Unidentified whale signals recorded in Cook Strait
Two yet-to-be identified species of beaked whales have been detected in the Cook Strait region. Identifying which species they are is important for understanding the status of marine mammal populations in New Zealand waters.
A Gray's beaked whale, one of five that stranded near Port Waikato in 2011. Signals from beaked whales, potentially from this species, have been collected using passive acoustic moorings in the Cook Strait region. [Photo: Avenue, Wikipedia]
A research team led by NIWA scientists has confirmed the presence of the beaked whales by analysing underwater acoustic data collected during two six-month deployments of six passive acoustic moorings in the Cook Strait region.
In the first project of its kind in New Zealand waters, the moorings recorded the entire underwater soundscape of the region, including sounds produced by marine mammals. One of the aims of this project was to learn more about the presence and distribution of whales and dolphins in the region.
The first published findings, by NIWA marine mammal experts Dr Giacomo Giorli and Dr Kim Goetz and their collaborators from JASCO Applied Sciences, are included in the latest issue of the Journal of the Acoustical Society of America. The paper concludes that two types of signals from beaked whales were identified in the Cook Strait region that differ from any beaked whale signals previously documented.
There are about 22 species of beaked whales globally, of which about 13 have been found in New Zealand, but very little is known about them, Dr Giorli says. Sightings are rare because they are deep diving animals that can spend more than an hour on a single dive and surface for a very short time.
"Most information about their presence in New Zealand waters has come from people reporting whale strandings but it is very limited. We really know very little about their behaviour."
What is known is that beaked whales, like all toothed whales (such as dolphins, sperm and killer whales), use echolocation, emitting sounds and listening to the echoes, to locate prey in the dark deep-sea environment.
The new signals were extracted using a multi-step process. First, an automated detector was applied, which was then validated through manual analysis. This process involved researchers examining a subset of the detections by looking at spectrograms - visual pictures of sound frequencies – to verify that the detections were correct. A click-by-click analysis was then undertaken.
From the reviewed subset of the data, which comprised just one per cent of the total collected, three distinct beaked whale signals were detected. One matched the Cuvier beaked whale – one of the most commonly-seen beaked whales – but the other two did not match those from any previously recorded beaked whale species. Dr Giorli speculates that the most likely possibility, based on stranding records, is that the signals belong to the Gray’s and strap-toothed beaked whales.
Dr Giorli says that matching the recordings of the beaked whales to the correct species can only be done by concurrent visual and acoustic observation, which has not happened yet.
The next stage is to examine the rest of the data set for similar signals to determine how often the sounds from the unidentified beaked whales were recorded.
The same data set is also being used to determine the presence of other whale and dolphin species in the Cook Strait region. Funding for this project was provided by OMV New Zealand Ltd, Chevron New Zealand Holdings LLC, Woodside Energy Ltd, and Marlborough District Council.