Demonstrators with bags of strong-smelling sludge protested against the approval of two salmon farms to be located in one of Nova Scotia's most productive lobster fishing bays.

About 75 fishermen, environmentalists and concerned citizens gathered in Halifax on Friday and brought sludge from existing salmon farms in other parts of the province to the protest outside the legislature.

The Nova Scotia government recently approved the two salmon farms in St. Marys Bay in the southwestern part of the province. Each farm will stock about 700,000 fish and is part of a $150-million expansion by New Brunswick-based Cooke Aquaculture.

The farms will total about 84 hectares.

Demonstrators said they want public consultation and answers to their concerns — which they said were ignored.

Lobster fisherman Sheldon Dixon said he believes the farms will create residue that will harm the bay's bottom and one of the province's most profitable lobster fishing grounds if the projects proceed.

He told the crowd that about 3,000 traps operated by 60 fishermen would be displaced by the sites.

"Where will we go? We have to go to somebody else's [ocean] bottom and all the other bottom is covered," he said.

Many demonstrators had to get up early on Friday morning for the four-hour drive from the mouth of St. Marys Bay to Halifax.

Cooke Aquaculture is a New Brunswick company that bills itself as North America's largest producer of farmed salmon.

The company said its aquaculture operations will create hundreds of jobs and put millions of dollars into the local economy.

Nell Halse, a spokeswoman for Cooke Aquaculture, said her company is trying to persuade local residents that the farms can operate without damaging the ocean bottom.

The pens, which Halse described as being smaller than an 18-hole golf course, can co-exist with fishermen, she said.

"It's not like we're trying to fill the whole coastline of Nova Scotia with salmon farms," said Halse.

Farm and fishing can co-exist: Cooke Aquaculture

She said she believes the environmental movement is attempting to polarize fishermen and aquaculture operators, despite evidence suggesting they can co-exist.

"We have had an open policy to accommodating lobster fishermen to set their traps around the farms and in fact they choose to do so," Halse said.

Cooke Aquaculture said the pens will comply with local environmental regulations, including camera scans of the bottom looking for signs of damage or degradation.

Demonstrators brought sludge from existing salmon farms in other parts of the province. (CBC)Greg Roach, the associate deputy minister of Fisheries and Aquaculture, said there will be third-party monitoring of the fish farm and the waters will be protected.

"There's confidence the lobster fishermen won't be negatively impacted by the footprint of this farm," he said.

But residents of Long Island, at the mouth of St. Marys Bay, overwhelmingly oppose the salmon pens.

St. Marys Bay is the heart of the most lucrative lobster fishing grounds in Nova Scotia, an industry valued in the hundreds of millions of dollars a year, providing hundreds of local jobs.

Opponents say the sewage produced by more than one million salmon, combined with the drugs needed to keep those fish healthy, endangers prime fishing grounds — underwater nurseries for lobster as well as scallop beds.

They say the practice of huge open-net salmon farms has already caused ecological damage in other parts of the world and that Nova Scotia should not head down that road.

With files from The Canadian Press