VANCOUVER, British Columbia - Eighteen prominent scientists and researchers say there is no question that sea lice from fish farms are lethal to wild salmon, no evidence to the contrary and a need for greater protection.

The scientists, ranging from David Suzuki to National Geographic Society explorer-in-residence Wade Davis, wrote in an open letter to Canadian Prime Minister Stephen Harper and British Columbia Premier Gordon Campbell that the future of juvenile wild salmon is at risk.

The open letter called for immediate installation of stronger barriers between wild and farmed salmon, closed containment rather than the typical open pens at fish farms, as the only safeguard.

Where farmed and wild salmon mingle in narrow passages such as around the Broughton Archipelago, off the northeast coast of Vancouver Island, long-term decline of wild salmon stocks is inevitable, the scientists wrote.

Installing closed containment systems will be expensive, but Canadians must decide whether the benefits of aquaculture outweigh the threats to wild salmon and to the ecosystems and economies that depend on healthy stocks, they added.