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Summary of fisheries and resources information for Mauritius

by
C.R. SAMBOO
and
D. MAUREE
Ministry of Agriculture and Fisheries,
Albion Fisheries Research Centre,
Albion, Mauritius.


ABSTRACT
1. INTRODUCTION
2. THE ARTISANAL FISHERY OF MAURITIUS (ISLAND)
3. THE ARTISANAL FISHERIES OF RODRIGUES AND AGALEGA
4. THE BANKS FISHERY
5. THE POTENTIAL FISHERY FOR DEEP SEA SHRIMP
6. BIBLIOGRAPHY


ABSTRACT

The overall catch for marine waters in 1986 is given as slightly less than 9,000 tonnes (not including tunas from industrial fishing). This derived from the efforts of some 3,900 fishermen operating from about 1,500 boats (plus 15 motherships). The contribution from the distant water handline fishery on the banks of the Mascarene Ridge was 63 percent. Almost all the remainder came from the lagoon and immediately adjacent areas around Mauritius (Island) and Rodrigues.

Applying the Schaefer (production) model to data for the artisanal fishery of Mauritius (Island) gave an estimate of MSY for the stocks in the lagoon that was less (by 11 percent) than the catch in 1986. This suggestion of full (or over-) exploitation is somewhat supported by the preliminary results also presented of an assessment on the rabbitfish (Siganus sutor). In respect to the off-lagoon stocks the estimate of MSY was less than the catch for that year (by 31 percent). No assessments have been undertaken for the stocks at Rodrigues.

The results of reasonably comprehensive assessments (from the application of both length and age based analytical models) for the mahsena emperor (Lethrinus mahsena), which contributes some 80-90 percent of the catches from the banks, suggests that these stocks are also at or near fully exploited. (The utilisation of other demersal species present in the deeper waters of the banks (beyond 50 m) is prevented by the presence of ciquatoxin in the flesh of these fish, which renders them unsuitable for human consumption.)

Reference is made to an under-exploited stock of deep sea shrimp (Heterocarpus laevigatus and H. ensifer) adjacent to Mauritius (Island). A substantial area of apparently suitable ground (2,000 km2 in about 500 to 1,000 m depth) exists to the north of the island, which provided catch rates exceeding 2 kg/trap/day during four days of exploratory fishing. A potential annual yield of 400 tonnes is tentatively suggested, on the assumption that the productivity is the same as for the grounds in the Pacific.

1. INTRODUCTION

The fisheries resources exploited by Mauritius are found in:

- the lagoon and off-lagoon areas of Mauritius (Island)
- the lagoon and off-lagoon areas of Rodrigues
- the lagoon area of Agalega, and
- the banks along the Mascarene Ridge stretching from St. Brandon (in Cargados Carajos group) to Saya de Malha and around the Chagos Archipelago.

Table 1.1 Summary of fishery statistics for Mauritius in 1986.


Mauritius (Island)

Rodrigues

Agalega

Banks

Lagoon

Off-Lagoon

Catch (tonnes)

758

569

1,900

30

5,619

No. of Fishermen

2,033

644

493

?

721

No. of Pirogues

869

150

215

?

233

No. of Motherships

---

---

---

---

15

Areas of Grounds (km2)

376

832

1,688

15

33,685

Catch per Fisherman (kg/fisherman/year)

373

884

3,853

?

6,730

Catch per Pirogue (kg/pirogue/year)

872

3,793

8,837

?

20,824

Catch per Mothership (tonnes/mothership/year)

---

---

---

---

323

Catch per Area (kg/km2)

2,016

684

1,126

2,000

167

Source: Various, see later.

Note: The areas of the fishing grounds are for depths between 0-100 m, except for the banks where it is for depths of 0-35 m.

Figure 1. Place locations for Mauritius.

All the lagoon and off-lagoon fisheries are artisanal in nature. Exploitation is believed to have started with the first settlements of the three main islands, Mauritius, Rodrigues, Agalega and the Chagos Archipelago; for locations see Figure 1. The fish stocks on the banks of the Mascarene Ridge were first successfully exploited in 1966, following surveys conducted in 1947 by Wheeler and Ommanney (1953). The exception is St. Brandon, which has been exploited for salted and dried fish since 1937. A selection of statistics are presented in Table 1.1.

