In the Canadian North Pole, there exists but one freshwater fish species: the Arctic char (Salvelinus alpinus). This keystone species is an indicator of ecosystem health, because it is highly sensitive to environmental changes. And, because many northerners depend on char for their survival, it also has great cultural importance. Arctic char are anadromous fish, meaning they migrate every year from the sea, up freshwater rivers, to spawn. Their epic journey is treacherous for several reasons, including the large temperature fluctuations – ranging from 0 to 21°C – that they face. Unfortunately, the future of the Arctic char is uncertain, as climate change is warming the Canadian Arctic three times faster than global averages. If the rivers the char encounter heat any further, it could doom the fish. Yet, little was known about the exact effects climate change might have on char battling to reach their spawning grounds. Given the scarcity of field stations and immense costs of research in the North Pole, a group of scientists has come up with an ingenious solution to overcome the challenges of working in such an inhospitable environment. Matthew Gilbert, from the University of British Columbia, Canada, along with biologists from three other Canadian institutions, decided to take the lab to the north and study how rapid warming could affect the char.

If it takes a village to raise a child, then it takes a community to build a lab in the middle of the Artic. With the help of the Ekaluktutiak Hunters and Trappers Organization and the Arctic Research Foundation, the team hauled a mobile shipping container to Cambridge Bay, Nunavut, and converted it into a self-sustaining laboratory, complete with state-of-the-art equipment, solar panels, wind turbines and a built-in toilet. They also brought along temperature-regulated tanks in which to test the fish. To see how climate change might impact the char, the team measured the fish's oxygen consumption and heart rate as they swam at different temperatures, by slowly heating the water in the tanks (2–5°C h–1), from 4 to 25°C. In one set of tests, the team determined the fish's ‘critical thermal maximum’ (CTmax), the temperature at which they toppled over and could no longer swim or their heart beats became erratic (a sign of cardiac failure), because there was not enough oxygen for them to survive the heat. For the second set of tests, the team investigated whether hotter temperatures would reduce the fish's athletic performance, by measuring the amount of oxygen they consume when swimming full speed, known as the aerobic scope; the harder the fish can swim, the more physiologically fit they are.

The team found that the char's heart was working at its hardest at 16°C, whereas fitness – aerobic scope – was impaired to the point that the fish were incapable of fast swimming. This indicates that Arctic char are already performing at their peak levels during their annual migrations. However, when the temperature was raised past 21°C, the char began to tip over and their hearts began skipping beats. This was a very worrying finding, as it showed that any further increases in river temperature could cause debilitating respiratory and cardiac problems and prevent the wayfaring fish from reaching their spawning grounds.

Once again, a scientific study has pointed out the damaging effects of climate change on an ecologically important species. It reveals that the lopsided rate of heating skewed to the Canadian north could have devastating consequences for Arctic char in the not-too-distant future. Without any effective environmental policies by governments or fast adaptation by the char, the physiological impairments imposed by warming will probably harm the long-term survival of these fish.

M. J. H.
L. N.
B. K.
J. S.
A. P.
The thermal limits of cardiorespiratory performance in anadromous Arctic char (Salvelinus alpinus): a field-based investigation using a remote mobile laboratory
Conserv. Physiol.
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