AUSTIN, Texas (REUTERS) - The Dallas Safari Club will auction a permit to hunt a black rhino in Namibia, possibly fetching up to US$1 million (S$1.27 million) with proceeds going to protect the endangered animals in a move seen by some animal rights groups as ethically dubious conservation.

The licence being auctioned on Saturday is supposed to allow for the killing of a single, post-breeding bull, with Namibian wildlife officials on hand for the hunt to make sure an appropriate animal is selected.

The club, opening its annual convention in Dallas on Thursday, expects the permit to bring US$250,000 to US$1 million.

The hunt will help in managing the population and provide an underfunded Namibian government hard cash in the expensive battle to thwart poachers, it said.

"The whole purpose of the auction is to raise as much money as possible to ensure that the black rhino population continues to grow," club executive director Ben Carter said.

"These bulls no longer contribute to the growth of the population and are in a lot of ways detrimental to the growth of the population because black rhinos are very aggressive and territorial. In many cases, they will kill younger, non-breeding bulls and have been known to kill calves and cows."

There are about 25,000 rhinos in Africa - 20,000 white rhinos and 5,000 black rhinos - with the majority in South Africa. Namibia is one of the leading habitats after that. Both countries allow for a handful of regulated rhino hunts each year with proceeds going to fund conservation.

Rhino protection has grown more expensive in the last few years due to a surge in poaching fuelled by international crime syndicates to feed demand in places such as Vietnam, where horn is used as a traditional medicine and sold at prices higher than gold.

Mr Wayne Pacelle, chief executive and president of The Humane Society of the United States, said the group has a general objection to trophy hunting and sees as morally questionable raising money for conservation by selling permits to kill endangered species.

"Killing an animal as a head-hunting exercise is archaic and inhumane," Mr Pacelle said. "We can't just cherry-pick the perfect set of facts to justify this gambit."

Mr Tom Milliken, leader of the elephant and rhino program for the international wildlife trade monitoring network Traffic, said Namibia had 1,750 black rhino as of the end of 2012 and the population has been steadily increasing under good management and protection.

"Traffic believes Namibia has demonstrated a sound conservation policy for its rhinos over the years and does not oppose Namibia's legitimate execution of its hunting quota which was approved through an international Cites oversight process," Mr Milliken said in an email.

Cites stands for the Convention on International Trade in Endangered Species and is a global regulator.

Nearly 950 rhino were killed by poachers in South Africa in 2013, its environment ministry said. In Namibia, little poaching has occurred over the past decade, with only 10 animals killed since 2006 - half of which were last year, Traffic said.

Up until about 2010, only a handful rhinos were poached in Africa but the number shot up when rumours circulated about the same time in Vietnam that a minister's relative was cured of cancer by rhino horn. There is no basis in science to support the claim.