Polar Bears Are Finding It Increasingly Difficult To Catch Enough Seals To Survive

It turns out that polar bears have a much higher metabolic rate than previously thought, and that as the Arctic warms they are finding it increasingly difficult to catch enough seals to maintain such high energy costs.

By monitoring the behavior, hunting success, and metabolic rate of wild polar bears as they wander the Arctic, researchers have been able to accurately measure the physiological mechanisms underpinning the declines seen in polar bear numbers.

“We've been documenting declines in polar bear survival rates, body condition, and population numbers over the past decade,” explains first author Anthony Pagano in a statement. “This study identifies the mechanisms that are driving those declines by looking at the actual energy needs of polar bears and how often they're able to catch seals.”

Publishing their results in Science, the researchers found that the bears' metabolic rate was a full 50 percent higher than previous estimates. Out of the nine bears that were tracked using GPS collars and metabolic tracers, they recorded that five of them lost weight during the study period. This was during the time of the year when the animals should in fact be putting weight on, but they simply were not catching enough fat-rich prey to counteract their high-energy needs.

There is a persistent myth that polar bear numbers have been increasing in recent years and that advocates of climate action must therefore be wrong. But as with most things, the bigger picture is a little more complicated than that, although the overall message is that the bears are most certainly set to suffer.  

It is true that "officially" there are more polar bears now than there were in the 1960s, but that is simply because 50 years ago no one actually knew how many there were. The often cited figure of between 5,000 and 8,000 recorded by Russian scientists in 1956 was never accepted by scientists, and the origin of other estimates from this period are not known.

It is important to note that there are thought to be around 19 subpopulations of bears, and these populations behave and react in different ways when exposed to pressures. While some of these subpopulations might see a bump in numbers, others are certainly in decline, and the fate of many others still not known.

The fact is that the bears need sea ice to hunt and thus survive. The extent, thickness, and season that the Arctic Sea is frozen is visibly decreasing, meaning that the bears have to wander further out and go longer without food. They are simply burning too much energy that they cannot replace.