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Researchers from the University of Southampton in the UK have discovered that salmon have their own natural chemical tag: their scales.
This finding precludes the need to artificially tag the fish, a process both tricky and expensive.
Studying the isotopes of carbon in historical records of Atlantic salmon, the team found that the fish scales mirror the composition of food and water in the habitat where they swim and feed, thus doing the work of a tag.
These findings were published in Scientific Reports.
“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.
Fish scales continue to grow as the salmon feed at sea, which means that the carbon isotope values of the scales reflect the values of the fish’s diets.
The researchers compared the scale values through time against satellite records of sea surface temperatures, whose fluctuations are thought to influence the species’ declining numbers during the past several decades across the North Atlantic Ocean. The team believes the locations where the time series match the best are the most likely to be the salmon’s 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 at sea,” said MacKenzie.
The fish may also respond differently to environmental shifts.
Study co-author Dr Clive Trueman said the team’s data would allow for better management of individual fish stocks by monitoring environmental conditions and fishing efforts both within the feeding grounds.
Further, the technique, MacKenzie explained, could be useful to aid the conservation of endangered animals such as turtles, tuna and seabirds and identify the best areas to take steps toward marine protection.
The research received funding from the Department for Environment, Food and Rural Affairs (Defra) and involved scientists from the Centre for Environment, Fisheries and Aquaculture Science (CEFAS), the Game and Wildlife Conservation Trust and the National Oceanography Centre.
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