, caloric values were adjusted based on the fuse and leftover material from the bomb that was titrated to adjust for nitrogen content.

The caloric values generated from the bomb calorimeter were expressed as calories per gram dry weight. A mean was taken for individual fish per species. Each species consisting of several individual means was treated as a block variable and analyzed using an analysis of variance (ANOVA) to test for differences in caloric density among potential prey species. I used Tukey HSD to determine where differences were present among species. Significant differences were declared at an alpha = 0.05.

Macroinvertebrate mean caloric values were taken from literature for total calories consumed (Cummins and Wuycheck 1971; Mcdiffet 1970; Oberndorfer and Stewart

1977).

Consumption

I first estimated consumption rate for an individual Flathead Catfish, then I calculated a population estimate to extrapolate total consumption for the Flathead

Catfish population in my study area. I calculated daily ration to quantify Flathead

Catfish prey consumption using methods described by Elliot and Persons (1978). Daily ration was estimated from the actual amount of food consumed per unit time:

(푆 −푆 푒−푅푡)푅푡 퐶 = 푡 0 , 24 1−푒−푅푡 26

where C24 is the amount of food consumed (% body weight) at a given time (t), t is time,

St is the amount of food present after t, So is the initial food in the fish’s stomach, and R is gastric evacuation rate/hour. Elliot and Perssons’ (1978) model estimates the amount of food consumed over a 24-hour period and is most suitable when each sample period is 3 hours or less; therefore, I ran two 12 hour field experiments using 2 hour (t) time intervals. Flathead Catfish were collected and stomachs were pumped during this time interval. A 12 hour sampling period was chosen because of the unpredictability of the

Missouri River at night and equipment limitations. Baumann and Kwak (2011) found that Flathead Catfish did not display crepuscular and nocturnal feeding so I assumed constant feeding throughout the day, therefore I doubled the 12 hour ration to estimate daily ration. Gastric evacuation rate (R) was calculated using the slope of the relation between stomach fullness and time:

R = Loge S(t+1) – loge S(t) / T,

where S(t) and S(t+1) are the mean stomach fullness at the beginning and end of the time interval (Boisclair and Leggett 1988, Boisclair and Marchand 1993, and Brewster 2007).

Caloric Consumption

To understand how energy flows to an apex predator population within this environment, the caloric need of Flathead Catfish was calculated by using prey items selected and the nutritional value of those prey items consumed by Flathead Catfish.

Conceptually, the diet metrics, along with the caloric metrics calculated herein were used to determine the amount of calories consumed by Flathead Catfish in our sampling 27 site (Figure 2-1). I calculated calories consumed for 25 mm incremental length groups ranging from100-500 mm. I used the average proportions of invertebrate and fish samples found within the diets in conjunction with daily ration estimates to determine amount of food (grams) the average fish within each length group consumed. Once I had the average food consumed (e.g., grams of invertebrates and fish) per length group,

I calculated an average weighted caloric value for fish and macroinvertebrates found within the diet samples. I estimated calories consumed per day for an individual and then scaled up to the sample population within the study area to get an idea of mass consumed.

I estimated abundance of Flathead Catfish in the study reach using Schnabel

(1938). Flathead Catfish greater than 200 mm were tagged from Late May-October

2015. I assumed this was a closed population with no immigration, emigration, recruitment, or mortality given no tagged fish was recaptured outside this reach during the sampling time frame. Abundance (푁̅) was calculated as:

푡 ̅ ∑푖=2 푛푖푀푖 푁 = 푡 , ∑푖=2 푚푖+1,

where t=number of sampling occasions, ni = number of fish caught in the ith sample; mi

= number of fish with marks caught in the ith sample; and Mi = number of marked fish present in the population for ith sample (Schnabel1938; Seber 1982).

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Results

A total of 784 Flathead Catfish were sampled (nspring=262, nsummer=207, nfall=315) for diet analyses, where 463 had food items present in their gut. Flathead Catfish that were brought back to the lab to determine lavage effectiveness had 100% of stomach contents removed during the lavage process. A total of 25 orders of vertebrate and invertebrate prey items were represented in the diet samples (Table 2-1). All but three orders were present every season (e.g., , Arguloida, and Perciformes).

The four most common diet items by mass included, Ictaluridae, Decapoda,

Ephemeroptera, and unidentified fish. The most common orders by count of macroinvertebrates found in the stomachs were Ephemeroptera, Trichoptera, and

Plecoptera. The most common orders of fish found in the stomachs by mass were

Siluriformes, , and Perciformes.

