Cannibalistic Blue Crabs Are Eating Their Younger Peers in Part of the Chesapeake Bay

The findings by Smithsonian researchers could help experts better manage this crustacean’s population. The creatures play important roles in the local ecosystem and food industry

Mary Randolph | Correspondent

March 18, 2026

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Young blue crabs find refuge from many predators in the mid-salinity waters of some spots along the Chesapeake Bay. But there, they face another threat: Getting eaten by their older peers.

At one of those sites east of Washington, D.C., adult blue crabs seem to be behind practically all the feasting on juveniles, according to a 37-year-long study published March 16 in the journal Proceedings of the National Academy of Sciences. The findings also hint that the shallowest waters are the safest zones for youngsters, an insight that could help fisheries managers protect the species from itself.

“We expected that we would see a mix of fish and cannibalistic blue crabs as the sources of mortality for these crabs,” study co-author Tuck Hines, a fish ecologist and director emeritus of the Smithsonian Environmental Research Center (SERC), tells WHRO’s Katherine Hafner. “We were surprised that we found no instances of fish predation.”

Blue crabs are well known for their cannibalistic tendencies. But they’re often on the run from fish like striped bass and red drum that dwell in high-salinity waters of the lower Chesapeake and low-salinity waters of the upper Chesapeake. To avoid becoming a meal, juveniles often spend time in places with a salt level somewhere in the middle. But researchers didn’t know how predation by their own kind versus by fish affected the species’ population, which could help experts better sustain the crustacean’s numbers.

So, from 1989 to 2025, Hines and his colleagues spent warmer months of each year placing nearly 2,700 young crabs in the Rhode River, a roughly 1,200-acre tributary with a maximum depth of about 16 feet. Each juvenile was attached to a roughly 3.2-foot-long tether line bound to a stake and placed in the water. After 24 hours, about 24 percent of the animals had been eaten by other crabs and 17 percent had been attacked by them, determined by marks on their bodies. In all, 97 percent of deaths or injuries stemmed from adult blue crabs. The remaining three percent were missing, but the researchers assume larger crabs took them.

“We’ve recorded a few of the tethering experiments with a high-resolution sonar,” says study co-author Matt Ogburn, an ecologist at SERC, in a statement. “In the sonar videos, most fish didn’t show any interest in the tethered crabs, and only adult crabs attacked them.”

Smaller crabs were more vulnerable to attacks than bigger juveniles, the team found. However, the shallowest tested waters—around 6 inches deep—provided somewhat of a safe haven for all young animals. There, they were 11 percent likely to be eaten by an adult, compared with 37 percent at the greatest studied depth. “These near-shore shallows, the knee-deep water, is an important depth refuge from cannibalism predation,” Hines tells Cody Boteler at the Baltimore Banner.

Blue Crab Cannibalism

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But these areas are at risk. People are building hardened shorelines and seawalls to protect coastal land from rising seas and erosion, and the structures are encroaching on important shallow marine habitats.

Still, the study will help experts better manage the blue crabs’ population. Their numbers have been declining; a survey last year found that the population dropped to its second-lowest estimate since annual data collection began in 1990.

“Everybody appreciates blue crabs as important food, but also, they’re really important as major predators in the system themselves,” Hines tells WHRO. “They’re helping to regulate the ecology and the food web of the bay.”

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Mary Randolph is a former editorial intern with Smithsonian magazine.