Inter- and intra-annual frequency variations of large-whale calls in the southern Indian ocean

in the past decades, an inter-annual decline of the frequency of blue whale calls is been observed worldwide (mc donald et al., 2009), along with an intra-annual variation, best described for the antarctic blue whale calls (balaenoptera musculus intermedia) (gavrilov et al., 2011; gavrilov et al., 2012; miller et al., 2014). the reasons for this decline and variations are still not understood.during the deflohydro project, a network of 3 autonomous hydrophones (mad, neams and swams sites; fig. 1) was deployed in the southern indian ocean from november 2006 to january 2008 to monitor the low-frequency sounds (0-120 hz) carried by the ocean, and provided a complete year of acoustic data in 2007. it was continued by the ohasisbio project, a network of 6 to 8 autonomous hydrophones deployed in january 2010 and still operational (august 2017; fig. 1). these acoustic data sets reveal the seasonal presence of several species and sub-species of large baleen whales: the antarctic blue whale (balaenoptera musculus intermedia), three acoustically distinct pygmy blue whale populations (b. m. brevicauda), and the fin whale (b. physalus). each of these populations has a specific vocal signature (fig. 2). the pluri-annual and multi-site acoustic data collected by the deflohydro and ohasisbio hydrophone networks provide a continuous monitoring (fig. 3) of the frequency of these vocal signatures. inter- and intra-annual frequency variations of the antarctic blue whale call are confirmed, and an inter-annual frequency decline is also observed for the other whale species (for the first time for the madagascan pygmy blue whale call and the fin whale 100 hz-pulse).this database gives the frequency measurements for five populations of whales recorded in the southern indian ocean. for the antarctic blue whale, they are based on individual z-calls (unit a), automatically detected with a z-detector (socheleau et al., 2015; leroy et al., 2016). for the other whales, frequencies correspond to specific units of interest (black boxes in fig. 2) and are measured at peak power in power spectral densities (psd). frequencies are provided for all sites when the given vocal signatures are present, in 2007 and from 2010 to 2015.we also provide daily average noise power-level in different frequency ranges (10-13 hz, 30-33 hz, 64-66 hz, 71-73 hz, 91-93 hz, 99-101 hz) calculated in the data recorded from 2010 to 2015. the seasonal variations of the call frequencies would be linked to the noise level. an interpretation of these data is discussed by leroy et al. (2017).figure 1 : layout of the deflohydro (stars with black contour) and ohasisbio hydroacoustic stations (all stars) in the southern indian ocean. © j-y royer / cnrs-u.brest lgo figure 2 : time-frequency representation of stereotyped vocal signatures of antarctic (a) and pygmy blue whales of the madagascar (b), australia (c), and sri lanka (d) type, and of fin whales (e). frequencies in the data base correspond to the peak frequency (i.e. at maximum amplitude) in the black rectangles. ©e leroy/ u.brest-cnrs lgo figure 3 : acoustic data recorded by the deflohydro and ohasisbio hydrophone networks. © e leroy / u.brest-cnrs lgo

在过去数十年间，全球范围内蓝鲸叫声的年际频率下降现象已得到观测（参见麦当劳等，2009年），同时伴随着年内的变异，其中南极蓝鲸叫声（Balaenoptera musculus intermedia）的年内变异描述最为详尽（参见加夫里洛夫等，2011年；加夫里洛夫等，2012年；米勒等，2014年）。这种下降及变异的原因至今尚未明了。在“去浮力”项目期间，自2006年11月至2008年1月，于南印度洋部署了一个由3个自主式水听器组成的网络（马德、NEAMS和SWAMS站点；见图1），以监测由海洋携带的低频声音（0-120赫兹），并在2007年提供了一整年的声学数据。该项目后续由“Ohasisbio”项目接续，该项目于2010年1月部署了6至8个自主式水听器网络，并持续运行至2017年8月（见图1）。这些声学数据集揭示了数种大型须鲸及其亚种的季节性存在：南极蓝鲸（Balaenoptera musculus intermedia）、三个声学上不同的侏儒蓝鲸种群（B. m. brevicauda）和座头鲸（B. physalus）。这些种群各自具有独特的声学特征（见图2）。通过“去浮力”和“Ohasisbio”水听器网络收集的跨年度和多站点声学数据，为这些声学特征的频率提供了连续监测（见图3）。南极蓝鲸叫声的年际及年内频率变异得到证实，其他鲸种也观察到年际频率下降（对于马达加斯加侏儒蓝鲸叫声和座头鲸100赫兹脉冲声，这是首次观察到）。该数据库提供了在南印度洋记录的五种鲸群的频率测量数据。对于南极蓝鲸，这些数据基于个体的Z叫声（单位a），通过Z检测器自动检测（参见索切莱等，2015年；勒罗伊等，2016年）。对于其他鲸种，频率对应于特定感兴趣的单元（见图2中的黑色方框）并在功率谱密度（PSD）的峰值功率处进行测量。当存在给定的声学特征时，所有站点在2007年和2010年至2015年间均提供了频率数据。我们还提供了2010年至2015年间记录的数据中不同频率范围内的每日平均噪声功率水平（10-13赫兹，30-33赫兹，64-66赫兹，71-73赫兹，91-93赫兹，99-101赫兹）。叫声频率的季节性变化可能与噪声水平相关。勒罗伊等（2017年）对这些数据进行了讨论。图1：南印度洋“去浮力”（黑色轮廓星号）和“Ohasisbio”水声站（所有星号）的布局。©J-Y罗耶/法国国家科学研究中心-布勒斯特大学LGO图2：南极（a）和马达加斯加（b）、澳大利亚（c）、斯里兰卡（d）类型的侏儒蓝鲸以及座头鲸（e）的典型声学特征的时频表示。数据库中的频率对应于黑色矩形中的峰值频率（即最大振幅）。©勒罗伊/布勒斯特大学-CNRS LGO图3：“去浮力”和“Ohasisbio”水听器网络记录的声学数据。©勒罗伊/布勒斯特大学-CNRS LGO