An overcrowded colony of about 1,000 koalas in Australia is being assessed this week for possible ill health in a survey that could lead to a cull, raising objections from animal welfare lobbyists.

The Victorian state government is concerned many of the koalas may be undernourished because the colony at Cape Otway has grown even as the supply of the koalas’ staple diet of manna gum leaves has diminished.

A team of experts will examine a sample of the population, ear-tagging and implanting fertility control in the females prior to release.

“Koalas will be captured and assessed by veterinarians using strict health assessment protocols and anything that is found to be in poor condition or suffering will be humanely euthanised while it’s under sedation,” said Mandy Watson, a spokeswoman for the Department of Environment, Land, Water and Planning.

Koalas are a protected species in Australia, where they serve as a major tourist attraction and fulfil the odd diplomatic role – world leaders including US President Barack Obama were pictured cuddling the docile animals at a G20 summit in Brisbane last year.

The government says culls are sometimes necessary, but campaigners are concerned there will be a repeat of a crisis in 2013 when 700 sick or injured koalas were euthanised and about 1,500 more died unaided at Cape Otway, a tourist spot along the Great Ocean Road. There are about 43,000 koalas left in the wild in Australia.

The colony has risen to unsustainable levels in recent years as the animals consume about 1.5kg of gum leaves each a day. Another 3kg are lost to damage each day.

“It is not over population of koalas; it is under population of trees and linked habitats,” said Deborah Tabart, a spokeswoman for the Australian Koala Foundation. “You cannot have it both ways.”