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)
Crabs in the Chesapeake Bay are experiencing an alarming increase in cannibalism. A long-term study of blue crabs along the Maryland coast indicates that these crabs are becoming a significant threat to their own species.
Cannibalism is a known phenomenon in the animal kingdom, observed in various species like caterpillars, praying mantises, giant salamanders, and octopuses. However, the conditions under which it occurs remain largely unclear.
In this research, scientists monitored 2,687 juvenile crabs from 1989 to 2025. The crabs were tethered to posts at different times of the year and at various depths in Maryland’s Rhode River, a tidal estuary in Chesapeake Bay. After 24 hours, researchers checked for signs of predation, determining if the crabs were dead or injured. Remarkably, 97 percent of the crab deaths or injuries resulted from cannibalism, with no evidence of fish predation.
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Anson “Tuck” Hines, who led the study, expressed that while crab cannibalism was expected, the absence of fish predation was unexpected. “All the predation was due to cannibalism by other crabs,” he noted.
An adult male blue crab attempts to cannibalize a smaller blue crab on a tether.
Fisheries Conservation Lab/Smithsonian Environmental Research Center
Hines and his team determined the cause of crab deaths or injuries by examining the remains. If fish were responsible, no crab remains would be left on the tether line, but if another crab attacked, one might find crab shell fragments or an injured crab.
By the conclusion of the study, over 40 percent of the young crabs showed signs of predation. Of these, 56 were found with remains on the line, and 41 percent were injured but alive—clear indicators of cannibalistic behavior. In 3 percent of cases, the crabs vanished without a trace, but researchers suspected adult crabs were involved.
Hines’s findings suggest that areas like the Rhode River could serve as safe havens for young blue crabs. While fish rely on sight to hunt, blue crabs use chemical and tactile signals, allowing them to excavate buried crabs.
These insights could aid fisheries in better managing the blue crab population in Chesapeake Bay, which is vital as half of all blue crabs harvested in the U.S. for consumption come from this region.
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