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Summary of fisheries and resources information for Zanzibar

by
N.S. Jiddawi
Institute of Marine Science,
P.O. Box 668, Zanzibar
and
V.M. Pandu
Division of Fisheries, Zanzibar
Ministry of Marine, Tourism and Forestry,
P.O. Box 774, Zanzibar


ABSTRACT
1. INTRODUCTION
2. THE ARTISANAL FISHERIES OF ZANZIBAR
3. THE LIGHT ASSISTED FISHERY FOR SMALL PELAGICS
4. THE OTHER FISHERIES RESOURCES
5. BIBLIOGRAPHY


ABSTRACT

The catches in recent years are claimed to be about 25,000 tonnes, almost entirely from the efforts of about 15-16,000 artisanal fishermen. Included is some 5,000 tonnes which is believed to be the quantity consumed locally by the fishermen and their families.

Reference is made to the results from the acoustic and trawl surveys involving the R/V Prof. Mesyatsev and R/V Dr Fridtjof Nansen. Despite these and other studies the potential yield for Zanzibar remains unknown. On the basis of the productivity per unit area being relatively high at about 5 tonnes/km2, the fisheries resources presently being exploited are judged to be at or near fully utilised.

A description is presented of the light assisted fishery involving the use of purse seines and scoop nets adjacent to Zanzibar town. The preliminary estimate of the landings from this fishery is about 3,000 tonnes.

The paper also presents summaries of the results from a number of biological investigations for particular species. The species include Sardinella gibbosa, Amblygaster sirm, Rastrelliger kanagurta and Nemipterus delagoae.

1. INTRODUCTION

The fisheries administration of Zanzibar (comprising Unguja and Pemba Islands) is largely (although not completely) independent from that of the mainland. The joint approval with the mainland administration is required in the case of licensing foreign fishing vessels for fishing adjacent to Zanzibar. To date there has been no licensed foreign fishing around the islands.

At the present time most of the catch is from the artisanal fishermen using a range of traditional methods. The major exception involves the use of purse seine nets (and scoop nets) from motorised traditional boats adjacent to Zanzibar town for catching small pelagics. The parastatal Zanzibar Fishing Corporation (ZAFICO) which operates one 12.5 m and six 9 m aluminium vessels also uses some of these in purse seining for small pelagics (and tunas). The larger of these vessels is sometimes engaged in trawling for shallow-water shrimp adjacent to the mainland near Bagamoyo. Two of the smaller ZAFICO vessels are engaged in drift gillnetting for large pelagics adjacent to Pemba Island.

The quantities of fish landed has ranged around 25,000 tonnes in recent years. This figure includes an estimate of about 5,000 tonnes, the quantity consumed in the fishermen households, which is not included in the official statistics. The per capita consumption of fish is high, between at least 25 and 40 kg/person annually. Only negligible amounts of fish are either imported or exported. Fish is the major contributor of animal protein in the diet of the average Zanzabari, and is almost the only animal protein for the lower income groups in the population. It represents about 22 percent of the total food expenditure in the average household (see FAO, 1988).

The number of persons directly employed within the fishery sector plus their dependents represent some 14 percent of the total population (estimated as 589,000 persons in 1987). This includes some 15,000 to 16,000 fishermen (many more have an occasional involvement in fishing) and at least another 2,000 to 2,500 distributors and sellers of fish (see FAO, 1988). In these calculations the number of dependents per household was taken as five persons.

2. THE ARTISANAL FISHERIES OF ZANZIBAR

Location: Fishing takes place along the entire coastlines of both islands, generally within a few kilometres from shore in depths less than 20 m. Some fishing occurs to depths of 100 m, and deeper in the case of drift gillnetting and line fishing for large pelagics.

Boats and Gears: Few boats exceed 10 m in length. Mostly they are dugout canoes powered by sail with outriggers (Ngalawa) or without outriggers (Mitwumbi). The larger dau and mashua are usually planked, and sometimes motorised. The numbers of boats by type, and the gears recorded during "frame surveys" in 1980 and 1985 (see Ngoile, 1981 and Carrara, 1986) are given below in Table 2.1.