There was no difference in Flathead Catfish diet composition among the three seasons (Global R = 0.03, Figure 2-3). Flathead Catfish condition was variable, but averaged 93 ± 1.3 showing a relatively healthy population (Figure 2-4). The length distribution was skewed to smaller length groups and the average length of all Flathead

Catfish sampled was 299 mm within my sample site (Figure 2-5). The modified index of relative importance showed an ontogenetic shift from insectivory to piscivory for

Flathead Catfish within my study site at a size of 325 mm (Figure 2-6). The percent empty stomach varied among seasons with 26% of stomachs sampled having food absent in the spring, 28% during summer, and 63% in the fall (Figure 2-7). 29

Mean stomach fullness of Flathead Catfish did not differ between length group and season (ANOVA; d.f.=2; F=1.41; P=0.2544; Figure 2-8) and averaged 16% during spring, 17% during summer, and 16% during fall (% total stomach capacity). Over half of the diets contained fish from Ictaluridae (49%) and unidentified fish (40%); whereas,

Ephemeroptera (7%) and Decapoda (5%) made up smaller proportions of the diets in spring. In the summer, basic diet composition contained Ictaluridae (40%), unidentified fish (14%), Decapoda (26%), and Ephemeroptera (20%). The basic diet composition in fall was predominantly fish, including Ictaluridae (34%) and unidentified fish (21%).

Ephemeroptera (3%) and Decapoda (41%) were dominant in the invertebrate portion of the diets.

The greatest frequency of occurrence of macroinvertebrates within Flathead Catfish diets was Isonychidae with a 49% occurrence in the diet samples (Figure 2-9).

Ictaluridae (16%) had the highest occurrence in the diets for fishes. Macroinvetebrates that had the lowest occurrence in diets were: Chloropidae, Corduliidae, and

Lepidostomidae with a 0.22% occurrence in the diet samples. Fishes that had the lowest occurrence in the diet samples included: Acipenseridae (0.22%), Perfciformes

(0.43%), and Poecilidae (0.65%).

Chesson’s α showed a positive selection for three fish species by Flathead Catfish

(Figure 2-10). The random feeding threshold (alpha) for fish was 0.1. The only fish that were actively being selected for were Common Carp Cyprinus carpio, Flathead Catfish, and Shovelnose Sturgeon Scaphirhynchus platorynchus. The highest prey selection was for other Flathead Catfish with an alpha value >0.50. Chesson’s α index for 30 macroinvertebrates showed a positive selection for two macroinvertebrate taxa

Ephemeroptera and Plecoptera (Figure 2-11). The random feeding threshold (alpha) for macroinvertebrates was 0.14 and the species with the highest alpha value was

Ephemeroptera (≥ 0.50).

A total of 154 fish, representing 21 species, were collected for bomb calorimetry analysis (Table 2-2). Caloric values differed among species (ANOVA, P=<0.005), where

Smallmouth Buffalo Ictiobus bubalus (1867.7 calories/gram wet weight) and Blue Sucker

Cycleptus elongatus (1726.3 calories/gram wet weight) had the greatest caloric values.

Conversely, Goldeye Hiodon alosoides (831 calories/gram wet weight) and Shovelnose

Sturgeon (788.7 calories/gram wet weight) had lowest caloric values. Most of the

Cyprinidae (e.g., minnows and chubs) had similar caloric values compared to each other.

Two separate 12-hour sampling periods were used to calculate daily ration. The first 12-hour sampling event took place in September, 2015. A total of 66 Flathead

Catfish diets were collected over the 12-hour sampling. The diel feeding chronology of stomach fullness for Flathead Catfish showed the feeding rate through the 12-hour sampling was variable through time (Figures 2-12 and 2-13). The gastric evacuation rate

(R) for Flathead Catfish during this sampling event was 0.49/hr leading to an estimated daily ration of 3.67 % body weight/day. My second 12-hour sampling event took place in October, 2015. I collected a total of 11 diet samples from Flathead Catfish during this sampling event. The gastric evacuation rate for Flathead Catfish in October was 0.74/hr.

The daily ration of Flathead Catfish in October was 2.33% body weight/day. I doubled 31 the 12-hour daily rations for both October and September samples to get the 24- hour daily rations (e.g., 7.34 and 4.66% body weight/day, respectively).

