Acoustic Monitoring of whales and dolphins in New Zealand’s Cook Strait region
The sounds of whales and dolphins rarely seen in New Zealand waters have been recorded in a pioneering underwater sound project.
Over half the cetaceans (whales and dolphins) on the planet are found in New Zealand waters yet little information is known about their seasonal distribution and abundance. Fixed passive acoustic monitoring (PAM) systems record the sound of everything in the vicinity. This technology is effective in determining the distribution and abundance of vocalizing cetacean species and has the additional benefit of recording both the natural (wind, waves, and earthquakes) and anthropogenic (vessel traffic and oil and gas exploration and extraction) contributions to the soundscape.
We use fixed PAM equipment for the first time in the greater Cook Strait region to:
- Document baseline ambient noise conditions in an area known for its strong currents and that is heavily used by industry.
- Address knowledge gaps about spatial and temporal distributions, habitat use, calling behavior, and migration paths of marine mammal species based on acoustic detections of their vocalisations.
This project is providing a unique opportunity to monitor the seasonal presence and distribution of cetaceans from the world’s largest (blue whales) to one of the world’s smallest (Hector’s dolphins) marine mammals. Information obtained from this exciting and novel research will help guide marine mammal conservation and mitigation efforts.
In June 2016, seven acoustic moorings were deployed in Cook Strait (four in deep water (> 500 m) and three shallow water (< 250 m).
In December 2016 and January 2017, a recovery mission was conducted to recover the acoustic moorings. Once recovered, 14 terabytes of acoustic data were downloaded for analysis.
In collaboration with JASCO Applied Sciences, the acoustic data were analysed. Some of these results are provided in the summaries below:
Anthropogenic and ambient noise measurements
The two main anthropogenic (human generated) noise contributors recorded during the monitoring program included vessel traffic and seismic surveys.
Vessel noise was often the dominant and sole contributor to the soundscape at the shallow water stations as compared to the the deeper water environments where the total soundscape was comprised of sources beyond noise from vessels and seismic activity.
Total, vessel, and seismic-associated daily sound exposure and equivalent continuous noise levels at station 1 (< 50 m depth).
Total, vessel, and seismic-associated daily sound exposure and equivalent continuous noise levels at station 6 (> 1,000 m depth).
Underwater recording of a small vessel
Underwater recording of a small vessel with a large outboard engine
Underwater recording of a large vessel
14 November 2016 earthquake
For many of the stations, the 14 Nov 2016 earthquake was the only irregularity in an otherwise stable soundscape, visible as a large increase in the levels in the 10–100 Hz band level. In fact, the maximum SPL values (164.4 dB re 1µPa) recorded during the study are associated with the earthquake and approached the maximum SPL values that can be resolved by the recording system (165 dB re 1µPa).
Sound level summary from 6 Jun to 21 Dec 2016 at station 5; (Top) In-band sound pressure level (SPL) and (bottom) spectrogram of underwater sound.
Marine mammal vocalizations and fish chorusing
The acoustic presence of marine mammals was identified automatically by detectors and verified by the manual analysis of ~300 hours of acoustic data. The manual review of data revealed the presence of:
- Pygmy and Antarctic blue whales (Balaenoptera musculus spp.)
- Humpback whales (Megaptera novaeangliae)
- Antarctic minke whales (B. bonaerensis)
- Southern right whales (Eubalaena australis)
- Pilot whales (Globicephala sp.)
- Sperm whales (Physeter macrocephalus)
- Cuvier’s beaked whales (Ziphius cavirostris)
- Sei whales (B. borealis)
- Hector’s dolphins (Cephalorhynchus hectori).
Below is a video which shows humpback whale detections at the seven acoustic recorders over time.
Below is an example spectrogram and sound clip of a humpback whale call.
Humpback whale (Megaptera novaeangliae) call:
Antarctic Minke whale call (Balaenoptera bonaerensis)
Pilot whale detections at the seven acoustic recorders over time.
Cuvier's beaked whale detections at the seven acoustic recorders over time.
Sounds made by large groups of fish communicating with each other, known as fish chorusing have also been recorded. These sounds play an important role in the behavioural functions of fish species. Fish chorusing events increased as the water temperature increased and often exhibited and seasonal and diel patterns.
Sound level summary from 18–24 Sep 2016 at station 6; (Top) in-band sound pressure level (SPL) and (bottom) spectrogram of underwater sound. The red highlighted areas indicate fish chorusing events.
To date, this project has proven successful in collecting high quality data to assess the soundscape of the Cook Strait region. However, we have only just scratched the surface.
Using lessons learned from the first deployment, we adjusted mooring locations. Six instruments were redeployed in February 2017 and will be recovered in August 2017. Stay tuned for more results.
[Images JASCO Applied Sciences unless otherwise credited]
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OMV New Zealand Ltd.
Chevron New Zealand Holdings LLC
Marlborough District Council
Woodside Energy Ltd.