Table 2.1. Numbers of boats, engines and units of each gear type recorded for Unguja and Pemba Islands in 1980 and 1985.

Items

Unguja Is.

Pemba Is.

Total

1980

1985

1980

1985

1980

1985

Boats:

Mashua

192

362

37

85

229

447

Ngalawa

1,052

1,149

661

758

1,713

1,907

Mitwumbi

273

247

1,290

1,026

1,563

1,273

Dau

336

379

49

121

385

500

Sub-Totals

1,853

2,137

2,037

1,990

3,890

4,127

O'board Engines

147

146

15

6

162

152

I'board Engines

na.

20

na.

0

na.

20

Sub-Totals

na.

166

na.

6

na.

172

Gears:

Handlines

4,023

4,938

3,954

4,552

7,977

9,490

Troll-lines

774

1,129

877

612

1,651

1.741

Basket traps

4,399

4,814

3,995

4,394

8,394

9,208

Weir traps

152

312

94

65

246

377

Gill nets

4,877

2.884

2,606

2,738

7,483

5,622

Seine nets

1,086

691

1,522

27

2,608

718

Beach seines

104

0

122

3

226

3

Cast nets

118

50

616

177

734

227

Scoop nets

122

187

0

15

122

202

Spearguns

208

262

72

106

280

368

Sources: Ngoile (1981) and Carrara (1986).

Fishermen: Extrapolating from the above-mentioned "frame surveys" of fishermen, boats and fishing gears conducted in 1980 and 1985, the Division of Fisheries estimates the present number of artisanal fishermen as some 15-16,000 persons (including those without boats).

Catches: The quality of the fisheries statistics is poor, and as such the values given in the following Table 2.2 should be considered with reserve, particularly those for 1986.

Table 2.2. Catch weights by month from 1982 through 1986.

Month

Catch Weights (tonnes)

1982

1983

1984

1985

1986

January

1,429

1,184

1,654

1,858

858

February

1,572

1,512

1,784

1,445

757

March

1,794

1,696

1,799

1,732

789

April

1,943

2,085

1,742

1,308

906

May

1,901

1,586

2,159

955

868

June

2,045

1,361

1,861

1,352

1,234

July

2,014

1,441

1,945

1,094

775

August

1,591

1,359

1,986

1,072

597

September

2,406

1,449

1,935

1,254

945

October

1,675

1,475

1,697

1,076

824

November

1,684

1,392

1,899

1,028

991

December

1,410

1,302

1,171

1,032

489

Totals

21,464

17,842

21,632

15,206

10,033

Source: Statistics Section, Division of Fisheries.

Catches per Unit Effort: These data are not available from the official statistics system, however, the "order of magnitude" is provided by multiplying the numbers of boats by an assumed 200 fishing days per year, and then dividing into the annual catches. According to the results from the "frame surveys" there were about 4,000 boats in 1980 and 1985. On this basis the catches per unit effort ranged from 19 to 27 kg/boat/day during the four years 1982 through 1985. These values are in rough agreement with those for earlier years as given in Table 2.3.

Species Composition: These are not provided from the official statistics. An indication of some of the important species is given in Table 2.3.

Productivities per Unit Area: Dividing the combined areas for both islands (4,001 km2) into the annual catches gives productivities per unit area ranging from 3.8 to 5.4 tonnes/km2 for the four years 1982 through 1985.

Resource Assessments: 1. The FAO/IOP Workshop on the Fishery Resources of the Western Indian Ocean South of the Equator, held in the Seychelles during 1978, provided very tentative estimates of potential yields for some of the resources adjacent to Zanzibar; see Table 2.5. These include some 3,320 tonnes of demersal trawlfish, being 25 percent of the estimated biomass. The latter were determined as the product of the areas of the trawl grounds and the densities of the fish.

The densities given for the trawlable grounds are based on the results from surveys with the R/V Prof. Mesyatsev. The values used for the areas within the Zanzibar Channel include grounds adjacent to the mainland. It is not stated whether much of the trawlfish potential would be accessible to the artisanal fishermen using traditional gears.

