Extent of zebra mussel invasion under investigation.

Extent of zebra mussel invasion under investigation

Zebra mussels were discovered in Thunder Bay in September, but it is still to be determined if the dreaded molluscs have actually established a colony there.

In other Great Lakes the mussels block water intake pipes leading to industries and communities, and they threaten the food chain because they eat plankton.

"We have not documented them to date in Thunder Bay harbor," says Dave Payne, Lake Superior co-ordinator for the north-central region of the Ministry of Natural Resources.

The molluscs were discovered in September clustered in the water intake pipes of the Canadian Coast Guard icebreaker Griffon.

Payne says there is optimism that the mussels are not yet established in the harbor.

However, he adds that everyone realizes that zebra mussels will be found to some degree in Thunder Bay harbor sooner or later.

It is hoped that the conditions in the harbor will prevent the mussels from increasing to significant populations.

The potential limiting factors are the low calcium level in the water and the cool temperatures.

If they do get established, it may be that there will only be a small colony,

In Duluth, Minn., where they are believed to have arrived in 1989, Payne notes that there has been very little spreading.

In Scandinavia the population increased, but then levelled off.

A number of monitoring sites had been set up in Thunder Bay prior to the arrival of the Griffon. There are five sites, one of which is close to where the Griffon docked.

The sites are to be examined this fall to determine if populations have been established.

Coast guard buoys and the hulls of ships will also be checked.

A sample of the mussels on the Griffon was taken to the ministry to be studied. Measurements were taken to determine the stage of growth, age and chances of reproduction in the harbor.

In the southern Great Lakes the numbers are still increasing. Payne explains that the rate of spread has been dramatic because of the warm water and high nutrient levels.

In Lake Erie the average population density is 32,000 mussels per square metre.

"We don't ever expect to find those densities in Lake Superior," Payne says.

In an ironic twist, he says the spread has probably been helped by the improving water quality in the Great Lakes. "These things can survive now."

Where the mussel population has grown, it has affected fish populations and left beaches covered with foul-smelling shells after die-offs.

Payne says it is a given fact that the mussels have been established in the Great Lakes. "There is nothing much we can do about that."

However, the fear is that the mussels will eventually move into inland water.

Payne says the message the ministry is trying to get out to boaters on the Great Lakes is to stop and think when transferring any boat, boating equipment or water to other lakes.

There are very few ways of controlling zebra mussels in open water, or in closed-in areas.

"Once they're established in a harbor, there is very little we can do to remove them," Payne says.

There has been testing of controls such as chlorine flushing of pipes and electric shock, along with basic manual removal by divers.

Another possible control is the Ethiopian soap berry or endod, which kills the mussels.

Research is still under way, but the substance is not yet licensed for use in Canada.

Even if it were, Payne noted that it would be impossible to put enough berries into the environment to control the mussels.

However, it may be useful in spot applications, such as flushing pipes.

The mussels have no commercial value. Payne explains that they are inedible, since they are very small and poor tasting.

Zebra mussels were found in Lake St. Clair in 1988 - the first discovery in the Great Lakes system. It is thought that they came across the Atlantic in the ballast water of ocean-going ships.

The province is spending $8 million and Ontario Hydro, $12 million on prevention and research into the mussels.

PHOTO : Bruce Thacker, a sport fishery technician with the Lake Superior fisheries unit of the Ministry of Natural Resources, examines a sampling of zebra mussels.