The ideal spawning burn has to have a few essential ingredients; first and foremost spawning gravel, without which no salmonids could exist. Secondly there must be juvenile habitat, shallow riffly water for the fry in their first summer is ideal along with deeper; cobbly or bouldery water, fast flowing, if possible, for the older parr. If there is the occasional deeper hole or shady undercut bank alongside a deep glide, to provide refuge for adults, you have the ideal mix. Someone went even further and published a paper on the ideal mix, concluding that what required was one unit spawning gravel, two units for the fry and three units parr habitat, That, it was stated was the formula for the perfect spawning burn. The perfect angling burn, or more likely river, requires something else, but that is not the subject of this blog.
We are blessed with many, many, burns in the Spey catchment that could be classed in the ideal category; the upper Fiddich, Livet, Allt a’ Gheallaidh, Tulchan Burn, Cromdale, Conglass and so on but not all…
I took the opportunity last week to spend the day getting to know an upper Spey burn that I had been meaning to get acquaint with since the summer of 2013, when I first met her. This burn, which shall remain nameless, posed a few questions after the initial date; why were there only parr at the upper site, that site should have supported more and what about the loch in the middle?
It was quite easy to answer the first question.
Moving downstream the first gravels were seen a short distance above the loch.
The loch is know locally as the Pike loch, although funnily enough the estate owner told me none are ever caught. The main characteristic lacking above the loch was spawning gravel; there was however an abundance of mixed juvenile habitat though, perfect for the few fry and parr present.
The source of this gravel was soon obvious, a tributary joined at the outlet, it was responsible for the transport of copious amounts of ideal spawning substrate.
The lower reaches of the tributary were lined with dense, even sized alders, the sure sign of a recent fencing enclosure. I walked up the tributary, curious to learn a little more of its character.
Back at the main burn the stretch below the loch was an almost continuous spawning bed for several hundred metres, there was however a distinct lack of parr habitat.
Further downstream the sediment became finer, the coarser material being deposited first.
As the loch was left behind the sediment became almost sandy, with weed beds before the burn changed character again as the gradient picked up.
Further down, closer to the confluence with the Spey, the habitat, for the first time, started to match the ideal spawning burn formula.
My understanding of this burn increased no end, on this, the second date. Virtually no spawning above the loch, too much below, morphing into trout spawning habitat, a bedrock section – again virtually devoid of habitat, before the great mixed habitat in the lower reaches. I’m not sure if it was beginner that designed this burn, or not. However not every burn can be perfect, it has however got a fair bit of biodiversity interest this particular one to make up for the design shortcomings.