The Dolphin Research Institute has been keeping records on the Port Phillip bottlenose dolphins for over 20 years, but it wasn’t until 2006 that we first sighted the common dolphins that we believe to be resident to Port Phillip, along the Mornington coastline. Prior to this, common dolphins had been sighted but they appeared to be casual visitors in the bay.
So what are the differences?
Common dolphins have a gold stripe along their flank and grow to approximately two metres in length. They are easily distinguished from bottlenose dolphins, which are grey with a lighter ventral (belly) side.
Our adult bottlenose dolphins are slightly larger than a fully-grown common dolphin and easily weigh a couple of hundred kilograms.
The dorsal fin of a bottlenose is falcate (hooked) with an even grey colouration while the common dolphin’s dorsal fin is more triangular with a paler centre.
Of great interest to us is the difference in community size. Over 100 bottlenose dolphins call Port Phillip home while we know we have approximately 30 common dolphins (some are more photo-shy than others; photos are used for ID). Common dolphins can be seen travelling in varying-sized groups, but they are often observed in open water in super pods consisting of over a 1000 animals, migrating in search of prey.
Why we have such a small community of common dolphins that call Port Phillip home is a mystery that will hopefully be unravelled over the next couple of years by the work of our Research Director, Sue Mason and her team.
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Saw a pod of 30 common dolphins in open sea on the Oban to Barra ferry. Sea birds followed them Sunday 14 May
Thanks for your observation. Common dolphins can occur in large to huge numbers in the thousands in open waters. It’s a great sight and they are very pretty creatures.