The death of 16 horses after a voyage on the Spirit Of Tasmania to compete in a polo tournament is under investigation by the Australian Maritime Safety Authority (AMSA).
The horses, from the Willo Polo club in New South Wales, travelled to Tasmania to compete in an event at the Barnbougle Polo club on January 20, Fairfax reported.
An AMSA spokesperson confirmed the truck carrying the horses completed the return trip across Bass Strait on January 28, arriving in Melbourne the next day.
"The Department of Primary Industries, Parks, Water and Environment (DPIPWE) is now investigating this incident. AMSA will assist where required," AMSA said in a statement.
"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.
"An AMSA surveyor attended the vessel on Tuesday 30 January."
It is unclear at which point in the return journey to NSW the deaths were reported.
The operator of the ferries, TT Line, said they could not comment while the investigation was underway.
A representative of the Willo Polo club said the matter was "in the hands of authorities" and refused to give any other details, other than to say the club is "hoping we will find out how it happened".
The Barnbougle Polo club, in north-east Tasmania, has been contacted for comment.
In a statement, DPIPWE confirmed an investigation into the deaths was underway.
"Tasmania is being assisted by other jurisdictions, such as the chief veterinary officers in Victoria and New South Wales," the statement says.
"As per standard practice, no further details will be released as this is an ongoing investigation."