Small temperature changes can have disproportionate negative effects
Alex Rose-Innes
A new scientific study published in Science Advances suggests the marine ecosystem already reached tipping point 17 years ago.
The study proved that salmon in Norway, the country providing 55% of the global supply, did not return to sea from their spawning grounds as usual – a phenomenon driven by climate change, warming of the ocean and lack of food.
The body size of more than 52 000 of the species were measured during the study and showed how it was decreasing, just as fishermen had been reporting for many years. This impacts not only this species, but could have adverse effects on all marine ecosystem wildlife.
Marine biologists compared salmon sizes from 1989 to 2016, using data from various research centres to investigate salmon stunted growth. Also, for the past three decades, fishermen in Norway provided scale samples from their catches to fisheries for research purposes. Salmon growth is measured in scale sizes on their bodies. Scientists expected that the change would occur gradually and was shocked by the latest data.
The shocking truth
Marine researchers said zooplankton, food for many marine species, had been reduced by 50%. This saw not only salmon, but also mackerel growth collapsing, especially in the North Atlantic Sea. Rising sea temperatures and the loss of frigid arctic water flowing south each year, could be blamed. As a result of climate change, it had been replaced by warm, nutrient-rich water, which researchers say resulted in widespread changes throughout the entire ecosystem.
“… as things warm up, the food web has shifted in ways and salmon become food-limited.” – Peter Westley, marine biologist.
A global catastrophe
Research ecologist, Lisa Cozier, was quoted in The Scientist as “not surprised by the findings.” Similar decreases in body size with increasing temperatures had also been documented in certain Pacific salmon species and not only the Atlantic salmon.
Scientists had for a long time suspected that climate change could bring about ecological systems change, rendering it increasingly fragile, but not so fast. Last year’s United Nations Climate Report identified 12 tipping points which could lead to irrevocable harm to certain ecosystems and spur further climate change. However, the impacts of these ecological shifts are still poorly understood and researches admit “there is still a lot we don’t know about the mechanisms.” Human activity, parasites and predation could also play a role.
Another recent scientific study found a genetic component to early salmon maturation directly and indirectly affected by commercial fishing in oceans. Salmon in rivers remained smaller in their early growth cycles making them less attractive to fishermen. Also, fishing for capelin, (a favourite food for salmon) to be used at salmon farms, reduced the amount of food available to salmon at sea.
Genetic analysis and the future
Ancient DNA analysis could be the answer to salmon management in future to show when shifts in the marine population will occur. Researchers admit that merely predicting cycles is too uncertain.
Genomic analysis of ancient chum salmon bones and cultural knowledge suggest that people in the Pacific Northwest managed fisheries for thousands of years by harvesting males and releasing females.
Scientists are now collaborating with the Tsleil-Waututh Nation, people who have inhabited the northwest coast of North America for millennia, to understand how local indigenous communities managed salmon fisheries for thousands of years without exhausting them. From ethnographic surveys and genetic data from ancient remains, it was concluded that fishers harvested mostly males.
“Without the DNA stuff, we wouldn’t be able to trace the history of this indigenous practice,” says Simon Fraser University archaeologist, Thomas Royle, told The Scientist. “And without the Indigenous knowledge, if we just discovered a bunch of male salmon, we wouldn’t have known what happened.”
Lia Chalifour, a salmon ecology and conservation doctoral student, said that these collaborations are the future of ecological studies and require an investment of time and openness to new ways of seeing and understanding the world.
