A new genetic tagging study has revealed where young salmon gather and begin to migrate during their first summer at sea.

The study found that they migrate along the continental shelves off Ireland, Scotland and Norway, and subsequently aggregate to feed in the Norwegian Sea west of the Vøring Plateau in international waters. Here, they are exposed to potential mortality from major commercial fisheries for other pelagic species, the paper says.

This genetic analysis of fish caught at sea demonstrates that the salmon stocks that make up this feeding aggregation are – unexpectedly – not from neighbouring Norwegian rivers, but are predominantly from southern rivers such as those in Britain, Ireland, France and Spain.

This points to fundamental differences in migration behaviours, and likely explains variation in how stocks from northern and southern European rivers have been responding to environmental change and, critically, to recent climate change. It may also account for the differences that have been observed among stock groups in marine survival.

“This report is the culmination of a major logistical and technical effort to synthesise the data from 385 marine cruises, 10,202 individual trawls, 9,269 captured post-smolts, spanning three decades and approximately 4.75 million km2 of ocean, and 3,423 individuals assigned to their region of origin,” said joint senior author of the paper Professor Philip McGinnity of University College Cork and the Marine Institute.

The sampling was largely carried out by research vessels from several European countries, including the Marine Institute’s RV Celtic Explorer, and the laboratory analysis by many European labs.

“This paper is the result of sampling efforts that were vast in space and time, and equally impressive collaboration including research agencies and universities from many nations,” added Professor Tom Quinn of the University of Washington’s School of Aquatic and Fishery Sciences, which is a leading world authority on salmon.

“These scientists have revealed rich variation in the early marine migrations of Atlantic salmon from different regions, and are entirely consistent with a growing body of research using similar genetic methods being conducted on Pacific salmon.

“It is clear that salmon migrate to distant, stock-specific locations at sea, despite never having been to these regions before, and having no older members of their cohort to lead them. The environmental conditions that they encounter in their respective locations will affect their access to food, hence growth, but also their exposure to predators and intercepting fisheries. Thus migratory routes are of great consequence for the persistence and recovery of salmon stocks, in addition to the marvel of animal orientation that they reflect.”

“Precise information on migration routes and timing are crucial for research into highly migratory marine species,” said Dr Niall Ó Maoiléidigh of the Marine Institute and a co-author on the paper, “especially as the main factors causing population declines may be unknown.”

The study was published in the international journal Fish and Fisheries and can be found in full here.

This story was taken from the latest issue of Fishing News. For more up-to-date and in-depth reports on the UK and Irish commercial fishing sector, subscribe to Fishing News here or buy the latest single issue for just £3.30 here. Main image credit: Niall Ó Maoiléidigh.


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