Open Journal of Marine Science, 2011, 3, 98- 1 07
doi:10.4236/ojms.2011.13010 Published Online October 2011 (http://www.SciRP.org/journal/ojms)
An Evaluation of the Selectivity Characteristics of
Different Juvenile Fish Escape Panel Designs for the
Demersal Trap Fishery of Abu Dhabi, United Arab
Emirates
Edwin Mark Grandcourt*, Thabit Zahran Al Abdessalaam, Stanley Alexander Hartmann, Ahmed
Tarish Al Shamsi, Franklin Francis
Biodiversity Management Sector, Environment Agency–Abu Dhabi, Abu Dhabi, United Arab Emirates
Received June 27, 2011; revised September 8, 2011; accepted September 18, 2011
Abstract
The selectivity characteristics of 4 juvenile fish escape panel designs and their utility for the regulation of a
multi-species demersal trap fishery were evaluated using a suite of objective socio-economic and biological
criteria. The panel designs consisted of a control (type A) which had a hexagonal mesh size which was the
same as that of the body of the trap (3.5 cm), a rectangular mesh (type B) which was representative of the
current regulation (5.0 × 7.6 cm) and 2 escape panels with square meshes of 7.5 × 7.5 cm (type C) and 10.0 ×
10.0 cm (type D). The results demonstrated that there was only a limited reduction in the proportion of juve-
nile fish and by-catch retained for the existing juvenile escape panel design (type B). Furthermore, as the se-
lectivity characteristics for the key species (Epinephelus coioides and Diagramma pictum) were similar to
the control type, the predicted increases in yields, revenues and spawning stock biomass were small by com-
parison. The escape panel with the largest mesh size (type D) retained the least un-utilized and discarded
by-catch. Whilst simulations predicted the highest spawner biomass per recruit, long term yields and reve-
nues for the key species, its use was associated with a dramatic short-term decline in revenues which were
23.3% of the value of the control type. Traps fitted with the type C which had a square mesh of 7.5 × 7.5 cm
had the lowest juvenile retention and the highest overall score for all the assessment criteria combined. The
study provides an empirical basis for gear regulations for the demersal trap fishery of the Emirate of Abu
Dhabi and the wider Arabian Gulf region.
Keywords: Trap Fisheries, Selectivity, Escape Panel, By-Catch, Multi-Species Fisheries
1. Introduction
The fisheries of the southern Arabian Gulf are typically
multi-species in nature with over 100 species being ex-
ploited. They provide a source of income, employment
and recreation at the same time as contributing to the cul-
tural heritage and food security of the inhabitants of the
littoral states [1]. Dome shaped wire traps known locally
as ‘gargoor’ operated from traditional wooden dhows are
the most common method used to exploit demersal species.
In common with other trap fisheries [2], the construction
material has changed over time from natural materials
(inter-woven palm fronds) to galvanized steel wire. The
diameter of the trap base varies between 1 and 3 m, they
are supported by tubular steel bars and have a funnel en-
trance [3].
Some of the demersal fish populations in the region
have been heavily exploited and fishing effort may be
above optimum levels for many species [4], furthermore,
the lack of appropriate data on most stocks underscores
the need to assess fisheries resources [5]. The results of
stock assessment studies for the key species caught in the
demersal fisheries of Abu Dhabi in the southern Arabian
Gulf have revealed that there are a large number of juve-
nile fish retained by the trap fishery. More than half of
the landed catches of the sparids (Acanthopagrus bifas-
ciatus and Argyrops spinifer) for example are composed
of immature fish [6]. Juvenile retention is a critical ma-

