The Impact of Waterfowl Production Area (WPA) Fish Communities Upon the Invertebrate Food Base of Waterfowl
by
P. Kelly McDowell
A Thesis submitted in partial fulfillment of the requirements for the degree MASTER OF SCIENCE
College of Natural Resources
UNIVERSITY OF WISCONSIN Stevens Point, Wisconsin
February, 1989 APPROVED BY THE GRADUATE COMMITTEE OF:
Dr. E. Nauman, Committee Chairman Professor of Wildlife
Dr. James W. Hardin Professor of Wildlife
Dr. Fredrick A. Copes Professor of Fisheries
i PREFACE
This paper is part of study 316 entitled "Duck and Pheasant Management in the Pothole Region of Wisconsin." Study 316 was initiated in 1982 by the Wisconsin Department of Natural Resources to determine methods of increasing waterfowl and pheasant production on private and public lands. As a part of study 316, 2 experiments were conducted to evaluate impacts of fish communities on waterfowl food resources. A paired pen study was conducted to evaluate impacts of fathead minnows on waterfowl invertebrate foods. Two paired pond experiments were conducted to further evaluate impacts of minnow and other wetland fish species which occur on federal and state Waterfowl. Production Areas. Pen study data are included in the first paper and appendix A. Paired-pond data are included in appendices B-K.
ii ACDONLEDGEMENTS
This project was multi-disciplinary by design. In the same manner, assistance to complete this project was multi disciplinary. I thank my advisor Dr. Lyle E. Nauman and Richard A. Lillie, for help in all stages of this project. Eldon McLaury facilitated and encouraged research in this area. Drs. Fredrick A. Copes and James W. Hardin provided editorial assistance and were members of my graduate committee. Gerry Wegner and Greg Quinn constructed and installed enclosures. Hannibal Bolton and Jim Milligan, U.S. Fish and Wildlife Service, provided the original fish stock and recommended stocking rates. Special thanks to Thomas Neuhauser and Dr. Robert Rogers for statistical and computing assistance. Dr. Robert Freckmann verified aquatic plant samples and Jeff Demick identified unknown aquatic insects. Labor, logistical, and technical support was provided by the Wisconsin Department of Natural Resources Research and Management Staff, including James Evrard, Scott Stewart-, Cindy Swanberg, Bill Fannucchi, and Bruce Bacon. I also extend a special thanks to the many University work study students who spent endless hours sorting invertebrates, particularly Bob Brua, Shelly Thilleman, and Gene Klees for laboratory and field assistance. A special word of appreciation is extended to my wife, Sandy, for her interest, support, labor, and help in the preparation of this report. Principle funding was provided by the Wisconsin Department of Natural Resources and the Federal Aid in Wildlife Restoration
iii Act under Pittman-Robertson project W-141-R. Additional support was provided by the U.S. Fish and Wildlife Service and the Wetlands Conservation League of Stevens Point.
iv TABLE OF CONTENTS
PREFACE------ii ACKNOWLEDGEMENTS------iii TABLE OF CONTENTS------v LIST OF TABLES------vi LIST OF APPENDICES------viii ABSTRACT------1 INTRODUCTION------2 OBJECTIVES------5 STUDY SITE------5
MEHTODS ------5 Enclosures------6 Fish Collections------7 Aquatic Invertebrate Sampling------8 Taxa Composition------9 Water Chemistry and Select Physical Measurements------9 Aquatic Plant Sampling------10 Data Analysis------10 RESULTS------11 Invertebrate Composition------14 Vegetation------23 Fathead Minnow Food Habits------23 Water Chemistry------28 DISCUSSION------32 MANAGEMENT IMPLICATIONS------39 LITERATURE CITED------41 APPENDICES------47 V LIST OF TABLES
Table 1. Student t-tests between stocked and control enclosure invertebrates (numbers and biomass) in 96 water column and benthic samples in Oakridge WPA, 1985. Values for 1 and probabilities represent results of nonparametric tests after ln conversions. ------12 Table 2. Paired t-tests between stocked and control enclosure invertebrates (numbers and biomass) in 107 water column and benthic samples in Oakridge WPA, 1986. Values for 1 and probabilities represent results of nonparametric tests after .ln conversion. ------13 Table 3. Comparison of percentage similarity of community (PSC) and coefficient of similarity (B) indices of taxa composition (numbers) in stocked and control enclosures in Oakridge WPA, 1986. ------15 Table 4. Comparison of percentage similarity of community (PSC) and coefficient of similarity (B) indices of taxa biomass (mg) in stocked and control enclosures in Oakridge WPA, 1986. ------16 Table 5. Percentage similarity of community (PSC) indices of taxa in stocked and control enclosures at depths (18-48 cm) in Oakridge WPA, 1986. ------17 Table 6. Percentage similarity of community (PSC) indices of taxa in stocked and control enclosures at depths (49-59 cm) in Oakridge WPA, 1986. ------18 Table 7. Percentage similarity of community (PSC) indices of taxa in stocked and control enclosures at depths of >59 cm in Oakridge WPA, 1986. ------19 Table 8. Paired t-test results of midge (Chironomidae), mayfly (Caenidae), and gastropod (Planorbidae, Lymneadae, and Physidae) populations between stocked and control enclosures in Oakridge WPA, 1986. ---·------20 Table 9. Paired t-test results of midge (Chironomidae), mayfly (Caenidae), and gastropod (Planorbidae, Lymneadae, and Physidae) biomass between stocked and control enclosures in Oakridge WPA, 1986. ------21
vi Table 10. Paired t-test results between stocked and control enclosures of midge (Chironomidae) and mayfly (Caenidae) average biomass (mg) in Oakridge WPA, 1986. ------22 Table 11. Results of· 1985 t-test, and 1986 paired t-test analysis of mean total vegetation stem numbers and biomass/m2 in stocked and control enclosures in Oakridge WPA. ------24 Table 12. Frequency of occurrence and aggregate\ dry weight of plant taxa in stocked and control enclosures in Oakridge WPA, 1985. ------25 Table 13. Frequency of occurrence and aggregate\ dry weight of plant taxa in stocked and control enclosures in Oakridge WPA, 1986. ------26 Table 14. Paired t-test results of dominant vegetation taxa/m2 between stocked and control enclosures in Oakridge NPA, 1986. ------27 Table 15. Fathead minnow food habits during May-August 1985 at Oakridge WPA, northwest Wisconsin, (D = 62). ------29 Table 16. Fathead minnow food habits during May-August 1986 at Oakridge WPA, northwest Wisconsin, (D = 114). ------30 Table 17. Limnological analysis from 6 stocked and control enclosures in May and July on Oakridge WPA, 1985. ------31 Table 18. Student t-test results from weekly water chemistry data from Oakridge WPA, 1985. Values for 1 were not·significant at the P < 0.05 level. ------33 Table 19. Limnological analysis from 6 stocked and control enclosures on Oakridge WPA, May 1986. ------34 Table 20. Student t-test results from weekly water chemistry data from Oakridge WPA, 1986. Values for~ were not significant at the ~ < 0.05 level. ------35
vii LIST OF APPENDICES
Appendix A. Number of undesired central mudminnows and pumpkinseeds in stocked and control enclosures in Oakridge WPA, 1986 ------47 2 Appendix B. Mean number and biomass (g/m) of invertebrates collected from fish complex (FC) and fathead minnow (FM) stocked and control ponds on Kostka WPAs in northwest Wisconsin, 1986. ------55 Appendix c. Mean biomass (mg) of Chironomidae from fish complex {FC) and fathead minnow (FM) stocked and control ponds on Kostka WPAs in northwest Wisconsin, 1986. ------56 2 Appendix D. Mean Diptera and non-Diptera emergence (#/m) from fish complex stocked and control Kostka ponds in northwest Wisconsin, 1986, (N = 3). ---- 57 2 Appendix E. Mean Diptera and non-Diptera emergence (#/m) from fathead minnow stocked and control Kostka ponds in northwest Wisconsin, 1986, (N = 3). 58 Appendix F. Mean number of invertebrates/liter in 3 zooplankton samples collected from stocked and control fish complex ponds on Kostka WPA in northwest Wisconsin, 1986. ------59 Appendix G. Mean number of invertebrates/liter in 3 zooplankton samples collected from stocked and control fathead minnow ponds on Kostka WPAs in northwest Wisconsin, 1986. ------61 Appendix H. Vegetative characteristics of stocked and control fish complex ponds on Kostka WPAs in northwest Wisconsin, 1986. ------63 Appendix I. Vegetative characteristics of stocked and control fathead minnow ponds on Kostka WPAs in northwest Wisconsin, 1986. ------64 · Appendix J. Weekly water chemistry data from fish complex (FC) and fathead minnow (FM) stocked and control ponds on Kostka WPAs in northwest Wisconsin, 1986. ------65 Appendix K. Limnological analysis for fish complex (FC) and fathead minnow (FM) stocked and control ponds in northwest Wisconsin, 1986. ----- 66
viii 1
Impact of Waterfowl Production Area {WPA) fish communities on the invertebrate food base of waterfowl.
