An Evaluation of the Selectivity Characteristics of Different Juvenile Fish Escape Panel Designs for the Demersal Trap Fishery of Abu Dhabi, United Arab Emirates

doi:10.4236/ojms.2011.13010

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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

E-mail: [email protected]

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

–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

1exp

tt tt

t tt

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

exp

1exp

tttt

ttt

NFSM tt

NFSM

FS M











 









 









max







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

and 1 if t ≥ t

where t

is the mean age at first capture. W

is the mean

weight at age t, such that:



1 - exp- -

WtaLk tt







where a and b are parameters of the length:weight rela-

tionship, L, and

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

ttt

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

–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.

200

400

600

800

1000

1200

00.511.522.5

cur

(a)

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

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

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.

100

00.511.522.5

Typ eA

Typ eB

Typ eC

Typ eD

Fishing mortality rate (F)

SBR (%)

(a)

cur

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)

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

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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