Preliminary Survey of the Pelagic Fishes of East Africa.
Item Type Report
Authors Williams, F.
Publisher Her Majesty's Stationary Office
Download date 04/10/2021 08:03:54
Link to Item http://hdl.handle.net/1834/7875 COLONIAL OFFICE
FISHERY PUB.LICATIONS No. 8, 195,~h~~!JI!I!II'Ii~=='1 soum APRJfI\JI.INS'J1'l1,TrE R)R AQUA11CBIODIVERSrrY 2009 -01- 0 7
PRIVATE BAG 1015, GRAHAMSTOWN 6148 • SOUTHAFRICA
Preliminary Survey of the Pelagic Fishes of East Africa
BY F. WILLIAMS, M. Sc. East African Marine Fisheries Research Organisation, Zanzibar
LONDON: HER MAJESTY'S STATIONERY OFFICE 1 95 6 CONTENTS
Introduction 3
Review of the Conditions of the Survey . 3
The Method of Fishing 7
Notes on Fishes . IS
Distribution and Seasonal Abundance ofthe Pelagic Fishes 46
Future Development of the Pelagic Fishery 66
Summary . 67
References . 68 INTRODUCTION
THE EAST AFRICAN Marine Fisheries Research Organization was set up in July 1949 to carry out "marine fisheries research into fishing methods and the migration, feeding and breeding habits of the fish of British East African waters, including the Zanzibar Protectorate". Initially the problem facing the Organization resolved itself into the kinds of fishes which could be caught with the means at hand-namely, a ship with trolling booms. Little was known about the pelagic fishes, which were believed to be more valuable economically than the bottom fishes. Thus the emphasis of the work of the Organization has been on the pelagic fishes. A start was made by Dr. F. D. Ommanney, then Assistant Director (now Director, Singapore Regional Fisheries Research Organization), on the distribution and species of pelagic fishes. From my arrival in December 1951 until May 1952 I worked under Dr. Ommanney while holding a Colonial Research Studentship. When Dr. Ommanney left in June 1952 to take up his post in Singapore, I was appointed to the staff of the Organization and carried on the work ofthe survey. This report records the preliminary survey carried out by this Organization on the pelagic fishes of the area during the period September 1951 to January 1954. Acknowledgements General acknowledgement and appreciation is extended to all members of the East African Marine Fisheries Research Organization without whose help this survey would not have been possible. Particularly to the Director, Dr. J. F. G. Wheeler, who, throughout the survey has given encouragement and much helpful advice, and who critically reviewed the manuscript and made suggestions for its improvement; Dr. F. D. Ommanney for his work and guidance in the initial stages of the survey; B. S. Newell for advice on all hydrographic matters; F. H. Talbot for help on general fishery problems and photography; Commander 1. P. Stevenson, Master of :'Research" for his unfailing interest and co-operation at all times; E. A. Larue, engineer, for invaluable aid in the maintenance and construction offishing gear; and to Mrs. C. H. Delbridge who has typed all stages ofthe manuscript. In addition thanks are due to Linda M. Newton, British Museum (Nat. Hist.) for the identification of the algre Skujcella erythrcea (Gom.), and to H. Copley, Fish Warden, Kenya, for a specimen of Caranx from the Sabaki estuary.
REVIEW OF THE CONDITIONS OF THE SURVEY
AT THE FIRST ME ETING of the Fisheries Advisory Committee it was agreed that the area of the survey be defined as "that part of the Western Indian Ocean bounded in the west by the coast and in the east by a line drawn from a point 30 miles off shore from the northern boundary of Kenya to a point 30 miles off shore from the southern boundary of Tanganyika". Thus the area extends from Dicks Head to Ruvuma Bay, and including the large islands of Pemba, Zanzibar and Mafia, gives a coast line of about 1,000 miles. Zanzibar, the headquarters of this Organization, is ideally situated midway between the northern and southern boundaries of the area under survey. For the purposes of this report the area has been divided into eight sections for easy reference. (See Fig. 1). The coast line of this part of British East Africa consists mainly of a series of coral reefs, which may extend from a few yards to several miles from the shore. Beyond the reefs the depth normally drops rapidly to over 100 fins. This is especially evident in the Mombasa and Lindi 3 ,/ ,/ Q,1',6..,HE.6:b
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Fig. 1. Extent of survey area and division into sections
4 sections. There are three large off-shore islands, each with its fringing reefs. Firstly Pemba Islan4;sepat:a,f~d from the mainland and Zanzibar by the 20-25 mile deep water (200-400 fms.) Pemba C4mnef::Secondly Zanzibar, separated from the mainland (some 20 miles distant) by the; ~hlUr():wEZ@~bar Channel-some 10-25 fins. deep. Thirdly Mafia Island, forming the souilii " . ~ '. arms of the shallow North Mafia Bay. To the south of Mafia Island, in thci:! ~ -4 ~ ~ ~ ~ EQUATORIAL COUNTER CURRENT ,, '. ,, " ...... WESTERN WESTEQN EAST 01 INDIAN DAFRICAN ~ OCEAN COASTAL OCEAN ~ TCURRENT \ SOUTH EQUATORIAL ~ ~ ~ '!- ""- CURRENT ~~ ~ ~ ~ SOUTH EQUATORIAL CAP DELGADO ~ -E:- ~ CURRENT t ~ ~ ~ +- ~ Fig. 2. Surface hydrographic conditions in the Western Indian Ocean Table 1 Comparison of the East African Coastal Current in each Monsoon East African Coastal Current Monsoon. N.E. S.E. Direction. . N. N. Speed (knots) . 0-2 2-4 Temp. (av.) 30 °C. 25°C. In the estuaries and bays ofthe four major river systems it has been found that the estuarine water, of a high temperature and low salinity, flows out on top ofthe normal surface water. Plankton hauls have been made on 52 occasions, mainly with the 2-metre Young Fish Trawl, and the samples have been preserved. A detailed examination ofthe samples is being carried out and may show a qualitative or quantitative change in the constituent members of the plankton in the different monsoons. Fish eggs, larval and post-larval fishes have been removed from all samples and separated, where possible, into their respective groups. The work is at present in an early stage and is hampered by the fact that little work has been done in the past on the developmental stages of many ofthe pelagic fishes found in this area. Nevertheless, some larval and post-larval stages have been indentified. The distribution and density ofthe macroplankton is ofimportance in relation to the feeding habits ofmany pelagic species. Likewise the collection and study offish eggs and developmental stages can help with knowledge of the spawning habits and life histories. The occurrence of large numbers of jellyfish and red brown floating masses of Skujcella erythrcea (Gom.) J. de Toni (Trichodesmium erythceum Gom.) (Myxophyecre) has been noted in the Pemba-Zanzibar-Mafia areas in December-January, 1951-2-3-4, i.e. at the commencement of the N.E. monsoon. The vessel used by this Organization is the m.v. "Research" (Plate I), a 70 ft. ex-Scottish drifter built in 1937 (beam 15/, maximum draft 9/). Previously the "Research" did service with the Mauritius-Seychelles Fishery Survey of 1948-49, where she sailed some 28,000 miles. She is an excellent all-weather ship, although there is a lack of both working and storage space for scientific and fishing equipment. Powered by a 4-cylinder Blackstone diesel engine of168 h.p., she has a normal maximum speed of about 8t knots. There are auxiliary engines for lighting, pumps and refrigerator. Fish storage consists of a refrigerated hold able to take about 5 tons of fresh fish. The Hughes M.S. 24 echo-sounder, installed in 1952, has not satisfactorily recorded sub-surface shoals ofpelagic fish. R.T. contact has been established with the Cable and Wireless station at Mombasa at various times during the survey. During the survey the "Research" has already sailed some 17,830 miles and has been at sea for 235 days, working for more than half this time on the pelagic fishery (for details of fishing hours etc. (see page 48.) METHOD OF FISHING THE MAIN MET HOD used for the capture of pelagic fishes during the survey was multiple trolling. Two other methods were begun during the period under review, namely gill-drift nets for the smaller pelagic species and deep long lining for tunny. They are not, however, discussed in this report. Before the survey started it was decided (see Introduction) that multiple trolling would be the most suitable method for use from m.v. "Research". Multiple trolling consists of towing lures in the water at the end oflong fishing lines suspended from booms pivoting into the mast. The number of lines towed depends on the size of the ship, length of booms and the type of fishes to be caught. In October 1950 Dr. F. D. Ommanney made a cruise with the French Tunny Fleet in the Bay ofBiscay to observe the multiple trolling technique. Itis described by him in an unpublished 7 report, "The Breton Tunny Fishery, October 1950, with a note on the Sardine Fishery". Trolling gear in the "Research" was originally based on Dr. Ommanney's experience with the French tunny boats. French catches consist almost entirely of one species of fish, Thunnus alalunga Bonnaterre, of 10-12 lbs., which exhibits no fight when caught. On the East Africa coast modifications had to be made to the gear to enable it to withstand the fighting tactics of fishes ofa vast variety ofspecies and a diversity ofweights. DESCRIPTION OF TROLLING GEAR Trolling booms or "tangons", each 45' long and pivoting into the base of the mast, were fitted in "Research" in 1951. Booms were made ofa local East Mrican wood, the butt diameter being 6" and the tip 4". In January 1953 an extensible arm or "whip" was fitted to the outer end of each trolling boom, increasing the total length from 45' to 55'. When fishing, the "tangons" are set at an angle of 30°-40° to the horizontal and the whips are hauled out. Fig. 3 (a) and (b) shows the rigging to support the booms. Two guys, AI and BI, run forward and two, Az and Bz, run aft from the boom to cleats on the inner side of the gunwale (Fig. 3(a) ). A wire stay is fitted between position A on the boom and the side of the ship. The tangons are raised and lowered by two topping lifts (Fig. 3(b». When not in use the whips are withdrawn, the tangons hoisted vertical and secured at the top ofthe mast (Fig. 3(c». The average number oflines trolled by the "Research" was 8-9 in the first halfofthe survey. From February 1953, with the addition ofthe whips, II lines were towed. Three stern lines were always towed when on passage or engaged in other work. Fig. 4(a) shows the general arrangement of the II trolling lines. Each unit of trolling gear (excluding stern lines) consists of a "standing line" with shock absorber and a "fishing line" complete with trace wire, lure, swivels and "haul-in line". Fig. 4(b) shows the details of one line (S.M.). The standing lines are made of I" manilla rope. The inboard end of each standing line is .. secured to a cleat at the base of the tangon. The other end ofeach line, to which is spliced a small wooden toggle, passes through the respective ring on the tangon for S.O., S.M., S.l. etc. The distance from the ring to the toggle was made sufficiently long for the toggle to be pulled to the side of the ship. The shock absorbers or "shocks" are placed midway between the boom and the toggle. The stopper is formed by a loop in the standing line. The fishing lines are attached to the toggle by an eye spliced in the line, below which there is a heavy duty swivel. Cotton fishing line, weight 3 lbs. per 60 fms., has been used for the "fishing lines" and "haul-in lines". The "haul-in lines" are attached to the "fishing lines" in the appropriate places (see Fig. 4(a». The trace wire of 7 X 7 stainless steel aircraft cord is 4-5 fms. long and has a heavy duty swivel spliced in at each end. The fishing line is spliced to Qne swivel and the other swivel is attached by a heavy brass split ring(s) to the lure. In the case of stern lines the fishing line is fastened direct to the stanchion posts in the stern of the ship, "shocks" are not used. Very many kinds of lures were used during the survey and a short description of the main types is required. Most of the lures were "horne-made" at a low cost. Exceptions were the stainless steel and "chromed" spoons. Standard size ofhook used was Mustad Kirby I/O ringed, tinned. Bone jigs (Fig. 5(a» were made from animal rib or shoulder bones. A screw passes through the eye ofthe hook and the jig and is secured by a nut on the under side. Normal sizes were 4"-6" long and I"-If' wide. Feather jigs (Fig. 5(b» were of two kinds. A simple type (i) was made by binding long wing feathers to the shank of the hook. The binding was then given a coating of enamel. The length of the feathers always exceeded the shank length of the hook. Another kind offeather jig (li) was made from Badminton shuttlecocks. A hook was attached to a short piece ofgalvanised wire and inserted through a hole bored in the cork head ofthe shuttle cock. The wire was then bent to form a towing eye for the lure. The normal white feathers can be painted various colours. Jigs with skirts (Fig. 5(c) ): the basic jig part (i) consists of a hook attached to a length ofheavy galvanised wire round which is wrapped a piece ofsheet lead. The weight of the lure is about 4-8 ozs. and the overall length 6"-10". In the beginning, skirts of 8 FORWARD GUYl! 2·eMANILLA /Al'~' B ~ (.t..."" ..It..... ) ~ ~.,,, TROLLING BOOM OR 'TANGON' AFTER GUYS 2fMANlLLA TANGON TOPPING LIFTS /::~~' 2r"MANILLA 11~~::=====/S7~'~~=====::z;,~.d:::-- T ANGON (9) 'TANGON' RIGGING (ft...... t....,) j------WIRE STAY DOWN HAULS FOREMAST FOREMAST ~ ~m".", _ 'OU lCI'~' TANGON ~ ~ (.f...... 4".