Patrick Kelly McDowell, University of Wisconsin-Stevens Point Stevens Point, WI 54481 Lyle E. Nauman, University of Wisconsin-Stevens Point Stevens Point, WI 54481
Abstract: Invertebrate populations were monitored in the presence and absence of fathead minnow (Pimephales promelas) populations within a series of paired enclosures. Stocking condition did not affect invertebrate numbers and biomass in water column and benthic samples. Chemical and vegetation parameters were similar between stocked and control treatments. Periphyton was present in 98% of fathead minnow stomachs and comprised 89% aggregate dry weight (APDW} while invertebrates occurred in 56% and comprised 4% APDW in 1985. In 1986, invertebrates occurred in 89% of fathead stomachs and made up 32% APDW while periphtyon was present in 73% and made up 561 APDW. Fathead minnows have the potential for competition with waterfowl but did not appear to impact invertebrate populations in this study. 2 IMTRODOCTIOM
Researchers are aware of the importance of invertebrates as protein in duckling and breeding waterfowl diets (Chura 1961, Perret 1962, Dirschl 1969, Schroeder 1973, Krapu 1974, Krapu and Swanson 1975, Reinecke 1977, Street 1978, Drobney and Fredrickson 1979, Pehrsson 1979). Past studies based on gizzard and gullet material over-estimated the importance of plant foods in diets of waterfowl and under-estimated the importance of animal foods (Swanson and Bartonek 1970).
Reported biases were related to differences in digestion rates of plant and animal foods and the time lag between feeding and collection. Therefore, past management of wetland habitat for waterfowl has emphasized seed production rather than invertebrate production. Seasonal variations in waterfowl feeding behavior are dependent on nutritional needs, stage of development and availability of food items (Chura 1961, Bartonek and Hickey 1969, Krapu 1974, Swanson and Meyer 1977, Drobney and Fredrickson 1979, Pehrsson 1979}. The availability of invertebrates appears to influence duck brood movements (Ball 1973, Talent 1980, Ringleman and Longcore 1982, Talent et al. 1982). Low invertebrate numbers may have contributed to low duckling survival in English gravel quarries (Street 1977). The abundance, composition and availability of invertebrate food items are directly related to aquatic plant characteristics (Krecker 1939, Berg 1949, McGaha 1952, Rosine 1955, Krull 1970, Mauser 1985). Aquatic plant characteristics 3 are related to various abiotic and biotic factors including water chemistry, sediment or soil characteristics, water level fluctuations, muskrat (Ondatra zibethicus) eatouts, and weather. Swanson and Nelson (1970) expressed concern that wetland fisheries may adversely impact waterfowl breeding habitat through the alteration or destruction of aquatic vegetation and/or direct competition for invertebrate food items. This concern has been voiced more recently by wildlife professionals in the Midwest (E. McLaury, pers. comm.), in particular, the possible impact of minnow stocking or removal by bait dealers on waterfowl production. The sale of live bait in Wisconsin generates $1.5 millon annually and is increasing (Threinen 1982). The potential conflict or incompatability in the use of existing resources by both wildlife and fisheries interests has been explored recently with varing degrees of success. Pehrsson (1984) documented that mallards (Anas platyrhynchos) in Sweden tended to select smaller, fishless lakes over lakes with fish. Erickson (1979) demonstrated that fledged goldeneyes (Bucephala clangula) preferred to lakes lacking fish populations. He speculated that the mechanism responsible for this selection was related to the availability of invertebrate food organisms as influenced by fish predation. Carmichael (1983) studied the dietary overlap of largemouth bass (Micropterus salmoides) and rainbow trout (Salmo gairdneri) with canvasback (Aythya americana) and redhead ducks (Aythya valisineria). He estimated co-utilization of food resources of 4
<40\, with greater overlap between canvasbacks and fish than between redheads and fish. The adverse effect of acidification on fish may produce temporary positive impacts on duckling food resources (Hunter et al. 1985 and 1986). They reported invertebrate numbers and biomass were greater on acidified ponds without fish populations in Maine. Ducklings gained more weight and spent less time searching for food and more time feeding on acidified lakes. This was presumably caused by the increased invertebrate availability due to fish extirpation. While the impacts of particular fish species or communities on invertebrate communities are well documented (Galbraith 1967 and 1982, Crowder and Cooper 1982, Gilinsky 1984, · Mittlebach 1984), little has been reported relative to minnow species resident to Wisconsin WPA's. Food habit studies of fathead minnows {Held and Peterka 1974, Isaak 1961, Saylor 1973, Zischke et al. 1983) suggest a potential dietary overlap with waterfowl during later life stages of minnows. Results of many food habits studies of the fathead minnow are conflicting. Pearse (1918) and Held and Peterka (1974) reported that fathead minnows feed primarily on zooplankton. Bottom ooze or slime was reported as an important food items of fathead minnows (Starrett 1950, Simon 1951, Copes 1970). Vegetation was the primary food source used by fatheads in Beckman's (1952) study, while Isaak (1961) found that invertebrates were important only to larger fry. In recent years, the fathead minnow has been used in 5 Minnesota for mosquito control (Becker 1983}. This study was designed to explore the potential impacts of fathead minnow populations on the invertebrate food base of waterfowl.
OBJECTIVES
Research objectives related to documenting interactions between fathead minnow and waterfowl populations are as follows: 1) Compare invertebrate abundance, diversity, and composition in the presence and absence of fathead minnows. 2) Determine the preference for invertebrate food items by fathead minnows. 3) Compare invertebrate parameters and minnow dietary preference to waterfowl diet literature to estimate overlap with resident waterfowl.
S'l'UDY SITE
The study site is located in the Wisconsin pothole region in northern St. Croix County, 6 (km} northeast of New Richmond, Wisconsin. Experiments were conducted on the south shore of Oakridge WPA. Oakridge is a groundwater depression or slope wetland with continuous groundwater flow to adjacent down slope wetlands (Evrard and Lillie 1985). The Oakridge basin is large (65 Ha) with a narrow margin of littoral zone (<10 m). Fish populations were dominated by fathead minnows and mudminnows (Umbra limi). Pumpkinseeds (Lepomis gibbosus) and golden shiners (Notemiqonus crysoleucas) were also common in Oakridge WPA. 6
METHODS
This study evaluated the impacts on invertebate populations by the dominant minnow species present in most WPAs, the fathead minnow. Evaluations were conducted within a series of paired enclosures. Fathead minnows were stocked at densities comparable to those generally found on WPAs in the pothole region of Wisconsin. Adjacent enclosures were established with no fish present. The vegetation and invertebrate communities within the enclosures were monitored from early May to mid July to document the direction and degree of changes occurring. Associated limnological data were likewise monitored. Approximately 10 fish were removed every 2 weeks for analysis of gullet contents.
Enclosures
2 In 1985, 6 pairs of 3.1 m, 3 sided, screened, enclosures were placed parallel to the shoreline in areas characteristic of depths and vegetation which are used often by waterfowl broods(< 1 m). Each enclosure was divided into 2 cells open on the shoreward side with one side in common with an adjacent cell. The sides of enclosures were approximately (O.Sm) above the water to prevent waves from transporting organisms into or out of the enclosures. Sides of the enclosures consisted of pulp mill drying felt {200 CFM). The felt allowed free circulation of water, but prevented movement of most organisms into or out of the enclosures. Sides of the enclosures were extended and buried in the subtrate approximately 30 cm to prevent 7 movement of fish and invertebrates into or out of enclosures. Algae growth on the sides of the barriers was removed as needed to maintain water circulation and minimize affects of shading. In 1986, the enclosures were modified to maintain adequate water levels in all the enclosures. Enclosures used during 1986 had 4 sides and were placed in deeper water (X=56 cm) compared to the shallower 3 sided enclosures used in 1985 (X=20 cm). A stocking rate of 50 adult fathead minnows/cell was used to replicate densities normally found on many WPA's in the pothole region of Wisconsin, (H. Bolton per. comm.) as supported by unpubl. data. Only males were stocked to prevent reproduction within enclosures. Stocking was done in early May. Male fatheads are generally larger than females of the same age class (Becker 1983), and may eat larger food items. Hence, the experimental design likely represents a "worst-case" scenario. Dead minnows or those removed for stomach analysis were replaced from existing male WPA populations. All fish were fin clipped initially before release. Bi-weekly sampling around enclosures and within the control portion of the enclosure was conducted to determine if minnows were escaping. Fin clipping was discontinued after 17 June 1985, because of fungal development.
Fish Collections
Minnows were collected by shocking within enclosures every 2 weeks during crepuscular hours. Minnows were preserved in 70% ethyl alcohol and stomach contents were removed later to identify contents. Food items were identified, counted, dried at 65 C for 8
24 hours and weighed on a HSl Mettler analytical balance to the nearest 0.01 mg. Minnows which were shocked and removed from the enclosures were replaced to maintain a constant stocking level.
