Very few books have been specifically written solely about sea trout fishing. The two classic books are
Graeme Harris & Moc Morgan 1989, Successful Sea Trout Angling, Blanford. ISBN 0 7137 1761 0
Hugh Falkus 1977, Sea trout Fishing, Witherby Ltd. ISBN 0 85493 115 5
If you have a lot of money to spare! you can purchase a deluxe edition of this classic from "The Flyfishers Classic Library" (£145 UK, $ 225 USA)
For Sea trout fly patterns:
Moc Morgan 1996, Trout and Salmon Flies of Wales, Unwin Books. ISBN 1873674252
Edited by Douglas Sutherland and Jack Chance 1982, Trout and Salmon Flies - a guide, Pelham Books. ISBN 0 7207 1396 X
In Welsh and written by one of our local keepers - Edgar Owen is an excellent light hearted account of his life time's experiences - well worth a read or get someone to translate bits for you if you don't understand Welsh. Emrys Owen (mentioned in the fishing reports is his brother), the third brother Griff caught the River Dwyfor's largest salmon - 32lbs - he is now in New Zealand.
"O Botsiar i Gipar" gan Edgar Owen - Carreg Gwalch - ISBN 0-86381-422-0 - "From Poacher to Keeper" by Edgar Owen.