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Passive acoustic monitoring (PAM) is a powerful method to study the occurrence, movement and behavior of echolocating odontocetes (toothed whales) in the wild. However, in areas occupied by more than one species, echolocation clicks need to be classified into species. The present study investigated whether the echolocation clicks produced by small, at-risk, resident sympatric populations of Indian Ocean humpback dolphin (Sousa plumbea) and Indo-Pacific bottlenose dolphin (Tursiops aduncus) in Menai Bay, Zanzibar, East Africa, could be classified to allow species specific monitoring. Underwater sounds of S. plumbea and T. aduncus groups were recorded using a SoundTrap 202HF in January and June-August 2015. Eight acoustic parameters, i.e. -10 dB duration, peak, centroid, lower -3 and lower -10 dB frequencies, and -3 dB, -10 dB and root-mean-squared bandwidth, were used to describe and compare the two species' echolocation clicks. Statistical analyses showed that S. plumbea clicks had significantly higher peak, centroid, lower -3 and lower -10 dB frequencies compared to T. aduncus, whereas duration and bandwidth parameters were similar for the two species. Random Forest (RF) classifiers were applied to determine parameters that could be used to classify the two species from echolocation clicks and achieved 28.6% and 90.2% correct species classification rates for S. plumbea and T. aduncus, respectively. Both species were classified at a higher rate than expected at random, however the identified classifiers would only be useful for T. aduncus monitoring. The frequency and bandwidth parameters provided most power for species classification. Further study is necessary to identify useful classifiers for S. plumbea. This study represents a first step in acoustic description and classification of S. plumbea and T. aduncus in the western Indian Ocean region, with potential application for future acoustic monitoring of species-specific temporal and spatial occurrence in these sympatric species.

Small coastal dolphins endemic to south-eastern Australia have variously been assigned to described species Tursiops truncatus, T. aduncus or T. maugeanus; however the specific affinities of these animals is controversial and have recently been questioned. Historically 'the southern Australian Tursiops' was identified as unique and was formally named Tursiops maugeanus but was later synonymised with T. truncatus. Morphologically, these coastal dolphins share some characters with both aforementioned recognised Tursiops species, but they also possess unique characters not found in either. Recent mtDNA and microsatellite genetic evidence indicates deep evolutionary divergence between this dolphin and the two currently recognised Tursiops species. However, in accordance with the recommendations of the Workshop on Cetacean Systematics, and the Unified Species Concept the use of molecular evidence alone is inadequate for describing new species. Here we describe the macro-morphological, colouration and cranial characters of these animals, assess the available and new genetic data, and conclude that multiple lines of evidence clearly indicate a new species of dolphin. We demonstrate that the syntype material of T. maugeanus comprises two different species, one of which is the historical 'southern form of Tursiops' most similar to T. truncatus, and the other is representative of the new species and requires formal classification. These dolphins are here described as Tursiops australis sp. nov., with the common name of 'Burrunan Dolphin' following Australian aboriginal narrative. The recognition of T. australis sp. nov. is particularly significant given the endemism of this new species to a small geographic region of southern and south-eastern Australia, where only two small resident populations in close proximity to a major urban and agricultural centre are known, giving them a high conservation value and making them susceptible to numerous anthropogenic threats.

Coastal dolphins are regarded as indicators of changes in coastal marine ecosystem health that could impact humans utilizing the marine environment for food or recreation. Necropsy and histology examinations were performed on 35 Indian Ocean bottlenose dolphins (Tursiops aduncus) and five Indo-Pacific humpback dolphins (Sousa plumbea) incidentally caught in shark nets off the KwaZulu-Natal coast, South Africa, between 2010 and 2012. Parasitic lesions included pneumonia (85%), abdominal and thoracic serositis (75%), gastroenteritis (70%), hepatitis (62%), and endometritis (42%). Parasitic species identified were Halocercus sp. (lung), Crassicauda sp. (skeletal muscle) and Xenobalanus globicipitis (skin). Additional findings included bronchiolar epithelial mineralisation (83%), splenic filamentous tags (45%), non-suppurative meningoencephalitis (39%), and myocardial fibrosis (26%). No immunohistochemically positive reaction was present in lesions suggestive of dolphin morbillivirus, Toxoplasma gondii and Brucella spp. The first confirmed cases of lobomycosis and sarcocystosis in South African dolphins were documented. Most lesions were mild, and all animals were considered to be in good nutritional condition, based on blubber thickness and muscle mass. Apparent temporal changes in parasitic disease prevalence may indicate a change in the host/parasite interface. This study provided valuable baseline information on conditions affecting coastal dolphin populations in South Africa and, to our knowledge, constitutes the first reported systematic health assessment in incidentally caught dolphins in the Southern Hemisphere. Further research on temporal disease trends as well as disease pathophysiology and anthropogenic factors affecting these populations is needed.