~") -----CHECK NUTS Fig. 3. Trolling booms or 'tangons' on m.v. Research 9 I> U'" 2 '"<", '" '"-J 2 i", "'- " "E '":::; "'2 1-" ~ ii::.J ., ., ~'" I > I S Q .. 0 :; en ~ El .. -J 2 u: :; >'" > ~ ~ "2 ·z zI> cloth painted different colours were used, but they were later made of bright plastic. The base of the skirt is rolled round the lead and secured by fine brass wire. The tails ofthe skirt extend from the lead so as to surround the head ofthe hook (ii). "Frayed out" pieces ofsisal or manilla rope were often bound to the basic jig part (either weighted or unweighted) in place of the 10 fA) BONE JIGS fBl FEATHER JIGS SECURING BOLT 1 & NUT I C:::=::===c:===:I]~)====~G\ 1!.1 I/O HOOK HEAVY \ (~ ':):;6' BONE HEAVY GALV, WIRE Ic) JIGS WITH SKIRTS II} BASIC JIG PARTS (2) WITH PLASTIC SKIRT I/O HOOK BRASS (Dl RUBBER JIGS BINDING WIRE TAILS OF SKIRT rEI SPOONS Ul PATENT TYPE (2) MADE ON 'RESEARCH' ALUMINIUM 0 R HEAVY SPLIT C~ROMIUM SPOON BRASS SPOON RING / ~ :J HEAVY I/O HOOK '=:r BRASS BINDING SPLIT TRACE RING "'" WIRE WIRE Fig. 5. Types of Lures used on ffi.V. Research plastic skirts. Red rubber jigs (Fig. 5 (d» were suggested by Dr. C. F. Hickling in 1953. They consist of a hook threaded through a piece of red laboratory pressure tubing. The end of the rubber tubing is split to form a "tail". Stainless steel and "chromed" spoons were from 5"-i' long and were originally fitted with small treble hooks. These were removed and replaced by Mllsta,d Kirby I/O'S (Fig. 5(e». The brass and copper spoons, 6" long and Ii" wide, were from the sheet metal. A short piece of trace wire with a hook spliced in at one end was along the centre line of the spoon. A second hook was attached with wire to the of the spoon (Fig. 5e (ii) ). II TROLLING When commencing trolling the lines are paid out one by one starting with the outermost. The SOO fishing line is hooked onto the toggle on the standing line and paid out from the side ofthe ship. The "haul-in line" is attached well forward on the stanchion rail and hangs in an arc. The next line, SO, is paid out so that the fishing line is above the halli-in line ofSOO, and so on until all the lines are out. Strikes and fish caught are indicated by the halli-in line jerking up taut and the expansion ofthe shock. In addition the fish often comes to the surface when hooked and can be seen from the ship. The appropriate fishing line is then pulled to the ship's side and hallied by hand. The length of trace wire does not allow, except with small fish, of the lifting on deck and the fish are usually gaffed. After removal of the fish, the line is paid out again. The weight of the lure and trace is sufficient to carry the line under the others and into the correct position. Tangling of trolling lines was not frequent, although occasional large fish making fighting runs did cause trouble. Strikes on stern lines are indicated by "watchmen" in the lines. Due to the 'position ofthe ship's lifeboat, fish caught on the centre stern line (ST.2) had to be passed to the side ofthe ship for gaffing. . The normal trolling speed of m.v. "Research" was 5-6 knots. EFFICIENCY AND LIMITATIONS OF GEAR Lines were towed from "Research" at trolling speed for 806 hours and caught 579 fish. At fllil speed, 8! knots, lines were towed for 1,420 hours and caught 78 fish. Most of this time at full speed is represented by stern lines towed whilst on passage, but 64 hours were trolled with all lines out. Total number ofunsuccessful strikes at the two speeds were 418 and 58 respectively. Table 2 shows the breakdown ofall strikes for the period November 1951 to January 1954. Table 2 - TROLLING SPEED FULL SPEED Unsuccessful strikes Unsuccessful strikes Successful Successful Cruise No. Date strikes= Due to Due to strikes= Due to Due to Fish caught breakage all other Fish caught breakage all other ofgear causes ofgear causes ---- 6 and 7 . Nov·/51 8 I 4 0 0 0 8,9 and 10 Dec·/51 27 6 9 0 0 0 II, 12 and 13 Jan·/52 35 13 9 0 I 5 14 and 15 Feb·/52 2 0 2 I 0 0 16 and 17 Mar·/52 94 13 54 7 0 3 18 and 19 Apr./52 16 8 7 0 I 0 20, 21 and 22 . MaY/52 49 15 36 II 6 7 23, 24 and 25 . June/52 4 2 4 3 0 I 26 and 27 JulY/52 18 5 10 0 I 4 28, 29 and 30 . Aug·/52 52 0 4 6 2 3 31 and 32 Sept·/52 41 6 34 5 3 I Oct·/52 0 0 0 0 0 0 33 Nov./52 32 2 24 3 I 0 34, 35 and 36 . Dec·/52 20 2 0 I 0 0 37, 38 and 39 . Jan·/53 59 12 24 3 0 0 40, 41 and 42 • Feb·/53 2 0 3 I 0 0 43 and 44 Mar·/53 27 I 23 5 0 4 45· Apr./53 0 0 0 0 0 0 46 and 47 MaY/53 15 3 8 8 I 2 48. June/53 6 0 3 5 3 0 49,50,51 and 52 JulY/53 4 I I 3 I 0 53 and 54 Aug·/53 2 I 5 2 0 0 55 and 56 Sept·/53 3 0 2 I 0 0 57· Oct·/53 I 0 0 0 0 0 58 and 59 Nov·/53 15 4 17 8 2 I 60 .. Dec·/53 9 2 5 3 I I -61 • Jan·/54 38 8 25 2 I 0 579 105 313 78 24 34 II33 12 The gear initially used by Dr. Ommanney soon proved much too light for the majority of fish found in these waters. Consequently strengthening of the gear took place and the gear described is that found to be most satisfactory. The following figures show -the decrease in unsuccessful strikes due to breakage of gear. Losses are expressed as a percentage of the total number of unsuccessful strikes. % November 1951 to April 1952 32'5 May 1952 to October 1952 24 November 1952 to April 1953 18'7 May 1953 to October 1953 26 The increase in the strength of the gear has not, however, been reflected in an increase in the fish caught. Fish caught are expressed as a percentage of the total number of strikes. In addition the average weight of the fishes caught has remained fairly uniform over each period. % Av. Wt. in lbs. November 1951 to April 1952 59'1 II'9 May 1952 to October 1952 58'7 14 November 1952 to April 1953 60·6 13 May 1953 to October 1953 62'0 13'6 Many authors have reported various speeds as being the most effective for trolling in different parts of the world. Fiedler (1941) gives 5-6 knots for tunny boats off the west coast of South America, Powell (1949) 6-6t knots for albacore trollers off Alaska and Ommanney 5 knots for the French tunny boats in the Bay of Biscay. Much higher speeds were found successful by Serventy (1947), 8 knots, in Australian waters and by Warfel (1950), 7-9 knots, in Philippine waters. Bates (1950) in the Line Islands found 8 knots too fast and suggested 5-6 knots. A great deal depends on the strength of the gear and the type and weight of fish caught. On the "Research" it was found that a trolling speed of 5-6 knots was most satisfactory and prevented undue strain on the gear. At full speed, 8-8t knots, the rate of unsuccessful strikes due to gear failure was nearly double that at trolling speed, 24 out of 53 as against 105 out of 418. Once again the fish caught as a percentage of the total number of strikes remained much the same at 57'4%. This suggests that at full speed the limiting factor in catching the fish was possibly the strength ofthe gear and not the speed ofthe ship, but it must be remembered that the stern lines, unlike the rest of the lines, have no "shocks". Table 3 shows the distribution of all strikes on fishing lines at trolling speed over the period November 1951 to October 1953. Figures for POO and SOO are not included as these lines were in use only from February 1953. All other lines were towed for approximately the same length of time. Table 3 Distribution of all strikes SO and SMand SI and Nov, 1951 to Oct, 1953 PO PM PI ST's Unknown Totals - Successful strikes = fish caught 152 101 143 52 55 503 lJnsuccessful strikes 82 74 130 55 - 341 - Totals 243 175 273 !O7 55 844 It would appear that the inner (SI and PI) and the outer (SO and PO) lines were more productive than the middle (SM and PM) and stern lines. The inner lines are fishing at the edge ofthe wake, whilst the outer ones are clear ofthe wake. Bates (1950) found that inner lines were the most productive. A careful check has been made of the "catching power" of the many different lures, Total number of lure hours at trolling speed was 6,822. Table 4 gives the number of lure hours and fish caught for each type oflure which has been trolled for more than 100 hours. 13 Table 4 Description of lure Lure hours Fish trolled caught Stainless steel or "chromed" spoons. .. 285 27 Copper or brass spoons 177 13 Tin or aluminium spoons 23It 8 Bone jigs. 543 33 Feather jigs . 196 15 Red rubber jigs . 138 6 Jig with white "skirt" 644 54 Jig with red "skirt" . 472 41 Jig with blue "skirt" . 52 7t 77 Jig with yellow "skirt" 190 31 Jig with green "skirt" 633 59 Rope unweighted jig . 1517 III Rope weighted jig 636t 26 From these results it would appear that the "catching power" ofthe lures is in the following order. (I) Jigs with yellow skirts. (2) Jigs with blue skirts. (3) Stainless steel or "chromed" spoons. (4) Jigs with green skirts.. (5) Jigs with red skirts. (6) Jigs with white skirts. (7) Feather jigs. (8) Rope unweighted jigs. (9) Copper or brass spoons. (10) Bone jigs. (II) Red rubber jigs. (12) Rope weighted jigs. (13) Tin or aluminium spoons. The jigs with yellow skirts (I) being nearly five times more effective than tin or aluminium spoons (13). The results, however, when analysed statistically, are not conclusive. There is also no indication that anyone species of fish is attracted or caught by a particular type or colour of lure. When the fishing is good all lures seem to be equally effective and the length ofthe fishing line is not critical. An incident on Cruise 28 was an example of this. The "Research" caught 42 fish of 5 species in 80 minutes. The fish struck indiscriminately at the lines throughout this period and it may have been due to the large concentration of fish in the area. When in small numbers the fish are possibly lure and line selective. At other times (see notes on "tunny shoals" page 47) all the lines seemed ineffective when fished at varying distances from the ship and at varying speeds. General observations on the gear bring forward the following comments. The trolling booms fitted in the "Research" were much too heavy and did not have sufficient "give" in them. Light trolling booms, 4/1 butt, of spruce or pine would have been easier to handle and required less complex rigging. The standing lines of i/l manilla proved satisfactory and were renewed every 6-9 months. The ideal type offishing line would be similar to the untanned cotton line, 3 lbs. per 60 fms., used on "Research". The use ofcopper preservative on the fishing lines on one side ofthe ship did not indicate an increased life compared with the untreated lines. It is possible, however, that the green treated lines were less visible in the water. All fishing lines must be stretched before use and renewed as required, average life being 3-6 months. The experimental use of braided nylon trolling line was begun on Cruise 58 (November 1953). Preliminary results are promising. Nylon line of 150 lbs. breaking strain or less is difficult to handle and kinks easily when wet, whereas that of 200 lbs. breaking strain was much more satisfactory. Many types of trace wire were tried. Heavy flexible copper wire, heavy galvanised wire and single-strand 14 stainless steel wire were all