Since 1979 a Mauritian vessel has been engaged in the offshore purse seine fishery for tuna, which is now centred around the Seychelles. A consideration of the tuna resources was not undertaken at the Workshop, however information on these is available from Stequert and Marsac (1986).

2. THE ARTISANAL FISHERY OF MAURITIUS (ISLAND)

Location: Fishing takes place within the lagoon which surrounds most of the island, and in the immediate off-lagoon areas to depths generally not exceeding 100 m.

Boats: Fishermen use 7-10 m pirogues equipped with oars and sails, outboard or inboard motors. Generally only motorised boats leave the lagoon area. The numbers of boats by type of propulsion for recent years is as follows:

Table 2.1 Numbers of pirogues for Mauritius (Island)

Year

Numbers by Type of Propulsion

Totals

Oars/sails

Outboard Motors

Inboard Motors

1984

530

415

35

980

1985

530

420

38

988

1986

539

433

47

1,019

Source: Albion Fisheries Research Centre

Gear: The most common gears are basket traps, lines, harpoons, large (seine) nets, gillnets and castnets. The large (seine) nets and gillnets are used within the lagoon, while the others are used both within and outside the lagoon. The typical lines used inside the lagoon are rigged with a single hook. The lines used outside the lagoon have 5 to 10 hooks. The number of basket traps per fisherman is between 10 and 15 traps when operating outside and about half this number when operating inside the lagoon.

Fishermen: The numbers of persons registered as fishermen is increasing annually although the number actively engaged on a "full time" basis is believed to be declining, and presently does not exceed 2,000 persons. Table 2.2 gives the numbers of registered fishermen by category of gear type for the recent years.

Table 2.2 Numbers of registered fishermen by gear type for Mauritius (island)

Year

Numbers of Fishermen by Gear Type

Totals

Basket Traps

Lines

Basket Traps & Lines

Large Nets

Gillnets

Castnets

1984

480

670

850

560

65

39

2,664

1985

490

685

870

575

70

46

2,736

1986

482

679

840

571

69

36

2.677

Source: Albion Fisheries Research Centre

Catch and Effort: The following provides the catches (tonnes) and fishing efforts ('000 fishermen days) in recent years for all gear types and species groups combined. About 35 to 40 percent of the catches within the lagoon are from the use of the large (seine) nets and gillnets.

Table 2.3 Total catches and fishing efforts for Mauritius (Island)

Year

Lagoon

Off-lagoon

Totals

Catch

Effort

Catch

Effort

Catch

Effort

1984

814

176

561

95

1,375

217

1985

801

160

533

89

1,334

249

1986

758

146

569

100

1,327

246

Source: Albion Fisheries Research Centre

Catches per unit effort: These have been computed as weighted means for each gear type and are as shown for recent years in Table 2.4.

Table 2.4 Catches per unit effort by gear type for Mauritius (Island)

Year

Lagoon

Off-lagoon

Lines

Basket Traps & Lines

Basket Traps

Large (seine) nets

Gillnets

Lines

Basket Traps

Basket Traps & Lines

1984

3.2

5.2

4.5

29

11.9

4.5

9.3

7.2

1985

4.6

5.3

4.8

30

13.7

4.4

8.3

8.6

1986

4.6

5.5

4.6

33

14.8

4.1

11.2

7.4

Source: Albion Fisheries Research Centre

Note: CPUE units are kg/fisherman/day for lines, basket traps and basket traps and lines categories, kg/haul for the large (seine) nets and kg/set for the gill nets.

Species: The catches by the artisanal fishermen contain many species. The families Serranidae (groupers), Siganidae (spinefeet, rabbitfish), Lethrinidae (emperors), Scaridae (parrotfish), Mullidae (goatfish), Percoids (perches), and octopus contribute roughly equally to some 65 percent of the catches (lagoon and off-lagoon combined). Considering the catches from the lagoon only, the main contributors are the Siganidae (16 percent) and octopus (15 percent).

