Strong positive relationships between eDNA concentrations and biomass in juvenile and adult pike (Esox lucius) under controlled conditions: Implications for monitoring

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Abstract
Reliable abundance information is the foundation for managing aquatic resources. Species with low catchability are, however, often overlooked in monitoring programmes. Thus, governing bodies lack the data necessary to make well‐informed management decisions. Environmental DNA (eDNA) can produce quantitative estimates of fish abundances, but the precision varies greatly depending on the species and system. It is, therefore, necessary to evaluate its performance and investigate how fish biomass and density affects eDNA dynamics on a case‐by‐case basis before eDNA‐based monitoring can be a viable option. Here, we evaluate how biomass and density of an ecologically and socioeconomically important top predator, the Northern pike (Esox lucius), relate to eDNA concentrations in controlled aquarium and mesocosm experiments. We carried out experiments using both juvenile and adult individuals and evaluated eDNA, biomass and density relationships at three different time points using a previously developed TaqMan assay, targeting the cytochrome oxidase I gene. We also evaluated the performance of multiple extraction methods (DNeasy Blood & Tissue kit, DNeasy PowerWater kit, and Chelex 100), and filtering systems (single‐ vs. double‐membrane filters). The results from both pike experiments showed a strong positive linear relationship between eDNA concentration and pike biomass (R2 = 0.74 – 0.87). Levels of eDNA dropped drastically within the initial 24 h of juvenile pike being removed from the aquaria, and low levels were detectable for up to 308 h. Of the extraction methods, Chelex 100 yielded the highest DNA concentration, offering a quick and cost‐effective alternative compared with existing widely used extraction methods. Using double membrane filters of different material showed no increase in DNA yield regardless of the extraction method but it allowed more water to be processed. Although several challenges remain, our results show that eDNA holds promise to become a useful tool for monitoring fish biomass in natural environments.
Funding Information
  • Naturvårdsverket (NV‐03728‐17)

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