Their rods resting on the bank, amateur anglers watch with an air of defeat as a trawler winches its enormous vertical net out of the waters of the Bosphorus. It is high season for a popular variety of tuna in Istanbul's strait and the area is teeming with shoals en route from the Black Sea to the Mediterranean. But between the fish and their destination, and between local anglers and their quarry, are the trawlers' huge nets, some more than 1,000 metres long.