UNIVERSITI PUTRA MALAYSIA

PROPER CONSTRUCTION AND SET UP OF MALAYSIAN FISH AGGREGATING DEVICES (UNJAM)

SAKRI BIN IBRAHIM

FPSS 1991 2

PROPER CONSTRUCTION AND SET UP OF MALAYSIAN FISH AGGREGATING DEVICES (UNJAM)

By

SAKRI BIN IBRAHIM

A Thesis Submitted in Fulfilment of the Requirements for the Degree of Doctor of Philosophy

in the Faculty of Fisheries and Marine Science Universiti Pertanian Malaysia

July, 1991

This work is dedicated to beloved wife:

Saidah @ Rohani Ibrahim

and sons:

Mohd. Hafizuddin

&

Ahmad Fadhli

ACKNOWLEDGEMENT

I am truly indebted to my Chief Supervisor , Associate

P r o f e s s or Dr . Mohd A z mi Amba k , and my S u p e r v i s or ,

Associate Professor Dr . Gunzo Kawamura for their guidance ,

useful comments and constant encouragement .

Dr . Kawamura has devoted so muc h of his t ime and

energy , sometimes at the expense of his other priorities ,

in supervis ing my work during the period of candidature .

My period of stay at Kagoshima Unive r s ity , Japan for

completing the last few chapters of my thesis would not

have been materiali zed without his assistance . I am also

e x t e n d i n g my a ppr e c i a t i o n t o J a p a n I n t e r n a t i o n a l

C ooperation Agency ( JICA ) for the f inanc ial a s s i stance

which has made possible the several visits of Dr . Kawamura

to Malaysia for the supervision of my study .

I am g r a t eful t o Dr . Mohd Azmi f o r h i s c omme n t s ,

suggestions and advice , and having his presence around has

given me an added advantage .

My thankful appreciation goes to Mohamad Muda ,

Ab. Manaf Md. Diah, Fadhil Noh, Awang @ Mohamad Embong,

and the crew of UNIPERTAMA III for their assistance during

the period of data taking in the field .

I am a l s o very t hank f u l to Univer s i t i P e r t a n i a n

Malaysia f or providing the financial assistance which make

this study possible .

111

Finally , this work will never be carried out without

the blessings of God .

