Has anyone ever thought of...
 

...Using one of those castnets to catch bait at the pier? I was thinking about using them but not sure of the practicality or the effectiveness of it... Any thoughts?

I dont think its legal to use one.

I used to use one back east for peanut bunker and it was almost impossible sitting down. Illegal here.

Good to know... If it was legal and possible it would be kinda cool. I wonder why it's illegal?

Umbrella nets are a lot easier to use from a kayak.

And they are legal

youd have to do a lot of corralling with the umbrella net though

I have used casting nets to catch mullet for grouper fishing in Florida. You need to be standing and on a large platform to use them. The word impossible comes to mind when I think of doing it from a sit down position on a kayak. To much body roll to sling the net.