The Ljubljana Zoo has lost its oldest resident, a charismatic 50-year-old Western Chimpanzee named Mojca. With her passing, elephant Ganga is now the most senior, at 49.

Two weeks ago, the staff noticed Mojca had suddenly grown weak. The deterioration was caused by a heart problem and the chimpanzee was put down in late June, the Ljubljana Zoo announced on 8 July.

"Mojca was unforgettable and charming, she had a strong character and charisma. We looked forward to every one of her visits and check-ups especially when she was healthy," head of veterinary services Pavel Kvapil was quoted as saying.

Mojca was mother to six chimpanzees and grandmother to four. Most chimpanzees in zoos live up to around 40 years, with females usually outliving the males. Chimpanzees can live to that age in the wild as well, said the zoo.

Mojca was a representative of the critically endangered Western Chimpanzee species. In the wild only between 18,000 and 65,000 individuals remain.

The Ljubljana Zoo is a member of the European Association of Zoos and Aquaria (EAZA), which has an advisory group for great apes and keeps a chimpanzee pedigree register.

EAZA zoos are home to some 250 Western Chimpanzees and have a joint goal to increase their population to 500. This would be a healthy zoo population that could be used to resettle the species in the wild if the need occurs.

Apart from the elephant Ganga, 49, the group of seniors at the Ljubljana Zoo also includes a 40-year-old pink pelican, the 37-year-old yellow-cheeked gibbons Liling and Liping, the 37-year-old chimpanzee Boris, as well as a 26-year-old ruffed lemur and the 22-year-old California sea lion Kalle.