At least 2,000 metric tons of fuel oil spilled into the sea, when a tanker split open and four freighters sank in a storm November 11, which also caused the death of at least six sailors.
"In the region around the Chushka Promontory, out of every 30-40 dead birds only one can be found alive, although without any chance of surviving," the Russian Bird Conservation Union said.
The conservation organization said the disaster-stricken area includes an important zone for 50,000 migrating birds and that up to 10 species of endangered birds can be spotted there at different times of the year.
Earlier reports said some 30,000 birds had been killed by the pollution in the strait. Tests of water samples showed that the contamination by oil products was 2.5 milligrams per liter, 50 times above acceptable levels.
The four sunken dry-cargo vessels had about 7,000 metric tons of sulfur on board, which could add to the environmental catastrophe.
A local fisheries department said damage from the spill could exceed 300 billion rubles ($12 billion) and warned that the use of chemicals to clean up the area will only double the environmental damage, as it assists the spread of oil products.