10P/TECH/79/26

INDIAN OCEAN PROGRAMME

western indian ocean fishery resources survey

" • • UNITED NATIONS ,DEVELOPMENT PROGRAMME

FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS Indian Ocean Programme !OP/TFIJH/79 /26 Technical Reports No. 26

WE:Jl'liml INDIAN OCEAN FISimtY RE30URCES SURVEY Report on the cruises of R/V PROFESSOR MESYATSEIJ December 1975 - June 1976/July 1977 - December 1977

by

L. Birkett Project Leader

FOOD AND AGRICULTURE ORGANIZATION O.F '!'BE UBI'l'ED NATIONS UNITED NATIONS DEVELOPME?fT PROGRAMME Rome, 1979 - ii -

'l'he deeigm,ti01111 employed a.nd the presentation of material in this pablioa.tion do not imply the expreasi11111 •f all;Y' opinion wbateoever on the part of the 1'.W. an4. Agriculture Organization of the lhrl:Md lla:Uou ooaoerning the legal status of an,y o011111try, territory, city or area or of its a.uth.ritiea, er cmceming the delimitation of its f'rC111tiers or bolllndaries.

Bibliosz:aphio llbtr;y: Birkett, L. (1979 ) Tech.Rep.Indian Oc~ Programme, (26):97 P• Western Indian Ocean fishery resources survey. Report on the cruises of R/v PROFESSOR MESYATSEV, December 1975 - June 1976/July 1977 - December 1977 Catch composition. Eoho surveys. Fish catch statistics. Fishery resources. Fishery surveys. Marine fisheries,. stock. assessment. Western Indian Ocean.

The copyright in this book is vested in the Food and Agricnilture Organization of the United Nations. The book may not be reproduoed.9 in whole or in part, by 8:lY' method or.process, without written permission f"rom the copyright holder. Applications for such permission, ti.i.th a statement of the purpose and extent of the reproduction desired, should be addressed to the Director, Publications Division, Food and Agriculture Organization of the United Nations, Via. delle Terme di Caracalla, 00100 Rome, Italy..

@ FAO 1979 -. iii -

This technical report summarizes findings and provisional analyses of the data a.ccumula.ted during the course of the resources survey in the coastal waters of eastern Africa, from Somalia south of the equator to 27°s, including Madagascar and the Mauritius­ Seychellea Ridge.· Due to le.te arrival of authorization, Ma.daga.eca.rand Somalia. waters were eventually excluded from the survey progrSlllme. Provisiona.1 results are presented in tabular form supplemented·by fish distribution/density maps. The survey data, after further analyses, will be presented in a.technical data report to fo~low. iv

TABLE OF CONTENTS Page

1o INTRODUCTION G 8 8 e e 9 8 C 9 8 8 0 • 0 e e G 9 9 G e e e 0 • 8 0 8 9 8 1

2. THE R/V PROFESSOR MESYATSEIT • • • • • e • • e • • • • • e • o • • • • • 1

A. The Research Vessel • • • • • a e • • • • • • • • • e • • • • • • • • 1 B. Specifications of Trawls used during the Survey o • • • e • • • • • • 2 C. Acoustic and other Equipment Funded by tJNI}P • m· e • o • • • 8 a • • • 2

.3. SCHEOOLE OF CRUISES • • • • • • • • • • • • • • • • • • • • • • • • • • 3

4. STAFF • • • 0 • • • • . • • • • • 0 • . • • • • • • • • • 0 • • • • • • • • 4

A. Headquarters Staff • • • • • • • • • 0 • Q • • • • • • • • • • • • • 4 B. Scientific Staff from u.s.s.R. • • • • • e o • o • e e a • • e e • o 4 c.. Participants from Indian Ocean Countries • • • • • 0 • • • • • • • • 4

SURVEY AREA. • • • • • 0 • • • • • • • • • • • • • • • • • • • • • • • • 5

A. Topography •••• D 8 9 • 9 8 e 9 • • • • • 0 • • 0 • • • • • • • • 5 B. Climate and Currents 9 • 9 • D • 0 • • • • • • • • • • • • • • . " . 6

6. SURVEY OPERATIONS 0 G 0 G 0 8 e 9 • e 9 • 9 e e • 9 0 Q 9 9 9 G 0 0 0 • 7

RESULTS OF THE SURVEY o e o e e o s e a • e o e e • o • o • • e e e e • 8

General • • • • • • • • • • • • • • • • • • ., • ., • • • • • • • • • 8 Pelagic Fishes - lllll.y-timu Versus Night-time Catches • • • • • ., e •• 9 Ea.et African Co~stal. Region • • • • • • • • • • • • • • • • • • • • • 9

A. Depths lesa than 200 m o e e • • • o • • e • e e • • • o • • e • 9

Pelagic fishes • • • ,. • • • • • • • e • • • • e • • • • • • 9 Demera&l fishelll • • • • • • • ., ., • • ., • • • • • ., • • • ., 12 Elasmobra.nchs (sh&rks, rays and skatea) ••• e e ••••• 15 Crustaceans· • • .. • • • • • • • • • • • • • • • • • • • .. • 16 Acoustic Survey • • • • •• • • • • • • • • • • • • • • •• 17

B. Depths greater than 200 m • • •• • • • • • • • • • e ... • • • • 18

4. Oceanic Banks 9 9 9 0 • G 9 e a 8 8 $ e e e 9 G 9 e e e 9 0 9 • 0 e 18

A. Seychelles Bank a.nd Saya de Malha Bank • • • • • • • • • • • • • 18 18 Pelagic fisheu • " • • • • • • • • • • • • • • • • • .. • • • Demer Bal fiehH ii • • • • • .. • • • • • • • • • • e • • • • 19 Ela.smobra.nchs " • • • e • .. " • • • " .. • • • • • • • • • • 20 Crustaceans .. " • • .. • • • • • • • .. • • • • . .. • • .. • • 21 Acoustic Survey '! .. e 21 !~ • • • • • • • • • • • " • • • • • " • B. Amira.ntes Ba.nk and Southern Banks • • • • • • • • • • • • • .. • .. 22

8. STANDlliG STOCK OF ll'ISilS AID PCJ!'m'l'IAL IlJ!LD • 0 0 0 & • • • • 0 • 0 • • 23

9. TABLES OF MEAN CATCH (Tablee 3-15) e • • • • o • • • • * • • e • • • • • 24 -v-

Page

Ex:pla.nator:y Notes • • 9 • • 0 • • • • • • • • • • • • • 0 • • • • 24

10. DISTRIBUTI

Ex:pla.na.tory Notes • • • • • • • • • • • •• • • • • • •• • • • • • • 25

{a) Results of Trawl Survey (Figures 4-40) • • • • • 0 • • 0 25 Kenya (Figures 4-8) • • • • • • • • • • • • • • • • • • 48 Tanzania (Figures 9-19) • • • • • • • • • • • • • • • • 53 Sophala Bay (Figures 20-24) •• • ••• o • • • • •• e 64 Mozambique (Figure 25.) • • • • • • • • • • • • • • • • • 69 Delagoa Bay (Figures 26-29) • • • • • • • • • • • • • • 70 Seychelles (Figures 30-32) • • • • • • • • • • • • • • • 74 Saya. de Malha (Figures 33-36) • • • • • • • • • • • • • 77 Mauritius to Nazareth (Figures 37-40) • • • • • • • • • 81

(b) Results of Acoustic Survey (Figlll'eS 41-53) • • • • • • • 25 Kenya {Figures 41-42) •••••• • • • • • • • • • • • 85 Tanzania (Figures 43-44) •••••••• o ••••• • • 87 Zanzibar (Figures 45-46) • • • • • • • • • • • • • • • • 89 Sopha.la Bay (Figures 47-49) • • • • " • • 0 • • ll • • 0 91 Delagoa Bay {Figures 50-51) • • • • o et • e •• e • 0 • 94 Seychelles (Figure 52) •••••••••••• o ••• ~ 96 Saya de Malha (Figure 53) • • •• • 0 • • • • Cl • • • • 91 - 1 -

1. INTRODUCTION

The Western Indian Ocean Fishery Resources Survey falls within the general objective of the Indian Ocean Programme to contribute.to the economic development of nations in the Indian Ocean area through fisheries development. Among the activities of the Indian Ocean Progratll'lle is the provision to governments of uaeable information on the distribution, magnitude and potential of coastal and offshore resources which will enable the governments to consider development and management strategies. The present resources survey was recommended in the Pla.n for Fishery Development in the Indian Ocean Programme (IOFC/DJW/71/1). It was anticipated in the Pla.n that the survey would be carried out as a bilaterally funded project. Following discussions between the UNDP, FAO and the U.s.s.R. authorities in September 1974, it wa.s a.greed to proceed with this project a.s a UNDP-funded activity within the framework and under "the direction of the Indian Ocean Programme. A fully equipped u.s.s.R. fishery research vessel including scientific a.nd technica.l staff was chartered to FAO for a period of one year and the project was implemented late in 1975. The survey area. eventually agreed upon.was the coastal waters of Eastern Africa f'rom Somalia south of the equator to 27°s, including Ma.daga.scar, and the fishing banks of the Mauritius-Seychelles Ridge. Ma.da.ga.scar and Somalia were eventually excluded due to late arrival of authorization from the respective Governments for the vessel to operate in their watera. The work and services to be executed included exploratory and experimental fishing for pelagic and demersal fishes, measurements of environmental factors, collection and analysis of acoustic and catch data for the estimation of standing stocks of fishes, prepa­ ration of fishing charts for the area a.nd on-job training for scientists and technicians from countries of "the region aboard the vessel. Limited information on the fisheries of the region had become available through the activities of several local research institutions and government fisheries departments. The present survey may be viewed a.a a first attempt to make a. syatema.tic investigation of the fishery resources of this large area, employing uniform techniques and equipment through­ out the area..

2 • THE R/v PROFESSOR MESYATSEV' A. The Research Vessel The vessel is an ATLANTIC II class stern trawler, commissioned in 1972 from a yard in the Democratic Republic of Germany and designed for both scientific research and commercial deep-sea fishing. She wa.s assigned to the project by the Ministry of Fisheries of the Soviet Union from its Yugrybpromrazvedka. {Southern Fisheries Development Service), Kerch, a.nd operated under the general rna.na.gement of SOVRYBFLC1l' (Soviet Fishing Fleet).

The vessel has an overall length of 82.5 m7 a. draught of 5.25 m, and a ORT of 241 tons. Her two ma.in diesel-electric engines develop 1 160 hp ea.eh, giving a. normal cruising speed of 12 knots a.nd sufficient power to tow a large bottom or pelagic trawl at speeds up to five knots.

Standard navigational aids include two radar sets, a. gyrocompass and radio-location equipment, all of Soviet ma.ke, a Decca plotter and a Loran plotter. This equipment was adequate for position-finding near to the coast, especially where navigational beacons were available. Further from the coa.et, and especially on the oceanic banks - the Seychelles Bank excepted - there a.re no navigational beacons and reliance had to be placed upon solar or astral fixes, much of the sailing between stations being by dead-reckoning. This inevitably must have affected the accuracy of position-finding adversely, particularly when combined with the strong currents which flow in most of the region.

Scientific accommodation includes labor~~~ries for chemical a.:nd ph;y'aica.l ocea.nograph;r, plankton, invertebrates, fish processing technology a.nd a wet-fish laboratory. The vessel - 2 -

has a single-line fish-processing system, a plate-freezer with a capacity of 2~ tone per day, a fishmeal pla.nt with a capacity of 12 tons per dCliY and a small experimental canning unit.

The two main electrically powered trawl-winches a.re placed at the stern. Each winch develops 130 kWt and can accommodate up to 2 500 m of warp. They are supplemented by smaller winches for handling the bridles, and for lifting the codend during the hauling process.

B. Specifications of Trawls used during the Survey

The main specifications of the trawls used during the survey a.re summarized in Table 1. The cod trawl, of standard pattern used widely on Soviet vessels in the Atlantic, was used most of all. The design of the net of this trawl is shown in Figure 2. The light trawl was similar in design to the cod trawl a.pa.rt from having a lighter footrope; it wa.s used only at five stations during Cruise 3, off Kenya. The lobster trawl had long, narrow wings attached directly to the doors, thereby increasing its sweep. Combined with the lightness of the footrope a.nd the lack of bobbins, this design feature increased the effectiveness of the trawl in searching for lobsters.

Table 1. Specifications of »ottom Trawls used du.ring the Survey Cod Trawl Lobster Trawl (all dimensions in metres)

Distance between doors 60-70 60-70 Headline length 32 55 Horizontal openingJ/ 16.4 50 Vertical openingS/ 6 4 Belly line length 56.3 32

Bridle length 100 none

Footrope - cod trawl: steel, with 400 nnn bobbins; lobster trawl: rope, with 200 mm rubber rollers. j/ wing-to-wing spread

~ assumed from calculations Only the results with the cod trawl are taken into account in calculating the mean catching rates and assessing the quantity of fishes. The codend mesh of this trawl was 100 mm bar, 160 mm stretched including one knot. Such a. large mesh would have allowed the escapement of small s~ecies and small individuals of larger species; to prevent this a small mesh (10 mm bar) inner lining.was attached. inside the end pa.rt of the codend ..

c. Acoustic and other Equipment Fu:nded by UNDP Before the start of the project, the PROFESSOR MESYATSEV went to Horten, Oslo Fjord, Norway, where she was fitted with the following Simra.d acoustic equipment:

Eoh<>-sounderEK-38 (scientific) Eoho-sounderllK-120 (scientific) Echo integrators Mk 11 QM linked with two Hewlett-Packard recorders - 3 -

Echo magnifier MA Netsonde recorder Elcternal transmitter for Ji.X-38 Beam width selector Echoscope for use with the EX-38 Sonar SQ with MS signal processor Sonarscope for use with Sonal' SQ Storage oscilloscope and teat panel Transducers, cables, hydrophonet and other ancillary equipment

This equipment was funded by UNDP. other equipment also provided by UNDP included: Na.nsen bottles, bathythermographs, thermometers, microscopes, electronic calculators, and office equipment. ·

3 • SCHEDULE OF CRUISES

Cruise 1: 27 December 1975 to 18 March 1976 Mombasa. - Dar ea Sa.la.am - Maputo - Mombasa

Cruise 2: 21 March to 22 April 1976 Mombasa - Port Louis - Port Victoria. (a) Cruise 3: 8 June to 19 June 1976 Mombasa - Kismayo (b) Cruise 4: 1 July to 12 September 1977 Mombasa - Dar ea Salaam - Maputo - Port Louis Cruise 5: 16 September to 4 November 1977 Port Louis - st. Brandon - Port Victoria - D1 Arros Island (Amira.ntes)

Cruise 6: 13 November to 1 Ilecember 1977 Dar ea Salaam - Mombasa Notes: (a) Between Cruises 2 and 3 the vessel went for refit to Aden.

(b) Cruise 3 was aborted by an engine-room fire which necessitated a prolonged refit~ The survey vessel was ma.de ready for sea again by November 1976, but it wa.s considered in FAQ that the survey should be resumed at the same time of year as it had been interrupted, viz~ June.

Cruise 1 was carried out during the latter part of the Northeast Monsoon (southern hemisphere summer) of 1975-1976; during this period, work was carried out off Kenya, Tanzania and Mozambique. Cruise 2 took place during the transitional period between the monsoons, and comprised the first survey of the Seychelles-Mauritius Ridge. -4-

Cruise 3 (Kenya., 1976) a.nd most of Cruise 4 (Kenya and Ta.nzania. 9 1977) were carried out during the latter part of the Southwest Monsoon., The work off Mozambique during Cruise 4 a.nd the second survey on the Seychelles-Mauritius Ridge (Cruise 5) were performed during the transitional period between the Southwest a.nd the Northeast Monsoon of 1977., The final work off Tanzania. a.nd Kenya (Cruise 6) was performed during the early part of the Northeast Monsoon (southern hemisphere l!IUD'llller) of 1977.

4.. STAFF

A., Headquarters staff The FAO Project Leader throughout the survey period was L. Birkett, who represented the Organization on board the survey vHsel except during the period 18 March - 3 May 1976 (Cruise 2) when I.J.D. Robertson deputized. The Organization also provided an acoustic specialist, J. Burczynski, who assisted with the calibration of the scientific acoustic equipment and supervised the Soviet acoustic experts on board during two periods - 29 December 1975 to 7 February 1976 and 27 June to 16 July 1977. B. Scientific Staff from U.s.,s.R.

