Phenology and biological traits of migrating brown trouts and sea trouts sampled by trapping in the Nivelle river (France).

Study Extent

Nivelle river, CdSandre=S52-0400 Latitude between 43.2426 and 43.3912; longitude between -1.4799 and -1.6694 Source latitude and longitude : 43.2173 -1.5231 Last confluence point latitude and longitude : 43.3854 -1.6639 The Nivelle is a 39 km long coastal stream of Pays Basque. It has its source in Spain and flows into the Bay of Biscay at Saint-Jean-de-Luz. Its drainage basin has a surface area of 238 km2, and is dominated by marly-calcareous formations. It is essentially agro-pastoral with more than 50% of the land area made of moors (Dumas, 2003). The oceanic climate, mild and wet (1700 mm year-1 in St-Pe´e-sur-Nivelle), provides a mean annual discharge of 5.4m3 s-1 downstream from the confluence of the main tributary, the Lurgorrieta, and 7 m3 s-1 at the mouth. The water, neutral to slightly alkaline, is of good quality upstream from Saint-Pée-sur-Nivelle, but deteriorates downstream.

Sampling

The Uxondoa and Olha traps are in continuous operation from March to January, except during periods of high flooding. The traps are checked at least once a day.

Method steps

1. Adult brown trout and sea trout have been monitored since 1984 by trapping at Uxondoa trap in the Lower Nivelle operating the whole year. Trap configuration allows only partial capture depending on the flow. A second upstream trap at olha in the upper Nivelle (since 1992) allows to estimate the effectiveness.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), sexed 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.

1. Salmo trutta (Linnaeus, 1758)
   common name: sea trout rank: species
2. Salmo trutta (Linnaeus, 1758)
   common name: brown trout rank: species

The Nivelle river in Basque Country (France). http://services.sandre.eaufrance.fr/Courdo/Fiche/client/fiche_courdo.php?CdSandre=S52-0400