Aquatic Invertebrate Sampling
Water column and benthic samples were collected on 6 dates between 24 May and 15 July in 1985 and 1986. Cells were subdivided into 6 transects perpendicular to the shoreline. One transect was selected randomly on each sample date. Each transect was sampled once at 3 locations: near the shoreline, midway and at the deeper end. One water column and one benthic sample was collected at each location. Benthic and water column samples were separated to detect differences that might arise. from fish predation. Benthic organisms were collected with a modified core sampler described by Swanson {1978a). Water column samples were collected with a column sampler similar to the one described by Swanson {1978b). Water column and benthic samples were poured through a #30 sieve and subsequently preserved in 70% ethyl alcohol. Samples were sorted and keyed to the taxonomic level of family for Diptera, Ephemeroptera, Coleoptera, Hemiptera, and Gastopods; to Suborder for Odonata: and to Order for other invertebrates. Invertebrates were counted, air dried and weighed to the nearest 0.01 mg on a HSl Mettler analytical balance. Analysis was not done for Copepods, Cladoceran, Oligacheates, and Collembolla, because of their potential to pass through a #30 sieve. 9 Taxa Composition
Taxa composition in stocked and control enclosures were compared using 2 similarity indices; the percentage similarity of community {PSC) as discussed by Whittaker (1952) and the coefficient of similarity (B) Pinkham and Pearson (1976). The coefficient of community was used to compare taxa similarity between stocked and control enclosures. These indices were selected because of favorable reviews (Brock 1977, Whittaker and Fairbanks 1958, and Washington 1984) and their ability to evaluate species occurrence and abundance. Two similarity indices were used because of reported inconsistencies between indices (Brock 1977). The B index is sensitive to changes in rare taxa numbers (Brock 1977), while the ?SC index emphasizes changes in abundant taxa {Whittaker 1952). Brock (1977) concluded that B index may over emphasize changes in rarer species and underestimate changes in more abundant species. The abundance of an invertebrate taxon is important in determining its availability to waterfowl (Swanson 1984, Serie and Swanson 1976). Samples were divided into 3 depths, shallow (18-48 cm), medium (49-59 cm). and deep { > 59 cm) to evaluate potential impacts of fish predation on taxa at different depths.
Water Chemistry and Selected Physical Measurements
Water samples were collected in May and August in 1985 and in June of 1986. Parameters measured included total alkalinity, color, turbidity, conductivty, pH and nutrients including total 10 nitrogen, total phosphorus, calcium, magnesium, sulfate and chloride. Analysis was conducted by the State Laboratory of Hygiene, Madison, Wisconsin. Total alkalinity (titrations}, conductivity (meter), pH (indicator dye-color comparator), dissolved oxygen (titration), and temperature were done weekly from May to July both years.
Aquatic Plant Sampling
Aquatic plant samples were collected in conjunction with water column samples. All living portions of plants in the water column samples were washed to remove attached invertebrates .. Aquatic plants were separated by species, force air dried at 80 C for 24 hours, and weighed to the nearest 0.001 g. Major plant communities were mapped· in each enclosure in early July in both years.
Data Analysis
Data were analyzed by year because of modification to the enclosures between 1985 and 1986. Invertebrate data were converted to 1n for non-parametric testing. Non-parametric testing was neccessary because of the contiguous distribution of invertebrates (Elliott 1977}. Paired t-tests were used to analyze 1986 invertebrate data. In 1985 Student t-tests were used because of missing sample sites due to low water levels and poor preservation of many samples. In presentations of invertebrate statistical analysis,~ values and probabilities represent results of 1n. transformed values, however means equal 11 actual values. Invertebrate water column number and biomass are reported per cubic meter and per square meter for comparison with other studies. Weekly water chemistry data were analyzed with a Student t-test. Vegetation was analyzed with paired t-tests. All analysis was done on a SPSSx statistical programming package.
RESULTS
3 Average densities of total invertebrates/min 1985 and 1986 were (X = 142,619) and (X = 24,330), respectively. Invertebrate numbers and biomass in 1985 water column or benthic samples were not significantly different(~< 0.05) between stocked and unstacked enclosures (Table 1). The stocking condition in 1986 did not influence(~< 0.05) invertebrate numbers and biomass in water column or benthic samples (Table 2). The central mudminnow was present in both stocked and control portions of enclosures in 1985. In 1986 both pumpkinseeds and mudminnows were present in stocked and control enclosures. The study design did not account for this type of intrusion. Stocked pens in 1986 contained more pumpkinseeds and mudminnows than did control pens. In 1985 effort of removal was not equal between stocked and control enclosures, so it was not possible to determine what influence mudminnows may have had on the study. Because it is impossible to determine what degree mudminnows could potentially influence the experiment in 1985, only basic statistical comparisons will be made. 12
Table 1. Student t-tests between stocked and control enclosure invertebrates (numbers and biomass) in 96 water column and benthic samples in Oakridge WPA, 1985. Values for~ and probabilities represent results of nonparametric tests after ln conversions.
Sample Type Stocked Control !. Value
Water Column 3 n/m 136,618 128,242 2 0.05 0.96 n/m 14,647 14,818 3 Biomass/m 115.650 83.632 2 1.13 0.26 Biomass/m 20.717 9.185 Benthic 2 n/m 9,889 10,488 -1.09 0.29 2 Biomass/m 5.131 6.782 1.67 0.10 13
Table 2. Paired t-tests between stocked and control enclosure invertebrate (numbers and biomass) in 107 water column and benthic samples in Oakridge WPA, 1986. Values for! and probabilities represent results of nonparametric tests after ln conversions.
Sample Type Stocked Control .t. Value
Water Column 3 n/m 19,456 17,668 2 0.50 0.62 n/m 10,590 10,095
3 Biomass/m 10.193 10.396 2 1.24 0.22 Biomass/m 6.044 6.895
Benthic 2 n/m 5,729 5,806 -0.52 0.61 2 Biomass/m 2.513 4.091 0.74 0.46 14 Invertebrate Composition
Comparison of the PSC and B similarity indices displayed different results between taxa composition in stocked and control enclosures, 1986. The PSC taxa composition indicies for numbers (95%) and biomass (63%) were much higher than the B indices for numbers {54%) and biomass (36%) (Table 3-4). Percent similarity coefficient (numbers) were similar at shallow {89%), medium (86%) and deep (88%) depths between stocked and control enclosures (Table 5-7). Biomass PSC indices for taxa composition between stocked and control enclosures were 82 \ at shallow, 27\ at medium, and 59% at deep depths. During 1986, midge and mayfly densities comprised 59 and 58\ of total invertebrate numbers in stocked and control enclosures, respectively. Total gastropoda biomass comprised 61% of stocked and 31% of control enclosures. Midge, mayfly, and gastropod taxa were analyzed separately because of their importance to waterfowl diets and dominant presence in St. Croix County WPAs. Numbers and biomass of the 3 invertebrate taxa were not significantly different (P< 0.05) between stocked and control -enclosures in the water column or benthic samples during 1986 (Tables 8-9). Average biomass of midge and mayfly in the water column were less in stocked enclosures than in controls, however differences were not significant at the P < 0.05 level (Table 10). 15
Table 3. Comparison of percentage similarity of community (PSC) and coefficient of similarity (B) indices of taxa composition (numbers) in stocked and control enclosures in Oakridge WPA, 1986. Stocked Control Taxa n n
