The potential for targeted surveillance of live fish movements in Scotland

Abstract

The network structure of the movements of live fish in the Scottish aquaculture industry has recently been demonstrated for 2003. In this paper, we enlarge this analysis to a longer three-year period from 2002 to 2004, the new data allowing complete coverage of at least one production cycle. The resulting network contains slightly more sites than that for a single year, and is denser with more arcs (directed site-to-site connections) present, but otherwise features recognisable in the one-year network are still recognisable in the three-year network. Arc removal algorithms (a proxy for targeted surveillance) were identified that could successfully reduce the portion of the network reachable from a node (a proxy for potential epidemic size) by approximately one third by removing as few as four arcs. This results from the high centrality of particular nodes and arcs. A strong community structure was identified in the network, corresponding with species farmed but only weakly geographical, with a high proportion of arcs occurring between management areas and catchments.