Cruises 1 and 2 Cruise 3 Qruises ~ 1 ~ and 6 Ship's Master Ju. I., Pavlov G.A. Ivanov v.r. Kutepov Chief Scientist A.D. Druzhinin D.A. Shubnikov D.A. Shubnikov Ichthyology V.. M. Borisov s.v. Busa.kin s.v. Busa.kin A.N. Rytov A.N. Rytov Oceanography - physical s.s. Pa.rfenovich n.v. Bogdanov D. V. ·Bogclanov - chemical V.F. Polu;ya.kt ov N.V. Mordasova N.V. Mordasova Invertebrates B.G., Ivanov B.s.· Averin B.S. Averin Fish Processing A.N. Golovin G.N. Golovkina. G.N. Golovkina Fishing gears E.A. Karpenko V.G. Bi den co v.a. Bidenco lf;ydroacoustics A.G. Artemov A.G. Artemov A.G. Artemov V.A. Prota.achuk v. Sa:fronov V.N. Slatvinsky Plankton v.v. Krylov V.M. Zhura.vlev V.M. Zhuravlev Tra.nslator/Interpreter L.G. Kuzichkina.* R.T. Grin co R.T. Grinco

* Cruise 1 only. c. Participants from Indian Ocean Countries

Cruise 1: K:enya - Se Abuga., M. Ngoia, A. Mraja, J. O~ri (27 December 1975 to 18 March 1976)

Tanzania - P., Chi5ara1 K. Ka.tonda. (27 December 1975 to 18 March 1976)

Cruise 2: Kenya. - B.M. Ogilo, J 0 K., Ka.ga.i, c.o. Okuthe, S.M. Njuguna. ( 18 March to 21 April 1976) Tanzania - I. Bryceson (18 March to 21 April 1976) Mozambique - L.F.P. da. c. Manuel (18 March to 21 April 1976) Seychelles - s.E. Vidot (18 March to 21 April 1976 - 5 -

Cruise 3: Ke:r.ya. N. Odero (Director, Department of Fisheries, Kenya.) (16-19 June 1976) E.K. Kariuki 9 J. Siwo (8-19 June 1976) Cruise 4: Kenya - B. Oduor, B. Mulandi, E. Mwa.kilengi (27 June to 15 August 1977) Tanzania. Se Osman, W. Ha.ulet Go Mabrieya, D. Mwanga.ile (27 JWle to 15 August 1977) Cruise 5: Mauritius J.D. Ardill (16 September to 10 October 1977) A. Venkatasami (16 September to 19 October 1977) Seychelles - J~ Tarbitt (16 September to 3 November 1977) Cruise 6: Tanzania. - B.M. Xissa.ka. (13 November to 1 December 1977) O.P. Msinge 9 M.A.K. Ngoile (21 November to 1 December 1977) 5. SURVEY AREA

The a.rea to be surveyed during the project (Figure 1) included the entire coastlines of Kenya, Tanzania and Mozambique - a. total of about 1 900 miles - and the oceanic banks of the Seychelles-Mauritius Ridge, which extends in a curving a.re for about 1 200 miles.

A. Topography

Much of the continental shelf of Fast Africa is narrow, the 200 m contour lying within 2-5 miles of the coast. Beyond the edge of the continenta.l shelf steep gradients lead down to the deep ocean floor. The presence of fl"inging coral reefs, outcrops of rock and coral, and deep fissures make it diffioult and hazardous to trawl in such areas.

Off northern Kenya, the shelf widens out to about 40 miles to form the North Kenya Ba.nks. Some trawling was possible here, but the ground is strewn with rocks and coralo There is a sharp sill off Ungama. Bay leading do'Wll to a. more gently sloping region with soft bottoms safe for trawling. The steepness of the slope immediately off Unga.ma Ba.y ma.de it difficult to sample the depth strata systematically.

The Pemba Channel is deep and the shel:f surrounding Pemba Island and on the coast of Tanzania in the Cha.nnel is very narrow, except at the northern end of Pemba Island where it extends to 10 miles. Some trawling was carried out on this shelf a.nd on the western side of the Pemba Channel.

The Zanzibar Channel and Mafia Channel are shallow, with minimum depths of about 20 mo The shelf is however only 3-5'miles wide on the oceanic sides of both these Islands. The Rufiji River debouches into the Mafia Channel and its delta is too shallow and complicated by reefs and narrow channels.. Trawling wa.s carried out in 25-500 m in the south and north Zanzibar Channel, and in 200-400 m on the north Mafia shelf. The presence of submarine cables on either aide of the Zanzibar Channel restricts trawling activities there.

From the Kihra. Me.in Pase, south of Mafia Island, to the northern end of Beira. Ba.y 7 a distance of 500-600 miles, the continental shelf is a.gain very narrow a.nd its bottom topo­ graphy is characterized by deep fissures, coral and roclcy outcrops, a.nd fringing reef. Only one suitable location for bottom trawlin§ was found along this stretch of coastline, at a position to the north of Pinda, ~bout 14 S; here there was a stretoh of smooth, level sandy bottom just long enough for two one-hour trawl hauls, but a.t either end the terrain wa.s rugged.

Beira Ba.y extends for about 300 miles, and is wedg&-sha.ped, being about 60 miles wide at its lower end. The Zambezi River debouches into the ocean in the centre of the Bay, and the Pungue River nea.r its southern end. - 6 -

Along the outer edge of this Ba.y, the 75 m, 100 m and 200 m depth contours occur within 1-2 miles of ea.eh other and these depths a.re quite untrawlable, the topography being marked by deep fisa~s, steep gra.dientSJ a.nd. rocky outcrops. :But the major part of the Bay above 75 m is safe for trawling, with ~a.ndy or muddy bottoms.

From Ilha. de Ba.za.ruto at the southern end of Beira. Bay to Punta Zavorra, a distance of about 180 miles, the shelf is &gain nal'l'ow and rugged; but trawling was feasible along this pa.rt of the shelf in depths greater than about 100 m.

In the northern pa.rt of Maputo Ba.,y1 off :Boa. Paz, there is a wide bank much of which wa.s found to be safe for trawling, though there exist unpredictable hazards such aa rocks and coral outcrops, which a.re not shown by echo-sounders. The shelf south of the River Limpopo is again ne.rrow and rugged, bu.t the deep bight opposite Maputo has soft bottoms and several trawl ha.uls were ca.rried out there.

Most of the East African continental shelf has been fairly well charted, and it was possible to locate suitable positions for trawling with the aid of the charts and uaing echo-sounders. But the indications from the echo-sounder were often deceptive, resulting in badly damaged nets on numerous occasions, on what appeared to be featureless bottoms. Except for the Seychelles Bank, however, the Seychelles-Mauritius Ridge is not well cha.:rtered. There seems little liklihood of trawling around Reunion, which wa.a not included in the survey area. South of Mauritius the shelf is extremely narrow, but limited tra.wlable ground was found in the vicinity of Flat Island. The main pa.rt of the Seychelles-Mauritius Ridge is a series of level-topped shallow ba.nks 9 rising to about 20 m or les$ in places, separated from bank to bank by deep, or very deep, water. There is a.n archipelago of islands on the Cargados Carajos Shoal, but elsewhere no other land apart frC>m the Seychelles group of Islands. The main ba.nks on the Ridge are, from south to north, Souda.n Ba.nk, -the Carga.dos Carajos Shoal, Nazareth Ba.nk 9 Saya. de Ma.lba Ba.llk and the Seychelles Bank, to the west of which is the Amirantea Bank, The westward slopes of all these Banks, and of the whole of the Seychelles Ba.nk 9 a.re steep to vertical from the 200 m contOUl' downwards. The eastern slopes have leseateep gl'adienta, but there a.re many deep fissures.

Limited trawling wa.s possible in the area from Soudan Bank to Nazareth Bank, ma.inly because of the widespread occurrence of dead coral heads. The greater part of the Saya de Ma.lha Bank a.ppeared to be safe for bottom trawls, with sandy bottoms down to a.t least 200 m depths. The Seychelles Bank is largely level bottomed9 but in the ea.stern pa.rt there are many steep-sided knolls rising to about 20 m above the seabed and there a.re shallow regions with coral in the northweet and around a.11 the islands. The Seychelles Plateau appears to be surrounded by a. shallow rim.

The Amirantes Bank is sepa.ra.ted from the Seychelles Bank by very deep water, and its sides a.re steep to vertical from about 200 m. The top of the Bank is level and sandy, but there are coral outcrops which greatly restrict the use of bottom gear.

B. Climate and Currents In the northern pa.rt of tho survey area, the dominating climatic feature is the monsoon regime, which strongly influences the pattern of surface circulation (Pigure 3). During the Southwest Monsoon (southern hemisphere winter, April-October), the East African Current flows strongly northwards, parallel to the coast of Kenya, bathing the shelf of Kenya. and Tanzania with water which is relatively poor in nutrienta. This current originates as a branch of the South »::ruatorial Current which flows towards the African Continent from the general direction of the northern pa.rt of the Seychelle&-Ma.uritius Ridge. o:t'her branches diverge and flow southwards along both sides of Ma.daga.sca.r. During the Northeast Monsoon (southern hemisphere aUll'l!ller, Octobe~oh), there is a oo~lete reversal of the windsa.nd of the wind-generated surface circulation north of about 10 s.. The East African Coastal Current ia weakened, and water flows e(a.Stwards as the E:ruatorial Counter-current. - 7 -

6 • SURVEY OPERATIONS

Two methods of stock assessment were employed in ea.eh pa.rt of :the survey area: the acoustic method of survey, using the specialized Sirnrad scientific acoustic equipment, a.nd trawling, chiefly using the bottom trawls (cod trawl and lobster trawl). These two methods should provide independent estimates of the standing stock of fishes, the acoustic method primarily that of the pelagic stocks, a.nd bottom· trawling that of the demersal fish a.nd other bottom-inhabiting organisms. The acoustic survey grids were planned to give a rapid coverage of the ground, and it also supplied information on the suitability of the bottom for trawling.

Nherever practicable, the acoustic s\U'Vey legs were parallel at distances of 15-20 miles a.part, and perpendicular to the coastline. On the narrow shelf of parts of Kenya., Tanzania and Mozambique, the acoustic grid track was a. series of zig-za.g lines, from the shallowest safe depths out to 500-600 m depths.

'l'he trawl survey should ideally have been planned upon random trawl stations stratified according to depth, type of bottom, etc. This was rarely possible due to the closeness of the depth contours, and to the inadequacy of the cha.rte and also of the navigational equipment. So it became necessary to carry out trawling wherever suitable bottoms appeared to exist; in this sense, a.nd only in this sense, the trawling effort was guided by the echo-sounders.

The catch resulting from each haul was a.nalyzed to species and the records show the weight and number of fish of the most numerous species, and the gross weight of each main category - sharks a.nd rays, bony fishes, crustaceans and squids, etc. From these data.the distribution of the various resources was plotted, a.nd estimates were prepared of the mean catch rates by region, season, depth range and category (Section 7, Results of the Survey; Tables 3-15 a.nd Figures 4-40). Biological sampling was carried out on the most abundant species. The records show size composition, length-weight relationship, sexual maturity, and feeding activity of these species.

Environmental parameters were measured as a.n integral part of the survey. Temperature, salinity, dissolved OJcy'gen a.nd nutrient content of the sea wa.ter at standard depths were recorded, the analyses being carried out on board.

Plankton sampling from 0-100 m, and 0-200 m, was carried out at the h;ydrogra.phic stations and also by nets attached to the trawl headline. The objective was to estimate the quantity of food plankton and the distribution of fish larvae. Finally, processing studies were carried out primarily to investigate the shelf-life properties of fish preserved under various conditions. National counterpart staff from the Indian Ocean countries pa.rticipa.ted in all the above activities as part of their on-the-job training. The Simrad echo-sounders were also used oontinuously to count fish during ea.eh trawl haul in order to provide a basis of calibration of the acoustic equipment. Electronic calibration of the Simrad acoustic equipment .wa.s carried out twice - in December, 1975 and June, 1977 - both times ~hile the vessel was at anchor in the Kilindini harbour at Mombasa. The calibration procedure involved the emplacement of a hydrophone at a fixed distance directly beneath the transducers. This work was performed by E.F. Akyttz of FAO who travelled to Mombasa specifically for this purpose in December, 1975; and by the team of divers who were members of the vessel crew from the u.s.s.R. It proved imprac- - 8 ~

tica.ble to carry out a ta.rget-atrcngth calibration with live fishes, due to the unavaila­ bility of live fish of the appropriate type and in sufficient numbers, and the lack of perfectly still conditions.

Original data sheets on which details. of the station position.e, schedule of operations, trawl catch analyses, acoustic integrator records, and hydrographic information (temperature, salinity, oxygen and nutrient•) were recorded and lodged with the Fisheries Department of FAO. The Fisheries Ila.ta Centre have stored the catch al'lalyaes and also biological analyses of fishes and crustaceans on tape; applications for print-outs of relevant sections of the material should be addressed to the Director, Fisheries Department, FAO, Rome.

7 • RESULTS OF THE SURVEY

1. General The survey area fa.lls naturally into two regions, the ea.stern seaboard of Africa - including the continental shelf and the adjacent parts of the' slope - and the ocee.nic banks of the Mauritius-Seychelles Ridge. The following account is similarly divided, and within each ma.in region there is a. subdivision of the trawl catch into four categories - pelagic and demersal teleo~ts (bony fishes), elasmobra.nchs (sharks and rays), and crustaceans (lobsters a..nd shrimps).

The larger pelagic fishes - tunas a.nd tWla.-like fishes and the larger cara.ngids - a.re not included in this report because no special effort was ma.de to catch them and they were only incidentally captured by the trawl.

The smaller schooling pelagic fishes ~ the clupeids (herrings, sardines) and Ehgraulids (anchovies) - were occasionally taken in quantity but they represent only a minor part of the whole catch by trawling, a.nd the overall distribution of small schooling fishes was only defined in outline while their abundance cannot properly be eatima.ted by trawling.

Some of the smaller fish@s may have escaped through the meshes in the forward parts of the trawl and oodend, but they would have been trapped by the srna.J.l meshed inner cover at the after end of the codend.

Demersal fishes were represented in the trawl catches by several hundred species among which, however, a few generally predominated. Regional differences in the list of dominant species are small. The larger fishes often weigh 3-10 kg each, so that a catch of 50-100 kg/h represents a rather small number of fishes and a large stock is not, therefore, necessarily very numerous, Intensive fishing on this category would seriously deplete the stocks, a.nd the stock represented in the catches of such species is moreover composed of old individuals with relatively low annual production. Pelagic fishes completely dominated the trawl catches in several areas, at least in certain seasons. This was the ca.se in the southern Zanzibar Channel at depths of 200-300 m in July and December; in the shallower :parts of Delagoa Ba.y (25-200 m) in january, in moderate depths in this Bay (200-300 m) in August; throughout the Seychelles Plateau in October; on the Sa.ya de ~lha Bank in April, and in its central part only, during October. This predominance of pelagic fishes is clearly brought out in the Appendix tables, in which the mean catch rates of pela.gio fishee a.re based 011 the day-time hauls only. In a later section of this report it is shown that there was a highly significant difference in the catches of pelagic fish in the bottom trawl between night and day in the regions mentioned above. In all these oases, oa.ra.ngids clearly dominate the pelagic fish category and are thus the most important single family of teleosts throughout the survey area. In other cases, even when not particularly abundant, oarangids still made the largest single component in the catches, au in Kenya. ( 15-200 m depths in June and July), south Zanzibar Cha.nnel (50-200 m depths, July) a.nd Beira. Bay (50-100 m depths, January)., But with the exception of the Seychelles Plateau, the areas over which pelagic fishes a.nd cara.ngids in - 9 -

particular predominate a.re small in extent, so that the total stocks a.re not necessarily large although they may be highly concentrated. An essential factor lea.ding to dense aggregations of pelagic fishes is high plankton production. In a region in which the surface waters are not particularly rich in nutrients, this implies, at least in a mild degree, either upwelling or overflow of the nutrient-rich sub-surface wa.ters onto the shelf or the oceanic banks. High production was amply demonstrated in these areas, but it cannot be said that upwelling or overflow wa.s definitely found a.n,ywhere where means of up to 2 OOO kg/h of pelagic fish were obtained.

On the Seychelles-Ml.uritius Ridge, the southerly banks - Nazareth to Mauritius - were consistently poor in fish, averaging 75 kg/h of demersal and only traces of pelagic, thus contrasting markedly with the Sa.ya. de Ma.lba Bank and the Seychelles Plateau, with means of up to 298 kg/h demersal and up to 2 478 kg/h pelagic, depending upon sub-a.rea.o Elasmobra.n.chs (sharks and ra;ys) were most abundant in the northern part of the African seaboard, Kenya and Ta.nza.nia, where mean catches ranged from 75 to 476 kg/h. Further south - 3eira. Bay and Maputo Bay - and on all the oceanic banks, ela.smobra.nchs averaged only 12 to 67 kg/h. Deep-sea lobsters (Palinuridae) appear to be present along the whole African seaboard at depths of about 200-300 m, at least as far as the rugged bottoms at these depths permitted the trawl to be used. The greatest concentrations of lobsters (up to 300 kg/h) were found off Ken;ya, in Beira Ba.y, and I·iaputo B~. On the oceanic banks substantial catches of lobsters were ma.de only on the eastern side of the Saya de Ma.lha Bank: they were also found, though in smaller quantities, on the eastern side of the Nazareth Ba.nk.

2. Pelagic Fishes: Day-time Versus Night-time Catches The regular vertical migrations of the pelagic fishes at twilight were often observed on the echo-sounder. During the da.ir-time, schools of pelagic fish would be concentrated in the bottom few metres of the water column where they were fully accessible.to the cod trawl with its high li:f't headline. At dusk, the fish would rise quickly as schools, dis­ persing gradually during the evening at depths between 20 a.nd 40 m below the surface. At dawn, the movement would be reversed. The effect on catches in areas where pelagic fishes were important was considerable, as Table 2 shows. The night-time catches of pelagic fishes were so small that they probably represent accidental catches during the few minutes the trawl was being li:f'ted from the seabed.

