Data from: Fish culling reduces tapeworm burden in Arctic charr by increasing parasite mortality rather than by reducing density‐dependent transmission

1. Two common Dibothriocephalus (formerly Diphyllobothrium) tapeworm species were significantly reduced by experimental culling of their fish host Arctic charr (Salvelinus alpinus) in a subarctic lake. 2. Between 1984 and 1991, funnel traps were used to cull ~ 35 metric tons of Arctic charr, reducing charr density by ~ 80%. As charr densities decreased, tapeworm prevalence and then intensity also declined over the following three decades, with D. dendriticus (formerly dendriticum) responding faster than D. ditremus (formerly ditremum). The two main hypotheses for how culling a host can decrease parasitism are reductions in parasite transmission due to reduced host density and reductions in parasite survival through increases in host mortality rates. 3. We found little evidence that charr density was the main driver for reduced parasite transmission. Instead, decreased survivorship in charr, initially, through fishing-induced changes in charr age structure, and later through increased predation rates by brown trout, led to increased parasite mortality. Although brown trout, which increased significantly after fish culling, are also hosts, they are often too big for the final host birds to eat, thus becoming parasite sinks. 4. Synthesis and applications: Fish populations with heavy parasite burdens constitute a management problem. Our results show how fish culling reduce indirectly transmitted parasites through increased parasite mortality. Managing overcrowded fish populations by culling can produce two desirable outcomes: an increase in fish growth rates and reduced parasite burdens.

1. 本研究在一处亚北极湖泊中开展实验性移除其鱼类宿主北极红点鲑（Salvelinus alpinus）的操作，结果显示两种常见的迭宫绦虫属（Dibothriocephalus，旧称裂头绦虫属Diphyllobothrium）绦虫种群显著减少。
2. 1984年至1991年间，研究人员使用漏斗陷阱移除了约35吨北极红点鲑，使其种群密度下降约80%。随着红点鲑密度降低，后续三十年间绦虫的感染率与感染强度均随之下降，其中树状迭宫绦虫（D. dendriticus，旧称树状裂头绦虫D. dendriticum）的响应速度快于三叉迭宫绦虫（D. ditremus，旧称三叉裂头绦虫D. ditremum）。关于移除宿主可降低寄生虫寄生水平的机制，目前存在两种主流假说：一是宿主密度降低导致寄生虫传播途径减少；二是宿主死亡率升高使得寄生虫存活率下降。
3. 本研究未发现足够证据表明红点鲑密度是降低寄生虫传播的主要驱动因素。实际上，红点鲑的存活率下降最初源于捕捞导致的种群年龄结构改变，后续则因褐鳟捕食压力升高所致，这一过程提升了寄生虫的死亡率。尽管在鱼类移除操作后种群显著扩张的褐鳟同样为该寄生虫的宿主，但褐鳟体型通常过大，无法被该寄生虫的终末宿主鸟类捕食，因此成为了寄生虫汇（parasite sink）。
4. 综合与应用：寄生虫负荷较高的鱼类种群会给渔业管理带来难题。本研究结果揭示了鱼类移除操作可通过提升寄生虫死亡率，间接降低间接传播性寄生虫的种群规模。通过移除操作管理种群过载的鱼类种群，可同时实现两个理想目标：提升鱼类生长速率与降低寄生虫负荷。