I recaptured 41 of 587 tagged Flathead catfish between June and October, 2015.

Using the Schnabel population model, I estimated 4,759 (CI ± 3,995) individual Flathead

Catfish within the 20 rkm sampling area. Using diet analyses (e.g., stomach fullness, caloric content of prey items, and daily ration), I was able to calculate calories consumed by a Flathead Catfish for each 25 mm length group ranging from 100-500 mm (Table 2-

4). I found that Flathead Catfish on average were consuming 175.3 ± 2.1 kcals (dry weight) on a daily basis. I extrapolated the average Flathead Catfish kcals (175.3 ± 2.1) to the population level based on the Schnabel population estimate giving an estimated total of 788,850 ± 9450 kcals (dry weight) consumed per day by the entire Flathead

Catfish population ≥ 200 mm in my study area. This is equivalent to consuming about

220.9 kg of biomass daily within my study site.

Discussion

Quantifying energy consumption through a common value (e.g., calories) is a useful approach to begin to understand trophic dynamics within an ecosystem. Most research looking at trophic dynamics for apex predators (e.g., Flathead Catfish) in aquatic ecosystems have focused on systems where predators have been introduced

(Brown et al. 2005; Pine III et al. 2005; Brewster 2007), but little research has looked at a native predator species within anthropogenic altered systems. My research helps fill the knowledge gap in what is known about predator-prey dynamics between native 32 predators that are effectively acting as an introduced species. Flathead Catfish had similar diets and mean stomach fullness among seasons as well as shifted to piscivory at a length consistent with both native and non-native Flathead Catfish populations. These results suggest native Flathead Catfish in the Missouri River could be operating in a similar manner to non-native populations.

Flathead Catfish abundances within the Missouri River have remained relatively steady over the past two decades compared to declining catch rates of other large- bodied predators (e.g., Channel Catfish and Pallid Sturgeon; UNL unpublished data;

Steffensen et al. 2014). Pre-alteration abundances are unknown for Flathead Catfish, but recent abundance estimates are thought to be much greater than what they would have been historically. For example, relative abundance for Flathead Catfish in 1983 was 0.29 fish per minute of electrofishing in a channelized reach of the Missouri River upstream of my sample site (Sandheinrich and Atchison 1986); whereas, concurrent sampling in 2016 resulted in a relative abundance of 2.45 (SE ± 0.23) fish per minute.

One important piece of information that could explain these abundance estimates is the closing of commercial catfish harvest in the Missouri River. Commercial harvest was allowed up through the early 1990’s, but was subsequently closed January 1, 1992.

Presumably, commercial harvest may have been keeping Flathead Catfish populations in check. The population could have been released from low survival rates when commercial fishing ceased due to removal of large numbers of individuals within the population. 33

Hogberg and Pegg (2016) reported similar stomach fullness of Flathead Catfish within the Missouri River bordering Nebraska during 2012 and saw much higher stomach fullness during the 2011 record setting flood. Stomach fullness estimates from this study (Figure 2-8) were similar to native (0.29 g/100 g; Hogberg and Pegg 2016) populations but dissimilar to Flathead Catfish in non-native populations (0.32 - 0.52 g/100 g; Brewster 2007). The difference of stomach fullness between a native population of Flathead Catfish and non-native populations suggests that the native population could have access to different prey items. Furthermore, the prey base is most likely different between native and non-native reaches due to environmental conditions (e.g., warmer water, faster flow, productivity, etc.), thereby influencing species composition. For example, Brewster (2007) found Flathead Catfish consumed a large number of Centrarcidae that are mostly pelagic species, whereas my study indicated selected species were mainly benthic.

The selection for prey items that share similar habitat (Flathead Catfish selecting for benthic species) points to an obligate feeding strategy that is seen in both native and non-native populations. To further explain this feeding strategy, habitat alterations within the Missouri River have significantly decreased available habitat for both predator and prey populations (Morris et al. 1968). Savino and Stein (1982) found that predator-prey interactions increased (e.g., number of encounters) between Largemouth

Bass salmoides and macrochirus when habitat diversity was low, and the restricted habitats within the Missouri River may be exhibiting similar interactions. For example, the diet selectivity index showed a positive selection towards 34 certain prey items that share similar benthic habitat (e.g., Common Carp, Flathead

Catfish, and Shovelnose Sturgeon). The energetic gain from consuming prey items that share similar habitat may be greater than actively searching for higher calorie species.

