In the third week of March, clams traded at Tokyo’s Tsukiji wholesale market at JPY 650 to 670 (USD 5.87 to 6.05, EUR 5.40 to 5.57) per kilogram – up 10 percent from last year, according to a Nikkei Shimbun report.
The price of some good quality Manila clams (Venerupis philippinarum) exceeded that of arc shell (akagai), a luxury food. At retail, clams in the shell are selling from 100 to 180 yen (USD 0.90-1.62, EUR 0.83-1.49) per 100 grams.
In Japan, Manila clams are produced in three large bays that have extensive tidal flats: Tokyo Bay (mainly on the Chiba Prefecture side), Ise Bay near Nagoya and Ariake Bay (mainly in Kumamoto Prefecture), as well as in a portion of the Seto Inland Sea bordering Yamaguchi and Fukuoka prefectures. However, only Kumamoto Prefecture recorded increasing production, while production in other areas is decreasing.
In a scientific paper published last year, Tokyo Bay Fisheries Laboratory Director Mitsuharu Toba wrote that natural clam stocks in Tokyo Bay are declining due to several causes. Those included river floods that washing away clams or covering them with silt; “blue tides” (upwelling of oxygen-depleted water); parasitic infestations of sea spiders; strong winter waves that carry clams out of their beds; and hypoxia (inadequate oxygen condition) of larvae.
Reduction of habitat by coastal reclamation, however, seems to be the biggest problem, as clam larvae spawned from a tidal flat spend a couple of weeks floating around freely in the bay until they settle again on a tidal flat. If the area they land upon is unsuitable, such as a seawall or built up area, they simply die.
In Ise Bay, production is sustained by transplanting juvenile clams from the Rokujo tidal flat in Mikawa Bay (a protected smaller bay attached to the larger Ise Bay), as other areas of Ise Bay suffer from hypoxic water flowing south from urbanized areas at the north end of the bay. However, strict waste-water regulation has resulted in less organic matter in the sea, reducing production.
But other factors are harder to fight. In the Seto Inland Sea, warming water due to climate change has allowed the spread of eagle rays (Aetobatus flagellum), which feed on clams.
This year is a continuation of a trend of declining clam production.
