29 October 2015
For what could be the last field trip in a project to determine the feasibility of conducting passive acoustic monitoring of snubfin and humpback dolphins, the research team headed to Cone Bay on the northeast tip of King Sound in the Kimberley to focus on recording humpback dolphins specifically.
I was fortunate enough to have the aid of fellow Murdoch University Cetacean Research Unit (MUCRU) researcher, Alex Brown, to help me in the field to focus on getting the recordings of the sounds that humpback and snubfin dolphins are making.
We were also fortunate to be joined and helped out by Dambimangari Rangers during several days of the fieldwork, who provided excellent dolphin spotting skills and assisted in photo-identification of the dolphins we encountered.
In September 2014, Alex and fellow MUCRU researcher Dr Simon Allen and Dr Stephanie King undertook a WAMSI trip to Cone Bay to determine the size of the dolphin populations there and reported consistent sightings of humpback dolphins around the Marine Produce Australia barramundi sea farm, in Cone Bay at Turtle Island.
Not only did Cone Bay provide consistent sightings of snubfin and humpback dolphins, it also provided an elevated land based platform that could provide information on the dolphins detection thresholds by comparing the dolphins location relative to the acoustic recorders.
The acoustic data that we are collecting will help to develop a better understanding of the acoustic repertoire of these species, whether there are geographical differences in the sounds they make within a species, and understand over what type of ranges these dolphins are using their sound.
The main objective is to determine the feasibility of conducting passive acoustic monitoring for these species, which is being conducted as a Bill Dawbin Fellowship and part of the Western Australian Marine Science Institution (WAMSI) Kimberley Marine Research Program dolphin project.
The trip to Cone Bay was a great success with encounters of humpback dolphins engaged often in very interesting social behaviour. The trip was divided up in effort with land based hilltop observations over the sea farm and boat-based recordings.
For the hilltop observations, we deployed several SoundTrap acoustic recorders around the farm and waited for humpback dolphins to come in around the sea farm. This did not always happen regularly and was difficult to determine exactly when during the day this would happen.
|Hilltop observations using SLR camera and binoculars overlooking the barramundi sea farm|
|A humpback dolphin jumping not far from an acoustic recorder|
The hilltop observations (using a Canon SLR and mounted GPS unit along with Vadar software) allows information on the range that sounds can be detected by the acoustic recorders to determine detection thresholds. This is done by the SLR camera recording many attributes of the camera and lens settings and the GPS function being capable of determining the bearing the camera is pointed.
The software Vadar takes the elevation of the land based platform along with the camera settings and is capable of geo-referencing the dolphins’ location which is corrected for the tide. This is then related back to the known positions of the acoustic recorders.
Alex on the water as we pursue mobile acoustic recordings
It wasn’t long before Alex and I realised the humpback dolphins were not around the farm for the entire day and we needed to increase encounter rates. So, remaining within VHF radio contact of workers at the farm who could radio us if they saw dolphins, we went out on the six metre research boat to increase our dolphin encounters. Generally, we were quite successful, coming across either a group of snubfin or humpback dolphins.
The other objective of this trip to Cone Bay was to see whether we could increase the number of genetic samples of the dolphins from that obtained in September 2014 and from photo identification we could see whether many of the previously identified dolphins were still in Cone Bay. Almost straight away it became apparent that many of the same dorsal fins of the dolphins were being sighted from the photo ID, although there were also some new fins that Alex could not recognise.
Being on the boat meant that we could get close to the dolphins and use the mobile acoustic recorder, which was a SoundTrap attached to a rope on a float. When we had sighted a group of dolphins we would establish the type of behaviour they were exhibiting ie foraging, socialising or travelling, which would largely determine the possibility of getting acoustic recordings. When the dolphins are socialising, they are less worried about the boat and will often not travel as far, providing a better opportunity for good acoustic recordings.
The main objective of the mobile recordings was to increase our understanding of the different types of social sounds they were making to identify their acoustic repertoire. The boat recordings provided some interesting sound recordings, particularly from a mixed group of four humpback dolphins in what appeared to be attempted mating of a single snubfin dolphin.
|A group of humpback dolphins socialising near the mobile acoustic recorder attached to the float|
Finally, after almost three weeks of what was pretty good weather and almost 12-hour days, we left Cone Bay for Cygnet Bay and eventually Perth, having collected as much data as the weather would allow.
In total, there is now approximately five hours of mobile recordings and 23 groups of humpback dolphin positional data to process to help with previous fieldwork to assess the feasibility of passive acoustic monitoring for humpback and snubfin dolphins.
Cone Bay definitely proved to be more reliable for acoustic recordings of humpback dolphins than previous Cygnet Bay fieldwork and provided a pretty amazing backdrop to this research.
This fieldtrip would not have been as successful or viable without the support of Marine Produce Australia and we are extremely grateful for their support.
The $30 million Kimberley Marine Research Program is funded through major investment supported by $12 million from the Western Australian government's Kimberley Science and Conservation Strategy co-invested by the WAMSI partners and supported by the Traditional Owners of the Kimberley.