Table 2.5 Areas of fishing grounds around Mauritius (Island)

Location

Areas
(km2)

Lagoon

376

Off-Lagoon (to 100 m depth)

832

Combined

1,208

Source: this Workshop

Areas of fishing grounds: Table 2.5 contains the results of determinations made at the Workshop using the available marine charts and a planimeter.

Productivity per unit area: The estimates given in Table 2.6 are based on dividing the catches for 1986 by the above estimates of area.

Table 2.6 Productivity per Unit Area for Mauritius (Island)

Location

Productivity per Unit Area
(tonnes/km2)

Lagoon

2.02

Off-lagoon

0.68

Combined

1.10

Source: this Workshop

Resource Assessments: (1) Preliminary assessments have been undertaken (Samboo and Mauree, personal communication) to determine the maximum sustainable yields (MSY) and the fishing efforts at MSY for Mauritius island. This was done by applying the Schaefer (production) model with the catch weights and catches per unit effort (kg/fisherman day) for the period 1977 through 1986. The resulting estimates are provided in Table 2.7.

Table 2.7 Estimates of the maximum sustainable yield and the fishing effort at MSY for Mauritius (Island)

Location

MSY
(tonnes)

Effort at MSY
('000 fishermen days)

Lagoon

676

165

Off-lagoon

745

203

Combined

1,699

728

Source: Samboo and Mauree, this Workshop.

(2) In addition there has been an assessment undertaken at this Workshop for the rabbitfish Siganus sutor which contributes about 10 to 12 percent to the catches from within the lagoon. Growth information was available from the ageing of fish (using otoliths), observations on captive fish kept in ponds, and from the length distributions of fish caught during surveys for juvenile shrimps. The estimates obtained for the growth and mortality parameters are given in Table 2.8.

Table 2.8 Estimates of the growth and mortality parameters for Siganus sutor from the lagoon of Mauritius (Island)

Length-Weight Relationship (according to W (g) =a.L (cm)b)


Males

a = 0.00005965;

b = 2.756


Females

a = 0.00005970;

b = 2.754


(these results are not significantly different)

Growth Parameters (according to von Bertalanffy equation)


Otolith Readings

Captive Fish (1)

Captive Fish (2)

Length Frequencies


L¥ cm

49.92

42.27

29.4

50.0


K year-1

0.66

0.75

0.88

0.77


t0 year

0.06

- 0.03

- 0.04

--.--

Mortality Coefficients


Z = 2.0 (from Length Converted Catch Curve)


M = 1.2 (from Pauly's Equation)


F = 0.8 (from difference)

Source: Jehangeer, this Workshop.

Note: All lengths given as total length.

Biological Research Programmes: There is presently little research being undertaken specifically directed towards providing an improved basis for managing the resources. The above-mentioned data on the rabbitfish Siganus sutor was collected in 1983 and 1984, as an incidental by-product of surveys to determine the presence of shallow water shrimps for mariculture studies.

Fisheries Statistics System: The present system is largely based on the recommendations of Banerji (1976). The landing sites are grouped into two strata. (Stratum 1 are the sites for which the catches were previously recorded by the Fisheries Protection Service. The other landing sites were grouped into Stratum 2). Every month some 26 to 32 sites are randomly selected from these strata and eight enumerators (including supervisors) record catch and effort data at each. These data are collected during selected hours covering half the day on each of six days per week. Raising factors are used to estimate the catches and efforts for each stratum separately.

Additional Information:

(a) Part-time fishermen. Large numbers of part-time fishermen use handlines within the lagoon to catch fish for consumption in their homes. The quantities caught may exceed the catch by the commercial fishermen. This is based on the belief that some 65,000 part-timers are operating during most days of the year, landing an average 0.5 kg per day (Moal, 1975). The common species in the catches are from the families Siganidae (rabbitfish), Serranidae (groupers), Lethrinidae (emperors) and Carangidae (jacks).

(b) Sports Fishermen. The landings by sports fishermen operating from the "big-game" fishing clubs were investigated in 1977. The estimated catch of marlins, sailfish and tunas etc. was about 400 tonnes in that year.