Indo-Pacific bottlenose dolphins (Tursiops aduncus) are a coastal species found in Thai waters off the coasts of the Andaman Sea and the Gulf of Thailand. This species was recently re-listed as near-threatened by the IUCN Red List, though the population status in Thai seas is not known. Here, we investigated genetic diversity, population structure, maternal lineage, and demographics by analyzing skin tissue samples (n = 30) of T. aduncus stranded along the Andaman coastline of Thailand between 1990 and 2019. This study was based on 11 microsatellite loci and 265 bp mtDNA control regions compared to data available through the National Center for Biotechnology Information (NCBI). From microsatellites, the observed heterozygosity (Ho) ranged from 0.46 to 0.85. The mean fixation index (F) value for all loci was 0.10 ± 0.04, which suggests some degree of inbreeding. Two genetic clusters (the most likely K at K = 2) were observed in T. aduncus through the population structure analysis using multiple criteria. For the mtDNA control region, a total of 17 haplotypes were found for dolphins in Thai seas (14 haplotypes from our samples; three haplotypes from the NCBI database) with high levels of haplotype diversity (h) at 0.926 ± 0.027 and nucleotide diversity (π) at 0.045 ± 0.002. A decline in the effective population size from 0.05 million years ago also was observed in Thai T. aduncus through Bayesian Skyline Plots analysis. A unique set of haplotypes was identified in our samples, which may have originated from the Australian and Indian Oceans rather than the Western Pacific Ocean. These results improve our understanding of the maternal lineage of the Indo-Pacific bottlenose dolphin, which can be used for monitoring population status and establishing better conservation plans for this species in the Thai Andaman Sea.

Emigration of individual animals is an important biological phenomenon that depends on both populations and ecosystem attributes. Off Mikura Island, a long-term identification survey of individual Indo-Pacific bottlenose dolphins has been conducted since 1994 using an underwater video system. Between 1994 and 2014, 277 individual dolphins were identified by this survey, with 41 individuals emigrating from Mikura Island during this period. Adults emigrated significantly more often than younger age classes. The sex and age classes of emigrants in 2008 and 2010 (the years with the greatest amount of emigration) differed, suggesting that social relationships within a population may affect emigration. Emigrants were observed among the Izu Island Chain and in Chiba, Shizuoka, Mie, and Wakayama Prefectures. The greatest distance dolphins emigrated from Mikura Island was 390 km to Tanabe in Wakayama Prefecture. Some individuals were observed to have emigrated to several areas during the period. The most frequent destination was Toshima Island, one of the Izu Islands Chain, where emigrants have been observed to reproduce. Emigrant groups were composed exclusively of individuals from Mikura Island; there were no immigrants to the Mikura Island area during the 20-y period of observation, although six emigrants eventually returned to their original range. Future studies of social relationships and habitat use by emigrants will reveal more about the reasons dolphins leave their habitats.

Previous sightings of bottlenose dolphins in Tañon Strait, central Philippines, in the late 1980’s to early 1990’s were limited to the southern section of the strait, in waters <500 m deep, and the species was formerly identified as Tursiops truncatus . Photo-identification surveys ( n  = 117) conducted in 2014 and 2015 in Tañon Strait resulted in 50 encounters of Indo-Pacific bottlenose dolphins Tursiops aduncus . No common bottlenose dolphin T. truncatus was seen. The Indo-Pacific bottlenose dolphin has only recently been confirmed to occur in coastal waters in the Philippines and thus very little is known of its local distribution and ecology. In Tañon Strait, the species was seen across a wide range of water depth (4–668 m, x̅ = 309 m) in groups ranging from 1 to ~60 individuals. We provide a photographic verification of this species and first evidence of a seemingly small population in a tropical protected seascape in the Philippines.