SWIOP/WP/55 - The First Three Years Experience in the Use of Fish Aggregating Devices in Mauritius













Table of Contents


by

Roullot J.1, A. Venkatasami2, and S. Soondron3

1 Team Leader, Project UNDP/FAO/MAR/83/006

2 Scientific Officer, Ministry of Agriculture and Fisheries and Natural Resources, Mauritius

3 Technical Officer, Ministry of Agriculture and Fisheries and Natural Resources, Mauritius

30/11/88

RAF/87/008/WP/55/90/E

The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever by the Food and Agriculture Organization of the United Nations concerning the legal status of any country, territory, city or area of its authorities or concerning the delimitation of its frontiers or boundaries. The views expressed are those of the authors.

This electronic document has been scanned using optical character recognition (OCR) software and careful manual recorrection. Even if the quality of digitalisation is high, the FAO declines all responsibility for any discrepancies that may exist between the present document and its original printed version.


Table of Contents


ABSTRACT

RESUME

1. Mauritian Fisheries

1.1 Fishery Resources

1.1.1. The banks of the Mascarene Ridge
1.1.2. The oceanic area
1.1.3. The artisanal fisheries

2. FAD Development in Mauritius

2.1 Background
2.2 Objectives of the current programme
2.3 FAD designs tested
2.4 The medium FAD

2.4.1. Oxidation, wear and tear

2.5 Loss of FADs
2.6 FAD locations

3. Fishing Craft and Gears

3.1 Fishing craft

3.1.1. Project vessels
3.1.2. The artisanal fishery
3.1.3. The sports fishery
3.1.4. Part-time fishermen

3.2 Fishing gears

3.2.1. Gill nets
3.2.2. Trolling (Annex 4)
3.2.3. Japanese longlines
3.2.4. Monofilament longlines
3.2.5. Handlines
3.2.6. Drifting floats

4. Analysis of catches

4.1 Catch per fishing day

4.1.1. Project vessels
4.1.2. Artisanal Fishery
4.1.3. Sports Fishery
4.1.4. Part-time fishery

4.2 Currents and lunar phases

4.2.1. FAD submersion under the effect of current
4.2.2. Catches in relation to the lunar phase

4.3 Catch Species Composition

4.3.1. Commercial Species
4.3.2. Non commercial species
4.3.3. Project boats
4.3.4. Artisanal fishery
4.3.5. Sports fishery

4.4 Length composition of Project vessel catches

4.4.1. Dolphinfish, Coryphaena hippurus
4.4.2. "Yellowfin" tunas, Thunnus albacares and T. obesus
4.4.3. Skipjack tuna, Katsuwonus pelamis
4.4.4. Wahoo, Acanthocybium solandri
4.4.5. Shark
4.4.6. Other species

4.5 Fish behaviour near FADs

5. Results of the FAD deployment programme

5.1 Activity around FADs
5.2 Annual yield per FAD
5.3 Comparison between FAD locations
5.4 Cost/Lifespan Relationship

6. Estimated Pelagic Fish Landings in Mauritius

7. Future prospects

REFERENCES

APPENDICES

Appendix 1: List of Species Caught and Found Around FADs Commercial species caught

Appendix 2: Cost of a FAD (November 1988)

Appendix 3: Logbook forms distributed to fishermen


ABSTRACT

Fish Aggregating Devices (FADs) have been set around Mauritius since 1985 and the observations, catch data and fishing techniques used since then have been analysed.

Following the development of a design suited to the Mauritian context, twenty-three FADs were set, fifteen of which are still in place. The average lifespan exceeds 500 days and the oldest is now more than three years old. It is envisaged that FADs may last more than 5 years. Fishing in the vicinity of FADs by artisanal, sports and part time fishermen is successful and is increasing progressively.

Réunion and Comores have adopted with success the type of FAD used in Mauritius. Seychelles, Madagascar, Haiti and Cap Verde are also about to build similar ones.

By conservative estimate, over 330 t of pelagic fish are caught annually around the FADs. The average daily catch per boat of the artisanal fishery is 50 kg, compared to a catch rate of less than 5 kg per fisherman in the lagoon and outer reef area.

The catch per FAD per year was estimated at around 47.5 t of fish. Comparative data are not available for other countries. The main species caught are dolphinfish, Coryphaena hippurus, and Yellowfin tuna, Thunnus albacares. Other associated species are wahoo, Acanthocybium solandri, skipjack tuna, Katsuwonus pelamis, marlins, Makaira mazara and M. indica, and sharks.

RESUME

Trois années après la mise à l'eau en 1985 du premier dispositif de concentration de poissons (DCP) à l'île Maurice, un bilan des données récoltées et des techniques utilisées est effectué.

Après le perfectionnement du modèle adapté aux conditions locales, vingt-trois DCP ont été positionnés; quinze sont en place. La durée de vie moyenne dépasse cinq cent jours, et le plus ancien est âgé de plus de trois ans. Il est actuellement envisagé que les DCP puissent durer plus de cinq ans. La fréquentation des DCP par les pêcheurs artisans et amateurs est en constante progression, et ceux-ci les exploitent avec succès.

Ce modèle de DCP a été adopté avec succès à la Réunion et aux Comores. Les Seychelles, Madagascar. Haïti et les îles du Cap Verde sont sur le point d'en construire de semblables.

Une estimation prudente considère que plus de 330 tonnes de pélagiques sont annuellement capturées par les pêcheurs autour des DCP. Les prises moyennes journalières d'une unité de pêche opérant autour des DCP avoisinent 50 kg. comparée à la capture lagon/hors lagon par pêcheur et par jour qui est inférieure à 5 kg de poisson.

La production par DCP et par an est évaluée à 47,5 tonnes de poisson, il n'existe pas d'estimations pour les autres pays utilisant ces dispositifs. Les principales espèces capturées sont les dorades, Coryphaena hippurus, et les thons jaunes. Thunnus albacares; les autres espèces associées sont les wahoos, Acanthocybium solandri, les listaos Katsuwonus pelamis, les marlins Makaira mazara et M. indica et les requins.

1. Mauritian Fisheries


1.1 Fishery Resources


Mauritius has a combined land area of 2 200 km2 and an EEZ of more than 1.6 million km2 due to the presence of outlying islands. Its geographical limits lie between latitudes 8°-21°S and longitudes 56°-70°E (Figure 1).

The continental shelf around the island is very limited in area and the primary productivity of the surrounding sea is considered one of the lowest of the Indian Ocean: 0.15 g/m2/day - (FAO/IOP, 1978) (Figure 2). Sea surface temperatures vary between 22° and 27°C.

1.1 Fishery Resources


1.1.1. The banks of the Mascarene Ridge
1.1.2. The oceanic area
1.1.3. The artisanal fisheries


The island of Mauritius is situated in the southwest of its EEZ. The low level of primary productivity has greatly influenced the level of development of fisheries.

1.1.1. The banks of the Mascarene Ridge

The bank resources comprise mainly demersal species, in particular of lethrinids, localized on coral bottoms and presently fully exploited by a national fleet. The landings in 1987 were around 6 000 t. Other resources are found on these banks: small pelagics, (Decapterus sp., Trachurus sp.), octopus (Octopus vulgaris), deepsea shrimp (Heterocarpus laevigatus), crabs (Ranina ranina and Thalamita sp.), and small lobsters (Puerulus sp.) (Birkett, 1979). These potential resources, presently not exploited, are outside the reach of artisanal fishermen.