iv

TABLE OF CONTENTS

Page

ACKNOWLEDGEMENT iii

LIST OF TABLES lX

LIST OF FIGURES x

�..BSTRACT

ABSTRAK

CHAPTER

I

II

xiv

xviii

INTRODUCTION 1

Malaysian Fishery 1

An Unj am 6

Material and Construction of Unj am 8

Fishing Gears and Methods for Catching Fish from Unjam 8

Present Problems 10

Objective of This Study 13

LITERATURE REVIEW 15

Variations of Moored FAD 15

Traditional FAD 16

Modern Moored FAD 19

Anchoring Power of Moored FAD 26

Type and Weight of Anchor 26

Material , Dimension and Length of Anchoring Line 27

v

I I I

IV

Types of Connections Between Parts , Their Materials and Dimensions 28

Shock Absorber for Anchoring Line 28

possibilities for Recovery of Anchoring Device if Raft or Buoy is Lost 29

possible Risk of FAD Loss 29

Fish Behaviour in Relation to FAD 30

Flotsam and Fish Behaviour 30

FAD and Fish Behaviour 33

Schooling of Fish 35

DISTRIBUTION OF UNJAM AND ITS RELATION TO SEDIMENT DISTRIBUTION

Introduction

Materials and Methods

Results and Discussion

ANCHORING POWER OF SANDBAG AND TENSION AT UNJAM LINE

I ntroduction

Methods

Anchoring Power of Sandbag

Theory

Tension at Unjam Line

Results and Discussion

Anchoring Power of Sandbag

Tension at Unjam Line

vi

44

44

45

46

54

54

54

54

56

58

62

62

65

v

VI

VII

VI I I

I X

SURFACE CURRENT PATTERN

Introduction

Materials and Methods

Results

Discussion

MOVEMENT OF FISHES AS INFERRED FROM DRIFTNET CATCH

Introduction

Materials and Methods

Results

Discussion

EFFECTIVE RANGE OF UNJAMS AS DETERMINED BY FISH RELEASING METHOD

Introduction

Materials and Methods

Results

Discussion

FISH DISTRIBUTION AROUND UNJAM

Introduction

Materials and Methods

Results and Discussion

MATHEMATICAL MODELS FOR PROPER SETTING OF UNJAMS

Introduction

Linear Mode l

vii

7 0

7 0

7 1

7 1

7 5

7 8

7 8

7 9

7 9

8 0

8 7

8 7

8 7

9 0

94

9 9

9 9

1 0 0

1 05

1 14

1 14

1 1 6

x

Assumption 1 1 6

Non-Linear Model 120

Assumption 120

Calculations of Non-Linear Model 123

Case Example 1 123

Uni-Directional Random Walk Model 128

Theory and Assumptions 1 2 8

Results o f the Computer simu lation 13 1

Discussion and Reco�nended Arrangements of Unj ams 131

The Linear Model 133

The Non-Linear Model 133

The Uni-Directional Random Walk Model 133

SUMMARY AND RECOMMENDATIONS 1 3 8

BIBLIOGRAPHY 146

APPENDICES 162

VITA 170

viii

Table

1

2

3

4

5

6

7

8

9

LIST OF TABLES

Marine Fish Landings by Gear Group in 1 9 8 3 ( 19 8 8 ) for Peninsular Malaysia

Value of Fixing Coefficient ( K ) of Sandbags on Different Bottom Types

Value of Fixing Coefficient ( K ) of Sandbags Rigged Differently

Shooting and Hauling positions of the Net and Drift of the Net

Number of Fish Caught by Spec ies , Enmeshed Direction and Result of X2-Test . N and Sf Denote Northward and Southward Enmeshing Respectively . The Catch on the 3�st Aug . was not Included in the Total X -Test as the Current on this Date was Southerly, in Contrast to a Northerly Flow on the Other Sampling Dates

Number of Fish Rel eased ( in Parenthesis ) and positively Headed to Unjam by Species and Released Distance from Unjam

Species of Fish Associating with Unj am

Breakdown of the Average Basic Cost I ncurred for Installing Unjams, a Case Example for Purse Seiner ( 37 H . P . ) . Depreciation Cost of the Vessels is not Included

Breakdown of the Average Cost of an Unj am

ix

Page

5

62

64

8 1

83

9 3

1 1 1

1 2 6

1 2 6

LIST OF FIGURES

Figure Page

1 Total Marine Fish Landings ln Malaysia 2

2 Construction of an Unjam 9

3 Sediment sampling Sites 4 7

4 Unjam Distribution in Relation to Sediment Pattern and Depth of Water 4 8

5 Rigging of the Tension Meter and Balance During the Experiment 57

6 Angle of Inclination of Unjam Line 6 1

7 Forces Acting on Sandbags , One Tied Behind the Other 64

8 Unjam Line Tension in Relation to Tidal Level ( 23/5 / 8 8 - 25/5/ 88 ) 6 6

9 Unjam Line Tension in Relation to Tidal Level ( 6/ 8 / 89 - 9 / 8 / 8 9 ) 6 7

1 0 Drogue Design Used in the Study 7 2

1 1 Track Charts o f a Drifting Drogue Released on 25th to 2 6th and 2 7th to 2 8th March , 1 9 8 9 . The positions of the Drogue arp Plotted at Half-Hourly I ntervals with Filled Circles Indicating the Rising Tide and Open Circles Indicating the Receding Tide . Arrows Indicate Drift Direction of the Drogue 74

1 2 Chart Showing the Dri.ft of the Net ( Dotted Line and Arrow ) , Enmeshed ( Arrow ) , Number of Fish Caught. ( Figure Beside the Arrow ) with an Inserted Map Showing the Hauling positions in the Waters off Terengganu 84

13 Study Area Showing the Locations of Experimental FAD . Dotted Lines Showing the I sodepth 8 9

x

14

15

1 6

1 7

1 8

1 9

2 0

2 1

22

23

24A &

24B

Diagram Showing Positively (+ve ) and Negatively ( -ve ) Headed Fish Towards t�e Unjam

Locations of the Surveyed Unjams Unjam 1 . 0050 4 1. 3 ' N

1030 OS.O'E Unjam 2 . 0050 3 8 . 4 ' N

1030 06 . 6 ' E

Radial Line Survey Courses . Arrows Showing Cruising Directions

Scores of Fish Echoes Based on Type and Density

Numerous Large Echoes Appeared on the Bottom and Mid-Layers . Recorded on the 27th April , 1 9 8 8 , Around Pulau Redang

