125 
National Marine 
Fisheries Service 
NOAA 
Fishery Bulletin 
@& established in 1881 << 
Spencer F. Baird 
First U.S. Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Abstract—This study, which included 
examination of the distribution and 
life history and a stock assessment of 
the flathead lobster (Thenus orientalis), 
is the first of its kind in the waters 
of Saudi Arabia in the Arabian Gulf, 
also known as the Persian Gulf. The 
flathead lobster is widely distributed 
in this region, although it is more 
abundant in the central and north- 
ern Arabian Gulf. Carapace lengths 
at 50% and 95% maturity are 59 and 
65 mm for females and 58 and 71 mm 
for males. The fecundity of 4 berried 
females ranged from 26,000 to 76,000 
eggs per spawning, and the fertilization 
rate exceeded 97%. Length—frequency 
data were consistent with just 2 cohorts, 
indicating that this species has a short 
life span and high growth coefficient 
(K=0.846 year‘). Large fishing boats 
(called dhows) accounted for more than 
98% of the total landings. Estimates 
of natural mortality rates from use of 
generalized depletion models have high 
statistical precision and a magnitude 
compatible with short life history. In 
addition, abundance levels estimated 
with the depletion model are sufficient 
to support a sustainable small-scale 
fishery either as bycatch of shrimp 
trawlers or as a resource targeted with 
specialized gear. A targeted fishery for 
flathead lobster could be set during the 
off months of the shrimp traw] fishery 
(February—July), reducing interference 
with the reproduction cycle. 
Manuscript submitted 2 November 2021. 
Manuscript accepted 31 March 2022. 
Fish. Bull. 120:125-137 (2022). 
Online publication date: 20 April 2022. 
doi: 10.7755/FB.120.2.3 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Ecology, life history, and fisheries potential 
of the flathead lobster (Thenus orientalis) 
in the Arabian Gulf 
Lotfi Rabaoui (contact author)" 
Lamia Yacoubi* 
Yu-Jia Lin’ 
Thadickal V. Joydas' 
Mohammad A. Qurban'?4 
Panickan Premlal' 
Jinoy Gopalan' 
Zahid Nazeer' 
Manambrakat Vijayakumaran' 
Syed Ajmal Khan’ 
Rubén H. Roa-Ureta® 
Email address for contact author: Irabaoui@gmail.com 
' Center for Environment & Marine Studies 
Research Institute 
King Fahd University of Petroleum & Minerals 
Dhahran, Eastern Province 31261, Saudi Arabia 
2 National Center for Wildlife 
Riyadh 12746, Saudi Arabia 
3 University of Carthage 
Amilcar, Tunis 1054, Tunisia 
The flathead lobster (Thenus orientalis) 
is a highly valued commercial lobster 
species, with increasing importance in 
the world (Spanier and Lavalli, 2006). It 
has a wide distribution in the Arabian 
Gulf, also referred to as the Persian 
Gulf, including in waters of Saudi 
Arabia in the northwestern part of the 
gulf, where it has been traditionally 
captured as bycatch by local, small-scale 
fishing operations during the season 
(August—January) of the trawl fishery 
for the green tiger prawn (Penaeus semi- 
sulcatus). Landing this lobster species 
was forbidden by managers because of 
a lack of scientific knowledge for deter- 
mination of sustainable catch rates and 
development of regulations oriented 
toward sustainability. This measure, 
implemented in 2008 and still enforced, 
was taken as a precautionary action 
pending studies of the life history and 
biological reference points of and a stock 
assessment for this species. 
The distribution of species of Thenus 
and other slipper lobsters (Scyllaridae) 
“ Deputy-Ministry for Environment 
Ministry of Environment, Water & Agriculture 
Riyadh 11195, Saudi Arabia 
> Centre of Marine Sciences 
University of Algarve 
8005-139 Faro, Portugal 
depends on several environmental 
factors (Spanier and Lavalli, 1998; 
Wardiatno et al., 2016), as observed 
in palinurids (Herrnkind et al., 1997; 
Butler et al., 2006). The nature of 
sediments and the depth of water are 
the 2 major factors that influence the 
abundance of slipper lobsters (Jones, 
2007; Lavalli et al., 2019). The flat- 
head lobster prefers soft, sandy sed- 
iment areas with medium-to-coarse 
particle size. Tropical slipper lobsters, 
including species of Thenus, may live 
at densities of 1-10 individuals/ha in 
areas that reflect the habitat pref- 
erences of the species (Jones, 2007). 
There is no evidence of aggregation 
due to reproductive stimuli in species 
of Thenus, but the presence of other 
species, such as prey, predators, and 
competitors, may influence the den- 
sity of these species in a particular 
habitat (Jones, 2007). 
Species of Thenus have greater 
mobility because of the highly devel- 
oped swimming ability that sets this 
