The smallest sizes of these typically have a drawstring to close off the opening at the top, but anything larger features a latched lid. Besides the increased capacity, these are better because it's easier to get bait into and out of the pen in a hurry. Also, you don't have to worry about tying the knot so tightly that it won't come undone, or so loosely that the baits will all escape.

In any case, make sure you choose one made of non-corrosive materials with the bottom ring weighted while the upper floats. This allows the pen to maintain its shape even in a swift current. The soft, 1--4-inch mesh netting allows the unit to collapse to a 4-inch height for storage. Rinse it off and let it dry before you do so to minimize odors and help it last.

If the plan is to harbor just a few odd pilchards remaining from the day before, a 2-foot wide pen will do fine. But if the intent is to store enough for a full day's fishing, that won't do at all. In that case, I would opt for the largest one my budget would allow. Understand that these things aren't exactly cheap. Even a 24-incher will command around 70 bucks, while one that's three feet around and sports a 130-gallon capacity goes for around $90. However, many is the time when I've been able to keep a dozen or more leftover baits for the next day thanks to having one at hand. They might not be as good as baits caught the day of the fishing, but they sure do the job.

For heavy-duty or more permanent use, I would save the collapsible pens for other applications and instead opt for a more rigid one. One option here is to take a white industrial garbage can with a lid. Another is to buy a standard, heavy-walled polyethylene baitwell. Significantly more expensive than the soft models, it will last a lifetime. These tanks require of course that you drill them with lots and lots of holes, so many in fact that the finished product will look more like a sieve than a container. Keep in mind that if you start your openings six inches or so off the bottom, it will allow enough water to remain in the pen that the baits won't be bruised should it have to be temporarily removed from the water for any reason. If you choose to go this route, you'll have to supply some form of flotation, unless of course, you prefer that it stay completely submerged for security. Just make sure you keep it from navigable areas if you do.

What I do is take some large pieces of styrofoam and cut them to fit around the tank, but round buoy markers fixed on a line will look more official. Be certain that they are positioned so that the tank floats evenly.

By far, you'll know you've graduated to the next level when you start to consider the next option: metal cages. Though I have known people who whipped together some coated chicken wire and an assortment of 1 x 2s, probably the best choice here is to buy one that is preassembled. Not only will it last longer, it will probably be significantly lighter than one you would build yourself.

Many of these, especially commercial versions, are kept completely submerged. I've seen some that were so heavy they required a winch to retrieve. These are placed beneath the surface not so much to prevent a hazard to navigation as to protect the contents. That much bait represents a lot of inventory and it's far from unheard of to come to the dock for a day of fishing only to find that someone has already helped himself. It never hurts to buy a lock.

How long can baits be expected to last in such a system? Goggle-eyes and runners have been known to survive for weeks on end provided that some sort of food source is supplied and they are handled properly. Often this will be little more than a bonito carcass lying on the bottom of the cage, but cut up chunks are even better. If you must touch the baits, use gloves and be gentle. Wipe off their protective coating of slime and sores will rapidly develop. Soon, they'll be dead on the bottom of the cage.

Bait pens aren't a necessity unless you are a professional. But if you like to fish with live bait and want to rest assured you'll have it when you need it, they're the only way to go--regardless if it's for big money or just plain bragging rights.