found to kink easily and were often broken by strikes of moderate weight fish. Stainless steel 7 X 7 aircraft cord, 0'076" diameter, made by British Ropes, was found excellent and after its introduction no fish were lost by the breaking oftrace wires. Tested minimum breaking strain was 560 Ibs. Length oftrace wire was increased from 2 to 5 fms. when the aircraft cord was used. General opinion of"trollers" is that long trace wires are more effective. Long gaffs were necessary consequent on the lengthening of the trace wires. Shocks made of i" rod rubber were used by Dr. Ommanney. A prolonged pull of50-60 Ibs. was required to extend them to the length of the stopper (36"). Normally the strike ofa fish did not appear to be taken up rapidly enough by these rubber shocks and this probably caused a loss offish. "Chromium" springs 12" X If' were obtained for use as shocks. In groups of three they required a pull of 70-80 Ibs. to be expanded to the stopper length of 48". The shock of the strike was taken up immediately by the springs. Single springs were easily stretched and distorted. The use of still heavier trolling springs (maximum expansion at 200 Ibs.) is recommended. Small barrel swivels were used at first but were not of sufficient strength. Hardy's No.2 Alma heavy duty swivels were used later on all trolling gear and found satisfactory. Split rings were used to connect the lure to the swivel on the trace wire. No split rings sufficiently strong could be obtained during the survey. Doubling up ofsplit rings helped to reduce losses but this always remained a source ofweakness in the gear. The splicing ofthe trace to the line would solve this problem, but would make rapid changing of lines impossible. The smallest hooks recommended are Mustad Kirby I/O ringed and turned. They have proved capable of taking fish over a considerable size range (3-80 Ibs.). Smaller hooks were invariably straightened by even small fish. The durability of lures varies considerably. Bone jigs; "chromed", silver, copper and brass spoons; and red rubber jigs last almost indefinitely whereas aluminium spoons soon corroded in sea water and had to be frequently renewed. Feather jigs were easily damaged but jigs with plastic or rope skirts lasted longer. In the latter case the damage done by the striking fish could soon be made good by the renewal of the "skirt". During the survey all the metal and moving parts of the trolling gear were greased at the end ofeach day's trolling operations to prevent corrosion. NOTES ON FISHES EIGHT FAMILIES OF FISHES are represented in the total catch of 657 taken by trolling. Classification as far as families is based on Berg, L.S. (1947). Sphyrrenidre 107 Belonidre I Serranidre 37 Carangidre 244 Coryphrenidre 36 Lutianidre 107 Scombridre (Cybiidre) 124 Xiphiidre I Two families, Lutianidre (less genus Aprion) and Serranidre are normally bottom fish, but take a trolled lure in shallow water. The remainder are true pelagic forms living at the surface or in mid-water. As in the Mauritius-Seychelles Fisheries Survey 1948-49 (1953) the following routine measurements were made of all fish caught: 1. Total length in ems. 2. Weight in Ibs. 3. Stomach contents with estimate of amount. 4. Condition of gonads. 15 Ovaries were divided into four categories: (a) Immature. Small, thin, thread or ribbon-like, translucent. Usually pinkish in colour. (b) Mature - ripening. Enlarged, firm and compact but not engorged with blood. Yellowish or whitish in colour. Eggs visible. (c) Mature - nearly ripe or ripe. Enlarged but no longer firm and compact. In various degrees flaccid and, in ripe ovaries, gelatinous in consistency. Engorged with blood and reddish in colour, at least in parts. Eggs distinctly visible. (d) Mature - spent. Flat and flaccid. Dark in colour with many large blood clots. Often with a speckled appearance. Ovaries which were losing or had almost lost their suffused appearance but were full of large blood clots and still rather flaccid were said to be "spent recovering". They had recently spawned, though less recently than "spent" ovaries, and were ripening again. Testes were similarly divided into four categories: (a) Immature. Very small, thread-like and inconspicuous. No milt. (b) Mature - not running. Enlarged and firm, containing milt. Small inconspicuous testes were often found to contain milt. These, however, have been considered as mature-not running and not as immature-mature (Mauritius-Seychelles Fisheries Survey 1948-49). (c) Mature running. Enlarged but not always as much as (b). Abundant milt which may be seen exuding from the external genital aperture with or without gentle pressure on the abdomen ofthe fish. (d) Mature - spent. Flaccid and collapsed. Little milt. Other observations, photographs and measurements of bodily proportions were made as and when required. ("Length" of fish, as opposed to "total length", refers to length to caudal peduncle. Depth is greatest depth ofbody). FAMILY Sphyrrenidre Only one genus-Sphyrcena Artedi has been identified in this area. SPHYR£NA COMMERSONl (c.v.) Plate II (S. picuda Bl. Schn. S. snodgrassi Jenkins). Barracuda, Picuda, Snoek (S. Africa), Mzia (Swahili), Tazard (Seychelles). Distribution: Widespread Indo-Pacific and Atlantic in tropical and sub-tropical areas. Abundant. References Day 1878-88 Jordan and Evermann (1903) 1905 (S. snodgrassi) Weber and de Beaufort 1922 (S. picuda) Barnard 1927 Wheeler and Ommanney (1948-49) 1953. Principal characteristics DV+I9 AI9 Depth about 8-9 in total length. Head 3'4-4 in total length. Eye about 6'5-7'5 in head. Maxilla reaches front edge of eye. Angle of preoperculum rounded. Two flat feeble spines at upper edge of operculum. Jaws with a single series of large strong teeth; single symphysial canine; 4-8 palatine canines with smaller teeth posteriorly. Fleshy knob at symphysis. Scales on lateral line 86-92. Pelvics much nearer lower jaw than caudal fin base. Origin of pelvics under middle of pectorals. First dorsal origin behind that of pelvics and just behind tip of pectorals. Caudal fin truncate. 16 Colour: Silvery body with round blackish patches on sides. Faint darker cross some. Dorsals and anal dusky with whitish tips. Caudal dusky. Number caught by trolling . Number caught by other means Largest fish .152 ems. 361bs. 64 ems. 4 1bs. Smallest fish { 65 ems. 3 1bs. Occurrence of specimens: J. F. M. A. M. J. J. A. S. o. N. D. 1951 I 1952 3 5 5 I 4 6 1953 6 10 3 4 III 4 I 1954 13 S. commersoni is found in East African coastal waters throughout the year. It is common in the native fish markets and this species is invariably taken by trolling. Largest numbers seem to pass through Zanzibar fish market in the period of the N.E. monsoon. Number offish and state ofgonads MALES - Immature Mature Spent Not running Running recovering J.F. I 20 - - M.A. I 8 - - M.J. . - 5 - - J.A. - 2 - - S.O. - - - - N.D. - 5 I - FEMALES Immature Mature Spent Ripening Ripe recovering J.F. - - - - M.A. - I 2 3 M.J. 5 I - I J.A. - I - - S.O. - 2 I 2 N.D. - 2 I 2 It is possible that the spawning period is a long one covering the end of the S.E. monsoon and the whole of the N.E. monsoon (September-May). Only 7 of the 69 specimens were immature. 17 Stomach contents Garfish (Tylosaurus sp. 7° ems.) . :1~} 9 Mackerel (Rastrelliger sp.) . Nemipterus sp. Sardinella sp. . Unidentifiable fish remains Post larval fishes and Squilla sp. . I Squilla sp. 3 Squid I Nil 55 Although the majority of stomachs examined were empty, there is little doubt that this barracuda is mainly a fish feeder. SPHYR£NA JELLO (C.v.) Plate 111. Barracuda, Picuda, Snoek (S. Africa), Mzia (Swahili), Becune (Seychelles). Distribution: Widespread Indo-Pacific. Abundant. References Day 1878-88 Weber and de Beaufort 1922 Barnard 1927 Blegvaad 1944 Smith}. L. B. 1949 Wheeler and Ommanney (1948-49) 1953. Principal characteristics DV+I9 AI9 This is a very variable species both in bodily proportions and colour. Probably 2 or 3 sub species or races in this area. Depth 7'5-8 in length, 8-9-9'4 in total length. Head 3'5-3'7 in length, 4-0-4'4 in total length. Eye 6'4-7'3 in head, 3-3-4 in snout. Maxilla reaches to front edge of eye or just before it. Preoperculum rounded. Operculum with 2 flat feeble spines at upper border. Compressed teeth in both jaws with canines posteriorly. Single symphysial canine. 4-8 palatine canines. Scales on lateral line 120-130. Pelvics nearer maxilla than base of caudal fin. Origin offirst dorsal behind that ofpelvics and above tip ofpectorals. Caudal deeply forked, centre rays sometimes slightly produced_ Colour: In some (Plate III) silvery, darker above with darker cross bars and patches on sides. Fins dusky. In others body yellow green to silvery, with dark cross bands. Fins all yellow ish dusky. Number caught by trolling 38 Number caught by other means 48 Largest fish (trolling) _ 127 ems. 19 lbs. Smallest fish (trolling) 67 ems. 3 lbs. Largest fish (hand lines) 75 ems. 4lbs. Smallest fish (hand lines) 45 ems. I lb. The 48 specimens taken on hand lines weighed on the average about 2 lbs. each and were taken on four occasions (3 in Msuka Bay, N. Pemba). Each time it was at night at the full moon. Ommanney found a similar phenomena in the Seychelles area, with the younger members of this species. The larger specimens have been taken by trolling throughout the area as with S. commersoni. They are darker than the small specimens taken by hand lining. Eleven specimens, taken by trolling in the sections south of Zanzibar, were of the second colour pattern, i.e. yellow green to silver. A detailed examination has not shown any specific differences from S. jello and they have been included with this species. 18 Number offish and state ofgonads MALES Immature Mature Spent Not running Running recovering J.F. - I - - M.A. 2 3 - - M.J. 2 4 I I J.A. - - - - S.O. I 7 - - N.D. - 3 I - FEMALES Immature Mature Spent Ripening Ripe recovering J.F. - 3 - - M.A. - I I 2 M.J. 8 2 - 2 J.A. 3 I - - S.O. 7 12 4 I N.D. I 5 5 - It is probable that S. jello, like S. commersoni, spawns over a long period covering the end of the S.E. monsoon and the whole of the N.E. monsoon (September-May). It is common in Zanzibar market throughout the year, especially the small specimens. Stomach contents Garfish (Tylosaurus sp.) I} Sardines (Sardinella sp.) I Atherina sp. I 15 Unidentifiable fish remains 12 Parrot fish (Callyodontidae) and Squilla sp. I Plankton . I ~il . 69 As with S. commersoni most of the stomachs were empty, the few with any contents suggest almost an exclusive fish feeder. FAMILY Belonidre Two species of Belonidce (Garfish) have been identified from the area under survey. Namely Tylosurus crocodilus (Le Sueur) and T. leirus (Bleeker). Only one specimen of T. crocodilus has been taken by trolling. Specimens of both species of varying sizes have been seen in Zanzibar market throughout the year, caught by trolling, harpooning or floating line. TYLOSURUS CROCODILUS (LE SUEUR) (Belone or Strongylura or Tylosurus choram Riipp.). Garfish, Songororo (Swahili), Langsar (E. Indies). 19 Distribution: Widespread Indo-Pacific. Common. References Day 1878-88 Barnard 1927 Weber and de Beaufort 1931 Smith, J. L. B. 1949. Principal characteristics D22 A20 Body almost cylindrical. No gill rakers. No detached finlets on body. Caudal forked. Dorsal originates above first or second anal ray. Colour: In life blue green above, silvery below. Some darkish marking on side behind pectoral. Fins yellow-dusky. Cruise 58 November 1953 Mafia 108 ems. 6lbs. Female ripe. Stomach nil. FAMILY Serranidre Three genera were caught during the survey by pelagic methods-Variola Swainson, Epinephelus Bloch and Plectropoma Cuvier. Normally bottom fishes found in and around coral reefs. VARIOLA LOUTI (FORSK.) (Serranus punctulatus Lac., S.flavomarginatus Riipp.). Chewa, Njombe (Swahili), Croissant queue jaune (Seychelles). Distribution: Widespread Indo-Pacific. References Day 1878-88 Weber and de Beaufort 1931 Smith, J. L. B. 1949 Wheeler and Ommanney (1948-49) 1953. Principal· characteristics D IX 13-14 A III 8 Depth 3.8-4'2 in tota1length. Body elongate with conspicuous crescentic caudal, the lobes produced. Large mouth with one or two canines at side of jaw as well as those in front. Gill rakers rudimentary. Colour: Brightly coloured fish. Orange red body with darker spots. Fins yellowish with spots. Inner edge of caudal yellow. Number caught by trolling . 