The California Abalone is a big gastropod and adheres to the rocks it lives on very tightly. This makes removal of them a tricky process. When the fringe of the abalone detects a visitor, the thick muscle pulls the creature tight against the rock. So to get them off the rock you need to slip one of these stout abalone irons under the shell very quickly, surprising the abalone and not allowing them to suck down tight. The edges are rounded so that it doesn't cut the abalone.
There are a wide variety of abalone irons, but it is probably a good idea to pick one with a built-in gauge. Divers are required to carry a measurement device with them whenever diving for abalone and having it built-in to the iron helps.
The other thing shown in this picture is a floatline. This one I made by feeding some fluorescent orange line through a length of polyethelene tubing. The ends are sealed with some plugs with a stainless steel ring at each end. I put some heat shrink tubing on there to neaten things up. The float line is then tied to the end of the abalone iron. It does not float enough to lift the iron, but it does float up and mark the spot where the iron is. So, when diving in rough murky conditions where the swell and current are moving you about, you may find an abalone lurking but not have enough breath left to spend time to remove it from the rock. Or you may want to come back to the spot for a second look. So all you need to do is drop the iron right there and surface for another breath. Then when you are ready, follow the line back down to where you were.
The float line also allows you to determine how deep you are diving or how deep the water is where you are. I'd consider it an essential accessory for any abalone or sea urchin diver.