Fish Echoes of Various Sizes Recorded with a 75 kHz Echo-Sounder . Obtained on the 2 7th April , 1 9 8 8 , Around Pulau Redang

Horizontal Distribution of the Total Fish Echoes

Values of m in Relation to the k Values f or the Effective Range of 0 . 1 8 km and 1 . 6 km

unj am Arrangement for the Model

Trapping Probability as a Function of width of Unjam-Influence-Free Water for Step-Lengths of 1 0 m, 2 0 m, and 3 0 m

Recommended Arrangements of Unj ams in the Model Water for the Effective Ranges of ; A : 0 . 1 8 km ( Top ) , and B : 1 . 6 km ( Bottom )

xi

92

1 0 1

102

104

1 0 6

107

108

127

130

132

135

LIST OF ABBREVIATIONS

wt = Weight of Sandbag

T = Rope Tension

F = Frictional Force

W ' = Vertical Component of T

K = Fixing Coefficient

w = Weight of Tension Meter

r = Readings Registered on the Balance

t = Readings Registered on the Tension Meter

A = Total Area of Model Water

m = The Cost of Catching a Unit Quantity of Fish ( in $ )

mF =

MFAD =

Mo =

c =

NF =

Ng =

E =

s =

Se = =

k =

=

The Cost of an unjam ( in $ )

The Total Cost of All Unjams ( in $ )

The Basic Cost Incurred for Installing All the Unj ams ( in $ )

The Number of Fish Caught at the Unj am

The Number of Unj ams in the Model Water

The Total Quantity of Fish in the Model Water

The Catching Efficiency

Area for One Unjam

Area of th� Effective Range of an Unjam IT ( Radius )

Density Coefficient of Fish Population Defined as k = Ng/A Quantity of Fish Per unit Area

xii

w = width of Model Water

L = Length of Model Water

v = Speed of Water Current

V = Average Cruising Speed of Fish

S = Step-Length of Fish

R = Radius of the Effective Range

xiii

Abstract of the s i s submitted to the Senate of Un iver s i t i Pe rtanian Ma lay s ia in f u l f i lment o f the requirements for the degree of Doctor of Philosophy .

PROPER CONSTRUCTI ON AND SET UP OF MALAYSIAN FISH AGGREGATING DEVICES (UNJAM)

by

SAKRI BIN I BRAHIM

July, 1991

Supervisor Associate Professor Dr . Mohd . Azmi Ambak

Faculty : Fisheries and Marine Science

T h i s study was carried out with an ob j ec t ive o f

improving the durabil ity o f unj ams and determining the

r a t i on a l a r r a n g ement and opt imum d e n s ity o f u n j am s .

Several experiments were conducted in coastal waters of

Terengganu in the South China Sea to determine a safe

anchoring power of unJ ams and parameters required for the

development of mathematical models that could produce an

optimum trapping efficiency .

Exper iment s on anchoring power showed s andy bottom

giving the highest value of fixing c oe f f icient ( 0 . 95 3 ) ,

f o l l owed by muddy bottom ( 0 . 9 0 3 ) , and sandy-mud bottom

( 0 . 7 3 1 ) . This value was found to be higher for two sand-

bags tied one behind the other than for two sandbags tied

1n one lump . The unjam's anchor was found to have a

xiv

reserved f ixing force of 6 7 . 3 4 kg , which i s 9 3 . 8 6% in

excess of what was requirp.d to anchor an unjam in place .

utilizing the required parameters ; current pattern

in the area , e f f ective ranges of the unj ams , and fish

m ov e m e n t p at t e r n , t h r e e mat h e m a t i c a l m o d e l s w e r e

developed .

T h e Linear mode l was f ound to be unre a l i s t ic and

invalid .

The Non-Linear mode l enables the derivation of

optimum catching efficiency graphically . with an area of

model water of 30 km x 1 0 km and two dif ferent effective

r a n g e s o f 0 . 1 8 km a n d 1 . 6 km , t h e numb e r o f u n j am s

required were found t o be 2 5 6 and 14 respectively , and the

cost of catching a unit quantity of fish , m, was found to

be 0 . 2 7 14/k and 0 . 003892/k respectively .

