The post-mortem examination of a humpback whale that died after swimming into the UK's river Thames this week has found that it was most likely killed by a ship.

Scientists from the Zoological Society of London (ZSL) carried out the necropsy on "Hessy" the humpback yesterday, revealing a wound that appeared to be afflicted by a passing ship. Further investigation revealed that the ship strike was most likely the cause of death.

"The main finding was a large wound on the underside of the head, associated with a fracture along the length of one of the mandibles (lower jaw)," Rob Deaville, ZSL’s Cetacean Strandings Investigation Programme project manager, said in a press statement given to IFLScience.

"Traces of blood clots around the fractured jaw and haemorrhage around the cut/torn surfaces indicate that the damage occurred before death and it was the team’s opinion that the injuries were most likely a result of shipstrike and this is considered to be the primary cause of death.

“It’s certainly possible that the whale was struck outside of the Thames and already had these injuries whilst it was seen swimming within the river at the beginning of the week – further tests of tissues taken during the examination are ongoing and may shed further light on the likely timescale around the injuries."

Analysis of the whale's intestines revealed the presence of parasites and suggested it had not eaten in a relatively long time. On one positive note, the researchers found no evidence of plastic ingestion.

Their examination also showed that the whale was a young female and larger than previously estimated, measuring 8.37 meters (~27 feet) from head to flukes. Typically, the species (Megaptera novaeangliae) can range from 12 to 16 meters (39 to 52 feet) in length, making it one of the largest animals on Earth.

The humpback whale was first spotted on October 6 near Gravesend in northwest Kent, some 35 kilometers (22 miles) from the bustle of central London. The mammal was later spotted motionless on the mudflats along the river at Greenhithe on October 8.

As you can imagine, the process of recovering the body and bringing it back to a lab was no small feat. After confirming the whale had died, ZSL and the Port of London Authority launched an operation to hoist the body out of the water with a crane and transport it across London in a truck. 

“The whale was so large that the patrol boats struggled to tow it. It was bigger than the patrol boat I was in, no doubt about it, and it was getting on for the length of the bigger patrol boat so I would say minimum 10 meters,” Martin Garside, a spokesperson for the Port of London Authority, who was involved in towing the whale, told Reuters.

“It is incredibly sad – I was literally two feet from this dead whale,” Garside added. “It was both poignant and a bit eerie really – road traffic was thundering overhead on the busiest motorway in Britain and oblivious to all the people in the cars and lorries there was a 10-meter-long beautiful whale floating dead beneath them.”