Scientific Journal Article Summary

Results of satellite tagging of Atlantic bluefin tuna, Thunnus thynnus, off the coast of Ireland
Michael J. W. Stokesbury, Ronan Cosgrove, Andre Boustany, Daragh Browne, Steven L. H. Teo, Ronald K. O’Dor, Barbara A. Block
Hydrobiologia (2007) 582:91–97

A sport fishery for Atlantic bluefin tuna began along the northwest coast of Ireland in 2000.  TAG teamed with Irish scientists to learn more about the migratory patterns and environmental preferences of these fish and how they relate to other bluefin in the North Atlantic.  Six giants were released with pop-up satellite archival tags in the fall of 2003 and 2004.  The tagged fish were over 7 feet long and weighed approximately 450 pounds.

The most intriguing result of the tagging was that two bluefin tagged within 15 minutes of each other traveled in opposite directions, ending up 3,200 miles apart in less than 7 months (Figure 1).  One traveled to the Bahamas , while the other swam to the waters off the southwest coast of Portugal.  The pop-off area in the Bahamas was near a proposed spawning ground, and the water was warm enough for spawning. It is possible that the fish had moved there to spawn.  Similarly, it is possible that the fish off Portugal was on its way into the Mediterranean Sea to spawn.

A third fish migrated to the spawning grounds in the Mediterranean Sea where it was caught by a purse seine fishing vessel near Malta 8 months after tagging (Figure 2).  During its time at large, this eastern bluefin tuna migrated west over the 45º west meridian into the ICCAT-designated range of the western bluefin tuna population.

The other three tags failed to report, possibly due to equipment malfunction or because the fish were caught but the tags were not returned.

Although the sample size was small, the results suggest that both eastern and western Atlantic bluefin tuna feed off the Irish coast.  Even if the Bahamas fish was not spawning and is of eastern origin, two of the three fish crossed the 45ºW stock boundary line.  This corroborates previous tagging studies by the TAG team, which have shown extensive mixing of western and eastern bluefin tuna on North Atlantic feeding grounds.

Figure 1. Location data showing the migrations of two bluefin tuna that traveled in opposite directions despite being tagged within minutes of each other.	Figure 2. Location data of a fish that traveled to a Mediterranean Sea spawning ground where it was caught by a fishing vessel (circles are color-coded for month).

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