1.1.2. The oceanic area

Landings of tuna in the Indian Ocean were over 600 000 t in 1987 (IPTP, 1988) little of which was caught in the Mauritian EEZ. Two Mauritian industrial purse seiners operate mainly in international waters. Their catch for 1987 was around 7 000 t, mainly of skipjack and yellowfin tunas. Other purse-seiners are expected to join the fleet in future years

1.1.3. The artisanal fisheries

The artisanal fisheries of Mauritius can be divided into two sectors: lagoon and off-lagoon. Landings are around 1 600 t and include over 400 t from the sports fishery. Statistical data for the last ten years show a considerable decrease in landings (Table 1).

This state of overexploitation is compounded by pressures due to population increase and to adverse effects arising from agricultural, industrial and tourist development. As the possibility of improving landings from the lagoon is very limited, the development of aquaculture could be an alternative to supply market demand, but its potential is still to be determined.

The lagoon has been exploited since the island was inhabited. Fishing techniques consist mainly of lines, basket traps, cast nets and harpoons. A substantial part of the catch is obtained by seines and gill-nets.

Table 1: Evolution of the Artisanal Fishery: 1979/1987

YEAR


1979

1987

Variation (%)

Catch in t



Total

1,945

1,597

-17.9

Lagoon

1,340

785

-41.4

Off lagoon

605

812

+34.2

No. of fishermen



Total

2,129

2,087

-1.9

Lagoon

1,569

1,099

-29.9

Off-lagoon

560

988

-76.4

No. of fishing days/year


Lagoon

185

190

+2.7

Off-lagoon

156

170

+8.9

Catch/Fisherman/year(kg)


Lagoon

854

714

-16.4

Off lagoon

1,080

821

-23.9

Catch/Fisherman/day(kg)


Lagoon

4.6

3.8

-17.4

Off-lagoon

6.9

4.8

-30.4

Source: Albion Fisheries Research Centre

The gear in use outside the reefs includes handlines and trolling lines as well as basket traps. Handlines are used in depths of 10-300 m to catch demersal fish. Basket traps are rarely set beyond depths of 50 m.

Approximately 80 vessels are involved in big game fishing largely involving tourists, here called sports fishing. Annual landings have been estimated for the recent years to be about 400 t. The catch is composed mainly of large pelagics, the target species being marlin.

Except for a few resources such as deepsea shrimps which are still untapped, the area accessible to professional fishermen is already overfished and there are few prospects for development.

The large pelagic resources are insufficient for an industrial operation, and have not until now been accessible to the artisanal fisheries due to the necessity for fishermen to make long trips to search for fish concentrations. The cost of fuel and small size of the pirogues have until recently limited the number of fishermen likely to exert a regular fishing effort on this resource.

This resource - composed mainly of tunas, dolphinfishes, marlins and sharks - could potentially support a transfer of fishing effort from the coast to the high seas.

2. FAD Development in Mauritius


2.1 Background
2.2 Objectives of the current programme
2.3 FAD designs tested
2.4 The medium FAD
2.5 Loss of FADs
2.6 FAD locations


The phenomenon of fish aggregating around objects floating or lying on the sea bottom, has been known to fishermen throughout the ages. This characteristic is successfully reproduced artificially - mostly in Southeast Asia - to aggregate both small and large pelagics. The example of the Philippines in particular, is frequently referred to and has formed the basis for several technology transfer operations.

The tuna fishery has placed great hopes on the introduction and utilization of fish aggregating devices (FADs) during recent years.

2.1 Background

A first attempt was made in 1983 by the FAO/UNDP SWIOP Project (RAF/79/065) to set two FADs off the West coast of Mauritius. However, the first was lost during deployment and the second was rapidly destroyed by fishermen. These FAD deployments, however, together with FADs set in Zanzibar, Tanzania and Comores by SWIOP pioneered design and techniques for setting from small boats.

2.2 Objectives of the current programme

The programme of FAD deployment in Mauritius reported on here was undertaken in order to divert some fishing effort away from the lagoon or from traditional demersal resources and to increase the supply of fish to the domestic market.

The objectives of the programme, therefore, were to optimise FAD location, design, materials and deployment techniques, to determine the most appropriate fishing techniques and catch rates in order to recommend appropriate investment levels, and to promote artisanal fishing around FADs.

2.3 FAD designs tested

Several models of FADs intended for the coastal fisheries were tested, all of the floating and anchored type (see Figs. 3, 4 & 5). A detailed description of the designs has been given by Roullot and Venkatasami (1986). Of the three types, light, medium and heavy, a medium design was found most suitable to the Mauritian context.

2.4 The medium FAD


2.4.1. Oxidation, wear and tear


The medium FAD was given a linear, articulated structure which can flex to swells and submerge progressively with increasing current.

The use of FADs in Mauritius has demonstrated the existence of strong tidal currents. These caused the early FADs, which had insufficient buoyancy, to submerge frequently. The depth attained by FADs during their submersion could not be precisely determined. Nevertheless, in the case of the first models, as confirmed by the collapse of floats attached to the FADs and by echosounding, it often exceeded 150 m.

Initially, the floatation was made of tyres filled with trawl floats. The first designs had four tyres and successive ones had only one. Subsequently, the tyres were eliminated in order to reduce dead weight and flotation was increased to reduce submersion. The ability to sink without damage should be maintained, however, in order to reduce the tension exerted on the mooring line and anchor1.

1 Calculations of current traction on mooring lines show that these can attain several tonnes for currents exceeding two knots (Ardill pers. comm). The use of flotation in excess of anchor weight would rupture the mooring line or float off the anchor in strong current situations.

The model illustrated in Annex 3 is the end-product of these improvements.

Considering the depth of mooring (800-3 500 m), rough sea conditions during periods of cyclones and trade winds and currents often exceeding 3 knots, very strong materials must be used. The upper section was made of rigid, resistant floats, mounted in line on 18 mm polyamide rope.

The upper section ended with a mast, bearing a radar reflector and a flag. A counter-weight to which were appended the attracting materials (old nets) was fixed to the lower end of the mast. The overall buoyancy exceeded 300 kg.

The mooring rope was of 18 mm diameter polypropylene material. With a view to reduce both construction costs and the drag of the rope to currents, two FADs were anchored with 16 mm diameter rope. The lifespan appeared to be the same, but the duration of immersion during strong currents was not significantly different. A scope ratio (the relationship between the length of the mooring rope and the depth) of 1.2 seemed most adapted to alternating periods of calm weather and strong current.

The anchor consisted of steel blocks, linked by chains and having a total weight exceeding 1 000 kg. Scrap steel blocks, which are relatively cheap, offer a favourable weight/volume relationship. This is important as the boat used for mooring does not allow the loading of less dense material such as concrete which would require three times the weight in air to achieve the same immersed weight.

Setting a FAD is a critical operation which has been described by Roullot and Venkatasami (1986).