E. M. GRANDCOURT ET AL.99
nagement issue because in combination with intensive
exploitation, it has resulted in both ‘growth overfishing’
where yields are in excess of the production potential and
“recruitment overfishing” where the populations have
been reduced to such low levels that their reproductive
capacity is impaired [7].
There are two principal benefits of increasing the size
at which fish become vulnerable to capture, firstly, the
fishery can benefit from increased yields as the full
growth potential of the resource base is realized, and
secondly, the stock size can increase through greater re-
productive capacity and a reduction in the proportion of
the stock that is vulnerable to capture. Higher yields in a
trap fishery in the Caribbean have been documented just
3 years after the introduction of larger mesh sizes [8].
Increasing the mesh-size selectivity of fish traps may
also result in a reduction of discarded by-catch species
[9]. Such benefits are consistent with management objec-
tives of resource/biodiversity conservation, stock rebuil-
ding and improving the socio-economic status of fishers.
Existing gear regulations for the demersal trap fishery
in the waters off Abu Dhabi include the requirement for
a stainless steel juvenile escape panel to be fitted to all
traps. The escape panel has a rectangular mesh of 7.6 ×
5.0 cm and given the potential for traps to ‘ghost fish’
after being lost [10], a magnesium/zinc alloy sacrificial
anode pin, which allows the panel to open after 2 weeks
is mandatory. As juvenile retention persisted following
the implementation of this regulation, there was clearly a
need for an objective evaluation of its utility in relation
to specified fisheries management objectives.
In this context, the aim of this study was to evaluate
the selectivity characteristics of traps fitted with the ex-
isting juvenile escape panel and two other designs with
larger mesh sizes against a control. A set of criteria based
on fishery management objectives were used to ascertain
which escape panel design is most appropriate for use in
the regulation of the demersal trap fishery of Abu Dhabi.
2. Materials and Methods
2.1. Escape Panel Designs
Escape panels measured 30 × 40 cm and were con-
structed of solid 304 stainless steel bar with a 4 mm di-
ameter. Plastic frames were used to attach the escape
panels to hemispherical traps constructed of galvanized
wire with a hexagonal mesh of 3.5 cm. Escape panels
were attached to the trap opposite to the funnel. Trap type
A was the control which only had a plastic frame secured
over the normal mesh of the trap. Trap type B consisted
of an escape panel with a rectangular mesh of 7.6 × 5.0
cm, the longer axis of which was orientated horizontally.
Trap type C consisted of an escape panel with a square
mesh of 7.5 × 7.5 cm and trap type D consisted of an es-
cape panel with a square mesh of 10.0 × 10.0 cm.
2.2. Sampling Protocol and Study Site
Sampling trips were conducted using a traditional woo-
den dhow between November 2005 and February 2008
in the waters off Abu Dhabi in the southern Arabian Gulf
(Figure 1). During each sampling trip, traps were set in
strings approximately 1 km apart. Each of the strings
contained 1 of each trap type arranged in a random order
and set approximately 20m apart. Traps were baited with
bread and dried sardinella held in a bait bag. Approxi-
mately 12 trap strings were set on each trip representing
48 trap sets per trip in total. The date and time of hauling
were recorded along with the depth. Catches from each
trap were bagged and labeled by trap type, fork or total
length (cm) and total weight (g) were later measured and
recorded for each species.
2.3. Data Analyses
1) The proportion of juvenile fish retained for key com-
mercially exploited species in terms of numbers and
weight.
The proportion of juvenile fish retained for key com-
mercially exploited species in terms of numbers and
weight was calculated for each escape panel type. Size at
maturity was obtained from published literature for Abu
Dhabi, when not available locally, the closest geo-
graphical location was selected (Table 1). Species were
excluded from the analyses if they did not occur in the
catches of all trap types, there were insufficient sample
sizes to make valid comparisons between trap types, or if
there was no data available on the size at maturity. Of the
65 species caught, 10 species were included in the
analyses representing 70.1% of the total catch weight.
2) The proportion of un-utilized and discarded by-
catch species retained by numbers and weight.
Species were classified as commercially traded target
species or un-utilized or discarded by-catch. The propor-
tion of un-utilized or discarded by-catch in terms of num-
bers and weight was calculated for each escape panel
type.
3) The simulated long term increase in yields using
differences in yield per recruit (YPR) as a proxy for key
commercially exploited species.
Yield per recruit simulations were conducted for Dia-
gramma pictum and Epinephelus coioides as these were
the only species which had sufficient data for all trap
types. Together they represented 68% of the total catch
weight (excluding by-catch) and were therefore collec-
tively representative of the most important commercial