Mayfly (Caenidae) 693 19.85 705 21.42 Caddisfly (Trichoptera) 19 0.54 23 0.70 Lepidoptera 4 0.11 2 0.06 Dragonfly (Anisoptera) 3 0.09 3 0.09 Damselfly (Zygoptera) 70 2.00 55 1.67 Pigmy backswimmer (Pleidae) 50 1.43 36 1.09 Water boatmen (Corixidae) 5 0.14 1 0.03 Water scorpion (Nepidae) 1 0.03 Water treader (Mesoveliidae) 3 0.09 Leaf hopper (Homoptera) 1 0.03 Midge (Chironomidae) 1364 39.07 1205 36.62 Biting Midge (Ceratopogonidae) 315 9.02 280 8.51 Cranefly {Tipulidae) 1 0.03 1 0.03 Soldierfly {Stratiomyidae) 1 0.03 Deerfly {Tabanidae) 5 0.14 6 0.18 Marshfly {Sciomyzidae) 2 0.06 1 0.03 Mosquito {Culicidae) 1 0.03 Scavenger beetle (Hydrophilidae) 10 0.29 6 0.18 Crawling water Beetle {Haliplidae) 1 0.03 Predacious diving ·Beetle (Dytiscidae) 1 0.03 4 0.12 Scirtidae 1 0.03 Staphylinidae 1 0.03 Leaf Beetle (Chrysomelidae) 2 0.06 2 0.06 Weevil {Curculionidae) 1 0.03 1 0.03 Leech (Hirundinae) 23 0.66 7 0.21 Water mite (Hydracarina) 26 0.74 19 0.57 Spider (Aranae)- 2 0.06 2 0.06 Ant {Hymenoptera) 1 0.03 1 0.03 Scud {Amphipods) 236 6.76 287 8.72 Orb Snail {Planorbidae) 601 17.22 576 17.50 Pouch Snail (Physidae) 46 1.32 45 1.37 Pond Snail (Lymnaeidae) 7 0.20 6 0.18 Pelecypoda 1 0.03 10 0.30 Total 3491 3291 PSC = 95%, B = 54% 16
Table 4. Comparison of percentage similarity of community (PSC) and coefficient of similarity (B) indices of taxa biomass (mg) in stocked and control enclosures on Oakridge WPAs, 1986. Stocked Control Taxa Biomass Biomass (mg) (mg)
Mayfly (Caenidae) 138.00 6.87 134.00 5.86 Caddisfly (Trichoptera) 28.00 1.39 76.00 3.32 Lepidoptera 2.52 0.13 0.31 0.01 Dragonfly (Anisoptera) 65.00 3.24 0.52 0.02 Damselfly (Zygoptera) 148.00 7.37 65.00 2.84 Pigmy backswimmer (Pleidae) 9.08 0.45 11.00 0.48 Water boatmen (Corixidae) 0.37 0.02 0.01 T Water scorpion (Nepidae) 0.04 T Water treader (Mesoveliidae) 0.08 T Leaf hopper (Homoptera) 1.03 0.05 Midge (Chironomidae) 67.03 3.34 92.03 4.02 Biting midge (Ceratopogonidae) 20.00 1.00 16.00 0.70 Cranefly (Tipulidae) 0.71 0.04 1.70 0.07 Soldierfly (Stratiomyidae) 1.90 0.08 Deerfly (Tabanidae) 2.21 0.11 7.57 0.33 Marshfly (Sciomyzidae) 1.56 0.08 0.01 T Mosquito (Culicidae) 0.01 T Scavenger beetle (Hydrophilidae) 1.22 0.06 1.09 0.05 · Crawling water Beetle (Haliplidae) 0.27 0.01 Predacious diving Beetle (Dytiscidae) 2.33 0.12 0.11 0.01 Scirtidae 0.37 0.02 Staphylinidae 0.22 0.01 Leaf beetle (Chrysomelidae) 1.80 0.09 0.36 0.02 Weevil (Curculionidae) 0.13 0.01 0.23 0.01 Leech (Hirundinae) 238.00 11.86 1100.00 48.10 Water mite (Hydracarina) 2.15 0.11 1.43 0.06 Spider (Aranae) 0.09 T 0.10 T Ant (Hymenoptera) 0.01 T 0.01 T Scud (Amphipods) 37.00 1.84 46.00 2.01 Orb snail (Planorbidae) 575.00 28.64 565.00 24.70 Pouch snail (Physidae) 102.00 5.08 115.00 5.03 Pond snail (Lymnaeidae) 554.00 27.60 24.00 1.05 Pelecypoda 9.98 00.50 27.00 1.18 Total 2007.45 2287.14 PSC = 63\, B = 36\ T = Taxa with <0.01 \ of the total invertebrate biomass. 17
Table 5. Percentage similarity of community (PSC) indices of taxa in stocked and control enclosures at depths (18-48 cm) in Oakridge WPA, 1986. Stocked\ Control\ Taxa Numbers Biomass Numbers Biomass
Mayfly (Caenidae) 16.80 16.37 14.00 12.43 Caddisfly (Trichoptera) 00.30 00.24 00.29 01.04 Lepidoptera 00.14 00.11 Dragonfly (Anisoptera) 00.01 00.10 00.43 00.29 Damselfly (Zygoptera) 02.30 24.55 03.03 15.26 Pigmy backswimmer (Pleidae) 01.30 02.32 02.30 01.44 Water boatmen (Corixidae) 00.10 00.01 Water treader (Mesoveliidae) 00.14 00.03 Leaf hopper (Homoptera) 00.10 00.47 Midge (Chironomidae) 46.40 08.18 39.39 06.22 Biting Midge (Ceratopogonidae) 07.40 01.54 08.37 01.09 Cranefly (Tipulidae) 00.10 00.32 Deerfly {Tabanidae) 00.20 00.74 00.14 00.80 Marshfly {Sciomyzidae) 00.10 00.56 Scavenger beeetle (Hydrophilidae) 00.57 00.55 Crawling water Predacious diving Beetle {Dytiscidae) 00.14 00.01 Leech {Hiriundinae) 00.11 00.34 00.14 00.05 Water mite {Hydracarina) 01.20 00.37 01.01 00.19 Spider (Aranae) 00.10 00.04 Scud (Amphipods) 06.30 02.94 07.94 06.22 Orb snail (Planorbidae) 15.70 30.92 20.35 33.10 Pouch snail (Physidae) 01.20 10.00 01.44 18.65 Pond snail (Lymnaeidae) 00.14 01.67
PSC Number= 89%, PSC Biomass= 82\ 18
Table 6. Percentage similarity of community (PSC) indices of taxa in stocked and control enclosures at depths (49-59 cm) in Oakridge WPA, 1986.
Stocked\ Control% Taxa Numbers Biomass Numbers Biomass
Mayfly (Caenidae) 18.34 02.87 15.32 09.83 Caddisfly (Trichoptera) 00.67 02.27 00.74 05.67 Lepidoptera 00.45 00.30 00.12 00.05 Dragonfly (Anisoptera) 00.11 T Damselfly (Zygoptera) 01.68 03.71 01.96 08.32 Pigmy backswimmer (Pleidae) 02.13 00.13 00.49 01.06 Midge (Chironomidae) 30.54 01.50 38.60 16.27 Biting Midge (Ceratopogonidae) 11.19 00.70 07.23 01.50 Deerfly (Tabanidae) 00.22 00.02 00.25 00.43 Marshfly (Sciomyzidae) 00.12 T Scavenger beetle (Hydrophilidae} 00.78 00.09 00.12 T Crawling water Beetle (Halipidae} 00.12 00.10 Predacious diving Beetle (Dytiscidae) 00.25 00.02 Leaf beetle (Chrysomelidae) 00.22 00.02 Weevil (Curculionidae} 00.12 00.09 Leech (Hiriundinae) 02.13 00.31 00.25 00.23 Water mite (Hydracarina} 00.34 00.02 00.37 00.17 Spider (Aranae} 00.12 00.03 Ant (Hymenoptera} 00.12 T Scud (Amphipods} 11.74 01.91 10.05 04.54 Orb snail (Planorbidae) 18.00 13.15 21.45 34.79 Pouch snail (Physidae) 00.67 02.27 01.59 16.64 Pond snail (Lymnaeidae} 00.78 66.25 00.12 00.06 Pelecypoda 00.49 00.03
PSC Number= 86%, PSC Biomass= 27\
T = Taxa which had number or biomass that made up <0.01 \ of the total invertebrate number or biomass 19
Table 7. Percentage similarity of community (PSC) indices of taxa in stocked and control enclosures at depths of >59 cm in Oakridge WPA, 1986. Stocked% Control% Taxa Numbers Biomass Numbers Biomass
Mayfly (Caenidae) 22.19 06.86 28.56 04.67 Caddisfly (Trichoptera) 00.50 00.29 00.72 03.22 Dragonfly (Anisoptera) 00.07 06.50 Damselfly (Zygoptera) 02.36 06.54 00.97 00.83 Pigmy backswirnmer (Pleidae) 01.22 00.29 00.85 00.23 Water boatmen (Corixidae) 00.29 00.04 00.06 T Water scoirpion (Nepidae) 00.06 00.02 Water treder (Mesoveliidae) 00.12 00.01 Midge (Chironomidae) 41.16 03.11 34.60 01.94 Biting Midge (Ceratopogonidae) 08.80 01.05 09.12 00.55 Cranefly {Tipulidae) 00.06 00.09 Soldierfly (Stratiomyidae) 00.06 00.06 Deerfly (Tabanidae) 00.07 00.05 00.18 00.03 Marshfly (Sciomyzidae) 00.07 00.03 Mosquito (Culicidae) 00.07 00.05 Scavenger beetle (Hydrophilidae) 00.21 00.05 00.06 00.01 Predacious diving Beetle (Dytiscidae) 00.07 00.25 00.06 T Scirtidae 00.06 00.02 Staphylinidae 00.07 00.02 Leaf beetle (Chrysomelidae) 00.12 00.02 Leech (Hiriundinae) 00.21 25.18 00.24 61.06 Water mite (Hydracarina) 00.79 00.12 00.48 00.03 Spider (Aranae) 00.07 T 00.06 T Ant {Hymenoptera) 00.07 T Scud (Amphipods) 03.51 00.95 07.31 01.00 Orb snail {Planorbidae) 16.25 38.58 14.55 21.95 Pouch snail (Physidae) 01.86 05.89 01.15 01.67 Pond snail (Lymnaeidae) 00.12 01.17 Pelecypoda 00.07 01.07 00.36 01.44
PSC Number= 88%, PSC Biomass= 59%
T = Taxa which had numbers or biomass that made up <0.01 % of the total invertebrate number or biomass 20
Table 8. Paired t-test results of midge (Chironomidae), mayfly (Caenidae), and gastropod (Planorbidae, Lymneadae, and Physidae) populations between stocked and control enclosures in Oakridge WPA, 1986.
3 2 Sample Type n/M n,/M .t. Value .f
Midge Water column Stocked 7,959 4,650 1.82 0.07 Control 6,918 4,297
Benthic Stocked 2,433 -0.42 0.67 Control 2,734 Mayfly Water column Stocked 3,924 2,292 0.77 0.44 Control 3,827 2,377
Benthic Stocked 0.00 0.99 Control
Gastropod Water column Stocked 4,560 2,667 0.57 0.57 Control 4,430 2,636
Benthic Stocked 1,615 0.33 0.74 Control 1,430 21
Table 9. Paired t-test results of midge {chironomidae}, mayfly (Caenidae} and gastropod (Planorbidae, Lymneidae, and Physidae} biomass between stocked and control enclosures in Oakridge WPA, 1986.
Sample Type Biomass Biomass ,t_ Value g/M3 g/M.2
Midge Water column Stocked 0.393 0.229 0.88 0.38 Control 0.511 0.317
Benthic Stocked 0.105 -0.22 0.83 Control 0.112 Mayfly Water column Stocked 0.785 0.459 -0.26 0.79 Control 0. 760 0.472
Benthic Stocked 0.278 -0.05 0.96 Control 0.294 Gastropod Water column Stocked 8.627 5.043 1.43 0.16 Control 4.400 2.619 Benthic
Stocked 3.865 0.35 0.73 Control 11.010 22
Table 10. Paired t-test results between stocked and control enclosures of midge (Chironomidae) and mayfly (Caenidae), average biomass (mg) in Oakridge WPA, 1986.