2.4.1. Oxidation, wear and tear

Two factors can reduce the lifespan of FADS: oxidation of the metallic parts and wear and tear of the mooring line. The use of hardware, chains and steel wire ropes of non-uniform metallic consistency gives rise to electrolysis which can cause the premature loss of a FAD. Several authors have underlined this constraint and recommended uniformity in the metals used, as well as their galvanization (de San, 1982; Boy and Smith, 1984), but it was not always possible to follow this advice because of the non-availability of materials.

The upper section of the first models of FADs set in Mauritius was mounted on 16.5 mm galvanized and greased steel wire rope. These sometimes broke after only 5 months of use, resulting in partial or total loss of the FAD. To solve this problem, the wire was changed every 5 months. This manoeuvre is difficult and also causes the loss of flora and fauna associated with the upper part of the raft. Therefore, the likely benefits due to the maturation of the FAD partially disappear following such an operation.

Steel wire rope is now replaced by a spun 18 mm nylon rope (polyamide). This has not completely eliminated wear and tear. However, the rope can be doubled at 5-6 month intervals without removing the original structure. It is advisable to change the top section completely after 16-18 months.

Due to the constant movements in the marine environment, ropes, hardware or floats in contact with each other inevitably wear out. To minimize this, it is good practice to use over-dimensioned materials and safety shackles, to weld loose steel parts and whip thimbles.

Despite these precautions, routine checks should be carried out on the upper section and, if necessary, those parts considered close to a level of wear which could endanger the existence of the FAD should be changed or reinforced. It is impossible to intervene on the lower section which runs to depths of over 1 000 m. However, on FADs which broke loose and were recovered, little fouling or deterioration was noted on the rope extending below the photic zone.

2.5 Loss of FADs

In two cases, losses of FADs were due to the steel wire rope parting. In two other cases, an excess of mooring rope floated to the surface and was cut by boat propellers. Another loss occurred when the mooring rope chafed against an underwater peak which was only detected afterwards. Recently, one FAD was pulled off by a drilling platform under tow.

The cause of loss remains undetermined in two other cases. One of the FADs was found drifting: its mooring rope had been sectioned over 30 m below the surface. Losses due to material failure are now virtually eliminated.

2.6 FAD locations

FADs should be accessible to artisanal fishermen for whom they are primarily intended. However, a certain distance from the coast and between each FAD should be maintained. In countries with abundant tuna resources, empirical observations as well as tagging experiments show that FADs should be at least 10 n.mi. apart (Holland, 1985; Cayré, 1986). The distance from the shelf edge should be at least 5.5 n.mi. but preferably 11 n.mi. or more"(Marcille, pers. comm.).

These theories were not verified in Mauritius. Until such time as artisanal fishermen were aware of the advantages of fishing around FADs it was essential that they should be located within the radius of their regular activity. Therefore, FADs were placed from 2.5 to 6.3 n.mi. from the coast and the distances between them varied from 3.9 to 9 n.mi. (Figure 6 and Table 2). Only later was one FAD placed 12 n.mi. from the coast.

Table 2: Lifespan of FADs and their distance from the coast

Name

Depth

Distance from Coast (n.mi.)

Date set

Date lost at
30/11/88

Lifespan
(days)

01 ALBION

1,130

2.4

07/11/85


1,147 +

02 ALBION BIS

1,250

2.5

07/11/86

21/09/88

674

02a ALBION BIS2

1,250

2.5

17/11/88


14 +

03 RIVIERE N

950

3.0

04/12/85

20/03/86

102

03a RIVIERE N2

950

3.0

02/06/88


910 +

04 MEDINE

2,500

5.5

18/03/86


977 +

05 MEDINE BIS

2,600

6.3

10/02/87


615 +

06 TAMARIN

1,800

3.0

27/05/86

27/12/86

214

06a TAMARIN 2

1,800

3.0

04/02/87

16/06/87

124

06b TAMARIN 3

1,800

3.0

28/08/87


447 +

07 LA PRENEUSE

2,300

5.0

14/07/86


859 +

08 TR/BICHE

875

2.0

29/10/86

12/03/87

134

08a TR/BICHE

1,125

3.2

13/03/87

30/11/87

262

08b TR/BICHE 3

2,000

5.5

13/04/88


231 +

09 BAIE/TOMB

1,050

2.5

05/11/86


715 +

10 ILE PLATE

800

5.0

14/11/86

10/03/88

483

11 TR/D'EAU/D

850

3.0

26/11/86


724 +

12 ROCHE NOIRES

1,000

2.2

08/12/86


711 +

13 PASSE DAN

920

2.8

12/12/86


707 +

14 GD/RIV/S.E

980

5.5

17/12/86

04/04/88

475

15 PORT LOUIS

3,000

12.0

16/09/87


428 +

16 RIV. N. LARGE

3,000

9.4

07/09/88


84 +

FADs were set in the first instance off the West coast in the lee of the island with respect to the trade winds. When the design and setting technology were mastered, a series of FADs was set off the eastern coast which is exposed to the trade winds and has much rougher conditions.

Other considerations in the choice of the West coast for initial trials were the limited lagoon area and narrow shelf on that side of the island. The lagoon is wider and deeper in the East, and the continental shelf extends to almost 5 n.mi. The artisanal fishermen of the East coast, with more abundant nearshore resources, were less likely to exploit pelagics. The West coast fishermen were thus more likely to show interest in FADs.

The major beneficiaries of the FADs off the East coast are the sports fishermen. They are almost the only ones operating around those structures. Their catch rates are considerable: landings during certain periods of the year are reported to amount to hundreds of kilogrammes per fishing day.

Unfortunately, despite guaranteed confidentiality, these fishermen have systematically refused to communicate their detailed catch data, even anonymously.

3. Fishing Craft and Gears


3.1 Fishing craft
3.2 Fishing gears


3.1 Fishing craft


3.1.1. Project vessels
3.1.2. The artisanal fishery
3.1.3. The sports fishery
3.1.4. Part-time fishermen


Four fishery categories exploited the FAD resources: project vessel, artisanal, sports (tourist) and part-time fisheries.

3.1.1. Project vessels

Two boats having similar characteristics fished alternately during a period of 37 months. The catch data are therefore assessed as for a single unit. These boats are 10 m LOA with 120 Hp engines and have a crew of 3 persons. They normally leave port at 4.30 in the morning and are back at 12.30. The daily fishing effort was considered to be of 6 hours' duration, with two hours for steaming to and from the fishing area.

The gears described below were all used on the project vessels.

3.1.2. The artisanal fishery

The boats used in the artisanal fishery are wooden, carvel-planked "pirogues" which measure 6.5 to 7.5 m in length. They are equipped with 8 to 15 Hp outboard motors and sails. They fish around FADs within a radius of up to 15 n.mi. from their base. They have a crew of 2 to 3 persons.

Fishing techniques employed are handlining with live or dead baits and trolling with dead or artificial baits.

3.1.3. The sports fishery

The boats of the sports fishery are 10 to 12 m LOA. They are powered by twin 120-350 Hp diesel engines and are equipped with trolling tackle for big game fishing.

They travel from one FAD to the other throughout the day in search of billfish. Around the FADs they usually catch skipjack to use as bait for their target fish. At the beginning or at the end of the trip, these boats commonly troll around FADs for dolphinfish, wahoo or sharks to vary the catches of the customers. In winter, outside the billfish season, these boats fish for tuna and dolphinfish using handlines around the FADs.

