Multiple restoration actions have been implemented in response to declining salmon populations, including adding salmon carcasses or artificial nutrients to mimic marine-derived nutrients historically provided by large spawning runs of salmon.
Researchers linked a food web model with a salmon life cycle model to examine if carcass additions in a river reach would improve conditions for salmon in the long term. Model results confirmed immediate increases in the biomass of periphyton, macroinvertebrates, and fish during carcass additions. In turn, juvenile salmon grew larger and their survival improved in freshwater, which translated to a greater number of adults returning to spawn. However, once additions ceased, salmon abundance returned to pre-treatment levels, which, based on the model, is owing to a combination of instream and out-of-basin factors. Overall, results of this work suggest that benefits during carcass and nutrient additions may not translate into persistent productivity of salmon unless additions are sustained indefinitely, or other limiting factors are addressed.
Benjamin, J.R., Bellmore, J.R., Whitney, E., Dunham, J.B., 2020, Can nutrient additions facilitate recovery of Pacific salmon?: Canadian Journal Fisheries and Aquatic Sciences, https://doi.org/10.1139/cjfas-2019-0438