In the poem "Sea Fever" by John Masefield what call does the speaker hear?

This is a poem that is all about the pull of the sea upon
us and how the speaker of the poem experiences "sea fever" as he feels an uncontrollable
desire to go to the "lonely sea and the sky." The "call" that he feels is obviously
related to this and is mentioned in the second
stanza:

I must
go down to the seas again, for the call of the running
tide

Is a wild call and a clear call that may not be
denied...

Having obviously
spent so much of his life by the sea or on the sea, this die-hard sailor finds that he
cannot live without it and that the "call" creates an impulsive desire to return to the
sea. Let us consider how this call is characterised: it is a "wild" and "clear" call
that cannot be "denied" by the speaker. Note how the words "wild" and "clear" create a
picture of the wildness and emptiness of the sea, creating a spirit of adventure which
is very attractive and characterises the speaker's thirst for a return to that adventure
and wildness that he has experienced in the sea before.