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The history of Chesapeake Bay's blue crab (Callinectes sapidus): Fisheries and management

  • The Terrapin Institute

Abstract and Figures

Major blue crab fisheries have existed on the Atlantic coast of the United States for at least 100 years, and on the Gulf of Mexico coast for more than 50 years. From 1990 to 1994, reported landings averaged more than 96 million kg per year, with a reported dockside value of more than $200 million. Until about 1950, Chesapeake Bay accounted for over 75% of the total reported U.S. harvest of blue crabs, but less than 50% over the last two decades. The United States blue crab fishery is made up of hundreds to thousands of small-scale fishermen. The commercial fishery has a hard crab component and a soft crab (recently molted) fishery. There is also a substantial recreational (casual) fishery for blue crabs. Since the 1950s, crab pots have accounted for the largest proportion of reported landings. Other major gears include the trotline, crab scrape and crab dredge. U.S. blue crab fisheries have undergone periods of low abundance. Changes in fishing effort and power, environmental conditions, ecological interactions and market forces have been hypothesized as causative factors. Management measures in the Chesapeake Bay blue crab fisheries have included size and life stage, season, and gear limitations, as well as entry restrictions. An historical perspective should be taken in the interpretation of the recent decline in reported harvests. A 1997 stock assessment concluded that Chesapeake Bay blue crab stocks were fully exploited but in no current danger of recruitment overfishing.
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The history of Chesapeake Bay’s blue crab (Callinectes sapidus):
fisheries and management
Cluney Stagg1 and Marguerite Whilden2
Fisheries Service, Maryland Department of Natural Resources
580 Taylor Avenue, Tawes B-21, C-22
Annapolis, MD 21401, USA
ABSTRACT. Major blue crab fisheries have existed on the Atlantic coast of the United States for at least 100 years,
and on the Gulf of Mexico coast for more than 50 years. From 1990 to 1994, reported landings averaged more than 96
million kg per year, with a reported dockside value of more than $200 million. Until about 1950, Chesapeake Bay
accounted for over 75% of the total reported U.S. harvest of blue crabs, but less than 50% over the last two decades.
The United States blue crab fishery is made up of hundreds to thousands of small-scale fishermen. The commercial
fishery has a hard crab component and a soft crab (recently molted) fishery. There is also a substantial recreational
(casual) fishery for blue crabs. Since the 1950s, crab pots have accounted for the largest proportion of reported land-
ings. Other major gears include the trotline, crab scrape and crab dredge. U.S. blue crab fisheries have undergone
periods of low abundance. Changes in fishing effort and power, environmental conditions, ecological interactions and
market forces have been hypothesized as causative factors. Management measures in the Chesapeake Bay blue crab
fisheries have included size and life stage, season, and gear limitations, as well as entry restrictions. An historical
perspective should be taken in the interpretation of the recent decline in reported harvests. A 1997 stock assessment
concluded that Chesapeake Bay blue crab stocks were fully exploited but in no current danger of recruitment overfish-
Key words: fisheries, management, blue crab, Callinectes sapidus, Chesapeake Bay.
Perspectiva histórica de la pesquería y del manejo del cangrejo azul
(Callinectes sapidus) en la Bahía de Chesapeake
RESUMEN. Importantes pesquerías de jaiba azul han existido en la costa Atlántica de los Estados Unidos por lo
menos durante 100 años, y en la costa del Golfo de México por más de 50 años. Desde 1990 a 1994, los desembarques
informados promedian más de 96 millones de kg por año, con un valor playa de más de US$ 200 millones. Hasta cerca
de 1950, la Bahía de Chesapeake contribuía sobre el 75% del total de la captura de jaibas azules informada para
EE.UU., pero menos del 50% en las últimas dos décadas. La pesquería de jaiba azul de los Estados Unidos está
conformada por cientos a miles de pescadores artesanales. La pesquería comercial tiene una componente de jaibas
duras y una pesquería de jaibas blandas recién mudadas. También existe una importante pesquería recreacional (ca-
sual) de jaibas azules. Desde los años 50, el uso de trampas para la captura de jaibas han contribuido en mayor
proporción a las capturas reportadas. Otros artes utilizados incluyen la “trotline”, rastra de jaibas y draga. Las pesquerías
de jaiba azul en EE.UU. han tenido períodos de baja abundancia. Cambios en el esfuerzo y poder de pesca, condiciones
ambientales, interacciones ecológicas y fuerzas de mercado han sido hipotetizadas como factores causales. Las medidas
de manejo de las pesquerías de jaiba azul en la Bahía de Chesapeake han incluido limitaciones de la talla y ciclo de
vida, períodos de pesca y limitaciones a los arte de pesca, así como restricciones al ingreso. Debe tomarse una perspectiva
histórica en la interpretación de la reciente declinación en las capturas registradas. Una evaluación de stock realizada
en 1997 concluye que los stocks de jaiba azul de la Bahía de Chesapeake están completamente explotados pero no en
actual peligro de sobrepesca por reclutamiento.
Palabras claves: pesquería, manejo, cangrejo azul, Callinectes sapidus, Bahía de Chesapeake.
1 Present Address: P.O. Box 673, 12 Cold Springs Road, Angwin, CA 94508.
Invest. Mar. Valparaíso, 25: 93-104, 1997
94 Investigaciones Marinas
The intent of this paper is to recount the history of
blue crab, Callinectes sapidus, fisheries and man-
agement in the Chesapeake Bay region and to briefly
examine other United States blue crab fisheries. In-
formation on reported landings and fishing effort is
included, as well as an accounting of specific man-
agement actions taken over the course of more than
a century.
Brief life history
The blue crab is found from Nova Scotia to Uru-
guay (Rathbun, 1896; Milliken and Williams, 1984),
occurring in rivers, sounds, and near-shore waters
of the Atlantic. Blue crabs are fished commercially
and recreationally in the United States from south-
ern New England to Florida and along the Gulf coast
to Texas.
The blue crab population in Chesapeake Bay
is considered to be a single stock, and is distributed
throughout the Bay and its tributaries (Rugolo et
al., 1997). Males are generally found in areas with
lower salinity levels than females and most mating
occurs in brackish mid-Bay waters. Mature females
move south to the mouth of the Chesapeake Bay in
late summer and fall where spawning occurs from
May to September of the following season. Larvae
are transported out of the bay along the coastal shelf
and then back into the bay (McConaugha et al.,
1983; Johnson et al., 1984; Johnson, 1985; Johnson
and Hess, 1990).
Conventional wisdom has assumed that blue
crabs in Chesapeake Bay live to a maximum of three
years (Van Engel 1958; Milliken and Williams,
1984). In the course of recent Chesapeake Bay Stock
Assessment Committee (CBSAC) research (Rugolo
et al., 1997), review of the literature revealed evi-
dence of blue crabs attaining an age of at least five
years, based on a North Carolina tagging study
(Fischler, 1965). Based on that study and other un-
published tagging data, the CBSAC stock assess-
ment assumed a maximum theoretical age, under
virgin stock conditions, of age eight.
