DOI: 10.5061/dryad.vmcvdncpj
title: Marine soundscape variation reveals insights into baleen whales and their environment: a case study in central New Zealand

description: Baleen whales reliably produce stereotyped vocalizations, enabling their
 spatio-temporal distributions to be inferred from acoustic detections.
 Soundscape analysis provides an integrated approach whereby vocal species,
 such as baleen whales, are sampled holistically with other acoustic
 contributors to their environment. Acoustic elements that occur
 concurrently in space, time and/or frequency can indicate overlaps between
 free-ranging species and potential stressors. Such information can inform
 risk assessment framework models. Here, we demonstrate the utility of
 soundscape monitoring in central New Zealand, an area of high cetacean
 diversity where potential threats are poorly understood. Pygmy blue whale
 calls were abundant in the South Taranaki Bight (STB) throughout recording
 periods and were also detected near Kaikōura during autumn. Humpback,
 Antarctic blue and Antarctic minke whales were detected in winter and
 spring, during migration. Wind, rain, tidal, and wave activity increased
 ambient sound levels in both deep- and shallow water environments across a
 broad range of frequencies, including those used by baleen whales, and
 sound from shipping, seismic surveys and earthquakes overlapped in time,
 space and frequency with whale calls. The results highlight
 the feasibility of soundscape analysis to quantify and understand
 potential stressors to free-ranging species, which is essential for
 conservation and management decisions.
description: Four Autonomous Multi-channel
 Acoustic Recorders (AMARs, JASCO Applied Sciences) were deployed from
 early June to mid-December 2016 around central New Zealand: in the South
 Taranaki Bight; in the narrows of Cook Strait; north-east of Kaikōura; and
 off the east coast of Wairarapa (henceforth referred to as STB, Cook
 Strait, Kaikōura and Wairarapa, respectively) (Figure 1, Table 1). Three
 AMARs were redeployed between late-February and early September 2017: two
 in the same relative Kaikōura and Wairarapa locations and one in STB, 25.2
 km southeast of the first STB deployment location (Figure 1, Table 1). A
 recorder was not redeployed in Cook Strait in 2017. The AMARs at Cook
 Strait and STB were bottom-mounted on metal baseplates, with the
 hydrophone 75 cm off the seafloor, in water depths less than 300 m. At
 Kaikōura and Wairarapa, ultra-deep AMARs were deployed in water depths
 exceeding 1000 m and were moored on vertical line moorings, approximately
 10 m above the seabed. All AMARs were retrieved <i>via</i> the
 use of acoustic releases and buoyancy aids. Acoustic sampling was duty cycled
 over 900 seconds: 630 seconds at a sampling rate of 16 kHz, 125 seconds at
 a sampling rate of 250 kHz, and 145 seconds of sleep. Only files with 16
 kHz sampling rate were considered in this study due to the focus on low
 frequency baleen whale sounds. Recorder sensitivity was calibrated
 <i>via</i> pistonphone, and all data were corrected by
 frequency- and recorder-specific sensitivity curves. The nominal pressure
 sensitivity level of the hydrophones was -165 dB re 1 V/µPa (± 1 dB) from
 10 Hz to 100 kHz. The pressure spectral density noise floor was limited by
 the hydrophone preamplifier at 32 dB re 1 µPa<sup>2</sup> /
 Hz. Power spectral density (PSD) was
 calculated with 1 Hz resolution for each 630 s, 16 kHz file using a Fast
 Fourier Transform with window length of 16,000 samples (Hanning window)
 and 80% overlap (pwelch function, MATLAB).
description: Data matrices contain the 1 Hz Power Spectral Density per
 630-second, 16 kHz file. The first column of the Data matrices displays
 the Frequency value, and all other columns contain data values. The
 associated file names (containing recording time and date information) are
 provided in the separate 'Header' files. The width of the Header
 file is the same as the width of the Data file due to identification of
 the Frequency column.