Temporal synchrony and variation in abundance of Atlantic salmon (Salmo salar) in two subarctic Barents Sea rivers: influence of oceanic conditions

Abstract

Long-term variation in Atlantic salmon (Salmo salar) stocks was analyzed in two Barents Sea rivers, the Teno and Näätämöjoki, that represent the northernmost distribution area of the species. In contrast to most of the North Atlantic area, these rivers are among a group of northern salmon rivers that, despite wide annual variation in catches, demonstrate no consistent trend for declining abundance. Variations in abundance were generally synchronous for the total catch and numbers of 1-sea-winter (1SW) and 2SW salmon during period of 1972-2003. Part of the variation observed in catches could be related to ocean climate conditions as the mean seawater temperature in July during the year of smoltification for the Kola section of the Barents Sea was significantly related to numbers of 1SW, 2SW, and 3SW salmon in the large River Teno. In contrast, NAO (North Atlantic Oscillation) indices were not related to salmon catches. The latest increase (1999)(2000)(2001) in salmon catches in these rivers reflects both temporarily improved oceanic conditions and past management measures affecting offshore, coastal, and river fisheries.Résumé : Nous avons analysé les variations à long terme des stocks du saumon atlantique (Salmo salar) dans deux rivières tributaires de la mer de Barents, la Teno et la Näätämöjoki, qui représentent l'aire de répartition la plus boréale de l'espèce. Contrairement à ce qui se passe dans la majeure partie de la région de l'Atlantique nord, ces rivières appartiennent à un groupe de cours d'eau qui, malgré d'importantes variations annuelles des prises, n'affichent pas de tendance soutenue de déclin d'abondance. Les variations d'abondance se manifestent généralement de façon simultanée dans les prises totales, les nombres de saumons ayant passé un hiver (1SW) et deux hivers (2SW) en mer durant la pé-riode de 1972-2003. Une partie de la variation observée dans les prises pourrait être reliée aux conditions climatiques de l'océan, puisque, les années de transformation en saumoneau, la température moyenne de l'eau de mer en juillet dans la section de Kola de la mer de Barents est significativement reliée aux nombres de saumons 1SW, 2SW et 3SW dans la grande rivière Teno. En revanche, il n'y a pas de relation entre les indices NAO (oscillation nord-atlantique) et les prises de saumons. La dernière augmentation des prises (1999)(2000)(2001) de saumons dans ces rivières reflète à la fois une amélioration temporaire des conditions océaniques et les mesures d'aménagement du passé qui ont affecté les pê-ches au large, sur les côtes et dans les rivières.[Traduit par la Rédaction] Niemelä et al. 2391

Spawning-Age Differences and their Temporal Trends in Wild and Sea-Ranched Atlantic Salmon Stocks, from Stock Mixture Data

“…Factors common to all stocks during the feeding migration include changes in the sea environment, such as the sea surface temperature, conditions in the feeding area, such as the availability of food, and the offshore and coastal fishery. This reasoning has proved correct in several previous studies related to salmon abundance, growth, and migration distance, in which synchronous trends have been related to common environmental factors [6,13,62,63]. The decrease in the proportion of old males has also been observed previous studies , as Järvi [64] reported approximately 11% of the spawners to be 4-6 SW salmon in the 1930s and 1940s, but an analysis sixty years later reported only 0.5-2% of salmon of that age [15].…”

“…The spawning age of Atlantic salmon varies from one to five years, calculated as the number of winters spent in the marine feeding areas after their two to five freshwater years in the river [11,12]. Occasionally, salmon are able to recover from their first spawning and return to the sea, and even spawn for a second time [5,13,14], but in the Baltic Sea the proportion of such fish is currently only a few percent [15]. As a nearly semelparous fish, the final body size of the Atlantic salmon depends on its age at maturity.…”

Getting into Hot Water? Atlantic Salmon Responses to Climate Change in Freshwater and Marine Environments

“…Similarly, Niemel ä et al (2004) found no correlation between the NAO and salmon catches in the rivers Teno and Naatamojoki (northern Finland), the stocks of which migrate to the Barents Sea and show large natural fl uctuations. Those catch time series date from the 1970s and are especially important because they run counter to the general pattern of recent stocks declines of Atlantic salmon (Niemel ä et al 2004(Niemel ä et al , 2005. Juvenile abundances increased over the period 1977 -2003 and strong smolt years were refl ected positively in subsequent returns of spawning adults, perhaps because of warmer oceanic conditions (Niemel ä et al 2004 ).…”

Twenty years of hydropower regulation in the River Alta: long-term changes in abundance of juvenile and adult Atlantic salmon

“…The size of the salmon spawning run in rivers may vary largely among years, both in terms of numbers and proportion of the different sea-year classes (e.g. Niemelä et al, 2004). This temporal variation is due to variation in freshwater smolt production (e.g.…”

“…Jonsson et al, 1998), variation in ocean climate (e.g. Jonsson & Jonsson, 2004a, b;Niemelä et al, 2004) and management measures affecting marine fisheries (e.g. Jensen et al, 1999).…”