Fletcher S, Le Boeuf B J, Costa D P, Tyack P L, Blackwell S B
Department of Biology, University of California, Santa Cruz 95064, USA.
J Acoust Soc Am. 1996 Oct;100(4 Pt 1):2531-9. doi: 10.1121/1.417361.
This study was the first phase in a long-term investigation of the importance of low-frequency sound in the aquatic life of northern elephant seals, Mirounga angustirostris. By attaching acoustic recording packages to the backs of six translocated juveniles, the aim was to determine the predominant frequencies and sound levels impinging on them, and whether they actively vocalize underwater on their return to their rookery at Ano Nuevo, California, from deep water in Monterey Bay. All packages contained a Sony digital audio tape recorder encased in an aluminum housing with an external hydrophone. Flow noise was minimized by potting the hydrophone in resin to the housing and orienting it posteriorly. The diving pattern of four seals was recorded with a separate time-depth recorder or a time-depth-velocity recorder. Good acoustic records were obtained from three seals. Flow noise was positively correlated with swim speed, but not so high as to mask most low-frequency sounds in the environment. Dominant frequencies of noise impinging on the seals were in the range 20-200 Hz. Transient signals recorded from the seals included snapping shrimp, cetacean vocalizations. boat noise, small explosive charges, and seal swim strokes, but no seal vocalizations were detected. During quiet intervals at the surface between dives, the acoustic record was dominated by respiration and signals that appeared to be heartbeats. This study demonstrates the feasibility of recording sounds from instruments attached to free-ranging seals, and in doing so, studying their behavioral and physiological response to fluctuations in ambient sounds.
本研究是对低频声音在北象海豹（Mirounga angustirostris）水生生活中的重要性进行长期调查的第一阶段。通过将声学记录设备附着在六只被转移的幼年海豹背上，目的是确定作用于它们的主要频率和声音水平，以及它们从蒙特雷湾深水区返回加利福尼亚州阿诺新的繁殖地时是否在水下主动发声。所有设备都包含一台索尼数字录音机，装在一个铝制外壳中，并带有一个外置水听器。通过将水听器用树脂封装在外壳中并使其向后定向，水流噪声被降至最低。用一个单独的时间深度记录仪或时间深度速度记录仪记录了四只海豹的潜水模式。从三只海豹身上获得了良好的声学记录。水流噪声与游泳速度呈正相关，但不至于高到掩盖环境中的大多数低频声音。作用于海豹的噪声的主导频率在20 - 200赫兹范围内。从海豹身上记录到的瞬态信号包括枪虾声、鲸类发声、船只噪声、小型炸药爆炸声和海豹的游泳划水声，但未检测到海豹的发声。在潜水之间水面的安静时段，声学记录主要由呼吸声和似乎是心跳的信号主导。这项研究证明了记录附着在自由活动海豹身上的仪器发出的声音的可行性，并且通过这样做，研究它们对环境声音波动的行为和生理反应。