Because of this, the average catches of pelagic fishes, particularly those of round scad (Decapterus) and horse mackerel (Tra.ehuru.s) are estimated on the basis of hauls ma.de in the day-time. In those comparisons between day-time and night-time catches which are based upon sufficiently large numbers of hauls, the differences are statistically significant. 3. Ehst African Coastal Region A. Depths less tha.u 200 m (a) Pelagic fishes (i) Cara.ngidaelf

More than 20 species of oa.rangids were identified in the catohes, but speoia.l economic interest resides in only a few, such as the round scads

The taxononzy and synon;ynzy"" of Oa.rangidae is at present unsettled; these ship-board identifications, ma.de with reference to Nekrasov (1968) are provisiona.l and are almost certain to be replaced when the family is reviewed. The ship-board identifications are retained here for convenience. - 10 -

Table 2. Diurnal Variation in Oa.tches of Pelagic Fishes in Cod Trawl (mean and standard deviation of catch in kg/h

Day-time Night-time Night Region Depth x 10<:>% n mean n mean Day

South Zanzibar 200-300 2 066 ! 1 095 Channel (July '77) 7 4 49 ~ 93 2.3%

South Zanzibar + 8 1 542 897 4 110 Channel (Nov. '77) ! 55 - 3.5%

+ Beira Bay <50 m 10 405 ! 554 6 9 - 9 2.2% + + (Jan. 1 76) >50 m 5 192 - 224 3 9 - 8 4-7%

Beira Bay (50 m 35 110 :!: 140 16 28 ! 34 2 .. 5% (Aug. '77) )50 m 16 468 ! 731 8 12 ! 13 2.5%

Seychelles 38 1 262 ~ 1 776 21 33 ! 72 2.6% (Oct. '77)

Saya de Ma.lha. 9 691 :!: 525 9 62 :!: 83 9% (Oct. 1 77, central)

n = number of trawl hauls - 11 -

(Deca.pteru.s ~i~iche and l!!. ma.oa.rellus) a.nd the horse mackerels (Trachurus indicus and T. dela.goa.}. The largest catches off Kenya. a.nd in the south Zanzibar Channel were o~en made up of a mixture of two or more of these species. Off Kenya, the Decapterus spp. produced a few large catches (up to 500 kg/h of D. macarellus in June, 532 kg and 1 344 kg/h of E.:, kiliche in July) 'but they were not as abundant as in a small area in the south Zanzibar Channel, where in depths of 250.-300 m depths hauls of 1 to 3.8 t/h were regularly obtained in January, July a.nd December. Elsewhere in Tanza.nia.n waters, the shelf north of Pemba Island yielded one good catch, 355 kg/h of D. macarellus, in July, 'but .ca.ra.ngids were generally scarce in the Pemba Cha.nnel, north Zanzibar Channel, a.nd on the shelf north of Mafia Island. There were several good catches of other, larger ca.rangids (Gnathodon s?Eciosus, Cara.ngoides ma.la.barious a.nd ~ crwnenophthalmus), 150.-230 kgh off Kenya, but these were not important off Tanzania.. The Deca.pterus spp. also yielded several smaller but good catches in the north Zanzibar Channel.

F\J.rther south, some isolated hauls off Pinda. (Mozambique, about 14°s) are of interest. The single haul here in January yielded 827 kg/h D. kiliche and 147 kg/h D. macarellus, suggesting that although the terrain between Mafia Island and the north end of Beira Bay had few trawla.ble grounds, the round scads rna.y have a con­ tinuous distribution along the whole seaboard of ea.stern Africa., since they were also found in Beira. Ba.y and Maputo Ba.y. The quantities in Biera. Ba.y and Maputo Baor were generally small, although a few good catches were ma.de: 500 kg/h D. maca.rellus, 1 100 kg/h MeElaspys cordyla, 252 kg/h Atule ~' mostly shaIT'ower tha.n 50 m in Sopha.la~ in January, 2 700 kg/h D. ma.ca.rerr'Us and D. kiliche, 500 kg a.nd 1 200 kg/h Caranx dinema in 55-65 m depths, Beira Bay in August; 500 kg/h D. kiliche in 44-50 m, 1 806 kg/h Trachurus dela~ in 210.-250 m depths in MaputoBay in January. The yield of carangids in Maputo B(\y was small in August.

Spawning grounds of these species off eastern Africa were not located during the survey, and it is possible that sparming takes place over deeper water, further offshore from the regions fished. Ripening of gonads was beginning among the round scads (Decapterus spp.) off Kenya in January, and in the larger carangids (Megala.spys cord,yla and Garangoides mala.baricus) in Beira Bay in January-February. Ripening gonads were also found in the round sca.ds in the south Zanzibar Channel in July, off Kenya, in both July and November, and in August in Beira Bay .. Spent or inactive gonads were observed in the round scads in the south Zanzibar Channel in January and July off Xenya. in March a.nd in Beira Bay in August; Tra.churu.s delagoa were spent or immature in Maputo Bay in February. It is possible that there are two spawning seasons among ca.ra.ngids - April to June and September to October - 'but the peak spawning seems to be in Ma.y-Jtme along much of the coastline. (ii) Clupeida.e and Engx:aulidae

Although there were some good catches of sardines and anchovies, small schooling pelagic fishes never predominated over large areas as in the case of the carangids. Neighbouring hauls often caught aubstantia.l qua.nti ties of completely different species, suggesting tha.t the schools were discrete a.nd locally distri­ buted, and only accidentally captured by the bottom trawl. - 12 -

The ma.in species cau~ht off Kenya and Tanzania were round herring { Etrumeus micropus), 152 and 224 kg/h off Kenya in July9 oil sardinellas (Sardinella mela.nura and~~), Indian pellona (Pellona ditchella) and!:. micropus in the shallower parts of the Zanzibar Channel, wh~re 9 particularly in the northern part of the Channel, heavy day-time echo traces were produced in the upper sub-surface water in July.

Further south, larger and more frequent catches were obtained in the south and north parts of Beira Bay but sardines and anchovies were not caught in any large amounts in Maputo Bay.. In Beira. Bay, the largest catches were in the shallower parts less than 25 m depth; E. micro s, P. ditchella, s. mela.nura at 127-530 kg/h in January, ..§.?. mela.nura 454'°kg h in August. In BeiraBay in August the most abundant clupeid was .E!. di tchella, yielding up to 216 kg/h. These catches are quite good if it is realized that the species are small and capable of escaping through the mesh in the forward parts of the trawl if not too crowded ..

(iii) Scombrida.e Ex:cluding the large tunas and their relatives, which were only sporadically and accidentally caught in the trawl, the ma.in scombrids were the kingfish or Spanish mackerels (Scomberomorus commerson and 2.!. gu.ttatus) and Indian mackerels (Rastrelliger ka.na.gurta, &_ bra.ohysoma.). These species yielded good catches at times, but they are large and active fishes (particularly Scomberomorus) and the bottom trawl is not designed to catch them.

The best catches were 209 and 1 01.1 kg/h of !h kana.gurta. in 30-50 m depths in Beira. Bavr and Maputo Bay in January-February; elsewhere &, kana.gurla yielded up to 50 kg/h occasionally off Kenya., Tanzania and Mozambique in January and March.

R. bra.c~ysoma. replaced R. ka.na.gurta in the Zanzibar Channel and off lfoza.mbique in Ju"!Y and0vember, giving catches of 387 and 554 kg/h in Beira Bay and rather less in Maputo Bay.

Large Spanish mackerel, Scomberomorus spp., were caught in all the shelf regions though rarely in substantial amounts. The largest catches were 55 and 137 kg/h in Beira Bay in July. (b) Demersal fishes (i) Lutja.nidae

Lar~ red snappers (Lutjanus ~), bloodsna.ppers (~.:. sangu.ineus) a.nd green jobfish (~prion virescens), the predominant lutjanids off Kenya., yielded several excellent catches of up to 220 kg/h in December, January and Ma.rch 0 particularly on tha.t part of the shelf adjacent to the southern end of Unga.ma Bay. Elsewhere a.nd at other times of the year, lutjanids were scarce on the Kenyan shelf a.nd 7 since they were totally lacking in the deeper zones, it appears likely that they had migrated into the shallowest zones where the .MESYATSE\T could not operate.

In the south Zanzibar Channel, snappers (h_ ~ and !!.:., sanguineus) made up half the demersal catches in July and November in 50-200 m depths, yielding some large catches. Lo sa.nguineus predominated, giving two hauls of 218 and 873 kg/h a.nd several others of 50-100 kg/h in July. The area in which the snappers were aggregated in the south Zanzibar Channel was fairly-small so, despite the high local densities, the stock is not a large one.

On the north Pemba Island shelf, the dominant species was the sharptooth snapper (Pristipomoides ~). Lutjanid.s here averaged 107 kg/h but only three hauls were done in less than 200 m depths. - 13 -

In Beira. Bay the predominant snapper wa.s L. sanguineus, which ,Yielded good hauls, 132, 250 and 280 kg/h in January but not more tha.n 50-60 kg/h in August, a.lthou.gh the average level of catch of lutjanids was higher in August than in January, and it wa.s also higher in :50-100 m depths tha.n above the 50 m contour. The red snapper (L. sebae) and the jobfish (A. virescens) were relatively scarce in Beira. Bay. -- -

Rather small catches of snappers were ma.de in Maputo Ba.y; they were absent at depths greater than 200 m. The zone 25-200 m produced small a.m01.U1ts both in January·, February and August.

(ii) Lethrinida.e

IDnperors were never particularly abundant, a.nd the various s~ecies of Lethrinus represented in the catches, L. nebulosua (which was the commonest), L. borbonicus, L. rivulatus and L. ma.hsenoides never exceeded 40 kg/h total. Such catches were O'i;tained only in January, March and November on the Kenya shelf, and in the south Zanzibar Channel in July. Emperors were sparsely distributed elsewhere along the African shelf, Beira Bay yielding mainly.!!!, miniatus and~ nebulosus in a few hauls, not exceeding 21 kg/h except for one catch which contained 58 kg/h of ~ nebulosus. (iii) Serra.nidae

Groupers were also poorly represented in the catches on the African shelf. The main species were Epinephelus tauvina, which off Kenya and in the south Zanzibar Cha.rmel occasionally gave catches of 20-50 kg/h in January or March, and one good haul only, 154 kg/h in Beira Bay; !!_ ~ which yielc',ed several hauls 45-57 kg/h in Beira Bay in January-February, and ~ chlorostigma. which was the commonest ivouper in the south Zanzibar Channel in July with a few catches in the range· 20-30 kg/h. This species also yielded two similar catches in Beira Bay, in August. Elsewhere, a.nd at other times, groupers appeared sporadically and were chiefly represented by~ a.lbomarginatus (50 kg/h, south Zanzibar Channel, January) a...'ld a few others which rarely exceeded 20-30 kg/h. (iv) Sph,yraenidae Barracudas were most prominent in the ca.tches in Kenyan waters where the dominant species was Spb.yraena. japonicus. In January one haul yielded 1 080 kg/h of this barracuda, and two others 21, 70 kg/h. In Jul,Y three ha.uls of~ japonicus were in the range 114-207 kg/h and one yielded 740 kg/h. Kenya also yielded ~ jello at 13-26 kg/h in January, June and November, one haul of 169 kg/h, and one haul of 121 kg/h ~ obtusata.

Large barracudas, ~ jello and s. japonicus, were otherwise sparsely distri­ buted, not yielding more than 24 kgjhin Tanzanian waters at any time, 41-82 kg/h occasionally in Beira. Bay in Janua.ry and August. The small species, .§.:. obtusata a.nd ~ acutipinnis, occasionally yielded up to 50 kg/h in Beira. Bay in August.

(v) Poma.daayidae Several species of grunts were prominent in catches off Kenya at all times, especially in November a.nd also in the Zanzibar Channel and Beira Ba.y. Elsewhere they were more sparsely distributed. In Kenya. there were good catches of Plector chus pictus (25-120 kg/h), Poma.daays maculatus (30-120 kg/h and also 142, 220 kg h , P. multima.culatus (20-76 kgfh in December to March) a.nd !'.!_ ~' which were scarce in December-March, June a.nd July bU.t in November gave three large catches of 250-740 kg/h. - 14 -

In the south Zanzibar Channel the main species was P. multima.culatus but it was less common than off Kenya. and never exceeded 51 kg7fi.. In Beira Day the main species were Plectorh.ynchus pictus (26-96 kg/h) and Poma.dasys ma.culatus (20-86 kg/h) in August-September., In January grunts were less common but .!'.!_ maculatus yielded one good haul of 115 kg/h and Plectorh;ynchus pictus 40 kg/h.

(vi) Leioe,nathidae These small fishes were widely distributed on the African shelf but parti­ cularly prominent off Kenya, in the north Zanzibar Channel and in the shallowest

parts of Beira Bay0 They apparently form dense local schools, sometimes comprising several species, from which good catches were obtained. Being generally sma.11, it is likely that the majority escape the meshes a~er being caught.

The commonest species were Leiogna.thus equulus, giving several catches of 30-270 kg/h off Kenya and in Beira Bay, and Secutor insidia.tor - several catches of 40-60 kg/h in the same regions. ~ minuta was less common but yielded a haul of 1 431 kg/h off Kenya in January, an indication of quite high local abundance.

(vii) Mullida.e Several species of goatfishes were prominent in the trawl catches, the most abundant being Upeneus sulphureus in both Kenya and Beira Baur. Off Kenya., two large catches of this species were made - 1 200 kg/h in July and 562 kg/h in November. In Beira Bavr the ma.in region producing goatfishes in quantity was the shallow part immediately beyond the Zambezi River outflow area where, in August, four hauls yielded 130-386 kg/h of.!!!. sulphureus, two hauls yielded 270 and 275 kg/h of Mulloidicht s aurifla.mma, and ~ bensasi was also common though not exceeding 50 kg h. other species which were more sparsely distributed but which gave large catches a.re u. vitta.tus (141 kg/h off Kenyav January) and u. molluccensis (30-50 kg/h off Kenya and in Beira Bay),. El.sewhere 1 on the shelf, these small benthos­ eating fishes were sparsely distributed.

(viii) s;ynodidae

As mentioned previously, the lizardfishes were the most important single category of demersal 9 and indeed of total teleost, fishes in the deeper zones, below 200 m depth in most regions of the survey area. They also frequently occurred in the shallower parts, sometimes giving good catches.

The dominant species of lizardfish was Saurida undosg:uamis which frequently gave catches of .50-150 kg/h on all parts of the African coastline. Less widely distributed was :le. tumbil 7 which was almost restricted to Kenya and Beira Bay, giving catches not exceeding 40 kg/h with one 68 kg/h. The most restricted species was s. gracilis which, however\! gave two large catches off Kenya in January - 120 and 236 kg/h. (ix) other Demersal Fishes Besides the above categories, which include most of the larger and economically valuable species of demersal fishes, every region produced ita quota of usually smaller species, less regular in occurrence but sporadically capable of giving a large catch and thus apparently forming dense aggregations locally. The ma.in elements comprising this class of demersal fish are.as follows:

~: threadfin breams (Nemipterid.a.e: Nemipterus delagoa in June); bigeye breams (P:r:iacapthid.ae: Priacanthus hamrur in January); catfishes (Ariidae: ~ thalassimus in July); ha.irtails (Trichiuridae: Trichiurus lepturus in - 15 -

June); sicklefish (Drepa.nida.e: DrepWe punctata.) la.rge-:.eye breams (Pentapodidae: ctymnocra.neus grizeus); moja.rras (Gerrid'.a.~ Gerres spp.); croakers (Sciaenidae: Argyrosoma hololepidotus, otolithes spp.}

South Zanzibar Channel: d.riftfish· (Ariommida.e: Ariomma indicus in November); Polymixia. nobilis in January and November; bigeye breams (Priacanthida.e: Priacanthus arenatus) Beira Bay: hairtails (Trichiurida.e: Trichiurus lepturus in August); triggerfish (Balistidae: Balistes stellaris in January a.nd August); croakers (Sciaenidae: otolithes ruber in January a.nd August); drif'tfiah (Ariommidae: Ariomma. indicus in January and August)j threadfin breams (Nemipterida.e: Nemipterus dela.goa.). -

Ma uto Ba : croakers (Sca.enida.e: various species, none prominent); driftfish e: Ariomma. indicus in August); breams (Sparida.e); Pagellus na.talensis gus , blueskin breams ( Sparidae: Polysteganua coeruleopunctatus in August).

The majority of the named species rarely exceeded. 30-50 kg/h but collectively they comprised the bulk of the "other demersal species" category.

(c) ~mobrauchs (sha.rks_t. r~ and skates)

Some species are very large, weighing 50-300 kg, and so even one or two specimens would outweigh the rest of the catch of fishes. Such large fishes would probably be more rarely captured in a smaller trawl than the one used during the survey. (i) Sharks

The largest catches of sharks were ma.de off Kenya. (below 200 m depth) a.nd in the south Zanzibar Channel ..

Off Kenya., sharks were dominated by the small milkshark (Scoliodon walbeehmi) (20-60 kg/h) with exceptional hauls of 99, 345 kg/h), the zebra shark (Stef}stoma fasciatum) (20-30 kg/hJ, and a sma.ll squalid shark (Centrophorus sca.lpratus (20-50 kg/h, one haul of 164 kg/h). Several species of carcha.rinid sharks generally of small size also occurred less frequently.

