It was summer 2018 when De Courcy Island oyster farmer Darrin Szaszik discovered nearly all his deep-water oysters were dead. He was devastated.
“It was like nothing that I have ever seen in 20 years,” he said.
His troubles weren’t a one-off. Last year was bad, too — he estimates he lost around 40 per cent of his crop.
When it takes up to three years for an oyster to make it from the hatchery to market, that’s significant.
“It’s kind of a painful subject,” he said. “I know a lot about mortalities, probably a lot more than a lot of people.”
Szaszik’s farm off De Courcy, which is halfway between Vancouver and Valdes islands, southeast of Nanaimo, is among the 511 shellfish aquaculture operations currently licensed in British Columbia. And many are feeling the negative impacts of climate change — especially oyster farmers, who are reporting increases in both the scale and frequency of die-off.
Jim Russell, the executive director of the B.C. Shellfish Growers Association, is concerned about the growing frequency of mass mortalities that shellfish growers are experiencing due to climate change.
“We’re seeing increasingly alarming levels of mortality, somewhere between 20 and 80 per cent, which is really quite remarkable given that only a couple of decades ago it was much less, about 10 per cent,” Russell said.
Changing ocean conditions
Ocean acidification, warming water temperatures and marine heatwaves are the likely culprits, according to Timothy Green, director of Vancouver Island University’s Centre for Shellfish Research. Acidification occurs when extra carbon dioxide produced by humans is absorbed by the ocean, and this dissolves the calcium carbonate needed for oyster larvae to grow their shells.
“We’re finding that there are oysters within the population whose offspring just can’t make a shell,” Green said. “And then also, on top of that, you have increasing temperatures and marine heatwaves that are associated with higher mortality of older oysters.”
Data collected in Baynes Sound since the early 1900s shows the mean sea surface temperature is rising by 0.03 C every year, according to Green. Baynes Sound, the channel between Denman and Vancouver islands, is a hotbed for shellfish aquaculture. Such rises may not seem like much, but they can lead to serious ecological consequences.
Fisheries and Oceans Canada reports that warmer ocean temperatures are linked to larger than normal toxic algae blooms and shellfish disease outbreaks like Vibrio parahaemolyticus, a gastrointestinal disease dangerous to humans.
Green said these compounded factors make him fearful that shellfish farmers will decide it’s time to quit the business.
Artificial selection: identifying adaptive traits in shellfish
Studying the genetics of oyster adaptation to environmental stressors, Green began a Pacific oyster breeding program at VIU’s Deep Bay marine field station in Nanaimo to “future-proof” the Canadian shellfish aquaculture industry against the changing climate.
Selective breeding of oysters involves testing oyster families for acidification stress before mathematically determining which families are best for reproducing, creating pedigrees. The ones that best respond to environmental stressors are then bred together.
It’s not a revolutionary concept. Humans have selectively bred plants and animals for desired traits for thousands of years — and what Green’s doing is no different.
Green and his university team have already seen some success with the program. Working closely with local farmers and Fisheries and Oceans Canada, they produced 44 oyster families resistant to acidic oceans last year.
This year, they want to measure how resistant their oysters are to warm water temperatures and continue studying oyster adaptation.
An additional challenge, Green said, is not only producing oysters that can withstand the stressors of climate change, but ones with a fast growth rate and that are ideal for eating.
If an oyster survives ocean acidification stress and temperature shocks but is very small and doesn’t produce many eggs or sperm, it won’t be able to pass its genes on to future populations, he said.
“We’re trying to find that fast growing, big, meaty oyster that farmers will want.”
He said he plans to begin supplying local hatcheries in the Gulf Islands with his best-performing brood stock next year, aiming to give them a competitive edge.
“I really hope this keeps people willing to continue farming oysters,” he said. “We’ve seen this achieved in other parts of the world, so there’s no reason it can’t happen in Canada. I think there’s huge potential.”
Szaszik said oyster farmers are resilient and the industry has a positive future despite the looming impacts of climate change. Until stress-resistant oyster seed becomes available at B.C. hatcheries, he’ll continue trying to adjust as best he can.
“I think the biggest thing is, you know, farmers have to learn to adapt, right? You just have to hang on.”