Fisheries Ecosystem Model of the Chesapeake Bay: Methodology, Parameterization, and Model Exploration Villy Christensen, Alasdair Beattie, Claire Buchanan, Hongguang Ma, Steven J. D. Martell, Robert J. Latour, Dave Preikshot, Madeline B. Sigrist, James H. Uphoff, Carl J. Walters, Robert J. Wood, and Howard Townsend U.S. Department of Commerce National Oceanic and Atmospheric Administration National Marine Fisheries Service NOAA Technical Memorandum NMFS-F/SPO-106 October 2009 Fisheries Ecosystem Model of the Chesapeake Bay: Methodology, Parameterization, and Model Exploration Villy Christensen1, Alasdair Beattie2, Claire Buchanan3, Hongguang Ma8, Steven J. D. Martell4, Robert J. Latour5, Dave Preikshot9, Madeline Sigrist2, James H. Uphoff7, Carl J. Walters1, Robert J. Wood6, and Howard Townsend6 1Fisheries Centre, University of British Columbia, 2259 Lower Mall, Vancouver BC, Canada V6T 1Z4. Telephone 604-822-5751; fax 604-822 8934; email [email protected] 2NOAA/Chesapeake Research Consortium, 410 Severn Avenue, Suite 107A, Annapolis, MD 20403 3Interstate Commission on the Potomac River Basin. 51 Monroe Street, Suite PE-8, Rockville, MD 20850 4Chesapeake Biological Laboratory, University of Maryland, Center for Environmental Science, P.O. Box 38, Solomons, MD 20688 (present address UBC Fisheries Centre) 5Department of Fisheries Science, Virginia Institute of Marine Science, P.O. Box 1346, Gloucester Point, VA 23062-1346 6NOAA Chesapeake Bay Office/Cooperative Oxford Laboratory, 904 South Morris Street, Oxford, MD 2165; email [email protected] 7Maryland Department of Natural Resources, Matapeake Work Center, 301 Marine Academy Drive, Stevensville, MD 21666 8NOAA Chesapeake Bay Office/Cooperative Oxford Laboratory/Versar, Inc., 904 South Morris Street, Oxford, MD 21654; email [email protected] 9Pacific Biological Station, Department of Fisheries and Oceans, 3190 Hammond Bay Road, Nanaimo, British Columbia, Canada V9T 6N7 NOAA Technical Memorandum NMFS-F/SPO-106 October 2009 U.S. Department of Commerce Gary Locke, Secretary National Oceanic and Atmospheric Administration Jane Lubchenco, Ph.D., Under Secretary for Oceans and Atmosphere National Marine Fisheries Service James W. Balsiger, Ph.D., Acting Assistant Administrator for Fisheries Suggested citation: Christensen, Villy, and Alasdair Beattie, Claire Buchanan, Hongguang Ma, Steven J. D. Martell, Robert J. Latour, Dave Preikshot, Madeline B. Sigrist, James H. Uphoff, Carl J. Walters, Robert J. Wood, and Howard Townsend. 2009. Fisheries Ecosystem Model of the Chesapeake Bay: Methodology, Parameterization, and Model Explanation. U.S. Dep. Commerce, NOAA Tech. Memo. NMFS-F/SPO- 106, 146 p. A copy of this report may be obtained from: Howard Townsend NOAA Chesapeake Bay Office 410 Severn Ave., Suite 107A Annapolis, MD 21403 [email protected] Or online at: http://chesapeakebay.noaa.gov Table of Contents 1 ABSTRACT 5 2 INTRODUCTION 5 2.1 The Chesapeake Bay 5 2.2 Multispecies management 7 3 METHODS 9 3.1 EwE General Methodology 9 3.2 Development of an Ecopath Model of the Chesapeake Bay 13 3.3 Development of an Ecosim Model of the Chesapeake Bay 16 3.4 Stock Assessment Methods for Developing Time Series 21 4 RESULTS AND DISCUSSION 29 4.1 Ecopath models 29 4.2 Ecosim simulations 29 4.3 Evaluating policy questions 34 5 CONCLUSIONS 38 5.1 Data availability 38 5.2 Stock assessment 39 5.3 Spatial modeling 39 5.4 Ecosystem boundaries and model structure 40 6 ACKNOWLEDGEMENTS 41 7 TABLES 53 7.1 Relating species and management plan entities 53 7.2 Questions 54 7.3 Basic parameters 55 7.4 Catches, species groups 1-12 57 1 7.5 Catches, species groups 13-35 60 7.6 Vulnerabilities for species groups 62 7.7 Bay anchovy simulation – change in biomass 62 7.8 Oyster fishing moratorium simulation 63 8 LIST OF FIGURES 64 8.1 The Chesapeake Bay 64 8.2 Model development 64 8.3 Foraging arena 64 8.4 Food web components 64 8.5 Ecoranger 64 8.6 Mixed trophic impacts 64 8.7 Time-series fit, biomass 64 8.8 Time-series fit, catches 65 8.9 Impact of nutrient loading on primary production 65 9 FIGURES 66 9.1 Figure 1. 66 9.2 Figure 2. 67 9.3 Figure 3. 68 9.4 Figure 4. 69 9.5 Figure 5. 70 9.6 Figure 6. 71 9.7 Figure 7. 72 9.8 Figure 8. 73 9.9 Figure 9. 