Carapace width modal analysis and laboratory
rearing studies have led most researchers to assign
approximate age classes as follows: Age 0 class-0
to <60 mm, Age 1 class-60 to <120 mm, and Age
2+ class(es)->120 mm (Rugolo et al., 1997). De-
finitive growth studies do not exist. Prior to the last
few decades of increasing fishing effort, male blue
crabs were routinely captured up to 180 mm cara-
pace width.
Because there are obvious morphological dif-
ferences between immature and mature female
crabs, reproductive maturity in female crabs can be
determined by visual inspection. Based on an ex-
amination of 6,500 crabs few mature individuals
were observed at carapace width less than 100 mm,
and essentially no immature individuals were as-
sumed at widths greater than 140 mm (Rothschild
and Ault, 1992).
Overview of the fishery
Blue crabs were harvested and cultured for local con-
sumption from colonial times (Churchill, 1921).
Since crabs were not easily preserved and trans-
ported, a wide market could not be established. Ice
and faster transport allowed for a broader regional
market. The soft crab (or molting crab) first gained
attention, as a luxury food, and by 1880, a directed
commercial fishery for blue crabs had begun in the
Chesapeake Bay region (Churchill, 1921), which has
subsequently spread throughout its range in North
The United States blue crab fishery has many
components, but in each region, it is a fishery made
up of hundreds to thousands of small-scale, some-
times artisanal, fishermen. The commercial fishery
is usually separated into a hard crab segment and a
peeler and soft crab fishery, the latter component
accounting for a small percent of the reported land-
ings. Hard crabs are sold in the “live-trade” market
to restaurants and directly to consumers, to proces-
sors where crab meat is prepared for resale, and in
overseas markets. Soft crabs are sold live or frozen
within the United States and in export markets. There
is also a substantial recreational (casual) fishery for
blue crabs.
Since the 1950s, crab pots (introduced in the
1930s) have accounted for the largest proportion of
reported landings. Other major gears include the
trotline, crab scrape and crab dredge. The balance
of this paper will discuss the evolution of blue crab
fisheries in the United States, particularly focusing
on Chesapeake Bay crabbing gears, regulations and
Mandatory reporting of commercial landings re-
placed voluntary reporting in Maryland in 1981, and
in Virginia in 1993. Major blue crab fisheries have
existed on the Atlantic coast of the United States
for at least 100 years, and on the Gulf of Mexico
coast for more than 50 years. From 1990 to 1994,
reported landings averaged more than 96 million
kg per year, with a reported dockside value of more
than $200 million. Until about 1950, Chesapeake
Bay accounted for over 75% of the total reported
U.S. harvest of blue crabs. Since that time there has
been a slow decline in the region’s market share to
an average of less than 50% and to as low as about
35% over the last two decades.
As reported by the United States National Ma-
rine Fisheries Service (NMFS), regions other than
the Chesapeake Bay began to develop their blue
crabs fisheries around 1945 (Fig. 1). The NMFS has
historically defined reporting regions as follows:
Middle Atlantic (New York, New Jersey and Dela-
ware), Chesapeake Bay (Maryland and Virginia),
South Atlantic (North and South Carolina, Georgia,
and Florida) and Gulf of Mexico (Florida, Alabama,
Mississippi, Louisiana and Texas). By 1950, the
South Atlantic and Gulf of Mexico regions were
beginning to bring considerable quantities of blue
crab to market. Although of some regional impor-
tance, the Middle Atlantic states contribute a rela-
tively small amount to the national total. From 1990
to 1994, 6.1%, 36.5%, 28.2%, and 29.2% of total
U.S. blue crab landings were attributed, respectively,
to the Middle Atlantic, Chesapeake Bay, South At-
lantic and Gulf of Mexico regions (NMFS, 1995).
The two states of Maryland and Virginia have his-
torically produced and continue to market more blue
crabs than any other region.
Chesapeake Bay
According to the original systematic study of the
blue crab, The Life History of the Blue Crab, the
species was first marketed in the United States
around 1873 when soft shell blue crabs were shipped
from Crisfield, Maryland to Philadelphia, Pennsyl-
vania (Churchill, 1921). The hard blue crab fishery
originated in 1878 with the opening of a cannery in
Virginia, and by 1880, demand was widespread.
Crisfield, Maryland became the hub for soft crab
rail shipments to northern cities. Demand grew for
both soft and hard crabs in the restaurants of Phila-
delphia and New York. Chesapeake crab stocks ac-
commodated rapidly increasing harvests to supply
an expanding market which grew from 4 million kg
in 1890 to 9 million kg by 1900. Available infor-
mation indicates that reported harvests continued
to increase from 1880 to 1915, perhaps largely due
to improved shipping facilities and the use of ice (Fig.
A 1924 report predicted the demise of the blue
crab stock and industry because of a 55% decrease in
reported harvests from 1915 to 1920 (Earle, 1925).
Thereafter, reported landings recovered somewhat,
Figure 1. Reported United States commercial blue crab landings by region, 1945 to 1994.
Figura 1. Registro de desembarques comerciales de jaiba azul por región en los Estados Unidos, desde 1945 a
Fisheries and management of Chesapeake Bay’s blue crabs
96 Investigaciones Marinas
Figure 2. Reported commercial blue crab landings for the Chesapeake Bay region (Maryland and Virginia),
1880 to 1995.
Figura 2. Registro de desembarques comerciales de jaiba azul en la región de la Bahía de Chesapeake (Maryland
y Virginia), de 1880 a 1995.
Figure 3. Reported Chesapeake Bay commercial blue crab landings showing long-term and 5-yr means, 1945 to
Figura 3. Registros de desembarques comerciales de jaiba azul en la región de la Bahía de Chesapeake mos-
trando medias de largo plazo y de cinco años, de 1945 a 1995.
there was year-to-year variability, and a new low in
reported harvest occurred during the period of World
War II (Fig. 2). In 1939, another comprehensive
study predicted depletion and collapse of the blue
crab resource unless a number of specific manage-
ment measures were taken (although in the same
report, the author noted that the blue crab’s high
fecundity and short life span enabled it to “survive
at great odds”) (Truitt, 1939). Thereafter, reported
harvests generally increased to record levels from
1945 until this decade, interspersed with intervals
of reduced harvests (Figs. 2 and 3).
Historically the blue crab fishery in Chesapeake
Bay has undergone periods of low abundance that
cannot be ascribed solely to reported changes in fish-
ing effort and power. If reported harvests are any
indication of abundance, there were three periods
of prolonged, relatively low abundance since 1929
(Figs. 2 and 3), superimposed over a long-term in-
creasing trend. These periods were from 1930 to
1945, although this is confounded by the effects of
reduced fishing during the second world war, from
1951 to 1960, and from 1968 to 1980. In each of
these periods apparent abundance was below the
long-term average from 1945 to 1994 (Fig. 3). En-
vironmental conditions, ecological interactions and
market forces have been hypothesized as reasons
for these periods of lower harvest (and probably
lower stock). Any interpretation of recent declines
in reported harvests must consider this historical
The three highest reported landings in the
Chesapeake Bay were in 1981, 1985 and 1990 at
roughly 45 million kg. There has been some debate
over the 1981 reported landings because at the time
Maryland changed from a voluntary census to a
mandatory sampling system (Summers et al., 1983a,
1983b). Although, there is evidence to suggest that
the apparent increase in abundance was not a re-
porting artifact (below). A year after one of the worst
harvests in Maryland, commercial crab catches in-
creased to 26 million kg in 1993, 50 million kg to-
tal for Chesapeake Bay the highest since commer-
cial records were kept. For the Chesapeake Bay,
reported landings were estimated to be about 40
million kg in 1995. These record harvests coincide
with the adoption of mandatory reporting in Vir-
ginia and the possibility that these record harvests
are at least partially an artifact of the new reporting
system should not be discounted.
