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

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). 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.

• 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). 
  

Fish chorusing

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. 

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.