74 10 APPENDICES – DESCRIPTION OF METHODS FOR ESTIMATING BASIC INPUT PARAMETERS AND DETERMINING TIME SERIES FOR CBFEM 75 10.1 Appendix A: Basic Input Parameters 75 2 10.2 Appendix B: Time Series 95 11 TABLES RELATED TO APPENDICES A AND B 107 11.1 Catches, species groups 1-12 107 11.2 Catches, species groups 13-35 109 11.3 Striped bass growth parameters 111 11.4 Striped bass biomass 112 11.5 Striped bass fishing mortality 113 11.6 Bluefish growth parameters 115 11.7 Bluefish biomass and fishing mortality 116 11.8 Weakfish growth parameters 118 11.9 Weakfish biomass and fishing mortality 118 11.10 Atlantic croaker biomass and fishing mortality 120 11.11 Summer flounder biomass and fishing mortality 122 11.12 Menhaden biomass and fishing mortality 123 11.13 American shad and blueback herring biomass 124 11.14 Bay anchovy biomass 125 11.15 White perch biomass and fishing mortality 126 11.16 Spot biomass 127 11.17 Blue crab biomass, effort, and fishing mortality 128 11.18 Eastern oyster biomass, effort, and fishing mortality 130 11.19 Zooplankton biomass 131 11.20 Diet compositions for high-trophic-level, multi-stanza, commercial fish 132 11.21 Diet composition for other commercial fish species 133 11.22 Diet composition for other fishes 134 11.23 Diet composition for commercial invertebrates 135 11.24 Diet composition for other invertebrates 135 11.25 Diet composition for birds 137 3 11.26 Non-piscivorous bird species included in the Chesapeake Bay Fisheries Ecosystem Model 137 11.27 Piscivorous bird species included in the Chesapeake Bay Fisheries Ecosystem Model 138 11.28 Hurricanes and their assumed impact on the relative P/B for clams 139 11.29 Estimated relative P/B for clams, carried over to years subsequent to hurricane events 140 11.30 Phytoplankton chlorophyll content 142 11.31 Confidence intervals for basic input parameters 143 11.32 Prices for commercial catches 144 11.33 Multispecies Production stock assessment model parameter values 145 11.34 Submerged Aquatic Vegetation biomass index 146 4 1 Abstract This report describes an ecosystem model of the Chesapeake Bay, the Chesapeake Bay Fisheries Ecosystem Model (CBFEM), prepared using the Ecopath with Ecosim approach and software. The CBFEM was created in response to a management need in the Chesapeake region for a quantified estimation of trophic pathways in the Bay. This information can be used to understand how one stock affects another within the food web and how the many Bay fisheries impact both target and nontarget species. Because the life histories and population dynamics of the thousands of organisms that live within the Bay are complicated, a model is necessary to provide an accurate estimation of the system. Model construction has been carried out in close consultation with Chesapeake Bay researchers through a series of workshops. Currently, the model includes 45 functional groups of organisms, some of which represent life history stanzas of individual species, representing all trophic levels. The input data primarily includes assessment results from the Chesapeake Bay (including biomasses, mortality rates, catches, and effort) supplemented with research vessel survey data (fisheries and biological oceanography studies), ecological studies (as available from researchers and institutions in the region), and parameter estimates obtained from literature where necessary to supplement local data. Activities are under way to refine the temporal and spatial resolution of the CBFEM and to continue to incorporate hydrographic data. This documentation is intended to facilitate use and further development of the CBFEM, so that it can serve as a ‘living’ model. Future revisions to the CBFEM and supporting documentation will be made available on the NOAA Chesapeake Bay Office web site (http://chesapeakebay.noaa.gov). 2 Introduction 2.1 The Chesapeake Bay The Chesapeake Bay is the largest estuary in the continental United States, located midway along the Atlantic coast of the United States. The surface area of the tidal portion of the Chesapeake Bay system is approximately 10,000 km2, while the area including tributaries is estimated to 18,580 km2. More than 20 major tributaries drain into the Bay from a watershed that stretches across six states: New York, Pennsylvania, Maryland, Delaware, Virginia, West Virginia, and the District of Columbia. The largest of these tributaries, the Susquehanna River, provides more than half of the freshwater flow to the Bay. The waters of the Chesapeake Bay and tidal portions of its tributaries are governed by Maryland and Virginia (Figure 1). The Bay is a partially mixed estuary, with an average tidal range of approximately 1 m at its mouth to less than 30 cm at its head (cited in 1989). Salinity within the Bay ranges from less than 0.5 ppt at its northern extreme to 32 ppt near its mouth. The Bay can be divided into three major salinity regions: oligohaline (0-5 ppt), mesohaline (6-18 ppt), and polyhaline (> 18 ppt). Water temperatures in the Bay vary greatly throughout the year, reaching 28-30ºC in late summer and 1-4ºC in late winter (Murdy et al., 1997). 