Building an Ecopath with Ecosim Model for the Galveston Bay Blue Crab Fishery Glen Sutton1*, Zachary Olsen2, and Tom Wagner3 Texas Parks and Wildlife Department- Coastal Fisheries, 1Dickinson Marine Laboratory, Dickinson, Texas 77539, 2Upper Laguna Madre Field Office, Corpus Christi, Texas 78412, 3Rockport Marine Laboratory, Rockport Texas, 78382 Introduction The Texas Blue Crab population has been in a state of decline for over twenty years (Martinez-Andrade et al. 2005) despite reduced fishing effort from TPWD’s license buyback program. Morris (2015) recommended possible management actions to address this decline, including protection of non-ovigerous mature females with seasonal or area closures, increasing minimum size to 5 ½ inches, increasing escape ring size, or reducing trap limits. There is a need to examine management options for the Blue Crab fishery in an ecosystem wide context. What is Ecopath with Ecosim? EwE is a mass balance modeling software that allows users to construct virtual food webs based heavily on local and published knowledge of trophic interactions (Pauly et al. 2000). This ecosystem model is then used to generate management scenarios in which scenarios of population increase or decrease are examined. Methods Model Inputs (data sources given in parentheses) Production and consumption estimates for key species groups (Literature Values). Percent dietary breakdown of all consumers (Literature Values). Fishery harvest and bycatch data for major fisheries including: bay and nearshore shrimp trawl fishery (TPWD Trip Ticket Program) blue crab trap fishery (TPWD Trip Ticket Program) oyster dredge fishery (TPWD Trip Ticket Program) commercial finfish fisheries (TPWD Trip Ticket Program) recreational finfish fisheries (TPWD Harvest Monitoring Program) Fishery-independent trend data used for verifying model performance (TPWD Fishery-Independent Monitoring Program) Figure 4. Hypothetical output from Ecosim run reducing blue crab trap fishery effort by 100% at year nine of the time series, showing effects on selected groups. Preliminary Results* Figure 5. Hypothetical output from Ecosim run for adult blue crab for entire time series showing examples of metrics useful to fishery managers (i.e. predation mortality, catch, and fishing mortality. Objectives Construct a mass-balanced food web model of the Galveston Bay Blue Crab fishery, including predators, prey, and fisheries affecting the species, (ONGOING). Evaluate ecosystem-wide impacts of management options to maximize benefits to Blue Crabs taking into account relevant trophic interactions (FUTURE). Calculated Trophic Level * Please note that model results are hypothetical and for presentation purposes only, as we are still in the process of gathering information and validating the Galveston Bay Blue Crab model with time series data. The general model structure was modified from that of Sutton and Guillen (2010). Study Area . Figure 2. The Galveston Bay food web output from Ecopath showing the many complex interactions between trophic levels. Some trophic guilds have been combined (e.g., Apex piscavores) due to dietary similarity and model simplicity. Implications and Importance This study highlights a need to move towards an ecosystem approach to fisheries management. Trophic models such as this are one tool for evaluating fisheries effects in the ecosystem context. The model is currently being verified and updated with input from a number of subject matter experts. By examining a variety of scenarios in this modeling context we can better understand what may be driving population dynamics of Blue Crabs in Galveston Bay and critically evaluate management strategies for this species.   Group name Trophic level Habitat area (fraction) Biomass in habitat area (t/km²) Biomass (t/km²) Z (/year) Production / biomass (/year) Consumption / biomass (/year) Ecotrophic efficiency Production / consumption 1 Seabirds 3.531 1.000 0.0110 0.250 35.000 0.000 0.007 2 Apex piscavores 3.932 0.0148 0.200 3.000 0.118 0.067 3 Gars 3.911 0.0100 0.500 0.167 4 Rays 3.104 0.0820 0.066 5 Red Drum 3.463 0.1000 1.100 5.100 0.158 0.216 6 Spotted Seatrout 3.601 0.0720 4.110 0.221 0.243 7 BlackDrum 3.031 0.0200 5.000 0.186 8 Flounder 3.532 0.420 6.360 0.453 9 Sandtrout 3.455 1.827 0.284 0.287 10 Hardheads 3.247 0.4000 7.600 0.262 0.132 11 Gafftop 3.464 0.800 0.057 0.105 12 Sheepshead 3.085 0.0250 8.000 0.429 0.125 13 Croaker_adt 3.037 4.3440 1.500 2.000 0.004 0.750 14 Croaker_med 3.012 2.5407 3.913 0.015 0.511 15 Croaker_juv 2.989 0.2026 3.500 10.714 0.777 0.327 16 Benthivores 2.897 0.9000 9.000 0.485 0.122 17 Menhaden_adt 2.578 1.3000 6.774 0.162 0.148 18 Menhaden_juv 2.189 0.7290 12.000 0.246 19 Mullet_adt 2.062 3.0000 0.037 20 Mullet_juv 2.056 0.3739 1.900 18.725 0.564 0.101 21 Anchovy 2.889 2.0320 2.530 14.000 0.106 0.181 22 Blue Crab_adt 2.968 2.0000 1.250 8.500 0.102 0.147 23 Blue Crab_med 2.699 0.6815 10.368 0.470 0.193 24 Blue Crab_juv 2.559 0.4891 2.500 13.073 0.861 0.191 25 Blue Crab meg 2.333 0.3571 5.500 22.644 0.901 26 Brown shrimp 2.438 0.772 0.600 27 White shrimp 2.276 0.683 28 Gastropods 1.0000 4.500 22.000 0.639 0.205 29 Bivalves 4.0000 0.577 30 Meiobenthos 2.078 10.0000 0.510 31 Oyster 2.222 0.633 0.045 32 Zooplankton 2.111 7.6420 36.000 89.000 0.519 0.404 33 Bethic algae 25.000 0.178 34 Plankton 25.0000 76.000 0.393 35 Detritus 100.0000 0.156 Figure 3. Basic estimates generated by Ecopath for model groups at the beginning of the time series (1990). Values in blue are calculated by the model. Want to become involved? The EwE modeling is a process that relies on extensive input from subject matter experts. If you are interested in learning more about this model or would like to provide subject matter expertise to the modeling process feel free to talk to one of the authors or join our Break Out Session Focus Group Meeting on Thursday, February 25th from 3:30-4:10pm in the Main Conference Room. Figure 1. The study area, including Galveston Bay, Trinity Bay, and the adjacent Texas Territorial Sea, comprise a total area of 3699 km2. References Martinez-Andrade, F., P. Campbell, and B. Fuls. 2005. Trends in relative abundance and size of selected finfishes and shellfishes along the Texas coast: November 1975-December 2003. Texas Parks and Wildlife Department, Coastal Fisheries Division Management Data Series No 232. Morris, A. 2015. Crab Fishery Enhancement presentation at TPWD Coastal Fisheries Division Regulatory Proposal meeting held July 22, 2015 at Victoria, Texas. Pauly, D., V. Christensen, and C. Walters. 2000. Ecopath, Ecosim, and Ecospace as tools for evaluating ecosystem impact of fisheries. ICES Journal of Marine Science 57: 697-706. Sutton, G.R. and G. Guillen. 2010. An Ecosystem Based Fisheries Model to analyze the Effects of Freshwater Inflow. Poster presented at Harte Institute Freshwater Inflow Conference, Corpus Christi, Texas, February 2010. Acknowledgements We would like to thank Brian Witt, Carey Gelpi, Christine Jensen, Claire Iseton, and Nicole Carrillo for their input and assistance with this ongoing project.