"Dolphin-safe" tuna is beginning to appear on grocery shelves, but environmentalists say consumers are still a long way from being assured the tuna they're eating did not cost the lives of dolphins.

New shipments from the three largest U.S. canned tuna processors - StarKist Seafood Co., Bumble Bee Seafood Inc. and Van Camp Seafood Co. Inc.'s Chicken of the Sea brand - already bear the dolphin safe label in some regions. The labels are expected nationwide by year's end.The labeling, announced by the so-called big three in April, is a voluntary guarantee from the companies that fishing methods harmful to dolphins were not used to catch tuna.

But marine conservationists warn that the proliferation of dolphin-safe labels may lead consumers to believe dolphins are finally protected from the tuna fishing methods that have slaughtered hundreds of thousands of dolphins in the past.

Conservationists say thousands of dolphins are still being sacrificed for the tuna in smaller brand or in-house cans. And they worry that voluntary dolphin-safe practices may be loosely monitored or slip over time.