The duration of the fishing trip is around 9 hours, from 7.00 hours to 16.00 hours, one hour being spent for steaming out and back from the fishing grounds. The crew is made up of two persons plus the customers. Each boat makes approximately 150 trips per year.

3.1.4. Part-time fishermen

The FADs were also visited by part-time fishermen; the number regularly active was estimated to be 16. They fish mainly on Saturdays, Sundays and public holidays, trolling and handlining. It was estimated that they fish for 6 hours per trip 40 days a year.

3.2 Fishing gears


3.2.1. Gill nets
3.2.2. Trolling (Annex 4)
3.2.3. Japanese longlines
3.2.4. Monofilament longlines
3.2.5. Handlines
3.2.6. Drifting floats


The water turbidity in Mauritius is one of the lowest of the Indian Ocean, often with over 26 m of underwater visibility. This low turbidity has a direct influence on the fishing techniques employed, as fish are able to see the gear. Fish can go around or pass under gill nets and seining operations should be carried out before dawn to avoid fish escaping. For trolling, handlining and long lining, artificial lures or natural baits have to be mounted on thin lines.

3.2.1. Gill nets

Gill nets had a combined length of 850 to 1 300 m with mesh sizes of 120 mm, 150 mm and 160 mm (stretched) in mono and multifilament and depths of 10.5 m, 24 m and 32 m.

This gear was mainly tested away from the FADs to avoid entanglement with the latter due to current shifts. Catch rates of 0.06 fish per 50 m of net were achieved. In comparison, during trials made in the Seychelles, the catch rate was 5 kg per net (one fish) (Taishing No. 1, 1986). The catch rate for albacore tuna in the Atlantic is 2.1 fish per net (Dremière, 1987).

The catch rates were below expectations and were considered to be too low to envisage extending this technique to the artisanal fishery. A similar conclusion was drawn for Rodrigues Island (Lozach'meur, pers. comm.). Nevertheless, nets made of very thin twine and mesh size 180 to 200 m with a 0.5:1 hanging ratio could probably be successful.

3.2.2. Trolling (Annex 4)

This gear (Figure 7) was used by project boats and is commonly used by artisanal and sports fishermen. Artificial lures, dead baits, live baits at the surface and at depth were tried. The best catch rates were obtained at dawn and decreased after 9 a.m., although some fish could be caught throughout the day (Figure 8).

3.2.3. Japanese longlines

This longline (Figure 9) was used drifting or attached to the FADs. The main line was made of polyvinyl polyester/alcohol of 6 to 8 mm diameter. The branch lines, 12 m long, were mounted at 50 m intervals and had snoods made of 1.5 mm steel wire cable.

The immersion time varied between 3 and 20 hours and the number of hooks ranged from 3 to 80. The catch rate was 16.2 fishes per 1 000 hooks for 12 hours. Table 3 shows the catch rates of this gear in different regions of the Indian Ocean and in Australian Waters for comparative purposes.

Table 3: Catch rates of Japanese longlines (All species)

Country

kg/1 000 hooks

No. of fish/1 000 hooks

Mauritius (MAFNR)

256*

16.2

Australia (SAFIC)

714

36.8

Saya de Malha (N. RESHETNIAK)

511

15.8

Seychelles (SFA)

377

Not available

Seychelles (IPTP)

Not available

14.0

* Shark weight, headed and gutted, other fish gutted.

The catch consisted mainly of sharks, tunas, dolphinfish, swordfish, marlins, sailfish and barracuda.

3.2.4. Monofilament longlines

This line was made of 0.8 to 1.4 mm monofilament nylon on which were mounted 10 hooks at intervals of 6 to 10 m (Figure 10). The hook lines of 0.8 to 1.2 mm monofilament were 2 m long. The line was attached to the FAD or drifting nearby. When drifting, it could be positioned near fish concentrations and in these cases could produce very good catch rates. Several such longlines could be linked to each other to cover a larger surface.

Catch rates improved with the use of fresh bait and was better still with livebait. Table 4 compares the catch rate of monofilament and Japanese longlines. The superior catch rate by weight of the Japanese longline was due to the large number of sharks caught by this gear. Dolphinfish was the main species caught by monofilament longlines.

Table 4: Comparison of catch rates of monofilament and Japanese longlines

Gear

kg/hr/1 000 hooks

Monofilament longline

3.4

Japanese longline

3.8

3.2.5. Handlines

This technique is widely used by artisanal fishermen. The gear consisted of 1 to 1.2 mm monofilament line with a single hook (Figure 11). The bait varied according to availability, but was generally live fish (goatfish, mullet and scad) caught with cast nets or beach seines before leaving for the FADs. During certain seasons, scad and carangids can be caught around FADs with very light lines. In the absence of live bait, strips of skipjack, squid, octopus or shrimp were also successfully used. Chumming could also be done with minced fish mixed with sand and oil.

The line generally remains close to the surface although large tunas have been caught at greater depth. Based on echo-soundings, it appears that better catches might be obtained at depths of 80 to 180 m.

Boats handlining were allowed to drift with the current and the wind close to the FAD, or were sometimes attached to it. While drift fishing, the pirogues can come closer to fish schools and the fishing rate is normally better.

The catch rate of artisanal fishermen was estimated at 4 kg/hook/hr, which was considered very satisfactory for Mauritius and even compares favourably with that of other countries like the Philippines where catch rates do not exceed 4 kg/hook/hr (Stequert, 1988). Project boats very rarely used this technique: their catch rates were 1.25 kg/hook/hr.

3.2.6. Drifting floats

This very simple gear consisted of a line 10 to 20 m long attached to a float (Figure 12). A series of drifting floats could be released around a FAD or fish school. Two to four floats were released during successive drifts. This gear is being adopted by artisanal fishermen due to its low cost and the good catch rates it produces.

4. Analysis of catches


4.1 Catch per fishing day
4.2 Currents and lunar phases
4.3 Catch Species Composition
4.4 Length composition of Project vessel catches
4.5 Fish behaviour near FADs


For the computer analysis of the data, a programme was prepared by Mr. R. Coppola of the Fisheries Data Centre, FAO, Rome.

4.1 Catch per fishing day


4.1.1. Project vessels
4.1.2. Artisanal Fishery
4.1.3. Sports Fishery
4.1.4. Part-time fishery


4.1.1. Project vessels

Fishing effort was calculated on 647 trips over two years. As the objective was more often of an experimental type, with fishing around several FADs during the same day rather than intensive fishing around one FAD only, fishing by the project vessels was classified as semi-commercial. Several fishing techniques were employed during the same trip, mainly trolling, handlining and longlining.

The average catch rate per fishing day of the project boats was 4.8 fishes or 35 kg per trip. This value is for a semi-commercial type of fishing and should be increased by 40% to compare to a professional activity.*

* Authors' estimation.

The average catch per day for each month in the vicinity of FADs is illustrated in Figure 13. It is possible to catch pelagic fish around the FADs throughout the year with a peak of abundance from October to mid-December and a second peak, which is less marked, in April/May.

4.1.2. Artisanal Fishery

Four skippers submitted fishing logs (Appendix 3) and their catch data provides a basis for the analysis of their activities.