In the south Zanzibar Channel very large hauls of~ scalpra.tus ( 140-400 kg/h, \·tith one catch of 860 kg/h) were frequently taken, a.nd this species dominated the shark catches in .July. In November the angel shark, Squa.tina. africana, predominated with catches of up to 107 kg/h, £:. scalpratus becoming inuoh less common.

In Beira Bay and Maputo Bay sharks were not an important component of the catches and no one species predominated. The average weight of catch is very much influenced by inclusion of a few large Caroha.rinus sp. (60 to 90 kg ea.eh).

(ii) Ra.:i::;s and Skates The largest concentrations of :rays were also found in the northern parts of the African shelf, off Kenya (in less than 200 m depth), in the south Zanzibar Channel, and the west side of Pemba Channel. The predominant forms were stingrays, Da.sya.tis species. Off Kenya., large D. brevica.uda.tus {up to about 100 kg each) predominated in January, D. uarnak, ~aephen and fusyatia sp. (unidentified) in July and N?vember. The various Dasyatid ray species often furnished catches of 100-200 kg/h, with exceptional catches of 400-1 OOO kg/h in January, July and November,. Several eagle­ ra.ys (Aetoba.tis narina.ri), of 45-60 kg each, were also caught throughout the year. - 16 -

Smaller rays were regularly represented by the guita.rfishes (!!Jl,Ynchobatus djeddensis and Rhinoba.tos schlegeli) of about 10-20 ke weight. Stingrays were also the dominant form in the Ta.nza.nian region, represented by Dasya.tis brevicaud.a.ta, .E.! uarnak, Do sephen and Da.syatis sp. (unidentified) giving a similar range of catches to those off Kenya. Smaller species included the skate Raja ~, but this never exceeded about 30 kg/h.

In Beira Bay and I~puto Bay7 sharks were sparsely distributed and rays rarely exceeded about 30 kg/h, with the exception of two large sa.wfish (Pristis cuapidatus. (360 kg) and P. microdon (225 kg)), a large guita.rfish (Rhina a.ncylostoma.J (100 kg), a large stingray (E.!_ ua:rnak) (120 kg) and a haul of 130 kglh of R. djeddensis.

(d) Crustaceans

(i) Lobsters

~he spiny lobster Puerulus ca.rinatus was the dominant species in 200-250 m off Unga.ma Bay, Kenya, where catches of 20-60 kg/h were frequently made in June, July and Novembero Catches exceeded 100 kg/h on a. number of occasions.

This small spiny lobster was also oonunon in the Zanzibar Channel, north and south, west Pemba Channel, and on the north Mafia shelf at similar depthso However, catches off Tanzania never exceeded 5 kg/ho Further south this species was absent except for a single haul in Maputo Bay, which yielded 2 k~/h. Palinurus dela.goa was the most abundant spiny lobster in Maputo Bay and on the shelf between Beira Bay and Ma,PUto Bay, again at depths of 200-250 mo In Maputo ~ catches rarely exceeded 10 kg/h during January-February, one haul containing 50 kg/h. During August when a more intensive search for the lobster was carried outj the largest hauls were 100, 120 kg/h but the g-eneral level of catches was about the sa.rneo

Linupa.ris aomniosuao This large lobster was the dominant form in the south Zanzibar Channel and on the north Mafia shelf at depths of 250 m. Maximum catches of 45 kg/h were obtained in both areas, and catches of 15-25 kg/h were ~onunono The species was also caught off Unga.ma Ba;r, particularly during November but it rarely exceeded 3-4 kg/h here. It was not recorded in Mozambique waters at all.

_2ther spin,y lobsters. Small amounts of Puerulus ornatus were caught off Kenya 9 in Beira. Bayj Maputo Bay and on the shelf between the two bays. Po angulatus was also rare off Unga.ma Bay, in the south Zanzibar Channel a.nd the west Pemba Channel, where it was caught in January only.

Two species of ahovelnose or slipper lobster were widespread throughout the regiono Thenus orienta.lis . yielded 20-50 kg/h frequently off Kenya., and insig­ nificant catches in Tanzanian waters and Sophala Bay. It was not recorded south of Beira Bay. Ibaous novemdent&cus occurred from Kenya to Maputo Bay, similarly yielding the largest catches off Kenya. (but even there not exceeding 10 kg/h) 0

The Norway lobster (Nephrops a.ndama.nicus) occurred in the deeper hauls off Kenya., Tanzania (all area.a) and in Maputo Bay" Its main depth range was about 300-500 m but it also occurred at slightly lesser depths, up to 240 m. The yield was usually not more than 3-4 kg/h except off Ungama Bay in November, in the north Zanzibar Channel in July and off Mafia in July and November where a few hauls yielded 15-25 kg/h and one yielded 52 kg/ho The lack of records of - 17 -

N. anda.ma.nicus off Beira :Ba.v is presumably due to the impossibility of trawling at the required depths there; a similar explanation probably accounts for the general lack of spiny lobsters off Beira Bay.

(ii) Portunids Large portunids (swimming crabs) were sometimes caught in commercial a.mounts but the yields were generally small. The best catches were of Char;rbdis sp. (Kenya, 250 kg/h; Beira Bay, several of 10-20 kg/h), and Porttums sa.nguinolentis) (Beira Bay, 137 kg/h). (e) Acoustic Survey (i) Kenya

Acoustic surveys off Kenya revealed few dense aggregations of pelagic fishes, most of the patches shown in the charts being a mixture of scattered small demersal and pelagic fishes with estimated densities of 4-10 t/n mi2 (metric tons per square nautical mile). Exceptions include a sma.11 patch east of Pate Island in March (2l t/n mi 2), in about 50 m depth, another in 200-300 m south of Malindi (15 t/n mi 2) also in IoU:Lrch; and in November a. small dense aggregation, thought to be rouna... scad (Decapterus macarellus) in 200-300 m (a.bout 90 t/n mi) which could not be fished due to ro~gh bottom topography, and a narrow band of mixed demersal and pelagic fish (20 t/n mi~) lying between the 50 and 200 depth contours from south of Malindi across the mouth of Unga.ma :Bay. Most of such aggregations as were found off Kenya were restricted to a narrow band about five miles offshore, in 50-100 m. Dense plankton interfered with the signals during June; no fish aggregations were observed during January or July.. The total biomass indicated within the patches were 5.5 and 2.6 thousand tons in March a.nd June respectivelye (ii) Tanzania

There was usually a fairly continuous distribution of dense traces of pelagic fish throughout the Zanzibar Channel, where fishing with the cod trawl and also with the pelagic trawl confirmed the presence of anchovies (Stolephorus) and round- scad (Decapterus ma.ca.rellus). At the lower end of the south Zanzibar Channel, the distribution of the dense D.. maca.rellus schools was charted in July and November; it was found to extend over-a ~omparatively small area, about 50 mi2, with densities between about 25 and 80 t/n mi • Total biomass of fish indicated from calculations were of the following order: January, 16 OOO mt; March, 2 OOO rot; early July, 20 OOO mt; late July, 12 OOO mt; and November 18 OOO mt.

(iii) Beira Bay

In January and February (2 surveys) small pelagic fish, probably mainly round­ scads (Deca.pterus spp .. ) were fairly evenly scattered over the whole Bay down to about 75 m depths, with average densities of 5-10 t/n mi 2• A marked interruption in pelagic fish distribution was observed both times across the ~ just north of the position where the Za.mbesi River debouches into the Indian Ocean. Small, dense aggregations of pelagic fish were located at a few positions, with densities of 50-80 t/n mi2 in January but rather less, 19 t/n mi 2, in February. The total biomass of fish indicated from calculations were 98 OOO and 36 OOO mt in January and February respectively. In August there was considerable interference from dense plankton in the coastal zone. Apa.rt from this7 the fish were both small and dispersed, and so more likely to be masked by the plankton., Under these circumstances it is not practical to make a quantitative assessment. - 18 -

(iv) Maputo :Bay

During the January-February survey, there was a large area. of dispersed pelagic fishes, probably lanternfishes (Y.tvctophidae) in the southern part of the bay over ·deep water. The density averaged. a.bout 8 t/n mi2 and the estimated biomass of fish here, 7 OOO mt. There was a.lso a small concentrated area of roundscads and horse­ ma.ckerel schools to the north just below 200 m depth, where the density averaged 23 t/n mi2 a.nd the biomass was estimated at 3 500 mt. A small concentration of mixed pelagic and demersal fish was located in 50-100 m near the coast, averaging 9 t/n mi2 with an indicated biomass of 2 OOO mte

In August the scattering layer was fairly dense and widespread, but there we:re no dense aggregations of pelagic fish and trawling yielded few pelagic fishes.

B. Depths greater than 200 m

Along the seaboard of eastern Africa depths greater than 200 m produced low average catches of demersal fishes and hardly a.ny pelagic fishes. The predominant fish in the deeper water were lizardfish (Saurida undosqua.mis a.nd ~ tumbil) (Synodidae), the catch of which only occasionally exceeded 100 kg/h. These species also occurred higher up on the shelf (above 200 m) and they are of some economic va.lue.

Lizardfish usually formed up to 50 percent of the total demersal catch in the deeper water. However, the deeper zones did exceptionally yield large catches of demersal fishes, the outstanding example being three successive ha.uls offshore from Unga.ma Bay, Kenya, in June, which yielded the hairtail (sablefish, ribbonfish) (Trichiurus lepturus (Trichiuridae)) at 1 2007 3 OOO and 3 300 kg/ho At no other time did this species exceed 60 kg/h in any region, and so it seems tha.t these were luc~catches, in that they located a rapidly migrating dense post-spawning aggregation of hairtailse

4. Oceanic Banks

A. Seychelles Bank and Sa.ya de Malha :Bank

(a) Pelagic fishes

(i) Carangidae

In April 1976 few trawl ha.uls were carried out on the Seychelles plat.flau. Two hauls contained small amounts of round.scad (~capterus macarellus and a Kiliche while the larger cara.ngids (Seriola spp., Gnathondon sp., and Carangoides app., appeared to be widespread but not present in large amounts. On the fuya de Malha Bank in April two large catches of mixed ca.ra.ngids - roundscads ~ kiliohe and D. macarellus) and horsemakerel (Trachurus trachurus) in more or less equal amounts, totalling 1 600 kg/h and 800 kg/h - were ma.de in 65-85 m depths, in the north­ western part of the Bank. A third ha.ul in the southeastern part yielded 335 kg/h of a similar mixture of cara.ngid species. Elsewhere the Sa.ya de Malha. also yielded these three species but in smaller a.mounts, perhaps because much of the sampling was at night-time. Few of the larger ca.ra.ngids were caught.

In October the level of catches was consisten.tly high in all parts of the Seychelles plateau, the predominant species being 12.!. kiliche. Two hauls exceeded 5 OOO kg/h of this round.scad, 13 between 1 OOO and 4 OOO kg/h, and several others from 500 to 1 OOOkgjh. The roundsca.d D., ma.carellus occurred less frequently, the largest catch being 724 kg/h. A form of Decapterus i·1hich was not full,Y identified, but which is probably closest to .E!_ kiliche, contributed up to 220 kg/h on several occasions, as did the horeemackerel (Tra.churus trachurus). The larger carangids (~ crumenophalnms and Seriola sp.) were occasionally caught in small amounts. - 19 -

In October the carangids were concentrated in the central parts of the Saya de Ma.lb.a Bank in 80-90 m depths. The catches were a mixture of roundscads (D. macarellus, E.!. kiliche) a.nd horsema.ckerel (Trachurus indicus), with the latter species predominating and yielding 210-538 kg/h in several hauls. D. macarellus was scarce on the Saya de r.'lalha. Bank. Apart from this, other parts of the Bank yielded very little in the way of carangids.

An important point to note is that the great majority of the roundscad (Decapterus kiliche) caught on the Saya de Ma.lha Bank and on the Seychelles plateau was small, immature specimens. Very few large mature specimens of either this species or of D. macarellus were caught in either April or September-October. The probabilitY:-is that the larger, adult rou.ndscads inhabit the deeper parts of the oceanic ba.nks, below 100 m depths, just as was the case in the coastal waters, and these deeper regions are generally not fishable with bottom trawls, especially on the Seychelles plateau where the edge falls off steeply. (ii) Scombridae

In April no soombrids were recorded on the Seychelles plateau and Saya de Ma.lha :Bank. In October the Indian mackerels Rastrelliger brach,ysoma and Ro kanagu.rta were infrequently caughtt the former being most abtuldant on the Seychelles plateau where one catch included 0.5 t/h of R. brac1lysoma. The mackerels were sparsely distributed on the Sa.ya de Malha Bank.

(iii) Clupeidae a.nd En.graulidae

The smaller schooling pelagic fishes were only caught in trace amounts on the Seychelles plateau and Saya de Malha Bank., The main species caught were the oil sardinella (Sardinella sirm) and the Indian anchovy (Stolephorus indicus) in April and October.- ""' - .

(iv) other. Pelagic Fishes

A few barracuda ('I'.hyrsites ~) appeared :l.n the trawl catches in the central pa.rt of the Saya de Ma.lha Bank in October.

(b) Demersal fishes (i) Lutjanid.a.e

Snappers were the predominant type of demersal fishes on the Seychelles Bank but were of little importance except locally on the Saya de Malha Bank and virtually absent further south.

The red snapper (Lut,;anus sebae) was by far the most abundant. The majority of ha.uls in all parts of the Se7chelles Bank yielded up to 50-100 kg/h of L. sebae, and several yielded 200-400 kg/h in both April and October. Very few blood snappers (6. sanguineus) were caught and catches of this species did not exceed 25 kg/h. The green jobfish (Aprion virescens) was widespread on the Seychelles Bank and frequently gave catches of up to 20-30 kg/h with two large hauls, 147 and 205 kg/h in April.

The very small species L. lineolatus was also widespread on the Seychelles Ba.nk, yielding usually up to25 kg/h and occasionally 60-120 kg/h. L. sebae wa.s the only snapper of importance on the Sa.ya de Ma.lha. Bank, but it was not often caught.

On the Nazareth Bank, one haul yielded 48 kg/h of Etelis ca.rbunculus, and on St. Brandon 23 kg/h; these apart, catches of snappers on the southerly oceanic banks were negligible. - 20 -

(ii) Spari dae

Breams were tmimportant on the oceanic banks except in the middle depths of the Saya de Malha Ba.nk where the blueskin (Polystega.nus sp.) was the predominant demersa.l fish. In April, ~ coerUleopunctatus occurred, though not very abundantly, in the central part of the Sa.ya de Ma.lb.a Bank.

In October, two species of f2.lyatega.nus, neither of which could be identified with certainty, were found in the southwest at depths of 100-165 m1 and on the east of the Bank at depths of 170-200 m. Of the two, one wa.s a large species with individual specimens of 3-5 kg or more, and the other a sma.11 species, averaging about 100 g each. Catches on the east included up to 300-400 kg/h of both species; in the southwest, 20-80 kg/h of both species with three large catches of the sma.ller species, 130-500 kg/ho (iii) Nemipteridae

Threa.dfin brea.ras were represented by three species (Nemipterus peroni 7 N. delagoa and N. nemurus) of which the last two were sparsely distributed both Ori the Seychelles.Bank a.nd on the Saya de Malha Bank. Catches of up to 60-80 kg/h of Nemipterus were quite common on both Ba.nks, especially in the shallower parts of Seychelles and in the centre a.nd northwest of Sa.ya de Malha. Exceptionally, hauls of 100-170 kg/h were also obtained, the largest being 260 kg/h of !!.:_ delagoa on the Seychelles in April. (iv) Synodidae The only lizardfish of importance was Saurida undosqua.mis, which was wides­ pread on both the Seychelles Bank and Saya de Ma.lha. 1 despite the comparative shallowness of both these Banks (compared to the coastal region). Catches in the range 50-200 kg/h were frequent on both these Banks, with a few larger hauls.

(v) Mullida.e

Goatfishes were widespread on the Seychelles Bank and were represented by several species of which Pseudupeneus seychellensis and Upeneus molluccensis were the most abundant, with catches usually in the range 20-80 kg/h. On the Sa.ya de Ma.lha Bank the commonest species was u. molluccensis with several catches of 50-100 kg/h but goa.tfishes were only commonly fomid in the central part of the Sa.ya de Ma.lha Bank, together with the r0UJ1.dsoa.ds (Decapterus sp.) a.nd horsema.ckerel (Trachurus).

(vi) other Tiemersal Fishes

On the Seychelles Bank, the largest fraction of "other" demersal species was the crocodile fish (Peristedion a.deni) which, however, appeared infrequently although yielding oat.chea of up to 30-120 kgfh at times. On the Saya de Malha Bank, most of the balance was ma.de up of the triggerfish (Aba.listes stellaris), yielding 20-40 kg/h with one catch of 199 kg/h. otherwise the balance was made up of a large number of species none of which appeared very frequently or in any large amounts.

(c) Elasmobranchs Catches of this category on the oceanic banks were very light compared to those off Kenya and Ta.nzania 7 the most notable difference being the small numbers of large stingrays, Dasyatis spp., caught. - 21 -

(i) Sharks

The small caroharinid shark (Loxodon macrorhinus), averaging 1-2 kg ea.eh, was the dominant shark on the Seychelles Bank giving catches usually in the range 20-50 kg/h. The balance was mostly made up of a few single specimens of Carcharinus spp., averaging 20-50 kg ea.eh.

