Kemberling and Darnell: Distribution, abundance, and reproductive output of spawning female Callinectes sapidus 355 
Fecundity (millions of eggs) 
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Carapace width (mm) 
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Figure 6 
Relationships between fecundity and (A) carapace width and (B) 
body mass for ovigerous female blue crab (Callinectes sapidus) col- 
lected during the groundfish trawl survey conducted in 2017 in the 
northwestern Gulf of Mexico as part of the Southeast Area Monitor- 
ing and Assessment Program. Lines indicate relationships from gen- 
eralized linear models. Shaded regions represent the 95% confidence 
interval. D’=deviance explained. 
Louisiana, and this pattern was consistent for both sum- 
mer and fall surveys (Fig. 4). This spatial pattern reflects 
reported inshore fishery landings, with areas off Louisi- 
ana accounting for 88% of the blue crab landings in the 
Gulf of Mexico in 2018 (NMFS’). The large numbers of 
blue crab caught offshore of Louisiana relative to catch 
in other regions likely reflect the low salinities present in 
estuaries of Louisiana. Egg hatching and larval survivor- 
ship is negatively affected by salinities <20.1 (Costlow 
and Bookhout, 1959); during the spawning migration, 
therefore, females move to spawning grounds suitable 
for offspring survival. It is possible that the low salini- 
ties in estuaries of Louisiana result in greater numbers 
° NMFS (National Marine Fisheries Service). 2018. Commercial 
landings query, release 3.1.0.2. Off. Sci. Technol., Natl. Mar. 
Fish. Serv, Silver Spring, MD. [Available from website, accessed 
March 2020.] 
of females migrating out of the estuaries and 
continuing to migrate into the offshore environ- 
ment, compared with the numbers of females 
that migrate out of estuaries in other regions. 
Although CPUE was highest off Louisiana in 
both seasons, the spatial distribution of the 
CPUE differed between summer and fall (Fig. 4). 
During summer, adult females were primarily 
caught in nearshore regions, at depths <36.6 m 
(<20 fathoms). During fall, adult females were 
primarily caught at depths of 36.6—73.2 m (20-40 
fathoms) off both Texas and Louisiana. 
Ogburn and Habegger (2015) conducted a sim- 
ilar examination of blue crab spawning in off- 
shore waters of North Carolina, South Carolina, 
Georgia, and Florida, by using data from the 
SEAMAP-South Atlantic trawl surveys, with sim- 
ilar results. The highest CPUE of mature female 
blue crab occurred during the summer, females 
were actively spawning offshore, and a substantial 
portion of the spawning stock in Georgia occurred 
in offshore waters. Using only data from summer 
surveys, we observed a maximum annual mean 
CPUE of 0.87 individuals/ha (SE 0.31) (in 2006), 
a level substantially lower than the maximum of 
1.58 individuals/ha observed (in 1991) by Ogburn 
and Habegger (2015). When interpreting this 
difference in CPUE, however, it is important to 
consider the differences in survey design between 
the SEAMAP trawl surveys conducted along the 
Atlantic coast of the southeastern United States 
and in the Gulf of Mexico. The SEAMAP-South 
Atlantic survey samples at depths of 4.0-10.0 m 
(2-5 fathoms), and the SEAMAP-Gulf of Mexico 
survey samples at depths of 9.1-109.7 m (5-60 
fathoms). If the SEAMAP-Gulf of Mexico data set 
examined in this study is limited to depths <15 m, 
mean adult female CPUE was 1.96 individuals/ 
ha (SE 0.97) in summer 2006, 1.58 individuals/ha 
(SE 1.13) in summer 2010, and 1.53 individuals/ha 
(SE 1.09) in summer 2000. 
Although densities of adult female blue crab observed 
in the SEAMAP study area were relatively low, the off- 
shore areas sampled in our study support a substantial 
portion (up to 79.7%, depending on the year) of the 
spawning stock in the northwestern Gulf of Mexico. We 
acknowledge that our estimates of total abundance of the 
spawning stock are rough, with multiple potential 
sources of error. A size-based cutoff was used to classify 
blue crab as adults or juveniles, rather than a visual mor- 
phological examination. Although the fishery-indepen- 
dent trawl surveys conducted by the LDWF and TPWD 
record maturity stage for blue crab, this information is 
not recorded in the SEAMAP trawl surveys. For consis- 
tency, we therefore classified all blue crab >125 mm CW 
as adults for data from all 3 survey programs. Addition- 
ally, these estimates do not account for differences in 
gear or gear efficiencies in the 3 survey programs. Actual 
abundances, therefore, are likely to be substantially 
