The contact structure of Great Britain’s salmon and trout aquaculture industry

A.E Jones,L.A Munro,D.M Green,K.L Morgan,A.G Murray,R Norman,D Ryder,N.K.G Salama,N.G.H Taylor,M.A Thrush,I.S Wallace,K.J Sharkey

doi:10.1016/j.epidem.2019.05.001

Abstract

We analyse the network structure of the British salmonid aquaculture industry from the perspective of infectious disease control. We combine for the first time live fish transport (or movement) data covering England and Wales with data covering Scotland and include network layers representing potential transmission by rivers, sea water and local transmission via human or animal vectors in the immediate vicinity of each farm or fishery site. We find that 7.2% of all live fish transports cross the England-Scotland border and network analysis shows that 87% of English and Welsh nodes and 72% of Scottish nodes are reachable from cross-border connections via live fish transports alone. Consequently, from a disease-control perspective, the contact structures of England and Wales and of Scotland should not be considered in isolation. We also show that large epidemics require the live fish movement network and so control strategies targeting movements can be very effective. While there is relatively low risk of widespread epidemics on the live fish transport network alone, the potential risk is substantially amplified by the combined interaction of multiple network layers.

Highlights

Finfish aquaculture in the United Kingdom continues to increase, with the UK-wide collated figures for 2014 reported to be 193 kt (Hambrey and Evans, 2016) with an imputed value of £762 m
A limiting factor in the sustainable expansion of the aquaculture industry is the management of infectious diseases which can lead to diminished production
We focus on two salmonid species groups, referred to as salmon and trout, where salmon include Atlantic salmon (Salmo salar) only, and trout refers to all other salmonid species stocked, here almost exclusively rainbow trout and brown trout

Summary

Introduction

Finfish aquaculture in the United Kingdom continues to increase, with the UK-wide collated figures for 2014 reported to be 193 kt (Hambrey and Evans, 2016) with an imputed value of £762 m. A limiting factor in the sustainable expansion of the aquaculture industry is the management of infectious diseases which can lead to diminished production. In a study of one marine Atlantic salmon farming company’s production data, an estimated one third of salmon mortality was attributed to infectious disease (Kilburn et al, 2012). Finfish diseases can have severe economic and social impacts on aquaculture. From 2007 to 2009, an outbreak of infectious salmon anaemia virus (ISAV) in Chile had a direct economic impact estimated at US$2bn, with a loss of 15,000 jobs (Mardones et al, 2011). Eight finfish diseases are notifiable in the UK under European Council and Aquatic Animal Health Regulations (Council of the European Union, 2006; Anonymous, 2009a, b). Controls, including the restriction of live animal movements, may be applied to premises and river catchments where notifiable disease is suspected or confirmed to be present (Anonymous, 2009a, b)

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