A thousand salmon have been tagged on the River Tweed in the past decade, as scientists try to find out how many fish are in the river and the number caught by anglers.
The Tweed Foundation has been carrying out the tagging work since 1994, with help to catch the fish coming from some of the in-river netting stations on the lower Tweed.
And at Paxton House’s netting station the 1,000th salmon, a 15-pounder, was tagged by Tweed Foundation biologist Kenny Galt.
The tagging of both salmon and sea-trout in the Tweed is aimed at finding out how many tagged fish are caught later by anglers upstream, which gives a good idea of the overall proportion of all fish caught.
Dr Ronald Campbell, the foundation’s senior biologist, said: “This is very important information as it shows the level of pressure being put by anglers – the ‘exploitation rate’ – on the fish.
“This is crucial management information as, obviously, if anglers are catching five per cent of the stock it is a very different situation from them catching 50 per cent of the stock.”
Dr Campbell added that there is an additional reason for tagging sea-trout.
He said: “The salmon coming into the river are on their last journey – very few survive spawning to return to the sea and recover to spawn again.
“Sea-trout, however, have a much higher survival rate and many survive to spawn again – up to five times on the Tweed.
“Tagging sea-trout therefore also has the purpose of finding out about their life at sea as recaptures of tagged fish shows their migration routes at sea.”
Since 1997, when tagging started in late September, the salmon recapture rate on average is 4.3 per cent, which shows that the pressure on the stock from angling is not high and is sustainable.
Dr Campbell added: “These results are only for late September fish.
“It is quite possible that fish that come into the river earlier and experience a longer period of fishing effort have a higher exploitation rate.
“There is, in fact, very little information on this from anywhere in the British Isles and the present tagging programme in summer is an attempt to find out what the exploitation rate of summer salmon on the Tweed is.”
The reported sea-trout recaptures from September taggings are even lower, at around 1.4 per cent.