Fishing Lines: Detectives aim to reveal the sea trout's true identity

IF EVER a fish needed a decent PR agent, it's the sea trout. With the looks and lifestyle of the salmon, plus a genealogy more interesting than the House of Windsor, it should be accorded as much fame as its close cousin. But most fishermen don't even know that it can change its spots.

Many books still list sea trout and brown trout as separate species. But the fish that spends most of its time at the seaside comes from exactly the same family as the trout that live in Hampshire chalk streams, Irish loughs or Welsh brooks. Nobody quite knows why a fish that is perfectly happy with river life should suddenly put on a bright silver coat and head for the sea. It may be that, like inner-city living, the overcrowding gets too much for them. Most sea-going fish are female and if there is a dearth of trout, most stay at home and don't bother with travelling to the coast. In many rivers, sea trout and brown trout interbreed freely.

It is interesting, all the more so because, in certain areas such as the west coast of Ireland, sea trout are such an important sporting fish that their virtual disappearance over the past couple of years (ironically, salmon farms are probably to blame) has had a huge impact on local economies.

Peter Mantle, who owns Delphi Lodge, at Leenane, Galway, said: 'Sea trout are the backbone of our business. Fishing is a major prop to this area. It is an industry and it supports hundreds and hundreds of jobs. Sea trout are the bread and butter of that industry.' The problems have become so serious, with many businesses on the verge of ruin, that Mantle is leading a Sea Trout Action Group to put pressure on the Irish government.

Until 1989, anglers flocked to fish for sea trout off the west coasts of Scotland and Ireland, as well as a few Welsh and West Country rivers. But, suddenly, only a tiny proportion of fish returned. On the river Gruinard, in Argyll, homecomers fell from hundreds to tens. On some rivers, none came back at all. Are lice to blame? Is it nature's way of saying: 'Stay home'? Why have some rivers been unaffected? Or is the sea trout just wanting some attention?

Detectives have been called in. Dr David Solomon, one of the country's leading fish biologists, is spearheading an investigation by the National Rivers Authority into sea trout. Much of the problem, Solomon believes, has been the assumption that anything applying to salmon would be bound to hold for sea trout too. The fish's sudden disappearance has brought home to scientists and anglers just how little they know about it.

'It is a fascinating fish,' he says. 'They mature much sooner than salmon - some after only a few months at sea. They spend a lot of time in estuaries and some never really go to sea at all.

'Small sea trout cannot adapt to cope with the osmotic shock of changing from fresh to sea water as well as salmon, yet they have tremendous precision. In some Cornish rivers, the fish will return to the same pool on the same tributary they were born.'

His first task is to collate what is known about sea trout, sort out the facts from the myths and identify what further studies need to be done. And from there, who knows? One thing is for certain. Sea trout will not be understudying the salmon for much longer.