E. M. GRANDCOURT ET AL. 100
Figure 1. Location of the Emirate of Abu Dhabi and the United Arab Emirates in the southern Arabian Gulf.
Table 1. Size at maturity by location and source for key commercially exploited species (L
F
–fork Length, L
Twenzhang
–total
Length).
Species Maturity Size (cm) Source Location
Diagramma pictum 31.8 (LF) [12] Abu Dhabi
Carangoides bajad 24.7 (LF) [17] Abu Dhabi
Lethrinus lentjan 28.4 (LF) [18] Saudi Arabia
Epinephelus coioides 45.2 (LT) [19] Abu Dhabi
Gnathanodon speciosus 32.5 (LF) [17] Abu Dhabi
Argyrops spinifer 26.9 (LF) [17] Abu Dhabi
Lethrinus nebulosus 27.6 (LF) [12] Abu Dhabi
Arius thalassinus 36.5 (LF) [20] Kuwait
Acanthopagrus bifasciatus 26.4 (LF) [6] Abu Dhabi
Lutjanus fulviflamma 18.7 (LF) [21] Abu Dhabi
species. The size composition of catches for each escape
panel type were grouped into 10 cm and 5cm size classes
for E. coioides and D. pictum respectively. Backwards
extrapolation of length converted catch curves was used
to estimate probability of capture data for each species
[11]. Selectivity ogives were generated using the logistic
function fitted to plots of the probability of capture
against size and used to derive values of the mean size at
first capture (Lc50) for each trap type. The mean ages at
first capture (tc) were obtained by converting the mean
sizes at first capture using the inverse of the von Berta-
lanffy growth function for E. coioides [7] and D. pictum
[12].
A yield per recruit (YPR) model [13], was used to es-
timate YPR (in grams) for each escape panel type for E.
coioides and D. Pictum as follows:
 
max
1/2
0
1exp
t
tt
tt tt
t tt
FS
YPRN WF SM
FS M





where tmax is the maximum observed age in the fishery and
is considered a plus-group. Ft is the instantaneous fishing
mortality rate, M is the instantaneous natural mortality
rate and Nt is the number of fish surviving to age t, cal-

E. M. GRANDCOURT ET AL.101
culated from the recursive equation:



maxmax max
max max
111
max
111
if 0
Nexp if0
if
exp
1exp
tttt
ttt
tt
R
NFSM tt
tt
NFSM
FS M







 




 




max
t



where R is the number of recruits and is set to one. is
the selectivity at age t. It is assumed that selection is
knife-edged and therefore set to 0 if t < t
c
and 1 if t ≥ t
c
where t
c
is the mean age at first capture. W
t
is the mean
weight at age t, such that:
t S
 

0 1 - exp- -
b
WtaLk tt 


where a and b are parameters of the length:weight rela-
tionship, L, and
0
are derived from the von Berta-
lanffy growth function. Simulations were conducted over
a range of fishing mortality rates for both species in order
to generate YPR curves for each escape panel type.
Demographic parameters for the YPR calculations were
obtained from the literature [7,12].
k t
4) The simulated long term increase in the adult stock
size using differences in the relative spawner biomass
per recruit (SBR) as a proxy for key commercially ex-
ploited species.
The yield per recruit (YPR) model [13] was used to
estimate the spawner biomass per recruit (SBR) for each
escape panel type for E. coioides and D. pictum over a
range of fishing mortality rates. Spawner biomass per
recruit (in grams), expressed as a proportion of the unex-
ploited level, was calculated as:
max
0
t
ttt
t
SBRNW G


where Gt is the fraction of mature fish at age t and was
assumed to be knife edged ie. set to 0 if t < tm and 1 if t ≥
tm where tm is the mean age at first sexual maturity given
by [7] for E. coioides and [12] for D. pictum.
5) The simulated long term relative increase in reve-
nue to fishers through increased yields of key species.
Simulated yield per recruit for each trap type for E.
coioides and D. pictum were converted to values using
economic data collected through the catch and effort data
recording system for Abu Dhabi. Specifically, the mean
wholesale value per kg for each species was used. Rela-
tive increases in revenues for the key species were sub
proportion of those obtained for the control (trap type A).
sequently calculated for each trap type and expressed as a
6) The initial short term loss in revenue to fishers
through reduced yields.
Total catch weights for all commercially traded spe-
cies were converted into values using economic data
collected through the catch and effort data recording
system for Abu Dhabi. Total catch values were calcu-
lated for each trap type and expressed as a proportion of
that obtained by the control (type A).
7) The diversity of the resource base vulnerable to
capture.
The number of commercially important species vul-
nerable to capture was calculated for each trap type.
Score function
For each of the specified criteria above, the perform-
ance of each escape panel type was ranked. The type that
came closest to meeting the desired outcome of the crite-
ria was given a score of 4 and that with the least desir-
able outcome a score of 1. The sum of the score was used
to evaluate the relative performance of each trap type
with an equal weighting basis for each criterion. A mean
value of scores of the criteria that relied on simulations
(criteria 3, 4 & 5) was taken so as to avoid bias as these
were intrinsically linked. This provided an objective in-
dication of the most suitable escape panel design for the
management of the demersal trap fishery of Abu Dhabi.
3. Results
A total of 81 sampling trips were conducted during
which 3,648 trap sets were made, 12,182 fish were
caught representing 65 species.
1) The proportion of juvenile fish retained for key
commercially exploited species in terms of numbers and
weight.
Whilst there was an overall decline in the number and
weight of juveniles retained with increasing mesh size of
the escape panel (Tables 2 & 3), the lowest proportion of
juveniles retained both in terms of numbers and weight
was achieved with traps fitted with the type C escape
panel. The control type had the highest juvenile retention
of the 4 types tested.
2) The proportion of un-utilized and discarded by-
catch species retained by numbers and weight.
The proportion of by-catch species retained by number
and weight declined with increasing mesh size of the
escape panel, type D had the lowest and type A the
highest values of by-catch retention in both cases (Table
4).
3) The simulated long term increase in yields using
differences in yield per recruit (YPR) as a proxy for key
commercially exploited species.
Both the mean size (Lc50) and age (tc) at first capture
increased with increasing mesh size of the escape panel,
however, there were only small differences in the selec-
tivity characteristics between the control (type A) and the

