Fishery Bulletin 118(4) 
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Early Middle Late 
Embryonic developmental stage 
Figure 7 
Mean egg volume for each embryonic developmental stage 
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 Monitoring and Assessment Program. 
Mean egg volumes are estimated marginal means from 
the generalized linear model. Error bars indicate the 
back-transformed 95% confidence intervals. The different 
letters above the bars indicate statistically significant dif- 
ferences between developmental stages. 
higher than the estimates presented here. It is also 
important to consider the fate of larvae spawned offshore. 
There may be some distance offshore beyond which it is 
highly unlikely that a blue crab larva could successfully 
make it back to an estuary. To date, most larval transport 
modeling efforts for blue crab in the Gulf of Mexico have 
focused on spawning occurring at or near the estuarine 
mouth (e.g., Johnson and Perry, 1999; Jones et al., 2015; 
Criales et al., 2019). Further work is needed to better 
understand the fate of larval blue crab that have been 
spawned offshore. 
Our analyses of the reproductive health of female blue 
crab collected in offshore habitats gave no indication 
that these females are of poor health or that they are 
of any lesser value to the spawning stock than females 
spawning in estuarine waters. Estimated fecundity was 
1.07-8.93 million eggs, with an average of 3.27 million 
eggs (SE 0.15 million). In comparison, Graham et al. 
(2012) reported fecundity estimates of ~0.9—7.0 million 
eggs for ovigerous blue crab collected from estuarine 
waters of Mississippi Sound, and Prager et al. (1990) 
reported fecundity estimates of ~0.5-8.0 million eggs 
(mean: 3.2 million eggs) for ovigerous blue crab col- 
lected from Chesapeake Bay. Egg size in our study was 
also similar to that found in previous studies of oviger- 
ous females collected in estuarine waters. We observed 
egg measurements of 243.6 pm (SE 0.5) along the long 
axis and of 236.1 pm (SE 0.5) along the perpendicular 
axis. In comparison, Graham et al. (2012) reported egg 
diameters of ~215-310 pm (~215-275 pm during the 
summer and fall only) for blue crab from Mississippi 
Sound, and Darnell et al. (2009) reported an average 
egg diameter of 267.5 pm (SE 1.9) for blue crab from 
North Carolina. 
Fecundity of blue crab declines with age, with the 
greatest fecundity in the first clutch of eggs produced by 
a female (Darnell et al., 2009). That females collected in 
offshore and estuarine waters produce similar quantities 
of eggs indicates that offshore females are at a similar 
stage of their reproductive period as females spawning in 
estuarine areas. This notion is supported by our observa- 
tion of a high percentage of eggs that were fertilized with 
embryos developing normally (91.7% [SE 0.01]). Darnell 
et al. (2009) observed a decrease in the percentage of 
embryos developing normally in later clutches, from 
96.7% (SE 0.9) in a female’s first clutch to 55.0% (SE 20.1) 
in its fourth clutch. Assuming a similar pattern in blue 
crab from the Gulf of Mexico, this finding indicates that 
the females assessed in our study were producing their 
first or second clutch of eggs. We observed full, developed 
ovaries in >50% of females collected offshore during the 
summer, indicating that these blue crab would spawn at 
least once more in their lifetime. Our results also indicate 
that oviposition and continued spawning is occurring in 
offshore waters, and we observed all stages of embryonic 
development. 
The results of this study indicate that the coastal and 
offshore waters of the northwestern Gulf of Mexico are 
an important spawning habitat for blue crab. Although 
densities of blue crab offshore were low, these crab were 
primarily adult females and were actively spawning. 
Given the large amount of available shelf habitat, our 
results indicate that offshore areas support a substan- 
tial portion of the spawning stock in the northwestern 
Gulf of Mexico. Fecundity of females caught offshore was 
similar to that reported for estuarine spawning crab, and 
these females are continuing to spawn multiple clutches 
of eggs in offshore waters. Additional research is needed 
to understand the causes of temporal and spatial varia- 
tion in densities of spawning female blue crab in the Gulf 
of Mexico. Furthermore, it is critical that this previously 
understudied portion of the spawning stock of blue crab 
in the Gulf of Mexico be considered and accounted for in 
future management and assessment efforts in the Gulf 
of Mexico. 
Acknowledgments 
We thank the Pascagoula Laboratory of the NOAA South- 
east Fisheries Science Center, the LDWF, The University 
of Southern Mississippi Center for Fisheries Research and 
Development, H. Olmi, and C. Hayes for assisting with crab 
collection during the SEAMAP trawl surveys conducted 
in 2017. P. Cagle (LDWF) and M. Fisher (TPWD) provided 
assistance with access to inshore fishery-independent sur- 
vey data for Louisiana and Texas, respectively. This study 
