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Plea to kill birds to protect salmon stocks

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Old Thursday 1st February 2018, 07:17   #1
JTweedie
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Plea to kill birds to protect salmon stocks

http://www.bbc.co.uk/news/uk-scotlan...tland-42894855

I've not seen the report mentioned (and typically the BBC do not link to it) so can't comment on how rigorous their study was nor on how strong the statistical correlation was between salmon mortality and bird predation.
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Old Thursday 1st February 2018, 08:50   #2
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I suspect that predation could be reduced if serious efforts were made to restore the quantities of woody debris within the rivers, such as fallen trees in the water instead of being removed. This would give the fish refuges to hide from both birds and larger fish, plus it would increase invertebrate biomass and diversify the channel structure i.e. more pools, fast-flowing channels and backwaters instead of just a uniform depth river bed.
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Old Thursday 1st February 2018, 10:33   #3
Hauksen
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Hi,

Quote:
Originally Posted by JTweedie View Post
http://www.bbc.co.uk/news/uk-scotlan...tland-42894855

I've not seen the report mentioned (and typically the BBC do not link to it) so can't comment on how rigorous their study was nor on how strong the statistical correlation was between salmon mortality and bird predation.
The German ornithologist Josef Reichholf in his book "Ornis" briefly discusses the Cormorant versus fish topic for the German rivers. He points out that there is very little data available on total biomass in rivers, but he provides an estimate based on data on fish killed by a toxic waste disaster in one of the major rivers.

Comparing that to the maximum hypothetical food intake of the relevant cormorant population, he arrives (if I remember correctly) at a low single-digit percentage of fish bio mass annually consumed by cormorants.

He points out that the reduction in fish bio mass seen over the past decades mainly is owed to an improvement in the effectiveness of sewage purification, which releases less anthropogenic nutrition into the rivers.

(Unfortunately I seem to have misplaced the book, so I'm unable to look it up at the moment.)

Of couse, the conditions in Scotland might be different.

Regards,

Henning
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Old Thursday 1st February 2018, 12:29   #4
Farnboro John
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Quote:
Originally Posted by King Edward View Post
I suspect that predation could be reduced if serious efforts were made to restore the quantities of woody debris within the rivers, such as fallen trees in the water instead of being removed. This would give the fish refuges to hide from both birds and larger fish, plus it would increase invertebrate biomass and diversify the channel structure i.e. more pools, fast-flowing channels and backwaters instead of just a uniform depth river bed.
Beavers are the answer.

John
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Old Thursday 1st February 2018, 23:21   #5
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Too right about the beavers. And they're even on the Tay, a major salmon river...
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