Salt Water Edit
Salt water yabbies, also known as 'Nippers' due to their prominent white, or pink claw, are excellent bait for a range of estuarine species. Whiting particularly love nippers, but they also attract Bream, Flathead, and Sole. Even the normally vegetarian Blackfish will sometimes take a nipper.
Nippers live in underground tunnels, usually on sandbanks that tend to be exposed at low tides. Their entrance holes are usually exposed, and are usually around half a centimeter in diameter. The holes made by other species (eg: blood worms) can sometimes be mistaken for nipper holes - nipper holes are generally densely congregated though - they won't have a 'sandy cone' surrounding the hole (which can be an indication of a worm hole), nor any small sand-balls around the hole (crabs). If you stand in once spot, and can count perhaps 50 holes within an arms radius, you're probably in reasonable nipper grounds.
The normal method used to collect nippers involves a 'yabby pump' - which is basically a tube, containing a rubber 'plunger'. Put the end of the tube on top of one of the holes, and at the same time as pushing down into the sand, pull the plunger handle up. This will suck a quantity of mud, water (and hopefully nippers!) into the tube. Pull the tube out, and push the plunger handle to squirt the collection of muddy stuff onto the sand next to you.
Hopefully, there should be one or more nippers exposed. Feel free to do three or four pumps out of the same hole. Nippers usually have adjoining burrows, so you can 'suck' nippers out of nearby tunnels.
If you're a little late, and miss low tide, you can still pump nippers in up to a foot of water, but make sure you have a nice floating box (eg: a milk crate), lined with flyscreen mesh. Try and pump the slurry into the box - the water and mud will go through the screen, leaving the nippers behind.