The Uni-Directional Random Walk model involved the

deve l opment of a math emat i c a l mode l . T h e r e s u l t s o f

c omputer s imulations o f the model showed that , when the

effective range was 0 . 1 8 km, 7�) unjams were needed with a

t otal trapping probability of 0 . 27 2 and a total cost of

$ 19 , 83 6 . When the e f fective range was 1 . 6 km, 2 7 unjams

were needed with a total trapping probability of 0 . 558 and

a total c ost of $ 7 , 3 5 6 . The t otal trapping probability

e stimated here is found to be fairly high . However , this

value c ould be reduced if a lower percentage of trapping

is considered .

xv

Abs t rak t e s i s yang dikemukakan kepada Senat Universiti Pertanian Malaysia sebagai memenuhi keperluan untuk I j azah Doktor Falsafah .

Penyelia

Fakulti

PEMBINAAN DAN PEMASANGAN WAJAR ALAT PENGUMPULAN IRAN MALAYSIA (UNJAM)

oleh

SAKRI BIN IBRAHIM

Julai, 1991

Profesor Madya Dr . Mohd Azmi Ambak

Perikanan dan Sains Samudra

K a j i a n i n i d i j a l a n k a n d e n g a n o b j e kt i f u n t u k

meningkatkan ketahanan unj am dan menentukan penyusunan

rasional s erta kepadatan optimum unj am . Beberapa u j ikaj i

t e l ah di j alankan di perairan pantai Tere ngganu d i Laut

China Selatan untuk menentukan kuasa menyauh yang selamat

bagi unjam dan parameter yang diperlukan untuk pembentukan

model matematik yang boleh menghas ilkan satu kecekapan

memerangkap yang optimum .

U j ika j i t entang kua s a penyauh menun j ukkan bahawa

dasar berpasir memberikan pekali ikatan yang tertinggi

( 0 . 95 3 ) , diikuti oleh dasar berlumpur ( 0 . 9 0 3 ) , dan dasar

pasir-berlumpur ( 0 . 7 31 ) . Nilai ini didapati lebih tinggi

bagi dua beg pasir yang diikat satu di belakang yang lain

berbanding dengan dua beg pasir yang diikat dalam satu

xvi

l on g g o k . S au h u nJ am d i dapat i mempu ny a i d a y a i kat a n

simpanan sebanyak 67 . 34 kg , iaitu 93 . 86% melebihi daripada

apa yang diperlukan untuk menyauh satu unjam .

Dengan menggunakan parameter perlu ; c orak arus d i

kawasan kajian , j arak be�kesan unj am, dan corak pergerakan

ikan , tiga model matematik te lak dibentuk .

Model Linear didapati tida.k realistik dan tidak sah.

Mod e l Non-Linear membolehkan penghas ilan pekal i

menangkap yang optimum secara grafik . Bagi satu perairan

model yang mempunyai keluasan 30 km x 10 km dan dua j arak

berkesan yang berlainan iaitu 0 . 1 8 km dan 1 . 6 km, bilangan

unj am yang diperlukan didapati sebanyak 256 dan 14 masing­

mas ing , dan kos menangkap s atu unit kuantiti ikan , rn,

didapati sebanyak 0 . 27 14/k dan 0 . 003892/k masing-masing.

Mod e l Uni - Direct ional Random Wal k mel ibatkan

pembentukan s atu mode l matematik . Keputusan s imu l a s i

komputer k e atas model menunjukkan bahawa , apabila j arak

b e r k e s a n i a l ah 0 . 1 8 km , 7 5 u n j am d i p e r l u k a n d e n g a n

kebarangkal ian memerangkap kese luruhan 0 . 2 7 2 dan kos

keseluruhan sebanyak $ 1 9 , 836 . Apabila j arak berkesan ialah

1 . 6 km , 2 7 u n j am diperlukan dengan kebarangka l i an

memerangkap keseluruhan 0 . 55 8 dan ko s keseluruhan s ebanyak

$ 7 , 3 56 . Nilai kebarangkalian memerangkap keseluruhan yang

dianggarkan di s ini didapati agak tinggi . Namun begitu ,

nilai ini boleh dikurangkan j ika suatu peratus memerangkap

yang lebih rendah diambilkira .

xvii

CHAPTER I

INTRODUCTION

Malaysian Fishery

The total marine fish landings in Malaysia from 1971

to 1988 showed a fluctuating pattern (Fig. 1). The total

catch peaked in 1981, afterwhich it experienced a downward

trend but later, with the introduction of deep-sea fishing

programme by the government, it peaked again in 1987.

