At least 2.7 tons of broiled eels, including an endangered Japanese species, were thrown away by retailers in the country last year, Greenpeace Japan said Monday, citing the result of a survey.

It is Japanese custom to eat spitchcocked eels in the hope of beating the summer heat in late July, and the product is extensively advertised during this special sale promotion period.

(File photo: Skewered eels are broiled at a restaurant in Osaka)

The Greenpeace survey showed that a large amount of cooked eels had been disposed of mainly because of best-before date expiration.

The environmental group conducted the survey from last September through January, contacting 18 broiled eel retailers, 16 of which responded.

The group said such disposal was confirmed by at least 10 retailers including Aeon Co., Maruetsu Inc. and Life Corp., which replied that the amount of disposed eel was "nearly zero." Only five companies disclosed the volume of dumped eels, amounting to a gross weight of 2.73 tons, equivalent to about 13,650 eels.

Only two retailers out of the 16 that replied -- Pal System and Yaoko Co. -- said they did not dump eels at all, while Seiyu GK, a Japanese subsidiary of Wal-Mart Stores Inc., gave an answer of "non-disclosure."

"The actual situation of its circulation, from catching young eel to selling, is quite opaque. The current problematic condition of marketing and consumption should be reviewed quickly," said Greenpeace Japan's Kazue Komatsubara, who was involved in the survey.

At one famous eel restaurant in Tokyo's Ginza shopping district, a grilled eel rice bowl is priced from 2,800 yen to 6,800 yen, or $25 to $62, depending on grade.