Overexploitation, habitat alteration, pollution and related anthropogenic pressures on their natural habitats have considerably reduced populations of this species by 60-70% during the last few years.

Tom Lester, a 52-year-old bayman who began fishing as a child with his grandfather, claimed that pollution and over-fishing by sports fishermen had reduced the number of all fish.

A heavy haze and pollution reduce visibility to about 20 miles from June through September.

Overfishing and pollution reduced the productivity of the Inland Sea fishing grounds; and San'yo is an area concentrated on heavy industry.

Still, she said, pollution and loss of habitat outside protected areas are reducing bird populations.

Mr. Salkeld said the percentage of days when pollution reduced visibility to less than five miles doubled from 1991 to 1997, to more than 8 percent.

Such genetic pollution from escaped aquaculture stock can reduce the wild population's ability to adjust to the changing natural environment.

Some reports said that pollution had reduced the effect.

Rain, fog, snow, smoke or pollution all reduce the strength of, or completely block, the light beam.

Over-fishing, smuggling and pollution caused by sewage entry into the Caspian Sea have considerably reduced the sea's sturgeon population.