Environmental DNA complements scientific trawling in surveys of marine fish biodiversity (Dataset 2021)
At the end of October and the beginning of November 2021, we selected 18 sites from the 2021 EVHOE survey for eDNA sampling. The French international EVHOE bottom trawl survey is conducted annually in autumn in the Bay of Biscay (BoB) to monitor demersal fish resources. All selected sites were located on the continental shelf at depths ranging from 30 to 230 m. At each site, we sampled seawater using an underwater pump equipped with two peristaltic heads (subspace), mounted on Ifremer’s Pagure sledge. We collected approximately 30 liters of water directly from the seabed at a flow rate of 1.0 L min⁻¹. For filtration, we used VigiDNA 0.20 μm filtration capsules (SPYGEN, Le Bourget-du-Lac, France) along with disposable sterile tubing. Each filtration device processed water along a transect, representing two replicates per sampling site. To prevent contamination during fieldwork, we adhered to strict protocols, including the use of disposable gloves and single-use filtration equipment. At the end of each filtration, we emptied the remaining water from the capsule and replaced it with 80 mL of CL1 conservation buffer before storing the samples at room temperature. We processed the eDNA capsules at SPYGEN, following the protocol outlined by Polanco-Fernández et al. (2020). Library preparation and sequencing were performed at Fasteris (Geneva, Switzerland). Specifically, we prepared four libraries using the MetaFast protocol (a ligation-based method) and sequenced them separately. Paired-end sequencing was conducted using a MiSeq sequencer (2 × 125 bp, Illumina, San Diego, CA, USA) on two MiSeq Flow Cell Kits (v3; Illumina), following the manufacturer’s instructions. We analyzed the sequence reads using the OBITools package (http://metabarcoding.org/obitools; Boyer et al., 2016), following the protocol described by Valentini et al. (2016).
Data content:
* rawdata/: contains the raw reads for each individual sample. One archive contains the paired-end reads specified by the _R1 or _R2 suffix as well as individually tagged PCR replicates (if available) together with an archive containing all extraction and PCR blank samples of the library. Reads have been demultiplexed using cutadapt but not trimmed, individual demultiplexing tags and primers remain present in the sequences.
* taxadata/: contains the table with all detected taxonomy for each sample after bioinformatic processing (see Polanco et al. 2020 for details; https://doi.org/10.1002/edn3.140) and associated field metadata.
* metadata/: contains two metadata files, one related to the data collected in the field for each filter, and the second related to the sequencing process in the lab (including the tag sequence, library name, and marker information for each sample)
