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National Observer
2 days ago
- Health
- National Observer
Distant Covid cousin correlates with calamitous oyster die-offs
A previously-unknown virus distantly related to Covid is "strongly associated" with mass die-offs of farmed Pacific oysters in BC, researchers have found. The virus showed up in about two-thirds of the dead and dying oysters the research team collected during a mass die-off on two oyster farms in BC in 2020. Wild oysters collected near the farms weren't infected, hinting at a possible link between the virus and the mass die-offs. The virus — Pacific oyster Nidovirus 1 — is specific to oysters, and doesn't pose a health risk to humans. "We have not demonstrated a causative effect between this virus and mortality at this point, but they're highly associated," said Curtis Suttle, a study co-author and professor of earth, ocean and atmospheric sciences, botany, microbiology and immunology, and the Institute for the Oceans and Fisheries. Pacific oysters are the primary shellfish farmed in BC, with the industry worth about $16 million in 2023. In recent years, the province's oyster farmers have lived under the threat of so-called "summer oyster mortality syndrome," a phenomenon where up to 90 per cent of a crop of oysters die within a few days of each other right before reaching market size. The mass die-offs are closely linked to higher water temperatures. As the climate crisis has deepened, BC's average water temperatures have increased by between 0.2°C and 0.6°C, particularly in shallow waters where oysters grow best. Climate change is also causing more extreme temperature swings — ocean heatwaves — which stress the bivalves further, said Suttle. "It's been pretty devastating for our industry," said Nico Prins, executive director of the BC Shellfish Growers Association. "This summer oyster mortality syndrome is a cascade of various stressors that just combine to just be too much for the poor animal to deal with, and they die." He doesn't think the virus will be a "smoking gun" pinpointing the cause of the mass die-offs, but could help offer more insight. Suttle said that his team found that farmed Pacific oysters in Europe and Asia were also routinely infected with the virus, but those infections weren't linked to mass die-offs. A previously-unknown virus distantly related to Covid is "strongly associated" with mass die-offs of farmed Pacific oysters in BC, researchers have found. But Suttle said the findings should be a reminder that oyster farmers need to be cautious about moving oyster seed — baby oysters — between farms and bodies of water. Most oyster farms don't produce their own seed, instead requiring a labour-intensive process where seed producers induce spawning in broodstock, then grow the larvae into small oysters that are sold to farms. Once at the farms, the oysters are suspended in underwater cages, where they grow to market size. Fisheries and Oceans Canada has few restrictions on where oyster seed can be sold and BC only has a handful of oyster seed producers. Stricter rules apply to older oysters, which can only be moved from farm to farm within specific zones, explained Prins. Jessie McMillan, operations manager at Manatee Holdings, one of BC's oyster seed producers, said that while he'll "definitely be paying attention" to emerging research about the virus, he isn't panicked. "There's no way to predict if it's a causative agent," he explained. Oysters stressed by heat or other well-known factors could be more susceptible to carrying the virus, even if they're asymptomatic. He's more concerned about problems that cause known stress to the shellfish, such as harmful chemicals and bacteria that lax provincial and federal pollution and wastewater regulations allow to enter the ocean, as well as climate change.
CBC
06-08-2025
- Science
- CBC
UBC scientists may have found the reason for a mass Pacific oyster die-off
Pacific oysters are the most widely farmed shellfish in the world, but have recently been dying in large numbers. Curtis Suttle, a marine microbiology professor at the University of B.C., says that the reason for the die-off could be a previously unknown virus that is a distant relative of coronaviruses.