The duration of trips varied with the season and the crew, but was estimated at 8 hours (from 4 am to 12 am). From observation, two hours should be allowed for steaming time and one hour for capture of bait.

Twenty pirogues are estimated to operate around the FADs off the West coast with an average of 168 fishing days per year. Landings occurred from le Morne to Grand Baie but most of the fishermen exploited the FADs situated between Black River and Pointe aux Sables.

Based on the analysis of the fishing logs, the daily catch of artisanal fishermen was 40 kg. It is thought that there was some under reporting and fishing logs were sometimes not filled in regularly.

In conclusion, it seems that the catches of the artisanal fishery were relatively stable throughout the year except during the winter months, June to September, when the climatic conditions limit the number of fishing trips.

4.1.3. Sports Fishery

The daily catch rates around FADs of the sports fishing boats amounted to 35 kg or 3.7 fishes per boat. This value was obtained from fishing logs of 21 boats for the period between November 1986 and November 1988. Entries in the log books were at times missing.

Again, under reporting of catches was suspected, despite assurances of confidentiality attached to data provided. Based on several observations, on verifications of fishing activities at sea and on declarations of fishmongers ashore, the underreporting for sports fishermen and artisanal fishermen was evaluated at 40%.

4.1.4. Part-time fishery

Three part time fishermen regularly kept fishing logs with regard to their catches. The reported catch rates of the part-time fishermen were of the order of 25 kg per trip. This figure could not be verified.

Table 5: Catch by fishery type

Fishery

Reported Catch
kg/Boat/Day

No. of fishermen/boat

Assumed
% bias

Calculated catch (kg)

Artisanal

40

2.5

40%

56

Sports

35

3

40%

56

Part time

25

3

n.a.

25

Project boats

35

3.5

40% (commercial)

49

Comparing the daily yield per boat in different countries on the basis of available literature, it is possible to note a similarity in the data obtained (Table 6).

Table 6: Yield per day of artisanal fishermen around FADs: trolling and handlining

Country

Author

Yield (kg)

Comores

Marsac et al (1987)

50

Hawaii

Marcille (1979)

140

Maldives

Stequert et al (1986)

200

Martinique

Sacchi (1986)

50

Mauritius

Roullot et al (1986)

50

Philippines

Stequert (1988)

55

Reunion

Albin (1988)

50

Seychelles

Stequert et al (1980)

50

Sri Lanka

Weerassoriya (1987)

50

Tahiti

Depoutot (1987)

150*

Thailand

Stequert et al (1986)

0

Vanuatu

Cillauren (1987)

80

* 49 fish = ± 150 kg

In Tahiti, where it is considered that available data is satisfactory, the increase in CPUE in terms of number of pelagic fish caught by the use of FADs is 35% (Depoutot, 1987).

4.2 Currents and lunar phases


4.2.1. FAD submersion under the effect of current
4.2.2. Catches in relation to the lunar phase


4.2.1. FAD submersion under the effect of current

A study was carried out based on observations during 14 consecutive lunar cycles (Figure 14). It seems that the FADs can sink at any phase of the moon, even though the probability is less during neap tides. FADs are subjected not only to surface currents, but also to deep subsurface currents whose force and direction are unknown. There is certainly a combination of tidal and oceanic currents.

Most probably, currents have an influence on the small pelagics and also on the schools of tuna and skipjack concentrated around FADs. The force of the current is thought to flush plankton and small fish away from the FAD, with the consequent departure of the large pelagics. Nonetheless, concentrations of fish and birds were frequently observed around momentarily submerged FADs. This indicates that, despite the strength of the current, fish tend to stay in the vicinity of the raft.

Strong currents also make fishing operations more difficult as, when passive techniques such as drift lines or longlines are used, the fishing gear remains within the proximity of fish concentrations for only a short period of time.

On average, FADs were submerged during 22% of the times they were visited by Project boats. (This percentage was reduced to less than 5% with the latest FAD designs). Maximum submersion occurred during the new moon (day 29 to day 4), the FADs rarely sinking during the first quarter (day 7 - 13).

4.2.2. Catches in relation to the lunar phase

The analysis of catches during 32 lunar cycles (Figure 15) shows little change in the vulnerability of the fish throughout the lunar cycle to the artisanal (handline) fishery.

For the Project boats, the most favourable fishing period appears to lie in a direct relationship with the current strength (as indicated by FAD submersion in Figure 14), with catches tailing off in the first quarter.

4.3 Catch Species Composition


4.3.1. Commercial Species
4.3.2. Non commercial species
4.3.3. Project boats
4.3.4. Artisanal fishery
4.3.5. Sports fishery


4.3.1. Commercial Species

Several species were present around and under FADs; their abundance varied with seasons. A list of species caught is found in Appendix 1. The most abundant were dolphinfishes, yellowfin tuna, skipjack and wahoo. Other important species were sharks, marlins, sailfish, swordfish, albacore and bigeye tunas, barracuda and rainbow runners.

4.3.2. Non commercial species

Prey species started appearing as from the first days and sometimes first hours after setting a FAD. They increased in number and species 'variety with time, their abundance fluctuating according to season. The species were identified from specimens caught by various techniques and from stomach contents of captured predators; a list is provided in Appendix 1. They consist mainly of small pelagics, i.e. scad, carangids and sardines. The following were also encountered: flying fishes, Tetradontidae, Nomeidae, Blenniidae, Antennaridae, Alepisauridae and rays. Crustaceans include shrimps and crabs. Marine algae, seaworms, bivalves and cephalopods were also present.

The species composition of catches varied with the fishery type (Figure 16). It was analysed in terms of numbers of fish caught. The same analysis expressed in terms of landed weight would show slight differences.

4.3.3. Project boats

For the Project boats, the seasonal abundance of the 3 main species, dolphinfish, wahoo and tuna is shown in Figure 17. Dolphinfish were present throughout the year, with high occurrence at the previously mentioned peak periods. The peak catch of dolphinfish in October/November was, largely the result of exceptional catches in 1987. Wahoo were also present during the periods of high abundance of the dolphinfish but were rarely caught during the remainder of the year. Tuna seemed to be present the year round with increased catches in May and November.

4.3.4. Artisanal fishery

The landings of tuna in terms of weight represent 78% (57.3% in numbers) of the catch of artisanal fishermen. Tunas were reported throughout the year except during the months of June, July and August when entries were not made regularly in the log books (Figure 18), but the fishermen affirm to have continued to fish tuna. No noticeable peak can therefore be observed and any interpretation of available data is to be made with caution. The seasonal abundance of dolphinfish followed that observed by the project boats.

4.3.5. Sports fishery

The catch of sport fishery boats around FADs showed similar seasonality to the Project and artisanal boats relative to dolphinfish and yellowfin tuna. However, catches of skipjack, highly targeted for bait for marlin fishing, were higher than in the other fisheries (34% of total catch) and showed strong seasonality, with catch rates declining markedly between April and November (Figure 19).

Other than for the artisanal fishery which targets on tuna, dolphinfish were the dominant catch around FADs. This difference was related to the fishing gears used: dolphinfish, found near the surface, are more vulnerable to trolling, whereas tunas are caught more frequently by handlining with live baits.

