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Atlantic salmon - Salmo salar 

 

 MANAGEMENT ISSUES

Summary of issues specific to the Baltic region

Power plant constructions have blocked migratory routes between spawning and feeding grounds for salmon populations in many rivers around the Baltic Sea. Only around 15 percent of previous salmon rivers harbour wild populations today. This has resulted in loss of intraspecific biodiversity as a relatively large proportion of salmon genetic variation is due to differences between populations inhabiting different rivers. Massive numbers of hatchery bred salmon are released into the Baltic Sea each year to compensate for lost or reduced reproduction in many rivers. There is a potential risk of loss of genetic variation in hatchery fish, and loss of local adaptations in natural populations due to straying of hatchery fish. The genetic effects of these releases are unclear and are the present focus of a collaborative effort (BaltSal) between BaltGene and The Swedish Agency for Water and Management (SwAM).

The genetic distinctness of each population means that each population should be managed separately. Additionally, the occurrence of two major lineages within the Baltic Sea should be taken into account, and transplantation between phylogeographic lineages should be strictly avoided.

Current management regulations

Atlantic salmon in the Baltic Sea is subject to both commercial and sport fisheries. There is a general consensus that Baltic salmon should be managed on a stock level, i.e. on a river-by-river basis. ICES currently monitor salmon in six assessment units in the Baltic Sea (Northeastern Bothnian Bay, Western Bothnian Bay, Bothnian Sea, Western Main Basin, Eastern Main Basin, and Gulf of Finland). These assessment units are based on both genetic data and information on migration patterns for different stocks.

Recent political suggestions include banning of large scale releases and banning of off-shore fisheries of salmon. The genetic pros and cons with such a ban is the focus of the collaborative effort BaltSal.  

Gaps between management and scientific evidence

The population structure of Baltic salmon has been known since mid 1980 and already then it was clear that the species should be managed on a population by population basis, and that releases were potentially harmful to native gene pools. These issues have been raised repeatedly over the years both from the scientific community and from NGOs and authorities. These discussions have recently resulted in the EU Commission to suggest a ban on compensatory releases in the Baltic Sea.

More information on baltsal 2012: https://sites.google.com/site/baltsal2012
Stopping compensatory releases of salmon in the Baltic Sea. Good or bad for Baltic salmon gene pools? Report from Batlic Salmon 2012 symposium and workshop, Stockholm University 9-10 
February, 2012, by Palmé A, Wennerström L, Guban P, Laikre L. 

GENETIC INFORMATION (January 2012)

Species Number of genetic studies Baltic population structure Baltic population diversity Baltic effective population size Temporal data Genetic risks Management recommendations
Atlantic salmon >20 Distinct populations Low Unknown Little information Loss of local adaptation Management on population level i.e. on a river-by-river basis 

 

Summary of key published genetic information

Atlantic salmon is without comparison the genetically most well studied species in the Baltic Sea. There are over 20 scientific publications concerned with population genetic patterns of salmon in the Baltic Sea.

Atlantic salmon in the Baltic Sea is a distinct genetic group, differentiated from other salmon populations in Europe and in the Atlantic Ocean (e.g. Ståhl 1987). Baltic salmon exhibit lower genetic variation than Atlantic populations. This is probably due to bottleneck events at the colonization of the Baltic Sea after the last ice age, or because of small population sizes during time in glacial refugia during the last ice age (e.g. Nilsson et al. 2001).

Strong homing to natal spawning grounds results in a pronounced genetic structure, where each river harbours at least one genetically unique population (Ståhl 1987).

On a larger scale there is an association between genetic and geographic distance (isolation by distance) between populations (Koljonen et al. 1999). There is also a genetic dichotomy in Atlantic salmon in the Baltic Sea where northern and eastern salmon populations form two different genetic groups. This is most likely due to colonization of the Baltic Sea of two different lineages, surviving the last ice age in different glacial refugia (Koljonen et al. 1999; Säisä et al. 2005).

 

Key publications

Ståhl, G. 1987 Genetic population structure of Atlantic salmon. In Ryman, N. and Utter, F. (eds) Population Genetics and Fishery Management. University of Washington Press, Seattle. pp 121-140.

Koljonen ML, Jansson H, Paaver T, Vastin O, Koskiniemi J (1999) Phylogeographic lineages and differentiation pattern of Atlantic salmon (Salmo salar) in the Baltic Sea with management implications. Canadian Journal of Fisheries and Aquatic Sciences 56:1766-1780. Abstract

Nilsson J, Gross R, Asplund T, Dove O, Jansson H, Kelloniemi K, Kohlmann K, Loytynoja A, Nielsen EE, Paaver T, Primmer CR, Titov S, Vasemägi A, Veselov A, Öst T, Lumme J. 2001. Matrilinear phylogeography of Atlantic salmon (Salmo salar L.) in Europe and postglacial colonization of the Baltic Sea area. Molecular Ecology 10:89-102. PubMed

Säisä M, Koljonen ML, Gross R, Nilsson J, Tahtinen J, Koskiniemi J, Vasemägi A. (2005) Population genetic structure and postglacial colonization of Atlantic salmon (Salmo salar) in the Baltic Sea area based on microsatellite DNA variation. Canadian Journal of Fisheries and Aquatic Sciences 62:1887-1904.

More information about herring at IUCN  - International Union for Conservation of Nature Resources

 

 

CONTRIBUTORS (January 2012)
Linda LaikreNils Ryman and Lovisa Wennerström, Stockholm University, Sweden


Responsible editor: Linda Laikre, Stockholm University
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