Free dolphin cruises spotlight Istanbul's Bosphorus bottlenoses

As the first dolphin fin surfaces from the Bosphorus, a ripple of excitement travels through a ship whose passengers are being treated to a free education on one of Istanbul's most graceful sights.

Whether they live there or are just passing through, dolphins and porpoises feel very much at home in the long marine corridor that bisects the Turkish city of 16 million.

Together with the World Wildlife Fund (WWF), the Istanbul municipality organizes summer boat trips -- free of charge -- to watch the sea mammals frolic and raise public awareness of the dangers facing them.