RESTAURANT menus dating back to the 1850s have allowed scientists to track the decline of marine species, providing crucial information that will assist efforts to protect the most vulnerable sea life.

A study of the cost of seafood on more than 200,000 American restaurant menus has revealed fluctuating prices that reflect the changing abundance of dozens of species over the past 150 years. The records show how the price, adjusted for inflation, of fish and shellfish, including lobster, swordfish, oysters, halibut, haddock and sole, has climbed as stocks have collapsed.

Lobster, for example, fetched little more than a couple of dollars a lb in the 1850s. “Prior to the 1880s, it was unusual to see lobster on menus at all except in bargain-priced lobster salad,” said Glenn Jones, of Texas A&M University, who led the research.

“It was considered a trash fish — it was not something you’d want to be seen eating. In colonial America servants negotiated agreements that they would not be forced to eat lobster more than twice a week.”

From the 1880s, people started to acquire a taste for it and prices rose. They fell slightly during the Great Depression of the 1930s, but ballooned from the 1950s as stocks became scarce with overfishing. Prices hit a peak of more than $30 (£17) a lb in the 1970s, but have fallen slightly, to about $25 a lb, because of improvements in fishery management and the exploitation of new lobster beds.

One of the most striking trends is in the price in San Francisco restaurants of abalone — a sea mollusc that is today considered a great and rare delicacy.

In the 1920s an abalone dish would set diners back about $7 in modern currency, and prices climbed slightly until the end of the 1960s. The price then began to rise between seven and ten times faster than inflation as stocks declined, and it now fetches between $50 and $70 a plate.

Abalone grow only 1cm (0.4in) a year, so they are particularly vulnerable to overfishing. They are now so rare off California that commercial fishing in the state is banned, and restaurants serve abalone imported from Australia and New Zealand.

Oyster prices remained relatively static for a century, before climbing sharply from the 1960s as beds became over-exploited. Similar trends can be seen with swordfish and sole, though prices of both have come down recently as fishing has become better controlled.

“As supplies dropped and prices rose, some of these species became a status symbol,” Dr Jones said. “It seems to confirm that many people simply want to eat something that is rare.”

The team will present their findings this week at the History of Marine Animal Populations conference in Denmark.

Poul Holm, the leader of the project, said that the research was providing a valuable baseline for historic fish and shellfish stocks. This is critical to conservation, as it allows scientists to establish the extent to which populations have declined.

“All this comes from a few crazy people who collected menu cards, but it’s a remarkable resource,” Dr Holm said.

Other research includes an analysis of captains’ logs and Swedish tax records that show the northern sixth of the North Sea supported 50,000 tonnes of spawning cod in the 1880s. The entire North Sea now contains about 50,000 tonnes of cod.

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