(c) Barachois. Barachois are small coastal bays, estuaries or indentations which have been enclosed by rock walls to allow a tidal interchange of water. They are used for the culture of fish, crabs and oysters. Presently there are 22 barachois having a combined area of 3.6 km2. The annual production from barachois was investigated in 1977 and then put at 11 tonnes (Samboo, personal communication).

3. THE ARTISANAL FISHERIES OF RODRIGUES AND AGALEGA

Location: Fishing takes place both within and outside the lagoon in the case of Rodrigues, and within the lagoon at Agalega.

Boats, Fishermen and Gears: There is presently no formal system for collecting fisheries statistics at either of these islands. Rough estimates of the numbers of boats and the numbers of fishermen (for Rodrigues only) during recent years are given in Tables 3.1 and 3.2.

Table 3.1 Numbers of boats (pirogues) at Rodrigues in 1986

Location

Numbers of boats by type of propulsion

Totals

Oars/sails

Outboard motors

Inboard motors

Rodrigues

207

4

4

215

Agalega

-

2

-

2

Combined

207

6

4

217

Source: Albion Fisheries Research Centre.

Table 3.2 Numbers of fishermen at Rodrigues in 1986

Location

Numbers of fishermen by gear type

Total

Basket Trap

Lines

Basket Trap & Lines

Harpoons

Nets

Rodrigues

100

106

5

150

132

493

Source: Albion Fisheries Research Centre.

Catch: Part of the catches at Rodrigues are exported as salted and dried product to Mauritius (Island); otherwise the fish are consumed locally. The outdated estimate for Rodrigues is 1,900 tonnes from Moal (1975).

In Agalega fishing is not a regular activity and the catches are all consumed locally. In the absence of any direct knowledge it has been assumed that the per capita consumption of fish is 100 kg/year, giving an annual catch of 30 tonnes for a population of 300 persons.

Species: The species composition of the catches is believed to be similar to that of Mauritius (Island). This view still remains to be tested.

Areas of Fishing Grounds: These areas are given as 1,688 km2. for Rodrigues (lagoon and off-lagoon combined) and 15 km2. for Agalega (lagoon). The former was determined at this Workshop and includes all depths to 100 m, while the latter is an estimate given in Moal (1975).

Productivity per Unit area: The estimates based on the catch information given earlier are given in Table 3.3.

Table 3.3 Productivities per Unit Area (at Rodrigues and Agelaga)

Location

Productivities per Unit Area
(tonnes/km2)

Rodrigues

1.13

Agalega

2.00

Combined

1.05

Resource Assessments: None have been undertaken

Fisheries Statistics System: Presently there is no system which routinely provides fish catch and effort statistics for either of the islands. At Rodrigues there are records available for the quantities received through the fishermen's cooperatives. Those data were not available to the Workshop.

4. THE BANKS FISHERY

Location: The fishery takes place mainly on the relatively shallow grounds along the Mascarene Ridge stretching from St. Brandon to Saya de Malha, including the Nazareth Bank. The latter bank is fished during the summer months only. In contrast the fishing season for the Saya de Malha Bank (much of which exists in international waters) is from September to June. In both cases the exploitation involves the use of motherships operated from Mauritius (Island). The fishing at St. Brandon is undertaken largely by locally based fishermen, who also crew on boats used in fishing the more distant grounds. Very little fishing occurs at the Chagos Archipelago because of its remoteness.

All the motherships engaged in the fishery are operated from Mauritius (Island), except for a single boat based at Reunion which is operated on the Saya de Malha Bank only, and two other boats also operated from Reunion that fish on the Soudan Bank. (No other data are available for these latter boats). The distances to each of the ground are given in Table 4.1.

Table 4.1 Distances from Mauritius (Island) to the banks fishing grounds

Location

Distances
(km)

Soudan

200

St. Brandon

370

Hawkins

425

Nazareth

650

Saya de Malha

1,050

Chagos

2,100

Source: Samboo and Mauree at this Workshop. Note: The Hawkins Bank is not fished.

Table 4.2 Numbers of motherships engaged in the banks fishery from Mauritius (Island)

Year

Numbers of motherships by length category

Totals

Less than 30 m

Between 30 - 45 m

Above 45 m

1984

1

5

3

9

1985

2

9

2

13

1986

2

9

4

15

Source: Albion Fisheries Research Centre.

