Trophy hunting of grizzly bears is exceeding the number of kills allowed by B.C. government limits, say two prominent environmental groups.

A joint study by the David Suzuki Foundation and the New York-based Natural Resources Defence Council found the B.C. government's limits on grizzly hunting were exceeded in 63 per cent of the grizzly populations at least once over a five-year period, between 2004 and 2008.

"Held up against the government's own estimates of what is sustainable, the number of grizzlies being killed in B.C. is excessive," said Dr. Faisal Moola, director of science and terrestrial conservation at the David Suzuki Foundation, in a release. Nothing is being done to stop it, he said.

The research linked the increased kills to trophy hunting, which accounts for 88 per cent of all deaths of grizzlies at human hands.

The data suggests the government's initial estimates of grizzly populations are wrong, said the report. "Recent local population inventories in some parts of the province have found that grizzly bear numbers are far lower — sometimes by as much as 100 per cent — than the government's initial estimates."

Moola questioned whether trophy hunting is sustainable. "This new research casts serious doubts on the sustainability of the trophy hunt given the fact that the government's own data show that humans are killing more grizzly bears than allowed."

The report calls for changes to the province's Wildlife Act, including the establishment of no-kill zones where grizzlies cannot be hunted.

According to the David Suzuki Foundation, almost 11,000 bears were killed by humans between 1977 and 2009, with 87 per cent legally killed by hunters. It predicts that if current hunting habits aren't changed, grizzly bears may be threatened or endangered by 2065.