
Mandurah’s Freeze Branded Dolphins
You may have noticed that some of Mandurah’s dolphins have faint numbers on their fins. Many years ago when dolphins stranded here in Mandurah, freeze branding was the method used to help identify and keep track of the dolphins. Mandurah has been identified as a dolphin stranding hot spot, with the Peel-Harvey area being so shallow, the dolphins can get stuck in the shallows as they are navigating into these areas whilst looking for fish and get caught out by the tide. Many of our dolphins have stranded several times! We are lucky enough to have the Mandurah Dolphin Rescue Group in Mandurah, who have been rescuing our dolphins for over 20 years.
The first time dolphins were freeze branded in Mandurah was in October 1990. A group of ten dolphins were found in Lake Goegrup, near the Serpentine River swimming in a pool of deeper water but were unable to get out as the rest of the surrounded area was too shallow. They may have become trapped after chasing fish into the lake and then been caught out with the receding tide. Unfortunately two dolphins had already died, however the remaining eight dolphins were found in time to be rescued and then released into the Mandurah estuary. Wildlife officers from CALM, Department of Conservation and Land Management as it was known then were called out and with the help of volunteers they were able to capture the dolphins. Each dolphin was tagged, numbered, measured and given an overall check before being released. These were the first dolphins to be freeze branded with numbers Zero one to Eight. Since then many others have stranded in the shallows of the Peel-Harvey area.
Above: Left – Adult male Zero One, 20 years after freeze branding ©Photo by Mandurah Dolphin Research Project. Right – Adult male Fourteen, 20 years after freeze branding ©Photo by Mandurah Dolphin Research Project. Freeze branding involves immersing a brand in liquid nitrogen (dry ice) and then holding it against the dolphin’s skin. The skin cells where the brand touches are killed and the end result is a white mark that matches the shape of the branding iron. The marks should remain for over 20 years. By having these long lasting visible marks it helps to identify the animals and gain valuable information as to how long they survive and whether they strand again. This method is no longer used with the last dolphin, Twenty three being branded in 1997.

Above: Twenty two in 1997 when first freeze branded © Photo by Mandurah Dolphin Rescue Group

Above: Recent photo of Twenty two, 20 years later. © Photo by Mandurah Dolphin Research Project

Above: Zero one and Fourteen, March 2018 © Photo by Natalie Goddard

Above: Twenty one and Nikaila, March 2017 © Photo by Mandurah Dolphin Rescue Group

Above: Recent photo of Twenty One, 20 years after freeze branding. © Photo by Mandurah Dolphin Research Project