"Shore leave" is the time sailors get off the ship, and this tiny poem catches that moment of release. The speaker has reached a port, and the first line, "A port to drink in," states the plan plainly: land, a bar, a drink. It sounds relaxed, almost like a shrug.
The second half is stranger and more interesting. The speaker says the fish "left my head and hands," as if the work and the sea had been living inside the body, in the thoughts and the labor of the fingers. The poem suggests a fishing life, though it never says so directly. Now those fish are handed back to "their sea of mischief," a playful phrase that makes the ocean sound unruly and a little wild.
The mood is wry and loose. There's relief in setting the work down, but also a hint that the sea still has a hold on the speaker, since it takes a drink to push it out of the mind.