Researchers at the Smithsonian Institution have discovered who ate the youngest blue crabs in the Chesapeake Bay—not people or even fish, but larger blue crabs with a surprising appetite for cannibalism.
You thought your uncle Danny held the record across the ocean.
Lead author Anson “Tuck” Hines, a former scientist at the Smithsonian Environmental Research Center in Edgewater, told Scientific American they knew cannibalism was a common threat to juvenile crabs.
“Surprisingly, we found no fish predation here – no examples of fish predation,” he said. “All predation is due to cannibalism by other crabs.”
The center has spent 37 years monitoring who eats baby blue crabs. They found that where and how deeply teenagers hid varied significantly. In the mainly saltwater part of the bay, between the freshwater of the Susquehanna River and the salty Atlantic Ocean, their biggest predators are older crabs. Invasive blue catfish prefer freshwater upstream, while predatory saltwater fish stay near the mouth of the bay.
Smithsonian researchers wrote that crabs are the primary predators on the bay bottom, often digging their claws into the silt or sand where young crabs usually hide to feed. Young fish hide better in shallow grass, but once they reach adulthood, about 4.7 inches across, researchers found they can fend for themselves.
A craving for Maryland crab may be a close second. According to the Maryland Department of Agriculture, Watermen harvested approximately 20 million crabs from the bay in 2024, worth $41 million. The Chesapeake Bay Foundation’s crab count estimate for the year was 238 million, the second-lowest dredger count since surveys began in 1990. Three years ago, crab numbers hit a record low in 2022 (226 million).
They tied juvenile crabs to posts at different depths and times of year and checked their health the next day. Since fish eat their prey whole, they hope to find a fish on their line after taking the bait. Instead, nearly all forage crabs were found with shell fragments or injuries when reported. Since crabs eat by crushing their hard shells with their powerful pincers, injuries in which crabs lose body parts or limbs have been blamed on crab predation.
The paper points out: “More than 97% of juvenile crab predation is cannibalism by large adult crabs; no fish predation behavior was observed; deaths caused by physiological stress are rare (less than 1%).”
They published their findings on March 16 in the Proceedings of the National Academy of Sciences.
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