The potential yields for the Pemba reef are based on the assumption of 5 tonnes/km2 at full exploitation. Potential yield estimates for the Unguja reef are not included.

Table 2.3. Catches, fishing efforts and species types recorded during 1974-1976 at three representative landing sites on Unguja Island.

Items

Zanzibar town (Malindi)

Mkokotoni

Chwaka

No. Landings Sampled

2,730

2,112

2,166

Quantities Landed (kg)

139,885

73,842

28,744


Catches/Effort

Percent Landed

Catches/Effort

Percent Landed

Catches/Effort

Percent Landed

Fishing Gear:







Traps-Dema

19.1

6.0

18.6

6.5

19.5

39.3

- Towe

17.0

8.0

11.6

3.1

9.2

2.1

- Uzio

-

0.0

-

0.3

-

6.3

Handline

17.7

14.3

16.1

0.4

11.3

15.4

Seine Net

217.0

37.6

72.9

1.1

26.0

32.3

Gill Net

43.0

18.6

39.9

87.6

22.7

2.4

Other Gear


15.9

1.0

1.9



Species Types in Landings:


%


%


%

Rays

26.0

Little tuna

34.6

Emperors

25.7

Spanish Mackerel

11.4

Rays

13.0

Spinefeet

22.3

Fusilier

9.7

Sailfish/

10.2

Parrotfish

12.4

Monocle Bream

7.2

Emperors

8.4

Snappers

7.2

Emperors

6.3

Sharks

6.9

Goatfish

6.2

Indian Mackerel

4.1

Spinefeet

5.9

Carangidae

5.7

Sailfish/ Marlin

3.8

Spanish Mackerel

5.6

Groupers

4.1

Source: Tarbit (1984).

Note:

1. The catches/effort in the table have units of kg/boat/day.
2. The species compositions are as percentages of the total landings at each site.

Areas of Fishing Grounds: The areas given in Table 2.4 were determined by reference to British Admiralty charts and "counting squares".

Table 2.4. Estimates of the areas of the fishing grounds.

Depth Ranges (fathom)

Areas of Fishing Grounds (km2)

Pemba Island

Unguja Island

0-10

886

1,143

10 - 100

393

1,579

Combined

1,279

2,722

Source: FAO, 1988.

Note: The western boundary of Zanzabari waters was taken as mid-way between the islands and the mainland.

Table 2.5. Biomass and potential yield estimates for waters adjacent to Zanzibar.

Location of Grounds

Area of Grounds
(km2)

Assumed Fish Density
(t/km2)

Biomass
(tonnes)

Potential Yield
(tonnes)

Pemba Reef

888

?

?

4,440

Pemba Channel

1,312

1.65

2,165

540

Zanzibar Channel (<200m)

6,192

1.65

10,220

2,500

Zanzibar Channel (>200m)

411

2.7

1,110

280

Source: FAO/IOP (1979), Venema (1984).

2. Length frequency data for the threadfin bream (Nemipterus delagoae) caught by line fishing adjacent to Zanzibar town (at Bawe Changuu and Murogo reefs) in the period June 1984 to May 1985 were used to obtain estimates of the parameters describing growth and mortalities; see Table 2.6. On the basis of these it was concluded that this resource was substantially under-exploited.

Table 2.6. Growth and mortality parameters determined for Nemipterus delagoae.

Total Length - Age Parameters (from von Bertalaffy plot)


Sexes Combined L (inf) = 25 cm; K = 0.4 (annual)

Total Mortality Coefficient


Z = 1.1 (from length converted catch curve)

Natural Mortality Coefficient


M = 0.9 (from Pauly's equation with T =?? °C)

Source: Jiddawi, this Workshop.

3. THE LIGHT ASSISTED FISHERY FOR SMALL PELAGICS

Location: The main fishing grounds are within a few hours travel of Zanzibar town. (Along the west coast of Pemba Island trial fishing has so far not located productive grounds for sardines or mackerel, although useful quantities of - sardines were caught; source ZAFICO).

