Fishing Lines: I'm fresh out of answers to The Great Swedish Sea Trout Mystery

On the weirdness scale, few angling experiences come close to catching fish where they really shouldn't live.

I was watching a huge shoal of tiddlers by the ferry jetty at Dalaro, a small, attractive town 25 miles from Stockholm. I assumed they were baby herring. In the interests of science, I bought a bread roll at the general store next to the ferry terminal, tied on a tiny hook and tried to catch one.

Turned out they weren't sea fish after all, but baby bleak, roach and bream – all fish we associate with fresh water.

Though the water here is really the Baltic Sea, it's sea in name only. You have to travel perhaps 60 miles west before it turns briny. So sea fishing means catching freshwater fish. I'm still coming to terms with catching pike among the seaweed, or pulling up an anchor and finding ragworms among the mud.

This is a fisherman's paradise. That odd mix of brackish water and rich feeding creates outsize pike, sea trout and salmon. (My guide, Ulf, has caught salmon to 60lb.) Early May is sea trout and pike heaven.

I'm here at the invitation of John Steele, a tough Carlisle-born former Navy diver who has spent the past three years guarding VIPs and convoys in Iraq. He's happy to talk about it, but has no plans to go back. He's been shot at too many times, watched too many friends die.

Fishing seems pretty tame after that, even if it is for sea trout that average 5lb and can weigh more than 30lb. This area is stocked annually (500,000 this year alone). So it should be easy. Trouble is, sea trout are twitchier than the annualSt Vitus school reunion.

I've never stalked deer, but sea trout must be the aquatic equivalent. Most UK seatrouting takes place in riversand at night, in the mistaken belief that you can surprise them. Fat chance.

Here, chasing this will-'o-the-wisp means fishing from boats and casting into bays. That makes it 10 times harder to sneak up on them. My companion, Andy Nicholson, said gloomily: "I reckon they hear us coming from so far away that they've already moved to the next island by the time we make our first cast." With 24,000 islands in easy distance, you move around a lot here.

Just when you're ready to say "That's it! I've had enough! To hell with sea trout!", your rod bends and a huge silver fish leaps into the air. But it's never easy.

John reckons a good day means catching six. Ulf, his best mate, has been fishing for sea trout for the past 25 years and still remembers a red-letter day of 15. The average is two or three. They may be whoppers, but you earn your fish.

For a lazy fisher like me, this is darned hard work. There must be an easier way. Andy and I have sat late into the night puzzling how to crack The Great Baltic Sea Trout Mystery (millions of fish, but where are the bodies?). It would baffle Miss Marple. We're trying to catch a fish that allegedly can't be caught in the sea. Except in this area of Sweden, it is.

Water temperature? Currents? Barometrics? Salinity? The right-coloured hat? We're no nearer the answer.

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