Boat traffic = zero. Yes I have an SMB but that is of no use at 3am when the closest humans are working in a grain terminal loading bulk freighters approx 1km away. Rules out noise makers whistles screaming shining torches for help. Entry (other than walking over the sand dune of death to get there) is benign straight off the shore walk in.
Why Night diving at 3am - insomnia. Chronic infuriating insomnia. Why solo? Most normal humans are in bed sleeping and don't appreciate me ringing them at midnight saying "Hey, what are you up to? Feel like going for a dive?"
Why the stopping diving solo there - geographically I'm in a shark "attack" hotspot. When I have some viz - the viz is usually pretty crappy here to begin with - I've been lucky enough to have two GWS cruise past and be in awe of their power and grace - however....
It's not actually our GWS that I'm conscious of, it's the fact the grain jetty has been the site of idiotic fishermen catching tiger sharks and hacking them to bits leaving their carcasses on the beach or under the jetty. What ever bumped me - could have been a sealion could have been a harmless port Jackson shark, could've been a tiger - hit hard enough to spin me around and drop my torch. By the time I recovered it whatever the bump came from was not visible when I did a light sweep (and admit got heart rate back to semi normal) I decided it was prudent to leave the water - call my own dive if you will.
Why do I worry more about Tigers than GWS? - late 1960s my fathers buddy was chomped in half by a tiger. I don't recall much of the incident (I was three) but I do know 50 years later he still seems uncomfortable talking about it. He didn't stop diving for another 20 years - I adjusted my night diving time to when there are usually other divers around and people on the beach.
I still dive there - sometimes solo when I know other divers will be around - or with a buddy who doesn't mind 8pm dives. I just don't like being "bumped".