In January 2008, CBSAC recommended maintaining an interim rebuilding target of 200 million total adult (age1+) crabs, and not to drop below a threshold of 86 million adult crabs, a level where the resource would be considered overfished.
Resource managers, including the governors of Maryland, Virginia, and PRFC agreed to the recommendations, and set forth plans to begin rebuilding the blue crab population. The first step to increasing populations was to protect female crabs. CBSAC suggested that a 34% reduction in female harvest was necessary to increase overall populations toward the 200 million target.
Each jurisdiction implemented new female blue crab harvest regulations in 2008 to reduce the female harvest. These regulations included closing the female harvest season earlier, daily bushel limits, and new gear requirements. The development of these regulations included input from industry watermen.
In September 2008, the Department of Commerce declared the Chesapeake Bay blue crab fishery a federal disaster due to the recent population declines. Maryland and Virginia qualified for federal disaster funds of approximately $15 million each, which provided economic support for industry watermen and supported restructuring fishery management. Projects supported by watermen included removing abandoned crab pots and marine debris, participating in fishery monitoring and habitat restoration projects and training in aquaculture practices.
On May 12, 2009, President Obama signed Executive Order 13508, also known as the Chesapeake Bay Protection and Restoration Executive Order. The Chesapeake Bay Protection and Restoration and Protection Executive Order Strategy specifically lists a Blue Crab Outcome to “maintain sustainable blue crab interim rebuilding target of 200 million adults (1+) years old) in 2011 and develop a new population target for 2012 through 2025”. By waiting until 2012 to develop a new population target, blue crab management could be based on the most current science provided by the 2011 blue crab benchmark stock assessment.
In addition to revising the population target, the Executive Order Strategy also calls to support continued interjurisdictional management. The Sustainable Fisheries GIT, which was officially chartered in 2009 as part of the Chesapeake Bay Program, serves as a coordination forum for these interjurisdictional management discussions. For example, the coordination provided by the Fisheries GIT allowed for a cohesive strategy in developing and implementing the new population target in 2012.
The 2011 blue crab benchmark stock assessment recommended a new management scheme based on female-specific reference points. The Fisheries GIT tasked CBSAC with providing recommendations on the new female-specific reference points that would replace the interim target of 200 million adult (male and female) crabs. CBSAC recommended a new abundance target of 215 million adult females (age 1+) and an overfished threshold of 70 million adult females. These new female-specific reference points were adopted by the Fisheries GIT in December 2011.
Maryland, Virginia and the PRFC implemented the new female-specific reference points for the 2012 blue crab season. The 2012 CBSAC Blue Crab Advisory Report states the current population status of blue crabs in the Bay as not overfished, and that overfishing is not occurring. The estimated abundance of female adult (age 1+) crabs is 97 million, which is below the target of 215 million, but above the overfished threshold of 70 million. The record high recruitment of 587 million juvenile crabs in 2012 is also highlighted. The report also provides management recommendations that include being cautious of depleting the 2012 year class (juveniles), which will enter the fishery in the fall of 2012 and will support next year’s fishery.
Future of Blue Crab Management
Male Reference Points
CBSAC recommends the development of a male-specific abundance target and harvest threshold to pair with the current female-specific parameters. The Fisheries GIT has asked CBSAC to begin developing these male-specific parameters before the end of 2012.
Commercial and Recreational Accountability
A reliable estimate of both commercial and recreational harvest of blue crabs is essential to determining the status of the blue crab population. The Fisheries GIT has recognized the need for a more reliable estimate of exploitation fraction, or the percentage of the total crab population removed by commercial and recreational harvest each year. This estimate could be improved through a more accurate system of commercial and recreational accountability.
Maryland DNR commissioned EDF to work with managers and industry watermen to improve reporting of commercial harvest data. Various technologies will be used in the pilot study to determine if a new reporting system will lead to timely, verifiable daily harvest data. This is also an effort to make long-term management improvements to the blue crab industry.
Currently, annual recreational harvest is assumed to be 8% of the total commercial harvest, but recreational harvest may be increasing as the blue crab population stabilizes.
Future Jurisdictional Allocation
The Fisheries GIT agrees to begin envisioning the future of the blue crab fishery by discussing allocations between jurisdictions. Jurisdictions will then divide their total allocation among sectors at their discretion.
In addition to the Advisory Report, CBSAC will also release an annual consensus statement beginning in March 2013 to provide preliminary analysis/recommendations on the WDS results before the state crabbing seasons begin in March and April.