Note: The boats operated from Reunion are not included.

Boats: A wide range of boat types and sizes are used in this fishery. The motherships range from 20 to 60 m in length. The fishing actually takes place from small dories (pirogues), with the number of dories being about 10 to 20 per mothership. The numbers of motherships operated in recent years is given in Table 4.2.

Gear: Handlining by fishermen from dories (5.5 m to 6 m in length) has proved the most suitable method for exploiting the reef associated species which comprise the bulk of the catches. Each fisherman operates one line rigged with 8 to 10 hooks. Large (seine) nets and basket traps are also used by locally based fishermen in the lagoon around St. Brandon.

Fishermen: The numbers of persons engaged in fishing from dories during recent years is given in Table 4.3. (The fishermen on the boat operated from Reunion are not included.) This represents an average of about 35 fishermen per boat, and 2 or 3 fishermen per dory. In addition each boat is manned by some 10 to 20 crew, who engage in fishing for only part of the time.

Table 4.3 Numbers of fishermen in the banks fishery

Year

Numbers of fishermen by boat length category

Totals

Less than 30 m

Between 30 - 45 m

Above 45 m

1984

15

169

140

324

1985

30

287

108

425

1986

30

304

219

553

Source: Albion Fisheries Research Centre

Note: The above are the numbers of fishermen operating in association with motherships from Mauritius (Island).

Catch: Table 4.4 provides the catches in recent years from the Mauritian boats. (The annual catch from the boat based from Reunion and fishing the Saya de Malha Bank adds roughly another 500-1,000 tonnes gutted weight). The contributions from the Saya de Malha and Nazareth Banks were about 54 and 31 percent respectively. The catch for 1986 is the highest total on record.

Table 4.4 Total catches by fishing location for the banks fishery

Year

Catches (tonnes) by location

Totals

Nazareth

Saya de Malha

St. Brandon

Chagos

1984

1,236

933

580 (240)

160

2,909

1985

1,201

2,472

852 (417)

183

4,708

1986

1,344

3,099

1,034 (437)

142

5,619

Source: Albion Fisheries Research Centre.

Note: All the values in the table have been converted to whole weight. The bracketed values represent additional catches taken within the lagoon and which have mostly been salted for export to Mauritius.

Catches per unit effort: The catch weights per dory per fishing day have been about 350 to 550 kg (gutted weight) in respect to fishing on the Saya de Malha Bank; Bertrand et al, 1986.

Species: The emperor Lethrinus mahsena is claimed to contribute to about 80 to 90 percent of the catches; Bertrand et al, 1986. This is principally caught in depths of 15 to 50 m.

Table 4.5 Areas of fishing grounds on the banks

Location

Depth Range
(m)

Areas
(km2)

Nazareth

0-35

8,125

0-100

15,750

Saya de Malha

0-35

15,780

0-100

28,350

St. Brandon

0-35

2,950

Chagos

0-35

6,830

Source: Mauree, this Workshop.

Areas of grounds: The areas of the grounds as determined at the Workshop are given in Table 4.5.

Productivity per unit area: The estimates given in Table 4.6 are based on dividing the catches for 1986 given earlier by the above estimates of area.

Table 4.6 Productivities per unit area in the banks fishery

Location

Depth
(m)

Productivity per Unit Area
(kg/km2)

Nazareth

0-35

165

0-100

76

Saya de Malha

0-35

196

0-100

98

St. Brandon

0-35

351

Chagos

0-35

21

Source: Samboo and Mauree, this Workshop.

Note: The productivities quoted for the 0-100 m depths are misleading in that the fishing from dories does not take place beyond 50 m. Reasonably abundant stocks of snappers and other demersal species exist at greater depths but are not fished due to some fish containing ciguatoxin.

Resource Assessments: (1) The biology of Lethrinus mahsena has been subjected to investigation by Wheeler and Ommanney (1953) and Lebeau and Cueff (1975 and 1976). The most recent published works are those of Bertrand et al, 1986 and Bertrand, 1986 for the stocks inhabiting the Saya de Malha Bank.

