Introduction
This section of the website considers the health of the
Tay's salmon populations. All anglers are aware that
in recent times numbers of salmon have decreased, but
what does this mean in an historical context? Should
we be worried for the long term sustainability of the
species?
Sources of information
There are three basic ways by which we can assess the health of the salmon stocks in the River Tay and its tributaries. These are:
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Catch data
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Fish counters
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Juvenile surveys
Catch data
Analysis of catch data is really the main indicator we have to rely on in interpreting changes in salmon numbers. Catch data have the longest duration and the greatest level of coverage.
However, catch data are not without drawbacks. Catches are after all only a proportion of the fish in the river and the proportion caught may change over time. Much of the catches are made in the lower part of Tay, and that again is not too informative when it comes to assessing individual populations.
Accepting all these drawbacks, catch data do provide some illuminating findings and for the Tay there is quite a wealth of information.
To go to the catch data analysis page click here
Fish counters
Fish counters are the best way of assessing stocks since of course they count all the fish. However, they have drawbacks because in a system like the Tay there are major technical and cost obstacles to their widespread use.
Nevertheless the Tay is pretty well served by fish counters and unlike most Scottish rivers the greater part of the Tay's spring run is in fact counted.
There are five counters within the district. All are of the resistivity type and operate on the principle that salmon swimming through a weak electric field cause a change in electrical resistance since a salmon's body is more conductive, being full of salts, than river water. Four of the counters are operated by Scottish & Southern Energy PLC and are used to monitor the effectiveness of fish passes at hydro installations. These are:
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Pitlochry Dam (River Tummel)
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Clunie Dam (River Tummel - upper)
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Stronuich Dam (upper River Lyon)
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Lochay Falls (River Lochay)
The TDSFB also operates a counter (a Hydro Board mk 10) on the River Ericht at Blairgowrie. This counter counts fish passing through a fish pass at a pre-existing weir.
Of all the counters the Pitlochry and Ericht counters are the most important. They count the two most productive spring salmon tributaries of the Tay and between them possibly count as much as two thirds of the Tay spring run.
However, no counters in the district count autumn running salmon. The costs of such an installation on the lower Tay for example is wholly prohibitive.
To view the results of the fish counters click here
Juvenile surveys
One drawback with counters and catch data is that one cannot tell whether a change in numbers has been caused by a change in smolt numbers going to sea or whether survival rates at sea have changed.
Electrofishing surveys of juveniles in the spawning tributaries can help to answer such questions. They allow salmon stocks to be monitored at the individual tributary level and are invaluable in picking up local problems which might exist.
Another method of surveying juveniles is to trap and count smolts as they are migrating to sea. However, there are no such installations in the Tay district at present.
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