Police said Motin, 59, of Primorsky, St Petersburg, had been remanded in custody since Monday.
The Russian citizen was arrested after the Solong T-boned the Stena Immaculate, which had anchored while waiting for a berth at a port on the River Humber.
The Russian embassy said on Friday it was in contact with Motin, as well as his wife in Russia, and was supporting both.
A police spokesman said: “On Monday, March 10, Humberside Police received a report at around 11am that a collision had occurred between the two vessels, resulting in one crew member being reported missing.
“Extensive searches were carried out by HM Coastguard to locate the missing crew member, now presumed deceased. The family are being supported by specialist trained officers and our thoughts remain with them at this difficult time.”
An American Government source reportedly told a maritime news blog this week that foul play had not been ruled out as a cause of the collision, which involved the container ship crashing into the tanker while doing 16.4 knots (30.4km/h).
The Stena Immaculate was being chartered by the US military when it was hit by a cargo ship. Photo / Kees Torn / Wikimedia Commons
Stena Immaculate had been chartered by the US Military Sealift Command and was carrying 220,000 barrels (34.9 million litres) of Jet-A1 aviation fuel.
The tanker is still at anchor at the point where the collision happened, about 19km off the East Yorkshire coast, near Withernsea.
The Solong drifted south of this location, to a point where it could be seen off the Lincolnshire coast.
All 23 American crew aboard the US-registered Stena Immaculate made it safely off after abandoning ship when it caught fire shortly after the collision.
One person from the Solong crew was treated by medical personnel in Grimsby after being rescued but the other 13 members of its company who made it ashore were unharmed, its owners Ernst Russ, of Germany, said.
On Friday, Paddy O’Callaghan, the chief coastguard, said the vessels were “stable” and salvors had boarded them both to continue damage assessments.
He said: “There are now only small periodic pockets of fire on the Solong, which are not causing undue concern.
“Specialist tugs with firefighting capability remain at both vessels’ locations.
“Regular aerial surveillance flights continue to monitor the vessels and confirm that there continues to be no cause for concern from pollution from either the Stena Immaculate or from the Solong.”
O’Callaghan said: “The UK Health Security Agency [UKHSA] is also assisting in the response, and continues to advise that any public health risk on shore is deemed to be very low.
“The UKSHA will keep risk assessments under continual review as further information becomes available.”
Sir Keir Starmer, the British Prime Minister, said on Thursday the situation was “reasonably contained”.
Pressed on calls for a Cobra meeting to assess the potential environmental damage, he said: “We are absolutely monitoring this 24/7 and I’ve got teams doing that and assuring me of what’s going on.
“At the moment, the situation is reasonably contained. And, obviously, we will do whatever is necessary.”
The Marine Accident Investigation Branch, which is leading the safety probe into the incident, has said the Solong “altered course” at about 1.30am on Monday, as it passed to the east of Longstone lighthouse, on to “a heading of approximately 150 degrees”, which is a southeast direction.
The crash happened eight hours and 17 minutes later. The Solong frequently travelled between Grangemouth in Scotland and Rotterdam and regularly used the route it took on the day of the collision, the statement said.
