Sixteen horses that travelled on the Spirit of Tasmania in January died.
It is understood the horses competed at the Barnbougle Polo on January 20 and belonged to Willo Polo Club in the Richmond, NSW.
The Primary Industries, Parks, Water and Environment Department are leading an investigation into the incident, assisted by the Australian Maritime Safety Authority.
An AMSA spokesperson confirmed the horses travelled on the Spirit of Tasmania on January 28, arriving in Victoria the following day.
The dates coincide with the heatwave that swept through both states.
It is not known if the horses died on the ferry or after they departed.
“An AMSA surveyor attended the vessel on Tuesday 30 January,” the spokesperson said.
“While investigations are continuing, at this point AMSA is satisfied that the vessel appears to have complied with AMSA requirements relating to the carriage of livestock.
“It would be inappropriate to comment further while the investigation is underway.”
A DPIPWE spokeswoman said Tasmania is being assisted by other jurisdictions, including chief veterinary officers in Victoria and NSW.
“As per standard practice, no further details will be released as this is an ongoing investigation,” the spokeswoman said.
Representatives from the Spirit of Tasmania and Willo Polo Club, both declined to comment.
According to the Spirit of Tasmania’s conditions of carriage, animal transport vehicles must be fit for purpose and passengers aren’t allowed to access the vehicle decks while the vessel is at sea, unless a veterinary certificate is provided.