ATLANTIC SALMON AT SEA - factors affecting their growth and survival

Informations

Funding country

Norway

Acronym

-

URL

-

Start date

1/1/2018

End date

12/31/2023

Budget

2,583,000 EUR

Fundings

Abstract

Atlantic salmon is an important source of local income through fisheries, and a symbol of environmental quality and sustainability. Population sizes have declined because of human impacts in rivers and coastal areas and ecosystem changes in the ocean causing increased mortality. After more than 100 years’ of intensive research, much is known of the life of Atlantic salmon in freshwater, but the ocean feeding migration has been much more of a mystery. Salmon are only 10-15 cm long when they leave freshwater and move to sea for feeding. The ocean phase is a very important part of their life, because this is when they grow to their large body size, and ocean mortality largely influence population abundance. Through this project, we have massively increased the insights into the marine migrations and distribution of salmon, and how the ecosystem in the Norwegian and Barents Seas impacts their growth and sea survival. Genetic data and satellite tags were used to map salmon ocean distribution, which is work that has redefined our understanding of the oceanic migration of salmon. Analyses of more than 25 year’s catches of salmon at sea provided new information on key foraging areas during their first months at sea. The different distribution of regional stocks points to fundamental differences in their migration behaviours, which may lead to inter-stock variation in responses to environmental change and marine survival. Following adult salmon with satellite tags also provided new and surprising results. The salmon used larger ocean areas and migrated further north and east than expected, made more use of oceanic fronts, performed deeper dives, and stayed in colder water than we knew before. Salmon from different regions used different ocean areas, but consistently migrated to and aggregated in assumed highly productive feeding areas at the boundaries between large-scale frontal water masses where branches of the North Atlantic current lie adjacent to cold polar water. Several studies in this project have shown the importance of fish larvae in the marine diet of young salmon, and how reduced prey ability during the first months at sea has contributed to the decline in salmon during the last decades. In periods of poor feeding opportunities, there was a clear reduction in how much food was found in their stomachs, and the fish were thinner and had been eating less energy-rich food such as fish larvae and Amphipoda crustaceans. Possible causes for the observed changes in post-smolt feeding are ocean warming, decreased primary productivity, and reduced recruitment of important fish larvae. Scientists have been puzzled by a large and drastic reduction in the marine growth of salmon around the year 2005. One of our studies uncovered why this happened - and at the same time revealed an ecological regime shift in the Northeast Atlantic Ocean. The supply of nutrient-rich Arctic water, which is usually transported naturally into the Norwegian Sea north of Iceland, was greatly reduced around 2005. The reduction of fish larvae in the salmon stomachs over a large geographic area may be result of a bottom-up driven process in the ocean ecosystem, through reduced nutrient-rich Arctic water masses and reduced zooplankton abundance. Climate change could be a possible explanation, but what controls the inflow of Arctic water is not fully known. Remarkable studies in this project have also demonstrated human activities as drivers of evolution - and how direct and indirect effects of fishing and hydropower development can induce rapid evolution in salmon life-history in terms of how long they stay at sea, and thereby how large they are when returning to the rivers to spawn. There has been great interest in the project results from managers, media, organisations and other interested people, which has resulted in a high dissemination activity. Project participants have contributed to several radio programs and podcasts, such as BBC world service and podcast, NRK P1 radio, TV news (TV2 Nyhetene), and newspaper articles (Aftenposten, Nationen, many local newspapers). Dissemination has been given high priority, and we have given many talks in different events and meetings. The project has a twitter account @SeaSalarScience and a web site www.SeaSalar.no.