Researchers aim to fill data gaps about Dungeness crab amid concerns of declining population

If you've spent much time wandering along B.C.'s coast, chances are you've seen a Dungeness crab crawling sideways across the shoreline — or at least one of its colourful carcasses leftover in the sand. 

The cold water crustaceans are the second-most valuable invertebrate fishery on the West Coast of Canada and an important food source for coastal First Nations, but researchers warn they may now be facing some threats.

Lauren Krzus, a research technician at the Hakai Institute, says they're hearing anecdotally that Dungeness crab stocks are declining, and says climate change is poised to further impact them. 

She's three years into a 10-year research project with Hakai coastal ecologist Heather Earle, studying the crab's populations from Prince Rupert down to the southern point of B.C.'s coastline. 

This year, they've recruited 300 data collection volunteers to help monitor 30 specialized traps that float at the surface of the water and use LED strips to draw young crabs in. In their last stage as larva, before they stop swimming and start crawling on the seabed, the creatures are attracted to the light.  

"When you haul the trap out of the water, everything drains into the bottom, you can unscrew that part and empty out your catch and take a look at what you've got," Earle told CBC's On The Island. 

Kruzus says they're catching the crabs in their larval stage because that's where one of their biggest knowledge gaps about the crustaceans exists. 

She says the project is interested in understanding what drives larval patterns and abundance from year to year, and that this data can be used to determine the health of fisheries along with potential future closures.

One goal they're working toward is creating a harvesting forecasting tool.

This has been researched south of the border, where University of Oregon biology professor Alan Shanks has used a single light trap to determine that an abundance of Dungeness crabs one year is a very good predictor of another abundance four years later. 

"It's been like a very powerful tool ... where that one light trap can predict the entire coast wide commercial catch for Oregon and even into Northern California," Earle said. 

"It's not something that we've done here yet in B.C. and it's a very different system, but it still holds a lot of potential. So it's something that we're looking into doing here as well."

According to the Government of Canada, Dungeness crabs are the most important crab species harvested in B.C. and the second most valuable invertebrate fishery on the West Coast of Canada.

Crabs accounts for approximately 34 per cent of the total wild shellfish landed value in B.C., and 12 per cent of the total landed value of all of B.C.'s wild fish species, according to Fisheries and Oceans Canada.

Although Dungeness crabs are not on Canada's endangered list, Earle says people who live along the Salish Sea are saying similar things — that the abundance of crabs that were once there are slowly diminishing. 

It's an issue coastal First Nations in particular have raised. 

In 2014, the Heiltsuk, Kitasoo/Xai'Xais, Nuxalk and Wuikinuxv First Nations in B.C. launched a research project after noticing years of declining catch rates. They temporarily closed half of their commercial and recreational fisheries and found both the number and size of Dungeness crabs caught in those areas increased. 

More recently, in 2022, the Washington Department of Fish and Wildlife, alongside tribal and state managers, closed a fishery in South Puget Sound because of a large decline in Dungeness crab populations. 

According to a study conducted by University of Toronto in 2023, climate change is causing Dungeness crab to lose their sense of smell, which they need to survive.

The study found that the crabs are impacted by ocean acidification, which is the result of the Earth's oceans becoming more acidic as they absorb increasing amounts of carbon dioxide from the atmosphere.

Krzus says that "ultimately, we just want to learn more about Dungeness crab."

"We're hearing anecdotally that stocks are declining throughout Puget Sound and the Salish Sea. They're impacted by climate change. So we want to gather as much information as we can about them in this larval stage, to fill in those knowledge gaps that we don't currently have."

The project began in 2022, and data collection will be ongoing until 2032.