wbuffetjr, those look like some huge very active scuds! I'd love to have a couple hundred thousand of those in my pond! Maybe this spring at ice out you can find a way to net those and I'd be happy to try them and reimburse you!

I don't know how they harvest but I suspect sweeping shallow areas with vegetation with a wide fine mesh net. Perhaps they cut out the ice in the shallow waters? Perhaps scuds congregate in 'warmer' waters in shallows in winter?