E. M. GRANDCOURT ET AL. 102
Table 2. Juvenile retention (%) for key commercial species by escape panel type.
Escape Panel Type
Species A B C D
Diagramma pictum 52.9 38.9 6.8 14.5
Carangoides bajad 86.0 53.1 68.4 20.0
Lethrinus lentjan 77.0 50.0 26.7 100.0
Epinephelus coioides 49.0 46.8 15.6 22.0
Gnathanodon speciosus 88.4 42.1 12.5 0.0
Argyrops spinifer 95.3 76.3 76.9 0.0
Lethrinus nebulosus 50.0 12.5 0.0 0.0
Arius thalassinus 27.3 33.3 0.0 100.0
Acanthopagrus bifasciatus 80.0 57.1 0.0 0.0
Lutjanus fulviflamma 21.8 44.4 81.8 0.0
Table 3. Overall number and weight of juveniles retained by escape panel type.
Escape Panel Type
A B C D
# juveniles retained 1823 710 110 31
% juveniles retained 59.7 42.3 12.9 15.7
Weight of juveniles retained (kg) 489.8 273.8 44.5 23.4
% juveniles retained by weight 28.8 20.8 4.5 6.3
Table 4. The proportion by weight and number of by-catch species retained by escape panel type.
Escape Panel Type
A B C D
% by-catch by weight 5.6 4.3 3.1 0.5
% by-catch by numbers 9.2 6.0 3.9 0.6
escape panel that is currently used in the fishery (type B)
(Figure 2, Table 5). Simulations of yield per recruit in-
dicated that the long term benefits in terms of increasing
catches would be small with the current escape panel
when compared with the control (Figures 3 & 4). In-
creases in yield per recruit were predicted to occur for
the type C panel. However, the greatest long term bene-
fits in terms of increasing catches for both E. coioides
and D. pictum were predicted to occur for the escape
panel with the largest mesh size (type D) (Figures 3 &
4). Yield per recruit was predicted to be 58% (E.
coioides) and 128% (D. pictum) greater than the control
(type A) for the type D escape panel (Figure 4). YPR
analyses also indicated that the current level of fishing
effort (2008) is greater than that required to maximize
YPR for all escape panel types for both E. coioides and
D. pictum.
4) The simulated long term increase in the adult stock
size using differences in the relative spawner biomass
per recruit (SBR) as a proxy for key commercially ex-
ploited species.
Simulations of spawner biomass per recruit indicated
that the long term benefits in terms of stock rebuilding
would be small with the current escape panel (type B)
when compared with the control (Figures 5 & 6). Large
increases in spawner biomass per recruit were predicted
to occur for trap type C for both E. coioides and D. pic-
tum. However, the greatest long term benefits in terms of
stock rebuilding for both species were predicted to occur
for the escape panel with the largest mesh size (trap type
D) (Figures 5 & 6). Spawner biomass per recruit was
predicted to be 398% (E. coioides) and 258% (D. pictum)
greater than the control type (type A) for panel type D
(Figure 6). The SBR analyses also indicated that even
with the escape panel with the largest mesh size, the SBR
would be less than the existing target reference point
(SBR40%) currently used for the management of the fish-
ery for both E. coioides and D. pictum.
5) The simulated long term relative increase in reve-
nue to fishers through increased yields of key species.
A limited increase in revenue was predicted to occur
for the type B panel (5.8%) for the key species (E.
coioides and D. pictum) by comparison with the control.
Revenues were predicted to increase by 44.9% and

