Abundances and biological traits of the juveniles lamprey sampled in the survey of lamprey abundance Indice on the Oir river (France)

Study Extent

Oir river, CdSandre=I9280600 Latitude between 48.6840 and 48.5985; longitude between -1.2949 and -1. 0994 Source latitude and longitude : 48.6667 -1.1138 Last confluence point latitude and longitude : 48.6305 -1.2943 Oir river is located at the southern edge of Normandy. It is a tributary of the Sélune, a coastal stream flowing into the Bay of Mont Saint-Michel. The Oir is 21 km long, and has an average gradient of 11 ‰. Its drainage area is 87 km², dominated by sedimentary schist land and corneal including some granitic enclaves. The water pH is near neutral and of reasonably good quality but with high nitrate concentrations. Human activities and land use are mainly from agriculture. The upper Sélune is not accessible to migratory fish. They are blocked at fifteen kilometers from the sea by a dam. The Oir, with 12 km accessible to Atlantic salmon, is the main spawning and most productive tributary of the Sélune hydrographic network.

Sampling

In the Oir, sampling is conducted at 4 sites spread along the mainstem. The sites are visited once a year in autumn (end of September to early October).

Method steps

1. From Lasne 2019 : The method is derived from Surber stream bottom sampler for. The frame is pushed into the substrate (maximum 15 cm deep, depending on soft substrate layer thickness) and the operator uses hands, protected by gloves, to gently dredge the substrate into the net until the substratum is removed. Thereafter, remaining sediments and larvae are dipnetted and transferred into a large sieve (1 mm mesh, about 0.4–0.5 m2). For better efficiency, the dipnet should be almost as wide as the bottom sampler. The net of the bottom sampler is removed and the dredged sediment is transferred into the sieve to be cleaned out and to sort out the larvae. Biometric measurement of the fish are recorded after their anesthesia with benzocaïne. The fish length is measured (1 millimeter precision) then weighed (0.2 g precision). All the fish sampled are then released in their original site.

1. Lampetra planeri
   common name: Lamproie de planer rank: species
2. Lampetra fluviatilis
   common name: Lamproie de rivière, Lamproie fluviatile rank: species
3. Petromyzon marinus
   common name: Lamproie marine rank: species

The Oir river in Normandy (France). http://services.sandre.eaufrance.fr/Courdo/Fiche/client/fiche_courdo.php?CdSandre=I9280600