Walruses have awesome faces. (Photo credit: Wikipedia)
If you’ve ever wondered why walruses have mustaches, the answer is that walruses use their sensitive vibrissae whiskers to find delicious benthic organisms to snack on. But do walruses only eat stuff living on the sea floor? Why no, no they don’t. Sometimes, walruses eat seals.
Near Halloween, I read a rather spooky paper from 1960 that claimed that walruses can either be facultative or obligate seal eaters (the paper called the obligate seal-eaters “carnivores”). I haven’t seen any recent literature contradicting Fay (1960), so here is an apparently accurate bit of spooky information for you:
“The obligate carnivore has never to my knowledge been observed by a biologist; the description of this type is based entirely on verbal reports from Eskimos. The obligate carnivores or “rogues” are said to be solitary bulls that feed principally or exclusively on vertebrates. In contrast to the facultative type, which is distinguishable from non-carnivores only by the stomach contents, the obligate carnivore has often a characteristic external appearance. It is relatively lean and slender, with shoulders and forelimbs appearing unusually large and powerfully developed; the chin, neck, and breast are impregnated with oil from frequent contact with seal blubber, and the oxidized oil imparts an amber colour to these regions and to the tusks (cf. Brooks 1954, p. 57). The tusks are exceptionally long, slender, and sharp-pointed, and their labial surfaces are covered with scratches. The exceptional length of the tusks might be due to a lack of the attrition which normally shortens the tusks of benthic feeders (Fay 1955, Mansfield 1958).”
So, there are “rogue” walruses with extra long tusks running around the Arctic, practically bathing in the blubber of the seals they kill. That’s bananas! But even when we ignore the rogues, normal walruses also eat seals sometimes, especially when other prey are hard to come by. And a decade ago, Rausch et al. (2007) predicted that increased sea ice loss would drive increased seal consumption by normal walruses.
You might be wondering why epic walrus-seal battles are interesting from a parasite ecology perspective. I’ll tell you! In the Arctic, there exists a parasitic worm called Trichinella nativa that infects many mammal species, including humans. I’ll talk more about Trichinella next time, but for now, let’s focus on transmission to humans. Humans in Arctic regions sometimes eat walruses, and because cooking walrus meat is not the norm, outbreaks of Trichinella nativa sometimes occur in Arctic populations. This has not been a huge risk, historically, because walrus populations generally have low prevalences of Trichinella infection. But apparently people avoid eating rogue walruses because their high seal diets make them more likely to be wormy. Similarly, Rausch et al. (2007) warned that in a warming world, Trichinella spillover from marine mammals to humans might become more common due to increased seal consumption by facultative seal-eaters.
The moral to today’s story is: you are (infected by) what you eat. And if climate change changes what you eat, climate change can also change what you’re infected by.
Fay, F.H. 1960. Carnivorous Walrus and Some Arctic Zoonoses. Arctic, 13(2): 111-122.
Rausch, R., J.C. George, and H.K. Brower. 2007. Effect of Climatic Warming on the Pacific Walrus, and Potential Modification of Its Helminth Fauna. Journal of Parasitology, 93(5): 1247-1251.