Scientists reveal fascinating facts of salmon migration
SALMON are known to migrate to feeding grounds in the Atlantic Ocean from the rivers in which they were born. A question that has remained unanswered for years is: “To get to the ocean, when Salmon descend rivers like the Boyne, do they turn left and migrate anticlockwise around the north coast of Ireland or do they turn right and migrate clockwise around the south coast of our green isle?
Fish scientists from Inland Fisheries Ireland and Northern Ireland’s Agri-Food and Biosciences Institute have revealed findings which show for the first time that young salmon leaving rivers on the east coast travel north to leave the Irish Sea, rather than south and west to join Salmon on the western coast.
Salmon hatch in their native river, spend their juvenile life feeding in freshwater and prepare for their long sea migration before returning as adults, usually one year later to mate in their native river. Genetic analysis has shown this loyalty to their native river which can be traced back to the last Ice Age.
The new evidence was established after researchers tagged young Salmon with coded transmitting acoustic tags in the Castletown and Boyne rivers in County Louth during the spring of last year. Three of the tagged salmon were picked up on listening devices in the coastal seas as they travelled northwards out of the Irish Sea towards the Atlantic Ocean.
One of the youngsters, called smolts, was recorded in Scottish waters, some 80 kilometres north of the Inishowen Peninsula. This smolt had travelled an estimated 250 kilometres in just over a month, one of the longest distances recorded for a salmon tracked at sea en route to its feeding grounds in the North Atlantic. Two more salmon smolts were tracked as far as receivers located off the Northern Ireland coast, further confirming the northward migration of the fish through the Irish Sea.
These Salmon also moved offshore quickly, behaving very differently from tagged Sea Trout, which remained closer to their spawning rivers and swam closer to the coast and river mouths.
In all, 130 Salmon were tagged. Acoustic receivers were then moored to the seabed along the coast from Drogheda to the north east coast by researchers to track the tiny acoustic transmitters in the Salmon as they migrated from the rivers to the open ocean.
To find out more about this research and the COMPASS project, visit www.compass-oceanscience.eu/salmonid-fish.