Sample Type Stocked Control !. Value
Midge Water column 0.06 0.17 -1.37 0.18 Benthic 0.05 0.04 0.58 0.57 Mayfly Water column 0.21 0.26 -1.49 0.14 Benthic 0.27 0.23 0.70 0.49 23 Vegetation
No significant {i < 0.05) differences in total number of stems and plant biomass between stocked and control enclosures were observed in 1985 or 1986 {Table 11). In 1985 emergent plant taxa were dominant {Table 12), while in 1986 submergent plants were more common {Table 13). Differences in plant communities between 1985 and 1986 were due probably to differences in the mean water column sample depths between 1985 (X = 20cm) and 1986 (X = 56cm). Vegetative composition and structure were similar between stocked and control enclosures within years of sampling. Watercolumn samples were dominated by 5 taxa; Myriophylum spp., Ceratophylurn spp., Potamogeton zosteriformis, ~- gramineus and natans. and Nymphea spp. in 1986. Biomass and number of 2 stems/m of these species·were compared separately from other taxa. Only biomass was compared for Myriophylum and Ceratophylum spp., because samples of these taxa often contained only portions of plants. 2 The number of stems and biomass/m of dominant plant taxa in stocked and control enclosures were not significantly {i < 0.05} different (Table 14).
Fathead Minnow Pood Habits
Measurable amounts of food ( >0.1 mg) were found in 62 fathead minnow stomachs in 1985 and 114 in 1986. Periphyton was the dominant food of fathead minnows in 1985 and was important in 1986. Periphyton appeared in 98% of 1985 fathead stomachs and 24
Table 11. Results of 1985 t-test, and 1986 paired t-test analysis between mean total vegetation stem numbers and biomass/~in stocked and control enclosures in Oakridge WPA.
Sample Type Stocked Control i Value
1985 Number stems 502 429 0.81 0.42
Biomass 96.4 125.4 -0.99 0.32
1986 Number stems 348 342 0.11 0.91
Biomass 73.9 69.9 0.43 0.67 25
Table 12. Frequency of occurrence and aggregate% dry weight of plant taxa in stocked and control enclosures in Oakridge WPA, 1985.
Taxa STOCKED CONTROL Freq. I Aggr. % Freq.% Aggr. %
Carex lanuqinosa 1 2 6 5
~ rastrata 1 T
Carex camosa 1 5
~ spp. 1 T 1 T
Ceratophylum-Myriophyllum 26 12 32 11 Phalaris arundinacea 15 35 26 49 Potamoqeton zosteriforrnis 6 2 1 1 L. qramineus & natans 6 2 6 3 Sparganiurn spp. 3 14 4 10
Lernna spp. 12 T 7 T
Spartina pectinatas 8 16 1 2 Agropyron respens 1 T Saqittaria latifolia 7 3 7 6 Circuta bulbifera 1 T 1 T Scirpus cyperinus 1 2 Scirpus validius 1 2 Juncus bal ticus 1 T 1 1 No vegetation 40 36 26
Table 13. Frequency of occurrence and aggregate\ dry weight of plant taxa in stocked and control enclosures in Oakridge WPA, 1986.
Taxa STOCKED CONTROL Freq. \ Aggr. \ Freq. \ Aggr. \
Unknown grass 1 T
Unknown 2 T
Nymphea spp. 7 6 8 10
Carex comosa 1 T
Ceratophylum demersum 32 22 34 34
Myriophyllum spp. 31 24 28 16
Potamogeton filiformis 2 T 2 1
Potamogeton natans 1 T
Potamogeton zosteriformis 16 5 24 7
L qramineus & natans 38 27 45 30
Sparganium spp. 2 3
Typha spp. 1 T
Sagittaria latifolia 6 5 3 1 cirpus validius 1 1
Naias spp. 6 4 3 T
No vegetation 11 13 27
2 Table 14. Paired t-test results of dominant plant taxa/m between stocked and control enclosures in Oakridge WPA, 1986.
Sample Type Stocked Control 1 Value
Myriophylum spp. Biomass {gm) 49.7 38.7 0.71 0.50 ~eratophylum demersum Biomass {gm) 46.2 34.2 0.82 0.43 Potamogeton zosteriformis Number stems 234.0 286.0 -0.64 0.53 Biomass {gm) 9.0 14.3 -1.34 0.19 f2t1mogeton gramineus & natans Number of stems 227.0 260.0 -0.66 0.51 Biomass {gm) 30.0 31.3 -0.21 0.83 Nympbea spp. Number of stems 94.0 94.0 0.00 1.00 Biomass {gm) 29.5 41.9 -0.47 0.65 28 made up 89% in APDW of their diet. Invertebrates followed in importance with 56% frequency of occurrence and 4% APDW. Ostracods were the most important invertebrate with 48% frequency of occurrence and 3% APDW followed by Ceratopogonidae with 5% frequency of occurrence and 1% APDW (Table 15}. The diet of fathead minnows was different in 1986. Invertebrates made up the major portion of fathead minnow diets in 1986. Invertebrates were recorded in 89% of fathead minnow stomachs and comprised 32% APDW. Ostrocods remained the major invertebrate food item {65% frequency of occurrence} but were lower in biomass (2% APDW}. Chironomids were the most important invertebrate prey in 1986, by weight (8% APDW} and occurred in 42% of the fathead minnow stomachs (Table 16). Periphyton remained the most important food item by weight (56% APDW) in 1986, and occurred in 73\ of the stomachs.
Water Chemistry
Water chemistry parameters remained constant between stocked and control enclosures in May and July 1985. Alkalinity and conductivity decreased from May to July in 1985. Turbidty was 4 higher in the July samples. Total N and P, Ca, Mg, So, and Cl concentrations were similar between stocked and fishless enclosures (Table 17}. Nutrient concentrations were slightly higher between May and July samples. Turbity in stocked pens was higher due to the presence of a muskrat in one pen. Increased nutrient 29
Table 15. Fathead minnow food habits during May-August 1985 at Oakridge WPA, northwestern Wisconsin, {.n = 62).
\ Freq. of APDW Aggr. Taxa n Occurrence ' Periphyton 98 98 89 Algae 2 T T
Detritus 37 1 4 Total invertebrates 767 56 1 4
Ostracods 755 48 1 3 Hydracarina 6 10 T T
Caenidae 1 2 T '1'
Ceratopogonidae 3 5 T 1
Chironomidae 2 3 T T 30 Table 16. Fathead minnow food habits during May-August 1986 at Oakridge WPA, northwest Wisconsin, (n = 114}. % Freq. APDW Aggr. Taxa Occurrence ' Periphyton N/A 73 68 56 Filirnentous algae N/A 7 T T Detritus N/A 35 9 11
Fish eggs 12 3 2 2 Total Invertebrates 1163 89 23 32 Ostracods 833 66 T 2 Cladocera 104 26 T 1
Copepods 56 20 T T Amphipods 8 6 T 1
Hydracarina 9 5 T T
Planorbidae 15 7 2 4 Unknown 25 13 4 5 Chironornidae 78 42 3 8 Larvae 62 38 2 5 Pupae 1 1 T T Adults 15 9 T 3 Ceratopogonidae 16 9 1 3 Larvae 15 9 1 3 Adults 1 1 T T
Caenidae 12 9 3 5
Ceongrionidae 2 2 4 1
Tabanidae 1 1 1 T
Stratiomyidae 1 1 T 1
Notonectidae 1 1 T T
Coleoptera 2 2 1 T 31
Table 17. Limnological analysis from 6 stocked and control enclosures in May and July on Oakridge WPA, 1985.
Variable H•!: lIYlI Mean Stocked Control Stocked Control
Chemical Parameters Alkalinity 144.0 138.0 112.0 111.0 (Mg/L)
pH 7.5 7.5 7.5 7.5 Conductivity 285.0 288.0 230.0 223.0 (Omhos) Color 35.0 33.0 25.0 28.0 Turbidity 4.5 1.9 5.6 15.8 (JTU)
Ion and Nutrient Concentrations (mg/L)
Ca 31.0 30.0 18.0 19.0 Mg 18.0 17.0 17.0 17.0 4 so 3.8 3.6 3.9 3.8 Cl 6.1 6.2 6.3 6.7 Total-P 0.051 0.046 0.120 0.695
Total-N 0.98 1.8 1.1 3.0 32
levels in the 1985 July control enclosures may have been associated with higher turbidity. Mean weekly water chemistry samples including pH, alkalinity, conductivity and dissolved oxygen did not significantly differ at the~< 0.05 level between stocked and control enclosures in 1985 (Table 18). Water quality in 1986 appear to be similar in stocked and control enclosures (Table 19}. Analysis of 1986 weekly water chemistry data showed no differences at the~< 0.05 level for all parameters between stocked and control enclosures (Table 20).
