American TV networks have lost almost a quarter of their audiences because of the Hollywood writers' strike, according to new figures, and executives fear that “orphaned” viewers may never return.

The Nielsen ratings organisation found that US viewership for last week's opening of the 2008 TV season was down 21 per cent compared with the same week last year, when new episodes of hit shows such as Desperate Housewives and Grey's Anatomy were aired.

Because the strike has shut down production of all scripted shows, the networks are now almost completely out of fresh material to broadcast, instead relying on reality TV franchises such as American Idol.

The channel CW - home of Gossip Girl and America's Next Top Model - lost 50 per cent of viewers in the 18 to 49-year-old bracket sampled by Nielsen. “It's hard to ignore the declines,” the Hollywood trade magazine Variety said. It said that last week's figures were the first real evidence of the damage from the strike because previous weeks had been skewed by sporting events and Christmas holiday programming.

Not everyone lost out. Perhaps because of the controversy over her pregnancy, Jamie Lynn Spears, the 16-year-old sister of Britney Spears, saw her sitcom, Zoey 101, on the Nickelodeon children's channel attract a record six million viewers.

The show was filmed last summer - before the strike and before Spears revealed that she was pregnant.

The Hollywood stoppage is costing the Los Angeles economy an estimated $20 million (£11 million) a day. Thousands are out of work. Small businesses, such as the props suppliers along Hollywood Boulevard, are struggling to stay afloat. The organisers of the Golden Globes lost $6 million in one night when their event was turned into a press conference because actors refused to cross writers' picket lines to attend the awards.

There is some hope, since talks between the Writers Guild of America and Hollywood studio bosses resumed last week after a long and acrimonious stand-off over the Christmas holidays.

“I'm hopeful,” said Devon Shepherd, a writer for Weeds and Chris Rock's Everybody Hates Chris. “We're all just hoping that with time passing, cooler heads will prevail.”

The biggest issue remains the royalties paid to writers for TV shows and films streamed over the internet, as well as content downloaded on iTunes. So far, the writers have had the support of the Screen Actors Guild, which will face the same issues when its contract runs out in June.

Writers as well as studios are worried that lost viewers may never return to TV, instead finding new ways to entertainment themselves, such as YouTube, Facebook or video games. The most recent figures show that YouTube has had an 18 per cent surge in traffic, while visitor numbers to other websites, such as Crackle, have seen doubled, albeit from small bases.

During the last writers' strike of 20 years ago, about 10 per cent of network TV viewers never returned, most of them going to subscription cable channels such as HBO.

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