ABSTRACT Title: PATTERNS IN THE DISTRIBUTION, DIET AND TROPHIC DEMAND OF THE HOGCHOKER, TRINECTES MACULATUS, IN THE CHESAPEAKE BAY, USA. Kiersten Lynn Curti, M.S., 2005 Directed By: Associate Professor Dr. Thomas J. Miller; University of Maryland Center for Environmental Science, Chesapeake Biological Laboratory The hogchoker, Trinectes maculatus (Achiridae), is a small estuarine flatfish that, due to its ubiquitous distribution and substantial biomass, is an important component of the Chesapeake Bay ecosystem. I quantified the abundance, distribution and diet of hogchoker in the Bay based on samples from a fishery-independent survey. Hogchoker abundance varied inter-annually and spatially. A generalized additive model (GAM) explained 14.8% of the variability in the distribution of hogchoker abundance. Depth, salinity, temperature and year were significant determinants of hogchoker presence, whereas salinity and temperature determined relative abundance. Hogchoker diet primarily comprised polychaetes, however, amphipods, isopods and bivalve siphons also represented important dietary components. Graphical analyses and nonmetric multidimensional scaling indicated seasonal, spatial and ontogenetic variation in diet within the Bay. Estimates of summer trophic demand indicated that hogchoker consumed up to 0.1% of the standing stock biomass of particular macrobenthic taxa in the mainstem of the Chesapeake Bay. PATTERNS IN THE DISTRIBUTION, DIET AND TROPHIC DEMAND OF THE HOGCHOKER, TRINECTES MACULATUS, IN THE CHESAPEAKE BAY, USA. By Kiersten Lynn Curti Thesis submitted to the Faculty of the Graduate School of the University of Maryland, College Park, in partial fulfillment of the requirements for the degree of Master of Science 2005 Advisory Committee: Associate Professor Thomas J. Miller, Chair Professor Edward D. Houde Professor Walter R. Boynton © Copyright by Kiersten Lynn Curti 2005 DEDICATION I would like to dedicate this work to my family, who has always provided unconditional support. They had faith in my abilities even at times when I started to lose faith in myself. ii ACKNOWLEDGEMENTS First and foremost, I would like to thank my advisor, Tom Miller, for four years of support and guidance. He repeatedly went above and beyond the call of an advisor’s duties. I would also like to thank my committee, Ed Houde and Walt Boynton, for their critical review and constructive suggestions that greatly helped to strengthen my thesis. I am fortunate to have the opportunity to write this acknowledgements section after my departure from CBL and as a consequence, I have a greater appreciation of the CBL community. I have always felt quite privileged to be part of the community, however, its unique character is now much more evident. It supports an environment that fosters both academic and personal growth and I feel like I grew an extraordinary amount during my time at CBL. I, of course, need to thank all of the members of the Houde and Miller labs, in addition to Sarah Kolesar, for all of their help in the field. Thanks also to the Miller lab group, both past and present, for always editing my work, helping me work through ideas, and most of all making me laugh. A very special thanks is also much needed for my housemates, Lori Roth, Steve Engstrom and Josh Dixon, for three years filled with fond memories. And last, but not definitely not least, I am indebted to my family for always standing by me. iii TABLE OF CONTENTS Dedication........................................................................................................................... ii Acknowledgements............................................................................................................iii Table of Contents............................................................................................................... iv List of Tables ...................................................................................................................... v List of Figures.................................................................................................................... vi Chapter 1: Rationale ........................................................................................................... 1 Chapter 2: The Distribution of Hogchoker in the Chesapeake Bay: Inferences from a Generalized Additive Model............................................................................................. 11 Introduction................................................................................................................... 11 Methods......................................................................................................................... 14 Sample Collection..................................................................................................... 14 Statistical Analysis.................................................................................................... 17 Results........................................................................................................................... 19 Discussion..................................................................................................................... 24 Chapter 3: Patterns in the Diet and Trophic Demand of the Hogchoker in the Chesapeake Bay .................................................................................................................................... 49 Introduction................................................................................................................... 49 Methods......................................................................................................................... 56 Sample Collection..................................................................................................... 56 Analysis of dietary trends ......................................................................................... 58 Trophic Demand ....................................................................................................... 61 Results........................................................................................................................... 63 Discussion..................................................................................................................... 71 Chapter 4: Summary ....................................................................................................... 115 Appendix: Justification of the Use of a Generalized Additive Model to Model Hogchoker Distribution in the Chesapeake Bay................................................................................ 119 References....................................................................................................................... 122 iv LIST OF TABLES Table 2.1. The percentage of stations with zero hogchoker catch (% Zeros) and the average (Avg), standard deviation (SD), minimum (Min) and maximum (Max) hogchoker CPUE (catch per minute of bottom time) at each station within each year, season and stratum.........................................................33 Table 2.2. Pearson correlation matrix for the environmental covariates included in the first stage of the GAM .........................................................................34 Table 2.3. Pearson correlation matrix for the environmental covariates included in the second stage of the GAM.....................................................................35 Table 2.4. Model fitting results from the first stage of the GAM (n = 731) for significance of smooth terms .....................................................................36 Table 2.5. Model fitting results from the second stage of the GAM (n = 154) for significance of smooth terms .....................................................................37 Table 3.1. Distribution of examined hogchokers utilized in dietary analyses from the CHESFIMS broadscale and shoal surveys ................................................83 Table 3.2. Distribution of the proportion of examined hogchokers from the broadscale and shoal surveys with empty stomachs..................................84 Table 3.3. Hogchoker relative abundance and total consumption in each year and strata...........................................................................................................85 Table 3.4. Hogchoker consumption of macrobenthic taxa (crustaceans, bivalves and polychaetes) in each year and strata assuming three different levels of hogchoker catchability...............................................................................86 Table 3.5. Summer hogchoker trophic demand, measured as percent of standing stock biomass, of macrobenthic taxa in each year and strata assuming three different levels of hogchoker catchability.........................................87 v LIST OF FIGURES Figure 1.1. Representation of the annual flow of carbon (mg*m-2 *yr-1) through the dominant food web components of the mesohaline Chesapeake Bay. Figure from Baird and Ulanowicz (1989)..................................................10 Figure 2.1. Sampling scheme for a CHESFIMS cruise................................................38 Figure 2.2. Relative abundance (catch per minute bottom time) of hogchoker in each season and year of CHESFIMS .................................................................39 Figure 2.3. Relationship between hogchoker relative abundance and the environmental covariates included in the full GAM model.......................42