Environmental Research Observatory (ERO) on Diadromous Fish in Coastal rivers (DiaPFC): Abundance indices and biological traits of juvenile salmon (Salmo salar).

The Environmental Research Observatory (ERO) on Diadromous Fish in Coastal rivers (DiaPFC) monitors three coastal rivers on the Atlantic and Channel coasts of France: the Oir in Normandy, the Scorff in Brittany and the Nivelle in the French Basque Country (Fig. 1).

Figure 1.  

Geographic location of the three coastal rivers in which the dataset was collected.

Oir river: Latitude ranges from 48.6840 to 48.5985; longitude ranges from -1.2949 to -1.0994 and elevation range from 9 and 80 metres.

The Oir River is located on the southern edge of Normandy. It is a tributary of the Sélune, a coastal river that flows into the Bay of Mont Saint-Michel. The Oir is 21km long and has a mean gradient of 1.1%. Annual mean discharge is 1.1m³/s and the drainage basin area is 85.4km². Geologically, the basin is dominated by sedimentary schist and metamorphic hornfels with granite inclusions. The water has nearly neutral pH and reasonably good quality except for high nitrate concentrations. Agriculture is the main human activity and land use. Migratory fish cannot access the upper Sélune because a dam 15km from the sea blocks their movement. The Oir, with 12km accessible to Atlantic salmon, is the main spawning ground and most productive tributary of the Sélune hydrographic network.

Scorff River: Latitude ranges from 47.7718 to 48.1682; longitude ranges from -3.2497 to -3.3404 and elevation range from 0 and 144 metres.

The Scorff River is a small coastal river in southern Brittany (France). The main river is 78.6km long, including a 15km estuary. The mean gradient is 3.6%, annual mean discharge is 5m³/s and the drainage basin area has an area of 480km². Agriculture is the main human activity and land use, with several areas of moors and forests. Atlantic salmon essentially colonise only a 50km stretch of the main river starting at the head of the estuary. Most reproduction of Atlantic salmon occurs in the main river (Bagliniere 1979).The Scorff has only three larger tributaries. Until recently, Atlantic salmon could colonise only downstream sections of these tributaries due to mill dams.

Nivelle River: Latitude ranges from 43.2426 to 43.3912; longitude ranges from -1.4799 to -1.6694 and elevation range from 6 and 75 metres.

The Nivelle River is a 39km long coastal river in the Basque Country. Its source lies in Spain and it flows into the Bay of Biscay at Saint-Jean-de-Luz. Its drainage basin has an area of 238km², which is dominated by marly-calcareous formations. It is essentially agro-pastoral with more than 50% of the land area consisting of moors (Dumas 2003). The oceanic climate, mild and wet (rainfall of 1700mm/yr in St-Pée-sur-Nivelle), provides a mean annual discharge of 5.4m³/s downstream of the confluence of the main tributary, the Lurgorrieta and 9m³/s at the mouth. The water, neutral to slightly alkaline, is of good quality upstream of Saint-Pée-sur-Nivelle, but degrades downstream.

Rivers are equipped with diadromous fish trapping facilities and have been thoroughly and continually surveyed since the mid-1980s. They are affiliated with experimental ecology facilities located in Rennes (Brittany) and Saint-Pée-sur-Nivelle (Basque Country). To quantify their abundance of juvenile Atlantic salmon, they are surveyed every year in early autumn (late September to early October). The electric fishing protocol of Prévost and Baglinière (1995) is used to monitor the fish. It targets young-of-the-year (0+ parr) Atlantic salmon, but older fish (juveniles ≥1+) are also caught and included in the dataset. This protocol is not a Water Framework Directive standard protocol but has been calibrated with density which allows comparisons with other protocols. Sampling is restricted to areas with shallow running water that flows over a coarse bottom substrate, i.e. the preferred habitat of 0+ parr. The data consist of abundance indices and biological traits measured for the fish sampled: sex, maturity status, length, weight and age. Scale samples are taken from all fish for which size is not well correlated with age (Baglinière et al. 1985;Baglinière and Le Louarn 1987).

