Salmon’s natural chemical tag

Salmon migrate in order to feed, and exactly where they eat could now be revealed thanks to a natural chemical tags the fish carry – their scales.

[caption id="attachment_23566" align="alignleft" width="200" caption="Salmon scales can provide clues to where they’ve been feeding"][/caption]

Artificially tagging salmon can be difficult and expensive, but researchers from the University of Southampton realised that the fish already have their own natural chemical tag in the form of their scales.

The researchers studied the isotopes of carbon contained in historical records of Atlantic salmon, and discovered their scales reflect the composition of food and water in the area they live and feed, acting like a natural tag.

“As every single salmon contains the natural chemical tag, we can now see when fish from individual rivers go to feed in the Atlantic,” said lead author Dr Kirsteen MacKenzie.

The scales grew while the salmon were feeding at sea, so the carbon isotope values of the scales reflect the values of their diets in the feeding grounds. The team compared the scale values through time with satellite records of sea surface temperature – a factor thought to contribute to the declining numbers of salmon – across the North Atlantic. The locations of sea where the time series match best are most likely to be feeding grounds.

“Interestingly we found that salmon born in two areas of the British Isles swim to feeding grounds that are far apart, and experience very different conditions while are sea,” said MacKenzie.

“This information allows for better management of individual fish populations by monitoring both environmental conditions and fishing efforts in the areas where they feed,” said co-author Dr Clive Trueman.

MacKenzie said the technique could also be used to aid the conservation of animals such as turtles, seabirds and tuna, and identify the best areas for marine protection measures.

The research – published in Scientific Reports –  was funded by the Department for Environment, Food and Rural Affairs, (Defra) and also involved scientists from the Centre for Environment, Fisheries and Aquaculture Science, the Game and Wildlife Conservation Trust and the National Oceanography Centre.