4.4 Length composition of Project vessel catches


4.4.1. Dolphinfish, Coryphaena hippurus
4.4.2. "Yellowfin" tunas, Thunnus albacares and T. obesus
4.4.3. Skipjack tuna, Katsuwonus pelamis
4.4.4. Wahoo, Acanthocybium solandri
4.4.5. Shark
4.4.6. Other species


The data for 2,962 fish caught by the Project boats were available for analysis. Each fish was measured (fork length) and weighed, prior to gutting and heading.

4.4.1. Dolphinfish, Coryphaena hippurus

Only one species of dolphinfish, Coryphaena hippurus, is commonly caught around Mauritius. The compilation of data based on 1,369 fish shows homogeneity in average length throughout the year (Figure 20). Few small dolphinfish were caught, the bulk of the catch consisting of fish with an average length of 100 - 120 cm (Figure 21).

4.4.2. "Yellowfin" tunas, Thunnus albacares and T. obesus

Few bigeye tunas were identified from initial catches around FADs, especially as far as juveniles were concerned. Later, identification was through systematic examination of the livers of the fish caught. This showed that less than 5% of the fish grouped in the "yellowfin" category were bigeye tuna. It could well be that they represented a higher proportion of catches during the first year when deep-longlines were used more intensively.

Therefore, the two species were grouped together. Figures 22 and 23 illustrate the size frequency of fish and average size caught during the period under study. There appeared to be some inter-annual as well as seasonal variation in the size frequency, with small fish (60 - 80 cm F.L.) dominating in 1986 and larger fish (120 - 140 cm F.L.) more numerous in the summer months of 1987 and 1988. The 80 cm F.L. class represents 40 - 50 % of all yellowfin catches.

4.4.3. Skipjack tuna, Katsuwonus pelamis

Size composition of skipjack are given in Figures 24 and 25 for the period under study. There was a tendency for the average size of skipjack to be smaller between May and September. In 1986 and 1987, the 60 cm F.L. class made up the bulk of the catches, while in 1988, the 80 and 100 cm classes were more numerous.

4.4.4. Wahoo, Acanthocybium solandri

Wahoo represented the second most numerous species in the catches of the Project boats. Their abundance was seasonal and the periods of high concentration coincided with the peaks for dolphinfish. Although the size frequency was strongly dominated by 120 cm F.L. fish, (Figure 26), there appeared to be a correlation between the periods of abundance of wahoo in February to April and September to December with a larger average size of fish (Figure 27).

4.4.5. Shark

Several species of shark were caught, but one species, Carcharinus longimanus dominated with 159 specimens landed. The sharks were predominantly of 120 cm F.L. Only in January and February 1987 were there any variations in average lengths. In relation to the number of specimens caught, these may not be significant (Figures 28 and 29).

4.4.6. Other species

Numerous other species were caught, but they represent a low percentage of the total catch. Besides the marlins and sailfish which constitute a major target of the sport fishery catch and which are not treated here, two species are to be highlighted. They are the swordfish, Xiphias gladius and the albacore tuna, Thunnus alalunga. Eight swordfish were caught by the Project boats during a fishing period of six months (Table 7). This fish, of high commercial value, is also highly sought after by sports fishermen. There is no doubt that there is some scope for this fishery in Mauritius. Apart from the swordfish caught by the Project boats, there is only one record of the catch of a swordfish whose tail was entangled in the mooring line of a basket trap. However, artisanal fishermen from Pointe aux Sables fishing around FADs have often been confronted with swordfish which attack hooked tunas and which they have attempted to harpoon.

Table 7: Swordfish caught by project boats

Date

Place

Gear

Weight (kg)

Length (m)

12/12/85

Riv. Noire

longline

470

n.a.

18/12/85

Médine

gill net

50

1.6

31/01/86

Trou E.D.

longline

30

1.23

31/01/86

Trou E.D.

longline

60

1.90

31/01/86

Trou E.D.

longline

80

2.00

21/02/86

Grande R.S.E.

longline

45*

1.50*

21/03/86

Albion

longline

4

0.75

30/05/86

Albion

longline

3

0.70

* Estimated (bitten by sharks).

Albacore tuna are taken on rare occasions by fishermen and are present in depths between 20 and 200 m. Seven of these fish were caught by the Project boats and Table 8 gives their respective lengths. It is interesting to note that certain fishermen of Reunion Island have recently caught albacore at depths of 30 m around FADs.

Table 8: Albacore Tuna caught by project boats

Date

Location

Gear

Weight (kg)

Length (m)

26/03/86

Albion

longline

17

1.06

30/04/86

Albion

longline

21

0.97

13/05/86

Albion

longline

16.5

1.04

30/05/86

Albion

longline

31

1.32

03/06/86

Tamarin

longline

16

0.98

17/07/86

Albion

longline

11.5

0.90

03/04/86

Port Louis

longline

22.5

1.09

Marlin, Makaira mazara and M. indica, as well as sailfish, Istiophorus platyterus are frequently caught by boats of the sport and artisanal fishery. The billfish are presumably attracted to FADs by the concentrations of skipjack and small tunas. FADs are rapidly becoming favoured fishing sites of the sport fishermen. More than 150 marlins have been reported by the sport fishery to have been fished around FADs during the 1987-88 season. This corresponds to about one-third of the number normally landed (de Ravel, pers. comm.).

4.5 Fish behaviour near FADs

Observations showed differing fish behaviour in the neighbourhood of FADs. Fish were observed visually and by echo-sounder and were caught up current of the FADs. These fish, mainly dolphinfish, small tunas, sharks and wahoo, were presumably stabilised for some time.

Schooling large pelagic fish appear to stay for a few hours or a few days. They move away during the first hours after dawn and return to the FAD at dusk. These fish schools were not found in any particular position relative to the FADs.

Fish were detected by echo-sounding under FADs at depths of up to 200 m. These appeared to be mainly small pelagics: scad and carangids found from 0 to 60 m depth and skipjack, yellowfin, bigeye or albacore tuna found to 200 m deep.

5. Results of the FAD deployment programme


5.1 Activity around FADs
5.2 Annual yield per FAD
5.3 Comparison between FAD locations
5.4 Cost/Lifespan Relationship


5.1 Activity around FADs

The progression in the number of visits to FADs by artisanal and sport fishermen was substantial between 1986 and 1987 and stabilised in 1988.

Observations from 647 trips at sea by project boats showed that over 20 pirogues fished regularly around the 7 FADs off the West coast. The movement of artisanal fishermen has reduced fishing effort in the lagoons and on the narrow continental shelf and fishermen also find fish around FADs which they rarely caught previously.

The number of boats of the sport fishery regularly visiting FADs was around 35 off the West coast, 45 others fishing more episodically. The number of part time fishing boats visiting FADs was estimated at 16.

5.2 Annual yield per FAD

In the absence of statistical data, the catch data of the project boats and fishing logs filled by the artisanal, sport and part time fishermen were used to estimate the yield of a FAD (Table 9).

The catch per day, the number of fishing days and the number of boats fishing around FADs are summarised. This exercise was carried out for the 7 FADs of the West coast where the information collected are considered to be reliable and where fishing effort on pelagic fish is more developed.