On the Sa.ya de Ma.lha Bank so few sharks were caught that no one species really predominates, the most numerous being the milk shark, Scoliodon walbeehmio The balance was again mostly Caroharinus spp. a.s single specimens.

On the southerly oceanic ba.nks 7 sharks were very rare a.nd were chiefly represented by large Carcharinus spp.

(ii) ~ Stingra.ys (Da.sya.tis spp.) were caught as single specimens, usually weighing 100-185 kg each, but rather infrequ.entlye (d) Crustaceans (i) Lobsters The spiny lobster (Puerulus carinatua) yielded catches not usually exceeding 4-5 kg/h (adjusted) in the southern a.nd <:astern parts of the Saya. de Mallia Bank, although a few catches in both pa.rte were in the 15-20 kg/h range. This species was rare on the Nazareth Bank and was not recorded from the Seychelles Bank (probably because of the inaccessibility of suitable depths) or from the ba.nks to the south of Nazareth.

During Cruise 59 an attempt wa.a made to locate spiny lobster concentrations in various areas on the south a.nd ea.at sides of the Saya de Malha Ban:k: and Nazareth Ba.nk, which at the time were being exploited by small u.s.s.R. trawlers. But the lobsters were not found in corrunercial concentrations.

Apart from P. carina.tus·, only the shovelnose lobsters, Thenus orientalis, a.nd Ibacus novemdentacua, deserve mention on the oceanic ba.nkso Catches were very light, rarely exceeding 2 kg/h but both species occurred on all the banks from Seychelles to Soudan. (ii) Fortun.ids A few large catches (40-48 kg/h) of Tha.lamita sp. were ma.de on the east side of Saya. de Tlia.lha Bank.. otherwise portunids (swirruning crabs}-were rarely recorded from the oceanic banks; no records were obtained from south of the Saya. de Ma.lha Banko

(e) Acoustic Survey During the April 1976 cruise (Cruise 2), the MllSYATSEll cut a number of transects across the oceanic banks. Dispersed pelagic fishes were encountered on Soudan Bank and Nazareth Bank. There were more dense schools over the Saya de Ma.lha Bank where pelagic fishes gave large catches, and also traces of ma.inly bottom fishes on the Seychelles Banko More intensive acoustic surveys were carried out during September-October (Cruise 5), particularly on the Seychelles Bank and Sa.ya de I'1a.lha Bank. On the more southerly OOJ:iks, there were no indications of pelagic fish aggregations a.nd 9 as the trawling results showed, pelagic fishes were scarce. - 22 -

(i) Seychelles Bank

Schools of pel~c fishes, principally rou.ndsca.ds (Decapterus) and anchovies (Ehgra.ulis japonic~J were registered within 2-6 m above the bottom during the day-time. Individual echoes from.snappers were also recorded. The schools of pelagic fishes occasionally spread to 20-30 m above the bottom in the day-time. Scattered small fish (or squids) were also registered almost everywhere in the surface layers0 At night, the fish schools were observed to disperse towards the surface lavrers and arry that remained near the bottom gave only s11Bll catches of small demersal species.

Fish were fairly uniformly distributed over the whole surface of the Seychelles Ba.nk 9 with few areas of rela.tively dense aggregations. Trawling showed roundscad (Decapterus kiliche) to be the dominant pelagic species, and the red snapper (fut,; anus ~) to be the dominant demersa.1 species.,

Average densities were 10-12 t/n mi2 9 a.nd the total estimated biomass of fishes 115 OOO rrrt.

In ma.ny parts of the Seychelles Ba.nk, the generally level bottom topography is disrupted by numerous knolls, rising 20-30 m above the sea.bed and perhaps a few hundred metres across., Small schools of small fish were usually observed "clinging'' to the sides and top surface of these knolls, but since no trawling could be carried out in these areas the fish could not be identified.

(ii) ~ de Malha. Bank The main concentrations of pelagic fishes were observed in the central part of the Saya de Malha. Bank, where rOWJ.dsca.ds (DecaJ;>terus kiliche and B.it. ma.carellus) and horsemackerel (Trachurus indicus) were fairly evenly distributed according to the trawling survey" Over an area of about 360 mi 2 the average density was about 19 t/n mi2 so the biomass there was about 7 OOO mto In other regionsv the same species also predominated with average densities of 7-16 t/n mi2? except on the ea.stern edge of the Ba.nk where the blueskin seabream (Pol7ste~us spo) was the dominant species and where the average density was about 33 t n mi o ·

In the central area about 20 hauls Hith the cod trawl, combined with echo integration, were made in a.n attempt to determine what fraction of the total population migrated up from the seabed at night.

In the south pa.rt of the ~ de I·lalha. Bank 1 ~ discrete and apparently massive schools of fish were observed in mid-watero These were identified, by towing the cod trawl through mid-water, as small porcupine fish ( Diodon ma.culifer)" The schools probably seemed more massive than they really were, due to the high target strength of this species., B., Amirantes Bank and Southern Banks

On the Amirantes Bank there were few areas suitable for trawlingo The only pelagic fishes caught were the round.scad (Deca;g!:erus kiliche) (68 kg/h) and trace a.mounts of the larger carangidso

The more southerly oceanic banks - Nazareth J3ank 9 St. Brandon Bank and Soudan Bank - were also practically devoid of pelagic fishes, apart from trace a.mounts of roundscads (~ macarellus and D,. kiliche) a.nd the larger cavallas · (Cara.ngoides spp,.). - 23 -

8 0 STANDING STOCK OF FISHES AND POTENTIAL IlELD

The following estimates of standing stock should be regarded as very preliminary, since they are based upon comparatively small a.mo:unts of fishing effort which, moreover, could not be distributed fairly over the whole grounds due to the frequent occurrence of hazards such as rocks or coral outcrops. The figures are based entirely upon the results of fishing with the cod trawl, not corrected for efficiency of the trawl, and they represent that part of the biomass which was vulnerable to the type of trawl used during the survey.

standing stock is given by the formula.:

standing stock = mean density x area (in 1 000 mt) (in mt/ n mi2) (in n mi2)

The area of ground within certain depth contours was calculated by planimetering, on large-scale British Admiralty charts (sea.le. 1:300 OOO where available) but the paucity of depth observations over much of the survey area must affect the accuracy of these estimates. This is particularly true of the Seychelles-Mauritius Ridge, except for the Seychelles Bank. Having planimetered the total area. enclosed by9 say the 25, 100 and 200 fathom contours on the charts, graphs were constructed from which the area within any desired metric depth range could be interpolated. These readings are summarized in Table 16.

The mean density of each category of fish was calculated from the mean catching rates of Tables 3-15 1 as explained in Secti6n9 (vi); that is to say, on the basis that the effec­ tive sweep of the cod trawl was the distance, 16.4 m, from wi.:ng-end to wing-end, and that the average speed of towing was four knots. Under these cond.i tions, the trawl would have swept on average an area of 0.035 n mi2 per hour, so the density of fish is given by the formula:

density of fish .. 1 I -3 0.028 x kg/h (in mt/n mi2)· o:o35 x kg h x 10 = The estimated standing stocks by categories are given in Table 17 on a regional and seasonal basis. Separate figures are given for the North Kenya Barile (20-200 m depth), for a region of similar depth adjacent to Unga.ma. Bay, and for the whole offshore region of Kenya. These regions have areas of 870, 300 and. 860 n mi2 respectively. Table 18 is a swnmary of the biomass estimates on a regional basis. Finally, potential yields were estimated from the data in Table 18, assuming that, as currentlv fished, they represent the virgin biomass of the stocks, B0 in the formula:

Y i::: 0 .. 5 x M x Bo - where Y"' potential yield; M = annual na.tura.l mortality

This formula is the one employed by Gulla.nd (J.A. Gulland: The Fish Resources of the ?cean. FAO(Fishing News (Books) Ltd., 1971). The natural mortality of marine commercial fishes 1n th~ trop1~al Indian Ocean is not known, so a range of values of M (M = 0.2, 0.3, 0.4) was substituted in the formula, to give the estimates of potential yield contained in Table 19 0 A. summary of the average present day annual landings by each country is given for comparison with the estimated potentials in Table 20. ' Of the national fishing activities undertaken in the area, the major part is carried. out in inshore waters which, because of the size of the vessel, could not be surveyed. The potential yield estimates are therefore for fishing grounds other than those presently exploited and poten­ tial yield estimation should be accepted in addition to the current total annual fish landings.

In Kenya and Tanzania there appears to be some limited scope for expansion of the fishe­ ries beyond the zone which is currently exploited by the artisa.nal fishingQ In the case of Mauritius and the Seychelles, it is not possible to apportion present day landings to the various banks which are fished also by men from Reunion. But the overall potential for the Seychelles-Mauritius Ridge is apparently quite considerable. - 24-

9. TABLE.3 OF ME!AN CA1l1CH (Tables 3-15)

Ex.planatOI"J Notes

(i) In prepa.ring the following tables, the catch in each haul was first adjusted to units of kilogrammes per hour trawling (kg/h)o The maa.n catching rates are based upon all valid hauls with the cod trawl onl;y~ excluding as non-valid hauls for this p-..u'pose those w:i.th a duration of under 30 mirmtesy and those i.n which the net was sufficiently badly damaged to enable part of the catch to bG lost o

(ii) In certain areas it was considered appropriate ·i;o presen·l; avere,ge catches for either sepa-rate depth-ranges (e .. g., Ken,ya.) 7 or sub-areas (eog" Saya de Malha Bankt Seychelles Bm-lk)~ or omHting night-time hauls in the case of pelagic fishesQ

(iii) Ea.eh table gives the total catch by major groupings: elasmobra:nchsv pelagic and demersal teleosts9 crustaceans; an~ certain domina..~t families of pelagic or demersa.l teleosts@

(iv) Choice of the families to be represented by name in the tables does not imply that other fo.milies may not be of commercial importa.noeo Generally spea.kingv there are fei-1 species of fish which are not consumed in some Indian Ocea.11 country 9 but the overall species list resulting from the whole survey includes well over 500 speciesg only a fraction of which were common and important enough to deserve mention.,

( v) The narrowness of the conU11ental shelf? or of certain depth stra.ta~ and the rugged nature of the sea.bed, often precluded any patterned or stratified sampli:o.go 1I'he average values given in the ·tables of this report are not weighed according to any principle of proportional representation..

( vi) Iltu-ing Cruise 2 (April 19·(6)~ large fingernail-shaped t1•aces wis:re often ooserved on the Simract recording papero The number of these traces lying within ·i;he d.i.sta.nce bett.,-.een the trawl doors w-i:1.s counted.. In seven hauls~ ·there were on average almor.:1t exactly four times as many of these traces between the doors as thel"e were lai~,ge sn.;,ppers in the catchg and the degTee of correspondence between the counts of ·l:::ca,ces and of snnppers was very closev Since the average distance between the doors is fo1.ir times that between the wi!lg'-ends, it is a. reasonable e..seump-Uon tlw,t the effective width of the cod trawl was equal to the spread between its wings; in other wo1~1.h:i,1 that there ws no net driving effect of the gear outside the wing-ends - b1~idles~ doors9 etc, ;.. n1ile this is &'1 unorthodox method of assessing the trawl' s effectj.v

been assumed that the path swept by 't:he cod trawl was ·1604 m wi.de 1 and that swept by the lobster trawl 50 m wide; 16.4 m is 0,,00885 nautica.1 mileso So wi·th an aver~,ge speed of towing t of 4 knots, the total area swept by the cod ·tra.wl W01:).],d be Oo 0354 n mi 2 o

So the mean catch in kg/h is converted into e. density as follows.1/ 0

kg/h x 00028 "" metric tonnes/n mi 2 or kg/h x 0.,0823 "" kg/hectare

For the lobster trawl, similar calculations give the following conversion factors~

kg/h x 0.,0092 .., metric tonnes/n mi2 kg/h x 0 .. 027 "" kg/hectare

Baaed upon ·the following factors: wing-to-wing spread, 16o4 ffii -1 km = Oo6214 mi Oo540 n r.li; 1 hectare (ha) "' 10 OOO m2 "' 0.,01 km2" - 25 -

Comparison between the two trawls is valid only for lobsters because of the different oharacteristics of the trawls. Lobsters probably had a better chanoe of es.caping capture by the cod trawl because the footrope wa.s raised up from the ground by its bobbins. But because of .its smaller _width of swept path, a ca.toh of 100 lobsters by the cod trawl is probably equivalent to at least 50/16.4 or three times as many in the lobster trawl. 100 DISJ:RIBUTION CHARTS

Ricplana.tory Notes

(a) Results of Trawl Survey (Figures 4-40) ·

For most regions the results of all the surveys are combined. The charts show the positions of trawl stations a.s circles, different symbols being used to indicate relative catch size in either kg/h or t/h in such a way that it can be seen at a glance where the -oest catches were obtained; and whether they tend to be concentrated in particular areas or evenly distributed,

The scale of catch rates is varied to suit the range for ea.eh a.rea or group of fishes as represented.

Hauls which were aborted because the tra.wl came fast, or which 1·rere not valicl. as defined above, a.re shown by crosses, except where they coincide with another valid haul. Not all stations could be shown in the more intensively fished areas. (b) Results of Acoustic Survey (Figures 41-53)

The charts show the cruise track of the vessel during each acousti~ survey. Patches within which significant amounts of signals were recorded from fishes are outlined and cross-hatched. No quantitative significance is given to these aggre­ gations., Depth contours on the charts a.re in metres. - 26 -

Table 3. .KllNYA - Summa.r,y of Mean Catch ~ates by Categories~ Season and .Depth Range (in kg/h)

(a) 1:z-200 m depths

1976 1977 January March June July November

rJ} 15 11 9 14 6 Total ELASMOBRANCHS 74 :!:. 100 121 ±. 197 117 ±. 122 476 ±. 411 369 :t 258 Sharks 14 21 12 17 95 Rays 60 100 105 459 274

Total PELAGIC FISH 79 ± 138 31 t. 40 100 ± 134 257 ± 515 109 ± 78 Ca.ra.nef dae 52 13 81 190 97 Scombridae 24 9 5 38 ·I- others 3 9 14 29 12 Total DEMERSAL FISH 419 t. 629 230 ±. 233 297 ± 362 452 "!:. 652 863 ±. 948 Lutjanid.ae 33 45 + + 7 Lethrinidae + 13 + + 10 Serranidae 7 19 + + -:- j Sphyraenidae 81 + + 87 74- Leiognathidae 114 11 19 35 '112 Poma.dasyidae 24 42 46 22 299 Nullid.ae + + 7 106 163 Nemipteridae 7 + 24 11 ~- Synodidae 13 6 29 15 16 others 133 88 166 171 181

J/ n = total number of valid hauls. Figures in Tables 3-15 are mean catching rates in kg/hi standard deviation is given for major groupings. - 27 -

Table 4. KFJ.r!A - SUmma.J::;y. of Mean Ca:tch Rates by Cate.6.ories.1 Season and Dejlth Ran~ (:i,n kg/h)

(b) 200-400 Ill degt;hs

1976 1977 January Ma.rch June July November

~ 4 9 7 10 1

Total ELASMOBRAlilCHS 559 ± 99 42 ± 36 20 .i 22 45 .± 58 11 Sharks 56 29 9 25 9 Rays + 13 11 20 + Total PELAGIC FISH + 43 ± 87 105 ± 205 10 .t 17 0 Carangida.e 43 105 10 Total DEMERSAL FISH 74 .:t 114 66 ± 6G 76 .± 53 132 ± 49 45 Synodidae 28 25 11 38 23 others 46 41 55 94 22

1/ n "' total number of valid haul1. - 28 -

Table 5o TANZANIA (SOUTll ZANZIBAR CHANNEL) - Su.mma.ry of Mean Catch Rates by Categories, Season and Depth Range (in kg/h)

50-200 m 200-300 m 300-500 m

July November January July November Ja.nuary, July, November n(n)Y 11(5) 1 1 13(7) 10(8) 8

+ Total ELASMOBRANCHS 117 - 98 82 40 246 2: 255 92 ~ 38 11 + 9 Sharks + 35 196 24 + Rays 116 82 5 50 68 11

Total PELAGIC FISH 207 ! 277 + 1 460 2 066 :!;; 1 095 1 542 :!: 897 + Ca.ra.ngi dae 160 + 1 458 2 062 1 542 Clupeidae 27 Scombridae 20 + + +

Total DEMffiSAL FISH 225 ! 355 132 628 229 :!: 197 312 ! 186 90 ! 63 Lutjanidae 136 69 + Lethrinidae 7 12 Serra.nidae 11 + Synodid.ae + 392 27 84 9 others 71 51 236 202 228 81

.!/ n = total number of valid hauls; (n) "" number of daylight hauls (0700-1800 h), valid for pelagic fish,. - 29-

Table 6. TANZANIA (Cll'H1lR REJIONS) - Summa.ry of Mean Catch Rates by Categories and Depth Range (in kg/h)

(a) Shallower than 200 m

North Zanzibar North Pemba West Peinba Channel· Shelf Channel

months Ja.n., July, Nov. July, Nov. Ja.n., July, Nov,.

