Intrinsic rate of increase is unknown. Blue crabs in the Gulf generally mature within 10-12 months (Guillory et al. 2000; Matherne 1995; Pellegrin et al. 2001); those in Chesapeake Bay and off North Carolina mature within 12-18 months (MDDNR 2001; NCDMF 2001). Overall, age at maturity is between 10 and 18 months (Orner, pers. comm., 2004). Aging crabs is difficult, as they lose in the molting process many of the characteristics that scientists generally use to define age. Blue crabs in a fished population usually do not survive longer than 2-3 years in the Chesapeake Bay (CBC 2001; MDDNR 2001; Pellegrin et al. 2001) and off the coasts of North and South Carolina (NCDMF 2002; SCDNR 2002; Van Den Avyle 1984). But these crabs reportedly survived as many as 5-8 years in the past (Guillory 2001a; NCDMF 2001; Pellegrin et al. 2001). Tagging studies in the Chesapeake Bay, which used only a very limited number of tags, show a maximum age of 8 years (Orner, pers. comm., 2004). The maximum age of Florida’s Blue crab is estimated at 4 years; that of the Blue crab in the Gulf of Mexico, 6 years (Guillory et al. 2000).

The native range of the Blue crab includes coastal waters of the Western Atlantic Ocean, from Nova Scotia to Northern Argentina, including waters around Bermuda, the Antilles, and in the Gulf of Mexico (Guillory et al. 2000; MDDNR 2001). But this species most commonly occurs in brackish estuaries and bays from Massachusetts to Texas (SCDNR 2002). The Blue crab has also been successfully introduced into coastal habitats in Asia and Europe (SMS 2001). We consider this to be a medium size range, thus no points were added or subtracted.

Blue crabs mature early--within 10-18 months overall. They mature earlier than other crabs (e.g., 4-7 years for king crabs; 5-6 years for snow crabs; 2-3 years for Dungeness crabs).

Blue crabs have high fecundity. Females generally mate just once in their lives. However, they store sperm for future spawnings, and may spawn several times in a single season, by fertilizing and brooding batches of eggs over time (CBP 1997; Guillory et al. 2000; MDDNR 2001; Van Den Avyle 1984). Unlike other crabs such as king crabs, which will brood eggs underneath their tail flap for approximately a year, female Blue crabs carry their extruded, fertilized eggs for 2 weeks until they hatch (Guillory et al. 2000; MDDNR 2001).

We chose not to add here, because female Blue crabs can only mate during the short period of time between their final molt and gaining their adult shell. Clearly the costs of this strategy can be high if they are not successful in mating during this period or mate with a genetically compromised male.

Blue crab abundance is highly variable and appears to fluctuate cyclically, with years of peak abundance usually followed by years of declining abundance, before the trend reverses. The factors associated with these fluctuations are still not fully understood. But the Chesapeake population appears to be most limited by spawning stock abundance/larval recruitment, whereas the Gulf population appears to be most limited by post-settlement biotic processes that affect juvenile survival (Guillory 2001a). However, it is unknown what the effect of broad-scale environmental change is on this variability.

There are no reliable quantitative estimates of the biomass of Blue crab populations relative to MSY in most of the regions where Blue crabs are caught. Other indicators show that abundance varies among the different regions and that abundance fluctuates cyclically, with years of peak abundance usually followed by years of declining abundance. In the Chesapeake Bay, the population is just slightly above the overfished threshold, which is defined as the lowest exploitable stock biomass observed in fishery independent surveys since 1968. Stock assessment scientists report that spawning stock abundance is at a historical low. Female spawning stock biomass is near the historical low established in 2000 (NOAA 2003). In other areas such as North Carolina, South Carolina, Georgia, Florida, and the Gulf of Mexico, tow surveys show variability in abundance and some data may not be reliable. For example, preliminary stock assessment data in North Carolina indicate that current catch levels are probably either at or exceed the maximum sustainable yield target level (NCSU 2002), but the MSY target is difficult to estimate and may not be reliable (NCDMF 2001). And in Florida, the only Gulf state showing major increases in abundance, data were collected in a reduced sampling effort, and probably do not accurately reflect current conditions (Guillory et al. 2000).

A medium score was awarded here to account for the regional variability in abundance and the lack of adequate estimates of abundance for most areas.

Trends vary according to region. However, in many areas Blue crabs are declining either compared to historic levels or in recent years. In the Chesapeake Bay, exploitable stock abundance, spawning stock abundance, and recruitment are all showing declining trends compared to historic levels (NOAA 2001). The decline has been attributed to a number of factors, including overfishing, predation, habitat degradation, and environmental factors (Greer 2000). However, since implementation of new regulations aimed at reducing fishing effort to target levels in 2000, the stock appears to have stabilized (NOAA 2003).

