Here is an example of the sidescan sonar imagery taken from Pelican's dinghy by Dale Appleton from Parks Vic. We spent a full day filling most of the gaps in the mapping of the deeper channels in Yaringa Marine National Park.The sidescan sonar sends out its signals like a torch beam and literally side swipes the hidden recesses of Western Port's channels.
Dale spoke about the surprising variety of habitats that have been kept secret for so long due to the often turbid waters of Westernport. He also knew that he shouldn't be surprised that the channel habitat is as complex as the land. But he said you become lulled by the uniformity of the surface of the water to expect a straightforward picture. This is never the case.
It is interesting that even in someone so connected to the marine environment this thought process occurs. No wonder the majority of people living on the water's edge have absolutely no idea about what really goes on under the rippling surface of the sea.
The scan above illuminates what can happen when a boat becomes stuck in the mud at low tide. The vertical running scar in the picture is the memory imprint of a boat propellor ripping through the seagrass bed. Dale told me this had happened quite some time ago.
Much of Victoria’s coastline including to depths of 10 metres has been recently mapped in detail through a state government program called Future Coasts. This program uses lasers fixed to planes that fly above the area being mapped which are able to very accurately measure the height of the land below, and the depth of water beneath them where the water is clear.
This method is generally fine but in the Western Port habitat with it's muddy bottom, any wave activity stirs up the sediment. So our work over Two Bays will give a clear reference point and provide the managing agencies with a powerful means to be able to detect and measure changes to these areas that may occur in the future.
Below is a picture of further scans of the Yaringa channel. The scans are of 100meter width, 50 meters either side of the dinghy, taken in strips 1.5 kms long. During Two Bays they managed to scan 100 hectares. This has filled in about 2/3 of the gaps needed to be scanned to finally get a thorough picture of the Marine Park's habitat. We still do not have detailed maps of benthic Victoria
Our return to Hastings port was heralded by an almost full moon, rising over the steel works.
