Fisheries Centre Research Reports, University of British Columbia

A Trophic Mass-Balance Model of Alaska's Prince William Sound Ecosystem for the Post-Spill Period 1994-1996, 2nd Edition

FCRR 1999, Vol.7 (4)

Okey, T. and Pauly, D. (eds). 1999. A Trophic Mass-Balance Model of Alaska's Prince William Sound Ecosystem for the Post-Spill Period 1994-1996, 2nd Edition

Abstract

Information about the ecological components of Alaska's Prince William Sound (PWS) has increased considerably since the 1989 Exxon Valdez oil spill (EVOS), but the structure and functional characteristics of the overall food web are still not well understood. A better understanding of the whole PWS food web and its dynamics was achieved by constructing a balanced trophic model using the Ecopath approach. This was the best available framework to summarize available ecosystem information in a trophic context, as it explicitly accounts for multi-species interactions. The PWS model is a cohesive synthesis of the overall biotic community with a focus on energy flow structure, and response to perturbations--both natural and anthropogenic. Flows of biomass among the various components of the food web were quantified using estimates provided by a collaborative group of over 35 experts on PWS ecosystem components.

The dynamic modelling routines Ecosim and Ecospace can be used to simulate the ecosystem-level effects of disturbances and management actions, and to provide insights into ecosystem-level changes and dynamics that may occur in Prince William Sound. The Ecopath model of PWS can be used to help guide future research programs in the region, to help assess impacts of the EVOS, and to help resource agencies and local communities achieve ecosystem-based conservation and management in the face of increasing human activities in the region. This approach can also be used to help distinguish the relative importance of physical forces and tropic forces in marine ecosystems.

An annotated list of Alutiik words was included in this volume to facilitate cross-cultural flows of ecosystem knowledge. This list might serve as one step in helping to promote a more community-based approach to management of the wild living resources of Prince William Sound.

Table of Contents

Abstract

Director's Foreword

VII

List of Exhibits

Preface to the 2^nd Edition

XII

INTRODUCTION (Thomas A. Okey)

Prince William Sound

The 1989 Exxon Valdez Oil Spill

Other Anthropogenic Stressors

Natural Disturbances and Cycles

Defining the PWS Ecosystem

Aspects of the Ecopath approach relevant to the PWS model (V. Christensen, D. Pauly, T.A. Okey)

Surface areas of PWS depth zones and habitats (Tom Dean)

MODEL INPUTS

PRIMARY PRODUCERS

ZOOPLANKTON

BENTHIC INVERTEBRATES

PLANKTIVOROUS 'FORAGE FISHES'

LARGER FISHES

BIRDS

MAMMALS

Detritus

PWS Fisheries

Constructing and Balancing the PWS Model (Thomas A. Okey)

Verification of web structure

Ecosim and Ecospace Methodology (Thomas A. Okey)

RESULTS (Thomas A. Okey)

Temporal simulations of perturbations

Spatially explicit simulations

Ecopath and Resource Management (Thomas A. Okey)

Ecosystem Models as Caricatures (Jennifer L. Ruesink)

An annotated list of Alutiiq words relevant to modeling the Prince William Sound ecosystem (Dave Preikshot and Jeff Leer)

ACKNOWLEDGEMENTS

104

LITERATURE CITED

105

Appendices

117

Appendix 1. List of contributors to PWS Ecopath model

117

Appendix 2. Workshop Agendas

122

Appendix 3. Monthly estimates for PWS zooplankton parameters

127

Appendix 4. Derivation of diet compositions of forage fishes

130

Appendix 5. Input diet compositions of PWS animals

135

Appendix 6. Diagram of arrowtooth founder spatial distribution

137

Download this report

Full Report