The use of reported landings data alone to as-
sess relative abundance is usually biased because it
does not account for changes in fishing effort and
power. Since 1981 it has been possible to estimate
catch per unit effort (CPUE) in the Maryland com-
mercial blue crab pot fishery (Fig. 4). CPUE has
closely paralleled Maryland total reported landings
since 1981.
Fishery independent sampling, if designed and
implemented properly, is more reliable than fish-
ery-dependent data because it employs standardized
sampling methods and it is not dependent on indi-
viduals who might have an economic interest in not
reporting their catch and effort accurately. Two no-
table fishery independent surveys have been con-
ducted to assess the status of the Chesapeake Bay
blue crab stock: the Calvert Cliffs pot sampling study
and the bay-wide winter dredge survey.
The Calvert Cliffs study, ongoing since 1968
and uses standardized sampling methods. Commer-
cial crab pots of 25-mm galvanized wire mesh were
used to sample crab stocks at three stations in Mary-
land near Calvert Cliffs from late spring until late
fall. The pots were generally fished every other week
(Abbe, 1983; Abbe and Stagg, 1996). Catch per pot
by size class (6.35 mm) and sex were recorded, and
average annual CPUEs were estimated.
The long-term trend indicates comparable rela-
tive abundances from 1968 to 1980 and from 1987
to the present, with a notable and significant increase
in relative abundance from 1981 to 1986 (Fig. 4).
This pattern is similar to that seen in reported catch
data and is evidence that the large increase in re-
ported landings in 1981 is not attributable to report-
ing changes. Correlation analysis has shown that the
time series of CPUE estimated from the Calvert
Cliffs data is significantly correlated with reported
Maryland commercial catch (r=0.70, p<0.0001),
Maryland commercial crab pot CPUE (r=0.881,
p<0.0001) and total reported Chesapeake Bay catch
(r=0.686, p<0.0001) (Abbe and Stagg, 1996).
The second fishery-independent sampling pro-
gram is the blue crab winter dredge survey begun in
1989 (Rothschild and Ault, 1992). The program was
based on the fact that blue crabs become inactive
when the water temperature falls below 10°C. Dur-
ing winter is then the best time to sample, when there
is little-to-no movement of crabs in or out of the
system. Crabs are randomly sampled throughout
Chesapeake Bay using a lined dredge (mesh of 12
cm) and has been shown to catch crabs as small as
Fisheries and management of Chesapeake Bay’s blue crabs
98 Investigaciones Marinas
Figure 5. Reported United States commercial blue crab landings by hard and soft crab market categories, 1945
to 1994.
Figura 5. Desembarques de jaiba azul informados por Estados Unidos para el mercado de las categorías de
jaiba dura y blanda, de 1945 a 1994.
Figure 4. Comparison of trends in Maryland reported blue crab landings (1968 to 1995), Maryland blue crab
CPUE (1981-1993), Calvert Cliffs blue crab pot sampling study CPUE (1968 to 1995), and bay-wide blue crab
winter dredge survey CPUE (1989 to 1996).
Figura 4. Comparación de tendencias en los desembarques de jaiba azul registrados en Maryland (1968 a
1995), CPUE de la jaiba azul para Maryland (1981-1993), CPUE del estudio de muestreo de Calvert Cliffs para
trampas de jaiba azul (1968 a 1995), y CPUE de la exploración de dragado en toda la bahía, en invierno (1989
a 1996).
15 cm reliably (Rothschild and Ault, 1992). Sex and
carapace width are recorded to the nearest mm, nomi-
nal age classes are assigned as age 0 (0 to <60mm),
age 1 (60 to <120 mm) and age 2+ (>=120 mm) (Fig.
4). Nominal age class 1 has been shown to be a good
predictor of (1) Maryland reported harvest and (2)
Calvert Cliffs Age 2+ CPUE in the same year as the
survey (Rugolo et al., 1997).
Hard and soft crab landings
United States blue crab markets are usually divided
into hard crab landings and peeler and soft crab land-
ings. Hard crabs have hard carapaces and are between
molts, whereas peelers are hard crabs showing signs
under the existing shell (the emerging new shell) of
imminent molting, and soft crabs are crabs that have
recently molted, and not yet hardened. Soft crabs are
caught in the wild in that state, but more often are
produced in an operation that holds peelers in shed-
ding tanks until molting occurs. This adds some sta-
bility to the industry.
Hard blue crab landings have historically ac-
counted for more than 90% of blue crab landings by
mass, not numbers (Fig. 5). From 1990 to 1994, U.S.
reported blue crab landings averaged 96.2 million kg
of which 98.4%, or 94.7 million kg were hard crabs.
The highest level of soft crab production is in the
Chesapeake region, where 2.7%, by weight, of re-
ported landings over the same period were soft crabs.
Soft crabs have always been more valuable on a
per unit basis than hard crabs, but not in absolute terms
(Fig. 6). From 1990 to 1994, hard crabs averaged
$1.38 per kg while soft crabs averaged $6.08 per kg,
a ratio of 1:4.4. The average combined value of U.S.
blue crab landings was $140.2 million from 1990 to
1994, of which 93.2%, or $130.7 million was derived
from hard crab landings. By contrast, Chesapeake Bay
landings averaged $53.1 million of which 89%, or
$47.3 million was attributable to hard crab landings.
Recreational and commercial landings
The magnitude of U.S. recreational or casual land-
ings is largely unknown. Surveys conducted in Mary-
land in 1983, 1988, and 1990 estimated recreational
harvest to be 18.7, 9.7 and 5.2 million kg (Stagg et
al., 1994). These values ranged from 25 to 80% of
the reported Maryland commercial landings in those
years, a sizeable component of total removals. The
surveys were a combination of access-intercept meth-
ods to determine catch rates at strategic points and
random-digit dialing telephone surveys to estimate
effort (number of trips per household). There is
some concern that biases relating to landings by
out-of-state crabbers and shoreline property own-
ers were not adequately dealt with in these sur-
With respect to value, the most recent esti-
mate of recreational harvest was for the 1990 sea-
son and was the lowest of the three available Mary-
land estimates. For the months of May through
October, about 2.5 million crabbing trips were es-
timated to have been made, with an average crab-
ber taking about five trips per season. From the
1991 National Survey of Fishing, Hunting and
Wildlife-Associated Recreation (USFWS, 1993),
it is estimated that the average saltwater angler
spent $562 for the season for all expenditures.