depth range 30-200 m 170-200 m 180-200 m n1I 7 3 2

Total ELASMOBRANCHS 163 ±. 117 95 + Sharks 151 95 + Rays 12

Total PELAGIC FISH 85 :!: 95 118 17 Carangida.e 66 118 17 Scombrida.e 13

Total DEMERSAL FISH 226 ± 125 157 33 Lutjanida.e 12 107 + Serranida.e 18 38 32 Sphyra.enidae 10 Leiogna.thida.e 19 Poma.dasyida.e 10 Ivlullidae 17 Nemipteridae 9 Synodida.e 30 others 101 22 +

1/ n = total nwnber of valid hauls. - 30 -

Table 7. TANZANIA ( armR RJIDIONS) - Sunuqa.:rJr of Mean Catch Rates by Depth Range {in kg/h)

(b} Deeper than 200 m

North Zanzibar North Pemba West Pemba North Mafia Channel Shelf Channel Shelf

months Ja.n., July, Nov. July, Novo July July, Nov.,

depth range 200-330 m 200-350 m 200-360 m 200-400 m

nY 4 6 1 9

Total ELASMOBRANCHS + 48 ± 65 151 40 :t 47 Sharks + 48 17 33 Rays + 134 7

Total PELAGIC FISH 0 + + +

Total Dl!MF.!iSAL FISH 200 t 28 :t 41 116 131 :!: 101 Synodidae 47 + + 51 others 153 28 116 80

1/ n = number of valid hauls. - 31-

Table 80 MOZAMBIQUE, BEIRA BAY - Summary of Mean Catch Rates by Categories, Season and Depth (in kg/h)

0-50 m 50-100 m

January 1 76 August '77 January 1 76 August '77 n(n)Y 24 (11) 51(16) 8(6) 24(16)

Total ELASMOBRANCHS 16 ± 21 32 :!: 74 15 :.!" 14 24 :!: 26 Sharks 14 7 13 14 Rays + 25 + 7 + Total PELAGIC FISH 369 .! 539 105 - 140 160 ~ 215 468 :!.: 731 Ca.rangidae 164 52 150 396 Clupeidae 94 24 29 Scombridae 111 34 10 33

Total DEMERSAL FISH 231 .:!: 364 123 ::- 98 190 ! 194 167 ! 156 Lutjanidae 16 + 58 12 Lethrinidae + + + 7 Serra.nid.ae 6 + 23 + Sphyraenidae 6 + 6 + Leiognathidae 26 7 + Pomadasyid.ae 10 6 10 6 Mullid.ae + 25 + 39 Nemipteridae 18 + + 10 Synodidae 34 17 6 14 others 121 71 87 80

.:!/ n = total number of valid hauls; (n) = number of daylight hauls (0500-1900 h) valid for pelagic fish. - 32 -

Table 9.. CENTRAL MOZAMBIQUE (BEI'WEllI BEIRA BAY AND MAPUTO BAY) - Swnma:cy of Mean Ca.tch Rates (in kg/h)

(Including 1 hauls in Janw 1916 and 11 in Awmst 1

n1I 18

Total ELASMOBRANCHS 12 ~ 8 I

Total PELAGIC FISH 18 !. 54 Ca.ra.ngidae 13 Scombrida.e 5

Total DEJ.1ERSAL FISH 66 ! 46 Serra.nida.e + Speyraenida.e and Mullidae Synodidae 11 others 55

2/ n = total nwnber of valid hauls. - 33 -

Table 10. MAPUTO BAY - Summary of Mean Ca.tch Rates by Ca.tegory, Season and Depth Range (in kg/h)

depth range 25-200 m 200-300 m 300-530 m Jan. & Jan. •76 Aug. Ja.n. Aug. '76 month/year '77 '76 '77 Aug '77 n(n)..!/ 4(3) 8~5} 6~3J 4~4' 17

+ + + + Total ELASMOBRANCHS 48 - 42 38 - 53 46 .:: 48 12 - 8 17 - 31 Sharks 26 34 43 77 8 Rays 22 + + 5 9

Total PELAGIC FISH 168 ! 438 48 :!: 75 642 :!: 1 041 + + Ca.rangidae 199 30 637 + + Scombridae 70 17 +

Total DEMERSA.L FISH 210 :!: 115 173 :!: 110 135 :!: 163 206 :!: 84 32 :!: 32 Lutjanidae + 23 Lethrinidae 1 Serranidae + 5 Spbyraenida.e 6 + Mu.llida.e 11 + Synodidae 39 + 49 28 + others 147 145 86 178 32

j/ n = total number of valid hauls; (n) number of da\Y'light (0700-1900 h) hauls valid for pelagic fish. - 34-

Table 11. SEYCHllLLE3 BANK - Summary- of Mean Catch Rates by Categories (kg/h)

(a) April 1976

n(n).1/ 12( 10) + Total ELASMOBRANCHS 44 - 46 Sharks 26 Raye 18

Total PELAGIC FISH 40 - GO Ca.rangi.dae 40

Total DEMERSAL FISH 285 ::!: 201 Lutjanida.e 175 Sarranidae 18 Mullidae 9 Nemipterida.e 25 others 58

2J n "' total number of valid hauls; (n) m number of dai}"light hauls valid for pelagic fish. - 35 -

Table 12 0 SEYCHELLES BA!ll( - Summary: of Mean Catch Ra.tea by Sub-areas (in kg/h)

(b) October 1977

Sub-arey mr NE SW SE (near )Y SE (far )Y Total 1 n(n) 10(9) 3( 1) 21(14) 16(9) 9(6) 613/ (39) - Total EL.ASlIOBRANCHS 33 .:!: 20 15 :!: 1 212 33 .:!: 23 65 .:!: 96 26 .:!: 38 . 38 :!: 55 Sharks 32 15 33 64 26 38 Rays + + +

Total PELAGIC FISH 890 .! 1 217 1 420 1 423 .! 1 667 717 :!: 795 2 478 :!: 3 503 1 236 :t 1 746 Carangitlae 890 1 420 1 383 717 2 478 1 222 Scombrida.e 38 + Total DJ!l.IERSAL FISH 121 - 43 159 :t 123 197 :!: 145 224 :!: 191 180 :!: ·126 1E6 :!: 143 Lutja.nidae 61 71 56 107 117 80 Lethrinidae + 7 7 + Serra.nidae + + 9 r.Iullidae 9 + 26 8 15 Nemipteridae + + 18 10 13 Synodidae 6 + 37 54 13 33 others 45 --81 53 45 41 45

:1/ n = total nwnber of valid ha.uls; (n) .. munber of daylight hauls (0600-1700 h) valid for pelagic fishes. Y SE (near) or (fa.r) - nearer to or farther from Mahe Island. JI Total includes 2 hauls on south edge of Bank. - 36 -

Table 13 0 SAYA DE .MALHA BANK - Summary of Mean Catch Rates by Categories and Dep-th Range (in kg/h)

(a) April 1976

depth range 20-200 m 200-270 m n(n)Y (15)7 2 ,.. Total ELASMOBH.A.NCHS 40 .:!; 100 25 Sharks 20 I Raya 20

Total PELAGIC li'ISH 402 :!: 620 0 Carangidae 402 + Total D:EMERSAL FISH 127 - 122 38 Lethrinidae 14 Nemipteridae 17 + Synodida.e 33 20 others 63 18

y' n total number of valid hauls; (n) number of fu\ylight hauls (0500-1800 h) va.lid for pelagic fiahe - 37 -

Table 14. SAYA DE MALHA BANK - Summary of Mea.n Catch Rates by Sub-area a.nd Depth Range (in kg/h)

(b) October 1271

Sub-area Central SW N~l East n(n).1/ 20(13) 16 8 11

Depth range 70-110 m 100-165 m 50-75 m 170-200 m + + + Total ELASMOBRANCHS 22 - 48 50 - 96 21 ~ 45 12 - 12 Sharks 5 25 5 9 Rays 17 25 16 + + + + + Total PELAGIC FISH 560 - 478 26 - 36 14 - 33 10 - 17 Cara.ngi dae 582 25 14 10 others 8 + + + Total DEMERSAL FISH 289 - 191 145 - 166 85 ! 72 172 ! 335 Lutjanidae + 24 I Mullida.e 32 + + + Nemipteridae 44 + 17 + I t Synodontidae 149 17 + + Sparidae 71 121 others 73 57 44 51

j/ n = total number of valid hauls; (n) = number of daylight hauls (0600-1800 h) valid for pelagic fish. - 38-

Table 15. SOUTHli.RN MASCARmE RIDGE - Summary of Mean Catch Rates by Depth Range (in kg/h) - (including hauls during April 1976 (Cruise 2) and September-October 1977 (Cruise 5) on Soud.an Bank, st. Brandon Ba.nk and Nazareth Bank)

Depth range 40-200 m 200-400 m nY 9 15

+ Total ELASMOBRANCIIS 67 ~ 163 12 - 18 Sharks 65 6 Rays + 6

'l'ota.1 PELAGIC FISH + + + + Total DEJ:.'II!RSAL FISH 75 .... 93 16 - 17 Lutjanidae 9 + Pomadasyidae 5 Others 61 16

:J./ n = total number of valid hauls. - 39 -

Table 16. Swmnary of Shelf and Bank Areas (inn mi2)

Depth from Ke:)a N.Z.Ch. S0 Z.Ch. Beira Ma.puto Seychelles S.d.M0 South *20 m to (a (b) (c) Bay Ba.r (d) Bank* Banks** (e) (f)

50 m 470 425 215 8 500 1 OOO 1 950 100 m 820 515 275 9 Boo 2 600 4 950 4 860 3 840 150 m 1 020 575 325 3 OOO 8 OOO 8 360 6 640 200 m 1 170 635 385 10 300 3 400 11 100 11 660 9 440 250 m 1 350 695 435 3 800 300 m 755 485 4 200 17 360 15 240 350 m 815 535 400 m 2 030 17 660 18 640

500 m 17 960 18 840

* Area leas than this depth not measured ** From 30 m depth only (a) North Kenya Bank, 20-200 m, 870 n mi2 (b) North Zanzibar Channel (c) South Zanzibar Channel (d) Seychelles: very diffioult to draw contours excluding regions shallower than 20 m since the bottom is very uneven and the shelf is surrounded by a shallow rim (e) Saya de Malha Bank, to 12°30 1 s (f) Nazareth Bank and Ca.rgad.os Ca.rajos Bank, 13°s to 17°30 1 S - 40 -

Table 17.. fil:ltima.tes of Standing Stock of Fishes by Regions, Depth-range and Season

(in 1000 metric tons)

1. KENYA

(a) 20-200 m adjacent to Ungama Eay (300 n mi2)

January Ma.:roh June July November Pelagic o.s 0.4 0.7 2.2 0 .. 9 Demers al 3.3 1.9 3.7 3.8 7.,3 Sharks/rays 0.4 1.1 1.3 4.0 3.1 Total 4.5 3.4 5.7 10.0 11.,3

(b) 20-200 m1 North Kenla Eank (870 n mi2) January March June Pelagic + 0.2 3.3 Demersal 13 .. 1 5.9 4.7 Sharks/rays 3.9 2.6 1.1 Total 17.0 a.1 9 .. 1

(c) 200-~0 m de2th (86o n mi2)

January March June July Pelagic + 1.0 2.4 0.2 Demers al 1.7 1.5 1.7 3.0 Sharks /rays 1.3 1.0 0 .. 4 1.0 Total 3.0 3.5 4.5 4.2

2., TANZANIA North Za.nzi bar Channel* South Zanzibar Channel 30-200 m 50-200 m 200-300 m (660 n mi2) (170 n mi2) (120 n mi2) July July November

Pelagic 1.6 1.. 0 7.,0 5o2 Demersa.l 4.2 1.1 o.,8 1.1 SharkB /rays 3.0 o.6 o.a 0.,3 Total a.a 2.7 8.,6 6c6 * January, July and N9Vember combined - 41 -

Table 17 (cont.)

3o MOZAMBIQUE a. - Beira Ba.y 20-50 m 50-100 m (8 500 n mi2) (1 300 n mi 2) January August January August Pelagic 88.6 25.2 Demers al 55.4 29.5 Sha.rks/ra.ys 3.8 1·1. Total 147.8 62.4

b - Ma.put o Eay 20-200 m 200-300 m (3 400 n mi2) (800 n mi2) January August Je.unar;y August Pelagic 25.7 4.6 Demersa.l 20.1 16.6 Sharks/rays 4.6 3.6 Total 50.4 24.8

4. SEYCHELLES-MAURITIUS RIDGE

a. - S&chelles Balllc (October)

Pelagic 280.0 Demersa.l 42.0 Sharks/rays 8.6 Total 330.6

b - SSNa. de Malha. Bame (October) Pelagic 62.0 Demersal 62.,0 Sha.rks/ra.ys 9.0

Total 131.0

c - Na.z&l.'e.th and Ca.l'gados 0&1.'a.jos Bank (April and October combinedl

40-200 m 200-400 m {9 440 n mi 2) {9 200 n mi2) Pelagic + + Demeraa.l 20 4.1 Sharks/rays 17 3.1 Total 37 7.2 - 42 -

Table 18. Summa.ry of' estimates of standing stock, based upon data in Table 17, on a regional basis

(in 1000 metric tons)

Sharks other Total

fin-fishes

Kenya 3 - 6 11 .;.,. 19 15 - 25

Tanzania 3 - 4 2 - 8 11 - 18

Mozambique 10 ~ 13 104 - 220 116 - 230 Seychelles 9 322 330 Saya. de Ma.l.ha. 9 124 133 - 43 -

Table 19. EBtima.ted potential yield of fish by regions, assuming vaJ:'ious levels of natural mortality (M)

(in 1 000 metl'ic tons per annum)

Sb.arks Other Total fin-fish a.) M"" 0.,2 Kenya. 0.3 - o.6 1.1 - 1.9 1.5 - 2.5 Tanzania. 0.3 - 0 .. 4 0.2 - o.8 1.1 - 1.8 Mozambique 1.0 - 1.3 10.4 -22.0 11 .. 6 -23.0 Seychelles 0 .. 9 32.2 33.0 S'\)"a de Malha 0.9 12.4 13.3 b) M"" 0.3 Kenya 0.4 - 0 .. 9 1.6 - 2.9 2.. 2 - 3.8 Tanzania 0.4 - o.6 0.3 - 1.2 1.6 - 2.7 Mozambique 1,,5 - 2.. 0 15.6 -33.0 17.4 -34.5 Seychelles 1.3 48.3 49.5 Scwa. de Malha 1 .. 3 18.6 20.0 c) M= 0.4 Kenya o.6 - 1.2 2.2 - 3.8 3.0 - 5.0 Tanzania o.6 - o..8 0.4 - 1.6 2.2 - 3.6 Mozambique 2.0 - 2.6 20.8 -44.0 23.2 -46.o Seychelles 1.s 64.4 66.o Seya. de Malha. 1.s 24.8 26.6 - 44 -

Table 20.. Average annual landings for the period 1971-1975, summarized from FAO Yearbook of Fishery Statistics Vol., 40 (1975)

(in •ooo metric tons)

Country Sharks other Marine Total Marine Fishes Fin-fishes

Kenya 1 3-7 4-8 Tanzania. 2-5 17-25* 19-30 Mozambique 7-10 Seychelles 1 2-3.5 3-4·5 Mauritius 5-7

* includes 30 percent snappers - 45 -

Figure 1

Bay SIEVCIHllELLIES GROUP

AMI ANTES[] .. }' GROUP/....,, ,. < v '"\' ·\> < ... __ ..... - y __ _ 10 f.. I \ ..._ IJ \.--'

_,. ~' I Nazareth \ Banik 0

H ! I --~ .. +-·------. '12° I REUINllOINI <5}, -- I :v I

0 i I I Maputo Boy I

Figure 1. General cha.rt of the survey area. - 46 -

Figure 2

r ' ---- 13 _, ___ :r ff

~- ~~ ft!J.:; 200mm ~ ?9.0 200mm "> g I f g ...... ~

9 26~ !

