A total of 11 Siberian tigers have died over the past 3 months in a zoo in northeast China's Liaoning Province, local animal protection officials said Thursday.

All the tigers were from Shenyang Forest Wild Animal Zoo in the provincial capital.

The tigers died due to malnutrition rather than infectious diseases, said Liu Xiaoqiang, vice chief of the Shenyang Wild Animal Protection Station.

The zoo only fed the tigers on cheap chicken bones since the zoo was not doing very well financially, Liu said.

Two hungry tigers from the zoo mauled a zoo worker in Nov, 2009. The worker was seriously injured but survived the attack.

The two tigers were shot dead in the rescue.

A total of 13 Siberian tigers have died in the zoo since Nov, 2009. The zoo has over 20 Siberian tigers left.

After the incident, Shenyang Administration of Work Safety asked the zoo to keep the tigers in cages, which further undermined their health, Liu said.

Since November, Shenyang Qipanshan Administration Committee has been providing the zoo with appropriate feed worth of 18,000 yuan (2,636 U.S. dollars) a day. But many tigers already had intestinal infections or kidney failure caused by the lack of food and died later.

The number of tigers in the zoo has dropped by half in a decade, from 1,020 of 61 subspecies in 2000 to 518 of 49 subspecies in 2010.

The zoo is mainly privately owned with the Shenyang Municipal Government having 15 percent of the share.

"Many privately-owned zoos were under financial pressure, and most of them fail to feed the animals well," said Liu.

Another privately-owned zoo in Shenyang, Guaipo Tigers Zoo, has over 30 Siberian tigers. But in winter when tourists are scarce, it has to buy tiger feed on credit and pay the suppliers back in the peak of the tourist season.

As for regulating the privately-owned zoos, there were legal loopholes which made enforcement of the regulations impossible, said Liu.

"Wild Animal Protection Law" does not provide for any punishment for irresponsible zoo owners who abuse the animals.

In addition, "Property Law" stipulates that zoo owners have the right to keep animals and animal protection authorities have no right to interfere, said Liu.

The Siberian tiger, an engendered species, is a subspecies of tiger which once ranged throughout western, central Asia and eastern Russia. It is estimated that the number of wild Siberian tigers is now between 350 and 450 worldwide.

China has around 20 wild Siberian tigers, among which 10 to 14 are in northeast China's Heilongjiang Province and eight to 10 are in its neighboring Jilin Province.

China established a breeding base for the Siberian tigers in Heilongjiang in 1986 and the number of captive tigers has increased from eight to more than 800 currently.

The global wild tiger population is estimated to be at an all-time low of 3,200, down from an estimated 20,000 in the 1980s and 100,000 a century ago.