Invasive tunicates — also known as sea squirts — are slimy creatures that attach themselves to mussels and either rob the shellfish of nutrients and water, or literally rip the mussels off the socks with their sheer weight. They are invertebrates that look like giant orange slugs.
"It makes you feel pretty sick actually," said Dale Cook, who owns a mussel farm in the waters off Corkums Island in Lunenburg Bay.
Cook said tunicates have devastated his business and cut his production by 90 per cent. He's since had to go into other fisheries.
Peter Darnell grew mussels at Indian Point Marine Farm for 31 years — but not this year.
"Once the tunicates came we just struggled with them for 10 years and the problem has just gotten worse and worse every year," he told CBC News.
"Now, it just feels like it's a waste of time struggling, it's just a waste of time and money."
Darnell said for the first several years, his farm was able to cope with the tunicate invasion since it was not too heavy and his cleaning and grading equipment could handle them.
Many of the tunicates also died off at the end of winter, allowing Darnell to serve local markets during the summer when the mussels were relatively free of the creatures.
Over the last few years, however, Darnell said the tunicates have become tougher and no longer die after the winter.
"If you look around you'll find that the mussel industry in Nova Scotia is just a shadow of its former self. The only mussel farms that are still active are on the Eastern Shore or in Cape Breton and that's because they haven't got tunicates yet," he said.
"All the fellows around here who have ever grown mussels, very few left doing it. It's because of tunicates."
Getting rid of tunicates is difficult and expensive — the only way to do it is to blast each sock with water from a power sprayer several times a season, which requires more employees, more gear, even another boat.
Darnell said all that does is buy a little time before the pests are back.
"Spraying is not the answer. It's too energy intensive. Just no money at the end," he said.
"We have to find a better solution for them if we're going to have a mussel industry."