25"1 2.5"0 I 2:f 2ffl 2r.s 1zo,.., I 2.18 2.18 I 6() ffO!Wnt 110() 1()()

80 (j

4() f'(JM t;.o {2.0

~ 40mtn l/f() !f6U# fO f61J#fOOmm ..,a ~ <:> - ~ ~ _l L

FIG. 2 11Treska Mu bottom trawl (cod ,Grawl) - 47 -

Figure 3

20' ao• 40• 50" 60" ·10• so• 90• 100· 110• 120• 30• 30°

20 20•

10• 10·

o• ~ o•

Q

10• 10'

2d' 20·

/\ f 30• \.. /j - CURRENT - 40" 4d' ~WINDS ------20- ao• 40° 50" 60' 10• 80' 90• 100° 110· 120"

Figure 3 (a). Pattern of surface circulation during Southwest M.:>nsoon (April-October)

20' JO' 10· 80' so" 100" 110' 120· 30' -.--- 30'

20" 20•

10° 10•

o· o'

10' 10·

20'~ 2rf ~ ~ '\ f 3o" -...... "' '/ - CURRENT - - - 411 " 40° ~WINOS '

20' 30' 40" 50' 60" 7fJ' 80' 90' 100• 110• 120'

Fi.gure 3 (b). Pattern of surface circulation during Northeast Monsoon (Ootober-Ma.roh) (After Wyrtki) - 48 -

Figure 4

40° 41 I /j // / 1// ,ii / /,'>;) /

..,J;::J // I ~ I/ I l"ATil 00/I I

./ 00 I / ~ 00 )if. 11/·

/ / i 0 .11 '/ : o I I L , I /0 /· n 111 aBay·~/-{) 0 _};! l (j0 pY,,cJj ; '-... North Kenya '1J 0 ~Q,\ .-\) Q ! ~0 \,) ;/ 30 ~/ / 30 I ,,.-- ---.... / / 06 0 I / I I KENYA I PELAGIC FISHES

! 0 0 - 200 kg/h ) • 200-400 '' • 400 -1000 '' • 1000 +

40

41°

Figure 4. Distribution of catches. Circles indicate trawl stations and relative catch size. - 49 -

Figure 5

40° 41°

,;I . // / // / ,j; / ";) / /, . 20 //I I I I

30 3"

,--...._ / / - 00 0 / ;f / -;:::~ ) I 110 \.1 I KENYA I . I DEMERSAL FISHES I J 0 0 - 0.25 T/h ) () 0.25-0.5 I . ' I I 0.5 - 1 • 1 + I II I I . • ~ Mz:!.:--+~------·----+- / / 40° 41°

Figure 5. Distribution of catches. Circles indicate trawl stations a.nd relative catch size. - 50 -

Figure 6

40° 41° I ;_i' // / /)- / r;f _/ /, I

30 ---!-----

,,,-- -...... 00 / 0 I / I I KENYA I ELASMOBRANCHS I 0 0 - 0.25 Tjh ) () 0.25-0.5 • 0.5 +

Figure 6. Distribution of oa.tches. Circles indicate trawl stations a.nd relative catch size. - 51 -

Figure 7

40° 41°

// ;/ 9/ /, / 20 . .

~\ "'"' / j I \~ ,,,f l/ uV..~ I/ l LAMU I. ,J 9 I I /,,,., i 0 0/ I / : 0 I I /6 I I I a a Bay ~._./ -i) 0 h/

1 l 0 0 ~ . ------. '-... North Kenya '1' ()~·~\\.-J 9-. 0 . . 0 \) \ '1; . . I I/ F3'-o ------+----l::i~~--i--~----+l-7-r':../_,:__--+------·-· 0 I ,,,,-- ...... __ / / - 00 6-0 I / I I KENYA I LOBSTERS I 0 0 - 25 kg/h () 25 - 100 •• " ) 100 +

Figure 7. Distribution of catches. Circles indicate trawl stations and relative catch size. - 52 -

Figure 8

// / 30 I ,,---- ...... / EB / - EB /fi / I I KENYA I SHRIMPS j 0 l\loSrlmps EB Present ' ) () 10 + kg/h

Figure 8. Distribution of catches. Circles indicate trawl stations a.nd relative catch size. - 53 -

Figure 9

39° 40° ' .,_ KENYA

TANZANIA

6"

Cruise 1 January 1976 PELAGIC FISHES

0 0 - 100 kg/h () 100 - 200 • 200 ·400 ..... 1000 +

40°

Figure 9o Distribution of ca.tohea. Circles indicate trawl stations and relative catch size. - 54 -

Figure 10

39° 40 KENYA .. ., 'Vo ao ' ' 11· 1·I fl A Y 5• ~ /r; 'I '···~ I; ~ II J .

/o1\ /\. ""' I \..-.. ~ ['"' ""' .," 0 \ \ ,J \_, \ j ( ) ' l ' ( fr . \ ) ( \ s• .J --\-----,.,.___~ _____J_ __ ~-~-- 60 I TANZANIA Cruise 4 July 1977 PELAGIC FISHES 0 0 • 0.5 T/h () 0.5 • 1 •• • 1 - 2 .. • 2 +

Figure 10. Distribu.tion of catches. Circles indicate trawl stations and relative catch size. - 55 -

Figure 11

40°

i I TANZANIA!

c...... 6 November 19?? PELAGIC FISHES

0 0 • 0.5 Tjh () 0.5. 1 • 1 • 2 ' ' • 2 +

Figure 11. Distribution of catches. Circles indicate trawl stations a.nd relative catch size. - 56 -

Figure 12

40°

60

TAN ANIA Cruise Jonu.. ry 1976 DEMERSAL FISHES

0 0 - 50 kg/h () 50 - 100 ' ' • 100. 200 ' • .. 200 +

Figure 12.. Distribution of catches,. Circles indicate trawl stations and relative ca.toh size. - 57 -

Figure 13

40 " ;""l / I/ !/ A I/l ~ 0

TANZANIA

TAN ANDA C~ulao 4 July 1977 DEMERSAL FISHES

0 0 - 100 kg/h () 100 - 200 . ' 200-400 .. • 400-1000 •• •..... 1000 + ' .

39° . 40°

Figure 130 Distribution of catches. Ciroles indicate trawl stations a:nd relative catch size. - 58 -

Figure 14

40

Cru1111e 6 November 1977 DEMERSAL FISHES

0 0 - 100 kg/h () 100-200 •• • 200-400 •• ... 400... • •

Figure 140 Distribution of catches. Circles indicate trawl stations and relative catch size. - 59 -

Figure 15

:!19 40 '-.. KENYA ......

TAN ANIA Crul•• 1 January , 1976 ELASMOBRANCHS

0 0 - 50 kg/h () 50 - 100 . ' • 100-200 ' . ... 200•

39° . 40°

Figure 15. Distribution of catches. Circles indicate trawl stations and relative catch size. - 60 -

Figure 16

40

6' TAN ANIA Cvulee 4 JUI)' 1977 ELASMOBRANCHS

0 0 - 100 kg/h G 100-200 • • • 200-400 , , ... 400+

39° 40°

Figure 16.. Distribution of catches.. Circles indicate trawl stations and relative catch size. - 61 -

Figure 17

40°

TAINI ANIA crul•• s November 1977 ELASMOBRANCHS

0 0 - 50 kg/h

() 50 " 100 I I

• 100 • 200 r '

• 200 + r I

Figure 17. Distribution of catches,. Circles indicate tra.wl stations a.nd relative catch size. - 62 -

Figure 18

40°

5 5"

TANZANIA cruises

LOBSTERS

0 No Lobsters $ 0 - 20 kg/h () 20 - 40 • 40 +

Figure 18.. Distribution of catches.. Circles indicate trawl stations a.nd relative catch size. - 63 -

Figure 19

40

70 7 .. \ ,.. 0 0 0 0 \ 0_ Crul11u1t 4,8 \\.. <:\ North B11nk 'i\0 Trawling positions 0 . 0 \ ""-\ \ c:O \ \(. \ .\\ . ·~~. \ I I I

80 I

3190 40°.

Figure 19e Distribution of trawl stations. Catch sizes were 0-100 kg/he - 64 -

Figure 20

35' 36° ,37° 38" 39"

I 17 ------rI ·------

18 ------i------··-·· .... _.l__..,~. ___1jf;i:

. I

1ir_ __ --+------· t------. ______19°

! I I ----1------:f0o BEIRA BAY

1 PEL.AGIC FISHES 0 0 - 0,25 T/h () 0.25-0.5 I 0.5 - 1 I • 1 + ..x Haul not valid 21°

37° 38°

Figure 20. Distribution of catchesv Circles iridicate trawl stations and relative catch eizeo - 65 -

Figure 21

315 315·' 37° 31f 39°

17° 1T --+----·-- !

18° . +-I

I I 19" i -t-· ·--··---····----i---J__ 19° I

1

'§ngue R.

Bll:RJ>o 204 _j - ·-··-·------·r---=-u20° BEIRA BAY DEMERSAL FISHES

0 0 - 200 kg h () 200 - 400 ~1. • 400 - 600 . ... 600 + 21° x __tiaul not ~lid

36' 37° 38° 39°

Figure 21. Distribution of catches •. Circles indicate trawl stations and relative oatoh size. - 66 -

Figure 22

35 3 39'

10'

19° ---,-----· ·-- ·- _____ )y'

I 20': I BEIRA BAY I ' I ELASMOBRANCHS I i 0 0 - 50 kg/h; () 50 - 100 • 100-200 • • 200 + 21° ------1--, x - Haul---··--- not valid

35°1 36° 37° 38° 39

Figure 22. Distribution of catches. Circles indicate trawl stations and relative catch size. - 67 -

Figure 23

35 38"

17°

I I 18'' .. ----L ·-·-·. ______1_8°

I ------+--1 ! I

19°

20°

1• 40 50 I~ present ' --+----+-- 21 I I

35° 36° 37° 38° 39°

Figure 23. Distribution of catches. Circles indicate trawl stations a.nd relative catch size. - 68 -

Figure 24

35 37° 38°

i i I I 17_'---+-- - 17° I I

10° -- ' ------+-----1!!·

I I i I i I 19° - ----t l - 19° I I

20° BEIRA BAY SHRIMPS

0 No Shrimps ~ 0 - 10 kg/h () 10 - 20 • 25 + 21° ··------·-·---- 21°

36° 37 38° 39°

Figure 24.. Distribution of catches. Circles indicate trawl stations and relative catch size. - 69 -

Figure 25

35° 36° ~lg\ ~ho ~o Bazaruto ~ \ I (/ ·~ \ . . lo\ 22° ·~11----·+------4-·--~+"1 ~\--- l \ b \ $ I \ \

0 0 I \ l lo 1 I \ I o \

Pontal de BaJra Falsa \0 I 23° --\°-J______--4---=2:::..Jl3° MOZAMBIQUE )0 \ SHELF BETWEEill BEIRA BAY AND I I MAPUTO BAY I \ Trawling positions I I cruises 1 and 4 I l I I I I

24°

35° 36°

Figure 25.. Distribution of trawl stations. - 70 -

MAPUTO BAY Cruise 1 and 4 PELAGIC FISHES >< Haul not valid 0 0 - 100 kg/h • 100 - 200 .. 500 - 1000 .. 0 (). / 1000 + 25 -=------~- ~- ---·-:::0---=.:::::_ ____ . ---- / I - --::::------/ -- - - ~ 0- .~. _>< -J:.,/ ~- ---- 'r 0 0 I / o• • p•• / 0 // '- • 8tJ I , 0 •• ;I '\ / • \ _/ I I • \ ,/ I J 0 •• I I I / I I 0 I .:'9-~/ I ) I 0 I I • 26 i I l-·------·-·--- 1 I J

/ 1 I I}

Figure 26. Distribution of catches. Circles indicate trawl stations and relative catch size. - 71 -

Figure 27

34' 35

MAPUTO BAY Cruase 1 and 4 DEMERSAL FISHES x Haul not valid 0 0 - 100 kg/h () 100 - 200 • 200 -400 - '

,__25 ______... 400 +

LimpopoR

0 oO 0 oo 0 / \ \ 0 0 "- --0. ___ _,.,.,,.. /

-----+---- .. ~- ··------26

34° 35·

Figure 27. Distribution o-£ oa.tches. Circles indica.te trawl stations and relative catch size. - 72 -

Figure 28

33 34 35

MAPUTO BAY Cruise 1 and 4 ElASl\llOBRANCHS x Haul not valid 0 0 - 50 kg/h • 50 -100 • 100 ... 0

26

33" 34" 35'

Figure 28. Distribution of catches. Circles indicate trawl stations and relative catch size. - 73 -

Figure 29

as . I // ( . ' I I MAPUTO BAY 1·;I . cnaa- "' I I ~o I / LOBSTERS / ! ~ x Ha.II not valid I /."' 6 / I .1 ~ 0 No Lobsters .-/ I I•/ • 1 - 25 kg/h • I / .

35'

Figure 29. Distribution of catches. Circles indicate trawl stations and relative catch size. 54° 55° 56" 5

. - .0-''-'-.. --...,.·'""\....t? /' .~· .__.." 0 1·- _,;. ../ c:.P . ..-,,, 08 \ 40 / 0 4" / \ I \ ~"" \ / Praslin '{} / I.~~ \ 0 "­ ~../ 0 9 Silhouette I. )

t:) ( __ ...... _. __•oo-...___. _ / l. "\ -·-<.... J '-·-"" ea ·7_,,...-. 0 . \ ,,.,- -· 0 '-- ·-.. lso I -~ 0 Sl x ~ '--· . /" ...... ____ --.. 0 ( --.... I 0 0 \ 0 0 0 () 0 \ SEYCHELLES BANK \ l ...._._ -·'\ n. ./· ~Cb00 PELAGIC FJSHES .J J "- 0 / X Haul not valid l ./ 0 0 - 05 T/h 000 () 05 - 1 ""'\~ ~/7' • 1 - 3 / /'-.. I • 3 .. ( ,,,,,./ ·~· \ 5• / 60 ~ ( / 54° 55° 56° 57° l '5 Figure 30e Tiistribution of catches. Circles indicate trawl stations a.nd relative catch size. 54° 55° 56" 57° I

-,-;-·'--\...~'-I) / -, --'"'- /.-_...../ I ,__._\ 40 / () 40 / \. I \ ..QQ \ I PrHlin I.~'°Q. \ / 0 ."- s./ • ~SilhouetteI. )

/ () ( ___ ...... __ _zoo-...._ / L_,__,_'--<-._ '\ J ------·7~·-.. \ 50 ' 0 x ~ ./'·-...... () I SEYCHELLES BANK \ 0. 0 i• l .....___ __ --·'\ (\./. ~~00 DEMERSAL FISHES "J "-- 0 X Haul not valid l 0 0 - 100 kg/h () 100-200 .. "/( t.J- • 200-400 •• :11 • 400+ ( / /"- __, I _,/ l '\ ...... , 60 / 60 ....

54° 55° 560 I / 57°

Figure 31. Distribution of catches. Circles indicate trawl stations and relative catch size. 54· 55 56" 57° /) /' - . -;- '--\..... --.....,"'-. Q -· --·""· 0 c:P ·---. .r·--/ 0 08 \ 40 / 0 40 / \ I l ..aa \ I PrHlinl.~f}~ / 0 \ ../ 9snhouette I. "-) '1 () . . / e:i ( / . ------200 ...... __ . -... L1-.-·._<..... \ / ...... __.--..,7 _,-. -· 8 . \ ,,-- -· 50 0 ,,.o '--·-. -.:i0\ "--. . /'·"--. )( --.... 0 ( .-..., () 0 \ \_ 0 0 II Q () 0 SEYCHELLES BANK \ l ...____·-.-· \ (~./· oQ;-oo ELASMOBRANCHS ) 'J 0 "'- 0 / X Haul not valid l / 0 0 - 50 kg/h ""' () 50 - 100 .. /( c!! • 100-200 •• ... 200+ ( ~ '\ 60 60 l w I\) 54° 55° 56° I / 57°

Figure 32. Distribution of catches. Circles indicate trawl stations and relative catch size. - 11 -

Figure 33

.\ \ 61° 62° 63° c, ) \ \ 9 ~-.....,, . \ .

"·" . \ , 1 ·, \ . .1 I '· . '--./ '-----:--_:..,, . ( (~....___ _// '""...... _ ..// _,.--· \ \ ~------X-·---/_/// .0 I ,-- __. . +·-·----. 0 . -···-.. j

""~"- 0 ~ 0 - \\ c#. \ . 0 \

I"\\ 0 0 \\ ., \ \ SAVA DE MALHA BANK j 0 0 --- \\ 0 ! ) PELAGIC FISHES '-. I -...._ . "' o'-- / / ) I x Haul not valid \ - // .../ I 0 0 - 0.25 T/h "\ () Q25-0.5 " I --- 12 0.5 - 1 • _....,.. / 1 ... J / .. I / I / I I 59° 61° 62° 63°

Figure 33. Distribution of catches. Circles indicate trawl stations and relative catch size. - 78 -

Figure 34

Mio 62° 90 \ \ 9 11=--+------'--l-+----'---h------+--·--~.--.----+--·---· \ \ (\~) h \ ~ ·\ i 1"-. ) I I ' \ '-/) "-._'-:- _;...,. // . - " 0 ...... ,. / -...... _, . . _30- .,_:-.....___ . (--...... '-..... // _..--· '"'--.. --.... "--...... "-. \ \ '-..._ '-::::. ~ -== ~:; / () - ~ -- '-.,. \_ ...... 10~0 --+------~ ,,- ~-- ---···-·...-+-~\-- ______"\.._. ---~.,...__\ ___ _ \.\ 0 __ ...... '"' . \ \. ' 0 .., \. ./ \ \ . \'.'I . ~ 0 I \ \ \ 1 09 () M \ 1 \ yJ ) q \ a..· // '"' \ lt ·-·------+--\-\'·_, _o __o_--l>''""---H'~,__ __\._. - ' \\ I ·. ~o p SAVA DE MAll..HA IBANK \ I I o~ 0 \\ 0 I ) I DEMERSAL FISHES ,---- '· o" / / ) I )( Haul not valid \ /__.../ ../ I 0 0 - 200 kg/h () "' \ I 12" 200-400 " 12° 400-600 • ' • / / 600+ ... / ---- I / / I I 59" 61° 62° 63°

Figure 34. Distribution of catches. Circles indicate trawl stations a.nd relative catch size. - 79 -

Figure 35

5 600 61° 62° 630 ·\ \ 9 \ \\ .) \. \ \ . \-./ . \ . '< '\ ' i I I- ."" \ .'-- ~/

----.... '-....'-:-_/. //. -200-.. .r ( ...... ~" ..._ /;/_. ~Jo-"':::....___ ...... _ "t"" \ \ ...... :_:__ _,,.,// - - ...... ""