3 Number caught by other means 39 Largest fish . 78 ems. 8 lbs. Smallest fish . 28 ems. tlb. This fish has been found on most of the coral reefs and banks of the East African coast, but is nowhere abundant. Ofthe 42 fish, 6 were males and 36 females. All were immature except I male and 6 females. Stomach contents Unidentifiable fish remains 14 Squilla sp. I Fish and crustacea 1 Nil 26 EPINEPHEL US TAUVIN A (FORSK.) Rock cod, Grouper, Chewa (Swahili), Vieille tukula (Seychelles), Vieille laboue (Mauritius). Distribution: Widespread and abundant in Indo-Pacific. 20 References Day 1865 (Serranus bontoo) Day 1878-88 (S. malabaricus, S. semi-punctatus, S. salmoides) Sauvage 1891 (E. malabaricus or E. abdominalis) Barnard 1927 Weber and de Beaufort 1931 Smith, J. L. B. 1949 Wheeler and Ommanney (1948-49) 1953. Principal characteristics D XI 15-16 A III 8. Very heavy body in adults- EPINEPHELUS FLAVOC£RULEUS (LAC.) Rock cod, Grouper, Chewa (Swahili). Vieille platte (Seychelles). References Day 1878-88 (Serranus fiavocceruleus) Sauvage 1891 Barnard 1927 Weber and de Beaufort 1931 Smith, J. L. B. 1949 Wheeler and Ommanney (1948-49) 1953. Only two specimens of this species ofrock cod were taken, one by trolling and one by hand line. Principal characteristics D II 15-17 A III 8-9 Both fish were a uniform dark violet colour with lighter lips, fins and head. (See Plate II, Mauritius Seychelles Fishery Survey (1948-49) 1953). Cruise 26 July 1952 Mafia-Zanzibar 61 ems. II lbs. Female ripe. Stomach, fish remains. B. 82 ems. 22 lbs. Female ripe spawning. Stomach nil. T. PLECTROPOMA MACULATUM (BLOCH.) (Plectropoma punctatus Q. and G., P. pessuliforma (Fowler». Rock cod, Grouper, Njombe, Chewa (Swahili), Vieille babonne (Seychelles). Distribution: Widespread Indo-Pacific. 21 References Playfair and Gunther 1866 Barnard 1927 Weber and de Beaufort 1931 Smith, J. L. B. 1949 (Pleetropomus maculatus) Wheeler and Ommanney (1948-49) 1953. Principal characteristics D VIII II-12 A III 8 Elongate compressed body. Large mouth with bands of fine teeth on jaws and palate. Strong canines. Anal spine feeble. Colour: A brilliantly coloured fish. Body background colour bright red, with numerous small blue ocelli. Tips of dorsal, anal and caudal fins sometimes uniform dusky. Also four indistinct wide, dark bands on body. Number caught by trolling . 28 Number caught by other means II Largest fishes 100 ems. 38 lbs. 101 ems. 36 lbs. Smallest fish 61 ems. 7 lbs. This fish has been found mainly close to the off-shore (easternmost) reefs in the Kilwa-Mafia sections and at Latham Island. Seen in the Zanzibar market occasionally. Ripe females were recorded in January, March and December and spent recovering in March, September and November. It is probable that the breeding season of P. maculatum is in the period ofthe N .E. monsoon, when the fish is most abundant. Stomach contents Flying fish . I} Parrot fish (Callyodontidce) 2 Parrot fish and Ccesio sp. I 20 Unidentifiable fish remains 16 Squilla sp. I Nil 18 Plectropoma maculatum is primarily a fish eater like most of the Serranids. It finds its food close above the coral but does come to the surface at times as shown by one stomach containing a flying fish. FAMILY Carangidre This family is represented by the following four genera: Megalaspis Bleeker, Caranx Lacepede, Chorinemus Cuvier and Valenciennes and Elagatis Bennett. Classification ofthe family as set out by Weber and de Beaufort (1931) has been used (except where mentioned). The identification and taxonomic position of certain members ofthe genus Caranx Lacepede has proved extremely difficult and as yet has not been finalised. A complete investigation into the taxonomy and biology of the East African members of this genus has been started. It is possible therefore that a revision of the identification of certain Caranx described here may be necessary at a later date. MEGALASPIS CORDYLA (L) (Scomber rottleri Bloch, Caranx rottleri Day). Torpedo. Distribution: Widespread Indo-Pacific. References Day 1878-88 Barnard 1927 Weber and de Beaufort 1931 Smith, J. L. B. 1949. 22 Principal characteristics D (I) + VIII I/IO-II + 7-9 A II 1/8-10 + 6-8 Torpedo-shaped body with long falcate pectorals. Lateral line with short curve, straight part armed with 50-58 scutes. Lateral caudal keel. Teeth feeble. Several detached finlets behind soft dorsal and anal. Gill rakers 20. Colour: Blue green dorsally, silver ventrally. Fins yellowish. First dorsal with black edge. Rays ofsecond dorsal and caudal dark at distal edges. Upper pectoral rays dark. Black opercular spot. Only three specimens of this species were taken by trolling during the survey: I95I-Cruise 7, Zanzibar Channel, November 1951, 49 ems. 21 lbs., Female ripening. Cruise 8, N. Mafia, December 1951, 45 ems. It lbs., Male mature. Cruise 16, Formosa, November 1952, 53 ems. 2 lbs., Female nearly ripe. Shoals of Megalaspis have been seen feeding in the Zanzibar Channel in March 1952 and September 1953. It does not readily take a lure and has only been seen in the Zanzibar fish market on a few occasions. Stomach contents The first two specimens contained plankton remains, mostly post larval fishes and pteropods; the other 2 Sardinella sp. CARANX (CARANGOIDES) FULVOGUTTATUS (FORSK.) (Caranx bleekeri Kliinzinger). Jackfish, Horse mackerel, Cavalla, Kingfish (S.A.), Kole Kole (Swahili), Carangue platte (Seychelles). Distribution: Western Indian Ocean. References Weber and de Beaufort 1931 Smith, J. L. B. 1949 Wheeler and Ommanney (1948-49) 1953. Principal characteristics D VII-VIII + I 25-28 A o-II + I 22-24 Breast naked ventrally and laterally to about half-way to pectoral base. Head about 4 in total length, depth about 4 in total length. Eye 5.5-7 in head. Maxilla does not reach front of eye. Jaw highly protrusible. Bands of villiform teeth in each jaw. Lateral line curve quarter longer than lateral line straight, which has 14-20 feeble scutes. Pronounced groove, with long ridge above, between orbit and nostril. Feeble adipose eyelid. Colour: In life blue green above, silvery below. Many golden spots mainly above midline. Three black patches on side; first below fourth dorsal rayon midline, second below twelfth dorsal rayon join oflateralline curve and lateral line straight and third below twenty-first dorsal rayon lateral line straight. In some specimens three small black patches anterior to these on midline. Many small black spots below pectorals. Dorsal fins yellow green, anal yellow green with leading edge and tips of fin rays whitish blue. Caudal and pectoral yellow green. Pelvics hyaline whitish blue. Black opercular spot. Pupil of eye black. Colour fades rapidly on death and in preserved specimens the gold and black spots and patches mayor may not be visible. Uniform green-silver. This fish corresponds to the Carangue platte (Seychelles) described by Wheeler and Ommanney (1953). Number caught by trolling . 13 Number caught by other means Largest fishes 101 ems. 19 lbs. 90 ems. 20 lbs. Smallest fish 61 ems. 5 lbs. Not common in the area under survey and not seen south of Kilwa. Very common in Seychelles where it is taken by hand lines in shallow water during the N.W. monsoon (November to April). Ripe females were taken in January, May and November and ripening females in January, May, August and December. Mature males in January, May, August and December. Ommanney found that the probable breeding season in the Seychelles area is November April. Also that C. fulvoguttatus females probably become mature in their fifth year (80 ems.) and males in the fourth-fifth year (60 ems.). Stomach contents Lethrinus sp. I} Sardinella sp. 2 7 Unidentifiable fish remains 4 Nil 6 As in the Seychelles area, it is probable that C. fulvoguttatus finds its food at all levels, from surface to coral bottom. CARANX (CARANGOIDES) SP. Five specimens ofa Carangid similar to C. fulvoguttatus (Forsk) were caught in 1952. Complete measurements of bodily proportions were not, however, taken. Principal characteristics D VIII + 125-28 A II + 122-24 Depth about 3 in total length. Head about 4 in total length. Breast naked ventrally. Lateral line with gentle curve. Curved part equal to straight, the latter having 15-20 feeble scutes. Maxilla reaches front edge ofeye. Jaws greatly protrusible. Fine rows ofteeth in jaws. Colour: In life bluish green above, silvery below. Sides of body with scattered golden or brass-coloured spots. Small black opercular spot. Fins yellowish hyaline. All caught by trolling. ems. lbs. Cruise 15 Tanga February 1952 67 6 Female immature Cruise 17 N. K.ilwa March 1952 87 15 Female immature Cruise 17 N. K.ilwa March 1952 71 9 Female immature Cruise 32 N. K.ilwa September 1952 74 10 Female ripe Cruise 32 N. Kilwa September 1952 74 8 Female ripe Cruise 32 S. Mafia September 1952 65 6 Male mature running Stomach contents: Leptoscaris vaigiensis (Q and G) Sardinella sp. Unidentifiable fish remains Squid remains I Nil . 2 Differences of this species from C. fulvoguttatus (Forsk) are-breast laterally scaly, greater depth of body and lack of the black patches and spots on the sides. The description of this Carangid is similar to that of C.(c) auroguttatus C.V. (Weber and de Beaufort 1931), except that the soft dorsal and anal fins are higher than the third dorsal spine, an opercular spot is present and size given is up to 35 ems. C. auroguttatus is listed as from the Persian Gulf (Blegvaad 1944) and the Red Sea, Muscat and East Indies (Weber and de Beaufort 1931). Until further specimens are obtained and studied, identification cannot be completed. It is possible that the specimens do represent G.(c) auroguttatus C.V. or that it is another species closely allied to it and to G. fulvoguttatus (Forsk). CARANX (CARANGOIDES) GY MN OSTE THO IDES BLKR. Jackfish, Horse mackerel, Cavalla, Kingfish (S.A.), Kole Kole (Swahili), Carangue balo (Seychelles). Distribution: Indo-Pacific. Not abundant. References Day 1878-88 Jordan and Evermann (1903) 1905 Fowler 1928 Smith, J. L. B. 1949 Wheeler and Ommanney (1948-49) 1953 Principal characteristics D VII-VIII + 127-30 A o-II + 123-26. Breast naked ventrally and laterally in a triangular shaped area extending to base ofpectorals. Head 3.3-3-8 in total length. Depth 3-2-3-6 in total length. Eye 6-8 in head, in these specimens all over 67 ems. long_ Maxilla does not quite reach front edge of eye. Bands of villiform teeth in both jaws. Feeble post adipose eyelid_ Pronounced groove from orbit to nostril, with long ridge above. Lateral line slightly curved, curved part a little longer than lateral line straight, which has IS-20 feeble scutes. Colour: In life greenish above, silvery below. Head becoming much darker on death. Dorsal and anal fins hyaline greenish, leading edge and tips of fin rays of anal lighter. Pectorals and pelvics hyaline greenish. Diffuse opercular spot. Pupil of eye black. Very similar to C. fulvo guttatus (Forsk) at a first glance but lacking the brassy spots and black patches. Five specimens caught by trolling in Formosa Bay: Cruise 28 August 1952 67 ems_ 9 lbs. Female ripening Stomach contents"':"'fish remains 73 ems. 12 lbs. Male immature Stomach contents-Nil 77 ems_ 121bs_ Male immature Stomach contents-Nil 77 ems. 14 lb~. Female nearly ripe Stomach contents-fish remains Cruise 33 November 1952 88 ems. 20 lbs. Male mature Stomach contents-Sardinella sp. Like C. fulvoguttatus, not common in Zanzibar market. In the Seychelles area it is a staple fish in the N_W. monsoon (November-April), and is mainly taken by hand line in shallow water. CARANX (CARANX) IGNOBILIS (FORSK.) Plates II,IV and V Jackfish, Horse mackerel, Cavalla, Kingfish (S.A_), Kole Kole (small specimens) Karambisi (large specimens) (Swahili), Carangue les dents (Seychelles), Carangue noir (Mauritius). Distribution: widespre ad Indo-Pacific_ References Jordan and Evermann (1903) 1905 Wakiya 1924 Barnard 1927 Weber and de Beaufort 1931 Nichols 1938 Wheeler and Ommanney (1948-49) 1953. (Caranx sexfasciatus Q. and G.). Principal characteristics D VII-VIII + I 19-21 A., II tI IS-17 Breast naked ventrally with central patch of scales. Naked area may be very small and inconspicuous. Scales forming central patch show considerable variation in size. Depth of body 2-7-2-9 in length, 2-8-3-S in total length; head 3-1-3-7 in length, 3-S-4-4 in total length_ Eye S in head, up to 8 in very large specimens (greater than 100 ems. total length). Posterior adipose 2S eyelid broad, length less than eye diameter (Plate V). Lateral line curve slightly shorter than straight part which has 25-35 (usually 28-32) heavily armed scutes. Colour: In life, uniform silver grey or black above, silver to white below. Head blackish. Dorsal, anal, caudal and pectorals dusky hyaline, pelvics whitish. Spinous dorsal and anal with whitish or yellowish edge to fins. Pupil of eye black. Diffuse or no opercular spot. Soon after death greyish green to black above, silvery below. Fins as before. Body later becoming uniform silver to dusky. This L.'1lportant species forms about 18% of the total catch during the survey. For a con siderable time the identification of this fish was uncertain, but an examination of museum specimens confirms the identification as Caranx (Caranx) ignobilis (Forsk.). The small differences between type specimens and those caught by "Research" are due mainly to the large size ofthe latter. C. ignobilis differs from Caranx (Caranx) sexfasciatus Q. and G., with which it was originally confused, in that the breast is never completely scaly, although the naked patch may be extremely small. In addition the depth of the body is greater and the eye smaller than in C. sexfasciatus. There is little doubt that C. ignobilis found here is identical with the majority ofthe fish described by Ommanney (1953), from the Seychelles-Mauritius area, as C. sexfasciatus Q. and G. Reference to unpublished log details ofthat survey show a similar variability ofbreast scaliness. Number caught by trolling . 