NOAA Technical Memorandum NMFS-AFSC-178 A Comparison of the Bering Sea, Gulf of Alaska, and Aleutian Islands Large Marine Ecosystems Through Food Web Modeling by K. Aydin, S. Gaichas, I. Ortiz, D. Kinzey, and N. Friday U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Marine Fisheries Service Alaska Fisheries Science Center December 2007 NOAA Technical Memorandum NMFS The National Marine Fisheries Service's Alaska Fisheries Science Center uses the NOAA Technical Memorandum series to issue informal scientific and technical publications when complete formal review and editorial processing are not appropriate or feasible. Documents within this series reflect sound professional work and may be referenced in the formal scientific and technical literature. The NMFS-AFSC Technical Memorandum series of the Alaska Fisheries Science Center continues the NMFS-F/NWC series established in 1970 by the Northwest Fisheries Center. The NMFS-NWFSC series is currently used by the Northwest Fisheries Science Center. This document should be cited as follows: Aydin, K., S. Gaichas, I. Ortiz, D. Kinzey, and N. Friday. 2007. A comparison of the Bering Sea, Gulf of Alaska, and Aleutian Islands large marine ecosystems through food web modeling. U.S. Dep. Commer., NOAA Tech. Memo. NMFS-AFSC-178, 298 p. Reference in this document to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA. NOAA Technical Memorandum NMFS-AFSC-178 A Comparison of the Bering Sea, Gulf of Alaska, and Aleutian Islands Large Marine Ecosystems Through Food Web Modeling by K. Aydin1, S. Gaichas1, I. Ortiz2, D. Kinzey2, and N. Friday1 1Alaska Fisheries Science Center 7600 Sand Point Way N.E. Seattle, WA 98115 www.afsc.noaa.gov 2University of Washington School of Aquatic and Fisheries Sciences 1122 NE Boat St. Seattle, WA 98105 U.S. DEPARTMENT OF COMMERCE Carlos M. Gutierrez, Secretary National Oceanic and Atmospheric Administration Vice Admiral Conrad C. Lautenbacher, Jr., U.S. Navy (ret.), Under Secretary and Administrator National Marine Fisheries Service William T. Hogarth, Assistant Administrator for Fisheries December 2007 This document is available to the public through: National Technical Information Service U.S. Department of Commerce 5285 Port Royal Road Springfield, VA 22161 www.ntis.gov Notice to Users of this Document This document is being made available in .PDF format for the convenience of users; however, the accuracy and correctness of the document can only be certified as was presented in the original hard copy format. Abstract Detailed mass balance food web models were constructed to compare ecosystem characteristics for three Alaska regions: the eastern Bering Sea (EBS), the Gulf of Alaska (GOA), and the Aleutian Islands (AI). This paper documents the methods and data used to construct the models and compares ecosystem structure and indicators across models. The common modeling framework, including biomass pool and fishery definitions, resulted in comparable food webs for the three ecosystems which showed that they all have the same apex predator—the Pacific halibut longline fishery. However, despite the similar methods used to construct the models, the data from each system included in the analysis clearly define differences in food web structure which may be important considerations for fishery management in Alaska ecosystems. The results showed that the EBS ecosystem has a much larger benthic influence in its food web than either the GOA or the AI. Conversely, the AI ecosystem has the strongest pelagic influence in its food web relative to the other two systems. The GOA ecosystem appears balanced between benthic and pelagic pathways, but is notable in having a smaller fisheries catch relative to the other two systems, and a high biomass of fish predators above trophic level (TL) 4, arrowtooth flounder and halibut. The patterns visible in aggregated food webs were confirmed in additional more detailed analyses of biomass and consumption in each ecosystem, using both the single species and whole ecosystem indicators developed here. iii Contents 1 Introduction ........................................................... 1 1.1 Purpose and Background of Past Models ................................ 1 1.2 Model Setting ...................................................... 3 1.2.1 Time scale .................................................... 3 1.2.2 Area description and maps ....................................... 3 1.2.3 Species breakdown and scale types ................................ 12 1.3 New Information and Improvements Over Previous Models ................ 15 1.4 Outline of Result Types ............................................. 15 2 Methods ............................................................. 