Nutrient limitation in Atlantic salmon rivers and streams: Causes, consequences, and management strategies

Abstract

Freshwater catchments can experience nutrient deficits that result in reduced primary and secondary productivity. The most commonly limiting nutrients are nitrogen and phosphorus, either separately or together. This review considers the impact of increasing nutrient limitation in temperate basin stream and river systems, focusing on upland areas that currently or previously supported wild Atlantic salmon (Salmo salar) populations. Anthropogenic changes to land use and increases in river barriers have altered upland nutrient dynamics, with particular impacts on salmon and other migratory fish species which may be net importers of nutrients to upland streams. Declining salmon populations may further reduce nutrient sources, reducing ecosystem and fisheries productivity below desired levels. Experimental manipulations of nutrient levels have examined the impacts of this cultural oligotrophication. There is evidence that growth and biomass of juvenile salmon can be increased via appropriate additions of nutrients, offering potential as a conservation tool. However, further research is required to understand the long‐term effects of these additions on salmon populations and stream ecosystems, and to assess the vulnerability of downstream habitats to eutrophication as a result. Although purposeful nutrient addition with the aim of enhancing and conserving salmonid populations may be justified in some cases, it should be undertaken in an adaptive management framework. In addition, nutrient addition should be linked to nutrient retention and processing, and integrated into large‐scale habitat restoration and recovery efforts. Both the scientific and the management community should recognize that the ecological costs and benefits associated with adding nutrients to salmon streams may change in a non‐stationary world.

Prospects for the future of pink salmon in three oceans: From the native Pacific to the novel Arctic and Atlantic

“…Pacific salmon die after spawning and release a substantial nutrient pulse into rivers where they have spawned; these nutrient pulses are iconic in the Pacific and have inspired many studies into the ecosystem responses of the eutrophication derived from salmon carcasses in rivers (Moore et al, 2007; Quinn et al, 2018). Some Atlantic salmon rivers are contemporarily suffering from oligotrophication due to barriers and land‐use changes that have limited the transport of nitrogen and phosphorus from headwaters to stream channels (Bernthal et al, 2022). Consequently, the arrival of pink salmon in such rivers may increase stream productivity and the growth of native salmonids and provide an alternative to proposals that have suggested artificial addition of nutrients to enhance stream productivity (e.g.…”

A jump-driven self-exciting stochastic fish migration model and its fisheries applications

“…There are several complex and mutually interacting factors, that can trigger fish migration, including but are not limited to, the water flow discharge [12], water temperature [13], nutrient limitation [14], environmental heterogeneity or genetic predisposition [15], and social interactions [16]. It is infeasible to fully describe the fish migration mechanism due to a number of random biological phenomena that can affect both inter-and intra-migration events, as suggested in the reported data for diverse case studies [17][18][19][20][21][22].…”

Early survival in Atlantic salmon is associated with parental genotypes at loci linked to timing of maturation

“…In this study we test whether the vgll3 and six6 loci are linked to early life survival in Atlantic salmon. We used data from a field experiment in which fertilized eggs from the same wild-origin families were divided among 10 experimental streams, all of which had become increasingly oligotrophic in recent years as a result of land management practices and anthropogenic barriers to the migration of anadromous fish (e.g., Bernthal et al 2022). Five of these streams were given an experimental supplement to restore nutrient that imitates conditions of natural spawning levels prior to the river became inaccessible to migrating salmon (Auer et al 2018).…”

“…In this study we test whether the vgll3 and six6 loci are linked to early life survival in Atlantic salmon. We used data from a field experiment in which fertilized eggs from the same wild-origin families were divided among 10 experimental streams, all of which had become oligotrophic in recent years (e.g., Bernthal et al 2022). Five of these streams were given an experimental supplement to restore nutrient levels (Auer et al 2018).…”