114 Number caught by other means I Largest fishes lI5 ems. 54 Ibs. 122'5 ems. 42 Ibs. Smallest fish 40 ems. 21 Ibs. This was the most common ofthe Carangids taken by trolling and has been found throughout the area. More were taken at Latham Island (47) and Mafia-Kilwa (47) than elsewhere. Caranx ignobilis attains a weight of 100 lbs. or more, although such specimens were not taken by us. Monthly catches J. F. M. A. M. J. J. A. S. o. N. D. 1951 8 1952 20 9 2 4 12 10 8 5 1953 9 2 2 I 2 I 2 4 3 1954 9 Number per '4 '1 '°5 '02 '3 '2 hour's trolling It would appear that C. ignobilis is most abundant at the time of the N.B. monsoon with possibly a second increase in July to September. Number offish and state ofgonads MALES I Immature Mature Spent Not running I Running recovering I.F. I 18 4 - M.A. 3 I - 2 M.I. I - - - I.A. . 2 6 - - S.O. 2 6 - - N.D. 2 12 I - 26 FEMALES Immature Mature , Spent Ripening Ripe recovering J.F. 3 6 5 - M.A. 4 I - 2 M.J. 2 I 2 - J.A. - 2 I I s.a. I I 2 - N.D. 7 3 I - There is a suggestion of a spawning period in the months ofthe N .E. monsoon (November March). Weight/length ratio is similar in males and females, except that males over 80 ems. are slightly heavier than females at the same length. Length frequency (Fig. 6) shows that both sexes reach maturity between 70-80 ems. Of the specimens taken from "Research" only 24% were immature. Although total numbers are small it is possible that these fish represent mainly one age group 70-75 ems. to 95-100 ems. and are probably four years old. Scales show marked rings but it is not known as yet whether they are in fact annual rings due to feeding, spawning, 15 MAI.li o IMMATURE NO. OF 10 • MATURE SPECIMENS 5 • 40 50 60 70 60 90 100 110 120 130 LENGTH IN CMS. 15 FEMALES 0 IMMATURE NO. OF 10 •. MATURE SPECIMENS o aJ I ... • • • 40 50 60 70 80 90 100 110 120 130 LENGTH IN eMs Fig. 6. Length frequencies-Caranx ignobilis (Forsk.) migration or hydrographic conditions. Specimens of 70-100 ems. have shown 4 growth rings. Further work on scales and otoliths should give information on age/length ratios so important in population studies. It has been noticed that fish taken from the same shoals are of a fairly uniform size, which would suggest that shoals ofC. ignobilis are ofa single age group. 27 Stomach contents Atherina sp. . I "I Siganus sp. . I Garfish, Tylosaurus sp. I Parrot fish (Callyodontidce) 3 42 Eel I Unidentifiable fish remains 35 Squilla sp. 5 6 Shrimps I Squid . 2 Nil 6r ?? 2 Caranx ignobilis, like most of the family, is primarily a fish eater. It feeds at all levels, as shown by the presence of surface and mid-water forms (Garfish, Atherinids, Squilla, and squids), as well as coral bottom fishes (Parrot fish, eels and Siganids) in the stomach contents. Pieces of Cymodocea sp.-Turtle grass-from sand bottom have also been found along with fish remains. CARANX (CARANX) SANSUN (FORSK.) Plates VI and VII Jackfish, Horse mackerel, Cavalla, Kingfish (S.A.), Kole Kole (Swahili), Carangue jaune (Seychelles). Distribution: Indian Ocean, especially in the N.W. section. References Day 1878-88 (C. jarra) Weber and de Beaufort 1931 Principal characteristics D VII-VIII + I 18-21 A II + I 15-17 Breast ventrally naked with scaly patch in front of pelvics. Scales of central patch large. Size and shape of naked area variable. Depth of body 2-8-3'3 in length, 3'3-3'4 in total length; head 3-3-3'4 in length, 3-8-4-4 in total length. Eye 5-8 in head. Posterior adipose eyelid, length less than eye diameter (Plate VII). Lateral line curve i to -!r less than lateral line straight, which has 30-36 armed scutes. Colour: In life, body bright yellow bronze above, yellow green below. Head dusky bronze, darker above eyes. First dorsal fin dusky hyaline. Second dorsal rays bright yellow, leading edge black. Anal bright yellow. Caudal yellow, distal third of dorsal lobe black. Pectorals and pelvics hyaline yellowish. Scutes on lateral line blackish. After death colour generally darker. It is unfortunate that Forskal's original specimen in his "Herbarium Ichthyologicum" is not now intact, as there are few museum specimens ofthis species with which to compare those caught during the survey. The East African specimens do agree satisfactorily with the descrip tions of C. sansun (Forsk.); the main differences are in the size of the eye and the length of the snout, but these are probably due to differential growth with age, and the fact that our specimens are so very much larger than those in the museum collections and those from which the original descriptions were made. Number caught by trolling . 38 Number caught by other means Largest fishes 83 ems. 13 lbs. 82 ems. 14 lbs. Smallest fish 57 ems. 6 lbs. This species has only been seen on the north Kenya coast in the Formosa and Lamu areas on four occasions, viz. Cruises 16,28,35 and 60 in March 1952, August 1952, November 1952, and December 1953. It is known in the Seychelles and is common in the Gulf of Aden. On all 28 four occasions large shoals of this Carangid were seen following the ship. Only on Cruise 26, however, were they taken in any number-31 in 80 minutes. They were remarkably uniform in length (67-83 ems.) and weighed from 7 to 14Ibs.; and probably represent a single age group. Number offish and state ofgonads MALES Immature Mature Not running Running Spent 13 2 - - FEMALES Immature Mature Nearly ripe Ripening or ripe Spent 5 II 2 5 It is interesting to note that in the specimens caught on Cruise 28 immature and mature females were taken including spent recovering; yet only one male, mature not running, was taken. Stomach contents Sardinella sp. 8} Atherina sp. . 1 30 Unidentifiable fish remains (probably Sardinella sp.) 21 Coral and shell 1 Nil 7 It would appear that this fish is also a fish feeder, mainly on shoals of pelagic sardines and Atherinids. The finding of coral and shell in one specimen shows that C. sansun may at times also find its food near the bottom. CARANX (CARANX) SEXFASCIATUS ELACATE (JORDAN AND EVERMANN) Plates VIII and IX Caranx (C) sexfasciatus Q. and G., Caranx elacate J. and E., Caranx forsteri C.V., Caranx hippos Day (nee. L.). Jackfish, Horse mackerel, Cavalla, Kingfish (S.A.), Kole Kole (Swahili), Carangue gros yeux (Seychelles). Distribution : Indo-Pacific. References Day 1878-88 (C. hippos nee. L.) Barnard 1927 (C. forsteri C.V.) Fowler 1928 Jordan and Evermann (1903) 19°5: 1930 (C. elacate) Nichols 1938 Smith, J. L. B. 1949. Principal characteristics D VII-VIII + I 19-21 A II + 114-16 Breast completely scaly. Depth of body 3 in length, 3'5-4·5 in total length; head 3·4 in ~"Ul::'Ll', 4'0-4·4 in total length. Eye 4·4-5·4 in head. Posterior adipose eyelid greatly developed, 29 wide, length greater than eye diameter (Plate IX). Lateral line curve t to t shorter than lateral line straight, which has 26-34 armed scutes. Colour: In life, silvery green above, silver below. Dorsal and anal fins hyaline dusky. Anterior lobe ofsecond dorsal and anal conspicuously white tipped; distal edges ofanal fin white. Caudal dusky silver. Small opercular spot. Pupil of eye black. Colour similar after death. The author agrees with Barnard 1927 that Caranx forsteri C.V. (Syn. C. sexfasciatus Q. and G.) is distinct from the true C. hippos L. of the Atlantic. The description of this Carangid is almost identical with that of C. elacate J. and E. ((1903) 1905). Weber and de Beaufort 1931 have included C. elacate J. and E. as a synonym of C. sexfasciatus Q. and G., whilst Nichols records it as a race of that same widely distributed Indo-Pacific form. Race elacate differs from the parent species by less body depth, the very large adipose eyelid and a low number ofscutes. However, in this report it is not intended to deal further with the taxonomic problems in the Carangidre. Number caught by trolling . 14 Number caught by other means I Largest fishes 77·5 ems. 8 lbs. 74 ems. 10 lbs. Smallest fish 35·5 ems. I lb. The smallest specimen was taken on a hand line in Mtwara harbour; the largest whilst trolling in the Lamu section. Although only 15 specimens have been taken it appears that this fish is present along the whole East African coast, but nowhere abundant. C. sexfasciatus elacate has been seen in Zanzibar fish market, but not in excess of 70 cms. -The young, about 30-35 cms. and I lb., occur in the markets fairly frequently and have been caught either on hand lines or in beach seine nets. A 25'5 cm. specimen of this species has been identified from the Sabaki River estuary in Kenya. Number offish and state ofgonads MALES Immature Mature Not running Running Spent 3 6 I - I i FEMALES Immature Mature I Ripening Ripe Spent I 2 I I - Figures are insufficient to suggest a breeding season. Stomach contents Chromid Unidentifiable fish remains Crustaceans and squid I Plankton remains . I Nil 7 This species is probably mainly a fish eater, and finds its food at all levels. 3° CARANX (CARANX) MELAMPYGUS c.v. Plate x Caranx (c) stellatus Eyd. and Soul. Jackfish, Horse mackerel, Cavalla, Kingfish (S.A.), Kole Kole (Swahili), Carangus verte (Seychelles), Carangue bleue (Mauritius). Distribution: Indo-Pacific. References Day 1878-88 Sauvage 1891 (C. cceuruleopinnatus) Jordan and Evermann (1903) 1905 Barnard 1927 Fowler 1928 Weber and de Beaufort 1931 Smith, J. L. B. 1949. Principal characteristics D VII-VIII + 120-24 A II + I 17-20 Breast completely scaly. Head about 3'4 in length, 4 in total length; depth about 2·6 in length, 3 in total length. Eye more than 6 in head. Jaw protractile. Maxilla reaches front edge of eye. Row of small conical teeth in each jaw, with inner row offine villiform teeth in upper jaw. Lateral line straight slightly longer than curved portion. 3°-36 armed scutes. Colour: In life, upper half of body and dorsal, anal and caudal fins electric blue, lower half of body silvery. Many black spots on body. Fades rapidly on death and becomes yellow green above, silvery below. Black spots more easily visible. Pectorals hyaline yellow green. Pelvics hyaline white. Other fins dark blue to black. Orange "rim" to eye. Pupil black. No opercular spot. Weber and de Beaufort (1931) discuss the descriptions of C. melampygus C.V., C. stellatus, Eyd. and Soul. and C. bixanthopterus C.V. as used by various authors. They say "these three species agree in fin formula, in the number of scutes, in the extremely scaly breast and in the dentition, but stellatus differs at once by the small, dark, irregular spots on the body, increasing in number and size with age, and by the pectorals, in youth pale with a median yellow band, in adult dusky till blackish, as also the dorsal, anal and ventral". The Carangids caught on the survey (all greater than 53 em. total length) would appear from this to be C. stellatus, and smaller specimens from Zanzibar fish market (less than 30 em. total length and without spots) to be C. melampygus. However, after examination oflarge numbers ofmuseum specimens ofthe two species the author must agree with Woods (I-) that there is a gradual colour change with age from the silvery type of C. melampygus to the darker maculate type of C. stellatus. Thus the two species must be combined under the older name of Caranx melampygus C.V. Number caught by trolling . 