16 2.1 Modeling Framework............................................... 16 2.1.1 Ecopath modeling ............................................. 16 2.1.2 Improvements over standard ecopath models ........................ 18 2.2 Input Data and Parameter Estimation Methods ........................... 19 2.3 Balancing Procedure with Data Quality Evaluation ....................... 20 2.4 The Ecosense Routines: Estimating Uncertainty .......................... 21 2.5 Analysis of Mass-balanced Models .................................... 25 2.5.1 Visualizing and comparing ecosystem structure ...................... 25 2.5.2 Ecosystem indicators and statistics ................................ 25 3 Results and Discussion ................................................. 27 3.1 Quantitative Results, Model Balance, and Food Webs ..................... 27 3.1.1 Reconciling data sources to achieve balanced models ................. 27 3.1.2 Visualizing the food webs and primary energy flows .................. 31 3.2 Single Species Indicators and Statistics................................. 38 3.3 Ecosystem Indicators and Statistics .................................... 55 3.3.1 Different ecosystem roles of Pacific cod ........................... 55 3.3.2 Consumption differences between ecosystems: forage base ............. 66 3.3.3 Trophodynamic comparisons of the EBS, AI, and GOA ............... 76 4 Summary and Conclusions ............................................. 107 5 Recommendations .................................................... 111 6 Appendix A: Description, Data Sources, and General Comparison for Each Species Group Across Ecosystems ................................. 115 6.1 Cetaceans ....................................................... 115 6.2 Sea Otters and Pinnipeds ........................................... 122 6.3 Seabirds ........................................................ 128 6.4 Fish (Includes cephalopods and forage fish) ............................ 136 6.5 Benthic Invertebrates .............................................. 181 6.6 Plankton and Detritus.............................................. 195 6.7 Primary Producers ................................................ 200 7 Appendix B: Detailed Estimation Methods ............................... 203 7.1 Benthic-Pelagic flows ............................................. 203 7.2 Cetacean Biomass ................................................ 203 7.3 Marine Mammal Production Rates ................................... 207 7.4 Marine Mammal Consumption Rates ................................. 208 7.5 Marine Mammal Diet.............................................. 211 7.6 Seabird Biomass.................................................. 211 v 7.7 Seabird Production Rates ........................................... 213 7.8 Seabird Consumption Rates and Diets................................. 213 7.9 Fish Biomass .................................................... 215 7.10 Fish Production Rates ............................................. 216 7.11 Fish Consumption Rates ........................................... 217 7.12 Diet Queries for Fish .............................................. 219 7.13 Adult Juvenile Parameters .......................................... 220 7.14 Fisheries ........................................................ 221 7.14.1 Halibut hook and line fishery ............................... 221 7.14.2 Crab fleet, herring fleet, salmon fleet, and shrimp trawl fisheries . 222 7.14.3 Subsistence fishery ....................................... 222 7.14.4 Groundfish fisheries ...................................... 223 7.14.5 Discard and fishery comparisons between models .............. 226 8 Appendix C: Model Inputs and Results: Values of B, EE, PB, QB, TL, Catch and Discards of Target and Non-target Species, and Diets in Each System. .................................................... 229 9 Citations ............................................................ 275 vi 1. Introduction 1.1 Purpose and Background of Past Models Modeling food webs for use in large marine ecosystem (LME) fisheries management has been identified as a key element of an “ecosystem-based” approach to management (EPAP 1998). Such models provide a context for traditional single species approaches, rather than a replacement (Hollowed et al. 2000a), as they may identify key shifts in marine populations that arise out of changes in prey availability, predation mortality, or may identify climatic changes as they appear through shifts in these parameters. Moreover, such models, updated on 3-5 year intervals, may provide a basis for: i) the calculation of indicators specific to energy flow through modeled ecosystems; ii) an evaluation