The wild salmon in rivers in Gulf of Bothnia has been somewhat of a success story. Since the crisis in the 1990s, when the river-stocks were close to collapse, the salmon has recovered and shown positive development. However, something has changed since 2023. Despite a historically low sea fishery for salmon, the number of adult individuals returning to the rivers to spawn has significantly decreased. The change is worrying, according to researchers at the Swedish university of agricultural sciences (SLU), who, in a new report, provide a broad overview of the situation for the Baltic Sea salmon populations.
The weak salmon migration in several rivers during 2023 and 2024 has been highlighted in media by various interest groups. Headlines such as "Wild salmon is threatened" and "A very serious situation for Baltic salmon" have appeared frequently.
How serious is the situation, according to SLU researchers?
"That so few salmon have migrated up in several of the rivers during 2023 and 2024 concerns us as well. But the situation seems to vary between rivers. In the northernmost rivers, such as the rivers Torneälven and Råneälven, the spawning migration was significantly weaker in 2023 and 2024 compared to previous years. This is troubling and impacts both the fishery in the sea and in the affected rivers. The situation further south, however, seems to vary more. In several rivers, the migration has been weak, while in some it has been closer to a 'normal year'," says Johan Dannewitz at the Department of aquatic resources (SLU Aqua).
"If the weak migration represents a temporary dip in the salmon's survival at sea, the situation might not be so serious. There are still relatively large numbers of juvenile salmon in the rivers, and previous experiences show that the stocks have the ability to recover quite quickly after, for example, disease outbreaks. But if survival in the sea remains at current low levels, the situation will become more concerning, as this is expected to result in a significantly lower abundance of salmon both in the sea and in the rivers. In such a situation, strong restrictions on salmon fishing and possibly other measures may be required," continues Johan Dannewitz.
The reduced migration appears to be due to fewer salmon surviving their time at sea, but what is behind the decline in survival is still unclear.
To understand why the Baltic salmon's sea survival has changed, a research project has been initiated on behalf of the Swedish agency for marine and water management. The first results from the project are expected by the end of 2025 or early 2026.
"We are collaborating with Finnish research colleagues and conducting statistical analyses of extensive existing data on factors that might affect salmon survival during the sea phase. We are investigating, among other things, food availability for salmon, how predation on salmon varies over time, and how fishing for other species may affect the salmon. The issue is complex, as it likely involves multiple interacting factors," says Johan Dannewitz.
The Department of Aquatic Resources has long been involved in extensive work on Baltic salmon, ranging from data collection and stock assessment to biological advice at national and international levels.
The recently published report "Swedish salmon stocks in the Baltic Sea" presents, among other things, status assessments for individual salmon stocks and estimates of the impacts of fishing and other factors on stock development. The report also discusses future challenges for the management of salmon and the ecosystems in rivers and seas that the species relies on.
The Baltic salmon consists of a large number of genetically unique stocks; essentially, each river has its own genetically distinct salmon. A significantly reduced sea fishery is considered the most important reason for the positive development since the 1990s, but restoration of river environments and low mortality from the disease M74 have also contributed to the recovery.
"Additionally, today, scientific advice and management authorities are focusing more on the development and status of individual river stocks. However, there is still a need to further develop stock-specific management to give weaker stocks a greater chance to recover," says Johan Dannewitz.
Johan Dannewitz, Researcher
Department of Aquatic Resources, Institute of Freshwater Research, SLU
johan.dannewitz@slu.se, +46 10 478 42 23
Stefan Palm, Researcher
Department of Aquatic Resources, Institute of Freshwater Research, SLU
stefan.palm@slu.se, +46 10 478 42 49