\\Y / , _) & I "'-~\ -+- (_y~I ' \ \

! SAVA DE MALHA BANK \ I / 0 j . \ \ oo/~ ) I!(_ , I ELASMOIBRANCHS , .__ · .. ' \ o--·~ .! / / ,{-)i I x Haul not valid "'- ._/.../: I 0 0 - 50 kgj'n 50 - 100 •• \ I • ··-·- --·· ---+---~- • 100 -200 •• --,t ... 200-400 •• / I I

59° 61° 63°

Figure 35. Distribution of catches. Circles indicate trawl stations and relative catch size. - 80 -

li'igure 36

s

\ \ 9

,ooo-- -- -...... ·' ""-

I 100 ! -t I I

11°

$ @$!~' LOBSTERS 0 ! / / ) I No Lobsters \ 0 r ' I E9 Up to 8 kg/h """ \ I 12° () a - 2s -----1--+------r----,--- 12°

/ J _..,.- / I / f / / I 59° 60" 61° 62° 63°

Figure 36. Distribution of catches. Circles indicate trawl stations and relative catch size. - 81 -

Figure 37

57° ~ w w f ~ , 182° 63u I r i/ I I I ~------" - l__ _, ______,. __ ------.J -- -~------1------+--=13410 MAURITIUS TO I,,--~ 1 NAZARETH BANIK - . · . r 1 . \ II - . ---. PELAGIC FISHES - ~ I ;I >' ·~- 14° x Haul not valid 111 ~r+~~~----+------+---,=-tl~ I ( J """-\ 0 (' ..t I - / "jP l I ,_ (., I \ 0 -- 1 / '--/II·'-:tf' I Nazareth f ( _,. 0 Bal'lk \ - _... • - - c;f.l 15° I 115' e------(it-- ;;>------1------! ______T_I ____ , - )\ ,,oo - / \ / 01 I 16° I 16° ··-- t---- ;f~I~-\~:=,)~~- I

Carga~os \ ~·:·;. ~ / . ; .1 Cara1os /1 1': ) oO - Shoats -'-- _,;,zv / ,o , 1 \.'.'! / I 17° ~ 1------le------l'---:_,.'"'-(:)_,t::.__----l--~.• ------~------4----'17!-;1° 1 /-- ~ ' I I I

11----1------+------'---- -_-,,,..-:---+.--,,,-'------l------~------+------+---'-18°"--ff .-- '---'/ / !' / ~ -6} · ---.. "- 10 /, C>udan Bank 1 t--+----+.-f+--/At-""i'\r-\-j___ L ___ :.-'--+1--_,.,.-~---_,,-::::.-:s_--+-~------t-----t------+--111-u"

. \)\ 0) r77} , I ~r:---:1. ", -I l_ -, ___ ) I- ) 2if n=---'-----Po-r-1t_L_ou_1~---n·m--l~.--~-LR-1T_1_u_s __ -+------__ ,______,__~ (I/I I

11----+-----. -~------t------1-----+---~------.-

80°

Figure 37. Distribution of catches. Circles indicate trawl stations and relative catch size. - 82 -

Figure 38

56° 58° 59° 60° 63" / 610 // r !620

~ ------1- ---·· ------~ / 1_ -----_j___ -----+~13'--flo MAURITIU~ TO NAZARETH BANK /~'~/ I /I -£?--.."- II DEMERS.AL FISHES .11 )'(\ 14° x Haul not valid __ µi_ __ ---.--+-) 100 + Nazareth ( . __, · I • Bank . __.,. ,o - g: I 15° 15' ~~----l~~- -+--~r-----1------+---ll _!(, I I - l ' I/ ,,. , .\)\ ~o0 )Cl'. - I I' 1

0 11-16_-+-;----+! ___ +-----~Jl~~~~~:f 1~~; ~i----+---'1~6° 1 Carga~o 'i ~~ ( / . ; ,,- 1

1

0 11-1_7°--+------+----J~ c:.:~;, :~~ f ~ / ,-··= n '----~-- • ------+--"17--l\ 1-0 1 x / ,,.I ~ ~ : 1.:.--:/ I ( I I ) \ I I ' I 180 I . X-' !!-"'--+------+-----f--·-- -.~...,,,,;--+------,,,,.~ --1------>------·---- ·--·---~---~ I / / I ---- ...__ / / '- )/ I ---. " ~·• i' ~OUdliln Blilnk

111° I /":-- 1· ..... - :-:::::.::t? 111° ~-+------+----1--P

110°

Figure 38. Distribution of catches. Circles indicate trawl stations and relative catch size. - 83 -

Figure 39

62° 63 56" 57° 58° 59° 60° 61° / I / .,______,_13" _____ ------MAURITIUS TO NAZARETH BANK

·.1 .... -----1 14 \ I • 500 + I 15' 15" -+-I - --,_,,_ ------+-.. 1 I 1----r-- I i 160 16" - r ...... ____ .. ___l .. -- +----

1 I

17"

i ·--1- ,,.,.--· ! / / 6l ·-...... lo // oud111n Bank "·\. 'v 19° ,,__19_"--+------' --- -10. \-- ___ __:-__~-- ~·~-=- .-- . -_, ------··-- -+------i------/ \) \ \ --.,) ) / i \ . I0) l. I ao0 /. l +----_, __. ____, .. --- - \ '------+---- I _iAA RITIUS I

21° 0-0-----1------·-----· ---- -+ 56° 59° 60°

Figure 39. Distribution of catches. Circles indicate trawl stations and relative catch size. - 84 -

Figure 40

56° 160° 63" I' a-:1.::..30--1------+--··-----+-----~'--!-7"'-----+------+-~130/ __,. MAURITIUS TO NAZARETtt BANK . I /~/. ·' ;/~ . -~"- . '- LOBSTERS ; ! ) ~- 14° X Haul not valid i I '\ 0 No Lobsters ·"' , I ( ! \ l" ) \. } () 1 - 5 kg/h ,P . ,. (0/.\1 . () ./ - \.. >'")) Nazareth I ( . _; / l 0 Bank \ . __.. • .. t-! / 15° 0 15' ------r------1------7~--. I c·---+------l---=-ll I I \I . ~ I ~ ~/ ~- i ,_____,16° I ---- -+-----G~-=3~~~ U: 10oJL ______~ I j ii r, \6o o ---1 ~.;., I

I I Carga~os \ w·:· ;-, c / . J ,.- ' :,I CaraJOS /, 1" ) o' . I, Shoal~ l\ '>'- ,1;,,~ / ,0° 1 0 I 110 ,._11___,___ -----,.------~-'h. / ( i t------+---'-'--ll l r;, f\ x / /-- - ! I ! \_~,/ I I I ! 1) \ i I I I 18° !---~------····

i

_,.,...-...... '\r·-...... ,_ .""../ ~ . "--. '--... "-. __ )

-·-·-·-·- - ·------!------~

~ ~ ~--1------· ------,,_ ------·---+------!------!------1------+--"'-ll

56° 57° 59° 60°

Figure 40. Distribution of catches. Circles indicate trawl stations a.nd relative catch size. - 85 -

Figure 41

40° 41°

2' 20

30 30

_,,------/ / I I I KENYA I ACOUSTIC SURVEY March 1976 I j

------+------40

40° 41°

Figure 41., H;ydro-a.cou.stic track a.nd distribution of fish traces recorded .. - 86 -

Figure 42

40° 41° /f // / /) / J/ .jl / 2" /, 20 //I I I I PATEi // I //I I

__,,,. / 1/

/ I I / I I / I / / II / ;lI /~/ I .!/ I . . 30 / _-;;-r-':L -+------'3=-lio I I M~LINDI !

KENYA

ACOUSTIC SURVEY

I November 1977 I 0 0 I . I I ) I I I I I I I 40 ~ef-1-l---- ~ Mo(,.eJ.sA / I 40° 41°

Figure 42.. lzy-dro-acoustic track and distribution of fish traces recorded,. - 87 -

Figure 43

4• 39° 4cf

5• .. -· ·----·----5·

TANZANIA

ACOUSTIC SURVEY January 1976 tf ·- .l.---·---- 6" 1 I

,. 7

Figure 43c Hydro-acoustic track and distribution of fish traces recorded. - 88 -

Figure 44

( 40° ( J \ (~/ I "-..__ "__/ \ . -- H ZANZIBAR CHANNEL ('.""' .\ "\ ACOUSTIC SURVEY ""' July 1977 ~- \ )· a round scad

( \. b plankton and . \ small fish 60 \ . 60 ~ \\ \.. \ \ . . \ ) .

Figure 44.. Hydro-acoustic track and distribution of fish traces recorded. - 89 -

Figure 45

40° ·~/ '--.._."J

SURVEY 1977 I

(

Figure 45. Hydro-acoustic track and distribution of fish traces recorded. - 90 -

Figure 46

40° I ( \ \ -..---""-. ZANZIBAR CHANNEL ""' . --.a'- .r.\~. \. ACOUSTIC SURVEY November 1977 ·~. ) ..) ·\ ab round scad, sardinella and anchovy ( rounds cad . \ \ . ( ~ \\ \. \ \ . . \ ) . . \ / . J

Figure 46., Izydro-a.coustic track and distribution of fish traces recorded. - 91 -

Figure 47

35' 37° j38° 39"

I le/ ...? 17" ··---LI ------r-----I ------17° /

1 I

i ! i I -+---- ·--·- --t---18° --~-- ---1---~ i ..- I I I I i I I Zambe~i R.

190 i 190 ------·-----~------l-----=-i !

20° ----'------

ACOUSTIC SURVEY early January - 1976

21° 21° ·+·-·· -·--·- -- .-L------· I I

0 \37° aa •

Figure 47. Hydro-acoustic trac and distribution of fish traces reoordedo - 92 -

Figure 48

37' 38° 39°

It-'-'------·--·-17'

18° 18°

I 19° I --t- -- T

1 i

Pungue l. ~ 20~-1- ···tI .....-- 20° 1 BEIRA BAY ACOUSTIC SURVEY late January - 1976 I ~!1c l I

I I I ~1- ·------·-·--t - --·-----~· -·------~--- ..

!36° 137° 38°

Figure 48.. Hydro-acoustic trac· and distribution of fish traces recordedo - 93 -

Figure 49

36° 37'· 31"

17''

i 18° ------~----

! !

19° -·r I

~ngue R.

I __) 11111!! RA 20° ---+--- .------1 --·-·----+-----='-Ii20° ! BEIRA BAY

ACOUSTIC SURVEY August 1977

21° 21°

36° 37° 38° 39"

Figure 49. Hydro-acoustic track a.nd distribution of fish traces recorded. - 94 -

Figure 50

35•

24 ----·--· ·- . ·-- -··------·--·- --·------t----·------· - - MAPUTO BAY ACOUSTIC SURVEY Janu-y, February - 1976

25 2s·

35•

Figure 50., Hydro-acoustic track and distribution of fish traces recorded. - 95 -

Figure 51

33° 34• 35°

24 . ------+------+------4 MAPUTO BAY ACOUSTIC SURVEY August 1977

I I 25 25 - ·------+-

af!- / ---:-/ ~A /~;-~-- /// ----~­ //, / / / '/ / / I; I I I f / I I f) I \__ !-' I ! I/ I ~--t.ri-'l.'l-'M=~ey:ro ~+------r ·--_ 1/j I I '' : ~ ~ )J I 33

Figure 51. Izydro-a.coustic track a.nd distribution of fish traces recorded. 54° 55° 56° 57° (? 0 \._ ~ - / --"'' ~·'"\.... -- ..___" 0 ...... ( \ ) 40 --·--··· 40 -----r------·------~--+ / \ I ) / \ I \ Q '-.. Q ') / c:i ( :__.,----.. -•oo--..__ } \ '---(_ J '-- ~ \0 °' - I 5" - _If

. "'-- \ \ SEYCHELLES BANK _l ~ \ 'ACOUSTIC SURVEY j October - 1977 / ; I i I ~ I 1 I V'I I\) sr· ...... _J ------}~- 60 • I 54° 55'~ 56° 57°

Figure 52. Hydro-acoustic track and distribution of fish traces recorded. - 97 -

Figure 53

59° 62° 63

aoa-· -- '-...... /' -...._

// --- -200~ / --- -...... : . ~Jo - ,-..___ ~(~"-'::I // ,,,-- "-.... - ../// ' \ 1 ·------/ lf-'-10~0-+------~ \ -- l '\.\ . \\.. \

11° \ \ ~--i------f--~------l-- \ \\ : SAVA DE MALHA BANK \ \\ ACOUSTIC SURVEY ' '------1" I October - 1977 \ i "" I ' ', I I " ' I I I '\ i ! -- -r------1+------~- - - ~------t- 12° I i / I I _____,, / .--+-' I / I / / I 59° 60° 63°

Figure 53. Hydro-acoustic track and distribution o~ ~ish traces recorded. - 98 -

TEX:HNICAL REPORTS OF THE INDIAN OCEAN PROGRAMME

1. Iran - Formation of a Fisheries ·Development Branch within the ADBI. Labon, A.,, IOP/TFCH/75/1.

2. P~cherie de Crevettes - Rapport au Gouvernement de la Republique Malgacheo Labon, Ao, IOP/TFr.H/75/2 (not published).

3a Fisheries Development Possibilities in the Republic of Kenya. Labon 1 Aov IOP/TFXJH/75/3o 4. A Report on the Building-up of a Statistical System for the Collection of Marine Fisheries Statistics in the United Arab :Ehtirateso Banerji, S.K0, IOP/T:&:H/75/4. 5. Report to the Ministry of Agriculture and Fisheries'- United Arab Emirates. Labon, A., IOP/TIDH/75/5.

60 Some Developments in the 'I'u.na. Fisheries in the Indian Ocean. Kearney, R.E,., IOP /TFr.H/75/6 .. 7. Statistical System of Marine Fisheries in Mauritius. Banerji, S.K., IOP/TFJJH/76/7. 8. Establishment of an Agricultural a.nd Fisheries Develo,Pment Authority in the United Arab Enirates. Gustafsaon, N., and GeFoKe Moore, IOP/TEX:H/76/80 9. United Arab Emirates - Programme of Development of Fishery Harbours and Landing Places Reconnaissance Survey Report. Guckia.n? W.,, IOP/TFJJH/76/9. 10. Fishery Statistical System in Sri La.nkao Banerji, S.K., IOP/TF!JH/76/10 (restricted).

11. Summary Report on Crniae of the R/v SHOYO MA.RU in the North Arabian Sea. Yamanaka., H., Yo Nishi~wap J. Morita (translated and edited by S., Hayaai, Indian Ocean Programme)~ IOP/TIDCH/76/11 (restricted).

12. The Sultanate of Oman Five-Year Fisheries Development Plan3 Labon, Ao 7 IOP/TFJJH/77/12 (not published).

13. Fisheries and Ma.rketin~ in the Yemen Arab Republic. Camplema.n, Ge, v. Perovic and Bo Simons, IOP/TFJJJi/77/13. 14.. Summary Report on Cruise of the R/V SHOYO MARU in the North Arabian Sea. Ya.manakav H,,, Mo Yukina.wa and I,. Nakamura (translated and edited by Sa Hayasi, Tokoku Regional Fisheries Research Laborato:cy)u IOP/TF£H/78/14" 15. Report of the Joint Mission to Plan Development of the Sardinella Fisheries in the Bali Strait, IOP /TIDCH/78/ 15"

16. Markets for Fish Meal in the Near East Region. Naylor, J.,, IOP/TFJJH/78/16~

Development of Fisheries in the Ex:clusive Economic Zone of Sri Lanlcao Camplemanw Go~ IOP/TIDCH/78/17 (restricted)e 18. Implications of the Extended Zones of Maritime Jurisdichon for the Fishing Industry of Thailand. Labon, A., J. Ca.rroz and Jo Gulland, IOP/TEGH/78/18 (restricted). 19. Report of a Mission to Examine the Implications of the New Ocean Regime for Fisheries Development in Somalia. Silva, LoloJ•t R,.Lo Payne 1 J.Jo Kambona and GoFoKo Moore. IOFC/TECH/78/19 (restricted). - 99 -

20. Development of Fisheries in the Elcclusive Economic Zone of the Seychelles. PSi)'lle, R.L., M. Savini, IOP/TECH./78/20 (restricted). 21. Small-Scale One Boat Purse Seining in Sri La.nka. Pa.jot, G., IOP/TECH./78/21. . . 22. Legal and Institutional Aspects of Fisheries Management in Sri Lanka with Particular Reference to the Control of Foreign Fishing in the Elcclusive Economic Zone. Moore, G., IOP/TECH./78/22 (restricted). 23. Monitoring and Control Systems for Fisheries in the Exclusive Economic Zone of Bangladesh. Moore, G., IOP/TECH./78/23 (restricted). 24. United Republic of Ta.tiza.nia: Fisheries Legislation in Zanzibar. Chrisi;y, L. c. , IOP/TECH./79/24 (restricted). 25. Fish Trade in the Near F.a.st Region. Hotta., M., IOP/TECH./79/25. 26. Western Indian Ocean Fishery Resources· Survey. Report on the Cruises of the R/v PROFESSOR MESYATSEV, December 1975 - June 1976/July 1977 - December 1977 by Birkett, L., IOPjTECH./79/26. 27. Improvement and Expansion of the Kara.chi Fish Harbour. Breill!er, M., IOP/TECH./79/27.