An Insight Into Sousa

It’s only 9am and already I’ve seen 20 flatback turtles and a unique sighting of Indo-Pacific Humpback Dolphins, otherwise known by their genus as Sousa. The observation was made from the Baldur, a backhoe dredge being used to construct an island which will be a part of what they are calling the Marine Offloading Facility (MOF). The water is relatively shallow here, with a mixed mud and rock habitat blanketed with macro algae and sponges, which would explain the high presence of turtles and dugongs; the dugongs feeding on the algae and the flatbacks eating the sponges. It may also explain the unusual Sousa sighting that had me confused for a few minutes.

It’s amazing what can be discovered with enough observation. I’ve been seeing small groups of Sousa around the MOF area for the last week, some with calves. Amongst the white caps of this beauford 4 morning I noticed their characteristic humped dorsal fins break the surface, a pod of around 15 individuals with at least 1 calf. Suddenly I noticed a golden brown round object emerge around the pod, which I at first thought was a dugong swimming near the dolphins. Then I saw a dorsal fin associated with the golden brown sphere, which eliminated the dugong hypothesis. I thought it must be a Sousa holding something out of the water in its mouth…but what? I have read that river dolphins have been observed holding rocks out of water as a display of fitness to females; but this did not look like a rock, it was corrugated and seemed too large for the dolphin to be holding it up with such ease. One of the engineers who I alerted to the sighting assumed it was a turtle, which I asserted that it definitely was not. I then remembered hearing somewhere that some dolphins use sponges to protect themselves from the poisonous barbs of fish while rummaging around the bottom; and that’s exactly what was going on here.

The adult animal was most likely teaching the younger dolphin the sponge technique. After looking up some articles online, this behavior has been observed in Shark Bay in Western Australia, which is relatively near Barrow Island, but in bottlenose dolphins. As far as I know no one has yet witnessed Sousa exhibiting these same behaviors. It is possible that bottlenose dolphins look similar to Sousa here and that I’ve miss identified them, but this is unlikely. I’ve seen plenty of bottlenose dolphins and quite a few Sousa in Eastern Australia, and I’m confident that the humped pale dolphins with a narrow rostrum were Sousa and not bottlenose. Perhaps the behavior is spreading through Western Australia, and not just between bottlenose dolphins but also through populations of Sousa. I’ve seen bottlenose and Sousa associating off of Straddie, so it’s possible the Sousa have picked up this behavior from bottlenose, or vice versa.

I small scientific discovery that has made my morning, now it’s back to counting turtles; I should get up to 50 today. Here’s a link to a National Geographic article about the usage of tools amongst bottlenose dolphins in WA if you’re interested:

http://news.nationalgeographic.com/news/2005/06/0607_050607_dolphin_tools.html

…..