Biomass: Approximately 97 million female adult (age 1+) crabs were estimated to be present in the Bay at the start of the 2012 crabbing season. This number is below the recommended target but still above the recommended threshold number of 70 million female spawning-age crabs. The estimated abundance in 2012 was lower than observed in 2011 and 2010. However, 2012 saw the largest juvenile (age 0) recruitment ever recorded, with an estimated 587 million juvenile crabs.
The graphs below show abundance estimates of female adult crabs and juvenile crabs, respectively, from the annual Winter Dredge Survey results for 1990-2012.
Biological Reference Points: With support from the Virginia Marine Resources Commission, Maryland Department of Natural Resources, and the NOAA Chesapeake Bay Office, benchmark stock assessments of the Chesapeake Bay blue crab have been conducted every three to seven years since 1992. The most recent assessment, completed in 2011, reevaluated biological reference points to ensure that success in rebuilding a sustainable blue crab population continues over the long run. The 2011 assessment generated new reference points for the female component of the blue crab population. These maximum sustainable yield (MSY)-based female reference points were recommended and eventually adopted as replacements for the previous Maximum Spawning Potential overfishing reference points, which took into account both males and females (see table below). Similarly, the 2011 stock assessment recommends replacing the empirical overfished age 1+ (both sexes) abundance threshold and interim target with an MSY-based threshold and target based solely on female age 1+ crabs.
The Chesapeake Bay blue crab stock is currently not overfished, and overfishing is not occurring. This is true according to both the new recommended female-only framework developed in the 2011 benchmark assessment and the former management framework.
Fishing and habitat: The blue crab is perhaps the most sought-after shellfish in the mid-Atlantic region, and is caught both commercially and recreationally. The majority of the catch is commercial. Blue crabs are usually harvested with simple gear: pot, trotline, handline, dip net, scrape, or dredge. Crab abundance tends to be higher in areas with ample cover, such as submerged aquatic vegetation. Most fishing gear used to catch crabs has little to no effect on habitat.
Male and female blue crabs have different life histories, and this affects the catch of blue crabs around the Bay. More female crabs are caught in the lower part of the Bay because they stay in higher-salinity water when they spawn. Males tend to stay in lower-salinity water. The maps below, generated by ChesapeakeStat, show the difference in male and female habitat distribution during the summer.
By-catch: Sublegal-sized blue crabs, various finfish, turtles, and even some mammals are considered by-catch in the blue crab fishery. Perch and Atlantic croaker are prominent finfish caught in crab pots, while diamondback terrapins, river otters, and raccoons have been found in lost and/or discarded traps.
Aquaculture: Blue crabs must shed their hard carapace shell in order to grow, and experienced crabbers can quickly spot signs that the crab is about to molt. These 'peeler' crabs are held for a short time in shedding tanks until they molt. After molting, the soft-shell crabs are removed from the water and sold. These shedding tanks are monitored continuously through the day and night. The Blue Crab Advanced Research Consortium is a multidisciplinary research and development program that focuses on hatchery technologies to produce juvenile crabs for potential enhancement of the wild stock and the development of aquaculture techniques for the year-round production of soft-shell blue crabs.
Science and Management
Blue crabs are managed directly by state jurisdictions—the Maryland Department of Natural Resources, Virginia Marine Resource Commission, and Potomac River Fisheries Commission (PRFC). Collaboration between these three jurisdictions is essential to sustainable blue crab management on a Bay-wide basis.
The NOAA Chesapeake Bay Office chairs the Sustainable Fisheries Goal Implementation Team (Fisheries GIT) of the Chesapeake Bay Program, which is a forum for discussing fishery policy issues, including blue crab management. The Fisheries GIT comprises federal agencies, state fisheries managers, watermen, and additional stakeholders in the Chesapeake Bay. The NOAA Chesapeake Bay Office Chairs this team. The goal of the Fisheries GIT is to promote ecosystem-based fisheries management by providing sound science to support informed management decisions across all Bay jurisdictions.
Blue crab management decisions discussed by the Fisheries GIT are based on scientific recommendations from the Chesapeake Bay Stock Assessment Committee (CBSAC), a workgroup under the GIT. CBSAC was formed in 1985 and provides scientific advice to managers. Each year, CBSAC produces a Blue Crab Advisory Report to advise management jurisdictions as they set regulations for the blue crab fishery. Since 2010, the annual CBSAC Blue Crab Advisory Report has been officially endorsed by the Fisheries GIT. The 2012 Blue Crab Advisory Report and accompanying figures are available.
