The poem is built around "by-catch," the fish and other sea creatures hauled up in nets by accident and usually thrown away. The speaker looks at a huge, unwanted load and asks who will take responsibility for it. "Sign for it" makes the question sound like a delivery receipt or a bill, as if death on this scale were just paperwork nobody wants to own.
The line "Some land must pay" suggests a cost that can't be avoided, though the poem doesn't say who or what that land is. It could mean a place, a community, or the earth itself. The final line, "I count the stations of the sea," echoes the stations of the cross, the sequence of steps in a story of suffering. Judging by that phrase, the speaker treats the waste almost like a religious burden, counting it out in a kind of grim ritual.
The mood is quiet, guilty, and uneasy. The lines are short and bare, so the questions hang in the air without any answer.