Before the introduction of the deep-sea fishing programme

in 1985, fishing operations were mainly restricted to

near-shore areas. In the pre-1985 period, the total trawl

landings peaked in 1980 and has been experiencing a

decreasing trend eversince. Although the total trawl

landings has been experiencing a downward trend after

1980, the total marine landings by other gears continued

to increase and peaked in 1981. Since then the total catch

has been decreasing from 792,354 metric tons in 1981 to

606,044 metric tons in 1986 (FAD Yearbook, 1986). The

importance of trawling as a major contributor to the total

catch has declined since 1977 when its share was 53.7

percent. In 1983, the share was a modest 37.1 percent

(Table 1). In the west coast of Peninsular Malaysia, the

trawl catch rates in 1978 was reduced to 1/5 of that in

1970 in the same fishing grounds (Lui, 1981).

1

1.000 r' -------------------------------

800 UJ (lJ c: c: o � 0600 o o

(f) l? 400 z H Cl Z o<l; ..:l

200

o

'"

Total Landings

� Total Trawl Landings �" ------, � ,

,. .

.

, . ' .

.

.

.

..

.

. ... .

. . , .. .

'" -- ---- , "

. .. . . . , . . . . . . ......... ----, � .

71

... . ' *, ___ .,,'" , 0 '

".;' .

.. . . . . . ' . ,.

.

. ,� . .

_ro.,... ·

72 73 74 75 76 n 78 YEAR

(Source: Ministry of Agriculture Malaysia 1972-1989)

. , '" '

Total Trawl Landings .... (Peninsular Malays�a)

79 80 81 82 83 84 85

Fig. 1. Total Marine Fish Landings in Malaysia.

86

, I

I I

87 88

N

The landing c ontributions of gear groups ln

Peninsular Malaysia were dominated by trawl nets and purse

selne s . In 1 9 8 3 , these two domi nant gears l anded 66 . 5

percent of the total marine fish landings , while gillnets

landed 1 0 . 0 percent . Other gear s contributed 2 3 . 5 percent .

The c ontr ibut i on o f hook and l ine gears has increased

sharply from 3 . 3 percent in 1980 to 5 . 6 percent in 1 9 8 6 .

The gaining of importance of hook and lines is probably a

re sult of the installation of Fish Aggregating Device s

( FAD ) by various government agencies a s well a s individual

fishermen .

In 1 9 8 8 , the total estimated number of fishing gears

operated were 2 2 , 3 4 5 unit s ln Peninsular Malaysia .

Gil lnet s represent the large st group with 1 0 , 0 4 7 unit s .

Trawls come next with 6 , 292 units , and 5 , 153 units ( 23 . 06

percent ) are unj am-as sociated fishing gears ( Ministry of

Agriculture Malaysia , 1 9 89 ) .

Un j am has been ut i l i z ed t radit ional ly by Mal aysian

fishermen and many unj ams are found installed in coastal

waters of Malaysia . In Terengganu , a state located on the

e a s t c oa s t of We st Malay s i a, an average of 3 0 0 u n j am

groups c ould be f ound in 2 0 0 square nautical mil e s o f

c o a s t a l wat er s , and many pe l agic and benthic f i sh e s

associate with unJams ( see Chapter 8 ) .

I n Ma l ay s i a , the most important un j am-a s s ociated

f i shing gear i s the hook and line s . I n 1 9 83 , there wer e

3

2 , 8 7 5 unit s of the gears contributing to 5 . 0 perc ent of

the total catch . Other unjam-cssociated fishing gears are

purse selnes , bagnets , and lift:nets . In terms of the total

c at c h , pur s e s e i n e s led the group by c ommanding 3 2 . 4

percent , with 2 ,�47 units of fishing gears . Then came the

bagne t s with 2 . 9 perc ent of the tot a l c atc h , and the

l i f tnet s , with 2 . 1 percent of the total catch . with a

total of 4 2 . 4 percent of total landings , unjam-associated

f i shing gears are In f act very important in Mal aysian

fisheries .