E. M. GRANDCOURT ET AL. 103
Table 5. Selectivity parameters for Epinephelus coioides and Diagramma pictum (L
c50
–mean size at first capture, t
c
–mean age
at first capture) by esc ape panel type.
Escape Panel Type
Species Parameter A B C D
D. pictum Lc50 (cm LF) 27.0 28.9 37.1 44.1
tc (yrs) 0.9 1.2 2.3 3.6
E. coioides Lc50 (cm LT) 37.2 38.8 49.4 55
tc (yrs) 1.9 2.1 3.5 4.4
Table 6. Total catch values and the proportion relative to the control (type A) by escape pane l type.
Escape Panel Type
A B C D
Total catch value (Dirhams) 23,447 17,327 12,900 5,469
Proportion (relative to trap type A) (%) - 73.9 55.0 23.3
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 10203040506070
Probability of capture
Fork length (cm)
Type A
Type B
Type C
Type D
(a )
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 102030405060708090
Probability of capture
Fork length (cm)
Type A
Type B
Type C
Type D
(b )
Figure 2. Selectivity ogives for (a) D. pictum and (b) E. coioides by escape panel type.
0
200
400
600
800
1000
1200
00.511.522.5
F
cur
(a)
0
100
200
300
400
500
600
700
00.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.91
Typ e A
Typ e B
Typ e C
Typ e D
F
cur
Fishing mortality rate (F)
YPR (g)
(b)
YPR (g)
Typ e A
Typ e B
Typ e C
Typ e D
Fishing mortality rate (F)
Figure 3. Yield per recruit curves by escape panel type for (a) E. coioides and (b) D. Pictum. Vertical lines show the existing
fishing mortality rate (F
cur
).
250.6% for trap types C and D respectively when com-
pared to those for the control (type A).
6) The initial short term loss in revenue to fishers
through reduced yields.
There was a consistent decline in the total value of the
catch with increasing mesh size of the escape panel. Trap

E. M. GRANDCOURT ET AL. 104
0
20
40
60
80
100
120
140
BCD
E. c o ioid e s
D. pict um
Difference in YPR (%)
Escape panel t type
Figure 4. The difference in YPR for E. coioides and D. pic-
tum for each escape panel type in comparison with the con-
trol.
type D had the largest and trap type B the smallest re-
duction in value relative to the control (type A) (Table
6).
7) The diversity of the resource base vulnerable to
capture.
There was a reduction in the number of commercial
species vulnerable to capture with increasing mesh size
of the escape panel, the number of commercial species
caught by trap type was; 41 (type A), 40 (type B), 35
(type C) and 25 for trap type D.
Score function
The score function summary indicated that whilst trap
types A and D were the highest ranked for 2 criteria each,
overall, trap type C had the highest total score (Table 7).
Trap types A and D had the lowest score for 3 and 2 cri-
teria respectively.
0
10
20
30
40
50
60
70
80
90
100
00.511.522.5
Typ eA
Typ eB
Typ eC
Typ eD
Fishing mortality rate (F)
SBR (%)
(a)
F
cur
0
10
20
30
40
50
60
70
80
90
100
00.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.91
Typ eA
Typ eB
Typ eC
Typ eD
Fishing mortality rate (F)
SBR (%)
(b)
F
cur
Figure 5. Relative spawner biomass per recruit (SBR) curves by escape panel type for (a) E. coioides and (b) D. pictum. Ver-
tical lines show the existing fishing mortality rate (F
cur
).
0
100
200
300
400
BCD
E. c o io ide s
D. pict um
Difference in SBR (%)
Escape panel type
Figure 6. The difference in SBR for E. coioides and D. pic-
tum for each escape panel type in comparison with the con-
trol.
4. Discussion
The selection of escape panels for use in the management
of demersal multi-species fisheries is problematic be-
cause of the difficulty in achieving suitable selectivity
characteristics for all important species. The same con-
clusion has been reached from studies of the selectivity
of different mesh sizes for the demersal trap fishery of
New South Wales in Australia [9,14]. Nevertheless, this
study has provided an empirical evaluation of the re-
source management utility of different juvenile escape
panel designs and the basis for gear regulations for the
demersal trap fishery of Abu Dhabi. The score function
developed is based on an equal weighting among criteria
and attention is drawn to the fact that the most suitable
escape panel design may vary depending on resource

