Preliminary analysis of echolocation signals produced by fleeing Irrawaddy dolphins(Orcaella brevirostris)

In this study, echolocation signals were recorded from a wild Irrawaddy dolphin(Orcaella brevirostris) in shallow water in the Bay of Brunei. During sound recording, a small fishing boat engine startled a nearby Irrawaddy dolphin and began chasing it on two occasions. Variations in the acoustic parameters were detected. When the Irrawaddy dolphin was startled and chased, the sound pressure level, number of click trains per minute, pulse number, and average inter-pulse interval(PI) per click train were all affected. The PI increased and exhibited a slight downward trend during the chase. The increase in PI indicated an increase in the inspection distance as the dolphin escaped. Thus, Irrawaddy dolphins may adapt their echolocation signals to stand out from ambient noise in the wild and to improve their search efforts in potentially risky situations. Appropriate management of the burst noise around the dolphins is important.

Short-term offshore extension of Brahmaputra-Ganges and Irrawaddy freshwater plumes to the central northern Bay of Bengal based on in situ and satellite observations

In this study, the short-term offshore extension of Brahmaputra-Ganges(BG) and Irrawaddy freshwater plumes to the central northern Bay of Bengal(BoB) was investigated based on in situ and satellite observations. In the summer and winter of 2015, two significant freshening events with periods of weeks were observed from a moored buoy at 15°N, 90°E in the BoB. Soil Moisture Active Passive(SMAP) satellite sea surface salinity compares well with the in situ data and shows that these freshening events are directly related to the short-term offshore extension of the BG and Irrawaddy freshwater, respectively. These data combined with the altimeter sea level anomaly data show that the offshore extending plumes result from freshwater modulated by eddies. During summer, the BG freshwater is modulated by a combination of three closely located eddies: a large anticyclonic eddy(ACE) off the northwestern BoB coast and two cyclonic eddies in the northern BoB. Consequently, the freshwater extends offshore from the river mouth and forms a long and narrow tongue-shaped plume extending southwestward to the central BoB. During winter, the Irrawaddy freshwater is modulated by two continuous ACEs evolved from Rossby wave propagating westward from the Irrawaddy Delta off Myanmar, forming a tongueshaped plume extending to the central BoB. Strong salinity fronts are formed along the boundaries of these tongue-shaped plumes. These findings confirm good capability of the SMAP data to investigate the short-term offshore extension of the BG and Irrawaddy freshwater. This study provides direct evidences of the pathways of the offshore extension of the BG and Irrawaddy freshwater and highlights the role of eddies in the northern BoB freshwater plume variability.

Preliminary Study on the Distribution of Irrawaddy Dolphin, <i>Orcaella brevirostris</i>, in Banten Bay

Irrawaddy dolphins (Orcaella brevirostris) are aquatic mammals with critically endangered status able to live in different water salinities habitats, like estuary, rivers and lakes. Banten Bay features estuarine area where rapid economic development, contributed from industry, ports, mining and fisheries, takes place, and thus the presence of Irrawaddy dolphins in the area faces various environmental threats. This research aimed to study the distribution of Irrawaddy dolphins in Banten Bay and explore environmental factors threatening its life. Dolphins observation was conducted from January 2013-February 2014, using direct visual effort by team of observer and indirect effort by local fishermen. Direct visual effort was performed on boat by three observers, with maximum vessel speed 15 km/hour and total length of transect was 404 Km. Indirect visual effort comprised of regular assessment by 32 local fishermen when they conducted capture fishing at two different areas (South and North of Banten Bay). Sightings data from direct and indirect visual observation compiled with respondents opinion were mapped using Arc View&reg?GIS 3.3, resulting in distribution map of Irrawaddy dolphin in Banten Bay. Irrawaddy dolphin was most frequently observed in the northeast, south and central areas of the bay. Environmental threats alarming the lives of Irrawaddy dolphin in the Banten Bay may include noise pollution, boat accident and entanglement.

A New <i>Stegolophodon</i>(Proboscidea, Mammalia) from the Irrawaddy Formation of Myanmar

The new fossil teeth of Stegolophodon (Proboscidea, Mammalia) were discovered from the terrestrial sediments of the Irrawaddy Formation, in Kyauksaungsan and Tebingan areas, Magway Region, central Myanmar. A new Stegolophodon species is established in this paper. Stegolophodon iravaticus shares the characters of the advanced Stegolophodon and the primitive Stegodon. The M3 of S. iravaticus is related to that of the molar of Sand Pit in Tha Chang, Thailand and that of from Dhedari, Pakistan which is included in the Stegolophodon group 6 of Saegusa et al. (2005).

Five newly recorded Cyprinid fish (Teleostei： Cypriniformes) in Myanmar

Freshwater fish from the Putao and Myitkyina areas were collected in three ichthyofaunal surveys of the Mall Hka River and tributaries in and around Khakaborazi National Park and Hponkanrazi Wildlife Sanctuary, Kachin State, from 2014-2016. Tor yingjiangensis Chen et Yang 2004, Tor qiaojiensis Wu et al. 1977, Garra qiaojiensis Wu et al. 1977, Garra bispinosa Zhang 2005, and Schizothorax oligolepis Huang 1985, originally described from the upper Irrawaddy （Ayeyarwaddy） River in China, are first reported herein as new records to Myanmar. Counts, measurements, descriptions, photographs, and distributions of the specimens of the five newly recorded species are provided.