There is nothing more “Chesapeake” than the blue crab. The Bay’s signature crustacean is one of the most recognizable critters in the watershed, supporting valuable commercial and recreational fisheries. However, the blue crab population has fluctuated over time in response to fishing pressure and environmental drivers including pollution and habitat loss. Water quality improvements, seagrass restoration and proper fishery management will help maintain this valuable resource.
Why are blue crabs important?
As both predator and prey, blue crabs are a keystone species in the Chesapeake Bay food web.
- Blue crab larvae are part of the Bay’s planktonic community, serving as food for menhaden, oysters and other filter feeders.
- Juvenile and adult blue crabs serve as food for fish, birds and even other blue crabs. Striped bass, red drum, catfish and some sharks depend on blue crabs as part of their diet. Soft-shell crabs that have just molted are particularly vulnerable to predators.
- Blue crabs are among the top consumers of bottom-dwelling organisms, or benthos. They eat bivalves (i.e., clams, mussels, oysters), smaller crustaceans, freshly dead fish, plant and animal detritus and almost anything else they can find.
- Blue crabs feed on marsh periwinkles (snails), helping regulate periwinkle populations. Scientists are concerned that a decline in the Chesapeake Bay blue crab population could negatively affect salt marsh habitat, as periwinkle populations feed on marsh grasses.
Blue crabs also support a large recreational fishery in the Bay, and are the estuary's most valuable commercial fishery. Over the past 60 years, blue crabs have dominated Chesapeake Bay fisheries, with an estimated one-third of the nation’s blue crab catch coming from the Bay.
How many blue crabs live in the Chesapeake Bay?
Each year, scientists use the winter dredge survey to assess the Chesapeake Bay’s blue crab population. Maryland and Virginia scientists visit 1,500 sites from December through March, using metal dredges to pull up and count crabs overwintering in the sediment. According to the results of the 2021 survey, 282 million blue crabs are estimated to be living in the Bay.
The Chesapeake Bay Program tracks the abundance of adult female blue crabs as an indicator of Bay health. In 2021, 158 million adult female crabs were estimated to be living in the Bay, an increase from 141 million in 2020.
What issues affect blue crabs?
Harvest is a primary source of blue crab mortality in the Chesapeake Bay. But environmental conditions including water quality, weather patterns and habitat also cause the abundance of blue crabs to fluctuate from year to year. Loss of habitat, particularly of underwater grasses and marshes, is a primary concern for the blue crab population in the Bay.
More than one-third of the nation’s blue crab catch comes from the Chesapeake Bay. Blue crabs—harvested as hard shell crabs, peeler crabs and soft shell crabs—are the most valuable commercial fishery in the Bay, earning millions of dollars of revenue each year. Blue crabs also support a large recreational fishery in the region.
From the mid-1990s to the late 2000s, there was a dramatic decline in the blue crab population. This decline was thought to be due to “recruitment overfishing,” which occurs when large removals of adults result in fewer juveniles being produced.
According to the 2021 Blue Crab Advisory Report from the Chesapeake Bay Stock Assessment Committee (CBSAC), 41.6 million pounds of blue crabs were harvested from the Bay and its tributaries during the 2020 crabbing season. Commercial and recreational crabbers harvested 19 percent of the female blue crab population, which is below both the target (28%) and overfishing threshold (37%) of harvest.
Blue crabs use underwater grass beds and marshes as nurseries, feeding grounds and refuges from predators. A decline in underwater grass abundance—due to warming waters, irregular weather patterns and pollution—has been linked to declines in the blue crab population. Because they are key feeding grounds and predator refuges, underwater grass beds and marshes increase juvenile blue crab survival and growth rates. Research has also shown that denser underwater grass beds can hold more crabs, indicating both the quantity and quality of underwater grass habitat can affect blue crab populations.
Does predation affect blue crabs?
Striped bass, Atlantic croaker, red drum and other predatory fishes feed on juvenile blue crabs. A significant change in abundance of these fish populations could affect the abundance of juvenile blue crabs, and consequently the future of the blue crab population.
How are blue crabs being protected?
Water quality improvements, underwater grass restoration and proper fishery management will help protect blue crab populations and maintain the resource.
Blue crab management
Blue crabs are managed as a single species, using minimum catch size and seasonal harvest limits to meet target levels of fishing pressure. The annual winter dredge survey helps scientists determine where the current blue crab abundance and harvest levels fall in relation to the management targets and thresholds. Under this strategy, the fishing target is set to a level that should allow for sustainable harvest that allows the population to persist at an acceptable level of abundance over time.
The Chesapeake Bay Program developed its first Chesapeake Bay Blue Crab Fishery Management Plan in 1989 to promote collaboration among the three jurisdictions that manage commercial crabbing in the watershed: Maryland, Virginia and the Potomac River Fisheries Commission (PRFC). The Bay Program’s Chesapeake Bay Stock Assessment Committee has continued to provide scientific advice to fisheries managers, publishing a Blue Crab Advisory Report each year.
Current restoration goals
As part of the 2014 Chesapeake Bay Watershed Agreement, Bay Program partners committed to two goals related to blue crabs. The first goal, Blue Crab Abundance, is to maintain a sustainable blue crab population based on the current target of 215 million adult females and to refine the population targets based on the best available science. In November 2020, the three jurisdictions formally adopted a new abundance target of 196 million adult females based on model results from a stock assessment update conducted in 2017. The second goal, Blue Crab Management, is to manage a stable and productive crab fishery by working with the industry, recreational crabbers and other stakeholders to improve commercial and recreational harvest accountability.
To protect blue crabs in the Bay watershed, consider protecting underwater grasses. Boaters should follow posted speed limits and no-wake laws to avoid harming underwater grass beds and steer clear of grasses growing in shallow waters.