SOME SECRETS OF SEA TROUT

 

Posted at horrabridge.org.uk

 

Fishing clubs in this area are being invited to contribute their views to a Tamar Catchment Fisheries Action Plan, and possibly help it by taking DNA samples from caught fish.

There was a Tamar Fisheries Action Plan in progress but the name has been changed to make it clear that its concerns apply to all contributory rivers, such as Walkham and Tavy, and also to neighbouring systems ending up in Plymouth Sound.

Last week, in the conference rooms at Roadford Lake, the fisheries officer for the Westcountry Rivers Trust, Bruce Stockley, announced the new emphasis at a meeting of the Tamar Fisheries Forum, a loose collection of government agents, land managers and anglers, which he uses as a consultancy body.

So far, the fishermen are mainly represented by serious salmon anglers from the Launceston area, frequenters of the Arundell Arms at Lifton, but Dr Stockley has been trying to get interest from these parts and The Bridge sent a correspondent on behalf of the London Inn and its fair assortment of angling interests.

As food for thought, Andrew King of Exeter University presented findings on “straying” by sea trout – meaning how far the fish are prepared to change course on the way home to their birth waters. The research covered 29 river systems in Devon and Cornwall, including Tamar, Tavy and Lynher.

The investigation started with proof of the theory that brown trout and sea trout are the same fish, living different ways. Genetic analysis confirmed it, said Dr King. Tiny marks in the DNA distinguished a Tavy trout from one living in the Tamar and both could be recognised as different from their cousins in the Dart or the Fowey.

And the same family signs are in the genes of the sea trout which come back – generally speaking, at least.

The sea trout were first to repopulate the rivers, after the last Ice Age. River trout were a spin-off population. But because of their enclosed lives, the river trout have kept the genetic pattern of their ancestors.

Dr King and his team wanted to know if a peal, after travelling the seas, was quite as fussy about only breeding at home.

First job was to build a database of brown trout tribes. Then it had to be checked over several years, to make sure it was reliable. At the same time, the Exeter team were collecting scale samples from fish stunned for counting by the Environment Agency or hooked by fishing clubs.

The preliminary findings are that some straying is not uncommon.

Some days as many as 30 out of a hundred peal turning up at Gunnislake should have turned off, strictly speaking, at the Lynher or the Tavy, and the average seems to be at least 10 percent.

However, none seem to get as far as the Lyd, which suggests they might turn back before the spawning grounds.

The Tavy was particularly interesting, said Dr King. He only had a small number of rod-caught samples, but nearly one in five were Dart and Teign types.

“The estuaries of Dart and Tavy are 100 kilometres apart,” Dr King commented, “but the headwaters gather on the same bits of Dartmoor, within 300 or 400 metres, so we are thinking in terms of the fish being led by a familiar smell.”

Again, he could not be sure the strays went on to spawn. But he could say that the lower Tavy and the lower Tamar were effectively mixed stock fisheries, contrary to received wisdom.

The findings might have a bearing on the heated debate about seeding rivers with salmon fry, which used to be done on the Walkham, using farmed Tavy salmon. Government agencies have discouraged the practice for some years because of the possible danger of artificial genetic mixing. If salmon behave in the same way as sea trout, it could well be happening naturally.

But Dr King cannot be sure even about the sea trout because he did not get enough data from the upper waters, where successful fish lay eggs. He would like to know if strayed fish are still in the fight at that point or whether most of them have turned around and got back on target.

Now, of course, his funding for the project has run out.

However, the base data is so interesting, somebody will use it again somehow, said Bruce Stockley.

He would be interested to hear from any organisations willing to keep collecting fish catch samples meanwhile and can supply a briefing on how to take them and what information to record.

The meeting moved on to discuss ominous noises in environmental politics about a universal catch and return law – meaning, no taking one home for the pot, even if it is legally caught.

There has been a lot of talk about further restrictions on recreational fishing for salmon – and some other species, including bass. The Environment Agency representatives at the meeting said outright bans were unlikely but they conceded that the possibility was probably being discussed, somewhere in Europe, and that it was not unlikely that catch and return rules would at least be applied much more widely.

The anglers said they feared a lot of people would stop bothering to buy licences and permits and the sport would suffer. The Agency said there was some interest in the idea of issuing every licensed angler with a small number of smart tags, which would authorise a limited legitimate take.

In a questions session, somebody asked for an update on the outbreak of fungus which led to emergency restrictions on salmon fishing in Devon this summer. Bruce Stockley said all tests for disease had come back negative. It seemed the salmon had simply been stressed – possibly by particularly cold water – and had succumbed to a parasite which was always waiting in the water.

Bruce Stockley can be contacted at bruce@wrt.org.uk/

This report was written by Chris Benfield: benfields@towers12.demon.co.uk/

Contact The Bridge magazine and website at thebridge2000@hotmail.com/

 

 

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