Warmer Water Poses Threat to Gulf of St. Lawrence


Warmer waters pose threat to province’s seafood stocks


Sept. 28, 2018

A University of Washington study shows the Gulf of St. Lawrence is losing oxygen faster than almost anywhere else in the world’s oceans, threatening a range of species vital to the Maritime economy.

Published last week, the study found the decline to be directly connected to climate change, as increased carbon dioxide from urbanization and industry seeps into ocean currents and flows into freshwater regions.

Study leader Mariona Claret said water from the Gulf Stream, which flows northwards along the eastern coast of North America, is filtering into the St. Lawrence Seaway as the Labrador Current – which flows southwards toward the Maritime region and typically blocks the entrance of gulf stream waters – weakens.

In turn, temperatures rise in deep-water areas of the Gulf of St. Lawrence, producing a decline in oxygen levels.

“The change is being amplified in this area because now what’s happening is that the Gulf Stream is blocking the Labrador current from transporting oxygen-rich waters toward the Grand Banks,” Claret explains.“Warmer water then enters the Gulf which lowers the oxygen level.”

Katja Fennel, a professor of oceanography at Dalhousie University, says the lower oxygen levels are unsuitable for species such as Atlantic wolffish, Atlantic salmon, Atlantic cod, and snow crabs, who dwell in lower levels of the gulf.

“Some species are better at withstanding lower oxygen levels than others,” she says. “But if these oxygen levels continue, Atlantic cod, for example, will not be able to thrive because of oxygen levels.”

Some of these species are crucial to New Brunswick fisheries. According to Fisheries and Oceans Canada, snow crab, is the second-most valuable commercial fishery in Atlantic Canada.

“The crabs are  also the least resistant to low oxygen levels, though,  which poses a problem for them in areas of the gulf,” says Fennel.

She notes that changing oxygen levels may lead snow crabs to migrate to other areas in the gulf, forcing commercial fishing zones to be redrawn.

“It could have an impact for fishing, yes, but it’s difficult to say where they would relocate and how that would be accommodated for fishing,” Fennel says.

Fennel says snow crab numbers dipped  in 2012 as a result of warming temperatures, but notes that the changes in temperature won’t always be consistent.

“There’s a lot of variability in the ocean, so some years oxygen will be low and some years it will be high. But we do know that, on average, the levels are declining, which in time-scales of three to four decades will pose problems for the fish.”

Declining oxygen levels in the gulf have been monitored for years. Fisheries and Oceans Canada has tracked rising temperatures in the St. Lawrence area since 1920, and began following oxygen levels in 1960.

In 2005, the department reported that oxygen levels declined dramatically, but could not specify the cause.

“What we show is that much of this change is related to climate change, and is associated with the carbon emissions that are released into the atmosphere,” says Claret.

“This is happening now,” says Fennel. “I can’t tell you whether it’s going to be in five or seven years when something really bad happens, but we’re talking about within our lifetime.”