Thursday, 28 July 2011

Hydraulic Support

Beavers often build dams close downstream to previously built 'high dams' to give the upstream dam hydraulic support. Before its breaching about three weeks ago there was a little dam about thirty metres downstream of the dam in the photo (now called the Third Dam) and this was breached at the same time. Since the 6th July the beavers have been building a dam about ten metres downstream of the main dam. What made them do that? Lars Wilsson, the Swedish zoologist would have said they were programmed to do this: the late Donald Griffin would have allowed them powers of problem solving. I tend toward the Griffin school of thought.

Here is the small dam that gives hydraulic support to the bigger one, seen from the parapet of the Third Dam.

Yesterday evening I sat by this pool as the dusk approached and video'd the parr of brown trout and, perhaps, Atlantic salmon as they fed on the invertebrates that flew about.

This is what I filmed in one of several clips that I took. - This turns out not to be of parr feeding, but of beavers and otters. I will try again.

Chris Potter, handyman and gamekeeper, told me recently that he had seen a salmon of about 10 lbs (4.5kg) in the Burnieshed burn sometime around 1990. As I may have mentioned in an earlier post, Chris said back in 2007 that he thought that we might be seeing salmon parr jumping in the first of the new pools that the beavers had created that year. It looks very much as though he was right, but the abundance of salmonid parr that we are seeing has to be due to the increase in area of habitat and the proliferation of invertebrates on which the fish may feed.

The reductionist management of salmon that cannot allow the presence of pike, or eels, or goosanders, or cormorants, or herons, or otters, or beavers should have no place these days. 

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