Detection and Quantification of Two Flatfish Species in the Sylt Outer Reef: Development of a q PCR Assay and Forecast Model Based on e DNA Copies

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ABSTRACT Assessing fish diversity and abundance is crucial for effective marine conservation and management strategies, particularly in ecologically sensitive areas such as the North Sea. Bottom trawling, one of the most commonly used fishing methods, is facing growing criticism, even for scientific purposes, and has already been banned in ecologically sensitive zones. Therefore, it is crucial to rapidly establish noninvasive monitoring methods for solid biodiversity and abundance or biomass assessments in marine habitats. In this study, the potential of environmental DNA (eDNA) multiplex qPCR analyses, combined with computational modeling methods, for the quantitative assessment of common dab ( Limanda limanda ) and European plaice ( Pleuronectes platessa ) was explored. The concordance between the detectability of qPCR eDNA results and bottom trawling as the reference method was around 90% with a specificity of qPCR of 100% and a sensitivity of 82% for both species. For biomass estimation the outputs of a newly developed nonlinear model, with depth as an additional variable, showed correlations between the number of eDNA copies and biomass CPUE estimates from bottom trawl catches of 80% and 60% for plaice and dab, respectively. The model performance was validated by using data from other sampling missions in the North Sea and Baltic Sea. A good validation was recorded for plaice (RMSE 26%) and to a lesser extent for dab (MAE 34%). These results demonstrate the potential of eDNA as a noninvasive tool, not only for biodiversity monitoring, but also as a proxy for biomass estimations for certain species, although further optimization steps are certainly required for a stand‐alone use.

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