black sea red data book - Department of Biology

Modiolus biocoenosis (at a depth of 60-70 m). Abundant in the Azov Sea, and also
occurring in the Caspian Sea but absent from the Mediterranean Sea.
Biology. Feeds mainly on molluscs, crustaceans and fish. A migratory, anadromous
species; in spring (February-May), it enters the rivers and in autumn (August-
November) it moves to its hibernation grounds in the sea. During their spawning run,
fish move separately or in small shoals. Sexual maturity is reached at 8-12 years
(male) and 13-15 years (female); after reproduction, adults return to the sea.
Population trends. Caught with drift and stake net, long lines and beach seines. In
June 1903 - March 1904, 85,160t were caught, in front of the St.Gheorghe branch of
the Danube, and 60,175 kg in the Portita zone. Compared with the 1920-1940 period,
the catches of 1940-1960 decreased by 80%; in front of the Danube, the catches
recorded were: in 1989-19,0001; in 1990-4,000 t and in 1991-15,000 t; for the 1993-
1994 period, there was an estimated (for the North-West zone of the Black Sea) stock
of 3,300,000 specimens, 180,000 of these were exploitable.
Threats. Overfishing, marine pollution, and reservoir-building on the spawning
rivers, blocking the traditional migration routes and destroying spawning grounds or
preventing access to them.
Conservation measures. Development of methods of artificial reproduction;
building of hatcheries to release fry to the sea. This species has been under protection
in Turkey since 1997. A special recovery and monitoring programme was started by
the Turkish Marine Research Foundation in the Sakarya and Kizilirmak estuaries.
Conservation measures proposed. Protection of the feeding sites of the fry in the
Danube mouth; interruption of fishing with pound nets during the great
agglomerations of fry in July-August; protection of spawners during migration and
spawning (April-July); production of fingerlings to repopulate the Danube river.
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