Given the relatively small investment in equipment
for recreational crabbing, an estimate of $225 per
season covering just expenditures for transporta-
tion, rentals, bait, ice and user fees is more rea-
sonable. These estimates suggest that the economic
effect of recreational crabbing in Maryland in 1990
was about $112.5 million.
Landings by gear
Blue crabs are captured by a variety of gears, most
notably crab pots, trotlines, scrapes, dredges, and
otter trawls. Following its patenting in 1938, the
crab pot quickly began to replace other gears in
the Chesapeake region as the gear of choice. Most
crab pots are 0.6 m squares constructed of 2.9 cm
steel wire, including two or more conical entry
ways leading to a baited compartment. Pots are
set in up to 18 m depths, and connected to the
surface by a buoyed rope. For the period of avail-
able data, 1964 to 1988, the percentage of the re-
ported harvest landed by crab pots ranged from
about 60 to 80% (Fig. 7). The crab pot is the prin-
cipal gear in use in all producer states.
Prior to the invention of the crab pot, the crab
trotline was the dominant gear and remains im-
portant, particularly in Maryland. Trotlines are
simply lines (up to 1.6 km long) with other baited
lines attached at regular intervals of 1.8 to 2 m.
From 1964 to 1988, the trotline accounted for 5 to
25% of reported landings.
The crab dredge, a 1.8 m toothed bar attached
to a steel mesh bag, is used exclusively in
Virginia’s winter fishery and accounted for 5 to
20% of the reported catch from 1964 to 1988 (Fig.
7). The crab scrape is similar in design to the dredge,
Fisheries and management of Chesapeake Bay’s blue crabs
100 Investigaciones Marinas
Figure 6. Value of reported United States commercial blue crab landings deflated to 1995 constant dollars, by
hard and sot crab market categories, 1945 to 1994.
Figura 6. Valor deflactado a dolar constante de 1995, de los desembarques de jaiba azul informados por Esta-
dos Unidos para el mercado de las categorías de jaiba dura y blanda, de 1945 a 1994.
Figure 7. Percent of reported United States commercial blue crab landings landed by major gears, 1964 to
Figura 7. Porcentaje de los desembarques comerciales de los Estados Unidos de jaiba azul capturados con los
artes más importantes, de 1964 a 1988.
however it has a burlap bag attached rather than a
steel mesh bag. It was developed in 1870, and has
historically been most important in the directed
peeler-soft crab fishery, although peeler pots (crab
pots having a smaller mesh than the standard crab
pot) have begun to account for more landings. In
the south Atlantic and Gulf of Mexico, crab pots
and otter trawls have been particularly important
A brief history of Chesapeake Bay blue crab man-
agement actions is presented below. There is prac-
tical benefit in comparing the implementation of
various regulations with periods of poor harvests.
To do this properly, the effects of other activities
such as the status of alternative fisheries, weather
patterns, national trends in nutrition and diet, and
conservation issues in general should be assessed.
However, such a comprehensive inquiry is beyond
the scope of this review, as is a comparative study
of blue crab management among producing states.
Since the first significant decline in blue crab
landings in 1924, implementation of management
measures have to some extent been responses to real
or perceived decreases in crab apparent abundance,
although as is the case with most natural resource
commodities, blue crab management largely came
about for economic reasons. Fisheries management
measures include, size and life stage, season, and
gear limitations, as well as entry restrictions either
through licensing or direct effort control. The his-
tory of blue crab management includes all of these.
An accounting of when specific types of regu-
latory measures were first enacted in the Chesapeake
Bay region follows: Licenses were first required for
blue crab harvesting in Chesapeake Bay in 1898.
The first closed season was initiated in 1906. In
1916, a prohibition on taking egg-bearing females
and a 127 mm size limit for hard crabs was estab-
lished. By 1941, the types of gear that could be used
to harvest crabs was restricted (dredges were elimi-
nated as a legal gear in Maryland) and a crab sanc-
tuary (area closure) was adopted. In 1943, the
amount of gear that could be deployed on one li-
cense was restricted, specifically number of crab
pots. In 1988 the Maryland legislature enacted a de-
layed entry program in an attempt to cap effort.
Early blue crab management, Pre-1925
Licenses were first required for blue crab harvest-
ing in Chesapeake Bay in Virginia in 1898 more for
revenue generation than for fishery management.
According to archive files, some local governments
in Maryland issued their own crabbing licenses as
early as 1903. Crabbing in Maryland was not li-
censed or taxed by the state until 1916; licenses were
issued on a county basis as watermen were required
to harvest within their county of license (some coun-
ties offered reciprocity). Non-residents were pro-
hibited from obtaining a crabbing license in Mary-
land until 1983 when both Maryland and Virginia
as a result of litigation recognized reciprocal licens-
New harvest methods continued to be devel-
oped. Watermen dredging oysters found “hibernat-
ing” crabs in their rigs and soon began dredging for
crabs during the winter months. In 1906, Maryland
established a crabbing season from May through
October, thus, eliminating a winter harvest. Virginia
continued to allow winter dredging, which in 1920
accounted for 13% of the total Chesapeake harvest
and remains an important harvest to this day.
After the establishment of a season and a li-
cense requirement, size and life stage limits were
the next management measures considered in the
Chesapeake region. In 1916, Maryland adopted a
127 mm hard crab minimum size in Somerset
County, and Virginia banned the taking of sponge
crabs between June 15 and August 31 and enacted a
season for winter dredging.
The following year, the Maryland size limit was
extended statewide and a prohibition on the posses-
sion of sponge crabs and peelers was implemented.
Based on reports published in the 1940s, enforce-
ment of these regulations was sporadic at best. For
example, a 1939 investigation of the soft crab
(peeler) industry revealed that mortality was as high
as 80% (possibly because watermen continued to
take peelers which were not ready to shed within a
two day period) (Truitt, 1939).
Blue crab management, 1925 to 1981
An important survey of the Chesapeake blue crab
was initiated in August of 1924 by the U.S. Bureau
of Fisheries. Much of what we know of the early
crab fishery was compiled in the report, The Survey
of the Condition of the Crab Fisheries of the Chesa-
peake Bay, which was published in December 1925.
The Survey stated in its purpose that the blue crab
Fisheries and management of Chesapeake Bay’s blue crabs
102 Investigaciones Marinas
fishery was “now faced with destruction.” The 1924
Survey listed in its synopsis that: the 1924 crab har-
vest was half of the 23,000 tons taken from the
Chesapeake in 1915; abundance had decreased 75%
since 1907; 75% of the adult stock was removed by
the commercial catch; 30 to 50% of peeler crabs were
wasted because they were taken too soon, among
other things.
There has been a tendency when landings have
fallen in the past for political involvement in the
management process to increase, and for political
involvement to decrease or disappear when land-
ings are stable. There is no better example of this
than the “crab crisis” of 1924. The perceived crisis
led to a meeting in September of 1924, between the
Governors of Maryland and Virginia. The State of
Maryland proposed four measures to be adopted by
both States: (1) Virginia should ban the taking of
sponge crabs during the entire year, instead of June
15 to August 31 (peak spawning period) as was in
place at the time; (2) Virginia should shorten the
dredging season from 6 months to 3 months (to re-
duce fishing on dormant overwintering females); (3)
Maryland and Virginia should increase minimum
size limits to 152 mm for hard crabs and 90 mm for
soft crabs; and (4) both States should ban the taking
of green crabs (under-sized crabs showing no signs
of molting). What is notable is none of these pro-
posed actions were put into place.
