Rabaoui et al.: Life history of Thenus orientalis in the Arabian Gulf 135 
Table 3 
Parameter estimates from the selected best stock assessment model for flathead lobsters (Thenus orientalis) 
fished as bycatch from the trawl fishery for the green tiger prawn (Penaeus semisulcatus) in waters of Saudi 
Arabia in the Arabian Gulf from 1995 through 2008. The estimated parameters include natural mortality 
(M), initial abundance (Nj), recruitment for each year (in millions of individuals), scaling (k), effort response 
(a), abundance response (f), and dispersion. Data are from 2 fleets in the shrimp fishery: small boats (called 
tarad) and large boats (called dhow). CV=coefficient of variation. 
Dhow boats Tarad boats 
Timing 
(month) 
Timing 
Parameter (month) Estimate CV (%) Estimate 
M (month“!) 0.1500 25.6 0.1500 
Np (millions) 109.1 14.5 109.1 
Recruitment 1995 (millions) 2.13 40.86 
Recruitment 1996 (millions) 41.08 34.5 0.55 
Recruitment 1997 (millions) 0.09 641.6 73.72 
Recruitment 1998 (millions) 0.41 - 0.38 
Recruitment 1999 (millions) 9.60 178.0 104.23 
Recruitment 2000 (millions) 0.05 2050.4 0.05 
Recruitment 2001 (millions) 11.69 235.1 1.60 
Recruitment 2002 (millions) 59.10 23.8 1.12 
Recruitment 2003 (millions) 0.95 277.6 9.62 
Recruitment 2004 (millions) 2.07 137.8 1.23 
Recruitment 2005 (millions) 2.24 334.5 34.30 
Recruitment 2006 (millions) 2.56 182.0 52.26 
Recruitment 2007 (millions) 52.14 - 1.65 
Recruitment 2008 (millions) 8.65 210.6 1.87 
k (1/number of days) 3.3969 x 10°° 473.9 3.3420 x 10° 
(oF 1.2433 39.2 0.0028 
B 0.7138 30.4 3.1669 
Dispersion 2.1160 x 10+ 14.1 8.6299 x 10°" 
No targeted fishery for the flathead lobster exists any- 
where in the world, and flathead lobsters form only a 
small percentage of the bycatch in the shrimp traw] fish- 
ery in waters of Saudi Arabia in the Arabian Gulf. Fish- 
ermen in the area have observed that flathead lobsters 
can be attracted to bright lights when swimming close to 
the surface and then caught with scoop nets. This type 
of fishing is done under bright illumination around oil 
platforms, or any other structure built in the sea that 
may act as a fish aggregating device. This method of fish- 
ing, which can be highly selective and non-destructive, 
must be scientifically studied to determine its efficiency 
and whether it targets a specific fraction of the popula- 
tion, particularly in connection with berried females. The 
results of our study indicate that a small-scale targeted 
fishery could complement landings by shrimp trawlers 
with a production level similar to the bycatch of flathead 
lobsters in the shrimp traw] fishery. This rate of exploita- 
tion would still take only 20% of the minimum biomass 
observed in some months during the fluctuation cycle 
observed in our stock assessment modeling. In addition, 
considering the main spawning period of November— 
December, a targeted fishery could be set during the 
off months of the shrimp trawl fishery (February—July), 
reducing interference with the reproduction cycle. 
Conclusions 
The results of this study indicate that the flathead lob- 
ster caught as bycatch in the shrimp trawl fishery in 
waters of Saudi Arabia in the Arabian Gulf could be the 
basis of a sustainable fishery connected to shrimp trawl- 
ing. The percentage of juveniles in bycatch of trawl sur- 
veys was negligible, and a majority of the samples in the 
catch were above the size at which 50% of females attain 
sexual maturity. Preventing the catch of berried flathead 
lobsters, especially during peak spawning in November— 
December, would further secure sustainability. Further- 
more, a targeted small-scale fishery that would operate in 
the off months of the shrimp trawl] fishery could be devel- 
oped as long as its output is similar to that of the bycatch 
of shrimp trawling. 
Acknowledgments 
The authors are grateful to the 2 anonymous reviewers 
who helped to improve the quality of this manuscript 
through their constructive comments and suggestions. We 
also thank all those who helped to conduct surveys in the 
field and process samples in the laboratory. 