Boats: In addition to four of the 9 m aluminium boats operated by ZAFICO, there is an unknown number (possibly about 25) of motorised mashuas. The latter are about 8 - 11 m in length and powered by 15 HP outboard engines. The ZAFICO boats are powered with 30 HP inboard engines. One or two light dinghies are used from each boat.

Gears: The fishing is undertaken at night and involves encircling the fish with purse seine nets as they aggregate adjacent to lighted dinghies. Virtually no fishing is done during the about ten days around the period of full moon, particularly on cloudless nights. It is common for the boats to be used for at least 15 nights per month, with a trip lasting from the mid-afternoon of one day to the early morning of the next. The dimensions of the purse seine nets used from the traditional boats are about 114 x 14 m. In some boats the fishermen use hand-held scoop nets rather than purse seines.

Catches: The annual catches from the traditional boats cannot be separated from the general statistics given earlier for the artisanal fishery. The catches in recent years are believed to be in the order of 3,000 tonnes, based on 25 boats x 20 trips/month x 500 kg/trip (see FAO, 1988). The catches from the four ZAFICO boats is about 200-300 tonnes/year.

Catches per Unit Effort: These data are not available from the official statistics. A very tentative value of 500 kg/trip has been suggested in respect to the traditional boats (FAO, 1988). During the first ten months of 1986, two of three ZAFICO boats achieved an average catch rates of about 300 kg/trip, and the other achieved 200 kg/trip (source ZAFICO). (The fourth boat was not operated for much of the period).

Species Composition: The data given in Table 3.1 derive from sampling the purse seine catches during 1979 to 1981. Much greater proportions of the Indian mackerel Rastrelliger kanagurta are found in the catches from using scoop nets; source Division of Fisheries.

Areas of Fishing Grounds: The area of the fishing grounds is not known.

Productivities per Unit Area: This is not known.

Table 3.1. Main species groups in purse seine catches

Family

Species

Percentage by Weight in the Catches

Clupeidae

Sardinella gibbosa

41

Sardinella sirm

30

Others

7



78

Scombridae

Rastrelliger kanagurta

8

Carangidae

Decapterus spp. & Caranx spp.

6

Engraulidae

Stolephorus spp.

2

Others


6

Source: Nhwani and Makwaia (1986).

Resource Assessments: 1. Length frequency data were obtained for the goldstripe Sardinella (Sardinella gibbosa) from sampling the catches of the ZAFICO vessels during the period May 1978 through October 1981. These were used, along with similar data recorded aboard the R/V Dr Fridtjof Nansen during surveys in Tanzanian waters in 1982 and 1983, to obtain estimates of the parameters describing growth and mortalities; see Table 3.2. The inability to observe growth when comparing the cohort mean lengths between samples was taken to indicate the occurrence of migration (which in turn would be reflected in the estimates obtained for the fishing mortality coefficient). In this context it was suggested that the resource may be common with that exploited adjacent to Dar es Salaam.

Table 3.2. Growth and mortality parameters determined from ZAFICO data for Sardinella gibbosa.

Fork Length - Age Parameters (from using von Bertalanffy plot)


Sexes Combined L¥ = 17 cm; K = 0.58 (annual)

Natural Mortality Coefficient


M = 1.46 (from Pauly's equation with T = 28 °C)

Fishing Mortality Coefficient


F = 0.5 to 0.7 (from Length Converted Cohort Analysis)

Source: Nhwani and Bianchi, this Workshop.

2. A slightly earlier work (van Nierop and Nhwani, 1986) provided the estimates for the growth parameters for each of the goldstripe Sardinella (Sardinella gibbosa), the spotted sardinella (Amblygaster sirm) and the Indian mackerel (Rastrelliger kanagurta) shown in Table 3.3. The data derived from sampling the purse seine catches of the ZAFICO vessels during 1978 through 1981. In the case of the first mentioned species it is the same data used by Nhwani and Bianchi (at this Workshop). For this species it was found that the assumption of seasonal growth enabled a slightly better fit between the estimated and observed lengths at age. The estimates of the growth parameters for R. kanagurta were suggested as less "reliable" than for the other species.

