But can offer some general observations. Using 200hz according to the display?There are a few patches of much longer tails on the main picture, but was the boat rolling much? The way that they are broken up makes it look like it may have just been boat roll. or a tight turn to go back and look?  Easy to tell at the time, you feel the roll, see the longer tails. If, however, the boat was not rolling, that would indicate harder bottom. So you are driving across broken bottom of hard patches and sand. You probably understand this already. Bottom lock is very good at separating growth on the bottom from the bottom itself, but it looks to extend too far off the bottom to be coral? Normally you would expect coral/sponge growth to reach up no more than about 1.5 m on bottom lock, usually under a metre. When we were using bottom lock to set pots in deep water, you'd have your bottom lock dialled right down to the smallest range , maybe only 2 fathoms on some machines, or 2 metres if metric units selected.Looking for growth less than a metre high, to indicate live bottom, and hence, crayfish.  Certainly a high, dense bottom lock reading. I'd be sort of excited to get that. Right in the middle of the first picture, it actually looks like very much like deeply ledged and broken bottom, but the tails under it are short, so probably not. 

so, overall, maybe just very dense aggregations of small fish, with a few larger ones in attendance.