Crabs are eaten by large fish, some fish-eating birds (like great blue herons), and sea turtles.Blue crabs eat almost anything, including clams, oysters, mussels, smaller crustaceans, freshly dead fish, plant and animal detritus-and smaller and soft-shelled blue crabs.The largest blue crab caught in the Chesapeake Bay weighed 1.1 pounds and was 10.72 inches (tip to tip across the carapace). While a blue crab usually weighs about ⅓ pound, the edible portion is much lower.However, they are usually harvested before they reach that size. Blue crabs can grow to about 9 inches across (from tip to tip) their hard shell (carapace).Females molt once, just before they are ready to mate. Males molt multiple times during their lives. Because they lose hard parts during the molting process, it can be difficult to determine the age of a crab. Crabs molt-they shed their hard shell-as they grow.But in the Chesapeake Bay, it may take 18 months. In the Gulf of Mexico, crabs may reach maturity within a year. Growth rates are affected by water temperature-they grow more quickly in warmer water. They reach maturity in 12 to 18 months.Blue crabs generally live for 3 or 4 years.The data are examined with respect to the reference points (from the benchmark stock assessment) to determine how the population is doing. It’s the only fisheries survey in the Chesapeake Bay that assesses population Bay-wide on an annual basis. Each year, Maryland and Virginia conduct winter dredge surveys to track blue crab population numbers.
An annual Blue Crab Advisory Report (PDF, 31 pages) developed collaboratively by the jurisdictions that manage Chesapeake Bay blue crabs helps decision makers, too. Resource managers use this number as a guide when they set regulations each year. A benchmark stock assessment completed in 2011 generated reference points for the female blue crab population in the Bay. In the Chesapeake Bay, NOAA, the Virginia Marine Resources Commission, and Maryland Department of Natural Resources work together to conduct stock assessments.In managing blue crab fisheries, resource managers look at overall trends rather than just the number of blue crabs in any given year. Blue crab populations naturally are highly variable from year to year.
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