Raw oysters are usually pretty tightly sealed and it requires a knife and deft hand to crack open the shell to get at the meat. I’m not clear on how a walrus is manipulating a clam into position with his mouth, forcing the shell open, then producing enough suction just with tongue action to pull the clam out.
Is there some movie or diagram showing how this works?
The trick is that you want to know what’s going on inside the walrus’ mouth as it’s feeding.
It’s really hard to get external images of walruses feeding in the wild - you can watch videos from a 2003 paper here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC270045/ (scroll down to supplementary material for 3 videos.) - you can see how little information one might get from such videos if these are some good ones.
It’s easier to get external videos in captivity, but it still won’t show what happens inside the walrus’ mouth, and I don’t know of an animation that might show it.
But I think you’re discounting the amount of crushing walruses do as they feed - it’s not like they will daintily suck only the flesh out without touching the shell, they most likely are crushing the shells to some extent, and feeding on molluscs smaller than what you might be thinking; a common size for a prey mollusc might be 1-4 ounces. Remember that walruses are large mammals, and can probably apply many hundreds or thousands of pounds of force with their jaws.
I did a Google Video search for “walrus feeding mollusc” and didn’t find anything useful. I doubt “mollusk” will return better results, but it might be worth a try.
Thanks for the link. I’m surprised in the paper that the precise mechanics of how locates food is still open to competing theories, you’d have thought that some enterprising marine biologist PHD would have laid it all out by now.
Appreciate the responses but I’m still not clear on the process. If (per the documentation) walruses are eating 3000 to 6000 clams at a time over a few hours of feeding there’s no way each clam is being individually positioned by the mouthparts for suction extraction. There’s just no time.
From Kastelein et al. 1991. The anatomy of the Walrus head. Aquatic Mammals v. 17.3, pages 178-179.
I’m not really enough of an anatomist to judge how accurately this paper may reflect reality, but briefly summarized, the Walrus traps clams with the siphon inwards at its lips using both whiskers and lip muscles. Using the tongue like a suction pump, it can suck out the meat. It seems to do so in about 10 seconds, which is not inconsistent (although it is quite an achievement! and probably represents an unusual amount of feeding time) with feeding on 6000 clams in a day, since such an effort would take about 17 hours.
There are photos and diagrams in the linked paper - but the scanned photos are none too useful, you might be able to Interlibrary loan the paper to get a better look, but I hope they help.
ETA: I should probably also mention this is likely not as clean a process as when humans eat clams. Walruses are likely to accept a certain amount of shell with the meat, probably more so than humans would.