Under the combined effect of global warming and human activity, the three oceans bordering Canada’s coasts are more than ever undergoing major upheavals that threaten several marine ecosystems and important sea resources, warns a Fisheries and Oceans Canada report. The Atlantic and the Gulf of St. Lawrence are not immune to these phenomena, which have accelerated in recent years.
As the United Nations Decade of the Oceans begins, worrying signals from the Arctic, Pacific and Atlantic are on the rise, according to the report. Canada’s Oceans Now, 2020. “Our oceans have all undergone marked physical and biological changes in recent years as a result of climate change and human activity – temperatures are rising, habitats are degrading, species distributions are shifting and food webs are shifting. [chaînes alimentaires] are transformed ”, we can read there.
Most of the health problems of the oceans along Canada’s coastline stem from the build-up of greenhouse gases in the atmosphere (primarily carbon dioxide) and climate disruption. “As Canada’s oceans absorb this heat and carbon dioxide, they warm and become more acidic, their oxygen levels decrease, summer sea ice in the Arctic decreases, and marine heat waves become more frequent, ”say scientists from Fisheries and Oceans Canada (DFO).
“Ocean currents and mixtures redistribute heat and carbon dioxide absorbed from the sea surface to deeper waters, causing further changes in marine ecosystems that could persist for decades,” they add.
Warming is occurring at an accelerated rate in Arctic waters, but researchers are also seeing increases in the Atlantic, as well as “successive records of high temperatures” in parts of the Gulf of St. Lawrence.
This warming affects several species such as the northern shrimp, a food resource “essential for many species” and which is the subject of significant commercial fishing. Rising temperatures also play a role in the “decline” observed in most populations of Atlantic salmon, a fish that is also an emblem of several rivers in eastern Quebec. The same goes for snow crab, which “has been affected by warming deep water, which has contributed to recent declines in some areas”.
This warming of surface waters further results in a decrease in mixing with the deeper layers of the ocean, which reduces the oxygen supply necessary for the good health of the entire oceanic food chain. This phenomenon of “hypoxia” is also worsening in the Gulf and in the estuary of the St. Lawrence, which has consequences in particular on various species of fish that cannot survive in poorly oxygenated waters.
Climatic upheavals are also causing “a reduction in the quantity and thickness of sea ice”, a phenomenon which is more and more visible off Newfoundland and in the Arctic, but also in the St. Lawrence. This decline in ice cover in winter has the effect of accelerating coastal erosion, a phenomenon clearly visible in the Magdalen Islands and in certain sectors of the North Shore and Gaspé.
Another phenomenon of increasing concern to scientists: acidification of marine environments. In the Atlantic and in the Gulf of St. Lawrence, for example, there is a constant increase in the acidity of the waters, a situation attributable to the absorption of CO.2 produced by the combustion of fossil fuels.
“In the lower estuary of the St. Lawrence, record warm temperatures at the bottom, additional nutrients from human activities and reduced oxygen have amplified the threat posed by acidification,” also warns the MPO report. . However, “this threat can be particularly serious for hard-shelled species,” insist the scientists, citing the lobster as an example. This crustacean, which sustains an entire fishing industry, has a higher mortality rate and development problems when the waters become acidic.
In addition to disrupting the climate, human activity causes various degradations of marine environments, from coastal habitats to deep waters. The MPO report cites as an example “physical disturbance”, such as fishing gear that affects the seabed, or “resource extraction”, but without naming oil and gas industry.
Federal researchers also point out that several animal species have not recovered from “overexploitation”, including herring, mackerel and capelin. Since all of these species are linked in the marine ecosystem, a decline like that of capelin “delays the recovery of cod that feed on them, and that of herring affects the health of seabirds such as terns and fish. puffin ‘. Other species are stable or declining due to the decline in the fish they feed on. This is particularly the case of gannets.
Fisheries and Oceans Canada did not respond to our interview request on Wednesday, saying no expert was available.