The trust yesterday posted photos to social media of a 4- or 5-year-old male sea lion with what appeared to be a loop of fishing line around its neck.
The sea lion was seen last week and again on Monday, first at St Kilda Beach and then Aramoana, the trust said.
Trust co-chairman Shaun McConkey appealed for any sightings of the animal to be reported to Doc.
Fishing line wrapped around a sea lion’s neck would eventually kill the animal, Mr McConkey said.
"It’s going to be going through quite a bit of pain and discomfort in the meantime.
"So the sooner we can get it off the better."
Doc biodiversity ranger Jim Fyfe said it was the second time this year he was aware of a sea lion that needed human intervention after becoming entangled in a "nylon collar", or loop of fishing line.
"Because it’s a human-caused problem — and it’s clearly going to be a ‘suffering death’ if nothing is done — we will certainly respond to situations like this," Mr Fyfe said.
"Two in one year is a bit of a concern," he said.
Earlier this year Doc staff, along with Dunedin vet Tony Malthus and sea lion trust members located a different sea lion with a loop of fishing line firmly around its neck at Victory Beach.
They sedated the animal and removed its nylon collar with a scalpel, Mr Fyfe said.
Mr Fyfe saw that sea lion about a month ago at Smaills Beach, and although scarring remained visible, the animal appeared to have made a full recovery, he said.
When a sea lion first became entangled in a nylon loop, the loop was often loose enough for it to be removed from a distance with a special hook with a cutting blade on one side.
As the animal kept growing, the intervention required would become more significant.
So too would the effect on the animal, he said.
The nylon loop would start cutting into the animal’s flesh as it grew.
It would lead to infections and eventually death.
"It needs to come off," Mr Fyfe said.
In the 1990s, fur seals faced a similar threat from blue plastic strapping on boxes — including bait boxes — he said.
These recent incidents served as a reminder to people to cut "any loops they might be responsible for" if there was any chance it could end up in the ocean.