Table 9: Catch around FADs (West coast)

Type of fishery

Catch per boat per day

No. of fishing
days/year

Catch per boat per year

No. of units

Catch per year all units

(kg)

(days)

(tonnes)

(tonnes)

Artisanal

40

168

6.7

20

134

Sport

35

150

5.25

35

183

Part time

25

40

1

16

16

Total catch




tonnes

333

This evaluation is based on possibly under-reported figures of catch per fishing day, as is discussed in Section 4. The production around the seven FADs on the West coast alone would then be at a minimum 333 t per year, i.e. a production 47.5 t per FAD.

In the Philippines some 3 000 payaos produced over 260 000 t of tuna in 1985 (Stequert, 1988), giving a yearly production per payao in the order of 87 t. The production of a drifting FAD used by Mauritian and Japanese purse-seiners operating in the Indian Ocean is estimated at 100 to 500 t for a drift that can last several months. It should however be underlined that the production of a drifting FAD cannot be compared to that of an anchored one, the conditions influencing aggregation and exploitation being fundamentally different.

5.3 Comparison between FAD locations

Landings of the 37 consecutive months do not show significant difference between catches obtained from FADs situated close to shore and those found further away. The main reason arises from the difficulty to exert a strictly identical fishing effort from one FAD to the other.

It was noted, however, that artisanal fishermen prefer nearshore FADs while sport fishermen would rather visit offshore ones.

5.4 Cost/Lifespan Relationship

As shown in Table 2, the lifespan of FADs as at 30.11.88 was 1 107 days for the oldest1. The minimum and average figures include accidental losses which are now rare.

1 The literature available on the lifespan of FADs in different countries gives an average lifespan of 257 days at the date of publication (Depoutot, 1987).

The cost of a FAD is M.Rs.35 000 and annual maintenance is valued at M.Rs.3 100. Based on an average lifespan of 506 days, the annual cost of a FAD is obtained by extrapolating for 365 days and adding the annual maintenance cost, which is as follows:

This gives a rounded figure of M.Rs.30 000 for a production of 47 t of fish valued at M.Rs.752 000 at the conservative rate of M.Rs.16/kg. The cost of a FAD, therefore, represents only 4 % of the net annual production value.

6. Estimated Pelagic Fish Landings in Mauritius

Over the last 11 years, the sport fishery landings have been estimated at 400 tonnes (Source: MAFNR). The number of boats in the sport fishery has increased from 40 to 75 units over this period. However, only 45 of these can be considered as fishing regularly, 40 along the West and North-west coast and 5 along the remainder of the coast. There is also the impact of FADs on their production. It is necessary, therefore, to update the estimate of production of pelagic fish.

The catch of one big game fishing boat in active operation is around 8 t/year*. This amounts to 360 t for 45 boats. If the other 35 boats land only 3.4 t each annually*, they would produce an additional 120 t. The total landings of the sport fishery would therefore be 480 t.

Some pelagic fish are caught by the 215 pirogues which fish outside the lagoon. Landings are evaluated above at 134 t for 20 boats, each fishing 6.7 t/year around FADs. The other 195 boats, each landing only 0.25 t annually, would produce 48 t*. The net landings of the artisanal fishery would thus be 182 t.

More than 70 part-time boats fish outside the lagoon. This gives 16 t for the 16 boats fishing around FADs and 5.4 t for the remaining 54 at a rate of 0.1 tonne each per year*. The part-time fishermen would therefore be landing 21 t of pelagic fish.

* Authors' estimation.

The total landings of large pelagic fish would thus be at least 690 t.

7. Future prospects

In the Mauritian context, the lifespan of FADs should in the future attain 5 years.

The number of FADs is expected to increase progressively, depending on demands from professionals and their preferred zone of activity.

Fishing effort is being distributed automatically, artisanal fishermen preferring the nearshore FADs whereas the sport fishermen exploit distant FADs.

The actual catch around the FADs which is estimated at 330 t for the West coast, could exceed 500 t in the next few years, thus contributing for more than a third to the domestic landings of fish.

REFERENCES

Anon., 1987 - Report on the result of the works of the SRTM "N. RESHETNIAK" in the waters of Mauritius during its 21 st. scientific research cruise (April - June 1987) Restricted circulation.

ANON., 1981 - Tuna longliner operations observed off South Australia. SAFIC 8 p.

ANON., 1987 - Des essais de pêche au filet maillant aux Iles Seychelles. "FRANCE PECHE TAISHING No. 1" p. 10.

BERGSTROM, M., 1983 - Review of experiences with and present knowledge about Fish Aggregating Devices, Bay of Bengal Programme/WP/23, 51 p.

BIRKETT, L., 1979 - Western Indian Ocean Fishery Resources Survey. IOP/TECH/79/26, 99 p. -

BOY, R.L. and B.R. SMITH, 1984 - Design improvements to fish aggregation device (FAD) mooring systems in general use in Pacific Island countries. Commission du Pacifique Sud, Handbook 24, 76 p.

CAYRE, P., J CHABANNE, G MOARII, and B. UGOLINI, 1986 - Premières experiences de marquage acoustique de thonidés en Polynésie Française. EVAAM Tahiti, Document Pêche, 11,45p.

CILLAUREN, E., 1987 - La pêche à la traîne autour des dispositifs de concentration de poissons, (DCP) à VANUATU, résultats préliminaires. Antenne ORSTOM/IFREMER BREST, 81 p.

DEPOUTOT, C., 1987 - Contribution à l'étude des Dispositifs de Concentration de poissons à partir de l'expérience Polynésienne. ORSTOM, Notes et documents No. 33, 154 p.

DE SAN, M., 1982 - Fish Aggregating Devices or Payaos. Commission du Pacifique Sud, CPS, Quatorzième conference technique régionale des pêches. SPC/Fisheries 14/WP.15, 17 p.

DREMIERE, P.Y., 1987 - La pêche du germon dans le N.E. Atlantique. Vers de nouvelles techniques de capture. Résultat de la campagne GERFIL 86. DIT IPCM Séte, 107 p.

FAO/IOP, 1978 - Workshop on the ressources of the Western Indian Ocean South of the Equator. Mahe, Seychelles, 23 Oct. 4 Nov. 1978 IOFC/DEV/79/45, 102 p.

LENS, D.J., M. GIUDICELLI, and J. ROULLOT, 1987 - Final report on investment review on UNDP/FAO Project MAR/83/006. Advanced Artisanal Fisheries in Mauritius. FAO-IC, 14 P.

MARCILLE, J., 1979 - Nouvelles techniques pour développer la pêche thonière à partir des territoires Français du Pacifique Sud. Résultats des essais effectués par la Pacifie Tuna Development Foundation. La Pêche Maritime, octobre 1979, 5 p.

MARCILLE, J. et W. BOUR, 1983 - Les techniques de pêche au thon utilisées aux Philippines. La Pêche Maritime, février 1983, 4 p.

MARSAC, F. et B. STEQUERT, 1987 - La pêche des thons autour d'épaves ancrées dans l'Océan Indien. La Pêche Maritime, juillet - août 1987, 7 p.

