Crooks in a Crab Pot

By KENNETH W. ABLE | Aug 02, 2017
Courtesy of: Kenneth W. Able An adult green crab, an invasive species from Europe, feeds on bait in a crab pot in the murky waters of Willitt Creek near the Rutgers University Marine Field Station. The photo was taken with a camera mounted at one of the entrances to the pot.

Most people in the bays and estuaries of coastal South Jersey, including places such as Barnegat Bay, have concerns about someone stealing their crab pots or lifting the blue crabs in it. This applies to commercial fishermen as well as the recreational potters. What neither of these groups realizes is that there are probably thieves in their crab pots as well. And these thieves often go undetected even though they are stealing during the day and night and at all stages of the tide. These thieves are the ones that steal the bait from the crab pots.

We learned about these thieves by placing a video camera in one of the mouths (tunnels) of a typical pot for blue crabs and dropping it into Willitt Creek with a feed that was attached to a monitor in my office. This approach allowed real-time observations and recording and also prevented me from getting a lot done when there was interesting behavior in the crab pot.

This short, 3,480-foot creek is shallow (4 to 6 feet deep) and narrow (20 to 30 feet wide), and is located near the Rutgers University Marine Field Station just inside Little Egg Inlet. The thieves we caught on film included small blue crabs, other kinds of crabs, shrimp and fish. One of the most common is the green crab (2.5 to 5 inches long, with lengths estimated relative to the size of the crab pot mesh), an invader from Europe. This crab climbs up on the bait bag in the center of each trap, and reaches in to tear off small pieces of the bait, typically menhaden. It can be collected unless it is so small that it slips through the mesh when the trap is retrieved. Green crabs are usually most abundant in crab pots in the spring of the year when the temperatures are cooler.

As the temperatures warm up, the small, local mummichogs (2.5 to 4 inches long), the same ones used for fluke fishing, become common in the pots. They can be quite abundant with up to 18 observed at one time. They feed on the bait by grabbing it through the mesh and tearing off a piece with a vigorous shaking of the head.  Sometimes they are small enough to get through the mesh of the bait bag to feed directly on the bait. These fish are seldom detected, like small green crabs, because they slip through the mesh of the outside of the pot when it is retrieved.

Other bait predators that are seldom encountered include shrimp, which can be observed all over and inside the bait bag. Small mud crabs can also be seen with the camera, no doubt attracted by the bait as well, as are whelk and tautog. Small blue crabs that also escape through the mesh or the escape ring have been spotted, too. Others not likely to be seen with the camera include sand fleas or amphipods.

Sometimes it is quite crowded in the pot with other kinds of animals that probably do not steal bait. Diamondback terrapins are no doubt attracted to the bait but can not easily get to it in the bait bag. These are less common than they used to be because the turtle excluders in each of the tunnels prevent most from entering. Small black sea bass (2.5 to 3.5 inches long) can also be common, potentially attracted by the pot itself, as they are a structure-loving species. Also, juvenile fluke (6 to 8 inches long) that were probably spawned in the preceding fall can be found in the pots in the creek in late summer and early fall. Potentially they are attracted by the shrimp attracted to the bait.

The dominant creature in the pots, not surprisingly, is the blue crab. These range from 1.5 to 6 inches long and are composed of juveniles and adult males and berried females, the latter carrying eggs on their apron during June and July.

There seems to be a strict hierarchical behavior in the pot community. From our video observations, the fish, of all kinds, avoided the blue and green crabs. This changed, however, when the crabs tore a piece of bait from the bait bag. Then the mummichogs would crowd around and try to steal the bait from the crab. Individual mummichogs did not try this. The mummichogs also appeared subservient to the slightly larger black sea bass, which chased them away from the bait bag, even within the small confines of the crab pot. However, when only mummichogs were present, both males and females (which could be distinguished by the different color patterns) would become territorial around the bait bag.

Green crabs were frequently observed to fight among themselves over a piece of bait pulled from the bait bag. Blue crabs were also aggressive to each other, usually around the bait. On occasion blue and green crabs reacted aggressively toward each other around the bait bag or when a piece of bait was pulled from the bag. At other times individual blue and green crabs retreated to a corner of the pot and remained there, perhaps because they had eaten their fill.

It should be noted that many of the bait thieves in these observations in a creek may not occur in crab pots set in deeper water. For example, mummichogs much prefer shallow or “skinny” water and do not occur in deeper water.

While the crooks that steal the bait in a crab pot may appear to present a problem, they might also increase the effectiveness of the pot. After all, blue crabs rely to a large extent on the sense of smell to detect food, mates, etc. Thus when a fish or another crab tears up the bait in a pot, it probably is spreading the smell of the bait over a larger area with tidal currents, not unlike a chum pot that spreads the bait and the smell of the bait around a broader area to attract target fishes such as winter flounder.

There may be broader implications of these observations as well. First, large numbers of blue crabs are removed from the fishing area, but we don’t know the effect. Is it possible that thinning out the crabs during potting enhances the growth and survival of the other crabs in the system as the larger ones are removed? Or does the removal of a large number of crabs influence the amount and abundance of food that they normally feed on? Second, it is clear that large numbers of fish, such as menhaden, are transported from the ocean, where most of them are caught in the bait fishery, into the estuary. They arrive there when bait is stolen from the crab pots and fed on by many of the fish and crabs mentioned above. This old bait is also dumped into the estuary when it is removed after the traps are retrieved, and then new bait is added. This may occur as often as every other day, depending on how frequently crabbers checks their pots.

How much old bait is added to the estuary is also a function of how many crabbers there are and how many pots they are fishing. In some ways, we are treating our waters like feed lots for blue crabs, which we feed until it is time to harvest them. All of these are examples of how the water surface is “penetrated” and influenced almost daily by humans, which influences the underwater world of the estuary.

Kenneth W. Able is a marine biologist and director of the Rutgers University Marine Field Station in Little Egg Harbor. This story and others about events underwater are part of a forthcoming book by the author on the natural history of the Mullica Valley to be published by Rutgers University Press.




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