Whistle signal variations among three Indo-Pacific humpback dolphin populations in the South China Sea: a combined effect of the Qiongzhou Strait's geographical barrier function and local ambient noise?

Geographic variations in the dolphin whistles could be useful in assessing association and isolation among populations. Whistle of free-ranging Indo-Pacific humpback dolphins (Sousa chinensis) among the Pearl River Estuary (PRE), Leizhou Bei (LZB) and Sanniang Bay (SNB) populations were investigated. A total of 2850 whistles with legible fundamental contour were extracted and 15 acoustic parameters were measured. Contrary to SNB, PRE and LZB had the same relative proportion of tonal type compositions with flat and sine representing the most frequent types. The generalized linear model analysis showed significant acoustic difference among populations and tonal types. All frequency parameters in SNB were significantly higher than those in PRE and LZB, where no significant variation was observed in most of the parameters either at the population level or within each tonal type. Canonical discriminant functions analysis showed a smaller difference between PRE and LZB than between PRE and SNB and between LZB and SNB. Compared with previous recordings, recent recordings demonstrated a consistent pattern of becoming higher in whistle frequency parameters in both LZB and SNB populations, suggesting that noise pollution in LZB and SNB increasing with time according to the acoustic niche hypothesis. Dolphin whistle's geographic variations could be shaped by the combined function of the geographical barrier function of the Qiongzhou strait and local ambient noise. Considering the isolated condition and the relatively smaller population size of the humpback dolphin in the SNB, more effective and proactive conservation actions should be taken to prevent the extinction of small populations.     

液哨超声波增氧后水中溶氧量变化的试验研究

为了研究低溶解氧含量的水体经过液哨超声波增氧装置之后，溶解氧含量的增加量及其随时间的变化趋势，本研究进行了增氧后试验水的静置试验，并监测了水体中溶解氧含量随时间变化趋势。研究共设置了6组实验，2个变量，即添加簧片与否以及流量变化。结果表明：该装置添加簧片组增氧后试验水中的溶解氧含量在2 h内还会继续增加，2 h达到最大值；2 h后，水中溶氧量会急剧下降；6 h后，溶氧量下降速率变缓；到20 h的时候，试验水溶氧量趋于稳定状态，达到7.4mg/L左右。而未添加簧片的对照组同样在2 h达到一个峰值，2~3 h的时候，溶氧量会有小幅度下降，之后溶氧量会继续增加，最后在20 h的时候，溶氧量趋于平衡状态，达到7.15 mg/L左右。实验展示了液哨超声波装置增氧后水中含氧量的变化趋势，并得出了一套科学的、合理的水体溶解氧变化的系列特征曲线，对该装置应用于水产养殖、污水处理以及增氧灌溉领域，提供了重要的理论验证和研究价值。     

Geographic variations in the whistles among three Indo-Pacific bottlenose dolphin <Emphasis Type="Italic">Tursiops aduncus</Emphasis> populations in Japan

ABSTRACT:   Whistles of Indo-Pacific bottlenose dolphins from three populations in Japan were collected and analyzed quantitatively. Geographic variations in the whistles among populations were found. Significant differences in the whistles among years within each population were also found, but those differences could not explain whole differences among populations because some parameters of the whistles had more differences among populations than among years within each population. As changes with time in the whistles within each population might cause the geographic variations among populations, researchers should take the yearly change within populations into consideration when they study the geographic variation in the whistle of dolphins.