Oir River migration monitoring station

The migratory fish monitoring station is located in the downstream of the Oir River, approximately 1.5 km from its confluence with the Sélune River. The upstream and downstream traps are located at the Cerisel mill, in the town of Ducey. Operational throughout the year, they enable monitoring the migration of salmon, trout, lampreys and eel.  

Trapping
The migratory fish monitoring station has been in operation since 1983 (Extended Lambert II GPS coordinates: E 333834 – N 2409347). It is located in the inlet channel of the Cerisel mill and consists of two traps, one each for upstream and downstream migration. Devices were installed to guide fish towards the station, but they allow for only partial capture, which means that the trapping efficiency must be estimated.

Three types of parameters are recorded during trapping :

• Environmental : date, general weather conditions, rainfall (measured using a rain gauge at the station), water level (measured using a gauge downstream of the traps), migration activity (whether or not spawning fish were observed jumping at the waterfall at the Geins mill downstream)
• Technical : the trap in which each fish was captured, time of capture
• Biological : species, type for migrating juveniles (smolt, silver, adult, etc.), sex (mainly for adults), lenght, weight, general condition, scale sampling depending on the species and size (placed in a numbered paper bag), additional samples taken for experimental purposes, type of marking observed and applied (upstream trap: salmon and trout are marked with Alcian blue on both pectoral fins. downstream trap: trout are individually tagged with PIT tags).
   

The number of fish migrating upstream and downstream, is estimated using capture-mark-recapture surveys to estimate trappin efficiency.
Depending on the species, age can be estimated using the Peterson methode (size distribution histograms) scalimetry or individual marking (PIT Tag).

Downstream fish trap
The trap that captures fish that migrate downstream has been in operation since 1984. The fish are first guided towards the mill’s inlet channel by a barrier of metal rods that swing in the water across the main channel. At the monitoring station, the fish encounter a fixed grid fitted with a leaf remover. They must take a side overflow, fall onto a sloping surface and are directed into a cage from which they cannot escape. A new downstream migration cage was installed in 2012. It has improved conditions for the fish (new stainless-steel grids and materials to prevent injury, and a larger water capacity) and the operators (better ergonomics for retrieving fish or cleaning the cage).

Technical specifications:
Cage: 1.46 m (L) x 1 m (W) x 1.40 m (H). Mesh size: 1 cm²
Screener: 3.84 m (L) x 1.95 m (W) x 1 m (H). Bar spacing: 1 cm. 70° incline
Inclined plane: 1.50 m (L) x 2 m (W). Bar spacing: 1 cm

Upstream fish trap
The trap that captures fish that migrate upstream has been in operation since 1983. The fish are first guided towards the mill’s side channel, where the trap is located, by an electric barrier system. The barrier consists of a generator that powers a deflection screen composed of bars, which drop into the water every 50 cm (cathode) and are suspended by a cable stretched across the river, and a bar (anode) placed on the riverbed parallel to the cathode, 1 m below the cable.
The fish enter the cage through a funnel and are not able to escape (fishing-trap system).

Technical specifications:
Cage: 3.20 m (L) x 2 m (W) x 1 m (H). Mesh size 1 cm²
2 funnels: maximum opening 76.5 x 76.5 cm and minimum opening 31 x 31 cm. One with a 2 x 2 cm mesh when there is not too much leaf litter and debris (May-September) and another with a 4 x 4 cm mesh for the rest of the year.
Electric fence: 4 m (L) x 1 m (W) x 1 m (H). Spacing between bars: 50 cm

Lamprey trap
An additional trap uses a guide rail to capture young lampreys (of any species). The lampreys pass through an opening at the bottom of the weir system, which maintains the water level in the headrace, and are directed into a net (guide net). This system has been in operation since 2008.

Glass eel trap
The monitoring station first attempted to trap glass eels in 2014, but only a few were captured. The system was modified in 2015 to improve its effectiveness.

	Salmon Monitoring salmon migrations since 1984
	Trout Monitoring trout migrations since 1984
	Lampreys Monitoring lampreys migrations since 1984
	Eels Monitoring eels migrations since 1984