During the last decade, blue crab populations in the Chesapeake Bay reached some of their lowest numbers ever due to overexploitation and habitat degradation. In response to prolonged low abundance, CBSAC recommended new management actions. The timeline below describes important blue crab management decisions since 2008. Click on each year to view a more detailed account of that year and learn more about the important role of CBSAC, the Fisheries GIT, science, and the states.
Life History and Habitat
Life history, including information on habitat, growth, feeding, and reproduction of a species, is important because it affects how a fishery is managed. The blue crab uses multiple habitats in the Bay throughout its life. Blue crab distribution varies with age, sex, and season: Blue crabs tend to be abundant in shallow-water areas during warm weather; in winter they are plentiful in the Bay's deeper portions. Males range farther up into the fresher waters of the Bay and its rivers than females, who congregate in saltier waters. Blue crabs are bottom-dwellers that use beds of submerged aquatic grasses as sources of food, nursery habitat for young, and shelter during mating, and molting.
Geographic range: Along the Atlantic Coast, the blue crab ranges from Nova Scotia to Argentina. Within the Chesapeake Bay, male crabs tend to prefer fresher waters in Maryland and upper tributaries, while females like the saltier waters in the mainstem and Virginia.
Habitat: Blue crabs occupy a wide variety of habitats throughout their life history. Offshore, high-salinity waters are used during early larval stages. Larvae move into the estuary and use intertidal marshes, seagrass beds, and soft-sediment shorelines as they grow. Crabs are highly tolerant of temperature and salinity variations and can live in just about any region of the Bay. Habitat loss and increased nutrient loading present the greatest threats to the population.
Life Span: Crabs generally live three to four years in the Chesapeake Bay and reach maturity in approximately 12-18 months. Determining age is extremely difficult due to the loss of hard parts during the molting process.
Food: Crabs are voracious predators and are considered scavengers, eating just about anything they can including fish, clams, oysters, mussels, snails, worms, and insects. They are extremely cannibalistic and are most vulnerable while in the soft-shell stage of molting.
Growth Rate: Growth of blue crabs is strongly affected by temperature. For example, up to 18 months is necessary for maturation in the Chesapeake Bay, while blue crabs in the warmer Gulf of Mexico may reach maturity within a year. In laboratory studies, growth virtually ceased at temperatures below 13° C (55° F), while the growth per molt was reduced above 20° C (68° F).
Maximum Size: The largest blue crab caught in the Chesapeake Bay was 10.72 inches and weighed 1.1 pounds.
Reproduction: Blue crabs mate and spawn from spring to fall (May to October) in the Chesapeake Bay. Male crabs tend to molt throughout their lives, while females have just the one 'terminal' or 'maturity' molt. Female crabs can mate only once during their lives (during their terminal molt when in the soft-shell stage), but store sperm for multiple spawnings. The male crab may cradle the female—a pose in which the two crabs are referred to as doublers—for a few days prior to her terminal molt to maturity, and may stay with her after mating while her shell hardens and to ensure another male doesn't mate with her. Females migrate to the mouth of the Chesapeake Bay to spawn and can produce between 750,000 and 3,200,000 eggs per brood. Eggs hatch into larvae and undergo a series of molts offshore in high-salinity waters. The larvae then migrate into the Bay, and a majority grow and mature in beds of submerged aquatic vegetation. Small crabs molt frequently, but molting decreases in frequency as crabs grow bigger.
Migrations: In general, males remain in lower-salinity waters. Females migrate to higher-salinity water to spawn. The creation of 'corridors' or 'sanctuaries' has been instrumental in protecting crabs as they travel among nursery, feeding, and spawning grounds.
Predators: Predation may play a major role in influencing the size of populations. Blue crabs are preyed upon by red drum, croaker, striped bass, and other blue crabs.
Commercial and Recreational Fishing Interest: Both
Distinguishing Characteristics: Five sets of legs, with major front claw and rear swimmeret. Males have blue claws and a narrow abdominal apron (referred to as the Washington Monument). Females have red-tipped claws ("painted fingernails") and a broad abdominal apron (referred to as the Capitol dome). Immature females have a triangular or V-shaped apron, narrower than the dome shape of the sook's apron.
Role in the Ecosystem
The blue crab is an integral player in the Chesapeake Bay ecosystem. Scientists continue to study the effects of predation on blue crab populations; the effect of blue crab on populations of their benthic prey species, such as soft clam; and the effect on the fishery as well as the effect of the fishery on the blue crab population itself. Due to the economic and iconic value of the blue crab, it is considered a keystone species influencing many aspects of the Bay's ecosystem.
Did You Know?
Updated August 2012