DISCUSSIOII
Fathead minnow predation did not appear to impact invertebrate populations in benthic or water column samples. However, it is difficult to be certain what effects stocking had on invertebrate populations in 1985 because of an undetermined number of central mudminnows in stocked and control enclosures. This species is a bottom dweller which burrows in the mud and is difficult to remove by electric shocking. Central mudminnows may also have burrowed under the enclosures. The central mudminnow is an opportunist, feeding mainly on invertebrates (Paszkowski 1983). Mudminnows and pumpkinseeds were found in enclosures in 1986. Pumpkinseeds spend much of their time in shallow water (Becker 1983), feeding primarily on insect larvae and Gastropods (Sadzikowski and Wallace 1976, Becker 1983). Predation by mudminnows and pumpkinseeds could have reduced invertebrate numbers to an undetermined amount. The study 33
Table 18. Student t-test results from weekly water chemistry data from Oakridge WPA, 1985. Values for i were not significant at the~< 0.05 level.
Chemical Standard i Value p Variable X Deviation
Temperature (C) Stocked 19.0 2.9 -0.07 0.94 Control 19.0 3.0 Alkalinity (mg/L) Stocked 118.2 12.0 -0.87 0.54 Control 120.1 11.0
pH (units) Stocked 7.31 0.33 -0.27 0.78 Control 7.33 0.30 Conductivity (umhos) Stocked 290.9 28.1 0.44 0.65 Control 288.6 26.4 2 Dissolved 0 (mg/L) Stocked 4.0 1.1 0.08 0. 93 .. Control 4.0 1.0 34
Table 19. Limnological analysis from 6 stocked and control enclosures on Oakridge WPA, May 1986.
Variable Stocked Control Mean
Chemical Parameters
Alkalinity 110.0 111.0 (Mg/L)
pH 8.3 8.3
Conductivity 226.0 228.0 (Umhos)
Color 27.0 29.0
Turbidity 4.5 4.3 (JTU)
Nutrient Ion Concentrations
Ca 19.0 20.0
Mg 16.0 16.0
S04 3.7 3.8
Cl 5.5 5.4
Total-P 0.038 0.036
Total-N 0.8 0.8 2 3 NO & NO 0.2 0.2 35
Table 20. Student t-test results from weekly water chemistry data from Oakridge WPA, 1986. Values for ,i were not significant at the~< 0.05 level.
Chemical Mean Standard .i Probability Variable Deviation Value
Temperature {C}
Stocked 20.5 0.9 0.00 1.0 Control 20.5 0.9 Alkalinity {mg/L}
Stocked 110.8 6.8 1.01 0.32 Control 108.8 6.6
pH {units}
Stocked 8.78 .59 -0.37 0.71 Control 8.83 .58 Conductivity {umhos}
Stocked 224.8 12.8 -0.08 0.93 Control 225.1 13.6 Dissolved 02 {mg/L) Stocked 2.7 0.4 0.30 0.76 Control 4.0 1.0 36 design did not account for this type of intrusion. In 1985, accurate records of removal of undesirable fish were unavailable and removal efforts were more intense in stocked enclosures. In 1986, the removal effort was constant between stocked and control enclosures and numbers of fish removed were recorded. Although more purnpkinseeds and mudminnows were found in stocked than in control enclosures, there were no differences (P < 0.05) in invertebrate numbers and biomass. Invertebrate populations may have already been impacted by an existing fish population, causing the fathead minnow to feed on more abundant available resources, particularly periphyton. The pens were in shallow water (X=20 cm) within emergent vegetation and fathead minnow mortality was high ip 1985 and they may have been displaced from their natural habitat. While electroshocking, few fish were captured in shallow water within emergent vegetation. Most fish were caught in slightly deeper water near the edge of the emergent vegetation and within submergent vegetation. This may account for the differences in food habits between·1995 and 1986. Differences in food habits from many studies suggest the fathead minnow is an opportunist selecting different food items in different regions. Regional differences in feeding have been observed in Wisconsin. Our 1985 data agree with Williamson (1939) who reported that stomach contents from fathead minnows from northern Wisconsin consisted of algae and organic matter. In southeastern Wisconsin, the fathead was observed feeding on 37 the bottom for insect larvae which formed over 90% of its diet (Cahn 1927). In 1986 more fathead minnow stomachs contained invertebrate foods, however, periphyton was more important by weight. Biomass of taxa varied between stocked and control enclosures, primarily at medium depth~. The biomass taxa composition coefficient showed only 27% similarity. The average weight of individual midge and mayfly larvae was less in stocked enclosures, although not significantly different at~< 0.05 . Numbers of invertebrates can increase in fish predated environments due to removal or reduction of invertebrate predator species (Gilinsky 1984). Numbers may remain constant while size or biomass of invertebrates are reduced (Galbraith 1967, Mittelbach 1984). Fathead minnow or mudminnow predation on larger invertebrate instars may explain smaller midge and mayfly average biomass. If the experiment were to occur over a greater time period invertebrate size, composition and abundance may have become significantly different between stocked and control enclosures. The littoral zone of Oakridge WPA had dense stands of aquatic vegetation. Gilinsky (1984) reported that macrophytes may serve as cover from fish predators for invertebrates, and structural complexity decreases predator efficiency. Wetland zones with dense stands of aquatic vegetation may provide a barrier from fish predation to prevent significant reductions in invertebrate foods for waterfowl. Invertebrate numbers in 1985 were higher than in 1986. Waterfowl invertebrate food resources in areas 38 with sparse emergent vegetation may be impacted greater by fish predation because of greater mobility of fish in these areas. This study suggests that there is a potential dietary overlap between food habits of fathead minnows and waterfowl. The primary nesting waterfowl Qn the study area and in Wisconsin are blue-winged teal (Anas discors) and mallards (Evrard and Lillie 1985, Jahn and Hunt 1964). Waterfowl ducklings feed primarily on invertebrates in the first weeks of development but gradually change to a plant diet as they mature (Cottam 1939, Mendall 1949, Sugden 1973). Periphyton was the staple food of fathead minnows in this study. Fathead minnows consumption of periphyton and organic matter have little potential overlap with duckling diets. However, fathead minnow diets consisting of invertebrate foods may impact invertebrate food resources used by resident ducklings depending on abundance and availability of invertebrate prey. Ruddy duck (Oxyura iamaicensis) ducklings are considered excellent strainers, eating primarily zooplankton (Collias and Collias 1963). However, even the ruddy duck did not strain the very small ostracods and mites found in fathead stomachs. In 1986, fathead food habits reflected greater potential for competition with waterfowl. Chironomids are often the dominant invertebrate food item in waterfowl producing wetlands (Maher 1984, Maher and Carpenter 1984, Mauser 1985, this study). The availability of emerging chironomids coincide with waterfowl breeding in Sweden and Australia (Danell and Sjoberg 1977, Sjoberg 39 and Danell 1982, Maher and Carpenter 1984). Lack of insect foods, particularly chironomids, may lower mallard duckling survival (Street 1977). Chironomids constituted an important food item of fathead minnows in 1986, occurring in 46% of the stomachs. However, minnow predation did not appear to impact chironomid populations in this study. Invertebrate densities in the study area are comparable to populations in good waterfowl producing areas (Mauser 1985). Predation by fathead minnows does not appear to significantly reduce waterfowl foods due to high densities of invertebrates on St. Croix County wetlands. Availability of invertebrates to breeding waterfowl and broods on St. Croix County wetlands is unknown. It is not known what higher than normal stocking rates of fathead minnows may have on invertebrate foods. Fall and winter food habits of fathead minnows on wetlands in northwest Wisconsin are unknown and should be explored for potential impacts on invertebrate populations during these periods.
MANAGEMENT IMPILCATIONS
Many wetlands in the pothole region of Wisconsin currently have deep basins with narrow fringes of littoral zones as the result of prolonged above normal precipitaion in the region. Deep water can reduce invertebrate availablity to feeding waterfowl (Nilsson 1972, Laperle 1974, Reid 1985). Deep basin wetlands normally support fish populations. Manipulations of water levels or wetland basins to achieve a shallow hemi-marsh condition would increase availability of invertebrates to waterfowl. Shallower wetlands may reduce fish populations by 40 increasing chances of winterkill, reducing potential competition between fisheries and waterfowl for invertebrate foods. Stocking bait fish on Waterfowl Production Areas is not recommended because of the potential for fathead minnows to compete for waterfowl invertebrate foods. Further research on interactions of natural populations of fathead minnows and conwnunities of fish with waterfowl is needed to determine the compatibility of producing fish and waterfowl on Waterfowl Production Areas. Harvest of bait fish may benefit waterfowl if done when disturbance to waterfowl is minimal. Presently bait dealers would need access to WPA's to harvest bait-fish. Use of heavy vehicles with live tanks may be neccessary to efficiently remove bait fish from wetlands. Movements of bait dealers on WPA,s could negatively affect waterfowl production by increasing predation on waterfowl broods and nests by the creation of predator lanes. Reproduction could be impacted by the daily disturbance which is neccessary to harvest bait-fish. The breeding season is a critical period in the life cycle of waterfowl. Waterfowl are often under critical energy deficits and human disturbance during this period could cause the abandonment of pair territories, nests and brooding rearing areas. Waterfowl production areas were purchased for the purpose of producing waterfowl and wetland species. Federal and state agencies should prohibit activities which would negatively impact the natural balance of wetland ecosystems and production of waterfowl. 41 LITERATURE CITED
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Appendix A. Number of undesired central rnudminnows and pumpkinseeds in stocked and control enclosures in Oakridge WPA, 1986.
Mudrn;i,nnow§ Pumekinseeds Enclosure Stocked Control Stocked Control
Pen 1 7 3
Pen 2 14 2
Pen 3 23 18 4
Pen 4 7 Pen 5 47 12 8
Pen 6 15 1
Total 113 32 12 4 Mean 32 5 2 0.6 48
APPENDICES B-K. Impacts of stocking fish communities on Waterfowl Production Area invertebrate populations. 49 The Impacts of Stocking Fish Conmunities on Waterfowl Production Area Invertebrate Populations.
