Acoustic Monitoring of whales and dolphins in New Zealand’s Cook Strait region

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The sounds of whales and dolphins rarely seen in New Zealand waters have been recorded in a pioneering underwater sound project.

The issue

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.   

The objectives

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.

The approach

In June 2016, seven acoustic moorings were deployed in Cook Strait (four in deep water (> 500 m) and three shallow water (< 250 m). 

Acoustic mooring deployment locations June 2016 - January 2017 (yellow stars).

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.

The results

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.

Typical day of vessel traffic at station 6..

Spectrogram of seismic impulses recorded at station 2 on 01 November 2016.

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.

Spectrogram of the 14 November 2016 earthquake.

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). 

Two unidentified beaked whale species as well as unidentified delphinid and dolphin species were also detected. 

See below spectrograms of Antarctic blue, New Zealand blue and humpback whale song.

Spectrogram of Antarctic blue whale song notes.

Spectrogram of New Zealand blue whale song notes.

 

Spectrogram of a humpback whale song.

 

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.

Example spectrogram and sound clip of a humpback whale.

Humpback whale (Megaptera novaeangliae) call:

Spectrogram and sound clip of an Antarctic minke whale.

Antarctic Minke whale call (Balaenoptera bonaerensis)

Spectrogram of southern right whale calls.

Spectrogram of pilot whale calls.

Pilot whale detections at the seven acoustic recorders over time.

Spectrogram of a sperm whale click train.

Spectrogram of a Cuvier’s beaked whale call

Cuvier's beaked whale detections at the seven acoustic recorders over time.

Spectrogram of a Hector’s dolphin click train.

Spectrogram of unidentified dolphin whistles.

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.

Future work

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.

Acoustic mooring deployment locations February 2017 - August 2017 (yellow stars). [Map: NIWA]

[Images JASCO Applied Sciences unless otherwise credited]

Further reading

Sponsors

OMV New Zealand Ltd.

Chevron New Zealand Holdings LLC

Marlborough District Council

Woodside Energy Ltd.

Contact

Dr Kim Goetz
Tel 04 382 1623

Page last updated: 
29 September 2017
Shallow water Autonomous Multichannel Acoustic Recorder (AMAR) [Photo: Hamish McCormick, NIWA]  
Dr Kim Goetz next to one of acoustic moorings that will reside in the ocean for the next six months recording the sounds of whales and dolphins as they pass through New Zealand's Cook Strait. [Photo: Dave Allen, NIWA]
Deep water Autonomous Multichannel Acoustic Recorder (AMAR) being launched. [Photo: Hamish McCormick, NIWA]