In the Oir, sampling is conducted at 11 sites along the mainstream and 2 others on the 2 major tributaries (Fig. 1). In the Scorff, sampling is conducted at 42 sites along the mainstem and 24 sites distributed over 12 tributaries (Fig. 1). In the Nivelle, sampling is conducted at 20 sites along the mainstem, 6 sites along the main tributary (i.e. the Lurgorrieta) and 2 other sites distributed over 2 smaller tributaries (Fig. 1). All sites are located in the area of the hydrographic network colonised by Atlantic salmon and visited once a year at the beginning of autumn (end of September to early October). Sampling by site and by year is indicated in Suppl. material 1.

Salmon Abundance Index is described in Prévost and Baglinière (1995). Since the beginning of data collection, fish have been caught with the same backpack electrofishing equipment (Martin Pêcheur®, DREAM Electronique, Pessac, France) tuned to produce a pulsed DC with 400 Hz frequency, 250-300 volts and a square-waveform 4-10% duty cycle. Fishing consists of the following steps:

1. Two large dip-nets with semi circular metal frames, one 60cm wide and 40cm high and another 80cm wide and 40cm high with 4mm² mesh are placed facing the current, are rested on the bottom and are maintained in a fixed position. Dip-nets never varied over time.
2. The area shocked is 4-5m directly upstream of the stationary dip nets so that fish disabled by the shocker are carried by the current into the dip nets.
3. Fish attracted to the anode and shocked go down into the nets guided by the electrode and driven by the water flow. When necessary, a small hand net is used to catch fish stuck on the bottom or in aquatic vegetation.
4. Individuals are transferred into a bucket previously filled with water.
5. The entire team moves laterally several metres from the area that was recently disturbed by the electric field; the carrier of the electrofishing equipment is careful not to step into the area the anode will next explore . When a bank is reached, the team moves a few metres upstream.

Steps 1-5 are repeated. Sampling at a given site stops after 5 minutes of fishing, i.e. the duration during which the electric field is applied in the water, this being measured directly on the counter of the electrofishing equipment. Juvenile abundance is quantified by the number of individuals captured per unit effort (5 minutes of fishing under the conditions specified above).

Biometric measurements of the fish are recorded after anaesthetising specimens with a solution of benzocaïne (Neiffer and Stamper 2009, Gilderhus 1989). Then length is measured from the tip of the mouth to the fork of the caudal fin (1mm precision). Fish are then weighed (0.2g precision), sex and certainty of maturity status is assessed by applying gentle pressure to the belly, which expresses sperm from mature males (the individual can be mature without sperm detection). After recovery from anaesthesia, all fish sampled are then released at their site of capture.

Age is estimated by scale analysis according to standard methods described in Richard and Bagliniere (1990), Baglinière and Le Louarn (1987)Baglinière et al. (1985).

Data are stored in a PostgreSQL database and are thus subject to an integrity check by the database management system. Consistency checks, mainly on size and weight, were performed when the field records were entered. Since 2016, length and weight are automatically measured and sent by bluethooth to avoid transcription errors. All our weighing devices are checked annually and the tool length measurement is calibrated at the beginning of a fishing session.

Use of the French National Service for Water Data and Reference Dataset Management (SANDRE, Service d'administration nationale des données et référentiels sur l'eau) guarantees interoperability with French water information systems. The Sandre is organised in a network of SIE-contributing institutes that bring their thematic knowledge, participate in the reference data sets management and ensure the overall coherence. Managed by AFB, this network is supported by a technical secretariat provided by the International Office for Water, which moves, develops and makes available these reference data sets.

For publication on the GBIF portal, data and metadata were transformed to compliance with Darwin Core standards Wieczorek et al. 2012 (Event Core and Occurrence Extension). These Global Biodiversity Information Facility datasets are Darwin Core Archive files, encoded in UTF-8 and permanently available on the GBIF portal.

Observations included in this dataset originate from three coastal rivers on the Atlantic and Channel coasts of France: the Oir in Normandy, the Scorff in Brittany and the Nivelle in the Basque Country (Fig. 1).

43.2426 and 48.6840 Latitude; -1.0994 and -3.3404 Longitude.

Fundamental features of the specie's life cycle, distribution and ecology can be found in Les poissons d’eau douce de France (Keith et al. 2011).