Deployments

Sites currently sampled are located: off the central NSW coast working out of Tuncurry / Forster (32o 16.2' S, 152o 57.0' E); south of Portland, Victoria (38o 32.5' S, 115o 0.1' E) with Portland the home port; west of Kangaroo island (36o 7.6' S, 135o 55.0' E) with this site serviced by the South Australian Research and Development Institute on the vessel RV Ngerin; and west of Perth in the Perth Canyon (31o 52.0' S, 115o 0.1' E). In addition to this, two sites were sampled from 2012-2015 with support from the Western Australian Government, these sites were located at: "Dampier" (19o 23.3' S 115o 54.9' E); and "Scott Reef" (15o 29.0' S, 121o 15.1' E) with the site names indicative only. The locations of all sites are shown in the figure below. The Perth Canyon has been sampled since 2008, Portland since 2009, NSW since 2010, Kangaroo island since 2015 (gear still in the water) and the north western WA sites over 2012-2015. A table with the exact co-ordinates and times of each deployment are listed in this pdf.

Locations of sites currently sampled for sea noise by IMOS (black) and the North Western Australia locations (red) which ceased operation in mid 2015.

Sites were chosen to be on or near the continental shelf break edge in order to access signals transmitted in the deep ocean. All sites are either on the shelf break (Perth Canyon) or within a few nautical miles inside of the shelf edge as given by the 200 m depth contour.

The Perth Canyon site was chosen as it was known to be a 'hot spot' for several species of offshore great whales and as data was available here from 2000 onwards (held by Curtin University).

The NSW site was chosen for multiple reasons, as its at the same latitude but on the opposite side of Australia to the Perth Canyon, its an area which is completely under-sampled from the perspective of long term sea noise records, as there are known to be regular, un-described movements of great whales offshore up and down the coast, as we had a good fishing port with high quality fisherman close by and as it is relatively free of deep water trawling. We were initially hoping to document movement of the eastern Indian Ocean pygmy blue whale, which is common in western and southern Australian sea noise records, as it moved up and down the eastern Australian coast. As it transpired, this did not happen, rather based on the IMOS passive acoustic records there is a separate pygmy blue whale sub-population which transits the eastern Australian coast, commonly referred to as the NZ pygmy blue whale but which would be more accurately termed the western Pacific pygmy blue whale.

The Portland site was chosen as several years of sea noise were available from this site, thus the shore based facilities were known to us, as its on what is termed the Bonney coast which has some of the largest seasonal upwelling events in Australia, the site is on a rocky ridge so is free of trawling and as its known to be commonly visited by various poorly known offshore great whale species. The Portland IMOS passive acoustic mooring is the only long term oceanographic mooring between the IMOS moorings in South Australia and moorings around Tasmania.

The Kangaroo Island site was chosen as it is near deep water IMOS oceanographic moorings thus making servicing easier and it is in a highly productive but poorly known (from the perspective of whale presence) and sensitive area.

The passive acoustic moorings are typically serviced every 10-12 months, with the duty cycle giving an 11-12 month duration (depending on batteries). We have not always been able to maintain this servicing frequency, notably there have been periods of funding uncertainty during which we did not know if we should re-deploy again, so we had to wait before scheduling field work. The NSW site is plagued by strong currents produced by the East Australian Current, which have precluded us from recovering gear, for almost a year in one instance.

The moorings are designed to decouple the sea noise logger and its hydrophone from the mooring, so reducing noise artefacts which are extremely easy to produce. Traditional in-line oceanographic moorings do not work for passive acoustic instruments especially in areas of high current. Given the mooring design we cannot release our moorings in currents of greater than around 2 knots as the buoys get pulled down and it is highly dangerous and near impossible to grapple in these conditions. To date we have lost two moorings, one in northern Western Australia (Dampier, 2013-2014) and one in the Perth Canyon. 

On recovery the instruments are calibrated post deployment (a second gain with frequency check is made), the instrument clocks checked for drift against GPS, UTC transmitted time and the data copied across and backed up. We generally run a routine which then reads all data files and saves a master table for that deployment of file names and sampling times. The data is then viewed as for the IMOS web viewer to identify any notable events and to assess data quality. The Perth Canyon data is subject to Defence restrictions and we may have to remove sections for security reasons. In general Defence are aware of and try to avoid our equipment. Data is copied to a hard disk and sent to IMOS in Hobart, whom archive it and make the data available upon request.