Mud Crabs

By Sid Dobrin

Fisherman get a clear picture of the little-known, but widely distributed, mud crab.

Redfish whips its tail above the surface as it digs a crab out of the mud or oyster shell in shallow water.

As Florida anglers know, there are a lot of fish that will gladly take various crabs as bait. For tarpon, permit, cobia and redfish, we often turn to blue crabs or swimming crabs. The diminutive fiddler crab, with its outsized arm, is a common choice for sheepshead, mangrove snapper, pompano, redfish and black drum.

An often-overlooked substitute for these is the mud crab. In fact, sheepshead, black drum and mangrove snapper have a voracious appetite for the mud crab, and the mud crab has proven to be an effective and reliable bait for all three species.

The mud crab can be particularly useful when other sources of bait are scarce. Moreover, learning about the crab's life history and place in the marine ecosystem will help build your understanding of Florida gamefish habits.

The term mud crab is actually a generic term that refers to about 25 different kinds of morphologically similar crabs in the family Panopeidae. Florida anglers are probably most familiar with the Harris mud crab, also known as the dwarf crab or white-tipped mud crab, taxonomically named Rithropanopeus harrisii. The Harris mud crab, a native estuarine species, can be found along Florida's Atlantic Coast from the northern border south to Cape Canaveral. They are also abundant along the Gulf coast from Tampa Bay north and across the Panhandle coast.

Interestingly, given the crab's resilience, and its ability to survive in varying degrees of salinity, the Harris mud crab has successfully invaded many other regions. Research published in the journal Aquatic Invasions by Dominique G. Roche and Mark E. Torchin, as well as studies published by the University of Delaware Graduate College of Marine Studies, show that the mud crabs are transported globally through ship ballast water and in shellfish exports. Specimens have been identified in Japan, and throughout many European waters. Australia identifies the crab as one of the top 30 invasive species of concern. (Floridians, accustomed to lionfish, snakeheads, cichlids and countless other imports, may be surprised to know we do our share of exporting, too!)

The Harris mud crab is a relatively small crab, not growing in size exceeding much more than an inch across its carapace. Generally, the crab is a brownish- green color, but can appear a darker brown or a deep, almost-purple black, as well. The claws are different in size, but not as predominantly distinct as, say, a fiddler crab's. The Harris mud crab can usually be identified by the white coloration on the tips of the claws, though many of the Gulf of Mexico variety are darker and the white tips tend to appear as lighter brown tips rather than white. Harris mud crabs are omnivorous and are as likely to feed on decaying plant matter as they are on animal matter.

Harris mud crabs reside in protected estuarine habitats. They prefer rocky, shelly areas or areas with substantial wood debris. They cluster in oyster shells on bars and water's edge, but can range as deep as 120 feet down. Their feeding habits exploit the areas where they are found; that is, they eat what they can find where they live.

Mud crabs will eat small invertebrates like freshwater shrimp, zooplankton, bristle worms, clams and oysters, but they are just as likely to eat algae, as well as leaf and mangrove detritus. In this way, the mud crab cycles nutrients found in decomposing plant life, like mangroves. Their omnivorous eating habits contribute directly to water clarity and energy circulation in habitats, like mangroves, critical to juvenile fish populations. Given that a single mangrove area can produce as much as four tons of detritus per year, the mud crab's work as a decomposer is a primary part of the detritus-based food ecology that supports fisheries populations.

Harris mud crabs are remarkably resilient to changes in salinity levels, Roche and Torchin have shown, which accounts for their ability to survive transport in ship ballast water and to adapt to new habitats, including freshwater lakes. Adult crabs have been found in waters ranging in salinity level from 0.5 to 41.

Likewise, as the University of Delaware report shows, the crab's ability to survive over large temperature ranges allows it to more easily adjust to new habitats.

Like other crabs, Harris mud crabs lay eggs, but unlike other crabs, the mothers do not molt prior to copulation, which generally takes place during the summer. Female mud crabs will bury themselves in sand to lay their eggs; the sand allows the eggs more mobility to attach themselves to the mother's pleopods, the smaller legs. Once attached, the mother will then take shelter in a more solid environment like wood debris, shells or heavy sediment for 15-19 days while the eggs mature. Female mud crabs can lay 1,200 to 5,000 eggs at a time and may do so as many as four times per breeding season.

Mud Crabs as Bait

Mud crabs, as their lifestyle suggests, are hearty baits that will remain alive on the hook for a decent duration. They can be rigged much like one would rig a fiddler crab for sheepshead. Because of the size of the mud crab, keep in mind that forcing hooks through the carapace or squeezing the crab too tightly can crush them.