STUDY AREA
The study was conducted in 1986 in the pothole region of north-west Wisconsin, 1 (km) north of Deer Park in Polk County.
Experiments were conducted in 4 wetlands known as the Kostka ponds 2a, 2b, 1-east and 1-west. Wetlands were choosen from the this complex because of their similar water chemistry, and aquatic invertebrate and vegetation communities. The Kostka ponds have not harbored fish populations since at least 1982. Ponds 2a and 2b were originally the same wetland separated .by a narrow littoral fringe. Ponds 2a and 2b were divided by a plastic sandbag barrier to prevent water and invertebrate movement between wetlands. Ponds 1-east and 1-west were originally the same wetland but were divided by a rock/gravel access road.
ME'l'IIODS
Pond 2a was stocked with 32 kg of fathead minnows on 12 May 1986, equivilant to natural populations of fathead minnows found in St. Croix County Waterfowl Production Areas (H. Bolton per. comm.), 2b was used as a fishless control. Pond 1-east was stocked on 12 May 1986 with fish characteristic of Wisconsin's prairie pothole WPAs, including yellow perch (6.8 kg), pumpkinseed (9.1 kg), golden shiners (1.5 kg), fathead 50 minnows (2.3 kg), and central mudminnow (1.5 kg). (H. Bolton per. comm.). Pond 1-west was used as a fishless control. Invertebrates were randomly collected using a modified stovepipe sampler 0.1 min diameter. Samples were collected by pushing the sampler into the wetland substrate until a seal was created. Water was removed and poured through a #30 sieve. Three benthos samples were taken inside the stovepipe sampler. During each of 5 sample periods, 3 column samples were collected randomly on both the stocked and fishless control ponds. Samples were placed in separate containers and preserved in 70% ethyl alcohol. Six pre-treatment invertebrate samples were collected during 1984-86 by the Wisconsin Department of Natural Resources (WDNR) on 2a, 2b, 1-east and 1-west before stocking. WDNR invertebrate collection methods were similar to this study, except that 2 core samples were collected (Evrard & Lillie 1987). Zooplankton were collected within 0.5 m of each invertebrate sample site. Zooplankton were collected by submersing a 5-gallon bucket in each wetland, invertebrates were concentrated with a #10 plankton net, placed in containers and preserved in 10% ethyl alcohol. Zooplankton were mixed thoroughly in containers, subsampled with a Hensen-Stemple pipet and placed in a 1 ml sedger-rafter cell. The subsampling procedure was repeated for each concentrated sample until at least 100 individuals were collected. Individuals were then extrapolated to numbers/liter. 51
Invertebrates were identified to order for Rotifers and Ostracods, suborder for copepods, family for insects, and lowest possible taxa for cladoceran with a l0x and 2.5x inverted compound scope. Plying and newly emerged aquatic insects on the shore line vegetation are the prefered food of small ducklings (Pehrsson 1979). The availability of flying and newly emerged aquatic insects was measured by using 3 floating emergent traps per pond. Each trap area was 0.5 m and covered with a plastic net cover leading to a capture chamber. Water chemistry information was collected from stocked and control ponds on 11 June and 16 July. Water chemistry work including total alkalinity (titrations), conductivity (meter), pH, dissolved oxygen and temperatures were recorded for each pond weekly between 9 June to 10 July. Aquatic plants were sampled using stovepipe sample collections. All-plants within the stovepipe sampler were collected, separated by species, oven dried, and weighed to the nearest 0.001 g on a Mettler HSl analytical balance. Before collecting plants, percent cover was estimated for each species as described by Daubenmire (1959).
RESULTS AIID DISCUSSION
Invertebrates were not affected by fathead minnow stocking. Invertebrate densities remained higher in the stocked ponds before and after stocking. Densities of emerging Diptera insects were lower in stocked ponds from May-July 1986. 52
Invertebrate densities were lower during June and early July in the fish complex stocked pond. Invertebrate densities were higher in control ponds on 22 May, 1986 and 13 July, 1986.
The 22 May, 1986 invertebrate sample was taken 11 days after initial stocking. Considering the short time in which fish populations were present it was unlikely any impacts on invertebrate numbers from fish predation would be observed. No differences in the average biomass of chironomidae larvae were observed (Appendix C). Average biomass of chironomids decreased in later samples. The resurgence of smaller instars of chironomid larvae could account for increased densities in the last samples from the fish complex stocked pond. Fish communities may impact emergent Diptera populations. Densities of emergent aquatic Diptera were consistently lower in fish complex stocked treatment. Zooplankton communities were not impacted by fathead minnow or fish complex treatments. Copepod densities were reduced in stocked treatments. It is likely that the study was too short in duration to evaluate impacts on zooplankton or aquatic invertebrate communities. Aquatic insects are probably most susceptible to predation while emerging. Emerging insects are probably more important to waterfowl because of their associations with the upper water surface, increasing availablity to foraging waterfowl. 53
The large vegetated literal zone of wetlands may prevent substantial predation of aquatic invertebrates by wetland fish except during emergence. Future studies should emphasize impacts of fish on emerging invertebrates and further evaluate the importance of emergent insects in waterfowl diets. 54 LITERATURE CITED
Daubenmire, R. 1959. A canopy-coverage method of vegetational analysis. Northwest Sci. 33:43-64.
Evarard, J. 0., and R. A. Lillie. 1987. Duck and pheasant management in the pothole region of Wisconsin. Wis. Dep. Nat. Resour. Prog. Rep. 114pp. Pehrsson, O. 1979. Feeding behavior, feeding habitat utilization, and feeding efficiency of mallard ducklings {Anas platyrhyncos L.) as guided by a domestic duck. Viltrevy 10:193-218. LO LO 2 lppendil B. Mean nmnber and biomass (g/m) of invertebrates collected from fish cOlll()le1 (PC) and fathead lllinnow (PM) stocked and control treatments on Kostka NPls in northwest Wisconsin, 19861.
P[e-treatmnts Treatments Taia and 23 Nay 6 June 22 June 10 July 4 June 25 April 22 Nay 6 June 17 June 3 July 13 July treatment 1984 1984 1984 1984 1985 1986 1986 1986 1986 1986 1986
l2t.ll. Invertebrates PM-Stocked 4166 5419 14839 9388 4388 4593 5582 7163 7292 11999 14741
PM-Control 4002 2528 7741 7600 2853 3541 2696 6704 7748 12784
PC-Stocked 5827 9967 7890 8862 2164 4531 5068 6642 10278 11548
PC-Control 10081 9509 9213 7723 2048 2353 3957 9778 21887 19020 10390 Chironollidae PM-Stocked 2858 4225 12870 7761 3224 3890 2109 3002 4183 9031 6093
PM-Control 2625 5561 6057 5546 1890 946 957 3288 3512 6333
PC-Stocked 2604 8067 6573 6678 2163 2300 1347 3961 5214 4693
PC-Control 4318 5136 5161 4836 1241 1107 1624 7313 15119 9491 1623 a Treatments consisted of 26 kg of fish in PC including: PIDIPkinseeds (431), yellow perch (331), fathead lllinnows (101), golden shiners (71), and central IIUdllinnows (71), and 32 kg of fathead lllinnows in PH. 56
Appendix C. Mean biomass {mg) of Chironomidae from fish complex (FC) and fathead minnow (PM) stocked and control ponds on Kostka WPAs in northwest Wisconsin, 1986.1,.
Treatment 22 May 6 June 17 June 3 July 13 July
PM-Stocked 0.53 0.39 0.31 0~17 0.21 PM-Control 0.39 0.35 0.23 0.23 0.16 PC-Stocked 0.39 0.21 0.29 0.28 0.14 PC-Control 0.25 0.23 0.37 0.25 0.16 a Treatments consisted of 26 kg of fish in re including: pumpkinseeds (431), yellow perch (331), fathead minnows (101), golden shinners (71), and central mudminnows (71), and 32 kg of fathead minnows in FM. 57 2 Appendix D. Mean Diptera and non-Diptera emergence (1/m) from fish complex stocked and control Kostka ponds in northwest Wisconsin, 1986 (N = 3). Date Diptera Emergence Non-Diptera Emergence Stocked ~ontu1l Stgcked contrgl
19 HaJ 29 47 1 5 21 Hay 61 87 3 11 23 May 87 164 17 15 28 May 21 44 5 1
30 May 27 89 6 3
1 June 33 77 21 5 3 June 26 135 12 3
5 June 10 147 11 2 7 June 24 111 7 1 9 June 37 183 7 1 12 June 16 183 1 3 16 June 29 45 0 5 18 June 35 199 1 3 20 June 20 136 13 5 22 June 11 105 7 6 24 June 33 172 1 0 26 June 34 107 2 1
28 June 75 216 3 2 30 June 61 175 1 5 2 July 43 146 1 4 4 July 79 176 3 9
6 July 63 73 6 5 8 July 112 62 1 12 58 2 Appendix E. Mean Diptera and non-diptera emergence (1/m} from fathead minnow stocked and control Kostka ponds in northwest Wisconsin, 1986 (M = 3). Date Diptera Emergence Non-Diptera Emergence ~tocked ~ontrgl §tocked Contrgl
19 May 29 17 11 5 21 May 107 .u 3 16 23 May 75 135 7 6
28 May 47 80 0 1 30 May 72 32 1 3 1 June 27 37 1 5 3 June 35 37 3 2
5 June 55 28 1 4 7 June 29 17 2 3 9 June 57 23 1 4
12 June 51 23 1 4
16 June 29 19 11 5 18 June 53 21 4 3
20 June 49 13 3 5
22 June 39 11 3 3 24 June 62 20 1 1
26 June 54 21 1 3 28 June 70 18 1 3 30 June 60 29 7 2 2 Jul1 33 21 3 3 4 July 68 43 2 5 6 Jul1 33 13 9 3 8 July 27 22 2 0 59
lppeadi1 r. Ne111mer of ia,ertebriles/liter ia 3 1oopl11tton s11ples collected fro1 stocked 11d control fish coaple1 poads 01 lostt1 IPAs ia northwest lisconsi1, 1986~.
