In recent times most of the fishery management interest in Tayside has centered around upland tributaries because those are the areas where spring salmon mainly spawn and much of the concern has been centred around spring salmon. However, significant problems exist in lowland parts of the Tay district, indeed probably much bigger problems than affect most upland tributaries.
Accordingly, in the early months of 2010, a survey commenced of tributaries of the lower Tay, the lower Isla and the lower Earn. The survey was conducted by staff from the Tay District Salmon Fisheries Board, supported by the Tay Foundation, which is grateful for financial support from a grant from the Scottish Government (administered by RAFTS). The tributaries surveyed are shown in the map below.
A number of previously unknown obstructions to fish migration were identified along with other issues. For example, high loads of fine sediment appear to be a major problem in some of the Isla tributaries in particular.
A detailed report of the findings can be obtained by clicking here.
Over the course of the next two winters it is hoped to survey all the salmon producing tributaries in the area (see map) and to develop improvement projects as a result of the findings.
Tributaries surveyed in 2010 are shown in black. Those with stippled lines are in the process of completion.
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The survey revealed that log jams might be a problem for fish migration in some burns
The survey also revealed that impassable waterfalls limited the distribution of migratory fish in some burns, as here on the St Martins Burn.
Some structures, like this bridge, can easily become blocked and require management if fish are to be able to pass upstream. By identifying such structures it will be possible to produce a monitoring and cleaning plan to ensure fish can pass at teh appropriate times of year.
This large weir was found on the Alyth Burn, in addition to another weir which was already known about. Electrofishing surveys have since shown that salmon only sporadically ascend this weir and do not fully populate this stream.
The Alyth Burn has the best physical habitat for salmon of all the tributaries of the Isla surveyed and woudl produce significant numbers of extra smolts if access for adult spawners was improved.
Many of the tributaries surveyed were on relatively low gradient arable land. These had all been straightened in the past, but riparian cover in the form of dense coarse grasses was generally good.
Some of the lowland tributaries clearly had high loads of fine sediment, as shown by deposits coating the bed. Such sediment comes from run-off from arable land and may seriously reduce the value of certain streams as a juvenile fish habitat.
In this burn the thick deposits of sediment even smothered the waterweed Ranunculus.
In some instances dense growth of riparian trees suppressed the growth of grasses and weed leading to a wide shallow stream with little cover for young fish.
As the predominant land use in the area is arable farming, only a small proportion of the channels surveyed had been seriously damaged by bankside grazing. In this instance grazing damage has created a wide shallow channel with reduced fish cover, but this was very much the exception rather than the rule.
Some tributaries, like the Auchrannie Burn pictured here, had stretches of very good juvenile habitat.
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