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

Study Extent

Scorff river, CdSandre=J5--0220 Latitude between 47.7718 and 48.1682; longitude between -3.2497 and -3.3404 Source latitude and longitude : 48.14 -3.283 Last confluence point latitude and longitude : 47.7371 -3.3474 The Scorff river is a small coastal stream of Southern Brittany (France). The main river is 78,6 Km long including 15 km of estuary. The mean gradient is 3,6%, the annual mean discharge is 5 m3 s- and the drainage basin area is 480 km2. Human activities and land use are mainly from agriculture, with some areas made moors and forests. Atlantic salmon colonization is essentially restricted to the main river over a 50 km stretch starting at the head of tide. Reproduction of Atlantic salmon takes place mostly in the main river (Bagliniere et al., 1979).The Scorff has only three larger tributaries. Up to recent years, their colonization by Atlantic salmon was restricted their down-stream end due to mill-dams.

Sampling

In the Scorff, sampling is conducted at 2 sites spread along the mainstream. The sites are visited once a year in autumn (end of August to early September).

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 from the tip of the mouth to the fork of the caudal fin (1 millimeter precision). Fish are then weighed (0.2 g precision) and maturity status is assessed by a gentle pressure on the belly that allows to get sperm in mature males. All the fish sampled are then released in their original site.

1. Lampetra planeri
   common name: Lamproie de planer rank: species
2. Petromyzon marinus
   common name: Lamproie marine rank: species

The Scorff river in Britanny (France). http://services.sandre.eaufrance.fr/Courdo/Fiche/client/fiche_courdo.php?CdSandre=J5--0220