Vocalizations of common minke whales (<i>Balaenoptera acutorostrata</i>) in an eastern North Pacific feeding ground

The minke whale (<i>Balaenoptera acutorostrata</i>) is a small species of baleen whale with a cosmopolitan distribution. Despite extensive study on the vocalizations of other balaenopterids, the acoustic repertoire of minke whales is not well known. Individuals of the North Pacific subspecies (<i>B. acutorostrata scammoni</i>) produce unique vocalizations (‘boings’) during their putative breeding season from fall to spring. However, no vocalizations have been previously reported for this subspecies in any eastern North Pacific feeding ground. We present two call types recorded in the presence of six minke whales, two of which were confirmed as female, in Cormorant Channel, British Columbia, Canada, during the summer of 2012. The calls consist of downsweeps and pulse chains. These call types share some characteristics with calls described elsewhere, although they are not identical to similar call types observed for other populations. Calling rates for minke whales in this study region are very low compared to those reported for this subspecies on its putative breeding grounds, as well as for other subspecies on their feeding grounds. We propose predation risk, sexual segregation and acoustic masking as potential causes of the low calling rates observed for minke whales in Cormorant Channel.小须鲸（*Balaenoptera acutorostrata*）是一种分布遍及全球的小型须鲸物种。尽管学界已对其他须鲸科（Balaenopteridae）物种的发声行为开展了大量研究，但小须鲸的声学发声曲目库仍未得到充分认知。北太平洋亚种（*B. acutorostrata scammoni*）的个体在其推测的繁殖季（秋季至春季）会发出独特的“嗡鸣（boings）”。然而，此前尚无关于该亚种在北太平洋东部任何觅食场地的发声记录。2012年夏季，研究团队于加拿大不列颠哥伦比亚省的鸬鹚海峡（Cormorant Channel）记录到6头小须鲸（其中2头经鉴定为雌性）发出的两类发声信号：下行扫频音（downsweeps）与脉冲链（pulse chains）。尽管此类发声与其他区域报道的同类发声存在部分共性，但与其他种群观测到的相似发声类型并不完全一致。相较于该亚种在其推测繁殖地的发声率，以及其他亚种在其觅食地的发声率，本研究区域内小须鲸的发声率极低。本研究提出捕食风险、性别分离与声学掩蔽，是导致鸬鹚海峡小须鲸发声率偏低的潜在原因。