London, Mar 11 (AP) British police arrested a man on suspicion of manslaughter as they searched for answers about why a cargo ship hit a tanker transporting jet fuel for the US military off eastern England, setting both vessels ablaze. One sailor was presumed dead.

Humberside Police said the 59-year-old was detained “on suspicion of gross negligence manslaughter in connection with the collision.” The man, who was not named by police, has not been charged.

UK officials were watching for damage to birds and sea life after jet fuel from a ruptured tank poured into the North Sea when the Portugal-registered container ship Solong broadsided the US-flagged tanker MV Stena Immaculate on Monday. The collision sparked explosions and fires that burned for more than 24 hours.

Footage filmed from a helicopter on Tuesday morning showed the fire appeared to largely be out on the tanker, which had a large gash on its port side.

The UK coast guard agency said Tuesday that “the Solong is still alight and the fire on board the Stena Immaculate has greatly diminished.” It said the cargo ship was drifting south, away from the tanker, and a 1 km (around a ½ mile) exclusion zone had been put in place around both ships. The government said the cause of the collision was being investigated, but there was no indication of foul play.

“No sign of pollution from vessels is observed at this time," Transport minister Mike Kane told lawmakers in the House of Commons. But he cautioned that it was a fast-changing situation, and said the cargo ship is likely to sink.

The government said air quality readings were normal and the risk to public health onshore was “very low”.

The collision triggered a major rescue operation by lifeboats, coast guard aircraft and commercial vessels in the foggy North Sea.

All but one of the 37 crew members from the two vessels were brought safely ashore in the port of Grimsby, about 150 miles (240 km) north of London, with no major injuries. One crew member was missing, and the coast guards called off the search late Monday.

“Our working assumption is that, very sadly, the sailor is deceased." Kane said.

The UK Marine Accident Investigation Branch has begun gathering evidence of what caused the Solong, bound from Grangemouth, Scotland, to Rotterdam, Netherlands, to hit the stationary tanker, which was anchored about 10 miles (16 km) off the English coast.

The investigation will be led by the US and Portugal, the countries where the vessels are flagged.

The 183-metre (596-foot) Stena Immaculate was operating as part of the US government's Tanker Security Programme, a group of commercial vessels that can be contracted to carry fuel for the military when needed. Its operator, US-based maritime management firm Crowley, said that it was carrying 220,000 barrels of Jet-A1 fuel in 16 tanks, at least one of which was ruptured.

The company said that it was unclear how much fuel had leaked into the sea.

The owner of the Solong, shipping company Ernst Russ, said that contrary to earlier reports, the vessel wasn't carrying containers of sodium cyanide, which can produce harmful gas when combined with water. It said that four empty containers had previously contained the chemical.

“Our team is actively engaged with all local authorities, and we will work with cleanup teams to ensure every effort is made to mitigate further impacts on the marine environment,” the company said in a statement.

Greenpeace UK said that it was too early to assess the extent of any environmental damage from the collision, which took place near busy fishing grounds and major seabird colonies.

Environmentalists said that oil and chemicals posed a risk to sea life, including whales and dolphins and to birds, including puffins, gannets and guillemots that live on coastal cliffs.

Tom Webb, senior lecturer in marine ecology and conservation at the University of Sheffield, said that wildlife along that stretch of coast “is of immense biological, cultural and economic importance”.

“In addition to the wealth of marine life that is present all year round, this time of the year is crucial for many migratory species," he said.

Alex Lukyanov, who models oil spills at the University of Reading, said that the environmental impact would depend on multiple factors, including “the size of the spill, weather conditions, sea currents, water waves, wind patterns and the type of oil involved.” “This particular incident is troubling because it appears to involve persistent oil, which breaks up slowly in water,” he said. “The environmental toll could be severe.” (AP) SCY