ABSTRACT: Hawaiian monk seals are among the most endangered marine mammals and the most basal of the phocid seals. The auditory biology of monk seals is compelling from behavioral, evolutionary, and conservation perspectives, but we presently lack substantive bioacoustic information for this species, with no formal descriptions of underwater vocalizations and limited data concerning hearing. These seals have been isolated for more than 10 million yr and have auditory structures differing from those of related species. Additionally, unlike other aquatically mating phocids, monk seals breed asynchronously and are not known to produce social calls in water. To address existing knowledge gaps, we trained a mature male Hawaiian monk seal to perform a psychophysical task while submerged. Detection thresholds were measured for narrowband sounds across the frequency range of hearing. We also conducted a year-round characterization of the seal’s spontaneous underwater vocalizations. This individual demonstrated best hearing between 0.2 and 33 kHz, with a lower high-frequency roll-off than that of related species. Hearing at all frequencies was less sensitive than in other true seals. Despite the absence of conspecifics, the seal regularly produced 6 different underwater calls with energy below 1 kHz. Calling patterns reflected a period of annual reproductive activity lasting about 6 mo, coincident with elevated testosterone levels. This study presents the first examination of underwater vocalizations in Hawaiian monk seals, provides insight into the auditory abilities of this species and the evolution of underwater hearing among phocids, and enables improved assessments of noise effects on these vulnerable seals.

中文翻译：

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濒临灭绝的夏威夷和尚海豹Neomonachus schauinslandi中的水下听觉和交流

摘要：夏威夷和尚海豹是最濒危的海洋哺乳动物之一，也是最常见的海豹。从行为，进化和保护的角度看，和尚海豹的听觉生物学是令人信服的，但目前我们缺乏该物种的实质性生物声学信息，没有关于水下发声的正式描述，也没有关于听力的有限数据。这些海豹已经隔离了超过一千万年，并且其听觉结构与相关物种不同。此外，与其他水生交配鱼类不同，和尚海豹异步繁殖，因此在水中不产生社交呼唤。为了解决现有的知识空白，我们训练了成熟的夏威夷男和尚海豹在下水后执行心理物理任务。在整个听觉频率范围内测量窄带声音的检测阈值。我们还对海豹的自发水下发声进行了全年的表征。该个体表现出0.2至33 kHz的最佳听力，并且高频滚降低于相关物种。与其他真正的海豹相比，在所有频率下的听力都较不敏感。尽管没有具体规格，但海豹仍定期以低于1 kHz的能量产生6次水下通话。呼出模式反映出持续约6个月的年度生殖活动，与睾丸激素水平升高相吻合。这项研究是对夏威夷僧海豹水下发声的首次检查，