Spatio-temporal monitoring of lake fish spawning activity using eDNA metabarcoding

Outlining the timing and location of fish reproductive events is crucial for the implementation of correct management and conservation schemes. Conventional methods to monitor these events are often unable to assess the spawning effort or can be invasive and therefore problematic. This is especially the case when threatened fish populations are the target, such as the Arctic charr (Salvelinus alpinus L.) populations in lake Windermere (Cumbria, UK). Arctic charr populations have been studied in this lake since 1960, and locations and characteristics of spawning grounds have been described in detail using techniques such as hydroacoustics, physical and visual surveys of the lake bottom. Here, we added a novel environmental DNA (eDNA) metabarcoding approach to assess the spatial distribution of the Arctic charr in the lake throughout the year to test whether this tool could allow us to identify spawning locations and activity in conjunction with established netting surveys. Seasonal sampling was carried out between October 2017 and July 2018 at three locations in the lake, covering putative and known spawning sites. In this study, eDNA metabarcoding enabled accurate spatial and temporal characterisation of Arctic charr spawning events. Peaks of Arctic charr read counts from eDNA metabarcoding were observed during the spawning season and at specific locations of both putative and known spawning sites. Net catches of mature Arctic charr individuals confirmed the association between the Arctic charr spawning activity and the peaks of eDNA metabarcoding read counts. Our observations demonstrated the ability of eDNA metabarcoding to effectively and efficiently characterise the spatial and temporal nature of Arctic charr spawning in lentic systems.