This positive selection for Flathead Catfish could also point to a self-sustaining prey source due to their high abundance throughout the Missouri River.

The diet selectivity index showed a positive selection for Shovelnose Sturgeon this selection should be used with caution due to gear biases and low sample size of

Shovelnose Sturgeon captured within these gears. A better understanding of

Shovelnose Sturgeon populations is needed to verify these positive selections. The consumption of Shovelnose Sturgeon may be indicative of both direct and indirect consequences between Shovelnose Sturgeon and other sturgeon species like Pallid

Sturgeon when present. Pallid Sturgeon is a federally endangered species and predation on Pallid Sturgeon by Flathead Catfish has been documented in the Missouri

River (French et al. 2014; Steffensen et al. 2014). Management for Pallid Sturgeon populations has been a priority throughout the Missouri River and its tributaries with substantial financial investment toward increasing survival of Pallid Sturgeon. However, the consumption of Shovelnose Sturgeon I observed may indicate other sturgeon species are also likely vulnerable to consumption.

Daily ration (24hr) for non-native Flathead Catfish populations in North Carolina were 3.06 % body weight/day in July and 7.37 % body weight/day in August based on 24 hour sampling (Brewster 2007). Daily rations (24 hr) for Missouri River Flathead Catfish were similar to this introduced population with 7.34 % body weight/day for September 35 and 4.66 % body weight/day for October. Similar daily rations found between the native population and non-native populations elsewhere indicate that Missouri River

Flathead Catfish could be displaying similar attributes to non-native populations. To better understand how this daily ration fits into the Missouri River food web, I compared our ration estimates to another large bodied predator River (Channel Catfish) found within the Missouri. Channel Catfish are known to have a daily ration of 5-10 % body weight/day within riverine environments (Kwak et al. 2006); there is the potential increased competition for food resources between these two large bodied predators within the Missouri River. The high abundances of Flathead Catfish compared to other large bodied predators (e.g., Channel Catfish) could be due Flathead Catfish exploiting available food resources.

The evaluation of caloric densities of fishes within aquatic ecosystems helps researchers determine available energy by putting energy into a quantifiable variable

(Fisher and Likens 1973; Eggelton and Schramm 2002). The correlating caloric values for the three positively selected fish and macroinvertebrate taxa were not the highest or lowest values, and further points to the idea that selectivity was based on similar habitat preferences. Similarly, the total average consumed caloric values of fish and macroinvertebrates were similar, but the amount of macroinvertebrates likely requires more energy to consume as many calories per gram of prey item compared to a single fish. On average, Flathead Catfish are consuming about 175.3 ± 2.1 kcals per day and the entire population is consuming about 788,850 ± 9450 kcals per day. Without knowing how many calories are available to Flathead Catfish within the Missouri River, the 36 ultimate impact they are having on the food web is unknown. Hogberg and Pegg (2016) found Flathead Catfish within the Missouri River exhibited a shift to piscivory at a smaller length group when presented with additional food resources (i.e., an increase in diversity). The flood of 2011 provided Flathead Catfish access to the historic floodplain and ultimately more food resources. Knowing the energetic demands and the adaptability of Flathead Catfish within the Missouri River can help explain the ability they have to capitalize on the highly altered riverine ecosystem and potentially out- compete other large river predators. The continued effort to quantify productivity and energy use within the Missouri River will help managers produce energy models to better identify the caloric demand Flathead Catfish have in this ecosystem. This information will not only help manage Flathead Catfish but other species as well through direct and indirect manipulations of Flathead Catfish abundances.

Research on trophic dynamics of freshwater ecosystems has mainly focused on primary and secondary producers (McQueen et al. 1989; Daskalov 2002; Pauly and

Christensen 1995) to understand “bottom up” effects in the food chain. Another approach is looking at “top-down” effects of a trophic cascade which has mainly been focused on introduced apex predators (Hedden et al. 2016; Baum and Worm 2009;

Frank et al. 2005). Previous studies often document invasive aquatic predators consuming large numbers of native prey, ultimately causing detrimental effects on trophic dynamics and changing the species composition and structure of these ecosystems (Gurevitch and Padilla 2004; Pine III et al. 2005; Albins and Hixon 2008;

Spurgeon et al. 2015). The abundant population of Flathead Catfish within the Missouri 37

River could be removing a large portion of the available prey, ultimately shifting the trophic dynamics of the Missouri River. The daily caloric consumption estimated for our sample population can be used towards a simplified bioenergetics model. For example, energy use from the entire sample population is on average equivalent to consuming about 108 kg of prey biomass per day. Putting the calories consumed into a common value (kg of prey items consumed) will help manager’s better dictate where to manipulate fish populations when needed.

