The SPCA is investigating an animal welfare incident on an Interislander ferry after as many as five dogs died on board earlier this week.
Interislander crew discovered the dead dogs in an aluminium box at the back of a ute on Monday evening and immediately reported the case to police.
Three other dogs, also found in the box, had to be euthanised due to the extent of their condition.
Police have confirmed to 1 NEWS they attended the incident along with an SPCA inspector, but say as this is an investigation relating to animals the case is the responsibility of the SPCA.
The SPCA said due to the nature of the investigation, it cannot provide comment.
The Interislander ferry is a state-owned and operated service.
The head of campaigns for animal rights group SAFE said the ferry company should hold responsibility for the care of animals on board as they cannot rely on owners to put their animal's welfare first.
"SAFE is appalled that these dogs have had to endure such horrific conditions. No animal deserves to be put through this suffering," SAFE said.
The group is now calling for an urgent review of both Interislander and Bluebridge's animal transport policies.
It was real bloody hot and the ute was right in the middle of the deck- Marty O'Dea, witness
Marty O'Dea, a passenger on the same ferry, said the box where the dogs were held didn't appear to have any proper ventilation.
"It looked more like a tool box. It wasn't a proper dog box. It was real bloody hot and the ute was right in the middle of the deck. Nothing was open on the box," Mr O'Dea said.
He said there were roughly six dogs involved and the owner appeared to be doing nothing to remedy the situation.
"I wondered if he was in a state of shock. He was doing nothing."
He said he witnessed the owner throw one of the deceased animals into the ute's tray, and claims there were three or four other dogs lying on the ground, not moving.
Interislander's General Manager, Mark Thomspon, called the incident tragic for everyone involved and stressed the company has specific policies for people carrying pets in cars that have been in place for many years.
"These are clearly stated on our website when booking travel. We make it very clear that keeping pets fed and watered is the owner's responsibility," he said.
Mr Thompson said pets travel on the Interislander every day and other owners manage to care for their animals in a responsible way.
Interislander ferry services have kennels available for hire on board. For $15 per crossing, the cages are in "shaded, well-ventilated" areas.
Frequent user Liz Wilkinson said this service has improved.
"When we first used the ferry [in 2017], we were placed in full sun and numerous dog owners were also upset about the lack of communications with dog care," she said.
Ms Wilkinson said although Interislander have become better with their animal care since her first experience with them, the kennels don't appear to be cleaned often and once smelt of urine when she went to place the family dog in one.
Mr Thompson said the system they currently have in place appears to work for responsible pet owners and the company has no plans to change its policy.
By Imogen Wells