In 2008 we started a preliminary study of porbeagles around Ireland using archival pop-up tags. We managed to tag three porbeagles with Archival Pop-up Tags. The sharks were caught by anglers using rod and line and were brought onboard for body-length measurement and tagging. Each tag was attached harmlessly via a short nylon tether to a small dart at the base of dorsal fin. Tags were able to measure water temperature and depth, as well as ambient light levels. This data was then used to calculate the sharks daily position over a period of 122 days, after which the tags detached and sent their data up to passing satellites. The tracks of the individual shark scan be followed on Google Earth below.
View 2009 Porbeagle Tags in a larger map
The tag from Shark 1 popped-up between the western coast of Morocco and the island of Madeira indicating a southerly migration of over 2400 km in a 4 month period. This shark travelled mainly along the shelf edge to the northwest Bay of Biscay, where it stayed for about 30 days before heading south in more open waters. Shark 2 didn’t travel very far and instead stayed in the oceanic waters around the shelf edge west of Ireland. Shark 3 also migrated southwards from the tagging site to the Celtic Sea and northwest Bay of Biscay, but it stayed here until the tag detached instead of travelling south like shark 1.
The results show that porbeagles live in oceanic waters close to the shelf edge during the winter time, and that they may undertake long-distance migrations to regions further south. The Bay of Biscay and the west coast of Ireland seem to be ‘hotspots’ for porbeagles and this may be due to increase food sources (for example, mackerel and blue whiting) in these regions. The results also show that porbeagles often occupy and traverse areas that are fished intensively by pelagic tuna and billfish fisheries. Fisheries management and assessment need to consider such broad-scale migration and it is apparent that the porbeagle shark should be considered for protected status listing on the Convention for the Conservation of Migratory Species of Wild Animals.