In the "A Most Amazing Squid Tale, Part 2 of 9", emma sent in this question in the comment section:

"How do you know the squid stay active in that layer and aren't just resting?"

This is what she read that prompted the question:

In one case, we caught a squid on the bottom at 300 meters (about 900 feet) and found the oxygen concentration there to be less than 10% of that at the surface – that's our working definition of the upper edge of a midwater zone of low oxygen known as the oxygen minimum layer (OML).

Although we know that squid must spend a lot of time in the OML, a place hostile to their fish predators (especially tuna), this was the first time that we had ever actually caught a squid at a known depth at exactly the same time and place where we found oxygen to be extremely low. We think that squid forage within this hypoxic zone, but we have no idea how they manage to stay active for long periods without an adequate oxygen supply

That's a really important question. The tags we use record depth at intervals ranging from 2 minutes to 1 second. There is no difference in the amounts of rapid vertical movements at the surface or in the hypoxic zone with data sampled at 2-minute intervals -- so the squid are not inert. It's possible they might be slightly impaired, and that would show up in analysis of the 1 second data -- but we haven't had a chance to do that analysis yet. But the 2-minute data show that they are not just resting. As far as the squid that was caught at the hypoxic depth -- we don't know for sure if the squid aggressively attacked the jig or not, but the squid must voluntarily grap the jig to be caught. So the squid was at least active enough to do that.