© Copyright 2019 Laura Elizabeth Koehn Advances in Models for Assessing Interactions of Forage Fish and Their Predators and Application to Ecosystem Based Fisheries Management (EBFM) Laura Elizabeth Koehn A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy University of Washington 2019 Reading Committee: Timothy E. Essington, Chair Phillip S. Levin P. Dee Boersma Program Authorized to Offer Degree: School of Aquatic and Fishery Sciences University of Washington Abstract Advances in Models for Assessing Interactions of Forage Fish and Their Predators and Application to Ecosystem Based Fisheries Management (EBFM) Laura Elizabeth Koehn Chair of the Supervisory Committee: Dr. Timothy E. Essington School of Aquatic and Fishery Sciences Ecosystem-based fisheries management (EBFM) involves considering tradeoffs between competing objectives in fisheries management. Forage fish world-wide are an important prey source for a wide range of predators but also support profitable fisheries. These two key ecosystem roles create potential tradeoffs; exemplifying a key EBFM issue. Commonly, large ecosystem models are used to explore these tradeoffs and interactions between forage fish, fisheries, and predators. However, structural assumptions of previous models create limitations for assessing tradeoffs. In this dissertation, I advance two models of varying complexity and apply a third, for the exploration of forage fish fishery-predator interactions, and reveal insights into these interactions that previous models could not. I explore forage fish-predator interactions through a large ecosystem food-web model with high taxonomic resolution of forage fish and their predators (Chapter 1) and potential tradeoffs of fisheries on these forage fish (Chapter 2). I also explore specific seabird-forage fish interactions through an ecological detailed seabird model (Chapter 3) and consider future avenues for EBFM implementation (Chapter 4). In the first chapter, I demonstrate that high model taxonomic resolution reveals lower ecological importance of individual forage species and lower reliance of predators on individual forage species (more generalist diets) in a large upwelling system, compared to models where species are aggregated into guilds. Though there are multiple pathways of energy flow in a system, Chapter 2 demonstrates that there are still tradeoffs to fishing forage fish, particularly large losses of non-market predators like seabirds and marine mammals. In many cases however, predator losses were only observed with increased fishing on a single forage fish species, so aggregation of forage fish species in models exaggerates tradeoffs of certain forage fish fisheries. Based on the key tradeoffs between forage fish catch and seabird conservation, in the third chapter, I demonstrate that in order to robustly apply ecologically-complex seabird models to further explore the impacts of forage fish availability on seabirds, more empirical information is needed on relationship between prey availability across a range of seabird demographic parameters. Finally, in the fourth chapter, I demonstrate that the capacity exists to apply a structured-decision making process for implementation of EBFM that explicitly addresses fishery tradeoffs. These results demonstrate the importance of constructing models around a specific question or objective to reveal insights into ecosystems that can help direct and focus future management and research. TABLE OF CONTENTS List of Figures ............................................................................................................................ iv List of Tables .............................................................................................................................. v Introduction ................................................................................................................................ 1 References .............................................................................................................................. 5 Chapter 1. Developing a high taxonomic resolution food web model to assess the functional role of forage fish in the California Current ecosystem ....................................................................... 8 Abstract .................................................................................................................................. 8 Introduction ............................................................................................................................ 9 Methods ................................................................................................................................ 12 Food Web Model............................................................................................................... 12 Parameterization and Uncertainty ...................................................................................... 15 Food Web Model Analysis ................................................................................................ 19 Metrics of Forage Fish Importance .................................................................................... 21 Results .................................................................................................................................. 22 Characterizing Food Web Linkages ................................................................................... 22 Food Web Model Structure................................................................................................ 24 Metrics of Forage Fish Importance .................................................................................... 25 Discussion............................................................................................................................. 26 References ............................................................................................................................ 32 Chapter 2. Trade-offs between forage fish fisheries and their predators in the California Current ................................................................................................................................................. 52 i Abstract ................................................................................................................................ 52 Introduction .......................................................................................................................... 53 Material and methods ............................................................................................................ 56 Results .................................................................................................................................. 64 Discussion............................................................................................................................. 67 References ............................................................................................................................ 74 Chapter 3. A seabird life history-specific model for evaluating seabird sensivity to forage fish fishing ....................................................................................................................................... 83 Abstract ................................................................................................................................ 83 Introduction .......................................................................................................................... 84 Methods ................................................................................................................................ 86 Seabird model ................................................................................................................... 86 Forage fish model .............................................................................................................. 93 Seabird parameters ............................................................................................................ 94 Scenarios and Model testing .............................................................................................. 96 Results ................................................................................................................................ 100 Discussion........................................................................................................................... 103 References .......................................................................................................................... 108 Chapter 4. Technical capacity for next-generation fishery ecosystem planning to support ecosystem-based fisheries Management .................................................................................. 123 Abstract .............................................................................................................................. 123 Introduction ........................................................................................................................ 124 Methods .............................................................................................................................. 127 ii Results ................................................................................................................................ 132 Overview of Components/Process ..................................................................................