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August 30. 2006

Three salmon recaptured with DST-micro tags

Depth (blue) and temperature (red) during one year of sea migration
In the spring of 2005, the Institute of Freshwater Fisheries in Iceland, in cooperation with the Star-Oddi company and the Laxeyri hatchery in Borgarfjörður Iceland, initiated a project designed for the release of salmon smolts tagged with DST-micro tags in the river Kiðafellsá in west Iceland.  Data storage tags have been used in Iceland for several years for tagging of fish.  In 2005 the Star-Oddi company produced a new line of tags, DST-micro that allows for the first time tagging of large smolts (> 60 g.) .  The tag makes it possible to measure temperatures and pressure (depth) at programmed time intervals. In June of 2005, 300 DST hatchery smolts were released in Kiðafellsa and additional 300 smolts in the spring of 2006.

The 17th of August 2006 three salmon were recaptured in the salmon trap in River Kiðafellsá with DTS-micro tags.  The tags recorded temperature and depth continuously every hour for the whole time from the time the smolts left the river in June 2005 until they returned as mature grilse in August 2006 (Fig. 1).  This the first time that such records are available for the marine life cycle of salmon.


The salmon tagged with DST tags
The aims of the study are to increase our knowledge on the marine life cycle of salmon, especially the temperature regime during the first and second year in the sea and by using information on surface sea temperature (SST) it will most likely be possible to map migratory routes and locate the feeding grounds of Icelandic salmon stocks.  The results of the three salmon recaptured so far, also show that the fish mostly stay in the sea surface layers, but the salmon also took occasionally dives down to 600 m depth, especially at the later stage of the marine stay.  It has been speculated that this behaviour may play part in the homing of salmon to freshwater spawning areas. 


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