Heartbreaking loss for our Riverpark dolphin community
Postmortem results find the likely cause of death for female resident dolphin Moon, and her newborn calf.
One of our most famous and regularly observed female resident dolphins, Moon, was seen mourning her deceased calf, carrying it around at the surface of the water in the Canning River on the 22nd of May 2025. It is common for dolphins to mourn their calves in this way, sometimes carrying them around for weeks. Two days later, the calf was found washed up on the shore, where it was retrieved by DBCA staff and taken for a necropsy by Dr Nahiid Stephens.
Unfortunately, only three days later, we received a report of another deceased dolphin that had washed up on Applecross foreshore, which we quickly identified as Moon. Again, DBCA rangers did a great job of quickly retrieving the body and taking it to Murdoch for necropsy by Dr Nahiid Stephens.
Preliminary postmortem findings on the deceased calf indicate it was either stillborn or died almost immediately after birth due to a congenital defect of its tail (its flukes were almost completely fused together), making it impossible to swim. Moon had not yet commenced producing proper milk, which suggests the calf may have been born prematurely.
Preliminary postmortem findings on Moon suggest that she likely died from sepsis, a severe systemic infection. This may have been caused by a tear in her uterus, which led to uterine discharge, blood and fluid entering her abdominal cavity, where her organs are located. As she had recently given birth, her cervix was more open than normal, which enabled bacteria from the outside environment to enter her abdominal cavity, leading to infection. While there were signs of a uterine infection, it’s unclear whether the infection caused the tear in her uterus, or if the tear happened during birth and then became infected. It is hoped further laboratory tests might help answer this question.
The mysterious lump on Moon
Moon also had a 10x8cm lump on her back that first appeared in April 2024, before disappearing a few months later and then reappearing in April 2025. Testing on the lump has found it was a small pocket of pus in the muscle. There was a scar-like tract nearby, but no clear opening on the skin or leftover object inside. It’s possible the lump started from a foreign object that had since been expelled from the body, leaving behind an infection that her body tried to contain. The initial cause of the injury will remain unknown.
We know everyone who has been following Moon’s story will be deeply saddened by this news, and our hearts go out to you all, including our dedicated Dolphin Watch community, who have spent many hours observing Moon over the years. We feel your heartbreak. Moon lives on through her two remaining calves, Djinda who is now an adult and has her own calf born in Feb 2025, and Nganga who is 5 years old.
Photos by Sue Harper
