Collection:  If you do fancy a go catching them yourself, they do bury themselves in sand, often in estuaries and typically they are only around at low water.  You will need a lidded bucket with water in it, and ideally a blunt thin bill hook called a vingler. A very keen eye and lightning fast reactions will help you a deal! The idea (!) is that you trap the sandeel in the blunt "eye" of the vingler with one of your fingers, often gloved. It works, honest!

Storage:  Sandeels can be kept in the bucket of sea water for a short period of time, and longer if you aerate the water with a fish tank air pump.  I know one angler with a two foot long salt water aquarium set up in his garage, just for keeping bait alive.  Most people however tap them on the head, and freeze them on a glass plate.  From this they can be removed and bagged in groups of a dozen for freezing.  Wrapping them individually in cling film means that they will defrost quickly on the mark.  Lumping them together or using paper in freezing is a bad idea - you end up with awful rubbish.

Bait Presentation:  If you have fresh sandeel, lucky you!  The flesh is firm and will take the hook well, however as with all thawed frozen baits, sandeels can split and fall apart.  Shirring elastic is important in presenting sandeels, but simply essential if using frozen baits.

Rigs or Traces:  The rig you use will depend on the target species and the local mark.  A common use for sandeel is to put them on a 3/0 hoook at the end of a long flowing trace for pollock or other big wreck haunting fish.  They also work for bass, spinning from the shore (in fact most bass and wreck lures mimic sand eels).  Some people advocate simply hooking it around the head and tying it on with elastic, leaving the entire body "swimming" behind the hook.  Others will tell you to thread the hook in from the head down towards the middle, and use elastic.  Finally I have seen some anglers hook several of them through the tail, and tie them on up along the shank of the hook, akin to a sausage of lugworms.  Given their cost around these parts, we don't do that!

Fish Species:  All predatory fish love sandeels, however a large sandeel is too big a bait for some smaller species.  Bass have a particular liking for them and they are an effective bait from the shore for a wide variety of fish, but mainly fast swimming predators.