4

5 Table 1

Marine Fish Landings by Ge�r Group in 1 9 83 and 1 9 8 8 ( in brackets ) for Peninsular Malaysia

===============================================================

Gear Groups

Trawls

Catch In 'GOO tons

2 25 . 7 0 (394 . 2 0 )

Purse seines 1 7 9 .35 ( 164 .35 )

Gillnets 6 1 . 1 0 ( 43 . 9 0 )

Shellfish 44 .36 ( 1 . 53 ) collection

Lines 3 0 . 2 8 ( 2 1 . 7 9 )

Other seines 1 8 . 00 ( 14 .3 1 )

Bagnets 15 . 55 ( 3 8 . 2 6 )

Traps 15 . 4 8 ( 7 . 05 )

Liftnets 13 . 04 ( 5 . 23 )

Push/scoop 3 . 7 0 ( 2 . 0 0 ) nets

Barrier nets 0 . 81 ( 1 . 0 8 )

Miscellaneous 1 . 7 1 ( 0 .34 )

%of total catch

37 . 1 0 ( 56 . 7 6 )

29 . 4 0 ( 23 . 72 )

1 0 . 00 ( 6 .32 )

7 .3 0 ( 0 . 22 )

5 . 0 0 (3 . 14 )

3 . 00 ( 2 . 06 )

2 . 9 0 ( 5 . 51 )

2 . 50 ( 1 . 02 )

2 . 10 ( 0 . 75 )

0 . 6 1 ( 0 . 29 )

0 . 13 ( 0 . 16 )

0 . 26 ( 0 . 04 )

Total 6 09 . 06 ( 6 94 . 45 ) 1 0 0 . 00 ( 10 0 . 00 )

Estimated no . of gears operated

6 03 8 ( 62 9 2 )

7 43 ( 73 1 )

1 0337 ( 1 0 0 4 7 )

13Q 8 ( 74 )

2 87 5 ( 17 64 )

1 7 04 ( 6 9 6 )

1 13 8 ( 7 6 5 )

965 ( 563 )

, 6 55 ( 86 )

4 9 0 ( 65 9 )

1 04 ( 2 8 8 )

695 ( 2 8 0 )

2 7 0 5 1 ( 2234 5 ) ==============================================================

( Source : Ministry of Agriculture Malaysia , 1 9 84 and 1 9 8 9 )

6

b�j� Fi shermen have learned from experience that the best

fishing and most desirable fish can be found around

f l otsams , reefs , and sunken boats in the ocean . FADs are

strategically placed at the surface , and on the seabed to

attract f i s h . Whi l e t here are l arge variations in it s

design and material , the traditional FAD is basically one

of two type s :

a ) placed on the bottom, called ' artificial reef ' ,

b ) moored with the attracting structure at the

water surface and/or midwater , referred to as ' un j am ' .

T h e t raditional art i f ic i a l r e e f s h ave been

constructed with stones and logs , while modern FADs are of

c oncret e , stee l , rubber , and even d i s c arded boat s and

cars .

The moored type s are tradit i onal ly moored bamboo

rafts or bamboo buoys and referred to by different names

in d i f ferent c ountries ; 'Un j am ' in Malaysia , ' Payaw ' In

the Philippines , ' Rumpon ' in I ndonesia , and ' Tsukegi ' In

Japan . They are now partly replaced with synthesized and

more durable types and some of them are al so anchored in

midwater .

The use of moored FADs is based upon the c oncept that

pelagic fishes are attracted to floating obj ects , much in

the s ame way as reef f i shes are attracted to artificial

benthic habitats ( Uda , 1 9 3 3 ; Kimura , 1 954 ; Koj ima , 1 9 5 6 ;

I noue et al . , 1 9 6 3 , 1 9 6 8 ; Good ing , 1 9 6 5 ; Gooding and

Magnuson , 1 9 6 7 ; Greenblatt , 1 9 7 9 ) .

As a management tool , FAD s should be acc e s sible to

the t arget population of f i shermen and l oc at ed in an

upwelling zone or along a migratory pathway of fishes . A

combinat ion of artificial ree f s with FADs c ould enhance

s everal types of f i sheries in the same area . FADs might

also be used to shift a f ishery closer to market or to a

s a f er l ocation . Landings of migratory p e lagic spec ie s

c ou l d be increased by l ocat ing FADs i n areas where

bottom- dwe l l i n g f i s h are e x p l o i t e d , provid i n g a n

alternative catch to preserve the livelihood of artisanal

fishermen ( Sainsbury et al . , 1 9 8 8 ) .

Preston ( 1982 ) noted that in being anchored ln known

l oc at i on s , FADs can lmprove the ec onomic s of a g iven

fishing operation by :

1 ) reducing time and fuel spent in fish searching ;

2 ) improving catch per unit of effort due to

increased vulnerability or availabi l ity of the targeted

species ;

3 ) improving the va lue of the c atc h , ln terms of

species or size composition , and ;

4 ) serve to increase the safety factor ln small scale

coastal fishing operations .

7