Physical modification of the seabed Sample Clauses

Physical modification of the seabed. The main habitat of Black Sea bottlenose dolphins – shelf area – is under relentless pressure of various man-made physical “improvements” of the seabed, coasts and rivers inflowing into the sea. Some of these activities represent important threats for cetaceans being because they are responsible not only for widespread habitat degragation, but also for permanent or periodical disturbance of dolphin herds: (a) channel dredging and marine dumping of removed sediments; (b) sand extraction from the sea bottom; (c) offshore gas and oil exploitation; and (d) bottom trawling. 7.2.2.1 Channel dredging and marine dumping of removed sediments Habitat deterioration and disturbance of Black Sea bottlenose dolphins can be induced by the dumping of bottom sediments removed due to the deepening of navigation canals and reconstruction of ports. The dredging and dumping works cause a noise pollution and lead to the decline in water transparency, destruction and silting of benthic coenoses, and, thereby, to the reduction of cetaceans foraging capabilities. These human activities are the most peculiar to shallow waters of the northwestern shelf area, estuaries of big rivers (Danube, Dnieper, Dniester and South Boug) and the Kerch Strait. According to Xxxxxxxxx et al. (1998), there are more than 30 dumping sites in the Black Sea coastal waters, and ten of them are in the northwestern area, where 5,000,000 m3 of soil have been dumped annually since 1963 by the USSR and Ukraine. In the Kerch Strait 21,000,000 m3 of soil were dredged and dumped during 1991-1997. In Romania from the mid 1980s to mid 1990s up to 7,000,000 m3 of sediments have been removed each year in order to enlarge the port of Constantza, and about 1,000,000 m3 were dredged annually from the entry of the Sulina channel connected with the Danube (Petranu, 1997). The rate of sediment accumulation at Black Sea dumping sites exceeds the natural sedimentation rate by more than 1,000 times (Xxxxxxxxx et al., 1998). 7.2.2.2 Sand extraction from the sea bottom for building industry is widespread in the northwestern Black Sea shelf area. As a deteriorative and disturbing factor this activity is similar to the dredging, but it does not result in marine dumping. Millions tonnes of sand are extracted in Ukraine in Dzharylgachsky, Xxxxxxxxxxx and Tendrovsky bays, from Odessa, Dniester and Shagany xxxxx xxxxx (Xxxxxxx, 1998) and Lake Donuzlav.