5 The estuarine circulation pattern of a flow of deeper, more saline water from the Atlantic Ocean into the Bay and its tributaries and surface fresher water out of the Bay serves to transport larval fishes and crabs from the ocean to their nursery habitats and juvenile fishes from tributaries to the coastal waters of the Atlantic. This transport mechanism is very important to the population dynamics of many Bay species. The mixture of freshwater from the tributaries and seawater from the coastal ocean creates and maintains a variety of brackish habitats within the Bay. Tidally influenced habitat types in the Bay include: pelagic waters, nearshore littoral areas, and the benthic zone. Littoral habitats, such as marshes on intertidal lowlands, aquatic grass beds in the shallow flooded flatlands, and oyster reefs, are highly productive, serving as nursery areas to many fish and shellfish species, facilitating rapid growth under relatively protected conditions. The diversity of habitats within the Chesapeake Bay system enables it to support nearly 3,000 species of plants and animals within its waters and tidal margins. Finfish species inhabiting the Chesapeake Bay have a wide variety of life history strategies. The American eel, Anguilla rostrata, is a catadromous species, spending most of its life in tributaries of the Chesapeake Bay, returning to the Atlantic Ocean to spawn. Some marine fishes, like the weakfish, Cynoscion regalis, enter the Bay to feed and spawn seasonally and then return to the coastal ocean. Anadromous species, like the American shad, Alosa sapidissima, and striped bass, Morone saxatilis, spend most of their adult lives migrating in the Atlantic Ocean, but return to Bay tributaries to spawn. Other species, like the white perch, Morone americana, spend their entire lives within the Chesapeake Bay system, undergoing ‘semi-anadromous’ seasonal migrations within the Bay. Due to the complexity of the Chesapeake Bay ecosystem, it is necessary to develop modeling tools like the CBFEM to simulate interactions between these many different species, to quantitatively estimate how they fit together within the larger food web and how human impacts are likely to affect this complex system. The diversity of habitats within the Chesapeake Bay, combined with wide ranges of temperatures throughout the year, result in very dynamic seasonal changes in fish assemblages. During late summer and early autumn, fish diversity reaches its maximum due to a movement of tropical species into the lower portion of the Bay. When the cooler temperatures of autumn arrive, most marine fish within the Bay begin to migrate either south to Cape Hatteras, North Carolina, or offshore to the edge of the continental shelf. During winter, the abundance and diversity of fish in the Bay is relatively low. However, by early spring, abundance and diversity rebound significantly as anadromous species enter the Bay, followed soon after by the warm-temperate and subtropical summer residents. Since the early 1800s, the Chesapeake Bay has supported a variety of large-scale commercial and recreational fisheries of both finfish and shellfish. The predominant invertebrate fisheries in the Chesapeake Bay have included the eastern oyster (Crassostrea virginica), blue crab (Callinectes sapidus), soft clam (Mya arenaria), and hard clam (Mercenaria mercenaria). The large-scale finfish fisheries have included striped bass, American shad, river herring (Alosa aestivalis), white perch, bluefish (Pomatomus saltatrix), Atlantic menhaden (Brevoortia tyrannus), summer flounder (Paralichyths dentatus), weakfish, Atlantic croaker (Micropogonias undulates), and spot (Leiostomus xanthurus). Several species, like white perch and Atlantic croaker, have sustained significant harvest levels, although trends in the commercial and recreational landings have varied over the last several decades. Striped bass landings may be the most dramatic in terms of variability from the 1960s to present. Many species, such as the eastern oyster, American shad, and striped bass, have suffered overexploitation in the Chesapeake Bay. Overfishing and the collapse of several Bay and coastal fish 6