The video clips of the spawning sea trout are recorded in conditions where the natural behaviour of the fish has not been disturbed.
In the video we see how the roe-carrying fish digs a nest for the roe and later also a fish with milt. Dwarf males and younger generations of sea trout as well as brown trout, the freshwater form of sea trout, move actively near the spawn. At digging nutrients hidden in the gravel drifts downstream and at the spawning all roe grains will not stay in the nest; so foragers join the spawners. Nature is rational, nothing should be wasted.
Scientists have not observed that salmonids loot the spawning nest of their own species.