Where was it? You said nothing, re:"fishing 5 metre tides and a muddy shelf that regularly dries out".
All over the deeper parts of the harbour they've been around for at least 6 weeks now a person can tell a Chum by their low sideways jump.
I saw a few this AM when I was cycling along Spanish Banks-don't you check the water regularly?
Probably the Best place to see Chum jumping in late summer into fall is from the pier @ the Royal Yacht Club but since you're not a member you're not allowed in-I know a number of members so am there regularly.
In addition, you should post a photo of yourself so we can easily identify yourself with your beater aluminum Lund, as we really want to follow your every move.
Just look for a small boat with a couple old Guys laughing/having fun and catching fish-lots of us around-the Harbour, Ambleside, the Bell Buoy you name it.
I note in 35 years of living a few blocks from the beach
I have never seen anyone fishing from the beach more than once as I said it's simply not worth it as you will soon find out.