A dolphin calf, affectionately named 'Meelan' by the Estuary Guardians Mandurah, is likely to have passed away just after being spotted entangled in braided fishing line, hooks and weeds.
The Estuary Guardians group posted that Meelan's mother had been sighted alone and that "she would not have left or given up on her calf until she had to".
Fishermen spotted the calf struggling and "significantly" entangled, weighed down in the tail area, and reported the sighting to authorities.
Meelan was relocated on October 6 by volunteers from the volunteer rescue group, who re-reported the issue.
A spokesperson for Estuary Guardians said the issue was made worse because there were no local resources to help.
"Unfortunately there are no locally-based marine or wildlife officers in Mandurah to assist - such resources based in Perth were also limited and was deemed past the time where any response was available," the spokesperson said.
"A small scale search next morning was unfortunately unsuccessful."
In the days after Meelan was last spotted, there were strong wind and weather warnings which significantly impacted search efforts by volunteers, who had been out on their own vessels looking for the calf.
The circle of life will continue in our waterways, unfortunately minus one small calf who could have lived another 40 years.
"With limited rescue resources available and often very bad weather conditions for resighting the pair, the odds were sadly always stacked against his survival."
Once Meelan's mother was spotted, the group accepted that the worst is likely to have happened, making him the third calf to die in the past few years in Mandurah's inland waterways due to entanglement.
"This is a tragic reminder of the need to keep our waterways clean and clear of loose fishing line," the spokesperson said.
"In particular braided fishing line which cuts like a knife through dolphin skin.
"What is important now is we all work together to make it a better future for our wildlife."
The spokesperson said there were a few "smaller but effective" ways to help wildlife, which included picking up litter and line, joining community cleanups, fishing responsibly and using fishing line bins provided and reconsidering braided wire where possible.
"The circle of life will continue in our waterways, unfortunately minus one small calf who could have lived another 40 years."
The Department of Biodiversity, Conservation and Attractions has partnered with a number of local wildlife groups to present Luca's Legacy Reel-it-in Clean Up Event, where volunteers and members of the public will gather together to clean up the waterways.
The event is in memory of Luca, a resident dolphin who sadly died from being entangled in fishing line in 2019.
Further details for the event can be found on the Facebook event page.