Table 3.3. Growth parameters determined from ZAFICO data for S. gibbosa, A. sirm and R. kanagurta.

Fork Length - Age Parameters (from using modified von Bertalanffy plot)


S. gibbosa


L¥ = 19.4 cm; k = 0.32 (annual) and t0 = -0.46 yr
(when non-seasonal growth is assumed)


L¥ = 22.4 cm; k = 0.24, t0 = -0.68 yr, C = 1.07 and ts = 0.68 yr
(when seasonal growth is assumed)


A. sirm


L¥ =21.6 cm; k = 0.43 (annual) and t0 = -0.14 yr


R. kanagurta


L¥ = 22.1 cm; k = 0.81 (annual) and t0 = -0.38 yr

Source: van Nierop and Nhwani (1986)

4. THE OTHER FISHERIES RESOURCES

Shallow-water Lobster:

Unknown but small quantities of shallow-water lobster are landed, mainly by divers using harpoons. It is claimed that Panulirus ornatus comprises about 80 percent of the catches; see Ameir, 1987. Hall (1960) reports 13.56 Ib (6.15 kg)/man/day as the mean catch rate by divers for six lightly exploited areas around Zanzibar and 9.98 Ib (4.53 kg)/man/day for two more heavily exploited areas.

Deep-water Lobster:

Lobsters identified as Linuparus somniosus and Metanephrops andamanicus were regularly caught in depths of 250 to 320 m at the southern end of the Zanzibar Channel during surveys with the R/V Prof. Mesyatsev (see Birkett, 1978; VNIRO, 1978; and Burczynski, 1976). The catch rates ranged up to 50 kg/hr (whole weight). Very small catches of these lobster were also obtained with the R/V Dr Fridtjof Nansen; see Iversen et al, 1984. This resource has not been subject to exploitation.

Shallow-water shrimp:

The abundance of shallow-water shrimp is very low. Their occurrence in the artisanal catches is during the rainy season, when they are flushed from the rivers; see Ameir, 1987. During 1987 the 12.5 m vessel owned by ZAFICO was used on a few occasions to trawl for shrimp adjacent to Bagamoyo on the mainland.

Deep-water Shrimp:

During surveys with the R/V Dr Fridtjof Nansen the highest catch rate of shrimp (130 kg/hr) was made east of Dar es Salaam in 325 m depth; see Iversen et al, 1984. Otherwise the catch rates obtained were rather poor. There is no exploitation of this resource.

Large Pelagics:

Tunas and other large pelagics are presently being landed by the artisanal fishermen, using drift gillnets and lines. During 1986 ZAFICO also commenced fishing for these species, with purse seine nets adjacent to Zanzibar town and drift gillnets off the west coast of Pemba Island. During the first three months of 1987 the purse seining provided 72 tonnes of little tuna Euthynnus affinis. Off Pemba Island a fishing effort of about 350 boat days during 1986/87 resulted in 10.1 tonnes of skipjack tuna, 13.8 tonnes of sharks, 6.7 tonnes of sailfish and 1.4 tonnes of other species (source: ZAFICO).

Experimental live bait and tuna pole and line fishing were undertaken during 1982 and 1983; see Lee, 1983. The fishing was done from the M/V Tauro, with the most interesting catch rates being obtained in the period October 4 to December 10, 1983, just prior to the project (UNDP/FAO URT/81/TO1) being terminated from lack of further funding. In this period there were nine cruises, each of about 2 to 5 days, for a total time at sea of 33 days. During 129 hours of visual searching, 115 schools of fish were sighted. Fishing took place on 26 of the schools for a catch of 10.5 tonnes, including 9.4 tonnes of skipjack tuna and 1.1 tonnes of yellowfin tuna. There were also some 392 hours of incidental trolling, for a catch of 85 fish weighing 342.5 kg. Seventy seven of the fish were tunas. Most of the fishing was done in oceanic waters adjacent to the southeast of Pemba Island.

