WHat is the THEME of this POEM???HELP?

Question

PLEASe can you please help me finding the THEME of this poem:

The Shark

He seemed to know the harbour,
So leisurely he swam;
His fin,
Like a piece of sheet-iron,
Three-cornered,
And with knife-edge,
Stirred not a bubble
As it moved
With its base-line on the water.

His body was tubular
And tapered
And smoke-blue,
And as he passed the wharf
He turned,
And snapped at a flat-fish
That was dead and floating.
And I saw the flash of a white throat,
And a double row of white teeth,
And eyes of metallic grey,
Hard and narrow and slit.

Then out of the harbour,
With that three-cornered fin
Shearing without a bubble the water
Lithely,
Leisurely,
He swam --
That strange fish,
Tubular, tapered, smoke-blue,
Part vulture, part wolf,
Part neither -- for his blood was cold.

Answer 1

the topic of the poem is a shark, the theme could be 'life', as in the life of the shark

Answer 2

um, i might be being really thick here, but isn't the theme a shark?