(Read: "Extinction Threatens Half of Primate Types, Study Says" [August 5, 2008].)
Worldwide, habitat loss affects roughly 40 percent of threatened mammal species, while human hunting affects 17 percent, Long said.
Seventy-eight percent of marine mammals are threatened by accidental deaths, such as becoming bycatch in fishing nets intended for other species.
Marine mammals are "threatened purely because humankind does not care enough to mitigate deaths that do not even benefit our species," Long said.
"All these threats represent human-driven activities that, if not controlled, will soon lead to a dramatic increase in the 76 species of mammal that are known to have gone extinct since 1500," Long said.
Timothy Ragen is executive director of the U.S. government's Marine Mammal Commission in Bethesda, Maryland.
"We are causing a period of excessive decline or loss in the diversity of nonhuman life over time," he said, adding that the problem will only get worse as human populations grow.
"If we expect to be good stewards, we will have to reexamine our relationship with other forms of life and be willing to make the changes needed to conserve our natural world," Ragen said.
The IUCN Red List is apolitical in scope, but political will is required to reverse species' downward spirals, added lead study author Jan Schipper, director of global mammal assessments for IUCN and the nonprofit Conservation International based in Arlington, Virginia.
"The species that are recovering are the ones we're focusing restoration and recovery efforts on," he said.
According to the report, 5 percent of threatened species have seen rebounds due to conservation efforts.
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