Identifying trophic dynamics is a multifaceted struggle that is often further confounded by biotic and abiotic responses that are not commonly predictable. This is especially true in large river systems that have been altered for anthropogenic needs. In this study, I have begun to shed light on energy uptake as well as a conservative estimate of demand by a top fish predator in a scenario where the predator population has been “released” from the typical population constraints that historically may have kept the population in check. The Missouri River and other large altered riverine ecosystems throughout North America may point to similar problems in shifting demands for energy. Knowing how much biomass Flathead Catfish need and the amount of available prey will give us guidance to knowing if they are putting too much pressure on the system from a top-down perspective. Better understanding available energy and energy inputs could potentially benefit other large river predators including the Pallid Sturgeon by helping managers to determine the forage needed to maintain these predators. My research helps open the door to exploring the issues of riverine 38 trophic dynamics where native predators have adapted and flourished where large scale habitat alterations have taken place.

39

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Table 2-1: Orders of prey items found in Flathead Catfish stomachs from the Missouri River, 2015. Quantity (Qty) is the numbers of stomachs that had the corresponding prey item present. Proportion is the number of stomachs (count) in which the prey item was present divided by the total number of stomachs with items in the stomach (n=463).

Order Qty Proportion Fish Acipenserformes 1 0.22 Cyprinadontiformes 2 0.43 Cypriniformes 9 1.94 Perciformes 6 1.3 Siluriformes 72 15.55 Unidentified 52 11.23 Invertebrates Araneae 1 0.22 Arguloida 2 0.43 Bivalvia 2 0.43 Coleoptera 2 0.43 Decapoda 58 12.53 Detritus 68 14.69 Diptera 4 0.86 Ephemeroptera 269 58.1 Hemiptera 1 0.22 Hymenoptera 1 0.22 Hirudinea 3 0.65 Lepidoptera 1 0.22 Megaloptera 21 4.54 Odonata 10 2.16 Plecoptera 55 11.88 Pseudophyllidea 11 2.38 Trichoptera 148 31.97 Unidentified 68 14.69 Other Mullberries 5 1.08 Testudines 1 0.22

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Table 2-2: Mean caloric values for potential prey items from the Missouri River, 2015. Shovelnose Sturgeon caloric value was taken from Deslauriers et al. (2016).

Calories/gram wet Calories/gram dry Species weight weight Goldeye 831.0 4347.0 Gizzard Shad 1079.2 5488.2 Speckled Chub 1250.9 5572.2 Sturgeon Chub 1115.0 4992.8 Silver Chub 1223.0 5080.4 Red Shiner 1403.1 5389.5 Emerald Shiner 1230.5 5257.9 River Shiner 1435.2 5271.7 Sand Shiner 1303.9 5331.8 Plains Minnow 1159.4 5255.9 Common Carp 1357.1 4952.3 Silver Carp 1147.5 4329.6 River Carpsucker 1471.2 4705.8 Blue Sucker 1726.3 5492.1 Smallmouth Buffalo 1867.7 5696.4 Blue Catifish 1128.0 5513.6 Channel Catfish 1024.8 4889.6 Flathead Catfish 1326.9 5330.9 Blue Catfish 1547.6 6317.9 Bluegill 1655.2 5738.7 Freswater Drum 1258.5 4937.9 Shovelnose Sturgeon 788.7 N/A

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Table 2-3: Mean calories per gram for orders of macroinvertebrates found within the diet of Flathead Catfish in the Missouri River, 2015. Plecoptera mean calories were obtained by averaging Oberndorfer and Stewart (1977) and Mcdiffet (1970) values.

