The
Tay salmon's lifecycle starts in the late autumn and
winter when the adult salmon spawn. Spawning commences
first in the highest coldest tributaries, usually about
the first few days in November. Spring salmon start
spawning first. However, in the warmer lower reaches
of the Tay and lowland tributaries fish tend to spawn
much later. These are mainly autumn salmon and nowadays
the main spawning in such areas may not occur even until
January.
The female salmon selects an area of clean gravel with a good current flowing over it and by repeatedly flexing her body dislodges stones to create a depression in the bed. Her eggs are ejected into the depression and simultaneously fertilised with milt from the male. The eggs are then covered over with more gravel which the female dislodges from upstream. The completed structure is known as a “redd”.
The fertilised eggs then incubate in the gravel at a rate determined by water temperature. The colder it is, the slower they develop. Water currents percolating through the gravel supply the eggs with dissolved oxygen and remove pollutants. If the water quality in the river is poor or if silt or clay blocks up the pores in the redd, the eggs may suffocate. Therefore it is vitally important the water is clean water and there should be little fine sediment in the river.
After some months the eggs hatch and tiny fish known as alevins emerge. These little fish can hardly swim and still have a soft bag of yolk attached under them. This source of food is gradually absorbed as the little fish continue to develop in the dark world under the gravel.
In late spring, once the yolk sac is absorbed, the little fish, now known as fry, wriggle upwards out of the gravel and commence feeding for themselves.
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Salmon in the process of redd
building in the River Tilt. They select areas
of clean but moveable gravel with a swift current.
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A newly completed redd can easily
be identified by the accustomed eye. A depression
in the gravel indicates where the female has been
digging and the deposit of loose clean stones
covers the incubating eggs. |
Hatching salmon eggs. Prior
to hatching the eyes of the fully formed embryos
are visible through the shells. Once hatched the
baby fish are known as alevins and are very delicate
creatures which are sustained by a sac of yolk
on their stomach. Only when this is absorbed after
some weeks do the little fish finally wriggle
out of their gravel nest, at which point they
become known as "fry" (below). |
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