What these two poems have in common is an excellent and evocative description of nature, represented by the pike on the one hand and the snake on the other, and the way that this example of nature still has the power to induce fear and terror in everyone that comes across it, even humans. Thematically, perhaps we could argue therefore that what these poems show us is that, in spite of all of our might and sophistication as humans, it is only foolhardy to think of nature as being something we have dominion over.
If we look at "Pike," the sheer malevolence of the carnivorous fish that is utterly ruthless is something that makes the poet fear a confrontation. He fishes "with the hair frozen on my head" out of fear of seeing "what might move," and the poem ends with a terrifying sense of suspense as he imagines the pike watching him, eyeing him as a predator does its victim before striking:
Owls hushing the floating woods
Frail on my ear against the dream
Darkness beneath night's darkness had freed,
That rose slowly towards me, watching.
The pike is described as an example of nature that is so ruthless that it is a danger to everything that it comes into contact with, and the poet feels the fear of this menacing symbol of man's impotence in the face of nature's power. Note the way that the silence is described as other animals are stilled, increasing the tension as we imagine the pike rising towards the fisherman.
In "Hunting Snake," there is a similar response from the humans in this poem to the sight of the snake. They "froze half-pace" as the snake "reels past" and they "lost breath to watch him pass." The sense of relief as this snake moves on and leaves them unmolested is palpable:
We took a deeper breath of day,
looked at each other, and went on.
There is a sense of mutual assurance as the humans look at each other and breathe deeply (note the alliteration in "deeper breath of day") and then move on, perhaps the wiser for the experience and sight they have just witnessed.