By 1929, Chesapeake harvests exceeded
27,000 tons, the record harvest up to that point, and
little more was adopted to further protect blue crab
populations in the ensuing decade. Fishing tech-
niques and participants remained reasonably con-
stant during the 1930s. There were approximately
2,400 Maryland crabbers in 1929 and nearly the
same in 1939.
A major turning point in the history of blue
crab fisheries and management came with the in-
vention in of the crab pot and by 1940 was in wide-
spread use. When introduced, the crab pot was less
labor intensive than other methods, permitted rapid
expansion in effort because it became relatively in-
expensive to enter the fishery. The same year the
crab pot was introduced produced a poor harvest
and the crab pot was offered as an explanation. The
Maryland legislature excluded the crab pot in a list
of legal gears during the 1941 legislative session.
The crab pot was reinstated as a legal gear in Mary-
land in 1943, permitted in the Chesapeake Bay
proper and the Potomac River. Crabbers were ini-
tially limited to 35 pots, but over the course of sev-
eral years the limit on crab pots has increased.
In 1941, in response to the concern over the
taking of sponge crabs, Virginia set aside a sanctu-
ary for crabs near the mouth of the Chesapeake Bay.
When the Department of Chesapeake Bay Affairs
was created in Maryland in 1964, a more compete
catch reporting system was established (e.g. land-
ings by gear type). By this time, the recreational
crabber was increasing in numbers, and judging
from the sequence of regulations enacted from 1964
to 1968, the recreational crabber was a segment of
the fishery which had not been an issue until the
1960s. Around this time, the crab pot was desig-
nated a commercial gear and not permitted to be
used by the recreational crabber.
Blue crab management, 1981 to present
A monthly sampling survey was initiated in Mary-
land beginning in 1981, the same year in which the
largest catch of record (27,000 tons) was landed.
Landings were so good during the 1980s that sev-
eral of Maryland’s crab management measures were
rolled back to what they were in the early days of
crabbing in the 1880s.
By 1985, the Department of Natural Resources
(MDNR) had issued over 18,000 crabbing licenses,
half of which were “non-commercial”. In an effort
to moderate the expansion of the state’s commer-
cial fisheries, Maryland adopted a “delayed entry”
licensing program for commercial licenses in 1988,
implemented in 1989. Applicants would pay the
licensing fee at the time of application and wait two
years to receive the fishing permit. Motivated by
the producers, who were working longer for fewer
crabs, this had less to do with conservation then in-
dividual economics. The number of commercial
crabbing licenses remained at about 6,000. The num-
ber of “non-commercial” licenses increased rapidly
from around 7,000 in 1990 to over 12,000 in 1992.
Between 1992 and 1994, Virginia enacted a
number of new laws and regulation pertaining to
blue crabs: a commercial license ($150) was re-
quired, two year delayed entry, limited entry in the
dredge fishery, the dredge catch limit was lowered
from 25 barrels to 20 barrels per day, a 59 mm cull
ring in hard crab pots was required, peeler pot fish-
ermen and soft crab shedders were licensed, man-
datory reporting was enacted, a recreational crab
licence ($29) was required as well as a five-pot re-
striction for recreational crabbers.
An advisory panel was convened in 1992 to
guide MDNR in implementing more protective man-
agement of the crab fishery. Consensus was to cap
fishing effort at then current levels. The Governor’s
Crab Action Plan was introduced in the Summer of
1993 with a focus on stabilizing fishing effort and
addressing the recreational crabbing issue. The 1993
crab harvest exceeded recent records making it dif-
ficult to adopt restrictive measures in the midst of
what appeared to be a natural recovery and abun-
dance. Nevertheless, legislation necessary to imple-
ment the Governor’s plan was introduced to the 1994
General Assembly and regulations were proposed
by the Department of Natural Resources.
By 1995, a growing atmosphere of concern that
crab stocks were in danger characterized blue crab
management in 1995. MDNR organized another
blue crab advisory committee and prepared a sum-
mary of all blue crab data to date and a blue crab
stock assessment was begun by the Chesapeake Bay
Stock assessment Committee (CBSAC). Landings
for 1995 were slightly below the 10 year average.
In an emergency measure the Governor’s of-
fice announced that a reduction in the harvest of
spawning stock was necessary to stabilize the com-
mercial crab industry. The State set a target of re-
ducing the female catch by 20%. Beginning Sep-
tember 1995, the Chesapeake Bay tributaries were
closed to commercial crabbing on Sundays; the main
stem of the Chesapeake Bay in Maryland was closed
to commercial crabbing on Mondays; commercial
hours were reduced to eight hours a day; recreational
crabbing was restricted to Fridays, Saturdays, and
Sundays; and the crabbing season was closed No-
vember 18, 1995.
A blue crab stock assessment was begun in
1995 by the NMFS CBSAC. The stock assessment
comprised a review, synthesis and analysis of all
available, relevant data on blue crab biology and
fisheries (Rugolo et al., 1997). Conclusions of the
completed assessment include the following: (1) the
Chesapeake Bay blue crab stock “appears stable over
the long term while the juvenile population has been
increasing over the last decade despite a dramatic
increase in commercial fishing effort”, (2) despite
this increase in effort fishing mortality has remained
relatively constant over the long term (“as a result
of gear saturation and/or gear competition”), and
(3) there are indications of “severe” overcapitaliza-
tion in the fishery.
The stock assessment did not directly address
the question of the effectiveness of the regulatory
measures outlined above. Market forces and reac-
tion to perceived crises have historically played a
major role in the specification of crabbing regula-
tions. Natural fluctuations in blue crab stocks driven
by environmental variables (Tang, 1985), as well
as the effects of human intervention, account for
the historic pattern of widely-varying blue crab
abundance observed in the Chesapeake Bay region.
Abbe, G.R. 1983. A study of blue crab populations
in Chesapeake Bay in the vicinity of the Calvert
Cliffs Nuclear Power Plant, 1968-1981. J.
Shellfish Res., 3: 183-193.
Abbe, G.R. and C. Stagg. 1996. Trends in blue
crab (Callinectes sapidus Rathbun) catches
near Calvert Cliffs, Maryland from 1968 to
1995 and their relationship to the Maryland
commercial fishery. J. Shellfish Res., 15: 751-
Churchill, E.P. Jr. 1921. Life history of the blue
crab. Bulletin U.S. Bureau of Fisheries, 36:95-
Earle, S. 1925. Maryland’s efforts to save the blue
crab of Chesapeake Bay. Conservation Bulle-
tin Nº 1, State of Maryland.
Fischler, K.J. 1965. The use of catch-effort, catch-
sampling, and tagging data to estimate a popu-
lation of blue crabs. Trans. Am. Fish. Soc., 91:
Johnson, D.F and K.W. Hess. 1990. Numerical
simulations of blue crab larval dispersal and
recruitment. Bull. Mar. Sci., 46: 195-213.
