Marine Scotland Science, Marine Laboratory, 375 Victoria Road, Aberdeen, AB11 9DB, UK.
Prev Vet Med. 2013 Mar 1;108(4):285-93. doi: 10.1016/j.prevetmed.2012.11.005. Epub 2012 Dec 4.
Scotland is the largest Atlantic salmon (Salmo salar) producer in the EU with an output of over 150,000 t, contributing over £500 million annually towards the economy. Production continues to increase, predominantly due to the increase in output per farm and reduction in losses due to infectious diseases. Farms are grouped within disease management areas whose boundaries are defined by where the closest pair of farms is separated by more than twice the tidal excursion distance (TE) Tidal excursion is defined as 7.2 km in mainland Scotland, or 3.6 km in the Shetland Islands). The majority of salmon farms are located within relatively sheltered inshore areas where non-tidal advective current speed is minimal. However there is an aspiration for offshore production where it might be possible to increase stocking levels and where current speeds will be greater so TE models could break down. Separation distances whereby farms would avoid infection risk were obtained using an analytical, discrete-time Susceptible-Exposed-Infectious-Recovered (SEIR) model coupled with a hydrodynamic transport expression representing transmission of pathogenic agents between fish farms. The model incorporated transmission, expression and recovery parameters as well as pathogen shedding and decay. The simplified hydrodynamic model incorporated residual advection, tidal advection and turbulent diffusion elements. The obtained separation distances were compared to a computationally intensive, numerical model and were demonstrated to be comparable, although the analytical model underestimated the variation within the transmission distances. Applying characteristics for a robust pathogen, infectious pancreatic necrosis virus type (IPNV-type), and less robust pathogens such as infectious salmon anaemia virus type (ISAV-type) and Aeromonas salmonicida type (AS-type) pathogens, it was possible to obtain separation distances whereby farms avoided infection. Simulation outputs indicated that separation distances should increase to avoid disease as farm size and current speed increase. The more conserved IPNV-type pathogen required separation distances of hundreds of kilometres, AS-type required tens of kilometres, whilst the distances for ISAV-type were within the scale of the current DMAs, that were developed for ISAV control. However, should production be moved to areas of faster moving currents and increased farm production the current disease management area principles might need readdressing.
苏格兰是欧盟最大的大西洋鲑鱼（Salmo salar）生产国，产量超过 15 万吨，每年为经济贡献超过 5 亿英镑。产量继续增加，主要是由于每个养殖场的产量增加，以及由于传染病导致的损失减少。养殖场被分组在疾病管理区，这些区域的边界是由最近的两个养殖场之间的距离超过潮汐往返距离（TE）的两倍来定义的。在苏格兰大陆，潮汐往返距离被定义为 7.2 公里，在设得兰群岛则为 3.6 公里。大多数鲑鱼养殖场都位于相对避风的近岸地区，那里的非潮汐平流速度最小。然而，人们渴望在近海生产，在那里可能增加放养密度，并且那里的海流速度将更大，因此 TE 模型可能会失效。使用分析的离散时间易感-暴露-感染-恢复（SEIR）模型以及代表鱼养殖场之间病原传播的水动力传输表达式来获得避免感染风险的养殖场分离距离。该模型结合了传播、表达和恢复参数以及病原体脱落和衰减。简化的水动力模型包含了剩余平流、潮汐平流和湍流扩散元素。获得的分离距离与计算密集型数值模型进行了比较，结果表明两者具有可比性，尽管分析模型低估了传播距离内的变化。应用具有稳健病原体传染性胰脏坏死病毒型（IPNV 型）和较不稳健病原体如传染性鲑鱼贫血病毒型（ISAV 型）和鲑鱼气单胞菌型（AS 型）的特征，有可能获得养殖场避免感染的分离距离。模拟输出表明，随着养殖场规模和海流速度的增加，应增加分离距离以避免疾病。更保守的 IPNV 型病原体需要数百公里的分离距离，AS 型需要数十公里，而 ISAV 型的距离在为控制 ISAV 而开发的当前 DMAs 范围内。然而，如果生产转移到流动速度更快的地区和增加养殖场产量，当前的疾病管理区域原则可能需要重新考虑。
