Scientists investigate as dead carp wash up in Lake Winnipeg cottage country

Provincial fish scientists are trying to figure out why hundreds, if not thousands, of dead carp are washing up on beaches in Lake Winnipeg cottage country.

The bodies of common carp, some more than a metre in length, are rotting on the sand and rocks on the east shore of Lake Winnipeg's south basin, between Patricia Beach and Victoria Beach.

On some stretches of shoreline, there are dead fish every few metres.

"I've never seen carp on the shore like that. You usually see one or two fish," said Dave Horbas, a councillor for the R.M. of St. Clements.

At Lakeshore Heights, writer-photographer Bramwell Ryan has been forced to shovel carcasses off the beach.

"In a typical year, I see maybe one or two dead carp. I've never seen this kind of volume before and the most surprising thing is the birds aren't eating them," said Ryan, who also counted 110 carp carcasses on a two-kilometre stretch of Grand Beach.

"That's really weird. I mean, that's hundreds and hundreds of thousands of pounds of basically fish flesh, sitting on a beach, and none of the scavengers are touching it. It's just odd behaviour. I can't figure that out."

Further north at the R.M. of Victoria Beach, residents removed 25 carcasses from one beach alone, said Reeve Penny McMorris.

Invasive species considered a pest

Common carp are an invasive species from Europe, introduced into Manitoba in 1886, according to the Invasive Species Council of Manitoba. They're considered a pest species because they stir up dirt and destroy vegetation at the edge of marshes.

Their rotting bodies, however, create an unsightly mess and malodorous stench. The province advocates people bury the carcasses at a depth of half a metre.

Scott Forbes, a University of Winnipeg ecologist, said there are three potential causes for a large fish kill.

One is anoxia, the absence of oxygen, but that's uncommon in stretches of open water such as Lake Winnipeg's southern basin, he said.

A second is high water temperatures, but it's too early in the season for Lake Winnipeg to become warm enough to kill fish, he said.

It's most likely that some form of disease is killing the carp, Forbes said.

Manitoba Fish and Wildlife officials are investigating this possibility, spokesperson John Neufeld said in a statement.

Tissue samples were taken from carcasses on Friday. They will take two weeks to process, he said.

"These samples will be analyzed for the presence of two viruses to which common carp are susceptible," Neufeld said.

One is the koi herpes virus, which was first found in Manitoba in 2008, when large quantities of dead carp were found in Lake Manitoba and Lake St. Martin, according to a provincial fact sheet published the following year.

The virus infects all members of the carp family, including koi and goldfish. It cannot be transmitted to people and does not render the fish unsafe to eat.

In live carp, symptoms of koi herpes virus include discoloured or blistered skin, sunken eyes, pale and rotting gills, notches on the nose and erratic swimming, according to the provincial fact sheet.

Provincial officials are also investigating whether the infected carp died of spring viraemia of carp, which is caused by a virus that also infects native fish species such as northern pike and pumpkinseed.

Spring viraemia of carp has never been found in Manitoba before, Neufeld said.

Fisheries and Oceans Canada is working with the province to determine the cause of the die-off, said Hilary Prince, a spokesperson for the federal ministry.

Disease transmission among carp would be high right now, said Forbes, because the fish are congregating in large groups as they spawn.