In North Carolina, some catch-per-unit-effort data suggest that the population is declining. Other data, however, show no clear trend. Landings have exceeded the estimated maximum sustainable yield in two of the last five years (NCDMF 2001). Data from Louisiana, Florida, Alabama, and Mississippi show no significant long-term trends in the overall relative abundance of populations fished, if annual values recognized by scientists as anomalies are omitted from the analyses. If these anomalies are not omitted, data indicate that the relative abundance of the population off Florida tripled between 1997 and 1998, that the relative abundance of the population fished off Alabama has been below average in recent years, and that the relative abundance of the population off Mississippi is at a significantly lower level than that observed in the late 1970s. Indices of overall relative abundance for the Texas fishery have been below average since 1995 (Guillory et al. 2000). Points were deducted here to account for the number of areas where Blue crab abundance is declining either in the long-term or in recent years.

Stock assessment surveys indicate a decreasing percentage of legal-size crabs and a decrease in the average size of crabs. CBC (2002b) warns that the reproductive potential of this population may be compromised due to the smaller size and lower abundance of mature males and females. The 2003 stock assessment reported the stock is at increased risk for recruitment failure (NOAA 2003).

Stock assessment data indicate that smaller, younger crabs have grown to comprise a greater proportion of Louisiana’s catch over time as the relative abundance of recruits has increased and the relative abundance of post-recruits has decreased. Scientists speculate that the increase in recruits may be due to the short-term effect of estuarine degradation, which is to increase shallow marsh-edge habitat, providing a favorable area for growth and survival of early juvenile Blue crabs. The decline of post-recruits is attributed to a significant increase in fishing mortality (Guillory et al. 2000).

Although Blue crabs have not been listed as "overfished," assessments in the Chesapeake Bay (NOAA 2003), North Carolina (NCDMF 2001; NCSU 2002), Florida (Pittman 2003), and the Gulf of Mexico (Guillory et al. 2000) have all concluded that Blue crabs are a species of concern.

Blue crabs play a critical role in the estuarine food web as voracious, opportunistic predators and as an important source of prey for many different species (Guillory 2001a). Blue crab larvae are consumed by fish, shellfish, jellyfish, shrimp, juvenile Blue crabs, and other organisms. Juvenile and adult crabs are preyed upon by a variety of fishes, including eels, bass, croakers, drums, toadfish, sharks, rays, trout, weakfish, catfish, and gars, and by turtles and alligators, seabirds, and even mammals, including raccoons and river otters (Guillory et al. 2000; MDDNR 2002b; Van Den Avyle 1984). In addition, Blue crabs are hosts to a number of commensals (Gannon et al. 2001). However, there is no indication at this point if current levels of Blue crab abundance is or is not jeopardizing other species or affecting the structure of the food web.

Most of the Chesapeake Bay catch is taken in baited wire crab pots (60% of Maryland’s hard crab catch; 80% of Virginia’s hard crab catch). But trotlines (a series of baited drop lines, which are extended from a mainline) (Guillory et al. 2000) and dredges are also used in Maryland and Virginia, respectively (CBP 1997). Softshell and peeler fisheries use scrapes (hand hauled devices), peeler pots (pots baited with live adult male crabs), and other traps or pounds, which are maze-like devices that direct crabs into a submerged trap. Peelers are also taken as bycatch when they enter hard crab pots (MDDNR 2001; VMRC 2002a). Recreational gears include baited hand lines, mesh rings, collapsible traps, trotlines, dip nets, and crab pots (MDDNR 2001).

In North Carolina, crab pots account for about 95% of the total Blue crab catch. The remaining catch is taken primarily with trawl gear. Hard crabs in the Gulf are taken almost exclusively with pots.

Blue crabs occupy a wide variety of offshore and estuarine habitats throughout their life history, including intertidal marshes, sub-tidal seagrass beds, and unvegetated, soft sediment shoreline habitats (Guillory et al. 2000). These ecosystems are threatened by a number of activities associated with human population growth and coastal development. But physical destruction of habitat and increased nutrient loading probably present the greatest threats to Blue crab populations. Eutrophication from nutrient loading also presents a real threat to Blue crabs, as eutrophic waters are characterized by frequent algal blooms and low levels of dissolved oxygen (Guillory 2001a). Guillory et al. (2000) report seasonal hypoxic conditions in deeper waters of the Chesapeake Bay and also incidences of high Blue crab mortality associated with periodic low oxygen conditions. Recovery time for such habitat areas is slow enough that high Blue crab mortality occurs. Habitat loss and/or degradation has reached “crisis levels” in some estuaries in the Gulf of Mexico (Guillory et al. 2000). And submerged aquatic vegetation has disappeared in many areas of Chesapeake Bay, raising concerns that Blue crabs might not have the high quality habitat needed to support their various life stages.

