Chemical analysis of scales shows where Atlantic salmon have fed

5 Jul 2011

This scientific breakthrough is being hailed as a tool which may help preserve dwindling populations.

The National Environment Research Council's Planet Earth website reports that the study has shown that fish from different parts of the UK migrate to very different stretches of ocean.In the face of marine mortality which has risen from 70% in the early 1970s to 90% by 2005, knowing where salmon spend their time at sea could form the crucial key to knowing why they thrive or fail to thrive.

The team of scientists from the University of Southampton, the Centre for Environment, Fisheries and Aquaculture Science, the Game and Wildlife Conservation Trust and the National Oceanography Centre in Southampton looked at collections of preserved salmon scales taken from two salmon populations - one returning to rivers on the UK's north-east coast, the other coming back to the River Frome in Dorset. The team analysed the ratios between different forms of carbon, known as isotopes, in salmon scales. These form a distinctive chemical signature that can trace each salmon to where it fed in its youth. Each stretch of ocean carbon imparts a distinct isotopic signature to the animals feeding there, largely because its waters are a different temperature and host different plankton communities.

The scientists compared changes in the scales' isotopic signatures over time with satellite records of sea-surface temperatures from across the north Atlantic. Areas where changes in the records match up show where each population is feeding.

Dr Kirsteen MacKenzie of the University of Southampton, lead author of the study, which appears in Scientific Reports said they had found that salmon from the two different populations swim to feeding grounds that are far apart, and experience very different conditions at sea.

Salmon returning to rivers on the UK's north-east coast face far more variable conditions at sea, suggesting they feed in the Norwegian sea - roughly what scientists had predicted. But salmon returning to the River Frome in Dorset turn out to feed further to the west, around the Faroe Islands and Iceland - this surprised the scientists.

This works links closely to the EU-funded SALSEA project, which was supported by AST, and is all part of exciting new knowledge about where salmon go to feed at sea.

AST is hosting a conference in London this December, where SALSEA scientists will outline the main results of their work, and its implications for management of salmon populations. You can find full details of the conference here.

You can read the full text of the article about the scale chemistry study here.


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