The Data Collection Framework (DCF) is a European-wide framework for collecting, managing, and using fisheries data to support scientific advice on the Common Fisheries Policy. As part of France’s national work plan, led by INRAE, mandatory data collection for sea trout has been in place since 2022. This monitoring includes stock assessments in rivers and during migrations. The goal is to improve abundance estimates of sea trout at different life stages (anadromous adults, smolts, juveniles) by standardizing estimation methods in small coastal rivers monitored by the ORE DiaPFC, particularly in the Basque Country (Nivelle) and Lower Normandy (Oir and Bresle).

To achieve this, Bayesian hierarchical models are used to integrate various spatial and temporal data sources, facilitating the transfer of information between years with abundant and scarce data. Data collection relies on combined methods: smolt and adult trapping in index rivers (except for the Nivelle, where smolt monitoring is not possible) and electrofishing in September-October to assess the juvenile stock (except for the Bresle, where this monitoring is too recent). The estimates cover abundance at different life stages and associated uncertainties from the early 1980s to the present day, contributing to a better understanding of population dynamics and more effective stock management at both local and international scales