Introduction

General description

Project description

Study area description: 

The research was carried out in the LTSER-ESTUARIES - Portugal (https://deims.org/664177a4-a21a-4f59-9601-00909e275868), more especially at the Lenta Marina (41°57'15.9"N 8°44'42.5"W), a small (660 × 80 m), semi-enclosed bay situated 14.5 km upstream in the Minho Estuary, which was chosen as a representative area of the estuary (Figs 1, 4). Lenta Marina occupies a location within an estuarine zone characterised by slight salinity fluctuations, with freshwater prevailing in accordance with the patterns of discharge of the river. In summer, Lenta Marina experiences minor saline intrusions, leading to relatively low salinity levels in the area. Specifically, salinity can range from 0 - 2 psu during late summer and drought conditions (Dias et al. 2016, Dias et al. 2020). The Minho Estuary is classified as a mesotidal estuary, characterised by an average depth of 2.6 m and reaching a maximum depth of 26 m (Alves 1996, Antunes et al. 2011).

Figure 1.  

Spatial representation of the study area and sampling locations in the Minho Estuary. A) A map of the Iberian Peninsula, with an indication of the sampling location within the Minho Estuary. B) A zoomed-in view of the study area, highlighting the representative deployment locations of the fyke nets (white circles) inside the Lenta Marina.

Figure 2.  

A photograph showing the removal of a fyke net from the water in the Minho Estuary (Photo by Carlos Antunes).

Figure 3.  

Days when samples were collected in the study area (Lenta Marina) in the Minho Estuary (i.e. days when fyke net(s) were underwater). Grey = fyke net(s) deployed; white = no fyke net deployed.

Figure 4.  

A photograph showing the view of the study area (Lenta Marina) in the Minho Estuary. The image shows the semi-enclosed bay, characterised by the presence of near-shore vegetation and the calm water surface where the fish sampling took place (Photo by Ronaldo Sousa).

Sampling methods

Sampling description: 

Fish samples were collected from January 2010 to November 2019. Fyke nets with a mesh size of 10 mm, a length of 7 m, a mouth diameter of 0.7 m and a central wing of 3.5 m were used to collect the fish (Fig. 2). These nets were consistently set in the morning and left submerged for 5.5 ± 2.6 days (average ± SD) (Fig. 3). To ensure even spatial coverage, the fyke nets were always set parallel to the shore and distributed close to the bay mouth at fixed locations (Fig. 1). Although the number of fyke nets used per sampling date varied due to technical issues (e.g. lost or damaged fyke nets), up to five fyke nets were employed per sampling date. After retrieving of the fyke nets, all captured individuals were identified (following Froese and Pauly (2023) and Martins and Carneiro (2018)) and counted (Fig. 5). During the entire study period, a total of 3,029 samples (i.e. individual fyke nets) were collected.

Figure 5.  

Treemap showing the total number of individuals of the most representative species during the long-term monitoring. The area of each rectangle is proportional to the total abundance of the species in all samples collected and the yellow numbers in the bottom right corner indicate the total abundance per species. Red background colour refers to the invasive species, with the category others corresponding to the least abundant species in the group, in this case, representative of two species: Gobio lozanoi (n = 255) and Carassius auratus (n = 20). Blue background colour refers to the native species, with the category others corresponding to the least abundant species in the group, in this case, it is representative of eight species: Mugil cephalus (n = 167), Salmo trutta subsp. fario (n = 162), Dicentrarchus labrax (n = 100), Chelon auratus (n = 51), Chelon labrosus (n=28), Squalius carolitertii (n = 20), Petromyzon marinus (n = 12) and Alosa (n = 1).

Permission to collect fish within the study area was obtained in correspondence with the Portuguese Navy.

Geographic coverage

Taxonomic coverage

Traits coverage

Temporal coverage

Collection data

Usage licence

Data resources

Additional information

Acknowledgements

Author contributions

References

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Supplementary material