The blade narrowly misses your rubber air hose and hits your tank, knocking it out of his hand. You grab hold of his arm and bend it around up his back.
Spinning him around you pull on his air hose with your other hand and wrap it around his neck, pulling it tight until his struggles become weaker and weaker and eventually cease altogether.
You let go of him and he sinks to the bottom.
You may look for the harpoon and ammunition (253) or swim away to shore before the sharks home in on the smell of your blood (350).