Cast netting is the best method for obtaining these baitfish ie, mullet, hardy head, herring (sprat), whiting etc. for more serious bait fish like scad, jigging is the way to go.
keep them alive in a bait bucket placed in the water, if your fishing from rocks or surf, try putting them in a small esky with a battery operated airater.
Most fish worth catching will take just about all of these baitfish, it's how you present your bait that will make the difference ie, unweighted, weighted, floated etc.