June 1, 2010

Noise Pollution Becoming A Threat To Fish

Scientists say that fish are being threatened by man-made noise pollution.

The scientists reviewed the impact of noise made by oil and gas rigs, ships, boats and sonar on fish species around the world.

They say that rather than live in a silent world, most fish hear well and sound plays an active part in their lives.

The increasing noise pollution may severely affect the distribution of fish, as well as their ability to reproduce, communicate and avoid predators.

"People always just assumed that the fish world was a silent one," biologist Dr Hans Slabbekoorn of Leiden University, The Netherlands, told BBC News.

However, Slabbekoorn and colleagues wrote in the journal Trends in Ecology and Evolution how the underwater environment is anything but quiet.

All fish studied to date are able to hear sounds, either by an inner ear or a lateral line that runs along a fish's side.

Different fish species have different sensitivities of hearing.

The researchers said Atlantic cod have "average" hearing abilities, while freshwater goldfish can hear at higher frequencies.

Fish hear best within 30-1000Hz, though species with special adaptations can detect sounds up to 3000-5000Hz.

Some species are sensitive to ultrasound, while others like the European eel are sensitive to infrasound.

The researchers say that means human-generated underwater noise has the potential to affect fish just as traffic noise affects terrestrial animals like birds.

"The level and distribution of underwater noise is growing at a global scale but receives very little attention," Slabbekoorn told BBC.

Most research has focused on the impact sound might have on marine mammals, such as whales and dolphins.

Some studies have reported that the Atlantic herring, cod and blue-fin tuna flee sounds and school less coherently in noisy environments.

That could mean fish distributions are being affected, as fish avoid places pleated by man-made noise.

So far, over 800 species of fish from 109 families are known to produce sounds.

Fish make sounds when fighting over territories, competing for food, within spawning aggressions and when under attack from predators.

Slabbekoorn published a report in the journal Behavioral Ecology earlier this year that suggested that cichlid fish in Lake Victoria, East Africa produce species-specific sounds that also correlate with the size of the fish.

They said the sounds play an essential role in mating and sexual selection among cichlids in the lake.

This means noise pollution could interrupt their reproduction, by causing stress or restricting their ability to find a mate or keep them from preferred spawning sites.

The researchers said that noise pollution may not be as big of a threat to fish as other environmental pressures.

"Fisheries for example are likely to be much more devastating," Slabbekoorn told BBC.

"However, none of the threats can be considered on their own: any negative consequence of anthropogenic noise will come on top of the fisheries impact, and together they may lead to more critical situations for some species."

"The phenomenon is concealed by the fact that underwater sounds are difficult to hear by people living in air."


Image Caption: Scientists have found that the European eel is sensitive to infrasound. Courtesy Wikipedia


On the Net: