Arctic foxes are certifiably cute, and certifiably in trouble. Several populations are vulnerable to incursions by other fox species like red foxes, spreading into Finland, and others are experiencing mysterious population declines. One group of researchers set out to determine why Arctic fox populations in some locations were dropping so precipitously, thinking they would find a pathogen or similar explanation, but instead what they discovered is chilling: like many animals worldwide, Arctic foxes are suffering from mercury poisoning.
Mercury continues to be used in a wide variety of consumer products and manufacturing processes despite a global commitment to reducing mercury levels in the environment, in recognition of the fact that this metal can cause serious health problems. For animals like Arctic foxes, the problem is especially acute, because they are subject to a process called biomagnification. Mercury pollution enters the world’s oceans (the world’s mercury content has doubled over the last 100 years), where it accumulates in microorganisms eaten by fish, who in turn develop a mercury buildup.
When those fish are eaten by seabirds and seals, they carry a toxic load with them. Arctic foxes bear the brunt of the load when they feed on seabirds and seal remains, consuming mercury along with their meals. The metal causes problems like infertility, death in young foxes, neurological issues and poor coat condition, which can be a big problem for animals living in the frozen regions of the world. Over time, mercury poisoning has taken its toll on Arctic fox populations living in the coastal regions of the world.
The researchers took a look at four populations of foxes. One was on Mednyi Island in the Bering Sea, where declines in fox populations have been noted with alarm. Other samples came from coastal and inland Icelandic foxes, and the researchers also took a look at museum specimens from the Commander Islands. They examined the hair and skin, when possible, of the foxes, because hair creates an excellent record of exposure to toxins, as it will hold on to them for an extended period of time, providing a kind of Rolodex of which toxins the animals have been exposed to during their lives.
In the study, the researchers found that foxes are being exposed to more mercury than before, over an extended period of time, which is a recipe for problems in both the current fox population and future generations. Pollution is an acute problem for coastal foxes, because their primary food sources are laden with the metal. Conversely, while the inland Icelandic foxes did carry some traces of mercury, it wasn’t as extreme as it was with coastal animals.
One thing they didn’t find in the course of their research was evidence of a pathogen that might explain the problem. All evidence points toward mercury as the culprit for drops in fox populations and the ill health observed in some Arc fox communities.
This has important implications for conservation strategies. Tragically for coastal foxes, the most efficient way to direct conservation efforts is to focus on inland fox populations. By doing so, scientists can help build a stable and diverse gene pool, protect the species and reduce the risk that they’ll vanish entirely. Coastal populations, meanwhile, would be very difficult to help because their diet is so dependent on heavy sources of mercury that it would be ecologically challenging to address their issues.
More broadly, this study also illustrates the dangers of biomagnification and the critical need to address rising levels of mercury and other pollutants in the natural environment. Arctic foxes aren’t the only ones suffering as a result of mercury poisoning, and the problem’s only going to get worse over time, especially with all indicators suggesting that there’s no projected drop in levels of this toxic metal, even with positive steps toward interventions like an international treaty to reduce mercury levels.
Photo credit: Eric Kilby