HUMBOLDT-UNIVERSITÄT ZU BERLIN Faculty of Agriculture and Horticulture “Comparative feeding ecology of Eurasian perch (Perca fluviatilis) and North American yellow perch (Perca flavescens)” Master thesis in the study program: M.Sc. Fishery Science and Aquaculture submitted by: Linzmaier, Stefan Markus Supervisors: PD Dr., Mehner, Thomas Department IV - Biology and Ecology of Fishes Leibniz-Institute of Freshwater Ecology and Inland Fisheries Prof. Dr., Arlinghaus, Robert Department IV - Biology and Ecology of Fishes Leibniz-Institute of Freshwater Ecology and Inland Fisheries & Department of Animal Science - Integrative Fisheries Management Humboldt-Universität zu Berlin - Faculty of Agriculture and Horticulture Berlin, 8.11.2013 i Contents Contents ............................................................................................................................. i List of Abbreviations......................................................................................................... ii List of Figures .................................................................................................................. iii List of Tables..................................................................................................................... v List of Appendices ........................................................................................................... vi List of Equations ............................................................................................................. vii 1 Introduction ............................................................................................................... 1 2 Eurasian Perch and Yellow Perch ............................................................................. 9 2.1.1 Systematics & Zoology ............................................................................... 9 2.1.2 Distribution ............................................................................................... 10 3 Material & Methods ................................................................................................ 11 3.1 Study Area ........................................................................................................ 11 3.1.1 American Lakes ........................................................................................ 11 3.1.2 German Lakes ........................................................................................... 12 3.2 Sample Collection ............................................................................................ 15 3.2.1 Fish ............................................................................................................ 15 3.2.2 Benthic Invertebrates & Zooplankton ....................................................... 15 3.3 Stable Isotopes: Sample Preparation and Analysis .......................................... 16 3.4 Statistical Analysis ........................................................................................... 19 3.4.1 Breakpoint Analysis .................................................................................. 20 3.4.2 Trophic Position ........................................................................................ 20 3.4.3 Trophic Niche Metrics .............................................................................. 24 3.4.4 Estimated Diet Composition ..................................................................... 25 4 Results ..................................................................................................................... 28 4.1 Trophic Position & Breakpoint Analysis ......................................................... 28 4.2 Trophic Niche Metrics ...................................................................................... 33 4.3 SIAR - Mixing Model ...................................................................................... 34 5 Discussion ............................................................................................................... 41 6 Conclusions ............................................................................................................. 50 7 Summary ................................................................................................................. 52 8 Zusammenfassung ................................................................................................... 53 9 References ............................................................................................................... 54 10 Annex ...................................................................................................................... 72 11 Acknowledgements ................................................................................................. 80 12 Erklärung ................................................................................................................. 81 ii List of Abbreviations YP yellow perch ha hectare (Perca flavescens) µm micrometer EP Eurasian perch mm millimeter (Perca fluviatilis) cm centimeter SI(s) stable isotope(s) m meter TP(s) trophic position(s) mg milligram TL total length g gram e.g. exempli gratia h hour etc. et cetera mL milliliter et al. et alii/aliae °C degree Celcius i.e. id est V-PDB Vienna PeeDee ZP zooplankton Belemnite MZB macrozoobenthos n sample size xC carbon isotope(s) SD standard deviation of mass x GLM generalized linear xN nitrogen isotope(s) model of mass x CD the mean distance Fig. figure to centroid Tab. table MNND the mean nearest Equ. equation neighbour distance YOY young of the year SDNND standard deviation of the nearest neighbour age-x+ in the year x distance after hatching DFO Department of Fisheries USA United States and Oceans (Canada) of America LELF Landesamt für GER Germany Ländliche Entwicklung, d measurement error Landwirtschaft und Flurneuordnung PA Lake Padden p probability value WA Walsh Lake F F-value WI Lake Wilderness df degrees of freedom DO Lake Dölln R2 coefficient VA Lake Väter of determination WU Lake Wucker max. maximum iii List of Figures Figure 1: Schematic figure of the habitat shifts between the littoral and the pelagic habitat during the early ontogeny of P. fluviatilis & P. flavescens (modified from Whiteside et al. (1985)). ......................................................................................................................... 4 Figure 2: Food web scheme for P. fluviatilis & P. flavescens with respect to ontogeny and energy pathways. Trophic links to aquatic consumers are illustrated with solid arrows. Diet shifts between size classes of perch are shown as dashed arrows. The scheme depicts (from top to bottom) the co-ocurring top predators (Esox lucius (upper picture) & Micropterus salmoides (lower picture), the different size classes of P. fluviatilis (upper pictures) & P. flavescens (lower pictures), their most important types of prey (zooplankton, benthic/epiphytic invertebrates and fish) and the bases of the littoral and pelagic food webs (phytoplankton, benthic & epiphytic algae) along their assumed trophic positions (modified from Rasmussen et al. 2008) – pictures: Wisconsin Department of Natural Resources, Bangladesh Fisheries Information, Fish Management in New York State & Fischereiverband für das Land Vorarlberg. ......................................................... 5 Figure 3: Photographs of adult P. flavescens (a) & P. fluviatilis (b) – pictures: wikimedia.org.................................................................................................................... 9 Figure 4: Aerial photographs and position of the studied lake ecosystems in North America and Europe (position and scale of the continents are not drawn to scale): Lake Padden (a), Walsh Lake (b), Lake Wilderness (c), Lake Dölln (d), Lake Väter (e) & Lake Wucker (f) - pictures: Google Maps ............................................................................... 14 Figure 5: Preparation of fish tissue samples: Weighing and measuring (a); tissue removal of the dorsal muscle (b); drying of samples in a drying oven at 60°C for 24 h (c); grinding the samples with mortar and pestle (d). .......................................................................... 17 Figure 6: An example of lake corrected baselines as they are used in this study to depict the δ15N-δ13C relationship in the context of habitats and the consequences for consumer trophic position (TP - i.e. the average position relative to primary producers at which an organism feeds). Primary consumers represent a TP of 2. In spite of similar δ15N-values, sculpins occupy lower TP due to their diet of 13C-depleted profundal prey (modified from Vander Zanden & Rasmussen) - picture of YP: Maryland Dept. of Natural Resources. 22 Figure 7: Trophic positions (TP - i.e. the average position relative to primary producers at which an organism feeds) of P. fluviatilis (green triangles) & P. flavescens (yellow triangles) at increasing total length (TL) and regression of TP and TL with breakpoints (* = significant) in TPs for P. fluviatilis (dotted, green line) & P. flavescens (dotted, yellow line) for all lakes combined. ............................................................................................ 28 Figure 8: Box-and-whisker plots of observed mean trophic positions (TP - i.e. the average position relative to primary producers at which an organism feeds) of small (a) and large (b) P. fluviatilis (green) & P. flavescens (yellow). Outliers are plotted as dots