Effective management of wild animal populations relies on an understanding of their spatio-temporal distributions. Passive acoustic monitoring (PAM) is a non-invasive method to investigate the distribution of free-ranging species that reliably produce sound. Critically endangered Antarctic blue whales (Balaenoptera musculus intermedia) (ABWs) co-occur with pygmy blue whales (B. m. brevicauda) (PBWs) around New Zealand. Nationally, both are listed as “data deficient” due to difficulties in access and visual sub-species identification. PAM was used to investigate the distributions of blue whales via sub-species specific song detections in central New Zealand. Propagation models, incorporating ambient noise data, enabled the comparison of detections among recording locations in different marine environments. ABW detections peaked during austral winter and spring, indicating that New Zealand, and the South Taranaki Bight (STB) in particular, is a migratory corridor for ABWs. Some ABW calls were also detected during the breeding season (September and October). PBW calls were highly concentrated in the STB, particularly between March and May, suggesting that an aggregation of PBWs may occur here. Therefore, the STB is of great importance for both sub-species of blue whale. PBW detections were absent from the STB during parts of austral spring, but PBWs were detected at east coast locations during this time. Detection area models were valuable when interpreting and comparing detections among recording locations. The results provide sub-species specific information required for management of critically endangered ABWs and highlight the relative importance of central New Zealand for both sub-species of blue whale.

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.

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The Queensland Shark Control Program (QSCP) uses pingers to prevent marine mammal entanglement in shark control nets along public beaches, in Queensland, Australia. Acoustic emissions of Fumunda F3 (designed for humpback whales) and F10 pingers (designed for dolphins) were measured and characterised. The acoustic signals consisted of tones (3 and 10 kHz, respectively) and harmonic overtones emitted for about 400 ms every 5 to 6 s. Directivity was more pronounced for the overtones. Broadband source levels were up to 135 dB re 1 µPa at 1 m for all pingers at all angles. Ambient noise was recorded in the vicinity of shark nets for 3 wk each quarter of 1 yr. Fish choruses, migrating humpback whales, dolphins, snapping shrimp, boats, sandpumps, wind and wave noise were identified. Beyond 1.5 km, pingers no longer contributed significantly to the ambient noise budget. Sound propagation was modelled to relate received pinger tones to measured ambient levels and to estimate the potential detection of pingers by local marine mammals (humpback whales, dugongs, dolphins). Mean transmitted levels were predicted to be audible over up to a few 100 m in range (depending on species). With currently 3 to 4 pingers per shark net of 200 m length, existing pinger type and arrangement were modelled to be adequate, even for marine mammals swimming straight at a net at top speed. Additional behavioural studies or long-term monitoring are needed to determine pinger efficacy.KEY WORDS: Pinger · Bycatch · ADD · Acoustic deterrence · Noise budget Resale or republication not permitted without written consent of the publisher Contribution to the Theme Section 'Techniques for reducing bycatch of marine mammals in gillnets'OPEN PEN

Underwater acoustic recordings of six Floating Production Storage and Offloading (FPSO) vessels moored off Western Australia are presented. Monopole source spectra were computed for use in environmental impact assessments of underwater noise. Given that operations on the FPSOs varied over the period of recording, and were sometimes unknown, the authors present a statistical approach to noise level estimation. No significant or consistent aspect dependence was found for the six FPSOs. Noise levels did not scale with FPSO size or power. The 5th, 50th (median), and 95th percentile source levels (broadband, 20 to 2500 Hz) were 188, 181, and 173 dB re 1 μPa @ 1 m, respectively.