Studies on the ecology of small cetaceans in the Istanbul Strait using acoustical information

Growing human populations and economic activity have a negative impact to marine ecosystem, such as marine pollutions, overexploitations, extinction of species and following shrink of biodiversity. Small cetaceans, which belong to suborder Odontoceti, are one of the important mammals that include likely-to-be-extinct species because of human activities in the last decade. More than half of small cetacean species are listed as “Endangered” or “Data Deficient” in the International Union for Conservation of Nature (IUCN) Red List. For effective conservation, the knowledge of their basic ecology is necessary. In the present study, I focused on the population observed in the Istanbul Strait. Three species are observed in this area; harbor porpoise Phocoena phocoena, bottlenose dolphin Tursiops truncatus and short-beaked common dolphin Delphinus delphis. All of them are threatened subspecies but their ecology based on long-term constant observation has not well documented. I applied passive acoustic monitoring (PAM) with new species discrimination and animal density estimation method to fit on the situation of the Istanbul Strait and obtained the ecological information. The PAM is now widely used for study on small cetaceans, but the species discrimination based on acoustic information is still challenging. I proposed the discrimination method between harbor porpoise and delphinids and evaluated the accuracy by model. Also, I proposed the animal density estimation method which combine the line transect distance sampling approach with point transect estimations in consideration of the misclassification rate of species. Two-year continuous PAM was conducted by fixed acoustic tag (A-tag) in the middle of the strait in 2010–2011. I revealed that harbor porpoise were detected most in spring (March–May), and there are almost no detections in winter (December– February). On the other hands, delphinids were observed throughout the year during nighttime. The porpoises distinctively showed short inter-click intervals that imply the feeding behavior in spring, suggesting that they were foraging the migrating pelagic fish in spring. It was supported by the previously reported stomach contents of the stranded porpoises which were found in the Marmara Sea and the Turkish coast of the Black Sea. The animal density and distribution in whole strait were estimated by towed PAM in 2013. Animal density and distribution are one of the most fundamental information for conservation. In the Istanbul Strait, only the distribution of bottlenose dolphin has been available so far. I applied proposed density estimation method which can cover wider range of area by line transect approach based on acoustic cue based point transect distance sampling estimation. Also, I considered misclassification rate of species in estimator. The density was estimated as average of all seasons, it was 0.013 individuals km -2 (CV = 0.612) for harbor porpoise and 0.033 individuals km -2 (CV = 0.823) for delphinids, respectively. The distribution of harbor porpoise tended to be dispersed in the strait, but that of delphinids tended to be localized in north entrance to the Black Sea. The 50% kernel core area did not overlap between harbor porpoise and delphinids, suggesting the core habitat separation. I developed the PAM methodology that is suitable for the small cetacean species appeared in the Istanbul Strait, and obtained the ecological information in present study. The results revealed the difference of seasonal behavior, distribution and animal density between harbor porpoise and delphinids within the strait. It implies the effectiveness of PAM also in the multi-species-observed noisy area, and the importance to consider the interspecific difference of ecology for effective conservation management. Studies on the ecology of small cetaceans in the Istanbul Strait using acoustical information