It's just my speculation that they were going to fish, but if it turns out to be the case, the psyche of the hunt might explain the human factors behind their decisions.Me too, but she's an experienced spearfisher, and I think that they try to minimize carrying extra tools.
For example, the victim going down on a second dive by herself because there was only one tank remaining. I wonder if that was intended to be the spare tank for the first dive.