Theories of inspiration assert inspiration is either external or internal. External inspiration would be like the Greek and Roman Muses or Spenser's Divine mimetic inspiration or the Romantics inspiration from emblematic Nature or Coleridge's divine wind: these are all external to Self. Internal inspiration would be like Locke's theory of resonating cognition, resonating thoughts, or Freud's troubled psyche or Jung's universal consciousness: these are all internal to Self.
Hughes see, feels, hears a run of salmon [the collective noun for salmon is "run"; "shoal" is the collective noun for bass], polar bears romping and dinning among the salmon, the sky, the water, the air, his fishing companion. All these external elements of his experience (based on a real fishing trip) provide inspiration. The beginning point of the deep inspiration, the epiphanic inspiration, was the run of salmon.
Hughes was fishing from the shallow waters, as one often does for salmon fishing, standing in chest-high fishing gear. The run of salmon suddenly came upon them, they were "Waist-deep in wild salmon swaying massed"; salmon brushed against their legs as they passed and came on and passed and came on and passed, group after group after group: "[salmon] That came on, came on, and kept on coming."
In Hughes' own words, these "creatures of light" carried him toward a "dazzle of blessing." The salmon became for him the inspiration of "a spirit-beacon / Lit by the power of the salmon." In a very real sense, Hughes' external inspiration of salmon of Colridge's and Wordsworth's Nature became the internal inspiration of Locke's resonating cognition that joined Hughes to a Jungian universal consciousness that was led by the "spirit-beacon" of the "power of the salmon."