Produced by Matt Rath
Overview
There is nothing more “Chesapeake” than the blue crab. The Bay’s signature crustacean is one of the most recognizable critters in the watershed, and supports commercial and recreational fisheries. But blue crabs are vulnerable to pollution, habitat loss and harvest pressure, and their abundance has fluctuated over time. Water quality improvements, underwater grass restoration and proper harvest management will help maintain this valuable resource into the future.
Why are blue crabs important?
As both predator and prey, blue crabs are a keystone species in the Chesapeake Bay food web. The crustaceans are both predators and prey in the Bay’s 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. Opportunistic feeders, they eat thin-shelled bivalves, smaller crustaceans, freshly dead fish, plant and animal detritus, and almost anything else they can find.
- Because blue crabs feed on marsh periwinkles, they help regulate periwinkle populations. Scientists are concerned that a drop in blue crab populations could harm salt marsh habitat, as periwinkle populations rise and the snails over-feed on marshgrass.
Blue crabs also support a large recreational fishery in the Bay, and are the estuary's highest-valued 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 measure the Chesapeake Bay’s blue crab population. Maryland and Virginia scientists visit 1,500 sites over the course of three and a half months, using metal dredges to pull up and count crabs over-wintering in the mud. According to the results of the 2017 survey, 455 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 2017, 254 million adult female crabs were estimated to be living in the Bay, compared with 194 million in 2015.
What issues affect blue crabs?
Habitat loss and harvest pressure have caused the abundance of blue crabs to fluctuate over time.
Habitat loss
Blue crabs use underwater grass beds as nurseries and feeding grounds. A drop in underwater grass abundance—due to warming waters, irregular weather patterns and pollution—has been linked to the decline of blue crabs. Research has shown that grass beds protect crabs from predators and boost their growth rates. Research has also shown that denser grass beds hold more crabs, indicating both the quantity and quality of grass habitat can affect blue crab populations.
Harvest pressure
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 highest-valued commercial fishery in the Bay, and bring in millions of dollars each year. Blue crabs also support a recreational fishery in the region.
Since the 1990s, there has been a dramatic decline in blue crab landings, as watermen expend the same amount of effort to catch fewer crabs. This could be linked to “recruitment overfishing,” which occurs when large removals of adults result in fewer juveniles being produced.
According to a 2016 report from the Chesapeake Bay Stock Assessment Committee (CBSAC), 49.6 million pounds of blue crabs were harvested from the Bay and its tributaries during the 2015 crabbing season. Recreational harvest was estimated to be 3.5 million pounds, while commercial harvests from Maryland, Virginia and those waters managed by the Potomac River Fisheries Commission (PRFC) were estimated to be 53.1 million pounds. The total harvest was below average but still 40 percent higher than the previous year's harvest of 35.2 million pounds, which was one of the lowest seen this century.
Because recreational and commercial harvests affect the blue crab population, CBSAC has named improving the harvest data a top research need.
Does predation affect blue crabs?
Debate has grown over the effect of predation on blue crab abundance. Striped bass, Atlantic croaker, red drum and other fish feed on juvenile blue crabs, and a change in these fish species’ populations could affect the abundance of blue crab “recruits,” or those crabs that are less than one year old.
How are blue crabs being protected?
Water quality improvements, underwater grass restoration and proper harvest management will help protect blue crab populations and maintain the resource into the future.
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 whether the target blue crab harvest level has been met or exceeded. Under this strategy, target fishing pressure is set to a level that should allow for increased blue crab 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 (CBSAC) has continued to provide scientific advice to fisheries managers, and publishes a Blue Crab Advisory Report each year that offers advice on harvest regulations.
Current restoration goals
As part of the 2014 Chesapeake Bay Watershed Agreement, Chespeake Bay Program partners committed to two goals related to blue crabs. The first goal is to maintain a sustainable blue crab population based on the current target of 215 million adult females. The second goal is to manage for a stable and productive crab fishery including working with the industry, recreational crabbers and other stakeholders to improve commercial and recreational harvest accountability.
Take Action
For Chesapeake Bay restoration to be a success, we all must do our part. Our everyday actions can have a big impact on the Bay. By making simple changes in our lives, each one of us can take part in restoring the Bay and its rivers for future generations to enjoy.
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.
