Adult cod have, one would think, the entire ocean at their disposal, and yet apparently each individual cod still chooses ‘their own’ local shipwreck, which they swim back to faithfully day after day.
This is just one of the fascinating results from research using acoustic tags which has yielded new insights into what cod get up to below the surface of the sea.
When Danish PhD student Junita D. Karlsen from DTU Aqua plotted the geographical positions of 15 acoustically tagged cod on a map, the cods’ positions formed a perfect silhouette of a shipwreck. This surprised her - not because the cod were located at a shipwreck, as it is well known that cod often gather at wrecks, but because her results show that the same cod return day after day to the same wreck and therefore can be said to have ‘their own’ local wreck.
"It is surprising that the cod return to the same wreck because they are highly mobile and can swim several miles a day. And of course the size of a shipwreck is very small relative to the area the cod could move around in," says Junita D. Karlsen, who on 12 April defended her thesis entitled: ‘Hot on the tail of hefty Atlantic cod: an interdisciplinary study on the behaviour at shipwrecks in the North Sea'.
In her work on the project, Junita D. Karlsen studied adult cod behaviour on shipwrecks in the central North Sea by tagging cod with so-called acoustic tags and by analysing the stomach contents of cod that were caught at shipwrecks. Her research reveals that adult cod are stationary, thereby contributing important new knowledge that can be applied in the management of North Sea cod.