Complex sentence: The professional fishing for eel, was previously substantial, but in 1997 the annual catch had fallen to 388 kg from a mere 14 tons and nowadays, the lake is exclusively fished by anglers.
Split into simpler sentences: The professional fishing for eel, was previously substantial, but in 1997 the annual catch had fallen to 388 kg from a mere 14 tons. Nowadays, the lake is exclusively fished by anglers.