In the Chesapeake Bay, management advisers have recommended the creation of “corridors” or “sanctuaries” that would protect Blue crabs as they travel among nursery, feeding, and spawning grounds (CBC 2002b). Virginia has established a seasonal 661-acre sanctuary to serve this purpose (CBC 2002b). Other states including North Carolina, Florida, and Louisiana have also created sanctuary areas to protect Blue crab habitat. Louisiana, which has already lost approximately 25 square miles of marshes (Guillory 2001a) has created some wildlife management areas, and hopes to establish over 1,800,000 additional acres of management areas and refuges in estuarine areas. And Florida has established 42 aquatic preserves, 32 of which are located along estuarine and continental shelf areas. Finally, three national sanctuaries have been created in Rookery and Apalachicola bays and in the Florida Keys, and a fourth west coast sanctuary is currently under development (Guillory et al. 2000).

Blue crabs are managed on a state-by-state basis. Although regulations vary among states, management measures are in place in the Chesapeake Bay, in the Southeast U.S., and in the Gulf of Mexico. In Maryland, for example, primary management measures include minimum size limits, seasonal, daily, time, and area restrictions, and prohibition on the possession of sponge (berried) crabs. These regulations affect both commercial and recreational fishermen (MDDNR 2001). And in Virginia, commercial measures include a license moratorium (expires 5/26/04); minimum size restrictions; a prohibition on the retention of dark sponge crabs (same tolerance limit as in Maryland); bycatch limits; seasonal daily catch limits (vary with gear and area fished); gear restrictions (including pot limits, mesh size) and requirements (including escape devices; buoy marking); seasonal, daily, and time restrictions (including shortened workdays and standardized days off), and area closures (VMRC 2002a) (including a seasonal 661-acre spawning sanctuary) (CBC 2002b). The Chesapeake Bay Blue Crab Fishery Management Plan, developed in 1989 and revised in 1997, is designed to assist the Maryland Department of Natural Resources, Virginia Marine Resources Commission, and the Potomac River Fisheries Commission in developing complementary management strategies for the Chesapeake Bay fishery (MDDNR 2001). A regional management plan for the Gulf fishery developed in 1990 and revised in 2001/2002 is designed to provide the same function in the Gulf.

Reference points for sustainability are in place in all regions, however, in North Carolina and the Gulf of Mexico these reference points are considered unreliable (NCDMF 2001; Guillory et al. 2000).

Despite the regulations that are in place, there is concern about Blue crabs throughout their range and evidence of their decline, indicating that management measures are not meeting conservation and sustainability goals.

Commercial catches are adequately monitored in the Chesapeake Bay and North Carolina. For example, Virginia and Maryland instituted mandatory commercial reporting systems in 1993 and 1994, respectively (CBP 1997). The first comprehensive stock assessment was completed in 1996 by the Technical Subcommittee of the Chesapeake Bay Stock Assessment Committee, with the support of NMFS. The survey was based on both fishery-dependent and fishery-independent data derived from trawl, dredge, pot, and other surveys (MDDNR 2001). The most recent stock assessment called for improvements in estimation of fishing mortality and to design a bay-wide data collection program. This program should be based on the need for additional information on: 1) catch and effort data for the commercial and recreational fisheries; 2) growth and natural mortality rates; and 3) the age, size, sex and maturity composition of the catch and population (NOAA 2003). In North Carolina, catch reporting was voluntary prior to 1994, but is now mandatory at point of sale. Pre-1994 landings data are considered unreliable. Recreational catches are generally unaccounted for, but could be significant (NCSU 2002).

Data on catches in the Gulf of Mexico, however, are inadequate. Recreational catches in this region are significant, but catch data are either nonexistent or poor. Population assessments are conducted in all areas, but data are lacking and the reliability of the assessments is questionable. Guillory et al. (2000) report that there are inadequate catch data in the Gulf of Mexico and no reliable effort data in the Gulf commercial and recreational fisheries. All states have commercial trip ticket programs in place, but at least one of those programs has been in place for only three years (GSMFC 1999). Florida is the only Gulf state that collects data on fishing effort (Guillory et al. 2000). Guillory et al. (2000) cite unreported landings as a serious problem. Actual soft crab production in recent years is estimated to be 14-19 times greater than reported production (Guillory 2001a). Recreational catches are substantial, but also inadequately documented. The states of Alabama and Mississippi do not even require that recreational fishermen be licensed (Guillory et al. 2000). Fishery managers recommend that existing monitoring programs be expanded in each state to provide consistent data on commercial and recreational fishing effort, participation, and catches. Florida’s trip ticket system is cited as a model (Guillory et al. 2000).

