This discussion made me look up an anecdote from Peter Benchley's nonfiction book Shark Trouble, in which he recounts an encounter with an OW in the Bahamas during a 1980s TV shoot. The trouble started when a crewman on the boat decided to go fishing while the divers were in the water; a hooked tuna shot between Benchley's legs, wrapped the leader around his ankle, and dragged him down. After getting loose, an OW took an interest in the wounded Benchley, who had a sawed-off broomstick for fending off sharks. The narrative makes me wonder about how effective a "poker" would be against an OW:
"I raised my broomstick and held it out like a sword, waving its blunt tip back and forth to impress upon the shark that I was a living being armed with the weapons and determination to defend myself.
"Longimanus was not impressed ..."
Personally, while having something to establish personal space with is all well and good, I have the feeling that it has to be combined with an offensive posture. Something holding position and lashing out with a pointy appendage is still on the defensive and potentially prey; something swimming right at the shark is another animal willing to confront it on even terms.