2017年3月31日，我室许肖梅教授课题组在国际声学领域权威期刊The Journal of the Acoustical Society of America（JASA）上发表研究论文“Classification of underwater vocalizations of wild spotted seals (Phoca largha) in Liaodong Bay, China”，系统报道了辽东湾野生斑海豹水下发声的研究情况。
斑海豹（Phoca largha）是唯一可在我国海域自然繁殖的鳍足亚目（Pinnipeds）动物，属国家二级重点保护动物。该物种繁殖期处于辽东湾冰封期，只能利用繁殖期尾声融冰阶段的短暂窗口出海进行数据采集，获取其野生状态下的发声数据极为不易。因此，关于野生斑海豹水下发声的研究在国内外相关领域一直处于空白。该研究论文首次利用被动声学技术对野生斑海豹水下发声进行了跟踪记录，并利用主成分分析和系统聚类分析相结合的方法对其水下发声信号进行了量化分类与描述。该研究对系统深入了解该物种自然状态下的声学行为有重要意义。同时，文章提出的分类方法可推广应用于其他海洋哺乳动物的发声研究。
论文第一作者为水声部重博士研究生杨亮亮，通信作者为其导师、水声部重副主任许肖梅教授。合作者包括：英国纽卡斯尔大学Per Berggren教授、辽宁省海洋水产科学研究院院长韩家波研究员、中科院三亚深海科学与工程研究所张培君副研究员、以及辽宁省盘山县渔政局斑海豹管护站李兵站长。论文第一作者和通信作者单位均为厦门大学水声通信与海洋信息技术教育部重点实验室。该研究工作得到了国家海洋局海洋公益项目、国家自然科学基金委与香港海洋公园保育基金委等项目的资助。
此项最新研究成果的发表标志着许肖梅教授课题组在海洋哺乳动物声学研究及国际化合作方面取得了重要进展，对提高厦门大学水声部重实验室的学术影响力和深化该领域的研究都具有积极意义。
Abstract: Underwater vocalizations were recorded and classified from wild spotted seals (Phoca largha) in Liaodong Bay, China. The spotted seals exhibited an extensive underwater vocal repertoire but with limited complexity. Four major call types, representing 77.8% of all calls recorded, were identified using multivariate analyses of ten acoustic parameters; knock, growl, drum, and sweep. The calls were relatively brief (12–270 ms, mean of −10 dB duration) pulsating sounds of low-frequency (peak frequency<600 hz) and narrow bandwidth (169–232 hz, mean of −3 db bandwidth; 237–435 hz, mean of −6 db bandwidth). frequency variables (−3/−6 db frequency bandwidth, center frequency, and top three peak frequencies) were the primary descriptors used to differentiate the call types. comparing the spotted seal underwater vocalizations with those of the closely related pacific harbor seal (Phoca vitulina richardii) indicated that the two species use similar bandwidths and peak frequencies but spotted seal calls were generally shorter. Knowledge of underwater vocalizations of wild spotted seals is important for understanding the species behavior and for planning future acoustic surveys of its distribution and occurrence.
FIG. 1. (Color online) Map showing the morning (1, solid dot) and evening (2, circle) locations where spotted seal (
Phoca largha) underwater vocalizations were recorded in Liao River estuary, in Liaodong Bay, China.
FIG. 2. (Color online) Oscillogram (a) with signal envelope (dotted line) and average energy spectrum (b) examples of spotted seals (
Phoca largha) underwater vocalizations recorded in Liaodong Bay, China, showing the vocal parameters measured for acoustic description and definition of the calls: -10 dB duration (τ
-10dB ), positive start-up time of oscillation (τ
PSO ) and negative start-up time of oscillation (τ
NSO ), top three peak frequencies (PF1, PF2, and PF3), center frequency (CF), -3 dB frequency bandwidth (-3 dB_BW), and -6 dB frequency bandwidth (-6 dB_BW). PF1 and PF2 represent two extreme amplitude points in the -3 dB bandwidth (NumE).
FIG. 3. (Color online) A dendrogram of the underwater vocalizations recorded from spotted seals (
Phoca largha) based on hierarchical cluster analysis. Different main clusters (similarity over 95%) are shown in different colors. 704 observations (calls) were analyzed and 548 of these (77.8%) were identified as four different call types (knock, growl, drum, and sweep).
FIG. 4. (Color online) Oscillograms (above) and spectrograms (below, sampling rate 80kHz, hamming window, FFT size = 1024 points, frequency overlap = 50%) of four underwater call types, knock, growl, drum and sweep, identified from recordings of spotted seals (
Phoca largha) in Liaodong Bay, China.
Citation：Liangliang Yang, Xiaomei, Xu, Peijun Zhang, Jiabo Han, Bing Li, Per Berggren. Classification of underwater vocalizations of wild spotted seals (Phoca largha) in Liaodong Bay, China. The Journal of the Acoustical Society of America, 2017, 141(3):2256-2262
Link to full text：http://dx.doi.org/10.1121/1.4979056
