Preliminary study of acoustic identification of odontocetes in the Istanbul Strait, Turkey

Abstract

In the Istanbul Strait, three odontocetes species are observed; the harbor porpoise which belongs to Phocoenidae and the common dolphin and the bottlenose dolphin which belong to Delphinidae. Previous visual observation conducted in the middle of this Strait showed, Phocoenidae appeared frequently in March and April, whereas Delphinidae appeared throughout the year. However, visual observation can only occur during daytime. On the other hand, acoustic observation can be used all day long, but is not suitable to identify and distinguish different species. In this study, we examined whether a two band acoustic comparison of biosonar sounds can identify family or species of odontocetes. We compared the sound intensity ratio of two frequency bands at 70 kHz and 130 kHz. Narrow-band sounds, with dominant frequency around 130 kHz, correspond to a large ratio of two band intensities, possibly originating from Phocoenidae. In contrast, broad-band sounds provide similar intensities at both frequencies, which possibly originating from Delphinidae. The results show Phocoenidae appeared frequently in March and April, whereas Delphinidae appeared during all months. These findings are consistent with previous visual observations and suggest that two band acoustic monitoring of small odontocetes could be useful for the identification of harbor porpoises from Delphinidae species in a long term study.