Scorff River migration monitoring station

The migratory fish monitoring station is located in the downstream reach of the Scorff River, at the edge of the estuary just beyond the zone of tidal influence, in the commune of Pont Scorff. The mill is open to the public, and fish are trapped throughout the year. The station captures fish that migrate upstream ordownstream. The main species captured are salmon, trout, eel, shad and lampreys.

Trapping

The migratory fish monitoring station, in operation since 1994, located downstream approximately 10 km from the harbour of Lorient (14 km from the sea). It is located on the inlet channel of the Princes mill in Pont-Scorff. The station consists of two traps, one each for upstream and downstream migration. A rocky breakwater was installed to guide fish towards the station, but it allows for only partial capture, which means that the trapping efficiency must be estimated.

The migratory fish monitoring station, in operation since 1994, is located approximately 10 km from the harbour of the town of Lorient (14 km from the sea). It is located on the inlet channel of the Princes mill in Pont-Scorff. The station consists of two traps, one each for upstream and downstream migration. A rocky breakwater was installed to guide fish towards the station, but it allows 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 Princes mill)
• 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), length , 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 are marked with Alcian blue on the abdomen)

The number of fish migrating upstream and downstream is estimated using capture-mark-recapture surveys to estimate the trapping efficiency.

Depending on the species, age can be estimated using the Petersen method (size-distribution histogram), scalimetry or individual marking (PIT tag).

Downstream fish trap

Some of the fish that swim downstream are first guided towards the mill’s inlet channel. At the monitoring station, the fish encounter a fixed grid fitted with a fish-removal device. They must take a side overflow and enter a cage.

Upstream fish trap

The fish that migrate upstream are first guided by a rockfill of boulders placed in the Scorff River towards the outlet channel of the Princes mill, where the trap is located.

The fish enter the cage through a funnel and are not able to escape (pot-trap system).

Main species monitored 

	Shad Monitoring of shad populations since 1994
	Eel Monitoring of eels populations since 1994
	Lampreys Monitoring of lampreys populations since 1994
	Mullet Monitoring of mullets populations since 1994
	Salmon Monitoring of salmon populations since 1994	See report
	Sea trout Monitoring of sea trout populations since 1994