Few marine fishes are endangered. But exotic introductions can be a serious threat to native species, especially around isolated islands such as the Hawaii group, where 30 per cent of the world's reef and shore fishes are endemic. Overfishing, pollution, destruction such as dynamiting coral reefs, and collecting for the enormous and expanding trade in aquarium fishes are the other factors. Marine sanctuaries, says the author, who is Chairman of the SSC Marine Fishes Group, are vitally important as both refuges and breeding grounds.