Marine Wildlife Project Officer with NSW National Parks and Wildlife Service, Andrew Marshall, said between May and September there were 35 reported whale entanglements off the NSW coast and only a handful of successful rescues.
"The rope itself often gets stuck on the animal for a period of time which can cause chronic injuries and chronic illness," he said.
"It's a very sad fate for most of those whales that are tangled and we can't rescue.
"There's probably been around six entangled whales rescued between Victoria, NSW and Queensland.
"Our success rate for rescues is normally quite high, but this season has just been a horror for getting good information at an appropriate time and then the sea and wind conditions being on our side as well.
In the past couple of days there have been reports of a humpback whale entangled off the NSW north coast, with the first sighting off Scotts Head.
"We have had a hazardous surf warning and strong winds, so it wasn't possible to get a vessel out yesterday, and that's been another feature of this season for us this year," Mr Marshall said.
"The whale is now likely south of Crescent Head and possibly around Port Macquarie and we do have a team ready to go if it is sighted."
Whale rescues 'incredibly dangerous'
Mr Marshall said any whale entanglement rescue was complex and carried a lot of risks.
"We are working out of a three to four-metre long inflatable rubber boat, so we are very vulnerable to wind and sea conditions," he said.
"Then add to that the unpredictable behaviours of a 25-tonne panic-stricken wild animal.
"Both the whales and other influences at these incidents can be incredibly dangerous without training and experience so only trained crews are allowed to engage in these rescues.
"There are at least three documented fatalities from rescuers trying to help whales and being struck or drowned in the process.
"The whales which seem 'compliant' with rescuers are more likely just exhausted, because the majority in our experience will defend themselves vigorously."
Fishing lines and buoys a big issue
Mr Marshall said it was a common misconception that whales were mainly getting tangled in shark nets or marine debris.
"That just doesn't stack up with our data; in the vast majority of cases, it's not debris and less than 10 per cent is nets," he said.
"The highest proportion of causes for entanglements is ropes with floats, which is probably associated with fishing equipment that's in use at the time.
"Thirty-two of the cases this year in NSW have been ropes and floats."
More whales, more entanglements
Mr Marshall said it was fantastic to see humpback whale numbers recovering and booming, but that also meant there would be an increasing number becoming entangled.
"The fishermen using the gear have not had to evolve their techniques to cope with the increase in the whale population," he said.
"That's playing to the increase in incidents of entangled whales.
"Really, no one in our generation has had to deal with the whale population at its current level.