36 Number caught by other means 2 Largest fishes 80 ems. 17 lbs. 77'5 ems. 18 lbs. Smallest fish 53 ems. 3 lbs. Only 8 females have been caught as opposed to 30 males. (1-) See Schultz, L. P. and others. Fishes of Marshall and Mariannas Islands, Vol. 1. Smithsonian Inst. Bull. 202. 1953· 31 Number offish and state ofgonads MALES Immature Mature Spent Not running Running recovering 4 22 4 - FEMALES Immature Mature Spent Ripening Ripe recovering I 4 5 I Mature running males were taken in December and March, and ripe females in December, January and March. Large specimens of this fish are not common on the coast, and have only been taken in the Pemba, Zanzibar, Mafia and Kilwa sections. Specimens are seen in the Zanzibar Fish. Market mainly during the N.E. monsoon. Stomach contents Soldier fish-Holocentrus sp. . I} Parrot fish-Callyodontidce 2 Lutianus sp. . 41 30 Blue mackerel-Ccesio ccerulaureus (Lac.) Unidentifiable fish remains 22 Nil 8 Caranx melampygus is also a fish feeder and would appear to seek its food amongst or just above the coral bottom. CARANX (CARANX) SP. Plate XI One specimen taken by trolling in North Mafia Bay on 12th September 1952; Cruise 32. Total length 60 ems. Weight 5 lbs. Female, ripening. Stomach contents-Nil. Principal characteristics D VIII + I 22-23 A II + I 18 Breast naked ventrally except for patch of small scales in front of pelvics. Head 4 in total length; depth 3·5 in total length. Eye 5.25 in head. Broad, short posterior adipose eyelid. Both jaws with row ofconjcal teeth. Maxilla reaches centre ofeye. Lateral line curve shallow, slightly shorter than straight part, which has 36-38 scutes. Scaly sheath to base of second dorsal and anal fins. Pectorals longer than head. , Colour: In life, green yellow above, silvery below. Small black dots scattered above lateral line. Dorsal fins dusky, anal yellowish with white edge. Caudal, dorsally dusky, ventrally yellowish with white tip. Black opercular spot. This species is related to C. ignobilis (Forsk) and C. sansun (Forsk). CHORINEMUS LYSAN (FORSK.) Queenfish, Five-fingered jack, Pandu (Swahili), Sabre (Seychelles), Lalong (E. Indies). Distribution: Widespread Indo-Pacific. References Playfair and Gunther 1866 Day 1878-88 Barnard 1927 Weber and de Beaufort 1931 Blegvaad 1944 Smith, J. L. B. 1949 Principal characteristics DI + VI-VII -H 19-20 A II + I 17-18 Elongate body of characteristic shape. Depth about 3 in length, about 4 in,total length. Head 4'3-4-7 in length, about 5-2 in totaltlength. Eye 4-5 in head. Maxilla reaches posterior border of eye. Lateral line not armed with scutes. Several partly detached "finlets" behind soft dorsal and anal, which are ofequal length, longer than abdomen. Colour: Silvery or dark above, silvery below. Fins hyaline yellowish. 6-8 large dark spots on and above lateral line. Number caught by trolling . 6 Number caught by other means ems. lbs. Cruise 16 March 1952 105 16 Female ripening Cruise 16 March 1952 98 10 Female ripening Cruise 33 November 1952 90 13 Male mature Cruise 33 November 1952 95 16 Female ripe Cruise 33 November 1952 91 12 Female ripe Cruise 60 December 1953 94 12 Male mature running Stomach contents Sard£nella sp. 3 Cephalopod remains I Nil. 2 All six specimens were taken during or at the end of the N.E. monsoon in the Formosa Bay area. Fairly large shoals of this fish seemed to be feeding on Sardinella sp., borne out by the occurrence of Sardinella sp. in the stomachs of five of the fish. Observations show occasional large specimens in the Zanzibar area throughout the year. ELAGATIS BIPINNULATUS (Q. and G.) Rainbow runner, Runner, Prodigal Son, Galathee (Seychelles). Distribution: Widespread tropical Indo-Pacific. References Day 1878-88 (Seriol£chthys bipinnulatus) Jordan and Evermann 1903 Barnard 1927 Weber and de Beaufort 1931 Smith, J. L. B. 1949 Wheeler and Ommanney (1948-49) 1953 Principal characteristics D VI + I 24-27 + 2 A O-II + I 15-17 + 2 Gill rakers 25. Lateral line with no scutes but about 100 tubules. Anal much shorter than soft dorsal, and not longer than abdomen. 2 rayed finlet behind dorsal and anal fins. Colour: An unmistakable fish, greenish blue above. Two blue bands on sides, with yellow band in between. Caudal yellowish dusky. Fades rapidly on death. Five specimens caught by trolling. 33 ems. lbs. Cruise 8 December 1951 Mafia 94 10 Female nearly ripe Stomach-Plankton remains Cruise 8 December 1951 Zanzibar 56 2! Female immature Stomach-Plankton remains Cruise 35 December 1952 Latham 72 4 Female nearly ripe Stomach-Plankton remains Cruise 43 March 1953 Mafia 79 5 Female ripe Stomach-nil Cruise 43 March 1953 Mafia 94 9 Male mature not running Stomach-nil. On Cruise 43 a large shoal ofRainbow Runners followed the ship, but only two were hooked. It is not abundant in the survey area. It was noted that the mature specimens were in almost spawning condition. FAMILY Coryphrenidre A single genus Coryphcena L. with one species found in the Western Indian Ocean. CORYPHlBNA HIPPURUS L. Dolphin fish, Dolphin, Dorado, Panje, Faloosi (Swahili), Dorade (Seychelles). Distribution: All tropical to temperate waters. References Day 1878-88 Jordan and Evermann (1903) 1905 Barnard 1927 Weber and de Beaufort 1931 Smith, J. L. B. 1949 Wheeler and Ommanney (1948-49) 1953 Williams, F. 1953 Principal characteristics D 55-56 A 25-30 Depth about equal to head. Head about 4.5-5.5 in total length. Eye 5.5-6.5 in head. Eye level with anterior portion ofpremaxilla. Maxilla reaches under centre or posterior halfofeye. Caudal deeply forked. Sexes easily distinguished externally by head profile. The male has an almost vertical frontal region whereas that of the female is rounded and oblique. Colour: An unmistakable, brilliantly coloured fish which undergoes many changes in colour and fades rapidly on death. In life, green to blue, darker blue above, yellowish below, with an overall golden irridescence. Dark blue or black "spots" scattered over the body. Dorsal and anal dark blue, caudal yellow to dusky. Number caught by trolling . 38 (Up to Cruise 63, March, 1954) Number caught by floating, baited lines 6 Largest fishes 140 ems. 15 lbs. lI5 ems. 19 lbs. Smallest fishes 67 cms. 2! lbs. 64 ems. 3 lbs. J. F. M. A. M. J. J. A. S. O. N. D. 1951 ------1952 I 4 3 18 I 1953 2 2 2 I 1954 2 8 Of these 44 Dorado, all taken within the coastal region, 35 were females and 9 males (4: I). 34 PLATE I m.v. Research Photo: E. A. Railways and Harbours Administration PL ATE II Group of three fish taken by trolling Sphyrcena c011l11lersoni (C.V.) Total length 79 ems. Caranx ignobilis (Forsk.) Total length 66 ems. Euthynnus affinis (Cantor) Total length 60 ems. (Life) PLATE III Sphyramajello (C.V.) T.L. 52.5 ems. (Life) Above P LA TEIV Caranx ignobilis (Forsk.) T.L. 74 ems. (Life) Left PLATE V Head of Caranx ignobilis T.L. 65 ems. H.L. 16.5 ems. Above PLATE v I Caranx sanSUIl (Forsk.).if(.L. 67 ems. (Preserved specimen) Left PLATE VII Head of Caranx sansun (Forsk.) T.L. 67 ems. H.L. 16 ems. Above PLATE VIII Caranx sexfasciatus elacate (Jordan & Evermann) T.L. 62 ems. (Preserved specimen) Left PLATE IX Head of Caranx sexfasciatus elacate (Jordan & Evermann) T.L. 62 ems. H.L. IS ems. PLATE X Caranx melampygcus e.v. T.L. 55 ems. (Preserved specimen) PLATE XI Caranx sp. T.L. 60 ems. (Preserved specimen) PLATE XII Lutianus bohar (Forsk.) T.Lt"ms. (Life) 38 PLATE XIII Lutianus rivulatus CC.V.) T.L. 56.5 ems. (Life) PLATE XIV Aprion vircscens (C.V.) T.L. 8r ems. (Life) PL ATE XV Scomberomorus sp. (Kanadi) T.L. 8r.5 ems. (Preserved specimen) Coryphcena is only found in Zanzibar market in the period January to June (IO years' records) and the period of maximum abundance is March, April and May. Ratio of females to males (personal observations I952, I953, I954) is about I5: I. Number offish and state ofgonads MALES Immature Mature Spent Not running Running recovering J.F. - - - - M.A. - 4 - - M.J. I 3 - - J.A. - - - - $.0. - - - - N.D. - I - - FEMALES Immature Mature Spent Ripening Ripe recovering J.F. I - 3 - M.A. I 5 7 - M.J. I I l4 - J.A. - - I - $.0. - - - - N.D. - - - - It is fairly certain that the dorado spawning period covers the months of January to June, with the majority spawning in March, April and May in the Western Indian Ocean (see Wheeler and Ommanney (I948-49) I953, Williams I953). No mature running males or spent females have been taken. The female dor~dos seen in Zanzibar market in the period March, April and May are mainly ripe or nearly ripe. Stomach contents Swimming crabs 2 Planktonic crustaceans (largely Zoea larvae) 2 Squilla sp. r Turtle grass . r Identified fish remains (r) 8} Unidentified fish remains 6 r9 Larval and post larval juvenile fishes (2) 5 (I) includes Sardinella sp., Atherina sp., Ccesio sp., garfish (Tylosaurus sp.), and flying fish remains. (2) includes Sardine and Atherina fry, pipe fish (S. biaculeatus), trigger fish (Balistidre), puffer fish (Diodon sp.), garfish, Siganus sp. and Leptocephali. Coryphcena hippurus, when in the coastal regions, feeds mainly on the shoals of small fish found in the surface waters, but does take other surface forms such as plankton and crustaceans. 35 FAMILY Lutianidre Two genera of this family have been caught during the survey. Lutianus Bloch and Aprion Cuvier and Valenciennes. The genus Lutianus is normally bottom living and the members were most frequently taken by hand lines. They do, however, appear to take a trolled lure on occasions in shallow water, as with the Serranids. Aprion is represented by Aprion virescens C.V. which is normally a mid-water form, which will take a trolled lure, floating or bottom line. LUT1ANUSBOHAR (FORSK.) Plate XII Red snapper, Kungu (Swahili). Vara Vara (Seychelles). Distribution: Widespread tropical Indo-Pacific. References Weber and de Beaufort 1936 Smith, J. L. B. 1949 Wheeler and Ommanney (1948-49) 1953 Principal characteristics DX 14 A III 8 . 7i/l . Lateral line scales 56-58. Transverse --. Robust body; the scales below the lateral line are 19-2 0 all parallel to the body axis, those above running obliquely upwards. Temporal region naked. Canine-like teeth in each jaw, with fine teeth on tongue, palate and vomer. Preopercular notch distinct but shallow and the interopercular has a small knob. Colour: In life, deep red black dorsally, red on sides to silver ventrally. Head orange red, Bye bright yellow. Two distinct silvery white patches, fading with age, are present below the posterior ofthe spinous and the soft dorsal fins respectively. Number taken by trolling 7 Number taken by other means 271 This is the most important of the bottom fishes taken by "Research" on the Bast African coast, although not common in the fish markets. This fish is thought to be identical with the Vara Vara ofthe Seychelles. The taxonomy and biology ofthis fish are being studied by F. Talbot ofthis Organization and are not discussed here. L UTI AN U SRI VULAT usc .V • Plate XIII (Diacope rivulata C.V., Diacope cceruleopunctatus C.V., Diacope albogutta C.V.). Blue speckled snapper, Gaga (B. Indies). Distribution: Widespread tropical Indo-Pacific but nowhere common. References Day 1878-88 Sauvage 1891 (D. rivulatus C.V.) Barnard 1927 Weber and de Beaufort 1936 Smith, J. L. B. 1949 Principal characteristics DX 15-16 A III 8-9 Lateral line tubules 40 -47. Transverse-0' Ctenoid scales. Depth about 2'25 in length. Large mouth with strong canines in front. Preo percle serrate with fairly deep notch. Interorbital more or less convex. Soft dorsal scaly. Colour: In life, yellow green with bluish white spots above lateral line. Below lateral line red to silver with bluish white dots and lines. A white spot in the centre of each scale. Head bronze 36 with bluish white dots and lines. Deep red immediately below upper edge of operculum. Four indistinct dusky vertical bands across body. Spiny dorsal yellow darkening to rose colour on soft dorsal. Caudal, anal, pectorals and pelvics rose coloured. Number caught by trolling . I Number caught by other means 3 ems. Ibs. Stomach contents Cruise 16 March 1952 57 8 Male mature. Fish remains Cruise 44 March 1953 55 7 Female ripe. Crab remains Cruise 44 March 1953 57 8 Female spent recovering. Nil Cruise 60 December 1953 64 II Female ripe. Nil. Only these four specimens have been taken from one bank in the Lamu section. Not seen in Zanzibar fish market. APRION VIRESCENS c.v. Plate XIV (Mesaprion microchir Bleeker). Kifimbo (Swahili), Job (Seychelles), Vacoas, vacquois (Mauritius), Kaakap (S.E. Indies). Distribution: Widespread Indo-Pacific. Common in E. Indies. References Jordan and Evermann (1903) 1905 Weber and de Beaufort 1936 Smith, J. L. B. 1949 Wheeler and Ommanney (1948-49) 1953. Principal characteristics DX II' A III 8 DepLh about 5 in total length. Lateral line 45-50. Interorbital flat and naked. Large canines. Pectorals about half head length. An unmistakable fish (see Plate XIV) with a uniform blue green body with largish scales. Number caught by trolling . 