MATSUMOTO, W.M., T.K. KASAMA and D.C. AASTED, 1981 - Anchored Fish Aggregating Devices in Hawaiian waters. Mar. Fish. Rev., 43 (9: 1-13

NAGEON DE LESTANG, J., 1988 - Tuna longlining in Seychelles 1984 - 1988. Expert consultation on the stock assessment of tuna in the Indian Ocean. Mauritius 22 - 27 June 1988, 16 p.

PETERS, C., 1982 - Maldives utilisation of anchored surface floating rafts. FAO Report for the project TCP/MDW/0001 and TCP/MDW/0105, 28 p.

ROULLOT, J. et A. VENKATASAMI, 1986 - Dispositifs de concentration de poissons, L'expérience Mauricienne - Expert consultation on the stock assessment of tunas in the Indian Ocean - Colombo, Sri Lanka, 4-8 décembre 1986, 20 p.

ROULLOT, J. et A. VENKATASAMI et S. SOONDRON, 1988 - Captures de grands pélagiques autour des dispositifs de concentration de poissons à l'Ile Maurice. - Expert consultation on the stock assessment of tunas in the Indian Ocean - Mauritius, 22 - 27 juin 1988, 31 p.

STEQUERT, B. et F. MARSAC, 1986 - La pêche de surface des thonidés tropicaux dans l'Océan Indien. FAO/DOC/TECH/PECHE/282: 213 p.

STEQUERT, B., 1989 - La pêche thonière aux Philippines. La Pêche Maritime - janvier 1989.

SACCHI, J., 1986 - Les dispositifs de concentration de poissons et le développement des pêches cotières. EQUINOXE No. 9 - juin - juillet 1986, 8 p.

WEERASOORIYA, K.T., 1987 - Experiences with Fish Aggregating Devices in Sri Lanka. Bay of Bengal Programme. WP/54, 10 p.

APPENDICES

Appendix 1: List of Species Caught and Found Around FADs Commercial species caught

Dolphinfish

Coryphaena hippurus

Skipjack

Katsuwonus pelamis

Yellowfin tuna

Thunnus albacares

Albacore tuna

Thunnus alalunga

Bigeye tuna

Thunnus obesus

Wahoo

Acanthocybium solandri

Barracuda

Sphyraena barracuda

Rainbow runner

Elegatis bipinnulata

Blue marlin

Makaira mazara

Black marlin

M. indica

Sailfish

Istiophorus platypterus

Swordfish

Xiphias gladius

Whitefin shark

Carcharinus longimanus

Tiger shark

Galeocerdo cuvieri

Blue shark

Isurus oxyrinchus

Hammerhead shark

Sphyrna lewini

Associated Species or Stomach Content

Scad

Decapterus macarellus

Horsemackerel

Selar crumenophthalmus

Carangid

Carangoides caeruleopinnatus

Sardine

Sardinella sp.

Seriola

Seriola rivoliana

Flyingfish

Exocoetus sp.

Triggerfish

Canthidermis maculatus, sp.

Tetradontidae

Arothron hispidus

Nomeidae

Psenes sp.

Blennidae

Aspidontus sp.

Xiphasia matsubarai

Antennariidae

Antennarius sp.

Alepisauridae

Alepisaurus ferox

Rays

Dasyatis purpurens

Mania birostris

Shrimp

Oplophorus gracilirostris

Penaeus sp.

Crabs

Scylla serrata,...

Sea worms

Annelid sp.

Algae

Halimeda sp., Canterpa sp.,

Codium sp., Corallina sp.,

Callophyllis, Gracillaria sp.,

Hypnea sp.

Bivalves

Pinna nobilis, Crasosstrea sp.

Corals


Cephalopods

Argonauta argo, Teuthoida sp.

Cirripeds

Anatife balans

Appendix 2: Cost of a FAD (November 1988)

A. Investment (1 US$ = 14 Rs)

ITEM

DIMENSION

QUANTITY

COST (Rs)

(US$)

REINFORCED PLASTIC FLOATS

200 mm

105

8,967

640

ROPE (PP)

18 mm

1,600 m

9,264

662

ROPE (PA)

18 mm

200 m

1,850

132

SAFETY SHACKLES

13 mm

5

200

14

SAFETY SHACKLES

16 mm

5

300

22

SHACKLES

12 mm

10

90

6

THIMBLES

18 mm

10

115

8

SWIVELS

16 mm

4

330

24

CHAIN

12 mm

50 m

3,860

276

CHAIN

16 mm

20 m

2,744

196

PLASTIC STRAP-BAND

12 x 4 mm

100 m

124

9

THREAD (PA)

280 x m/kg

1 kg

155

11

PIPE (GALVANISED)

34 mm

1

125

9

RADAR REFLECTOR


1

200

14

CHAIN

14 mm

20 m

600

43

SCRAP IRON BLOCKS


1 tonne

1,000

72

WELDING RODS



250

18

PAINT



30

2

LABOUR



2,500

180

TRANSPORT/DEPLOYMENT COSTS



1,549

111

MISCELLANEOUS



250

17

TOTAL



Rs. 35,073

2,466

B. Maintenance: Annual costs

ROPE, CHAIN, SHACKLES,

1,300

LABOUR

800

BOAT COSTS (FUEL/CREW)

1,000

TOTAL

Rs. 3,100

Appendix 3: Logbook forms distributed to fishermen

Figure

Figure 1: The islands and banks around Mauritius

Figure 2: Primary production in the Indian Ocean

(From Yu. G. Kabonova)

Figure 3: Light FAD

Figure 4: Heavy FAD

Figure 5: Medium FAD

Figure 6: FAD deployment positions around Mauritius Island as of November 1988

Figure 7: Trolling gear

Figure 8: Average number of fish caught per hour by trolling in relation to the time of day.

Figure 9: Asian type longline

Figure 10: Monofilament longline

Figure 11: Handline

Figure 12: Drifting vertical line - Yoka

Figure 13: Average number of fish per day caught monthly by the Project and Artisanal Fishery boats.

Figure 14: Percentage occasions when FADs were observed to be submerged

Figure 15: Average number of fish per trip of the Project and Artisanal Fishery boats throughout the lunar cycle

Figure 16: Species composition by percentage of Project, Artisanal and Sport Fishery boats

Figure 17: Average number of dolphinfish, yellowfin tuna and wahoo caught per trip by the Project boats

Figure 18: Average number of dolphinfish and yellowfin tuna caught per trip by the Artisanal Fishery boats

Figure 19: Average number of dolphinfish, yellowfin and skipjack tuna caught per trip by the Sport Fishery boats

Figure 20: Average fork length of dolphinfish caught by Project boats in every month

Figure 21: Length frequency distribution of dolphinfish caught by Project boats in 1986, 1987 and 1988

Figure 22: Length frequency distribution of yellowfin tuna caught by Project boats in 1986, 1987 and 1988

Figure 23: Average fork length of yellowfin tuna caught by Project boats in every month

Figure 24: Length frequency distribution of skipjack tuna caught by Project boats in 1986, 1987 and 1988

Figure 25: Average fork length of skipjack tuna caught by Project boats in every month

Figure 26: Length frequency distribution of wahoo caught by Project boats in 1986, 1987 and 1988

Figure 27: Average fork length of wahoo caught by Project boats in every month

Figure 28: Length frequency distribution of shark caught by Project boats in 1986, 1987 and 1988

Figure 29: Average fork length of shark caught by Project boats in every month