THE TAY SALMON LIFECYCLE
SALMON Salmo Salar SPAWNING AND REDDS
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.