Juro the carcasses from the Herring Roe fisheries are; exported for food, ground up and used for bait in crab fisheries, used as is in some longline fisheries, and some is gound for dumping back into the water to become part of the on going chain of life. From time to time when the cold storages in Alaska are grinding up "Waste" you will see big schools of juvenile Cod and Sablefish feeding by the thousands on the "waste".
I remeber somebody converted Herring from the sac roe fishery into Oregon Moist Pellets for hatchery feed the problem was that the product was too lean and had a much higher percentage of bone than normal. This caused a huge number of fish in the hatchery systems with eye Cataracts.
At first blush everything we waste seems terrible but sometimes it ain't so bad especially when its part of a well manged fishery.