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CBSAC 2012 Blue Crab Advisory Report Figures. Figure 1. Winter dredge survey index of total blue crab abundance (density of males and females, all sizes combined) in Chesapeake Bay, 1990 through 2012. Error bars represent 95% confidence intervals. - PowerPoint PPT Presentation
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CBSACCBSAC
2012 Blue Crab Advisory Report 2012 Blue Crab Advisory Report
FiguresFigures
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1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012
Year
Den
sity
(cra
bs/1
000
m s
q)Figure 1. Winter dredge survey index of total blue crab abundance (density of males and females, all sizes combined) in Chesapeake Bay, 1990 through 2012. Error bars represent 95% confidence intervals.
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Abundance of Age 1+ female blue crabs (Millions)
Exp
loit
atio
n f
ract
ion
of
fem
ale
blu
e cr
abs
(%)
annual exploitation fraction
target exploitation fraction = 25.5
threshold exploitation fraction = 34
Figure 2. The female-specific control rule for the Chesapeake Bay blue crab fishery. In 2011, abundance was below the overfished target, while the exploitation rate was below the overfishing target. Reference points were derived from a statistical assessment model incorporating multiple surveys. Please see text for explanation of terms.
2011
Overfished
Abundance
too Low
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90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09 10 11 12
Year
Nu
mb
er o
f A
ge
1+ F
emal
e C
rab
s (m
illi
on
s) age 1 + female abundance
Recommended threshold = 70 million crabs
Recommended target = 215 million crabs
Figure 3. Winter dredge survey estimate of abundance of female blue crabs age one year and older (age 1+) 1990-2012 with female-specific reference points. These are female crabs measuring greater than 60mm across the carapace and are considered the ‘exploitable stock’ that will spawn within the coming year.
Spawning-age abundance too low – population is overfished
Figure 4. Winter dredge survey estimate of abundance of male blue crabs age one year and older (age 1+) 1990-2012. These are male crabs measuring greater than than 60mm across the carapace and are considered the ‘exploitable stock’ that will spawn within the coming year.
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90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09 10 11 12
Year
Nu
mb
er o
f A
ge
1+ M
ale
Cra
bs
(Mil
lio
ns)
age 1+ males average age 1+ males
Figure 5. Winter dredge survey estimate of abundance of juvenile blue crabs (age 0), 1990-2012. These are male and female crabs measuring less than 60mm across the carapace.
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90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09 10 11 12
Year
Nu
mb
er o
f A
ge
0 C
rab
s (M
illi
on
s) age 0 - new recruits age 0 mean
Figure 6. Maryland and Virginia Chesapeake Bay commercial blue crab harvest in millions of pounds, 1993-2011.
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Year
Ha
rve
st
(mill
ion
s o
f p
ou
nd
s)
MD
Maryland Average
VA
Virginia Average
PRFC
PRFC Average
02468
101214161820
2008 2009 2010 2011
Year
Har
vest
(M
illi
on
s o
f P
ou
nd
s)
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Ab
un
dan
ce o
f C
rab
s (m
illi
on
s)
Virginia Female Harvest
Maryland Female Harvest
Female Abundance
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2008 2009 2010 2011
Year
Har
vest
(M
illi
on
s o
f P
ou
nd
s)
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300
Ab
un
dan
ce o
f C
rab
s (m
illi
on
s)
Virginia Male Harvest
Maryland Male Harvest
Male Abundance
Figure 7. Trends in Bay-wide male and female blue crab abundance and male and female commercial harvest within Maryland and Virginia since the implementation of female-specific regulations.
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90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09 10 11
Year
Per
cen
tag
e R
emo
ved
Percentage of Crabs Removed Female-specific target
Female-specific threshold
Figure 8. The percentage of female crabs removed from the population each year by fishing relative to the female-specific target and threshold levels 1990 through 2011.
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Year
Pe
rce
nta
ge
Re
mo
ve
d
Percentage of Crabs Removed Target Percentage = 46%
Threshold Percentage = 53%
Figure 9. The percentage of male and female crabs removed from the population each year by fishing relative to previously used target and threshold levels 1990 through 2011.
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