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Spatial distribution and abundance 
The spatial distribution and abundance of flathead lob- 
sters were determined by using the data collected during 
5 trawl surveys conducted in the waters of Saudi Arabia in 
the Arabian Gulf between 2013 and 2016. Three traw! sur- 
veys were conducted on the commercial outrigger Afrah 
(which had a trawl net with a knot-to-knot mesh size of 
15 mm) in March and July 2013 and in May—November 
2016. Two trawl surveys were completed on the Kuwaiti 
RV Bahith IT (which had a trawl net with a knot-to-knot 
mesh size of 36 mm) in June—July 2014 and in May—June 
2015. In total, trawl surveys were conducted at 189 sta- 
tions (88 stations in 2013, 31 stations in 2014, 40 stations 
in 2015, and 30 stations in 2016). 
A systematic grid design was applied for the trawling sur- 
veys. In 2013, equally spaced stations were set along pre- 
determined transects perpendicular to the coast, covering 
all territorial waters of Saudi Arabia in the Arabian Gulf. 
In 2014 and 2015, we visited stations set as close as possi- 
ble to ones we previously surveyed, with a few additions or 
reductions in station numbers because of constraints, such 
as poor weather and validity of fishing permits. In 2016, 
the team surveyed the locations where flathead lobsters 
occurred often in previous surveys, to increase sample size 
for biological analysis and habitat characterization. We 
assumed that there were no differences in size selectivity 
between the gears used by the 2 vessels employed for the 
surveys. This assumption is justified because the mesh size 
of both trawlers is selective for fish under 40 mm in total 
length, meaning carapace length plus the tail (Lin et al., 
2021a), and the smallest total length of all flathead lob- 
sters caught during surveys was 52 mm. Therefore, given 
this assumption of equal selectivity, we pooled the lobster 
catch and biological data from the surveys conducted on the 
2 vessels to increase the sample size. 
Standard operating procedures were applied in all sur- 
veys. In other words, the following actions were taken: 1) at 
each station, we recorded environmental variables, such 
as temperature, salinity, and depth before trawling; 2) the 
duration of each trawl was fixed at approximately 30 min; 
3) once the catch was on deck, the bottom type (sand, mud, 
or rock) was determined by examining debris; 4) the entire 
catch was photographed and weighed; and 5) 5—-100% of the 
catch, including the debris, was randomly sampled for fur- 
ther analysis in the laboratory. 
The catch per unit of effort, expressed as kilograms per hour 
of trawling, was determined for each survey and included only 
the stations where at least one flathead lobster was encoun- 
tered. The abundance and biomass of lobsters for the trawled 
area, expressed as the number of individuals per 100 square 
meters of trawling and grams per 100 square meters of trawl- 
ing, were calculated for each survey. The spatial distributions 
of abundance and biomass of flathead lobsters were plotted 
for the cruises from 2013 through 2016 by using the packages 
rworldmap (vers. 1.3-6; South, 2011) and rworldxtra (vers. 
1.01; South, 2012) in R, vers. 4.0.2 (R Core Team, 2020). The 
spatial heatmaps were plotted by using the package akima 
(vers. 0.6-2.1; Akima and Gebhardt, 2020) in R. 
Reproductive biology and growth 
A total of 302 flathead lobsters, collected during trawl 
surveys and from auction centers, were used for detailed 
morphometric studies. All collected lobsters were trans- 
ported to the laboratory, where they were measured (for 
total length) and weighed (for total weight) and their sex 
was determined. The reproductive biology of the flathead 
lobster was studied by recording the morphological and 
morphometric changes that occur at maturity, the gonado- 
somatic index (GSI), and the maturity stages of gonads. 
The maturity stages of female gonads were determined 
following the classification proposed by Kennelly et al. 
(1997) and Haddy et al. (2005) (see Suppl. Table 1) (online 
only). Similarly, 5 maturity stages of male gonads were 
determined by dissecting the lobster as well as by using 
histology. The color and condition of the fresh gonads were 
noted, and their wet weight was recorded to the nearest 
0.001 g after wiping water from the gonads with blotting 
paper. Fecundity was examined by counting the eggs in 
the pleopods of berried females. We estimated fecundity 
by taking the total weight of eggs carried by the female 
after stripping it, counting the eggs in a minimum of 3 
samples weighing from 0.1 g to 1.0 g, and extrapolating 
the numbers to get the total count in the whole egg mass. 
The fertilization rate of eggs was estimated by counting 
the number of unfertilized eggs in the egg mass. Unfertil- 
ized eggs are cream or pink in color, and fertilized eggs are 
dark yellow or orange (Kizhakudan}). 
The GSI was calculated for each mature female as the 
percentage of body weight accounted for by ovary weight. 
The maturity status of the lobster by carapace length was 
estimated by using a logistic model: 
Sy Sa (1) 
iL ab GANS 
where S(L) = the proportion of mature individuals at car- 
apace length L in millimeters; 
g = the intercept parameter; and 
h = the slope parameter. 
The model was fit to data of counts of immature and 
mature individuals at length categories with logistic 
regression. The carapace lengths at which 50% (L;,) and 
95% (Lo;) of individuals were mature were calculated by 
using the following equations (Roa et al., 1999): 
Ls9 = Se and (2) 
h 
1 R 
|] -—g 
19 
Los, _ a ae (3) 
! Kizhakudan, J. K. 2016. Hatchery technology and seed produc- 
tion of lobsters. In Course manual: winter school on techno- 
logical advances in mariculture for production enhancement 
and sustainability (I. Joseph and B. Ignatius, eds.), p. 106— 
118. Cent. Mar. Fish. Res. Inst., Kochi, India. [Available from 
website.] 