Johnson, D.R. 1985. Wind-forced dispersion of
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McConaugha. 1984. Studies of a wind mecha-
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Rathbun, M.J. 1896. The genus Callinectes. Pro-
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Vaughan. 1997. Chesapeake Bay blue crab
stock assessment. National Oceanic and Atmo-
spheric Administration, National Marine Fish-
eries Service, Chesapeake Bay Stock Assess-
ment Committee, Annapolis, Maryland.
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Kline and D. Logan. 1994. Evaluation of the
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striped bass fishing surveys, and design of a rec-
reational blue crab survey. Maryland Dept. Of
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Fisheries Review, 24(9): 1-10.
Summers, J.K., H.W. Hoffman, and W.A. Richkus.
1983a. Randomized sample surveys to estimate
annual blue crab harvests by a multi-gear fish-
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North Am. J. Fish. Mngt., 3: 9-20.
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Bonzek, H.H. King and M. Burch. 1983b.
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Recibido el 03 de diciembre de 1996.
Aceptado el 23 de mayo de 1997.
... The blue crab is commercially exploited throughout most of its native distributional range and supports a socioeconomically important fishery along the Atlantic coasts of USA (e.g. Stagg and Whilden 1997;Bunnell et al. 2010;FAO 2019). ...
... Zostera (Zosterella) noltei] (Guimarães et al. 2012) that constitute critical nursery habitats for C. sapidus (Orth and van Montfrans 1990;Epifanio et al. 2003;Rodrigues et al. 2019) and provide suitable refuge against predators especially during the vulnerable moulting and soft-shell stages (Millikin and Williams 1984). The size range of the present six records of C. sapidus (191-236 mm CW) corresponds to adults presumably in the age class 2+ (≥ 120 mm CW) (Stagg and Whilden 1997;Rugolo et al. 1998) and is above the size at sexual maturity estimated in diverse populations (CW 50 ≈ 120-170 mm depending on geographical location) (e.g. Tagatz 1968;Cadman and Weinstein 1985;Prager et al. 1990;Sumer et al. 2013). ...
Full-text available
The present study reports six new and consecutive records of the Atlantic blue crab (Callinectes sapidus Rathbun, 1896) in the southern coast of Portugal. Specimens were caught during less than two months (22nd November 2018 – 18th January 2019) as bycatch of trammel nets operated by small-scale fishing boats in scattered locations along the Algarve coast and in the Ria Formosa lagoon. Four adult males (221–236 mm carapace width) and two adult females (191–207 mm carapace width) were caught at relatively shallow depths (1–6 m), on muddy and sandy bottoms in the Ria Formosa lagoon and in the Algarve coast. Morphometric parameters of the specimens are compiled and the respective occurrences are mapped for biogeographic purposes. These first three occurrences in the Algarve coast and the second, third and fourth records in the Ria Formosa lagoon, further supported by additional anecdotal evidences and recent sales at the wholesale market, reveal a rapid westward expansion and confirm the establishment of C. sapidus along the southern coast of Portugal. Possible sources of introduction and causes for the distributional expansion are evaluated. The potential impacts of this invasive species on local ecosystems and fishing/harvesting resources are discussed.
... Each year 50,000-100,000 tons are taken (Tavares, 2002); its economic and culinary F I G U R E 1 Tonga Lake, in northeastern Algeria F I G U R E 2 Calinectes sapidus male specimen captured in Tonga Lake (at left: dorsal view; at right: ventral view) importance is considerable on the Atlantic coast of the USA, in particular, in the states of Louisiana, Maryland, North Carolina and New Jersey. In the Chesapeake Bay, a significant drop in the tonnages caught of blue crab has been noted in recent decades; various factors such as overfishing, environmental degradation and an increase in pathologies have been mentioned to explain this situation (Stagg & Whilden, 1997). ...
... The commercial fishery of the Blue Crab had begun in the Chesapeake Bay region in 1880 (CHURCHILL, 1921). In the United States, the fishery is made up of hundreds to thousands of small-scale, sometimes artisanal, fishermen (STAGG & WHILDEN, 1997). ...
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Callinectes sapidus is considered one of the worst invasive species in the Mediterranean Sea. After its first observation in 1948, the species has colonized several Mediterranean areas. In this work, we report the first records of the species in Latium and Campania (northern-central and central Tyrrhenian Sea respectively), filling a gap in its distribution along the Italian coasts. We also provide a review of Italian records.
... The blue crab C. sapidus is a voracious predator, playing an important ecological role as a regulator of the local populations of prey (Oliveira et al., 2006). The species is also an economically important fishery resource and sustains substantial fishing pressure throughout its distribution area (Stagg and Whilden, 1997;Severino-Rodrigues and Pita, 2001;Ruas et al., 2014). The blue crab is overexploited, and there are still many gaps in the understanding of the ecology and behavior of this species. ...
Full-text available
The blue crab Callinectes sapidus is an important ecological and commercial species. It plays a fundamental role in the structure and function of coastal benthic food webs, with global catches of approximately 74,357 tons. This is the most exploited portunid species in Brazil. However, few studies about the ecology and population dynamics of C. sapidus have been published. This study aimed to analyse the preferred areas for the spatial distribution of juveniles and moulting individuals of C. sapidus in shallow areas of the Patos Lagoon estuary and the adjacent marine reproductive area, and their relation to water and sediment characteristics. Juveniles and moulting individuals preferred the embayment of the upper estuary, where the sediments are finer, with higher contents of organic matter and the presence of submerged vegetation. There was also a temporal variability in the abundance of juvenile size classes, with two marked increments of smaller individuals: 1) in late spring and summer and 2) in winter, indicating two recruitment peaks. Special environmental conditions that took place in summer of the first year, when an increase of fine sediments and organic matter, in conjunction with low salinities in the adjacent marine area, allowed recruitment of individuals there. We suggest better attention to the embayment around the Marinheiros Island (upper estuary) for management and protection measures due to the overlapping of recruitment preferences of the blue crab, pink shrimp and fish species in this area.
... In the U.S.A., Brazil and in some Western European countries (e.g. UK) C. sapidus has a significant economic value (Stagg and Whilden, 1997;Severino-Rodrigues et al., 2013). The main products are soft shell crabs or live bait. ...
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The blue crab, Callinectes sapidus Rathbun, 1896, is native to the Atlantic coasts of the Americas and globally one of the most highly invasive marine species. In the present study, the species diet and the foraging behaviour was studied in the Thermaikos Gulf and Papapouli Lagoon for the first time. Surveys were undertaken using fyke nets, shore surveys, scuba and snorkelling. Additional data were compiled from systematic interviews with mussel farmers, shellfish traders and fishermen. In both Thermaikos Gulf and Papapouli Lagoon C. sapidus was found to prey on a wide variety of species including economically important molluscs, fishes, and crustaceans, indicating a substantial potential impact on fisheries and aquaculture in the region. Observation showed that over 6 (2009-2014) years, the blue crabs became dominant in Papapouli Lagoon at the expense of the native commercially fished crab Carcinus aestuarii Nardo, 1847 according to fisheries data. Potential management implications are discussed.