Marine Algae:

The collection of naturally occurring seaweeds was undertaken previously, with some few hundred tonnes per year of dried product being exported. Subsequently the production declined (in response to lower demand) with almost none being exported in recent years. During 1987 the Government granted approval for a seaweed farming joint venture which is expected to commence in 1988. It is proposed to establish the intensive farming of the species Echeuma spinosa over 750 hectare of inshore tidal waters at both Unguja and Pemba Islands. The projected annual production is 6,000 tonnes of dried product (source: Division of Fisheries).

5. BIBLIOGRAPHY

Ameir, A.A., (1987) - Country Statement on the Crustacean Fisheries in Zanzibar. Proceedings of the Crustacean Management Workshop; Mauritius, October 1-11, 1985. SWIOP Document RAF/79/065/WP/38/87: 181 p.

Birkett, L., (1978) - Western Indian Ocean Fishery Resources Survey. Report on the cruises of the R/V Prof Mesyatsev, December 1975 - June 1976/July 1977. Tech. Rep. Indian Ocean Programme, (21): 97 p.

Burczynski, J., (1976) - Echo survey along the East African coast from Mombasa to Laurenzo Marques by R/V Prof. Mesyatsev in January/February 1976. FAO Fisheries Travel Report and Aide Memoire, (1162) Suppl. 1: 28 p.

Carrara, G., (1986) - Artisanal Fishery Catch Assessment Survey Plan, Zanzibar. SWIOP Document. RAF/79/065/WP/39/86/E: 27 p.

FAO, (1988) - A Plan for the Fisheries Sector of Zanzibar. A report prepared for the Project Mission to Fisheries in Planning, Management (Legislation) and Development (FI: TCP/URT/5755 (F)). Field Document: 94 p.

FAO/IOP, (1979) - Report of the workshop on the fishery resources of the western Indian Ocean south of the equator. Mahe, Seychelles, 23 October - 4 November 1978. Dev. Rep. Indian Ocean Programme, (45): 102 p.

Hall, D.N.F., (1960) - A note on the Zanzibar rock-lobster fishery. Ann. Rep. EAMFRO: 32-8.

Iversen, S.A., S. Myklevoll, K. Lwiza and J. Yonazi, (1984) - Tanzanian marine fish resources in the depth region 10-500 m investigated by R/V Dr Fridtjof Nansen. The Proceedings of the NORAD-Tanzania Seminar to Review the Marine Fish Stocks and Fisheries in Tanzania; Mbegani, Tanzania, 6-8 March, 1984: 186 p.

Lee, R., (1983) - Live-Bait Pole-and-Line Fishing for Tuna. Report prepared for Technology Transfer in Zanzibar Fisheries Project (FI: URT/81/TO1): 27 p.

Ngoile, M.A.K., (1981) - A survey of fishing units in Zanzibar and Pemba. Tanzania Notes and Records No. 88 and 89., 89-96 p.

Nhwani, L.B. (1986) - and E.D. Wakwaia. The biology and fishery of small pelagic fishes in the coastal waters of Tanzania. Research Project Progress Report. Tanzania Fisheries Research Institute, Dar es Salaam: 6 p.

Tarbit, J., (1984) - Inshore fisheries of the Tanzanian coast. The Proceedings of the NORAD-Tanzania Seminar to Review the Marine Fish Stocks and Fisheries in Tanzania; Mbegani, Tanzania, 6-8 March, 1984: 186 p.

van Nierop, M. and L.B. Nhwani. (1986) - Growth parameters of the goldstripe sardinella (Sardinella gibbosa), the spotted sardinella (Amblygaster sirm) and the Indian mackerel (Rastrelliger kanagurta) from Zanzibar waters. SWOP Document. RAF/79/065/DP/??/86: 36 p.

Venema, S., (1984) Resource surveys other than those by R/V Dr Fridtjof Nansen. The Proceedings of the NORAD-Tanzania Seminar to Review the Marine Fish Stocks and Fisheries in Tanzania; Mbegani, Tanzania, 6-8 March, 1984: 186 p.

VNIRO. (1978) - Western Indian Ocean Fisheries Resources Survey. FAO/UNDP/USSR Cooperative Project. Dev. Rep. Indian Ocean Programme, (46): 130 p. (limited distribution).


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