On the French Mediterranean coast, more than thirty lagoons are classified as transitional water masses under the WFD. The lagoons selected for the INPOLAG project were chosen to cover the different levels of two gradients: connectivity to the sea and eutrophication. These two gradients can take values ​​from 1 to 3, with:

• For connectivity to the sea: 1 (Weakly connected) to 3 (Strongly connected)
• For eutrophication: 1 (Weakly eutrophicated) to 3 (Highly eutrophicated

Furthermore, the sediment types and the types of dominant vegetation cover within each Mediterranean lagoon was also used to stratified the survey sampling (Menu et al., 2020). The sampling strata corresponded to the crossing between:

- sediment typology: Sand (S:> 75% sand), Muddy sand (SV: 50-75% sand), Sandy mud (VS: 25-50% sand), Mud (V: < 25% sand)

- dominant vegetation cover: Algae (A), Phanerogams (P) or Nude (Nu).

For each stratum, ideally a minimum of 3 replicates were sampled.

The fishing gear used was a 10m wide and 2m high fine meshed beach seine (4mm mesh side). This fishing gear mainly targets benthic-demersal fish species for which the swimming abilities are relatively low (slow-moving species or individuals at the juvenile stage). Decapods (shrimps, crabs) may also be very abundant and were also recorded as they can provide information on the ecological quality of water bodies.

The stations were reached by boat to ease access and transportation of equipment, catch and operators. The beach seine was deployed by two operators over depths ranging from 0.5 to 1 m deep and over a distance of 25 m. At station, various environmental and physico-chemical parameters were measured. In order to validate the sedimentary facies, a sediment sample was also collected for particle size analysis in the laboratory. The dominant vegetation cover on each station was determined visually following the deployment of the beach seine

For each seine haul, the whole catch was sorted and weighted at species level based on various relevant identification keys or were taken back to the laboratory for further identification if needed. For a representative sub-sample of each species, individuals were weighted and measured (total length for fish and length or width of the cephalothorax for decapods). When sex could be observed externally, this information was also noted.

The data is in the ELevated FIsh Catch (ELFIC) format, were all sub-sampled observations were elevated to the level of the total catch in the catch table (ELFIC.V1.1, 2023-11-13).

The present dataset is composed of 6 tables.

1. The "lagoon table" recalling lagoon names and codes as well as their connectivity and eutrophic levels.

2. The "operation table" gives information about each operation (survey, date, location, strata, etc).

3. The "catch table" gives information on species catch raised as total number or total weight (kg) in the haul.

4. The "Biological_parameters table" gives information on measured individual length, weight or sex.

5. The "Other_parameters table" gives information on observed % substrate cover (algae, phanerogams or sediment), salinity, temperature, depth, oxygen saturation, current speed, wind direction, cloudiness, sea state.

6. The "sediment table" gives information on particle size distribution in 5 fractions (< 2µm; 2µm< x <20µm; 20µm< x <50µm; 50µm< x <200µm; 200µm< x <2mm) and organic matter content. This last table does not have records for all the stations.