348 
Fishery Bulletin 118(4) 
Gulf of Mexico” 
T 
94°W 
9g2°W 
Figure 1 
A map of the study area in the northwestern Gulf of Mexico showing the locations 
where blue crab (Callinectes sapidus) were collected in groundfish trawl surveys as 
part of the Southeast Area Monitoring and Assessment Program (SEAMAP). Small 
gray dots indicate locations of trawl tows for the study period 2000-2019. Black circles 
indicate locations where adult female blue crab were caught, for reproductive analyses, 
during the SEAMAP groundfish surveys conducted in 2017, with circle size propor- 
tional to the number of blue crab collected from that location. The boxes outlined in 
gray and the numerals inside them indicate shrimp statistical zones (defined by the 
National Marine Fisheries Service), which were used in the stratified random sampling 
design. The black line indicates the 109.7-m (60-fathom) depth contour, which is used 
as the outer limit for SEAMAP groundfish surveys. 
(chosen haphazardly from the total catch) and the sex of 
every fifth measured crab were recorded for each station 
(GSMFC%). 
Long-term patterns of distribution and relative abundance 
Our analyses focused on the period 2000-2019 and 
included only offshore areas that were sampled before 
and after the change in survey design in 2008 (SSZ 11 and 
SSZ 13-21). Chandeleur Sound in Louisiana (SSZ 12) was 
excluded because this inshore area was not consistently 
sampled. Over this 20-year period, 7-119 trawl tows were 
conducted in each SSZ per year (Suppl. Tables 1 and 2) 
(online only). Data collected prior to 2000 were not included 
because of uncertainty surrounding species identifica- 
tion. Data were filtered to include only tows of 12.2-m 
trawl nets with stretched mesh sizes ranging from 40.3 
to 41.9 mm and conducted at depths >9.1 m (>5 fathoms). 
Any sampling events with incomplete data for geographic 
location or vessel speed or with operation codes indicat- 
ing a bad tow (e.g., if the doors came up crossed, if the 
* GSMFC (Gulf States Marine Fisheries Commission). 2016. 
SEAMAP operations manual for trawl and plankton surveys, 61 
p. GSMFC, Ocean Springs, MS. [Available from website.] 
codend came untied, or if the net was fouled or torn) were 
excluded from analysis. 
Maturity stage is not recorded for blue crab; therefore, it 
was necessary to classify crab as adult or juvenile on the 
basis of CW. We classified blue crab >125 mm CW as adults, 
following the cutoff used in recent Gulf-wide (VanderKooy, 
2013) and state-level (West et al.°) blue crab stock assess- 
ments. Because not all blue crab are measured and only 
a small proportion are assigned a sex, it was necessary to 
estimate the catch of adult female blue crab from each trawl 
tow by using the total catch multiplied by the proportion of 
measured blue crab from the tow that were >125 mm CW 
and by the proportion of blue crab from the tow that had 
their sex determined and that were classified as female: 
adult female catch = total catch x proportion adult x 
proportion female. 
For a small number of trawl tows (n=385 tows, 4.3% 
of the tows in the data set used in analysis), sex was 
not recorded, even though adult blue crab were caught 
during the tow. For these tows, the mean proportion of 
5 West, J., H. Blanchet, and P. Cagle. 2019. Update assessment of 
blue crab in Louisiana waters: 2019 report, 32 p. Louisiana Dep. 
Wildl. Fish., Baton Rouge, LA. [Available from website.] 