... sapidus) dominates the diet (Smith, 1995). Although the cobia exhibits apparent selectivity, as indicated by Knapp (1951), the dominance of crabs in the diet of cobia in USA seems to be more related to the availability of prey items in the environment since crustaceans are abundant in that region (Stagg and Whilden, 1997). ...
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The feeding habits of cobia, Rachycentron canadum, was described along the coast of Pernambuco State, northeastern Brazil. One hundred ten specimens were caught between February 2004 and August 2006 with fork length ranging from 40.0 to 137.0 cm (mean and standard deviation: 85.8 ± 18.0 cm) and total weight between 0.4 and 29.8 kg (7.5 ± 4.4 kg). The importance of each food item in the diet was evaluated using the index of relative importance (IRI). Among the one hundred ten stomachs analyzed (52 females and 58 males), 92 (83.6%) had food items, while 18 (16.4%) were empty. Bony fish were the main food item (IRI = 98.7%), being squirrelfish (Holocentrus adscensionis) and porcupine fish (Diodon sp.) the most frequent prey items (30.7% and 8.2%, respectively). Elasmobranchs, crustaceans and cephalopods were also present in small proportions (IRI < 1% for each). No significant differences in diet were found between sexes or size classes (forklength: < or ≥ 69.8 cm; estimated L50 for the species). The present data demonstrate that cobia is a carnivorous predator along the coast of Pernambuco State, with a preference for demersal bony fish, independently of the size and sex of the individuals analyzed.
... The blue crab C. sapidus is a voracious predator, playing an important ecological role as a regulator of the local populations of prey (Oliveira et al., 2006). The species is also an economically important fishery resource and sustains substantial fishing pressure throughout its distribution area (Stagg and Whilden, 1997;Severino-Rodrigues and Pita, 2001;Ruas et al., 2014). The blue crab is overexploited, and there are still many gaps in the understanding of the ecology and behavior of this species. ...
Estuaries are extremely rich areas that act as nurseries for many species of fishes and crustaceans. This study is the first to address the juvenile distribution of ecologically significant size classes of blue crabs in estuaries from their southern region of distribution. We investigated the spatial and temporal distribution of the populations of juvenile blue crabs in Tramandaí-Armazém estuary (TAE) and Patos Lagoon estuary (PLE), southern Brazil, to determine possible areas of protection. The hypothesis that physical factors can direct the distribution of crabs was tested through correlations of the abundance of different size classes with some environmental parameters, in order to determine the concentration areas of blue crab juveniles. Four sites in each estuary were sampled with a bottom trawl for 18 months. Temporal patterns were more evident than spatial ones in the distribution of blue crabs. There were two recruitment peaks: one during the warmer months of spring and summer and another during the winter. Increased rainfall apparently delayed the first recruitment peak during summer–autumn of the second sampled year. The timing of winter recruitment may be associated with a reproductive cycle delay evidencing the existence of a delicate year-by-year balance in the recruitment. The spatial distribution of the blue crab was discrete in PLE, whereas it was more homogeneous in TAE. Salinity played an important role in the distribution of blue crabs in PLE, where recruits preferred the upper estuary embayments that offered shelter in spite of the lowest salinities. A clear salinity gradient is absent in TAE and was not correlated with the spatial distribution of blue crabs. The upper shallow areas of PLE are critical for the recruitment of the blue crabs, and therefore efforts should be made to preserve this nursery area.
... They are also an important benthic predator and prey in estuarine ecosystems (Millikin and Williams, 1984). Historically, adult blue crab population abundance in Delaware Bay and Chesapeake Bay has been volatile ( van Engel, 1958;Stagg and Whilden, 1997), with variation in adult abundance mirrored by juvenile abundance indexes (Wong, 2010). One potential explanation for highly variable interannual adult abundance is changes in larval supply (Johnson and Hess, 1990;Epifanio, 1995;Ogburn et al., 2012). ...
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External morphology has been shown to influence predation and locomotion of decapod larvae and is, therefore, directly related to their ability to survive and disperse. The first goal of this study was to characterize first-stage blue crab zoeal morphology and its variability across larval broods to test whether inter-brood differences in morphology exist. The second was to identify possible correlations between maternal characteristics and zoeal morphology. The offspring of 21 individuals were hatched in the laboratory, photographed, and measured. Zoeae exhibited substantial variability, with all metrics showing significant inter-brood differences. The greatest variability was seen in the zoeal abdomen, rostrum, and dorsal spine length. A principal component analysis showed no distinct clustering of broods, with variation generally driven by larger zoeae. Using observed morphology, models of drag induced by swimming and sinking also showed significant inter-brood differences, with a maximum twofold difference across broods. In contrast to trends in other decapod taxa, maternal characteristics (female carapace width and mass and egg sponge volume and mass) are not significant predictors of zoeal morphology. These results suggest that brood effects are present across a wide range of morphological characteristics and that future experiments involving Callinectes sapidus morphology or its functionality should explicitly account for inter-brood variation. Additionally, inter-brood morphological differences may result in differential predation mortality and locomotory abilities among broods.
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The two invasive blue crabs, Callinectes sapidus and Portunus segnis have spread rapidly in the Mediterranean and no data exists on the connectivity of populations. Determining the source and recruitment areas is crucial to prioritize where population control measures should be put into immediate action. We simulated the dispersal of blue crab larvae using a Lagrangian model coupled at high resolution to estimate the potential connectivity of blue crab populations over a 3-year period. Our results reveal that the main areas at risk are the Spanish, French, Italian Tyrrhenian and Sardinian coasts for Callinectes sapidus with high populations connectivity. Tunisia and Egypt represent high auto recruitment zones for Portunus segnis restricted to the central and western basins. This study provides an overview of the connectivity between populations and will help define priority areas that require the urgent implementation of management measures.
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Blue crabs are an important commercial fishery in South Carolina, but landings have decreased over the past 15 years, sparking debate about how to effectively manage this population. It is unclear whether this decline is more related to drought or changes in fishing effort. The objective of this study is to measure recreational catch-per-unit-effort (CPUE) and total recreational catch of blue crab in South Carolina coastal waters, and determine the impact of recreational fishing pressure on the commercial fishery, and how this interaction changes with flow conditions and hypothetical seasonal closures for female harvest. Using a spatially-explicit individual-based population model, the South Carolina Blue Crab Regional Abundance Biotic Simulation (SCBCRABS), we compared the efficiency of commercial versus recreational traps during periods of flood, normal and drought conditions, and during hypothetical seasonal closures (no harvest of females, no harvest of females during full spawning season, partial harvest of females during spawning season). We found a significant decrease from 1997 in the recreational fishery (-63%), with evident seasonal catch patterns, and shifts in preferred gear type used from 1997 to 2015. Additionally, SCBCRABS modeled the phenomenon of trap interference with competition between commercial pots.
