Wild salmon
Back from the brink
A new study suggests that captive breeding to restore native stock can help to revive ailing wild salmon populations BY ROBERT OUTRAM
C
AN stocking programmes offer a lasting solution to the problem of declining fish numbers in Scotland’s salmon rivers? A recent study carried out by a team at the University of the Highlands and Islands sought to answer that question. During the 1990s, the River Carron in Wester Ross saw a dramatic decline in salmon numbers. The owners, Riparian, with biologist and keen salmon fisherman Bob Kindness, set up the River Carron Conservation Association, which has been adding to the wild stock since 1995. The stocked fish are all native to the Carron. Initially stocking was carried out using eggs stripped from wild salmon hens, but the available numbers were quite limited. From 2001, the association has been using captive broodstock – all Carron fish – to bring the numbers of fry released up from 5,000–10,000 to 150,000 or more. Judging by recorded catches, the number of salmon in the Carron has gone up steeply, increasing from a five-year annual average of 10.6 in 2001 to 187.2 in 2020, according to Marine Scotland Science (MSS). MSS does not support stocking from captive broodstock, however, as Bob Kindness explains: “If a river’s salmon stock is low, the only way to obtain enough eggs for stocking to be effective,is to create a captive broodstock as insufficient wild brood fish can be taken from the river.” MSS is also against stocking out young fish beyond the un-fed stage. Kindness adds: “There is a suggestion that any fish that is reared in captivity before release loses its ability to cope in the wild. MSS believes that if you rear fish in tanks they become domesticated - they can’t feed
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in the wild and they can’t avoid predation.” So,could the increase in salmon numbers be attributed to the stocking programme or was it due to some other cause? One way to find out was to see how many of the adult fish and smolts in the river were from the programme. Tagging or otherwise marking fish is intrusive so it was decided to use DNA analysis. The Rivers and Lochs Institute at Inverness College, University of the Highlands and Islands (UHI), have now analysed the DNA from three years of salmon catches. The results were then compared with DNA from the salmon broodstock used in the stocking programme to find out whether the stocked juvenile fish were surviving to return as adults. They compared samples from fish in the river with records of the 2014 broodstock. The latter actually comprised three groups: two separate groups of captive broodstock and one “wild” group hatched from eggs stripped from wild fish and fertilised in the hatchery. They were able to do this because Kindness has been collecting samples for DNA analysis from catches on the river over the past decade by clipping a small piece from each salmon’s tail fin. As well as adults returning from the sea to spawn, the team also analysed DNA from smolts caught in a screw trap on their way out to sea.
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11/01/2022 14:52:13
