Kemberling and Darnell: Distribution, abundance, and reproductive output of spawning female Callinectes sapidus 
area. Recorded CWs were 3—281 mm (median: 136 mm), 
with 99.5% of blue crab having CWs of 20-200 mm. 
Although sex was not recorded for all blue crab, 93.0% 
of the 1597 blue crab for which sex was determined were 
female. Adult female blue crab were caught in 17.1% of all 
trawl tows, with a total of 6355 caught. The overall mean 
CPUE of adult females was 0.25 individuals/ha (standard 
error of the mean [SE] 0.01) over the full study period, with 
annual mean CPUE ranging from 0.06 individuals/ha 
(SE 0.02) in 2013 to 0.53 individuals/ha (SE 0.09) in 2010.: 
Annual frequencies of occurrence for adult female blue 
crab ranged from 8.5% in 2000 to 25.7% in 2011 (Table 1). 
The maximum annual mean CPUE of adult females 
observed during the summer surveys was 0.87 individu- 
als/ha (SE 0.31) in 2006, and the maximum annual mean 
CPUE of adult females observed during the fall surveys 
was 0.29 individuals/ha (SE 0.09) in 2011. 
Following comparisons of candidate models, the selected 
model included year, season, an interaction of year and 
season, and separate smooth terms for geographic location 
in each season (Table 2), with the selected model explain- 
ing 47.9% of the deviance in catch. Results of the Wald 
Table 2 
Candidate models used to estimate catch of adult female 
blue crab (Callinectes sapidus) collected from the north- 
west Gulf of Mexico between 2000 and 2019. Model selec- 
tion criteria also are given for each model: the difference in 
Akaike information criterion (AIC) between each model and 
the model with the lowest AIC (AAIC), AIC weight (wajc), 
and the proportion of deviance explained. The characters 
“s()” indicate that a continuous variable was included as 
a smooth term. All models included an offset term for the 
area swept by the trawl to account for differences in sam- 
pling effort among trawl tows. 
Model formulation AIC AAIC Waic D? 
Year + season + 12,947.7 0.00 1 
(year x season) + 
s(geographic 
location) x season 
Year + season + 13,072.6 
s(geographic 
location) x season 
Year + season + 13,302.3 
351 
Table 1 
Summary information by year for adult female blue crab 
(Callinectes sapidus) collected in the northwestern Gulf 
of Mexico during groundfish trawl surveys conducted in 
2000-2019 as part of the Southeast Area Monitoring and 
Assessment Program. The number of trawl tows; total 
catch (number of individuals); mean catch per unit of 
effort (CPUE), calculated by dividing catch by the area 
swept by the trawl (number of individuals per hectare) 
and given with standard error of the mean (SE) in paren- 
theses; and percent occurrence of female adult blue crab 
are provided. 
No. of Total Mean Percent 
Year trawl tows catch CPUE (SE) occurrence 
2000 585 159 
2001 525 179 
2002 575 
2003 528 
2004 533 
2005 517 
2006 529 
2007 510 
2008 642 
2009 689 
2010 431 
2011 381 
2012 336 
2013 261 
2014 342 
2015 346 
2016 309 
0.14 (0.06) 8.55 
0.14 (0.03) 10.86 
0.19 (0.03) 17.39 
0.26 (0.05) 16.48 
0.26 (0.05) 14.63 
0.31 (0.04) 22.63 
0.48 (0.16) 18.34 
0.26 (0.05) 16.86 
0.23 (0.05) 13.86 
0.33 (0.05) 20.90 
0.53 (0.09) 23.43 
0.49 (0.08) 25.72 
0.16 (0.04) 15.18 
0.06 (0.02) 9.58 
0.11 (0.02) 15.79 
0.12 (0.02) 18.21 
0.16 (0.03) 20.71 
2017 333 0.26 (0.05) 19.82 
2018 308 0.13 (0.02) 17.86 
2019 0.17 (0.03) 18.35 
(year x season) + 
s(geographic 
location) 
Year + season + 13,410.7 
s(geographic 
location) 
Year + s(geographic 13,636.8 689.07 
location) 
Year + season 14,560.2 1612.55 
Year 14,797.0 1849.35 
chi-square test indicate that all predictors had a significant 
effect on catch (Table 3). Averaged over the full study period, 
CPUE of adult female blue crab was higher during the sum- 
mer surveys (0.39 individuals/ha [SE 0.03]) than during the 
fall surveys (0.11 individuals/ha [SE 0.01]), although this 
pattern was not consistent across all years (Fig. 2). The 
spatial distribution of adult female blue crab also differed 
between the 2 seasons (Table 3). In summer surveys, CPUE 
was generally highest in nearshore regions off Louisiana 
and along the central and upper coasts of Texas, primarily 
at depths <36.6 m (<20 fathoms). The CPUE from fall sur- 
veys was generally highest off southeastern Louisiana and 
at intermediate distances from shore (Fig. 3). 
Estimated marginal mean CPUE for each year, stan- 
dardized relative to the 20-year average, provides a stan- 
dardized index of abundance for the offshore spawning 
stock of blue crab in the northwestern Gulf of Mexico 
(Fig. 4). With the exception of 2010 and 2011, the index 
of abundance for each year was within 1.5 standard devi- 
ations of the mean value. The index indicates a trend of 
slight increases in abundance from 2000 to 2009, followed 
by a large increase in 2010, a sustained high level of abun- 
dance in 2011, and a marked decrease after 2011. After 
a low in 2012, the index has steadily increased back to 
average levels of abundance. 
