The Port Phillip common dolphins

Most people know that there is a species of bottlenose dolphin that is resident to Port Phillip, but did you know that there is a second species of dolphin that is resident to our bay?

And it’s a smaller one than the bottlenose dolphin community!

This second resident species of dolphins in Port Phillip are the (short-beaked) common dolphins.

We might be biased, but common dolphins are really quite a pretty species of dolphins. They are smaller than bottlenose dolphins and can be easily identified by the beautiful gold and grey hourglass colouration on their side.

We estimate the community of common dolphins to consist of 40 individuals, whereas there is likely to be about 120 bottlenose dolphins in our bay.

Our common dolphins are a little different

While common dolphins can be observed in many locations across the globe, they are usually found offshore. This distance from the coast can make them difficult to study. They can also gather in huge groups of 1000+ individuals and migrate with seasonal bait fish events.

You will often see common dolphins in Attenborough documentaries feeding on huge balls of fish alongside seals and sharks with gannets diving around them.  We are very lucky to have them in our bay and on our doorstep.

Common dolphin
A Port Phillip common dolphin. Image taken under a DELWP research permit.

How can we determine common dolphin gender non-invasively?

Mature male common dolphins can be easily identified by the presence of a post-anal keel while mature females are often recognized by the regular presence of a calf swimming alongside them.  With this in mind, it appears as though the Port Phillip common dolphin community is comprised of more females than males. This contrasts with the social structure of common dolphin communities outside of the bay and makes the Port Phillip community even more special.

More females than males?

Why more females that males?  We are not 100% sure why but can only suggest that it has to do with the productivity of Port Phillip, which meets the needs of the many nursing females in the community.

Common dolphin
Local common dolphin leaping. Image taken under a DELWP research permit.

Where can the Port Phillip common dolphins be seen?

The Port Phillip common dolphin community is much smaller and more spatially restricted than the species of bottlenose dolphins that also resides in the bay.  The bottlenose dolphins are thought to use the majority of Port Phillip, which covers an area of almost 2000 km2.  In contrast, the common dolphins are often seen between Mt Eliza and Mt Martha, especially during the cooler months. Surveys indicated that the area regularly used by the resident common dolphins is less than 150km2.  Even smaller again are the key areas of their habitat, which is estimated to be only one-fifth of their range, with the larger of the two key areas located offshore from Mornington.

How can you help with the science?

Common dolphins in Port Phillip show a degree of seasonality; they move closer to shore during the cooler months as the baitfish move closer to the coast. Because they can observed from land, keep an eye out for them when you are walking along the beaches, between Mt Eliza and Mt Martha. We would love to receive your sightings so that we can continue to monitor their presence in our bay.

The work presented here was completed as part of the PhD research by Sue Mason and was completed through Curtin University, in conjunction with the Dolphin Research Institute.

By being a cetacean steward and reporting your sightings, whether in Port Phillip or beyond, you can help our scientists make further sense of the presence of common dolphins in Victoria waters.