The presence of grayling is an indicator of excellent water quality. Grayling is a cold-water fish family made up of 6 species. Grayling need rivers and streams with strong flows and cool, clean, well oxygenated water. The riverbed needs to be made up of gravel and sand with riffles and rapids separated by pools. They are thought to be less tolerant of pollution than trout. Young grayling (fry) eat mostly midge larvae and as they become adults they will eat more and more different invertebrates. Grayling in the river Rye have been studied and it was discovered that they tend to stay within 1km of their home range although in some cases day-to-day movements were quite substantial. They don’t migrate out to sea like salmon and trout do.
Because grayling have an ‘extra fin’ – a small fleshy part between the dorsal fin and the tail – they are part of the salmonid family. They are smaller than trout. It is often a silvery colour although males can be darker during the mating season.
Grayling mature between two and four years old. Once mature they can spawn annually. This happens every spring between March and mid-May, starting when river temperatures are between 3 degrees C – 11 degrees C. The males put on a vibrating display which attracts the females. For successful egg development, grayling need good, clean, well-oxygenated and silt-free gravel. Males and females can be told apart by the size and shape of their fin. The development of the tiny eggs (3mm) is temperature dependent although in water above 13.5 degrees C their survival decreases. They can live to up to 32 years old.
Movement of grayling is sometimes hampered by different man-made obstacles. The can sometimes mean that a population gets cut off and becomes genetically isolated. If climate change means hotter, drier summers then this can lead to a rise in water temperatures and less dissolved oxygen. Low river flow in the summer also reduces the survival of the young. The ideal is to have stable river flows and limit temperature increases.
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