Till 22 117 S June 11 June 3 J1)7 13 Jul1 Stocked Coatrol Stocked Coatrol Stocked Co1trol Stocked Control Stocked Control
Rotifer 113 as 101 80 11 '° 4' 3S '2 34 Ostncod 34 11 7 2S s 7 ' s 1rdncari11 1 1 2 1 Copepoll 44 30 47 Sl 36 S7 s 31 12 20 crclopoid 41 29 37 so 19 21 2 24 13 1 Calaaiod 1 1 ' 3 1 s 2 ' s 111p1li 79 3S 7l 132 61 140 2, ,2 14 103 Cladocen 113 80 128 113 m 114 46 '3 131 75 tolnbgus pedic:alllS 43 2 31 a 1 Bolopedio• gi•bern 4 I s a 3' m.bwspp. I 41 34 5 71 13 11 5 Siaocepbaly spp. 2 S£12bole•eci~ spp. 1 4 1 <) Ceriodaphnia spp. 14 JS 4 1' llliliuspp. streblocem smimdahs 1 23 2 3' 2' ' 28 SJ Jhocmtus spp. 4 Ch7dorinae 44 20 53 1, 103 14 19 2' 100 17 l!I.UiJ Jatissiu lppe1cli1 ,. (coatimcl) Tlll 22 llaJ S J11ae 17 Jaae 3 J1lJ 13 JulJ Stocked Control Stocked Control Stocked Control Stocked Coatrol Stocked Coatrol llm ,,,. ' Cuoboridae 3 2 1 1 1 b oner 5 2 2 1 1 Tobi m m m m 384 130 m 250 231 a Stocte4 treat•at coasisled of 2, kg of fisb i1cladi19: pu■pkinseeds (431), Jellot percb (331), fatbead ■iuo, (101), 9olde1 shianers, (7\), aad central ■ innovs (7\). b Ta1a iacllde Tricoptera, IJgoplera, Ceratopogoaidae, Culicidae, and Pleidae. 61 lppeadh G. leu 1111tber of i1,erte~rates/liter i131ooplaakto1 saaples collected fro• stocked and coatrol fathead 1inno1 po1ds lostka IPls i11orthvest liscosi1, l916f. Tua 22 liar 5 Jue 17 June 3 J11lr 13 Julr Stocked Cotrol Stocked Control Stocked Control stocked Control Stocked Coatrol Rotifer m m m m 213 no 91 81 m m Ostracods 357 341 53 153 57 S7 17 1 8 2 BydracariH 2 1 1 Copepod " n 1' m 27 '1 39 74 " 85 crclopoid '1 17 74 100 10 51 11 48 32 20 Cala■ iod 1 3 7 4 ' 11 a 40 nup11i 99 51 " m 35 119 " as 68 222 Cladocen m 211 m m 290 278 210 83 339 82 Polnhms udicglqs 2 s 13 3 PiaphaaosON spp. ' 1 BPhRc4iu illhIP 4 2 4 2 s ' 16 2 74 14 bRb.iJ spp. 4 5 1 J7 2 H ~c12bolcbtci1 spp. 4 14 8 3 ccciodaphgia spp. 75 2 3) 41 38 16 34 17 18 s Uccblmcu mrimdahs ' 4 3 1) 14 38 15 61 30 11,occrptus.spp. 2 ' Chydorinae 182 284 m 608 212 222 88 22 )79 14 lli1il latissiN llinJ spp. 4 11 11 39 20 13 9 llw i!!ll.W 4 9 ll!ll rectaggula 2 62 lppeui1 G. (coatiate4) 22 1a, S Jue 17 Jue 3 J1h 13 Jul 1 Stoc:kecl Control Stoc:tecl Co1troJ Stocked Control Stocked Co1trol Stoctecl Control llgella spp. 11 2 21 4 42 1 3 Aimil• min 11 2 21 4 37 1 3 Plnr11u spp. 1 18 1 tlurons llii!bl 2 1 ~ sphaericu 146 271 573 m 109 m 83 19 )70 14 lasects 4 1, 12 " n 16 5 58 13 Chiroto■idu 4 10 12 28 14 12 1 S4 13 Cbaoboridae 3 3 ~ ' other 2 1 4 4 4 8 Total Jm 991 1067 1440 m 796 441 m m m 1 Stocked tre1t1e1t consisted of 32 tg of fathead 1i1101s. ~ Ta1a i1cl1de Trieoptera, IJ9optera, Pleidae, Poduridae, Ceratopogoaidae, and Culieidae. 63 lppe1di1 I. fe9etati,e characteristics of stocked ud coatrol fisb co1ple1 po1ds 01 lostta IPls i1 aortnest lisco11i1, l!li!, SfOCID COfflOL Pret, of I lelathe 11 of l99r. I Pret, of I lelathe i I of l99r. I Tua Occar. I I Ste■s/1 lio■ass Occar. I Steu/1 Bio■ass b ' mlSPP, 18t 17 33 lppeadil I. Ye,etati,e eharaeteristies of stoetH ud eo1trol fathead 1inao1 ponds OB lostka IP&s ia 1orth1est liscoasin, 19861, S!OCIII COfflOL rre,. ,f I lelathe I I of lggr. I Preq, of I Relathe I I of lggr. I fHI Occ1r. I st•/• linass Occar. I Steu/1 Bioaass a ' ' ... SJP, 28 • Stocke4 treat■eat coasisted of 32 kg of fathead li1101s. b Iacl ued the occareace of lllciJ llilw., e St• 114 biouss i1for■atio1 ,ere 1ot cellecte4. 65 lppe1di1 1. later c•eutrJ uta froa fi•• c01ple1 (PC) u4 fathead li.1101 (Pl) ,tocked ud coatrol poads oa lostta IPb ia aorthlest li1co1si1, 1n,1, late lllaliatr I.bill --ll ,,,u,, ~oa••~t,itr (Uabos) Dissot,ed ~ il!fil Stocke4 Coatrol Stocke4 Co1trol Stocke41 Coatrol Stocked Control re Treataot 6/'/16 12.0 12.0 6.3 6.3 " so 2.38 1.88 6/1'/16 t.5 5,0 6.3 s., so 47 1.71 2. 77 '/13/H 7.1 4.0 6.0 S.7 40 30 3.07 3.n 7/3/16 1.0 3.0 5,3 S.7 40 30 2.21 2.11 7/10/16 7.t 4.1 S.7 5.5 3S ,0 2.18 2.28 leu 1.7 s., s., s.a 4S 35 2.34 2.48 Pl Treat•t 6/9/16 ,.. 10.S 5.7 6.3 40 so 3.37 3.86 6/1'/8' 3.0 7.5 5,9 5.t so 45 2.28 2.77 ,,23/16 6.0 3.0 S.7 s., 40 25 2.28 1.98 7/3/16 4.0 s.o S,4 S.1 20 40 2.S7 1.88 7/10/16 3.0 4.0 S.3 S.t 20 3S ,.oa 2.57 leu 4.4 ,.o s., s., 34 39 2.SO 2.61 I Stoctecl treatlelts cnsisted of 26 kg of fis• i1 re i1cl1di19: poptiaseeds (43\), Jello, perch (331), fat•ead li.1111s (101), 9olde1 shiners (71), aid ceatral ndlia101s (71), ud 32 kt of fatlead li1111s inn. 66 lppeadil I. Li•olotical ualysis for fis• coaple1 (PC) ud fathead ai1no1 (Pl) stocked and control ponds, on lestka IPls ia aort••est liscoasia, 19161. htu1d liuu lt2cku iU ce1tr2l T[eatae1ts Pi1~ Co11l11 ltocked 11d Cggtrol tr11tu1t1 faria•le lllt J1l! llll l•l! Stocked Coatrol Stocked Control Stocked Control Stocked Control CIDICU PUUlfDS I lllaliaitJ ,.o 11.0 4.t ,.o 11.0 1.0 1.0 6.0 (19/L) -I pl 5.9 6.1 6.t 6.0 6.3 6.5 6.0 5.9 (81it) I Coad1cthitJ 14.0 27.0 1.0 17.0 21.0 23.0 17.0 11.0 (8uos) I Color IO.O 110.0 40.0 55.t 100.0 110.0 so.o ss.o .{hits) I hr.iditJ 1.6 2.2 o., 1.7 1.7 2.2 7.0 3.6 (Jfl) ffllIDt IOI COICDffltlOIS -I ea <1.0 2.0 <1.0 2.0 2.0 2.0 2.0