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Fishery Bulletin 118(4) 
been sampled for at least 8 years during the period 2006-— 
2018. Additionally, only stations west of the Mississippi 
River were included, to correspond with the spatial extent 
of the SEAMAP data used for offshore abundance esti- 
mates. Annual mean CPUE of adult (=125 mm CW) female 
blue crab was then multiplied by the total available habi- 
tat area to estimate the total abundance of mature females 
in estuarine waters of Louisiana west of the Mississippi 
River for each year. Total available estuarine habitat area 
in Louisiana was calculated by using the NOS80K shore- 
line data set from the NOAA Office of Ocean Resources 
Conservation and Assessment (NOAA’). This shoreline 
layer was created in 1994, however, and substantial land 
loss has occurred in Louisiana since that time (Couvillion 
et al.°). The total available estuarine habitat in the 
Louisiana portion of their study area was, therefore, cor- 
rected on the basis of observed rates of coastal land loss in 
our study area (Couvillion et al.°). 
Condition and reproductive output of spawning females 
Mature female blue crab were collected offshore during 
the summer and fall SEAMAP groundfish trawl surveys 
in 2017 for analyses of overall condition and reproductive 
output. Mature females were haphazardly selected from 
the haul of each trawl tow, individually bagged and frozen, 
and sent to the Gulf Coast Research Laboratory in Ocean 
Springs, Mississippi, for analysis. During the summer sur- 
vey (30 May—2 July 2017), 109 blue crab were collected 
from 48 stations, and during the fall survey (13 October—8 
November 2017), 11 females were collected from 10 sta- 
tions (Fig. 1). 
Following thawing, CW and total mass were recorded for 
each crab. Gills were inspected for the presence of the par- 
asitic gooseneck barnacle Octolasmis muelleri and for the 
parasitic nemertean worm Carcinonemertes carcinophila. 
Spermathecae, the paired sperm storage organs, were 
located to determine if the female had recently mated. A 
female was determined to have recently mated (within 
the past 3-5 weeks; Wolcott et al., 2005) if her spermathe- 
cae had a large size, firm texture, and pink color (Wolcott 
et al., 2005; Ogburn and Habegger, 2015). Because females 
mate only once in their lifetime, following their terminal 
molt, large, firm, pink spermathecae serve as an indica- 
tion that a female moved offshore soon after her mating 
or that a female mated while offshore. Each female was 
determined to be spawning capable if she had developed, 
full ovaries or carried an egg mass. 
For ovigerous females, the egg mass was carefully 
separated from the pleopods and weighed. A subsam- 
ple <1 g (typically 500-1000 eggs) was then removed 
7 NOAA. 1994. NOS80K: medium resolution digital vector U.S. 
shoreline shapefile. Strategic Environ. Assess. Div., Off. Ocean 
Resour. Conserv., Natl. Ocean Serv., NOAA, Silver Spring, MD. 
[Available from website, accessed May 2020.] 
e Couvillion, B. R., H. Beck, D. Schoolmaster, and M. Fischer. 
2017. Land area change in coastal Louisiana 1932 to 2016: 
U.S. Geological Survey scientific investigations map 3381, 16 p. 
[Pamphlet.] [Available from website, accessed May 2020.] 
and weighed, and the total number of eggs in the sub- 
sample was counted by using a stereoscopic microscope. 
Total fecundity was estimated for each ovigerous female 
by dividing the number of eggs in the subsample by the 
mass of the subsample and multiplying by the mass of 
the entire egg mass. Relationships between fecundity 
and body size were examined by using generalized lin- 
ear models (GLMs) with a Gaussian distribution and log 
link function and with fecundity as the response variable. 
Separate GLMs were fit to model fecundity as a function 
of CW and body mass (excluding the mass of the egg 
mass). Because of missing data for body mass of 16 of 
the 73 ovigerous blue crab, it was not possible to directly 
compare the model fits by using AIC or the AIC corrected 
for bias of small sample sizes (AICc) because the 2 mod- 
els used slightly different data sets. For comparisons, the 
GLM with CW as the predictor was refit by using only 
individuals with data for both CW and body mass, and 
then the models were compared by using AICc. 
The embryonic developmental stage for each egg sam- 
ple was determined by visual examination under a com- 
pound microscope and classified as early (stages 1-3 of 
DeVries et al., 1983), middle (stages 4-6 of DeVries et al., 
1983), and late (stages 7—9 of DeVries et al., 1983). The 
percentage of embryos that were developing normally 
(Darnell et al., 2009) was visually assessed for each egg 
mass on the basis of 20 eggs chosen at random from the 
subsample. Egg size for 20 normally developing embryos 
was determined by measuring along the long axis and 
the perpendicular axis with a compound microscope. Egg 
volume was calculated for each measured egg as the vol- 
ume of a prolate spheroid by using the short and long 
axis measurements. Egg volume measurements were 
averaged for each egg mass, and this mean volume for 
each egg mass was then used in subsequent analyses. 
Egg volume was analyzed by using a GLM with a gauss- 
ian distribution and a log link function and with egg vol- 
ume as the response variable. Egg volume was modeled 
as a function of CW and embyronic developmental stage 
(early, middle, and late). 
Results 
Long-term patterns of distribution and relative abundance 
A total of 8996 trawl tows were conducted in offshore 
waters across the study area in 2000-2019. During that 
time, 97.7% of summer sampling occurred in June and 
July, with 1.3% occurring in May and 1.0% occurring in 
August. Fall sampling was primarily (97.7%) conducted 
during October and November, with 2.2% occurring in 
September and 0.1% occurring in December. Depths sam- 
pled were 9.2—109.5 m. Salinities measured at the bottom 
of the water column at sampling locations were 10.9-39.5, 
with 97.3% of trawl tows conducted in waters with salini- 
ties >30.0. Bottom temperatures were 16.0—30.5°C. 
Blue crab were caught in 19.4% of all trawl tows, with 
11,021 caught during 2000-2019 across the full study 