Unlike fiddlers, the mud crab's claws—both of them—are brutally effective pincers. Try breaking off either the fixed finger or dactyl portions of the claws with a pair of needle-nosed pliers before trying to rig the crab. Given their size, however, it is sometimes also easier to simply break off the claws entirely. Leaving the claws intact can result in a painful pinch. Once declawed, mud crabs can be rigged with a jighead or a hook. The best method for hooking mud crabs is to push the hook point in under the carapace at the rear leg joint and exiting through another leg joint toward the front of the crab. The difficulty with doing this is that if you put too much pressure on the hook, you will tear the legs away from the crab and the hook won't hold the bait. You can also press the hook point through the posterior underside of the crab up through the carapace. The difficulty with doing this is that the carapace can be rather tough and if you press too hard on the hook, the carapace will likely crack, killing the crab and not providing a sturdy hold for the hook. Try slowly twisting the hook point back and forth as you press it through the underside of the carapace to help bore a small hole in the shell. This tends to keep the shell from cracking.

Given the mud crab's relatively small size, a 1 or 1/0 hook usually works best. You may want to use a wide gap hook, preferably with an extra sharp point which makes hooking the crab a bit easier. If rigging with a hook rather than a jighead, you may want to add a small split shot, as well. Keep in mind, too, that the mud crab will instinctively look to dig into the bottom or find cover under shells or rocks, so be alert to potential snags when fishing rockier areas like oyster bars. A float may be placed above the hook to help avoid snags.

A note on artificials: There are a number of artificial crabs on the market, but nearly all are blue crab imitators. Given the blue crab's reputation as bait—especially among redfish and tarpon anglers— this makes sense. While there are not any lures intentionally designed and sold as mud crab imitators, some of the Savage Gear TPE Manic Crabs, for example, do an excellent job of imitating a mud crab. Of the Savage 2-inch crabs, the best mud crab imitator is the Amber Glow, which is a darker brown color. However, the 2-inch crab is a bit larger than most mud crabs, so the 1-inch version makes a more applicable substitute bait. Again, the Amber Glow color best imitates the mud crab, but the New Penny and Blue Crab colors work well, too, especially when rigged with Savage's standup jighead, which gives the TPE crab the action of a retreating crab in a defensive posture. The DOA ¼-ounce, 2-inch Soft Shell Crab—again somewhat large where mud crabs are concerned—is available in dark shades such as Motor Oil and Brown. Berkley's Gulp! Saltwater Peeler Crab lures do not come in colors dark enough to imitate mud crabs, but their shape and scent are certainly attractive to crab-eaters. Fly fishermen, of course, can choose from many yarn- or felt-body crab patterns, and customize accordingly.

Catching Mud Crabs

Catching mud crabs is a relatively simple endeavor. The Harris mud crab can be found in rocks, shell piles, mangrove roots, pilings and oyster bars. Simply flip over a few clumps of exposed shell, rocks or oysters and the crabs will scurry for cover. If you break open a clump of oysters, dozens of the smaller, juvenile crabs will run out like a nest of disturbed spiders. The larger, bait-sized crabs tend to hole up under the clumps, making it easy to locate them. You may find some nice sized crabs tucked deep in the oyster clumps when you break them apart.

Be sure to wear heavy gloves when gathering mud crabs. These little crabs pack a nasty pinch, so you'll want the protection of a good fillet glove or mate's glove. Neoprene gloves are not the best for mud crabbing as the crabs' aggressive pinching will tear the gloves. Likewise, given the mud, oyster residue and other slimes, you may not want to use a pair of gloves you want to last. I prefer the orange wet-grip utility gloves because of their price and my lack of concern for their well-being.

Storing mud crabs is fairly easy, given their resilience. I find that just putting a handful of them in a coffee cup with a lid or any other closeable container with a bit of water will keep them alive and handy for the day.

One final note about gathering mud crabs: The Harris mud crab looks a lot like a juvenile stone crab. Young stone crabs that have not yet matured to a size of more than an inch may be colored dark purple or dark tan, which looks similar to the body of a mud crab.

Because stone crabs are highly regulated in Florida and have strict requirements for claw size and seasons, possessing a handful of immature stone crabs you mistook for mud crabs can be a costly mistake.

The easiest way to tell a mud crab from a stone crab is to check the crab's legs. A stone crab's legs have distinctive white bands no matter the age of the crab; a mud crab's legs do not have these bands. Also, a stone crab's carapace may have several white dots, whereas a mud crab will not have the dots. FS

First published Florida Sportsman September 2015