According to these it seems that this species is a protogynous hermaphrodite, with few females having fork lengths exceeding 35 cm (age 8 years) and few males with lengths less than 20 cm (age 3 years). The earliest onset of sexual maturity for the females occurs at lengths of 18 to 20 cm (age 3 years). There appears also to be a single spawning season each year, whose timing varies from October-November on the north of the Saya de Malha Bank, to January-February further south. The estimates obtained for the growth and mortality parameters are given in Table 4.7.

Table 4.7 Estimates of growth and mortality parameters for L. mahsena from the Saya de Malha Bank.

Length - Weight Relationship (W (g) =a.L (cm)b)


Females

a = 0.012;

b = 3.160 (r = 0.98; n = 106)


Males

a = 0.016;

b = 3.077 (r = 0.99; n = 76)

Growth Parameters (according to Von Bertalaffy equation)


Females

L¥ = 55.4 cm;

K = 0.10;

to = 1.4 yr (n = 63)


Males

L¥ = 50.0 cm;

K = 0.16;

to = 0.2 yr (n = 105)


Combined

L¥ = 59.8 cm;

K = 0.10;

to = -1.8 yr (n = 168)


(October - November 1983)



Females

L¥ = 50.4 cm;

K = 0.13;

to = -0.9 yr (n = 231)


Males

L¥ = 55.6 cm;

K = 0.12;

to = -1.0 yr (n = 253)


Combined

L¥ = 61.0 cm;

K = 0.10;

to = -1.0 yr (n = 484)


(November, 1984)


Natural Mortality Coefficient


M = 0.2 (for ages less than 8.5 years)


M = 0.7 (for ages greater than 8.5 years)

(comparison of different cohorts in same year, using data for 1968 and assuming negligible fishing mortality)

Fishing Mortality Coefficient


F = 0.4 (using 1982-83 data)


F = 0.3 (using 1983-84 data)

(comparison of cohorts, with the assumption that M = 0.2)

Source: Bertrand et al, 1986.

Note: All lengths as fork lengths.

(2) Again in respect to L. mahsena on the Saya de Malha bank, Bertrand et al, 1986 attempted to establish a relationship between the catch per unit effort and fishing effort, using the Fox (production) model. The data used in this analysis are included in Table 4.8. The work proved unsuccessful however, which prevented a preliminary estimation of the maximum sustainable yield (MSY). Nevertheless it was concluded that the prevailing catch was less than the MSY.

Table 4.8 Catches, efforts and catches per fishing effort for L. mahsena of the Saya de Malha Bank.

Year

Catch Weights
(tonnes)

Fishing Efforts (dory days)

nominal

effective

1977/78

1,700

5,513

4,787

1978/79

1,490

5,207

4,158

1979/80

1,170

4,095

3,209

1980/81

920

2,253

2,004

1981/82

2,060

5,133

3,920

1982/83

2,500

6,694

5,247

1983/84

1,570

4,712

3,432

1984/85

2,635

7,297

4,814

1985/86

2,222

18,307

4,950

1986/87

3,390

12,477

7,908

Source: Biais and Samboo at this Workshop.

Note: The above data relate to exploitation from both Mauritius and Reunion. Small quantities Lethrinus variegatus are included in the catches. The catches are as gutted weight (gutted weight X 1.12 = whole weight). The nominal effort is the sum of the efforts for all dories, whereas the effective effort has been standardised to reflect the fishing power of the dories operated with the mothership from Reunion.

In commenting on the results it was suggested that the maximum economic yield (corresponding to maximum profit to the fishery) would be substantially less than the MSY, as a consequence of the high costs of fishing. On the assumption that the average catch per unit effort of 300 kg/dory/day is required to generate an acceptable profit, the associated equilibrium yield was determined as 1900 tonnes; see Bertrand et al, 1986. The higher catches in the more recent years (1985 and 1986) were judged as somewhat contradictory and the need for additional research was identified.

(3) The most recent assessment was undertaken at this Workshop for the stock of L. mahsena inhabiting the Nazareth Bank. Length frequency data were used which had been collected between 1977 and 1987. The estimates for the growth and mortality are given in Table 4.9. The conclusion obtained from applying these values with the Thompson and Bell yield per recruit analysis is that the contemporary catches are close to the maximum sustainable yield.