Order Cal/g DW Citations Ephemeroptera 5469 Cummins and Wuycheck 1971 Odonata 5117 Cummins and Wuycheck 1972 Coleoptera 5371 Cummins and Wuycheck 1973 Trichoptera 4999 Cummins and Wuycheck 1974 Plecoptera 5545 Oberndorfer and Stewart 1977 and Mcdiffet 1970 Megaloptera 5210 Cummins and Wuycheck 1974 Diptera 4276 Cummins and Wuycheck 1974

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Table 2-4: Caloric consumption ± SE by Flathead Catfish for length groups 100-500mm in 25mm increments for the Missouri River 2015. Average calories consumed ± SE are included for all length groups combined. Average weighted fish and invertebrate caloric values ± SE are included for all fish and invertebrate species found within the diet samples.

Length Group Calories (kcal) SE 100 7.0 0.2 125 9.7 0.3 150 15.9 0.8 175 23.7 1.0 200 33.8 0.7 225 37.5 2.6 250 51.7 4.3 275 75.2 4.1 300 103.9 6.3 325 135.6 7.9 350 147.3 16.1 375 225.1 7.8 400 296.2 17.7 425 355.0 26.6 450 412.4 15.2 475 481.2 19.0 500 569.3 22.2

Average Calories (cal/gram dry weight) 175.3 ± 2.1 Fish Calories (cal/gram dry weight) 5326.1 ± 160.1 Invertebrate Calories (cal/gram dry weight) 5102.6 ± 190.8

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Figure 2-1: Map of study site on the Missouri River, 2015.

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Figure 2-2 Conceptual diagram showing the process to determine the total number of calories consumed within the 20 kilometer sampling site.

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Figure 2-3: Nonmetric multidimensional scaling plots of diet for Flathead Catfish among seasons in the Missouri River, 2015. Top figure shows all stomach samples. Bottom figure is circled area from top figure.

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130

120

110

100

Relative Weight Relative 90

80

70

100 200 300 400 500 600 700 800 900

Length Group (mm)

Figure 2-4: Flathead Catfish condition mean relative weight ± SE for all length groups and all seasons. Length groups were split into 25mm groups.

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120

100

80

60

Frequency 40

20

0

200 300 400 500 600 700 800

Length Group (mm)

Figure 2-5: Flathead Catfish length-frequency histogram of all fish collected within study site including fish with stomachs lavaged and fish that were not lavaged in 2015. Length groups are split into 25 mm groups.

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2.5 500

Invertebrates (except crayfish) and crayfish 2.0 400 Calories

1.5 300

1.0 200

0.5 100

Relative Importance Relative

0.0 0

Calories Consumed (Grams Dry Weight) Dry (Grams Consumed Calories

0 100 200 300 400 500 600

Figure 2-6: Mean (± SE) of relative importance for invertebrate and vertebrate/crayfish prey items found in Flathead Catfish diets in 2015. Calories consumed per grams dry weight for Flathead Catfish for each 25mm Length group.

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0.8 Food Present Food Absent

0.6

0.4

Percent

0.2

0.0 Spring Summer Fall

Figure 2-7: Percent empty stomachs of Flathead Catfish by season

59

120

100 Spring Summer Fall 80

60

40

20

Mean Stomach Fullness (%) Fullness Stomach Mean

0

-20

100 150 200 250 300 350 400 450 500

Length Group (mm)

Figure 2-8: Mean Stomach Fullness ± SE of Flathead Catfish by season for 25 mm length groups from the Missouri River, 2015.

18 60

16

14

12

10

8

Percent

6

4

2

0

Cyprinidae Ictaluridae Poecilidae Perfciformes Acipenseridae

60

50

40

30

Y Data

20

10

0

Perlidae ArgulidaeBaetidae Corduliidae Libellulidae CambaridaeCantharidaeChloropidae Corydalidae IsonychidaeLeptoceridae Limephilidae Chironomidae EphemeridaeHeptageniidae Pentatomidae SphaeniodeaTricorythidae Coenagrionidae HydropschyidaeLepidostomidaeLeptophlebiidae Polymitarcyidae Polycentropodidae

Figure 2-9: Percent of occurrence for prey items (by count) for fish and macroinvertebrates found in the Flathead Catfish diets in the Missouri River, 2015.

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0.6 0.6

0.5 0.5

0.4 0.4

0.3 0.3

Chesson's Alpha Chesson's 0.2 0.2

Relative Abundance Abundance Relative

0.1 0.1

* 0.0 0.0

Red Shiner Mosquitofish Shoal Chub Common Carp Freshwater Drum Channel Catfish Flathead Catfish Shovelnose Sturgeon

Figure 2-10: Chesson’s alpha diet selectivity index (dots) for prey items (fish) found within the Flathead Catfish diets in the Missouri River 2015. The line located at 0.1 is the random feeding threshold line where an alpha value over 0.1 indicates positive prey selection. Alpha values below 0.1 represents random feeding. Relative abundance of each prey item (bars) are represented on the right y-axis. *Shovelnose Sturgeon were not sampled in proportion to their abundance.

