Irish Times

Study shows survival rates of young salmon are in decline

Derek Evans

Feb 24, 2019
A new study shows how salmon survival leaving freshwater is an important factor in declining European salmon populations, according to early results from a project examining early migration phase of salmon smolts from rivers across Europe.

Leading salmon scientists from Denmark, Spain, Sweden, UK and Ireland recently attended a conference in Dublin, hosted by Inland Fisheries Ireland (IFI), to mark International Year of the Salmon (IYS).

The scientists discussed findings from the international Smoltrack project, the results of which reveal factors in the known decline of salmon stocks.

The project, which is funded by the North Atlantic Salmon Conservation Organisation, aims to help determine survival rates of young salmon as they move from rivers into the marine environment.

Work commenced in 2017, and early results show that survival during movement from rivers to the sea is lower than expected.

While it was already accepted that salmon are impacted by a number of factors including effects of climate change, limited feeding opportunities and sea lice induced by fish farms, the low survival rate in river systems presenting in this research is a new development.

The low survival of smolts in some river systems could be attributed to changes in temperature and flow, while predators have also been shown to impact on numbers entering the sea.

Survival varies by catchment and, in a bad year, survival can be three times lower than in a good year. These results will be published in international journals on completion of the research.
Leading salmon scientists from Denmark, Spain, Sweden, UK and Ireland attending a meeting about the Smoltrack Project in Dublin.

Radio transmitter tags

The international project involves scientists from each participating country tagging salmon smolts with miniaturized acoustic and radio transmitter tags in rivers, and track their migration journey through lower parts of rivers, estuaries and coastal areas.

In Ireland, work is being undertaken on the river Erriff (IFI’s National Salmonid Index Catchment) and the river Bush (Northern Ireland), river Tamar (England), rivers Ulla and Minho (Spain), rivers Göta and Högvadsån (Sweden) and rivers Skjern and Storaa (Denmark).

This information will help scientists to understand survival rates of salmon smolts during migration under varying conditions ranging from cooler climates in Sweden to warmer climates in Spain.

Already Smoltrack is providing new data on the initial migration of salmon smolts which will inform future management and conservation measures for this iconic species.

Dr Cathal Gallagher, IFI’s head of research and development, said: “We have seen a substantial reduction of salmon returning to Irish shores in recent decades. This project is examining what is happening to our young salmon as they migrate to sea and what the international community needs to do to help salmon populations.”

International Year of the Salmon is a joint worldwide initiative of Nasco and the North Pacific Anadromous Fish Commission alongside other partners across the globe, creating an international framework for collaborative outreach and research.

More Posts