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Are these the smallest salmon fry in Wester Ross?

Posted: Monday 1 September, 2008 @ 14:17:36

Salmon fry from the River Gruinard (David Mullaney)

With good spawning habitat and extensive areas of prime nursery habitat for juvenile salmon (stable streambed of well-sorted pebbles and cobbles full of voids in which small fish can hide), densities of salmon fry in some parts of the Gruinard River and Little Gruinard River are sometimes high, with three or more fish per metre square of river bed. However, growth rates tend to be very low: a consequence of many mouthes competing for a limited food supply.

These fish were taken during an electro-fishing survey on 20th August 2008. In other rivers, salmon fry (young of the year) have been of 45-55mm in average length in August; these Gruinard fry appear almost stunted. Their small size may be partly a consequence of the drought in May and June and dewatering of food [invertebrate larvae] producing areas. What happens to them? Are they washed out of the system during the winter when the river is in spate? Are they eaten by larger parr? In rivers where there are more fish than there is food to support them, it is perhaps not suprising that other predators (e.g. Red-breasted merganser) are often seen.

Perhaps smolt production rates (and smolt sizes) would be higher with fewer, faster growing juvenile salmon in the river?