Table 4.9 Estimates of the growth and mortality parameters for L. mahsena on the Nazareth Bank.

Growth Parameters (according to von Bertalanffy equation)


sexes combined

L¥ = 61.7 cm;

K = 0.1;

t0 = -0.71 yr

Total Mortality Coefficient


Z = 0.45 (from length converted catch curve, and the method of Jones and van Zalinge)

Fishing Mortality Coefficient


F = 0.23 (from Jones length converted cohort analysis)

Natural Mortality Coefficient


M = 0.22 (from difference)

Source: Bautil and Samboo, this Workshop.

Note: The value for L¥ is as fork length.

Biological Research Programme: Data are collected at the landing site, and include the species composition of the catches and the fork length distributions of L. mahsena. The location of capture is identified from the position of the fish in the holds of the boats and with the aid of information from the skippers. It is not possible to know the sex of these fish as they are gutted at the time of capture. In the past scientists from Reunion have sampled catches at the Saya de Malha Bank; see Bertrand et al, 1986. This allowed the collection of more detailed information. Presently there are no plans to continue the at-sea sampling.

Fisheries Statistics System: In respect to each landing the skipper of the vessels are requested to submit a summary of the trip details, including the duration of the trip, the number of fishing days at each fishing location, the number of days of inactivity, the number of dories and fishermen, and the catch weight for each fishing location.

5. THE POTENTIAL FISHERY FOR DEEP SEA SHRIMP

Location: Exploratory fishing has established that deep sea shrimps are widely distributed within the region. They occur at the seabed in the depth range of 400 to 1,000 m.

Boats: Intermittently from 1984 through 1986, two privately owned vessels were engaged in commercial feasibility fishing mainly along the west coast of Mauritius (Island). These were the F/V UMBRINA (24 m length) and a smaller "big game" fishing boat. Subsequently the larger of the boats was used during four days of exploratory fishing on more distant grounds having suitable depths immediately to the north of the island. Presently neither are engaged in the fishery.

Gear: The gear used were traps attached to long lines. The larger boat was operated with a single line having up to 45 traps, while two lines of 10 traps each was used from the smaller boat.

Catch: Catches were possibly up to 5 tonnes (whole weight) from the two boats in a full year, although the details are not known.

Table 5.1 Catches per unit effort of deep sea shrimp obtained off the northwest coast of Mauritius (Island)

Months

Catches per Unit Effort
(kg/trap/day)

November '85

1.7

December (first half)

1.7

(second half)

2.5

January '86

1.0

February

0.8

March

0.8

Source: Pellegrini (1986)

Catch per Unit Effort: When operating on previously unfished grounds the catches per unit effort were generally between 1 to 2 kg/trap/day (24 hr). Repeated visits resulted in lower catch rates. A rest period of twelve months was suggested as being required to achieve an improvement in the catch rates; see Pellegrini, 1986. The mean catch rates for a selected period are given in Table 5.1.

The catch rates achieved during the four days exploratory fishing on the distant northern grounds are given in Table 5.2. The most productive fishing depth was identified as 750 to 850 m. The catch rates obtained at these depths exceeded 2 kg/trap/day.

Table 5.2 Catches per unit effort obtained north of Mauritius (Island)

Date

Number of traps set

Fishing Depth
(m)

Catch per Unit Effort
(kg/trap/day)


28/10/86

4

800-830

2.65


29/10/86

8

680-800

1.49

(2 traps lost)

30/10/86

5

800

0.70

(3 traps lost)

2

450

-

(both empty)

31/10/86

6

700-750

2.23


Source: Roullot and Soondron (1986)

Species Composition: Most of the catches were of Heterocarpus laevigatus. Small quantities of Heterocarpus ensifer were taken in depths of 350 to 500 m.

