Data for: Detection and quantification of two commercial flatfishes (Solea solea and Pleuronectes platessa) in the North Sea using environmental DNA

Sustainable fisheries management requires regular scientific monitoring of
fish stocks. When information on certain fish stocks is limited,
environmental DNA (eDNA) holds promise to complement traditional
monitoring surveys. However, a better understanding of how eDNA
concentrations relate to fish abundance and biomass is needed. Here, eDNA
quantification of two commercially important flatfish species in the
North‐East Atlantic, common sole (Solea solea) and European plaice
(Pleuronectes platessa), was assessed. First, species‐specific,
probe‐based assays for plaice and sole targeting the mitochondrial
cytochrome b and cytochrome c oxidase subunit I gene, respectively, were
developed (for sole) and validated (for both species). Subsequently, two
mesocosm experiments revealed a significant and positive relationship
between both abundance and biomass and eDNA concentrations for both
species at three eDNA emission time periods (5 min, 1 h, and 24 h). Larger
plaice shed significantly more eDNA (copies L-1) than smaller
conspecifics. Finally, eDNA was obtained from seawater collected during
research surveys in the Belgian part of the North Sea in spring 2020
(i.e., local scale) and the southwestern North Sea in autumn 2020 and 2021
(i.e., regional scale). eDNA concentrations were compared to the observed
abundance (individuals per km2) and fish density in terms of biomass (kg
per km2) as observed in the trawl at the same station. Local eDNA
concentrations of both sole and plaice were positively correlated with
observed abundance and fish density. The correlation between regional eDNA
concentrations and fish density was positive and significant for sole in
2020 and 2021 and for plaice in 2020, but not in 2021. The correlation
between regional eDNA concentrations and observed abundance was positive
and significant for sole and plaice in 2020, but not in 2021. These
results illustrate the potential of eDNA to estimate abundance and biomass
parameters for stock assessments of flatfishes in the North Sea.