Fin Fish Farming Effects - Baysian Network Model

From Report: An estimate of the scale of expected benthic effects associated with fish farming in the Firth of Thames Wilson Bay Marine Farming Zone was obtained by carrying out a Bayesian network analysis supported by literature studies. In addition, estimates of the likely spatial extent of benthic effects were provided based on previous published studies as a first step to predicting the footprint of finfish cages. The Bayesian network used in this study is a modified and re-parameterised version of an existing Bayesian network that was developed to quantitatively assess the relationships between benthic fish farm impact parameters and site and farm characteristics based on data published in peer-reviewed international journals from finfish farms located in temperate zones. The scale of benthic effects expected from establishing finfish farms in the Wilson Bay Marine Farming Zone was examined using selected case studies that represent realistic farming scenarios for this area. Case studies were created by examining different combinations of fish stocking density and water depth, which are expected to influence the scale of benthic impact. The focus of this report was to highlight the differences in benthic impacts predicted from the case studies and the trends generated from varying the input parameters, rather than making predictions of absolute variable values. The Bayesian network analysis suggested that of the examined input parameters the free water depth below fish cages has the largest effect on the severity of benthic impacts and it is recommended that the minimum free water depth below cages should be 10 m. It is general practice in finfish aquaculture to use cages between 10 and 15 m depth and allow for a similar depth of water below cages to promote the dispersal of faeces and uneaten food, consequently the most suitable areas for the installation of fish cages are those with water depths of 20 m or more. Changes in stocking density only resulted in small changes in the probability distributions of most variables. Selected literature studies were reviewed to examine the usefulness of monitoring parameters for the assessment of benthic impacts in the Firth of Thames that were not included in the Bayesian network. Full details available in report (see below). Purpose: This report presents an exploration of the benthic carrying capacity of the Firth of Thames for finfish farming to provide some background information for the management of aquaculture by Environment Waikato. This report aims to estimate of the scale of expected benthic effects associated with fish farming in the Firth of Thames Wilson Bay Marine Farming Zone based on benthic effects observed at finfish farms in similar temperate environments.

Contents page of report: Executive Summary 1. Introduction 1.1 Background 1.2 Brief overview of benthic effects of finfish farming 2. Scope and stipulations of this report 2.1 Finfish species 2.2 Wilson Bay hydrographic conditions 2.2.1 Water depth 2.2.2 Current speed 2.3 Case studies 3. Bayesian network analysis 3.1 Bayesian networks 3.2 Bayesian network for assessment of potential benthic effects of finfish farming 3.3 Predicted benthic effects of finfish farming in the Firth of hames 4. Sensitivity to increases in FCR 5. Review of selected literature studies 5.1 Trace metals and video surveys 5.2 Biogeochemical processes and sediment trap deployments 5.3 Opportunistic macrofauna species 5.4 Stable isotopes 6. Estimates of farm footprints in the Firth of Thames 6.1 Spatial extent of benthic impacts 6.1.1 Estimates based on peer-reviewed literature 6.1.2 Estimates based on New Zealand monitoring data 6.2 Implications for buffer zones of farm blocks in the Wilson Bay Marine Farming Zone 7. Summary and recommendations 7.1 Bayesian network analysis 7.2 Reviewed studies 7.3 Spatial extent of benthic effects 8. References 9. Appendix

Firth of Thames marine farming area.

Review undertaken in 2007 of previous studies.

The Bayesian network used in this study is a modified and re-parameterised version of an existing Bayesian network that was developed to quantitatively assess the relationships between benthic fish farm impact parameters and site and farm characteristics based on data published in peer-reviewed international journals from finfish farms located in temperate zones.

Assessment of overall environmental effects of finfish farming in the Wilson Bay marine farming zone, Firth of Thames.

Report freely available from Environment Waikato.

Related information: Carrying capacity for finfish farming Natural character and visual impact assesment for finfish farming.