Another possibility might be that this is related to the mass strandings we see from humboldts occasionally, and that it really wasn't all that healthy. Still, the idea that Dosidicus gigas forages in shallow sand is appealing.
Rather bizarre; not what I would have considered to be normal ommastrephid behaviour. It likely has jetted water through to funnel to help excavate that depression within which the head, arms and tentacles are sitting, though why it would do this in such shallow water is beyond me.
I have observed Humboldts in shallow water in the morning about 9am patrolling the shoreline. They went back and forth several times and did not strand. I think that the small ones will cruise the shallows for the blue crabs or flounder in close.
I saw two last month in two feet of water in front of my house. There were a couple of them beached at the time though. the ones I observed in Gonzaga Bay in Baja CA were no injured and were cruising in formation in 1m of water on the edge. It dropped off to 6m very quick then stays about 10m to the edge of an underwater canyon about 3 miles to the south. They did not appear distressed in any way and you could see the eye rotate up at you when they swam by.
I dont know what it means I can only report my observations
I wonder if you put bait out every morning if you could "train" them to visit daily. I was thinking about something like the racoons and skunks in the parks that get used to humans feeding them ... Then you could get out the camera and SHARE some of your "observations" ;>)
If they could indeed be "trained" to recognize that they are being fed in a certain area at a certain time, you could also see whether or not more will actually come in to the coastline to the feeding site, which might reflect on true pack behavior and possibly communication of some sort.