Blue crab fisheries in the Chesapeake Bay and the Gulf of Mexico are overcapitalized. In the Chesapeake, regulations are designed to achieve a gradual 15% reduction in fishing effort and catch to stay within the target fishing mortality rate of F20%. Fishery advisers have identified several additional needs, including limiting access to the fishery (MDDNR 2001), addressing latent effort, and improving scientific understanding of the relative effects of ecosystem-based interactions (CBC 2001). In the Gulf of Mexico overcapitalization of Blue crab fisheries has resulted in conflicts among various user groups. For example, Guillory et al. (2000) report conflicts among Blue crab fishermen (theft of crabs or pots resulting from turf wars, capture of undersized crabs); between Blue crab fishermen and shrimpers (crabbers claim loss of or damage to pots due to shrimping activities; shrimpers complain that pots are getting caught in trawl nets); and between commercial Blue crab fishermen and the recreational sector (conflicts over loss of or damage to pots due to recreational activities; complaints by property owners in some areas that they are unable to get out of their dock areas because the pots are so thick).

Fishery managers have identified the need to reduce the number of Blue crab fishermen and the number of pots fished. Texas has implemented a limited entry program and sets aside 20% of commercial license and transfer fees to be used only for the purpose of buying back licenses from willing holders. Texas has also instituted a 200-pot limit (Guillory et al. 2000). Florida is currently considering a license moratorium (GSMFC 1999). There are no provisions for limited entry in the Louisiana fishery, but there was a commercial crab pot license moratorium with qualifying criteria from 1996 to 1998 (Guillory et al. 2000). Points were deducted here to account for overcapitalization in many of the Blue crab fisheries.

The biomass of the Chesapeake Bay stock remains slightly above the “overfished” threshold. But fishery managers have responded to the observed decline by conducting a comprehensive assessment to examine the biological status of the stock and to determine optimal catch levels, establishing biological reference points (MDDNR 2001), creating a 661-acre sanctuary to protect the spawning stock (CBC 2002b), and, most recently, implementing regulations designed to reduce fishing effort to target levels within a three-year period (MDDNR 2001). States have not yet had to act on a call by assessment scientists for a rebuilding program.

Bycatch is not generally monitored in Blue crab fisheries, although bycatch of sublegal Blue crabs, along with other invertebrates, finfish, turtles, and mammals does occur. In the Gulf of Mexico at least 23 species of fish (including spotted seatrout, red and black drum, and southern flounder) and four species of invertebrates have been observed in Blue crab pots. Diamondback terrapins, river otters, and raccoons have also been observed in ghost pots (Guillory et al. 2001). In the Chesapeake, mortality of Blue crabs from incidental catches, discards, and ghost fishing is generally unmonitored and unaccounted for (Guillory 2001b). However, Guillory (2001b) reports that pots are inefficient with respect to size selection and may retain excessive numbers of sublegal Blue crabs. For example, the percentage of undersized crabs taken in pots exceeds 50% in some areas of Louisiana where there are high densities of sub-legal crabs. They note that, contrary to the popular perception that culled sub-legal crabs are generally released unharmed, mortalities do occur related to injuries that occur in the pot or during handling. Estimates of mortality range from 6-8% of the incidental catch. And aberrant behavior resulting from secondary physiological damage after exposure-induced stress and physical injury, such as limb loss, may also contribute to delayed mortalities (Guillory 2001b). Efforts by the Chesapeake Bay Program to gather information on bycatch through competitive research grants has been unsuccessful. Managers report that researchers have not responded to requests for projects to assess bycatch (Orner 2003).

A substantial number of Blue crabs are taken in Gulf of Mexico shrimp fisheries – a number that greatly exceeds the commercial Blue crab catch. This number is particularly high in Louisiana and Texas, where shrimping effort is high (Guillory 2001b). The annual Blue crab catch in the Texas inshore shrimp fishery is estimated at 85,000,000 crabs; that in the Louisiana shrimp fishery is estimated at 20,500,000 pounds. The average mortality rate of Blue crabs captured in trawls has been estimated at 36% overall, with 26% occurring during the winter months and 80% during the summer (Guillory et al. 2001). Guillory (2001b) reports that even those discards that survive trawling and culling activities, and that escape initial predation from birds, marine mammals, and fishes, may be subjected to future increased predation rates because of altered behavior, or may succumb to bacterial and viral infections (Guillory 2001b).

Many states including Virginia, North Carolina, Florida, Texas, and Louisiana require escape rings for crab pots. Guillory et al. (2000) reports that the mandated use of escape rings in crab pots has been successful in reducing the bycatch of sublegal crabs. A 1993 study conducted in Louisiana fisheries reported mortalities of 17.3 crabs/pot (without escape rings) and 5.3 crabs/pot (with escape rings) over a three-month period (Guillory et al. 2001). Some states employ additional measure such as closed areas.