Using fish mortality data to assess reporting thresholds as a tool for detection of potential disease concerns in the Scottish farmed salmon industry

Abstract Authorities have a requirement to establish methods of monitoring emerging disease issues in production animals including farmed Atlantic salmon. One such method has been the development of benchmarking criteria for the reporting of mortality events (which may be indicative of an emerging issue) derived from the observations from a single company production database. Here we use data obtained by the Scottish Environment Protection Agency between 2002–2009 for the entire Scottish farmed Atlantic salmon industry to demonstrate that similar production patterns occur for differing production cycles and geographic regions compared to the observations of a single company, suggesting that the reporting criteria can be applied nationally. Furthermore, the data demonstrates that had the current mortality criteria been in operation during 2002–2009, there would have been conditions resulting in 489 reporting events – a mean of five reporting events (95% CI [0,12.25]) month − 1 equating to 62 (95% CI [30.45, 94.6]) year − 1 – from 190 production sites, with summer months having greater reporting incidence. However, from a peak in 2003, there would have been a decline in reporting events, suggesting an improvement in health and welfare management. Statement of relevance This work supports the previously described benchmarking thresholds for reporting mortality events as an indicator of emerging diseases issues. This work considers data for all producers in Scotland across geographic regions and represents fish production cohorts between 2002–2009. By having a reporting threshold, it will enable the fish health inspectorate to reduce production losses through diseases issues and also provide a means of acting as an early warning system for potential emerging diseases issues.