Well spotted. believe it or not they are long tailed sea lice!
Fish caught over the next few days often had them.
For interest the camera angle allows perhaps a view width of about 5 or 6 feel in vid one, a little narrower in Duncans vid. The whole video is 35 minutes long, and we could see fish at all times. The pool is very wide and i would expect the density of fish did not vary much over a third of the river, and remember we could only see perhaps 5 feet of it on screen. lokng to both sides the fish were as thick as you can see in the video. Visability was some 4 mrt and the camera dpth of field is just a couple of meters.
We both saw some giants, fish of 3-4 ft long, you can hear my reaction as a monster went past. We saw many thousand fish, few seatrout, You can see one big one in my vid and a few eels.
Almost no par and a few flatties.
It was some experience, and we would like to take in a full size recorder, rather than the digital minicams we took on that dive.
D