Dozens of fish species are in danger from overfishing, or fishing methods that risk damage to other marine life or the environment. They include exotic offerings such as parrotfish. wild caviar and golden eye perch, but equally Dover sole, Dublin Bay prawns and common haddock, halibut and hake are at risk. The Marine Conservation Society has 69 such species on its “fish to avoid” list.

One of the biggest risks to these endangered species is not just the giant factory ships, vacuuming up endangered fish and dolphins among the catch in their giant nets, although they are clearly a threat. There is another danger and it is from an unexpected quarter.

Some of the finest restaurants, whose chefs should not need lessons in sourcing food sustainably, are serving endangered fish. Charles Clover, the Sunday Times environment columnist, has been investigating where the fish in Britain’s restaurants comes from. A documentary based on his findings, The End of the Line, will be broadcast this week and some of its findings are shocking.

Nobu, the Japanese restaurant chain, has endangered bluefin tuna on its menu. Cocoon, in London’s Regent Street, still serves wild Sevruga caviar from endangered sturgeon. Rick Stein, perhaps Britain’s most famous fish restaurateur, has halibut, wild salmon, turbot and Dover sole on his menu, all on the Marine Conservation Society’s list.

Compass, the catering firm with 6,500 outlets in Britain, has banned the society’s 69 endangered fish species from its menus, including Atlantic cod. It should be applauded for doing so. Some food retailers, notably Waitrose and Marks & Spencer, have worked hard to ensure the fish they sell is from sustainable sources, which include properly run fish farms, responsible for about a third of the fish the world eats. Some restaurants, it seems, think that is beneath them.

That can change if customers are prepared to do something about it. Mr Clover is launching fish2fork.com, a website that shines the light on top restaurants which have endangered species on their menus. The best include the Loch Fyne and, appropriately, the Fish! chains. Users are encouraged to “rat on a restaurant” or “pat a chef on the back”.

The worst offenders get the site’s worst ratings: five red fish skeletons. Those which take the trouble to source fish properly receive one or more leaping salmon. Avoid the skeleton restaurants and they will change their ways. Good food should be sustainable food. Restaurants contributing to the disappearance of fish species need to get that message. Their customers can help to make sure they do.