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0.6 0.30

0.5 0.25

0.4 0.20

0.3 0.15

Chessons's Alpha Chessons's 0.2 0.10

Relative Abundnace Abundnace Relative

0.1 0.05

0.0 0.00

Diptera Plecoptera Hemiptera Trichoptera Coleoptera Hymenoptera Ephemeroptera

Figure 2-11: Chesson’s alpha diet selectivity index (dots) for prey items (macroinvertebrates) found within the Flathead Catfish diets in the Missouri River 2015. The line located at 0.14 is the random feeding threshold line where an alpha value over 0.14 indicates positive prey selection. Alpha values below 0.14 represents random feeding. Relative abundance of each prey item (bars) are represented on the right y- axis.

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50

40

30

20

Mean Stomach Fullness (%) Fullness Stomach Mean 10

0 600 800 1000 1200 1400 1600 1800

Time

Figure 2-12: Diel feeding chronology of Flathead Catfish in the 20 kilometer sampling site in the Missouri River in September 2015 as determined from changes in stomach fullness (mean fullness ± SE). Stomach fullness was determined from a 12 hour sampling period.

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16

14

12

10

8

6

4

Mean Stomach Fullness (%) Fullness Stomach Mean 2

0

600 800 1000 1200 1400 1600 1800

Time

Figure 2-13: Diel feeding chronology of Flathead Catfish in the 20 kilometer sampling site in the Missouri River in October 2015 as determined from changes in stomach fullness (mean fullness ± SE). Stomach fullness (N = 10) was determined from a 12 hour sampling period.

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CHAPTER 3 CONCLUSIONS AND MANAGEMENT CONSIDERATIONS

In this study I aimed to better understand energetic needs for Flathead Catfish, the most abundant apex predator within the channelized Missouri River. Flathead

Catfish energetic demand has been studied where introduced populations have been established, but little research has looked at a native population where habitat alterations have potentially increased abundances higher than would be historically present. I looked at diet metrics and consumption rates for Flathead Catfish in a 20 km stretch of the channelized Missouri River to estimate energetic demand. Flathead

Catfish were consuming similar diets among spring, summer, and fall, but exhibited different proportions of diets with food items present and absent. Flathead Catfish were selecting for three fish species (Common Carp, Flathead Catfish, and Shovelnose

Sturgeon) and two macroinvertebrate taxa (Ephemeroptera and Plecoptera).

Consumption and stomach fullness rates were similar to studies where Flathead Catfish have been introduced showing that they potentially consume similar amounts of prey items in both native and introduced populations. I also found that the caloric contents of potential and realized prey items was significantly different. Flathead Catfish were not selecting prey that had the highest nor lowest caloric values, rather selecting prey that likely share similar benthic habitat. Lastly, I found that an individual Flathead

Catfish was consuming on average a total of 175.3 ± 2.1 kcals (dry weight) per day.

Using the population estimate from the sample site, I extrapolated caloric consumption 66 to biomass consumed from the estimated population which was around 160kg of biomass consumed on a daily basis (Table 2.4).

Management Implications

3.1 Decrease abundance of quality Flathead Catfish.

The length frequency histogram shows a large number of smaller individuals within my sample site. Additional data collected on Flathead Catfish throughout the channelized Missouri River shows similar size groups being dominant. The consumptive demand of quality sized Flathead Catfish could be directly affecting macroinvertebrate abundances available to other predators within the Missouri River. Decreasing abundance of these smaller Flathead Catfish could help increase numbers of available prey to smaller bodied predators within the Missouri River, ultimately increasing forage abundance. Removing smaller bodied Flathead Catfish could also create a population that will be self-regulating due to the high positive selection for other Flathead Catfish found within diets. Furthermore, this management strategy may increase size structure of the Flathead Catfish population, increasing angler satisfaction. Until better knowledge on the available energy within the Missouri River is understood, this management action could potentially help decrease food consumption by Flathead

Catfish in the channelized Missouri river, ultimately freeing up food resources for other fishes.

