New Zealand, like the United States, has an endangered species act. The structure of the act, however, is different from ours. Rather than requiring a government agency to list the numerous, small numbered and obscure species that are endangered in New Zealand, it lists the modest number of species that are thriving and common place. Everything else is protected.
An article by Marcus Ranum discussed over at Pit of Babel looks at similar issues in the area of computer security, where it makes far less sense to try to enumerate bad programs like viruses, whose multitudes are uncountable, than it does to try to affirmatively list the handful of programs whose use is legitimate and not a security threat. It is worth your time to read.