A Kemp’s ridley sea turtle native to the Gulf of Mexico is largely thriving after he was found nearly dead on a beach in Wales in late 2023, nursed back to health and then flown to Houston recently to continue recovering – though scans revealed signs that the creature has been grappling with lingering pneumonia, according to his caretakers.

Rhossi’s condition was detailed in a blogpost on Friday from the Houston zoo, whose veterinary team was tasked with caring for the creature – believed to be no older than age four – and giving him the best chance possible at an eventual, successful return to the wild.

A local dog discovered a 2lb (0.9kg), cold-stunned Rhossi, belonging to one of the world’s most endangered sea turtle species, on a beach in a Welsh village in December 2023. Rhossi was about 5,000 miles (8,000km) from the Gulf of Mexico region where Kemp’s ridley sea turtles are native – and from where they have been known to be swept away for vast distances, including across the Atlantic Ocean, by powerful marine currents.

Wales’s Anglesey Sea zoo subsequently took Rhossi in and spent the next two years nursing him to health again. His frame had more than tripled, and he had bulked up to 46lb (21kg) before he took a helicopter ride from Wales to London’s Heathrow airport – and then a transatlantic flight to Houston on 10 August.

The Houston zoo’s sea turtle staff by then had committed to taking over the administration of Rhossi’s recovery, the facility said in its blogpost on Friday. And after an initial evaluation, Rhossi’s caretakers placed him in a deep-water tank to let him become acclimated to his new surroundings.

Rhossi then had a more comprehensive medical examination performed by Dr Joe Flanagan, a senior veterinarian who briefly came out of retirement for the assessment, the Houston zoo said.

The resilient turtle had his organ function, eyes, mouth, shell and flippers checked. He also had X-rays and a CT scan to take a closer look at his lungs, according to the Houston zoo.

Rhossi largely acquitted himself as “healthy, active and vigorous” during the examination, the facility reported.

“He’s very strong,” Flanagan said in a Reuters video report. “He swims normally. He dives. He surfaces. He breathes fine.”

A Houston zoo employee shines a light on Rhossi as the turtle lies on an exam table in Houston, Texas, on 11 August. Photograph: Evan Garcia/Reuters

But, after having endured the north Atlantic’s perilously frigid waters before his rescue, “his scans revealed a concern for lingering pneumonia”, and his return to the Gulf of Mexico would evidently “take a little longer than expected”, the zoo wrote.

The zoo nonetheless added: “Rhossi’s medical team will continue to monitor him and provide additional treatment, as needed, to ensure the best possible chance of a successful return to the wild.”

Houston’s zoo said Rhossi’s story illustrated the “incredible dedication and careful coordination of … multiple agencies and non-profit organizations”. The facility specifically mentioned the US Fish and Wildlife Service, the National Oceanic and Atmospheric Administration, the Anglesey Sea and Houston zoos, the Texas state aquarium and the Welsh helicopter pilot Darren Briggs.

Underlying those entities’ efforts is the fact that the population of nesting Kemp’s ridley females is estimated to be only between 7,000 and 9,000, according to the Sea Turtle Conservancy.

The US government furthermore has considered Kemp’s ridleys as endangered since 1970, at risk of extinction within the foreseeable future because of threats from humans such as egg collection and killing for products such as meat, information from the conservancy says.

Frankie Hobro, the Anglesey Sea zoo director and owner, expressed high hopes for Rhossi as he settled into the Houston phase of his recovery.

“It looks like in a couple of years, he’ll be fit for breeding out in the wild,” Hobro said in the Reuters video. “So that’s really exciting news for us.”