In an effort to understand some of the consequences of increased fishing pressure on the Maryland blue crab population, we have analyzed data collected along 12 km of western Chesapeake Bay in Calvea County from 1968 to 1995. Commercial peeler crab pots of 25-mm-pore-size mesh, baited daily with menhaden, were used to sample crab stocks at three locations with up to 60 pots fished during alternate weeks from June through November. Station catches were sorted, measured, and weighed by sex. From 1968 through 1995, 113,002 crabs were caught in 18,106 pots, of which 73% were legal size (127- mm carapace width). Although annual mean catch per unit effort (CPUE) varied considerably, it appeared to be within some normal range. Total CPUE ranged from 0.85 in 1968 to 2001 in 1981 (legal CPUE ranged from 0.73 to 13.57); Maryland commercial landings ranged from 4.7 x 106 kg to 27.1 x 106 kg during the same years. From 1968 to 1980, legal CPUE averaged 3.60; from 1981 to 1985, it averaged 8.14; and from 1986 to 1995, it was 3.66. Thus, the legal CPUE of the most recent period was nearly identical with that of the earliest period. There are, however, several trends that have become apparent, indicating that increased fishing pressure may be having a deleterious effect on the blue crab population. A significant correlation between this fishery-independent data and Maryland Department of Natural Resources' fishery-dependent data demonstrates the relevance of these trends. From 1968 to 1982, the annual male percentage decreased significantly from 66 to 38% (r2 = 0.79; p < 0.01). Since 1983, this percentage has shown greater fluctuation among years, but has shown no further decrease. The mean carapace width and weight of females have not changed significantly over time, but the mean width of males (r2 = 0.47) and the mean weight of males (r2 = 0.34) have both decreased significantly (p < 0.01). Percent legal size crabs, which constituted 64-86% of the annual catch between 1968 and 1991, has had its three lowest years (averaging 52%) since just 1992; the percentage of legal males in the catch decreased from 56% in 1968 to 19% in 1995 (13% in 1994) (r2 = 0.75; p < 0.01). These downward trends related to the size of males indicate that they are being removed from the population shortly after reaching legal size. With fewer large males available to crabbers, even more pressure may be exerted on females, which could eventually result in further decreases in population size and stability.
ABSTRACT Reproductive success in species that have retained a planktonic stage is dependent on the release of larvae during periods when abiotic and biotic factors are optimal. Analysis of stratified plankton samples collected from May through September 1980 indicated reproductive activity for Callinectes sapidus throughout the summer with a peak in late July. Presence of stage I larvae was positively correlated with temperature. Seasonal distribution of megalopae was bimodal with a broad peak occurring in late August through September. This suggests a two phase recruitment. Timing of reproduction and recruitment coincide with seasonal changes in current patterns that would enhance larval retention in the offshore waters near the mouth of Chesapeake Bay.
Catch-effort, and catch-sampling data along with the results of a tagging study are used to estimate the size of the blue crab, Callinectes sapidus, population in the Neuse River, North Carolina, during 1958. At the beginning of July, estimates of the crab population, determined by three methods, were 716,000, 703,000, and 722,000 pounds, respectively. Catch, recruitment, and emigration of mature female crabs from the river affected abundance, whereas natural mortality and predation upon crabs were considered insignificant. Of the 2.1 million pounds of crabs estimated as being available to the fishery during 1958, 1.7 million pounds were caught.
Pilot surveys of commercial trotliners, sport trotliners, and collapsible-trap crabbers were conducted to provide information on which to base a comprehensive 1981 catch survey. A 1979 census of commercial crab potters also was used for this purpose. Several random sampling techniques were designed to estimate the harvest of blue crabs (Callinectes sapidus) by different gear types in the Maryland portion of the Chesapeake Bay. The most efficient, comprehensive sampling design included simple random sampling of 323 sport trotline crabbers and 148 crabbers using collapsible traps; random sampling, stratified by month, of a total of 1,148 commercial trotline crabbers; and random sampling stratified by month and county of residence of 5,379 commercial crab potters.
Simple and stratified random sample surveys were conducted in Maryland to ascertain the magnitude of the blue crab (Callinectes sapidns) harvest in 1981. The total harvest was approximately 65 x 10 6 lbs with a 95% confidence interval of 58,519,617-70,646,509 lbs. Commercial crab potters and commercial trotliners accounted for 51 and 36% of the annual harvest, respectively. Sport crabbers landed the rest of the estimated catch with trotlines or collapsible traps. The results of the 1981 survey were used to evaluate sampling needs for 1982 and led to reductions in sample sizes.
Wind- and current-induced drifts of blue crab larvae hatching near the mouth of Chesapeake Bay, Virginia, are simulated using numerical models to examine the relationship between larval recruitment and environmental forcing. The circulation is produced with a three-dimensional model of the bay and adjacent continental shelf. The circulation is then used by a drifter advection model to produce Lagrangian drift tracks. Observed winds at Norfolk, Virginia, predicted tides from harmonic analysis, and daily river discharges from major tributaries are used as driving forces. The model includes both density and wind forced circulation. We model the release of near-surface drifters from 132 hatch locations in and near the bay mouth. Because higher numbers of larvae have been observed at some locations than at others, each location of a simulated hatch is given a probability weighting. Model hatches occur on three different days in both 1980 and 1982, and drifters are tracked for 45 days. At the end of that time, the location of each drifter is analyzed. Those within the bay are categorized as recruited. Weighted recruitment ranges from 3 to 67%, with a mean of 42% of the total larvae. Although in the simulations some larvae are retained in the bay and never leave (averaging 13%), a majority of larvae leave the bay (87%) and a large number (29%) leave the Bay and later return in the surface waters. In cases where drifters are moved to the bottom after 35 days, subsequent recruitment is severely reduced. By alternately removing forcing by winds, river flow, and density differences, the relative influence of the three forcings is also evaluated. The wind component is found to have the greatest effect on larval recruitment, although wind can either increase or decrease recruitment. River flow and gravitational circulation each have a smaller influence.
This report forms part of an on-going effort to understand the large yearly variations in blue crab harvest of Chesapeake Bay. Recent sampling programs have indicated that the larvae are transported out of the bay immediately after being spawned, and spend their first month offshore at the sea surface. Although it is well established that a mid and outer shelf southward flow occurs during all seasons in the Middle Atlantic Bight, very little is known of the nearshore currents. This study constitutes an effort to determine if the characteristically light, but northward, wind stress during the critical summer months is sufficient to drive northward counter flow at the surface and, hence, to reduce the chances that the larvae are being advected south and lost from the area of Chesapeake Bay.We investigate a local model of wind-driven currents on the continental shelf with vertical decoupling at the pycnocline. Additional driving forces include an alongshore sea surface slope and horizontal pressure gradients. With characteristic forcing values, it is found that the wind stress is indeed sufficient to drive a light northward flow within 25 to 50 km of the shoreline. We expect, then, that blue crab larval recruitment back to Chesapeake Bay may be partially dependent on summer wind stress. A comparison between a wind index time series and harvest several years later is strongly suggestive of such a dependency.
A modification has been made to the simple Ricker stock recruitment model in order to account for density-independent mortality through fluctuating environmental conditions as well as density-dependent mortality. The modified model is applied to the blue crab fishery data from Chesapeake Bay, Maryland.The model results in a family of stock recruitment curves which assist in the understanding of a complex relationship between spawning stock and recruitment, thereby providing a better basis for recruitment prediction and fishery management. A management strategy for a fishery subject to fluctuating levels of recruitment is also discussed.