Imprinting of Juvenile Salmon

[smigel]

Does anyone know how long it takes for juvenile salmon to become imprinted with the scent of the river they are in? When does it happen in their lives?

Does it make sense to release smolts in different places in a catchment, or is it already too late to change anything?

[betanut]

Now that is an interesting question - well, all of your questions above are interesting
First bit I can't answer off the top of my head - although I have heard conjecture that it's at a genetic level and doesn't happen at any given point per se. That's possibly a duff line though as I recall a river on the west coast that had a supply of smolts from a hatchery in Hampshire grown on in water from aquifers rather than river water - these fish were tagged and subsequently returned to the river as adults - so open to much conjecture.
Second part - hell yeah Get the fish spread out as much as possible - there's no reason to assume that if you 'seed' them from hatchery stock and any imprint of 'home' isn't at a genetic level then they should return to whence they were seeded - well, the same river at least ;D

[kercock]

On the Delphi fishing in the west of Ireland,they,as I recall,brought the eggs on to smolt size, then released them into the river. The report about it was in the T+S many moons ago. they reckoned to have about a 10%return from the sea to the river. Not sure how they worked that out.! I also recall that the cost was around 60p per smolt to rear. That would be a large bill for the Tay,the board reckon to put in around 3 million eyed ova in tubes this year NOW whats three million times 60p, ONE two ............three.......................oh shi# ONE..............................

[johnmac]

Its a point that i should know.... but im afraid i cant remember! I'd have to look up my old books! The cost of a Salmon smolt is generally £1.00 from a fish farm....... they have to make a profit, so Dennis is right with the 60p estimate of production cost. At 60p it still aint cheap!

Im pretty sure that the hatchery on the Tay is at Almondbank on the River Almond? So obviously the fish are getting water from part of the system in which they are going to be released. I know of several angling clubs on the west coast, particularly the Clyde, that have purchased sea trout parr, salmon parr and smolts from a farm in Dumfriesshire, and they have a tagging system which shows that some of the fish have returned in later life.........

.............i just dont think from a genetic point of view that buying fish which are from a completely different river system is a good idea.

Bottom line is that its an expensive way of producing fish! Most commercial fish farms produce their smolts in six months using photo-period to simulate several summers and winters...... however in the wild it can take anything up to 6 or 7 years if the feeding is poor...... so there you see the problem. More needs to be done to find a natural solution.... you cant rely solely on farming and stripping if numbers continue to fall.......... and this leads me to the problems that need to be addressed for the wild stocks

Agricultural run-off..... pesticides, fertilisers etc etc
Off shore Salmon farms, with their sea lice infestations
Sewage plants..... in Summer low levels the Ericht is unfishable half a mile either side of the "treatment" plant!

Lastly, and this is something which will get worse as time goes on! Upland planting of Conifer forests!

Anyway.... i think none of that answers the original question! But i thought it might get a few opinions! feel free to jump in!

[betanut]

kercock said:

....I also recall that the cost was around 60p per smolt to rear. That would be a large bill for the Tay,the board reckon to put in around 3 million eyed ova in tubes this year NOW whats three million times 60p, ONE two ............three.......................oh shi# ONE..............................

Aye, but handy thing is that eyed ova don't get fed so cost "not a lot" by comparison - costs still add up mind, it's the care and attention that's required of the wee silver guys and gals that's the big cost