3.2 Better understand prey abundances and composition throughout the channelized

Missouri River. 67

This project provided caloric densities for several predator and prey items within the Missouri River. However, I was not able to quantify abundances of these prey items throughout the channelized portion of the Missouri River. I recommend future studies determine abundances of prey fishes throughout the channelized portion of the

Missouri River. This will help us better understand available food and energy to large predators. This information will help inform management goals focused on energy availability for predators and prey within the Missouri River.

3.3 Research Flathead Catfish diets and abundances in unchannelized portions of the

Missouri River to compare with channelized portions.

My research looked at a population of Flathead Catfish within a channelized segment of the Missouri River. River modifications within this stretch have created habitat that is much different than what occurred naturally. The unchannelized portions of the Missouri River have been modified, but available habitat is more similar to what occurred naturally compared to the channelized segments. To further understand the influence that Flathead Catfish have on native populations in the channelized Missouri

River, it would be beneficial to determine energetic needs and abundances of Flathead

Catfish in the unchannelized river. This information will provide us with a better understanding of the energetic needs for Flathead Catfish in conditions that are closer to pre-alteration and help to further determine the positive or negative effects the alterations of the Missouri River are having on energetic demands for Flathead Catfish.

68

3.4 Determine how Flathead Catfish are utilizing habitat restoration projects in the

channelized Missouri River, specifically Deer Island.

Habitat renovations are important to several fish species that have been affected by river modifications (Wohl et al. 2005). Within the Missouri River bordering Nebraska, there have been several restoration projects ranging from restored side channels to river widening. The Deer Island project was implemented by the U.S. Army Corp of

Engineers to widen the Missouri River and create shallow water habitat for fishes (US

Army Corps of Engineers 2011). This area was sampled for Flathead Catfish in 2016 as a part of the Riverine Sportfish and Ecology project (F-75-R). A wide range of Flathead

Catfish sizes were collected during this sample period, and anecdotally, most of these

Flathead Catfish had full (e.g., bulging) stomachs. Stomach samples were not collected for this effort, but I recommend collecting Flathead Catfish diets from this area. The feeding strategy of Flathead Catfish allows them to consume a wide variety of prey items that could be negating some of the goals and objectives for these restoration projects including creating increased habitat for food items.

General conclusions

3.5 Investigate the potential for competition between Flathead Catfish and other large

bodied predators within the Missouri River.

In this study, I looked at the energetic needs for Flathead Catfish, which is only one of several native large-bodied predators within the Missouri River. I recommend 69 looking at potential competition between Flathead Catfish and other native large- bodied predators (e.g., Channel Catfish, Blue Catfish, and Pallid Sturgeon) to begin understanding the interaction among trophic levels. The complexity of the Missouri

River and its tributaries creates a unique opportunity to begin researching energy flow at a large scale and also to gain insight into the anthropogenic influences that are effecting the energy flow. The current environment found in the channelized Missouri

River may provide a unique aspect of competition between several large predators cohabitating a shared, restricted habitat.

3.6 Estimate Flathead Catfish abundances and movement throughout the channelized

segments of the Missouri River.

My research only looked at Flathead Catfish using a small portion of the channelized Missouri River. Previous studies have collected data that could be used to better estimate abundance and movement of Flathead Catfish throughout the entire channelized portion of the Missouri River. I recommend creating an abundance estimate for Flathead Catfish to better understand energetic demands throughout the entire reach of river. This will help managers determine what management actions need to be implemented, if any, in each segment to increase or decrease Flathead Catfish abundances to increase forage for other fishes.

3.7 Develop an ecosystem energy budget to better understand energy flow throughout

all trophic levels within the Missouri River. 70

Ecosystem energy budgets have been used in several small streams throughout the world to better understand trophic dynamics (Fischer and Likens 1972; Fischer and

Likens 1973). Using small scale energy budgets and scaling them up to developed an energy budget for an aquatic ecosystem as large as the Missouri River has not been attempted to date. Immense knowledge of inputs and outputs of the ecosystem would be needed to create an energy budget, but with the amount of anthropogenic alterations to rivers and streams that have occurred throughout the world, it would be beneficial to the scientific community to determine the major implications of habitat alterations. The creation of a Missouri River energy budget would be beneficial in helping the restoration efforts of endangered species (e.g., Pallid Sturgeon) due to the knowledge of energetic demands large predators need within the Missouri river.

71

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