Crabs are cannibalizing one another with surprising rapacity in parts of the Chesapeake Bay
A 37-year study in the Chesapeake Bay revealed that a major predator of young blue crabs might be their own kind
A blue crab (Callinectes sapidus)
The Chesapeake Bay’s crabs are tearing themselves apart. A decades-long study of the blue crabs living along the Maryland coast suggests that cannibalism is so rife that the crabs are their own major predatory force.
Cannibalism is common among the animal kingdom—it’s been witnessed in a diversity of creatures, from caterpillars and praying mantises to giant salamanders and octopuses—but how, where and when it arises is less understood.
In this study, researchers observed 2,687 juvenile crabs between 1989 and 2025. The team tethered the crustaceans to posts at varying times of the year and at varying depths of Maryland’s Rhode River, a tidal estuary in Chesapeake Bay. After about 24 hours, the researchers would look for signs of predation—basically, if the crabs were dead or injured. Incredibly, they found that a whopping 97 percent of crab killings or injuries could be attributed to cannibalism—fish, meanwhile, were nowhere to be found.
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The fact that the crabs were preying on one another wasn’t a shock, says Anson “Tuck” Hines, emeritus director of the Smithsonian Environmental Research Center and lead author of the study. “What was surprising was that we found here no fish predation—not a single instance of fish predation,” he says.
“All the predation was due to cannibalism by other crabs,” he says.
An adult male blue crab attempts to cannibalize a smaller blue crab on a tether.
Fisheries Conservation Lab/Smithsonian Environmental Research Center
The way Hines and his team worked out what had killed or maimed the released crabs was by looking for clues in their remains. If the crabs were killed by fish, other research suggested there would be no crab remains left on the end of the tether line. Instead there’d be a fish—”sort of like fishing with live bait,” Hines explains. But if the crabs were attacked by their own kind and those crustaceans’ shell-crushing pincers, you’d expect to find bits of “carapace”—crab shell—or an injured crab at the end of the line.
By the end of the study period, a little more than 40 percent of all the young crabs tethered in the river showed any sign of predation. Of those, about 56 were killed “with remains” left on the line, the authors found, and about 41 percent were left “alive and injured”—both smoking guns for a cannibalistic crab culprit. In just 3 percent of predation cases, the crab went completely missing—but without a fish at the end of the line, the researchers couldn’t directly attribute these disappearances to any specific cause. (Still, even in those cases, the predators were presumed to be adult crabs.)
Hines’s research suggests that estuaries such as the Rhode River may provide an “important refuge” for the bay’s young blue crabs, which try to survive by burrowing themselves into the sediment. Fish tend to be visual predators, he says, whereas blue crabs use “chemical and tactile cues”—they dig around in the sediment to hunt, which might, in some areas, make them better at uncovering a hidden young crab.
The results could help fisheries better assess the blue crab stock in the Chesapeake Bay, information which matters for another well-known crab predator: us. Indeed, an estimated 50 percent of all blue crabs harvested in the United States for consumption comes from the Chesapeake Bay.
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