A crewmember who fell asleep during his watch was likely responsible for the grounding of a tug that caused thousands of litres of fuel to spill into the waters off Bella Bella, B.C., according to an American government safety agency.

The second mate of the Nathan E. Stewart had been on watch for a little more than two hours when the tug ran aground in the Seaforth Channel in the early hours of Oct. 13, 2016, a marine accident brief from the National Transportation Safety Board (NTSB) says.

"According to the captain, approximately an hour or an hour and a half after the grounding, the second mate admitted, 'I fell asleep,' during a discussion with him about the accident," says the report, dated Nov. 21.

Nathan E. Stewart

More than a month after it sank, the Nathan E Stewart is lifted off the ocean floor onto a salvage barge. (Zoe Hopkins)

The brief also lays blame on the failure of the entire crew to follow their employer's safety management system procedures for standing watch, which required a second person to be in the wheelhouse at certain defined times.

The articulated tug and barge, owned by the Kirby Corporation of Texas, spilled an estimated 110,000 litres of diesel and another 2,000 litres of lubricants into the waters where the Heiltsuk First Nation harvest manila clam and other shellfish.

Navigating narrow channels

The days and hours leading up to the spill are laid out in detail in the NTSB brief.

The vessel was on its way south through the Inside Passage from Ketchikan, Alaska, at the time of the grounding. The route is marked by narrow channels which are often subject to strong currents because of the tides.

The captain, chief mate and second mate were rotating through four-hour navigational watches as the Nathan E. Stewart weaved through the passage. According to the brief, the second mate started his shift an hour early on the night of the incident, relieving the captain at 11 p.m. on Oct. 12.

Underwater

Heiltsuk Nation divers were able to capture photos and video under the wreck of the Nathan E. Stewart in 2016. (Heiltsuk Nation/April Bencze)

At 12:53 a.m., the second mate missed a navigational waypoint near Ivory Island, failing to alter the course of the tug.

At 1 a.m., a crew member who was performing rounds tried to contact the second mate using his UHF radio, but didn't receive a response. When he tried again 30 seconds later and couldn't rouse the second mate, he started making his way to the upper wheelhouse.

"En route, he felt what he described as 'shuddering.' During a third attempt to contact the second mate, the tankerman was informed by the second mate that the vessel had grounded," the brief says.

The starboard propeller had struck a rocky area off Athlone Island known as Edge Reef.

2nd mate had 'adequate' rest

By 9:30 a.m., the Nathan E. Stewart's stern was partially submerged. The barge floated free about nine hours later, leaving the tug resting on the rocky floor of the channel.

The second mate told investigators that he wasn't taking any medications at the time of the grounding, didn't have a sleep disorder and felt that he'd had "adequate" rest in the previous three days.

The Heiltsuk First Nation is still recovering from the disaster, which resulted in Fisheries and Oceans Canada closing the area around the spill to shellfish harvesting.

Spill

Diesel leaked onto the shoreline of islands within the Great Bear Rainforest for weeks after the Nathan E. Stewart sank near Bella Bella. (April Bencze/Heiltsuk Nation)

The Heiltsuk estimate that their manila clam beds bring in up to $200,000 for the community every year. Officials with the First Nation have said they are considering legal action to recover some of the damages they've suffered in the last year.

Just this week, the waters off Bella Bella were hit by another near-disaster when rough seas caused a massive oil-loaded barge to break free from its tug, the Jake Shearer. There were no reports of a fuel spill, but the barge had to be anchored overnight before a commercial tug arrived to bring it to safety.