E. M. GRANDCOURT ET AL. 105
Table 7. Rank scores by criteria and escape panel type (shaded cells highlight the highest ranked escape panel ty pe for each
criterion).
Escape Panel Type
Criteria A B C D
1 1 2 4 3
2 1 2 3 4
3, 4 & 5 1 2 3 4
6 4 3 2 1
7 4 3 2 1
Total Score 11 12 14 13
management priorities and associated criteria weightings.
Previous investigations of the selectivity characteris-
tics of trap mesh have shown that body shape is a critical
factor in determining retention size, with slender fishes
being more likely to escape than species that are laterally
compressed [15]. Our results support this pattern with
much higher juvenile retention rates being observed for
the deeper bodied species such as the sparid (Argyrops
spinifer) by comparison with species with a more
rounded profile such as the serranid Epinephelus coi-
oides. The number of species for which selectivity pa-
rameters could be determined was limited due to inade-
quate sample sizes for all escape panel types. An alterna-
tive method using a parlour trap should be considered in
future experiments as selectivity can be determined with
fewer fish, and consequently less sampling effort [9].
The control type escape panel which had a mesh size
which was the same size as that of the body of the trap
(3.5 cm), had the most undesirable selectivity character-
istics overall with the highest levels of juvenile and
by-catch retention. As this type also had the smallest and
youngest mean size and age at first capture for the key
species (E. coioides and D. pictum), predicted estimates
of yields, revenues and spawning stock biomass were the
lowest amongst the different types tested. Whilst the
control had the highest catch rate and provided the larg-
est revenue it was the least suitable option based on the
objective assessment criteria.
The results demonstrate that the existing juvenile es-
cape panel design (type B) currently used in the fishery,
only has marginal benefits in terms of its intended objec-
tives. Specifically, there was only a limited reduction in
the proportion of juvenile fish and by-catch retained.
Furthermore, as the selectivity characteristics for the key
species were similar to the control type, the predicted
increases in yields, revenues and spawning stock bio-
mass were negligible. Consequently, the existing escape
panel design had the lowest overall score of all types
(excluding the control) and was not ranked highest in any
of the assessment criteria.
Escape panel type C had the lowest juvenile retention
of all the panel types tested. Whilst it was not ranked
highest in any other category, overall it had the highest
score for all the assessment criteria combined. There
were large differences in the selectivity characteristics by
comparison with the control and type B for the key spe-
cies (E. coioides and D. pictum). Consequently relatively
large increases in yields, revenues and spawning stock
biomass were predicted to be associated with this escape
panel type.
The escape panel with the largest mesh size (type D)
retained the least un-utilized and discarded by-catch.
Furthermore, it had the largest and oldest mean size and
age at first capture for the key species (E. coioides and D.
pictum), consequently, simulations predicted the highest
spawner biomass per recruit, long term yields and reve-
nues for this design. Of particular note is the large pre-
dicted long term increase in revenue (250.6%) for the
key species when compared to the control type. However,
the use of the type D design would be associated with a
dramatic short-term decline in revenues which were
23.3% of the value of the control type. Furthermore, 16
commercial species which were vulnerable to the control
type were not caught with traps fitted with this escape
panel, indicating that only a limited portion of the re-
source base would be accessible to fishers.
The results of the yield and spawner biomass per re-
cruit simulations indicate that both growth and recruit-
ment fishing are occurring for the key target species (E.
coioides and D. pictum). This supports the widespread
recognition that in places where wire-mesh fish traps
have been used extensively, the target specie are cur-
rently over-exploited [14,16]. A critical finding of the
study is that at existing fishing mortality rates, resource
management targets of stock rebuilding cannot be
achieved for the key species using gear regulations alone
for the escape panel designs tested here. This supports
contentions from previous assessments [7,12] that reduc-
tions in fishing effort are also required for the demersal
trap fishery in the southern Arabian Gulf. As the species
and principal fishing method for exploiting demersal
fisheries resources are similar throughout the region, the
results obtained here should be applicable to fisheries
management authorities in a wider geographical context.

E. M. GRANDCOURT ET AL. 106
5. Acknowledgements
This study was conducted as part of the ‘Experimental
Fishing Project’ (Project no. 02-23-0009-06/07), imple-
mented by the Biodiversity Management Sector of the
Environment Agency–Abu Dhabi. The management of
the Environment Agency–Abu Dhabi are thanked for
their support for this work. The owner and crew of the
dhow (#1402) are thanked for their help, particularly in
setting and hauling the traps. Hamad Al Shamsi provided
assistance during some of the research cruises and John
Hoolihan helped in the overall development of the ex-
perimental fishing project.
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