Simulating brown trout demogenetics in a river/nursery brook system: The individual-based model DemGenTrout

The brown trout (Salmo trutta L.) is among the most biologically diverse vertebrate species. Human activities are threatening this biodiversity, and many endemic populations now face a medium-term risk of extinction. An individual-based model called DemGenTrout was developed to improve the management of these populations. The model was parameterized, optimized and validated with demographic, genetic, and environmental data collected over 7 years on the Lesse River drainage (Belgium). The sensitivity of the model to its parameters was analysed. The model was then used to assess how the demogenetics of a wild trout population might be affected by anthropogenic disturbances. From the sensitivity analysis, we found that modifications in survival and spawning parameters could lead to important changes in the demogenetics of the studied brown trout population. Two parameters were identified as the most influential in the DemGenTrout model, the survival rate of fry in the brook, and the mean of the spawner condition factor distribution. Two scenarios were simulated over 35 years and compared: (i) a barrier to upstream spawning migration, (ii) stocking with hatchery-reared trout during a 10-year period. Both of them appeared to have a strong short-term impact on the demogenetic structure of the wild trout population. The migration barrier mostly impacted abundance, while genetic issues arose when a significant number of stocked fish survived in the wild. Stocking also appeared to act on a longer time frame if hatchery and wild trout had similar survival and spawning probabilities.