'Fish farm impact needs studying'

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Record numbers of sockeye salmon returned to spawning grounds in Canada's Fraser River last month - the highest in a century.

The arrival of the 34 million fish followed a year when just one million made the journey - the lowest in decades - prompting questions about why fish stocks were declining.

Biologist and environmental activist Alexandra Morton explains why she believes salmon farms on the migration route have a negative effect on wild salmon.

Read more about the global issues affecting the world's fisheries on Susan's blog.

Watch Susan Watts' film from British Columbia on Newsnight on Tuesday 26 October 2010 at 2230 BST on BBC Two.

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