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Fishing for Answers: analysis of ecosystem dynamics, tropic shifts and salmonid population changes in Puget Sound, 1970-1999

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Fisheries Centre Research Reports, Vol. 9 No. 6 Pages: 35pp
2001 | PDF

Edited by Preikshot, D., and Beattie, A.

INTRODUCTION

The impetus for this study arose from the shocking declines in early marine survival rates of South Puget Sound (SPS) coho salmon (Oncorhynchus kisutch) after 1990. This phenomenon coincided with declines in other species and prompted an inter-agency working group1 to seek ways of investigating the ecological relationships between salmon and other marine organisms in SPS. Ecosystem modelling, and the Ecopath with Ecosim (EwE) software in particular were determined as the most efficient method to summarize marine organism relationships in response to changing anthropogenic and environmental stressors. In general, it was hoped that EwE could address the following areas of concern:

assimilate the available data on the SPS area,
organize that data in terms of biomass,
determine the reliability of the available data, and
determine relative marine productivity in SPS.

More specifically, it was hoped that the EwE approach could elucidate the factors influencing coho early marine survival rates and determine crucial trophic relationships among the organisms of SPS. The EwE modelling of SPS is envisioned as the first phase of a three-phase process to evaluate ecosystem-level processes in Puget Sound. It is hoped that additional funding might be obtained to complete phases two and three. The second phase consists of building ecosystem models for two other sub-regions of Puget Sound: Hood Canal and the 'Central Basin'. The third phase of this process involves the synthesis, evaluation, and potential application of the information derived in phases one and two for use in an ecosystem level assessment of Puget Sound.

Glossary	2
Director's Foreward	3
1. Introduction	4
2. South Puget Sound Now and Then: What Happened?	5
2.1 The physical and chemical setting	5
2.2 Changes in the biological community of South Puget Sound: Into the Abyss	7
3. Phytoplankton	9
4. Algae / Kelps / Seagrasses	10
5. Zooplankton / Benthic Invertibrates	10
5.1. Zooplankton	10
5.2. Benthic Invertebrates	10
6. Herring, Forage Fishes, and Demersal Fishes	11
6.1. Herring and Forage Fishes	11
6.2. Demersal Fishes	11
7. Salmonids	11
7.1. General Issues	11
7.2. Biomass and Catch Estimations	14
7.3. Diet Composition	15
7.4. A salmon bioenergetics model	16
8. Birds	18
9. Marine Mammals	19
10. Balancing and Analysing the South Puget Sound Ecopath Models	19
10.1 Balancing the Models: SPS 1999	19
10.1.1. Primary Producers	20
10.1.2. Invertebrates	20
10.1.3. Salmonids	20
10.1.4. Demersal and Forage Fishes	20
10.2. Balancing the models: SPS 1970	20
10.2.1. Invertebrates	21
10.2.2. Salmonids	21
10.2.3. Demersal and Forage Fishes	21
10.2.4. Marine Mammals and Birds	21
10.3. Results from the 1990s and 1970s models	21
10.4. SPS 1990s vs. SPS 1970s: Discussion	23
10.5. Moving to an SPS Ecosim model	25
11. Using the Ecosim Model to Evaluate Historic Cahnges to the South Puget Sound Ecosystem	26
11.1. Introduction: Ecosim Features	26
11.2. Validating the model	26
11.2.1. Changes to the Ecopath baseline	26
11.2.2 Vulnerabilities	27
11.2.3. Hatchery effects	27
11.2.4. Estimating historical primary production anomaly	27
11.2.5 Conclusions	28
11.3 Improving the model	30
11.4. Comparison with the Strait of Georgia model	30
11.4.1. Overall fits	30
11.4.2. Historical production anomalies	31
11.5. Conclusions	31
References	31

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FCRR

Fishing for Answers: analysis of ecosystem dynamics, tropic shifts and salmonid population changes in Puget Sound, 1970-1999

Editors

Publication

INTRODUCTION

TABLE OF CONTENTS