July 19, 2021 — Open-net pen Atlantic salmon aquaculture is big business on Canada’s east coast. Given the industry’s size, much has been studied and written about its effects on wild salmon. But how might fish farms be affecting other species in their vicinity—such as lobster? Lobster is one of the most economically valuable wild species, and the bulk of the world’s catch is made along the eastern seaboard of North America. Inka Milewski, who studies the interactions between aquaculture and the wider ecosystem at Dalhousie University in Nova Scotia, recently parsed the scientific literature to determine the ways in which salmon aquaculture is affecting wild lobsters.
Milewski and her colleagues identified a multitude of factors that could affect lobsters, their habitat, and the lobster fishery. Net pens change oceanographic conditions, for example by reducing current speeds, increasing turbulence, and breaking up waves. The farms also generate waste, such as excess food, fish feces, and urine, as well as the chemicals used to control pests and diseases. Lights, noises, and odors associated with the farms can disrupt lobster behavior.
Milewski says she was most surprised by how sensitive lobsters are to the particulate and dissolved organic and inorganic waste that result from fish feces and uneaten food. These chemicals can disrupt critical lobster behaviors like feeding, spawning, and mating. Her review identified studies that show that these waste products can change the quality of lobsters’ diets and promote harmful algal blooms near farms.
“There is a tremendous amount of waste generated by fish farms,” Milewski says. “I don’t think people have a sense of the scale.” A fairly typical farm of about 600,000 fish will generate around 40 tonnes of waste every month during its 22-month production cycle. “It’s understandable how that waste can change lobsters’ behavior, distribution, and abundance,” she adds.
But the review also identified serious gaps in our understanding of the interactions between aquaculture operations and lobsters. While some aspects, such as the use of chemical pesticides, have been well studied, information on others, including waste discharges, disease, and noise, are limited or entirely lacking.