ABSTRACT: Host density is a key driver in parasite population dynamics, and often the number of parasites increases rapidly with host density. In the context of Norwegian salmonid farming, this mechanism has led to a disparity between the desire to increase cultured salmonid production, and to reduce the negative effects of parasite infestations. Salmon lice infestations are detrimental to animal welfare due to salmon lice treatments and spillover from farms to wild salmonids. Here, we examine how a redistribution of the salmonid farm biomass may hamper exchanges of lice larvae between farms, and consequently reduce the salmon lice burdens and treatment frequencies. More specifically, we use a stochastic simulation model, fitted to empirical data from Norwegian aquaculture, to examine how lice abundances and treatments responded when the biomass in the system was distributed onto fewer, larger farms situated farther apart. To maintain realistic fish growth, seasonality and cohort development, lice population dynamics were simulated on top of historic production data from Norway. We simulated several scenarios, where an increasing number of farms were closed, and their biomass was redistributed to other farms with matching cohorts. The results indicate that fewer and larger farms reduce lice numbers and treatment frequency, and that a strategic removal of farms, based on their importance for connectivity in an oceanographic lice dispersal network, improves this effect. Some core mechanisms are highlighted that should be considered in regional production planning, and in the allocation of production concessions in salmonid farming.

中文翻译：

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模拟研究中养殖鲑鱼的地理重新分布减少了鲑鱼虱子侵扰和治疗频率

摘要：寄主密度是寄生虫种群动态的关键驱动因素，寄生虫的数量通常随着寄主密度的增加而迅速增加。在挪威鲑鱼养殖的背景下，这种机制导致了增加养殖鲑鱼产量的愿望与减少寄生虫感染的负面影响之间的差距。由于鲑鱼虱子治疗以及从养殖场蔓延到野生鲑鱼，鲑鱼虱子感染对动物福利有害。在这里，我们研究了鲑鱼养殖场生物量的重新分配如何阻碍养殖场之间虱子幼虫的交换，从而减少鲑鱼虱子负担和治疗频率。更具体地说，我们使用随机模拟模型，拟合来自挪威水产养殖的经验数据，来研究当系统中的生物量分布到距离较远的更少、更大的农场时，虱子丰度和处理措施如何反应。为了保持真实的鱼类生长、季节性和群体发育，根据挪威的历史生产数据模拟了虱子种群动态。我们模拟了几种场景，其中越来越多的农场被关闭，它们的生物量被重新分配到具有匹配队列的其他农场。结果表明，更少和更大的养殖场可以减少虱子数量和治疗频率，并且根据养殖场对海洋虱子传播网络连通性的重要性，战略性地移除养殖场可以改善这种效果。强调了区域生产规划和鲑鱼养殖生产特许权分配中应考虑的一些核心机制。