Scales ‘reveal where fish migrate’

Analysis of fish scales has helped scientists track down where Atlantic salmon migrate to from the UK, information that it is hoped will help protect the declining species.

Salmon scales contain collagen laid down during growth, with the composition of the carbon in it varying in relation to the sea surface temperatures in the area where the fish are feeding.

Scientists examined the portion of scales that grew while the salmon were out at sea, and matched the information with satellite records of ocean surface temperature to find out where they had been feeding away from the UK.

The analysis of more than 500 scales from samples at the Centre for Environment, Fisheries and Aquaculture Science and the Centre for Ecology and Hydrology revealed that fish from different rivers headed for widely differing parts of the sea when they left the UK’s shores.

According to the results, salmon from rivers such as the Tyne, in the northeast, headed towards the Norwegian sea, while fish from the River Frome in Dorset were feeding close to Iceland.

The research, published in the online journal Scientific Reports, helps solve questions over where wild Atlantic salmon go to feed out at sea, and could give clues as to why their numbers have declined in recent decades.

It is hoped they will also help experts improve protection for species such as salmon and identify where best to put marine reserves.

Kirsteen MacKenzie, of the University of Southampton and lead author of the research, said: “As every single salmon contains a natural chemical tag, we can now see where fish from individual rivers go to feed in the Atlantic.

“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 at sea.”