99 Number caught by other means 13 Largest fishes 100 ems. 24 lbs. 89 ems. 25 lbs. Smallest fish 51 ems. 2 lbs. This fish has been taken mostly by trolling but is also taken by hand lines in 0-15 fms. One specimen has been taken along with other fish at 75-80 fms. on deep wire lining equipment. In the Seychelles more specimens were taken by hand lines than by trolling. This fish represents 13"i-% ofthe total number offish taken by trolling. J. F. M. A. M. J. J. A. S. O. N. D. 1951 I ° 5 1952 3 I 21 4 2 3 10 7 2 1953 31 I 8 I I 4 I 1954 6 Number per hour. '41 '06 '18 '10 '10 '04 '15 '10 '13 '14 Length frequency graph Fig. 7 shows that maturity is normally reached between 60-75 ems. in both sexes. Aprion virescens would appear to be most abundant during the N.E. monsoon (November to March). 37 IS ~ o IMMATURE NO. OF 10 • MATURE S PE C IMENS • ... 40 SO 60 70 80 90 100 110 120 130 LENGTH IN eMS. IS FEMALES o IMMATURE NO. OF 10 • MATURE SPECIMENS • 40 SO 60 70 80 90 100 110 120 130 LENGTH IN eMS. FIG. 7. Length frequencies-Aprion viriscens (Val.) Number offish and state ofgonads MALES Immature Mature Spent Not running Running recovering J.F. - 21 - - M.A. 4 6 2 - M.J. 4 3 - - J.A. 2 - - - S.O. 2 5 - - N.D. I 7 2 - FEMALES I Immature Mature Spent Ripening Ripe recovering J.F. 4 8 3 - M.A. 6 3 I 3 M.J. 2 - I - J.A. - 2 - - S.O. 2 2 I - N.D. I 5 3 - The weight length ratio is much the same in both males and females. It would appear that the main breeding season is the period ofthe N.E. monsoon. Ommanney found the breeding season of Aprion to be the N.W. monsoon (N.E. here), when the fish was most abundant in the Seychelles area. Ommanney suggests that fish over 70 ems. are probably 4 years old or more. From the figures of this survey this cannot be confirmed or denied. Much additional work needs to be carried out on growth rings on scales and otoliths. Although found throughout the survey area, it is most common during the N.E. monsoon along the eastern-most reefs ofthe Kilwa and Mafia sections. Kifimbo is very rarely seen in Zanzibar market and the natives on the East African coast do not seem to catch it in any numbers. Stomach contents Identified fish remains . 5 } Unidentifiable fish remains 16 21 Cephalopod remains 4 Plankton remains . II Crustacea remains . 9 Fish, Cephalopod and Crustacea I Turtle grass . 2 Seaweed I Nil 63 The identifiable fish remains included Siganus oramin (Schneider), Ccesio ccerulaureus (Lac.), Sphyrcena sp., and Sardinella sp. Crustacea were crabs, shrimps, and Squilla sp. The plankton remains usually consisted oflarge numbers oflarval and post larval fishes. Aprion virescens seems to find its food at all levels and this would seem to be confirmed by the fact that the fish is taken by surface trolling and bottom lines. FAMILY Scombridre (CYBIIDlB) Berg 1947 reverts to the name Cybiidre for this family, but as I have used the paper of Fraser Brunner (1950) for the classification within the family, I have preferred to keep to the name he uses, viz. Family Scombridre. Five genera of this family of true pelagics have been taken during the survey: Thunnus South 1845, Gymnosarda Gill 1862, Euthynnus Jordan and Gilbert 1882, Scomberomorus Lacepede 1802, and Acanthocybium Gill 1862. THUNNUS (NEOTHUNNUS) ALBACORA (LOWE) (Thunnus macropterus Temminck and Schlegel). Yellow fin tunny or tuna, Jodari (Swahili), Thon jaune, thon grand orielles (Seychelles). Distribution: Cosmopolitan-all tropical and sub-tropical seas. References Day 1878-88 (Thunnus macropterus) Kishinouye K. 1923 (Neothunnus macropterus) Smith, J. L. B. 1949 (Germo albacora) Fraser Brunner 1950 Weber and de Beaufort 1951 (Thunnus macropterus) Wheeler and Ommanney (1948-49) 1953 Principal characteristics D VIII-IX 12-14 + 8-9 A 14-15 + 8-9 Gill rakers 8-n + 19-22. Body robust and completely scaled. Teeth small and conical in jaws and on palate. Caudal peduncle with 3 keels. Origin of soft dorsal fin posterior to middle of length. Length of soft fin lobes would appear to be variable according to age, older specimens having longer fins. Those fish caught by "Research" showed considerable variation. Colour: In life, dark blue black dorsally, silver grey ventrally. Spiny dorsal, anal and all finlets bright yellow. Caudal dusky yellow. Number caught by trolling . 12 Number caught by other means 39 Largest fish . 131 ems. 63 lbs. Smallest fish 64 ems. 6i lbs. Specimens caught, 195I-Oetober, November, December 1952-Mareh, May (3), June, August (2), November I953-January. Yellow fin tunny are found throughout East African waters. From observations of shoals seen at sea and specimens in Zanzibar market, the yellow fin tunny appears most abundant at the end of the South East and the beginning of the North East monsoons (July-January) (see page 47). These shoals of yellow fin tunny are normally feeding at the surface and the fish do not take a trolled line readily. The specimens taken by "Research" have been from sub surface shoals not visible from the ship. Local (Zanzibar) fishermen catch the fish in November December in the Zanzibar Channel by using a bright silver fish tied on to a trolled hook. Details of specimens MALES ems. lbs. State ofgonads 64 6i immature 66 81 immature 76 13 immature 83 141 immature 99 32 mature not running 100 36 mature not running FEMALES ems. lbs. State ofgonads 61 8 immature 70 II immature 71 II immature 99 29 nearly ripe 99 29 ripe 131 63 ripening Stomach contents Plankton remains 4 Nil I Sardinella sp. 1111 Flying fish . A therina . sp. 5 Unidentifiable fish remains 2J Fish and Squid I *Fish, squid and crustacea I *This yellow fin tunny contained the following mass of material Nemipterus delagoce (Smith) (7 ems.) I Caranx sp. (7 ems.) I Balistid I Fish Ccesio sp. (2'5 ems.) I Unidentified deep sea fish with large jaws (3'8 ems.) 30-35 Unidentifiable fish (I '25 ems.) I Crustacea Shrimps (5-8 ems.) 40-45 Shrimp (9 ems.) I Squid (2 ems.) . 6 Squid (10 ems.) I A skipjack caught at the same time contained a similar mass ofmaterial. The yellow fin tunny would appear to feed on squid, plankton (including larval and post larval fishes) and small shoaling pelagics (e.g. Sardinella sp.) found in the surface waters. This agrees generally with reports on the feeding habits of yellow fin tunny from other parts of the world. GYMNOSARDA UNICOLOR (RUPPELL) (Pelamys nuda Gunther). Riippell's Bonito, Tunny, Jodari (Swahili), Thon gros yeux (Seychelles). Distribution: Tropical Indo-Pacific. Not common. References Kishinouye, K. 1923 Fraser-Brunner 1950 ,Wheeler and Ommanney' (1948-49) 1953 Principal characteristics D XII-IXIV 13 X 6-7 A II-I2 + 6. Gill rakers 12-13. Body robust, naked except corselet and lateral line. Teeth slender. 3 lateral keels on caudal peduncle. First and second dorsal fins contiguous. Margin of first dorsal fin straight. Colour: Greenish bronze dorsally, silver ventrally. Rest of body uniform blue. Mid-lateral yellow green streak, first dorsal bluish green, second dorsal and anal bronze with whitish tips. After death a uniform silver grey. Only three specimens taken simultaneously on lures off the East coast of Mafia, January 1953· Specimens caught: (1) 142 ems. 78 lbs. Male mature running. Stomach contents-nil (2) 125 ems. 45 lbs. Male mature running. Stomach contents-unidentifiable fish remains (3) 121 ems. 41 lbs. Male mature running. Stomach contents-nil. This fish has not been seen in Zanzibar fish market. It is possible that a few of the shoals of Tunny recorded (page 47) as Yellow fin are indeed Riippell's Bonito. Little is known about this species in the West Indian Ocean. EUTHYNNUS AFFINIS AFFINIS (CANTOR) Bonito, Eastern little tunny, Jodari (Swahili). Bonite (Seychelles). Distribution: Widespread Indian Ocean to East Indies and Australia. References Fraser-Brunner 1949, 1950 Weber and de Beaufort 1951 (E. alleteratus affinis Cantor) Wheeler and Ommanney (1948-49) 1953. Principal characteristics D XV + XVI II-13 + 8 A 13-14 + 6-7 Gill rakers 7-10 + 22-23 Body robust, scaleless except for corselet and lateral line. Slender teeth in jaws, fine teeth on palatine and vomer, 3 keels on caudal peduncle. Dorsal fin separated by a small space, less than eye diameter. First dorsal margin strongly concave. Colour: Body bluish black above, silvery below. Regular wavy black lines on posterior half ofdorsal surface.I -6 thoracic black spots (or all absent), all below base ofpectoral. Number caught by trolling . 29 Number caught by other means Largest fish 84 ems. 16 lbs. Smallest fish 44 ems. 2 lbs. Specimens caught J.P. M.A. M.J. J.A. S.O. N.D. 4 9 4 6 0 6 The Bonito, E. affinis, has been found throughout the area at all times of the year. It does appear that the fish is slightly more abundant in the period of the N.E. monsoon. Large shoals have been seen feeding in various localities during the survey, but do not readily take a lure (see page 47). The Bonito appears more often in Zanzibar market in the N.E. monsoon than the 41 S.E. monsoon but is never abudant. Of the 29 Bonito taken only 2 were immature, one female, 56 ems., and one male, 44 ems. The remainder were, with one exception, over 60 ems. and all mature. It is possible that 55-60 ems. is the minimum mature size of E. affinis. Ommanney suggests that the fish is then in its third year. Occurrence of spawning or "spawned" fish MALE MATURE Running Spent recovering J.F.. 1 M.A.. 2 M.J. 1 J.A.. S.O.. N.D.. FEMALE MATURE Ripe Spent recovering J.F.. 1 M.A.. 4 1 M.J. 1 J.A.. 1 1 S.O.. N.D.. 1 Stomach contents Atherina sp.. .. 51 Fish Sardinella sp.. .. 2;1 12 Unidentifiable fish remains Crustacea... PIankton Post larval fishes .. 2 Crustacean {Squillat sp. .. .. 2 remains Unidentifiable crustacea remains 1 Squid 3 Squid and fish . 1 ~l 8 It is obvious that the Bonito feeds at or near the surface, mainly on the small shoaling pelagic fishes, squids and plankton found there. EUTHYNNUS (KATSOWONUS) PELAMIS (L) Skipjack, Striped bonito, Oceanic bonito, Jodari (Swahili). Distribution: Widespread Indo-Pacific and Atlantic. References Day 1878-88 (Thynnus pelamis) Kishinouye, K. 1925 (K. pelamis) Smith, J. L. B. 1949 (E. pelamis) Fraser Brunner 1950 Weber and de Beaufort 1951 (E. pelamis). Principal characteristics D XIV-XV n-I2 + 7-8 A 12 + 7. Gill rakers 15-16 + 38-40 Similar to previous species but larger number of gill rakers and no palatine or vomerine teeth. In addition conspicuous blue black longitudinal stripes along lower side ofbody. No wavy blue black lines dorsally. Only 5 specimens have been taken, as the fish does not readily take a trolled lure. Seen only occasionally in Zanzibar fish market. Shoals of skipjack have been seen in the survey area throughout the year (see page 47). Specimens caught ems. Ibs. Cruise 16 March 1952 Malindi 62 8 Male mature not running Cruise 24 June 1952 Pemba 56 7 Male mature not running Cruise 42 February 1953 Mombasa 65 7 Male mature not running Cruise 42 February 1953 Mombasa 60 5 Female ripening Cruise 44 November 1953 Malindi 58 6 Female ripe Stomach contents Rastrelliger sp. 2 1Deep sea fish (60-70) ~} Plankton remains I Squid. I Nil I lSee yellow fin tunny stomach contents. SCOMBEROMORUS COMMERSON (LACEPEDE) Kingfish, Spanish mackerel, Nguru (Swahili), Goulue (Seychelles). Distribution: Indo-Pacific. Common. References Day 1865 (Cybium commersoni) Day 1878-88 (C. commersonii) Sauvage 1891 (C. commersonii) Barnard 1927 Munro, 1. 