Side Scan Analysis – Goat Island, Sydney Harbour


Side Scan Analysis – Goat Island, Sydney Harbour

The long-awaited Part 2 of our side scan analysis series is here and this time we are looking at Goat Island.

This little island lies between Balmain and Balls Head and is located near one of the deepest parts of Sydney Harbour. Goat Island takes the full tidal force of any water flowing under the Harbour Bridge.

I did two laps of Goat Island in a clockwise direction to get these readings and the tide was in the final stage of coming in. I overlaid the images on Google Earth with views of both the Western and Eastern sides of the island shown below.

So, let’s look at some pictures off the sounder. ***CLICK IMAGES TO ENLARGE***


1. Red Floating Channel Marker



The floating channel marker sits in the main channel and gets a huge amount of tidal flow going past it. At this time the tide was coming in under the Harbour Bridge and pushing up against this marker and the front of the island.

A large school of fish can be seen hanging on the drop-off right near the channel marker.

Some larger fish arches are little further along closer to the end of the island. These are showing as individual fish arches on the side scan which indicates they are quite large (bait usually just shows as a fuzzy ball). (Click Image to Enlarge)

2. Front of the island


Here we have a hole 15m deep rising to 10m that was receiving quite a bit of water flow from the incoming tide. The red circle indicates where some larger fish were hanging around the front and top of this small bump.

At this same location on the side scan we can see a clear division in the water column. I think this is a thermal break where the tide is pushing up against the front of the island. The fish seem to be holding in the lower section of the water column possibly waiting for food to be pushed up against the island. I have never captured a thermal break on the sounder and this is very cool.

The black circle on the side scan seems to be a bait school and we can see that casting a light shadow off to the right of the side scan image.

3. Disused Jetty


On the right side of the scanner image we can see the pylons from a disused jetty (where they filmed the TV series Water Rats).

The left side scan image shows the bottom drops away to deeper water and there are many items sitting on the seabed through this section.

Interestingly, there are also many items around the jetty which may have been dropped in the water during operation or be parts of the jetty when it was partly dismantled.

While it looks promising, this section would be very difficult to fish with the wind, tidal flow and huge amount of boat traffic making for very challenging and sometimes uncomfortable conditions.

4. Barge or Boat?



It wasn’t until I put the sonar readings on the map overlay that I realised this could be a sunken barge or workboat. On the side scan image it looks fairly unremarkable sitting in 10m of water.

On the map it appears to have a clear box-like structure with two parallel sides and possibly a square transom. I can’t make out what the front looks like.

As it lies just off a working shipyard I suspect it might be a small barge.

Note the increasing amount of items on the seafloor particularly on the right side.

5. Shipyard


GoatIslandSideScan5This location is directly off the shipyard. We can see several mooring blocks on the bottom with ropes going up to moored ships and barges at the wharf.

On the bottom right of the sidescan we can see the bright spots indicating where the pylons for the wharf are.

At the top right we can see where the tracks for the slipway enter the water (the green shed in the photo above).

Notice the schools of bait hanging around the mooring blocks and a couple of larger fish circled in red.

6. Red marker pole

GoatIslandSideScan6I almost ran over the red marker pole here (circled in black). Note the shadow extending off to the left side of the screen.

The bottom around this marker (circled in red) is significantly more contoured than I thought and explains why this is a popular fishing spot.

Check out the reef in the top left of the side scan panel (black arrow). It’s 15 meters deep and I’m picking up the ripples in the sand on the bottom. This area cops a huge amount of water flow and this area appears to be quite scoured out.

Equipment Used:

Sounder: Humminbird Helix 5 SI GPS
Range: 30m
Sensitivity: 12
Contrast: 10
Speed: 3
Boat Speed: 3.5kts

If you found this useful head over to our Facebook page and let me know which area you want scanned next.

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The charm of fishing is that it is the pursuit of what is elusive but attainable, a perpetual series of occasions for hope.

John Buchan