PICTURED: The Titan mothership returns to shore in Newfoundland

The mothership that launched the doomed submarine Titan has returned to port in Canada after the submarine’s catastrophic implosion while diving to the wreckage of the Titanic.

The Polar Prince support vessel arrived in St John’s Harbor, Newfoundland, on Saturday morning, docking at about 8:15 a.m. local time as the sun broke through the morning haze.

Crew members in orange helmets were seen on the deck of the ship, which returned to port with five fewer souls on board than the 24 it left with eight days earlier.

The ship had taken part in a massive search for the Titan about 430 miles south of St. John’s, which ended Thursday with confirmation that the submarine had imploded deep underwater, likely shortly after it launched on Sunday.

The winding down of salvage efforts comes as the Transportation Safety Board of Canada (TSB) announced it would conduct a safety investigation into the fatal deep-sea vessel implosion.

The Polar Prince is a decommissioned Canadian Coast Guard icebreaker now owned by Miawpukek Horizon Maritime Service Ltd and chartered by the extreme tourism company OceanGate as a support vessel for the Titan’s fatal dive.

OceanGate founder and CEO Stockton Rush was killed aboard the company’s submarine, along with passengers Shahzada Dawood and his son Suleman Dawood, British adventurer Hamish Harding and Titanic expert Paul-Henri Nargeolet.

Two Canadian Coast Guard (CCG) vessels participating in the search also returned to the port of St. John’s on Friday evening, one of which remained at the scene of the disaster.

A crowd gathered at the dock to watch the return of the CCGS Terry Fox and CCGS Ann Harvey, while the CCGS John Cabot remained on site to provide assistance and support in the salvage and salvage operations.

In a statement issued before their ships arrived in port, the CCG said: ‘The Canadian Coast Guard extends our sincere condolences to the family and friends of the Titan’s crew for their tragic loss.

“Search and rescue operations have ended.”

Authorities in the US and Canada have now started investigating the cause of the Titan’s fatal implosion.

The US Coast Guard said on Friday that no formal investigation has yet been launched as maritime agencies are still searching the area where the ship was wrecked.

The debris was about 12,500 feet underwater, several hundred feet away from the Titanic wreckage it was on its way to explore.

The US Coast Guard led the first search and rescue mission, a massive international effort likely costing millions of dollars.

The investigation into the cause of the disaster and any attempt to recover wreckage from the ocean floor is likely to be difficult and painstaking.

“This is an incredibly unforgiving environment down there on the sea floor,” said Rear Admiral John Mauger of the Coast Guard’s 1st District.

Meanwhile, Canada’s TSB said a team of investigators had been sent to St John’s to “gather information, conduct interviews and assess the incident.”

In a brief statement confirming the investigation, the safety agency said: “The TSB is launching an investigation into the fatal incident involving the Canadian-flagged ship Polar Prince and the private submarine Titan.

“In accordance with the Canadian Transportation Accident Investigation and Safety Board Act and international agreements, the TSB will conduct a safety investigation into the circumstances of this operation conducted by the Canadian-flagged ship Polar Prince.

A team of TSB investigators travels to St John’s, Newfoundland and Labrador to collect information, conduct interviews and assess the incident.

“In the coming days, we will coordinate our work with other agencies involved.”

The TSB does not establish any civil or criminal liability and conducts investigations for ‘the promotion of transport safety’.

It was not entirely clear who would be given the authority to lead the disaster investigation, which will undoubtedly be complex and involve several countries.

The Titan submarine is registered in the Bahamas, but OceanGate, the company that owned and operated the vessel, is based in the US.

OceanGate was headquartered in Everett, Washington, but appears to have ceased operations after the Titan was confirmed lost.

Meanwhile, the Titan’s mothership, the Polar Prince, flies the flag of Canada, and the dead were citizens of England, Pakistan, France and the US.

The National Transportation Safety Board said Friday that the US Coast Guard has declared the loss of the submarine Titan a “major marine accident” and that the Coast Guard will lead the investigation.

An NTSB spokesman said information was provided to senior management of the agency by Coast Guard officials and that the NTSB has joined the investigation.

The Coast Guard has not confirmed it will take charge. Coast Guard headquarters said the Coast Guard 1st District in Boston will discuss future operations and plans, but did not say when.

The First District did not immediately respond to a DailyMail.com message Saturday morning asking for comment.

Developing story, more to come.