"The dead calf has since been freed from the crab pot, but remains in the water with the mother dolphin as she grieves.
"Dolphins are highly intelligent creatures and are known to stay with their young for a period of time following a death."
The department says it will continue to monitor the pair and remove the dead calf from mum "when appropriate to do so".
"We ask the public to stay well away from the dolphin and her dead calf during this time," the post said.
People on Facebook are mourning the loss of the baby dolphin.
"So sad and so preventable," a Facebook user wrote.
"Sadness caused by carelessness of people," another person said.