The river clean-ups are having their annual winter vacation due to access restrictions- the dark winter months are trout spawning times.
And for those who might be interested, here is a brief, but concise, spawning tutorial:
Trout lay their eggs in nests in the river gravels, known as redds. The female (hen) builds the nest, usually between November and January when the water is cold and carrying lots of oxygen, because that is what the eggs need to hatch.
She looks for gravel with a good flow of water passing through, so the gravels need to be loose and largely free from silt. She will dig a hole, turning on her side and flexing her body.
This activity will attract the attention of males who will chase each other and attempt be in place just when she lays her eggs. The process of digging and chasing can last for hours or even days.
Eventually the hen fish will release some of her eggs into the redd and the male (cock) fish will fertilise them. The hen then digs again to throw up gravel to cover the fertilised eggs.
The eggs will hatch in 60 to 97 days. Generally, it is assumed that most eggs hatch in February.
The newly hatched trout are called alevins, and they live in the gravel, feeding off the remaining yolk that is attached to their body for 14 – 30 days.
Once the yolk has been eaten, the alevin become fry, emerge from the gravel, move towards the light and start to feed on tiny insects in the water.
Mortality rates at this highly vulnerable stage are very high. The fry are just a few centimetres long and consume a lot of energy, so they need to find food quickly, and plenty of it. They also become territorial – they want to be out of sight of other fry, so need habitat that has plenty of stones and plants to enable them to hide from the neighbours. And they are still very tiny, so they need shallow water (1 – 40cm) that isn’t too fast flowing.
The transition from living off the yolk to independent feeding is a critical life stage, and the one at which the majority of mortality takes place.