Areas of Grounds: The areas of grounds having suitable depths (600 to 1,000 m) have been identified as about 40 km2 around Mauritius (Island) and about 2,000 km2 on the more distant grounds immediately to the north; see Roullot and Soondron, 1986. It remains to be established what proportions of each of these areas are capable of sustaining commercial catch rates. No consideration has yet been given to the possible exploitation of the much more distant grounds, such as the Nazareth and Saya de Malha Banks and elsewhere.

Resource Assessments:

(1) The operator of the F/V UMBRINA suggested that the productive grounds adjacent to Mauritius (Island) exist in a narrow depth range (750 to 900 m) along some 110 km of coastline (40 km along the west coast and 70 km along the east and south coasts). A boat operated with 20 traps during 26 days each month might achieve a mean catch rate of 1.9 kg/trap/day, and would need to utilise some 10 km (coastline length) of grounds per month.

Thus when applying the fishing strategy of exploiting each 10 km strip only once each year, the potential yield estimate for the total grounds is about 10 tonnes per year. The implication here is that the resource is sufficient to support only one or two boats.

(2) Concerning the much larger expanse of grounds to the north of Mauritius (Island), Roullot and Soondron (1986) suggested the possibility of using boats of 14 to 20 m length for 150 days/year, at catch rates of 2 kg/trap/day or 160 kg/boat/day, for an annual catch per boat of 24 tonnes. Assuming a productivity of 200 kg/km2 (as for Pacific island countries in King, 1986) over the entire 2,000 km2 of grounds, gives a potential yield of 400 tonnes per year; and hence the possibility of employing some 16 boats of the type just described. The extent to which this could be achieved requires testing and hence Roullot has proposed the need for a year-long commercial feasibility fishing venture.

6. BIBLIOGRAPHY

Baissac, M.J. de B., (1953) - Contribution a l'étude des poissons de l'ile Maurice. V. Proc. R. Soc., Mauritius 1: 185-240.

Banerji, S.K., (1976) - Statistical System of Marine Fisheries in Mauritius. FAO/IOP/TECH/76/7,?? p.

Bertrand, J., (1986) - Données concernant la reproduction de Lethrinus mahsena (Forsskal 1775) sur les bancs de Saya de Malha (Océan Indien). Cybium. 10 (1): 15-29.

Bertrand, J. et al., (1986) - Pour une évaluation des ressources en capitaine/dame berri (Lethrinus mahsena) des bancs de Saya de Malha. Rapport du Groupe de Travail. IFREMER/Albion Fisheries Research Centre (Mauritius), 23 - 25 juillet 1985: 39 p.

Birkett, L., (1979) - Western Indian Ocean Fishery Resources Survey FAO/IOP/Tech/79/26, 99p.

FAO/IOP (1979) - Workshop on the Fishery Resources of the Western Indian Ocean South of the Equator, Mahe, Seychelles, 23 October - 4 November 1978. Devt. Rep. Indian Ocean Programme., (45): 102 p.

King, M.G., (1986) - The fishery resources of Pacific island countries. Part 1. Deep-water shrimps. FAO Fish. Tech. Pap., (272.1): 45 p.

Lebeau, A. and J.C. Cueff, (1975) - Biologie et pêche du capitaine Lethrinus enigmaticus (Smith 1959) du banc de Saya de Malha (Océan Indien). Rev. Trav. Inst. Peches Mark., 39 (4): 415-442.

Lebeau, A. and J.C. Cueff, (1976) - Biologie et pèche des Letrinides sur les hauts-fonds de Saya de Malha. Trav. et documents, ORSTOM., 47: 333-348.

Min. of Agric., (1983) - Fish. and Nat. Resources, Mauritius. Proceedings of Seminar on Marine Fisheries Development in Mauritius, University of Mauritius. July 18-19, 1983. (S. Bhoojeedhur, Editor).

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Samboo, C.R., (1982) - The Mauritius banks fishery. Bull. peches OISO Victoria. (2): 4p.

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Wheeler, J.F.C. and F.D.P. Ommaney, (1953) - Report on the Mauritius-Seychelles Fisheries Survey 1948-49. Colonial Office Fishery Publication. HMSO.

Wijkstrom, U.N. and T. Kroepelien, (1979) - Revitalisation of the Mauritian Bank Fishery: An appraisal. FAO, Rome IOP/TECH/79/35.


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