1943 Smith, J. L. B. 1949 FraserBrunner 1950 Weber and de Beaufort 1951 Wheeler and Ommanney (1948-49) 1953. Principal characteristics D XVI-XVII 14-16 + 9-II A 16-17 + 9-II. Gill rakers 3, feeble. Body completely covered with fine needle-shaped scales. Teeth strong, sub-triangular. Maxilla more than half head length. Lateral line single and bent down abruptly below soft dorsal fin. Colour: Silvery blue body. Young with oblong dark blotches, adult with numerous irregular dark cross bands. Number taken by trolling 61 Number taken by other means Largest fishes 125 ems. 41 lbs. 129 ems. 28 Ibs. Smallest fish 72 ems. 4 Ibs. Occurrence of specimens J. F. M. A. M. J. J. A. S. O. N. D. 1951 I 4 1952 I 12 2 4 3 6 2 5 I 1953 7 I 4 I 2 4 1954 2 It would appear that shoals of S. commerson are present throughout the year. It is common in Zanzibar market but is most abundant during the N.E. monsoon (November-February) and at the beginning of the S.B. monsoon (March-July/August). During this latter period shoals of this and the following species (Kanadi) are common in the Zanzibar section. 43 Number offish and state ofgonads MALES Immature Mature Spent Not running Running recovering J.F. - - I - M.A. I 7 - - M.J. - 3 - - J.A. - - 4 - S.O. - - - - N.D. - 3 I - FEMALES Immature Mature Spent Ripening Unripe recovering J.F. - I I I M.A. 4 I 3 4 M.J. 3 I - 4 J.A. I I I - S.O. - I I - N.D. I 3 4 4 It would appear that the breeding season is possibly in the period of the N.E. monsoon and long rains (November-May). The occurrence of 4 mature running males in August suggests, however, that the breeding season may be longer. Only 10 of the kingfish taken were immature. Figures suggest that females possibly mature between 80-90 ems. and that most males over 75 ems. are mature. Weight/length ratio is similar in the two sexes. Stomach contents Blue "macker~l" Ccesio sp. Caranx sp. (small) Coryphcena hippurus (small) Unidentifiable fish remains Squilla and fish remains I Zostera sp. I Nil 37 S. commerson is mainly a fish eater, living on the smaller pelagic fishes. SCOMBEROMORUS SP. Plate XV Kingfish, Kanadi (Swahili). Principal characteristics D XV 15-17 + 9-10 A 15-16 + 9. Gill rakers 2 + II (or 3 +10) 44 Elongate compressed body, covered with fine needle-like scales. Lateral line single and not angulate. Moderately strong sub-triangular teeth in jaws. Maxilla half length of head. Pectoral fins completely scaly. Origin of soft dorsal very slightly behind middle of length of fish (not total length). Colour: Body bluish above, silvery below. Sides with black longitudinal streaks and spots. Leading edge of first dorsal black. This species has not been identified as yet. From the key to the species of the genus Scomberomorus (Fraser Brunner 1950), this "Kanadi" would lie in the same sub-division as S. reJ?alis (Bloch), i.e. "Pectoral fin almost completely covered with scales. Sides with longi tudinal dark streaks and spots". It differs, however, from S. regalis in gill raker count which is 2 -j- !I (13) instead of 3-4 + 12-15 (15-17). Dorsal spines XV instead ofXVII and maxilla not more than half head length. S. regalis is only recorded from the Western Atlantic Ocean from Cape Cod to Brazil. Specimens are being taken to the British Museum (Natural History). Three specimens taken by trolling ems. lbs. Cruise 20 Mafia May 1952 91 9 Male mature running Cruise 20 Mafia May 1952 82 7 Male mature running Cruise 32 Formosa September 1952 80 7 Female'spent recovering Although only these three specimens were taken by us, large shoals of this fish, and also S. commerson enter the Zanzibar area each year about March-April and "leave" about August September (see page 47). Highest numbers are caught in May-June. The Kanadi is one ofthe staple fishes of the Zanzibar market at this time of the year and is very much sought after as food. Although a shoaling pelagic, it is mainly caught by set nets in fairly shallow water. Large numbers are also caught on hand lines using whole fresh sardines as bait. Average weight of fish is about 8 lbs. From observation of specimens passing through the market each year the gonads appear to be in the ripening (female) or mature not running (male) stage. ACANTHOCYBIUM SOLANDRI (c.v.) Wahoo, Peto, Nguru (Swahili), Gulue (Seychelles). Distribution: Cosmopolitan in tropical and subtropical seas. References Jordan and Evermann (1903) 1905 Kishinouye, K. 1923 Munro, 1. 1943 Smith, J. L. B. 1949 Fraser Brunner 1950 Weber and de Beaufort 1951 Wheeler and Ommanney (1948-49) 1953. Principal characteristics D XXV-XXVIII 10-13 + 9-10 A IO-II + 8-9. No gill rakers Elongate compressed body with small scales. Teeth strongly compressed, sub-triangular. Lateral line single. Pelvics small. No abdominal groove. Colour: In life dark blue above, silvery grey below, with dark blue vertical bands. Colours fade rapidly on death to uniform blue grey. Eleven specimens ofthis large solitary pelagic fish have been taken (6 males, 5 females). Largest fish 154 ems. 55 lbs. Smallest fish . 108 ems. 15 lbs. Average weight of eleven specimens-33t lbs. The wahoo is found throughout the East African area mainly in the period of the S.E. monsoon. It has been seen at intervals in Zanzibar market. 45 Stomach contents Bonito (Euthynnus Sp.) I Bonito (Euthynnus sp.) and Squid 2 Unidentifiable fish remains 3 Sardine I ~l 4 The wahoo is a fish eater living on the shoaling pelagics such as bonito, sardines, as well as squid. Most of the wahoo examined had many parasites attached to the inner wall of the stomach. FAMILY Xiphiidre XIPHIAS GLADIUS L. Swordfish, Broadbill, Nduaro (Swahili). Distribution: Cosmopolitan in tropical seas. References: Smith, J. L. B. 1949. Only one immature specimen of this large and powerful fish was taken, off Mombasa in October 1951. Total length 138 ems., weight 9i lbs., female immature. Stomach contents: Fish remains. Table 5 Summary of fish caught by trolling (September, 1951-January, 1954) Family Sphyramidace Chorinemus lysan 6 Sphyrcena commersoni 69 Elagatis bipinnulatus 5 Sphyrcena jello . 38 Family Coryphcenidce Family Belonidce Coryphcena hippUrtlS 36 Tylosaurus crocodilus . 1 Family Lutianidce Family Serranidce Lutianus bohar . 7 Plectropoma maculatum 28 Lutianus rivulatus 1 Variola louti . 3 Aprion virescens .. 99 Epinephelus tauvina . 5 Family Scombridce (Cybiidce) Epinephelus fiavocceruleus 1 Thunnus albacora . 12 Family Carangidce Gymnosarda unicolor . 3 Megalaspis cordyla . 3 Euthynnus affinis 29 Caranx fulvoguttatus . 13 Euthynnus pelamis . 5 Caranx sp. •. 5 Scomberomorus commerson 61 Caranx gymnostethoides 5 Scomberomorus sp. . 3 Caranx ignobilis . II4 Acanthocybium solandri II Caranx sansun. . 38 Family Xiphiidce Caranx sexfasciatus elacate 14 Xiphias gladius . Caranx melampygus 36 Caranx sp. 1 DISTRIBUTION AND SEASONAL ABUNDANCE OF THE PELAGIC FISHES SEASONAL ABUNDANCE AND MIGRATION Some ofthe pelagic fishes described inthis survey display a marked seasonal abundance apparently due to a migration in and out ofthe area. Others remain throughout the year, although they too may show a marked seasonal variation in abundance. The Sphyrrenids and Carangids are present all the year round but the Carangids appear to be more numerous in the N.B. monsoon. Elagatis and Chorinemus (Carangidre) were seen only in the N.B. monsoon but so few were taken by "Research" that no information as to their migration has been forthcoming. The Serranids and Lutianids, normally bottom and mid-water forms, are taken throughout the year. Like the Carangids, however, they are more numerous in the N.B. monsoon, especially Plectropoma maculatum and Aprion virescens. It is possllble:/l Aprion moves downwards in the rough weather of the S.B. monsoon, a specimen being taken on deep lining equipment at 75 fms. in October 1953 off North Pemba Ballie specimens followed the gear to the surface. The S.E. monsoon was blowing strongly at the time of the operation. It is interesting to note that in the Carangids, Lutianids and Serranids taken by us, the gonads are at or near the spawning stage in the N.E. monsoon, the time of apparent maximum abundance. Coryphcena hippurus makes a transitory appearance in the coastal area from January to June. It has been described earlier (Williams, F. 1953) that in all probability this is a spawning migration. Period of maximum abundance is April to May when the gonads are ripe (see page 35). By June the shoals ofCoryphcena have disappeared from the coastal area, by which time spawning would seem to be complete although no "spent" fish have been taken by "Research". The fish are probably to be found in the surface waters of the open sea. It is extremely unlikely that the disappearance of this true pelagic from June to January is due to a downward migration into deeper water in the coastal area. Amongst the Scombrids the Kanadi (Scomberomorus sp.) is virtually absent from the Zanzibar area except in the months of May, June, July and August. Scomberomorus commerson is taken all the year round but is much more abundant at the same time as the Kanadi. Olliy 3 specimens of the latter were taken trolling but observations have been made on the large numbers of specimens passing through Zanzibar market in these months. The majority of the gonads are at the ripening or mature-not-running stage. It is doubtful therefore whether this migration into the area is a spawning one. It is possibly a feeding migration, as large shoals ofsardines are known to be present in the Zanzibar area at this time ofthe year. Kishinouye (1923) stated that S. commerson, unlike the other Scombrids, enters Japanese waters when the temperature is low. It is possible that the appearance ofthat species and the Kanadi in this area in the S.E. monsoon is connected with the lower surface water temperature. However, the temperature in the S.E. monsoon is considerably higher than that in Japanese waters. The tunny like Scombrids were also not taken in large numbers by "Research", but numerous shoals ofthese fishes have been observed at many points in the coastal region throughout the year and in all weather conditions. They appear to be more numerous in the N.E. monsoon. These shoals are of three types: (I) Bonito (E. affinis) and/or Skipjack (E. pelamis) or in some cases Megalaspis cordyla (Carangidre); (2) Yellow fin tunny (Thunnus albacora) and/or Riippell's Bonito (Gymnosarda unicolor), or an as yet unidentified species of tunny; (3) Rastrelliger sp. or a similar small Scombrid. A detailed "log" of most of these shoals was kept from January 1953 to January 1954 and is given as Table 6 (together with a distribution chart as Fig. 8). It must be emphasised that these observations were made from olliy one boat in the large area under survey and that these shoals were probably much more numerous and widespread than is apparent from this "log". These tunny-like shoals, when seen from "Research", were usually feeding and did not take a trolled lure. The shoals ofYellow fin tunny seem to make their appearance at the end of the S.E. monsoon and stay throughout the N.E. monsoon. CATCH The total catch of fish by multiple trolling in the period November 1951 to January 1954 was 8,635 lbs. Of this total 7,803 lbs. were caught at trolling speed in 6,822 line hours. This gives a catch rate of 1'14 lbs./line/hr. The remaining 832 lbs. were caught at full speed whilst on passage, a catch rate of 0.22 lbs./line/hr. .. Table 7 gives the details of line hours, lbs. of fish caught and rate in lbs./line/hr. for each month during the survey. The families of pelagic fish are represented in the following percentages of total weight of fish in lbs. % Carangidre (mainly C. ignobilis) 42 '5 Scombridre (mainly S. commerson) 22'0 47 Sphyrrenidre 12'0 Lutianidre (mainly Aprion virescens) II'O Serranidre (mainly Plectropoma maculatum) 8'2 Coryphcena hippurus 4'2 The suggestion has been made that the pelagic fishes are more numerous in the months ofthe N.E. monsoon and long rains-November to May. The monthly catch rates given in Table 7 do seem to suggest that this may be correct, although in 1952 good catches ofpelagic fishes were taken in July, August and September, i.e. in the S.E. monsoon. In 1953 however, the catches were very small throughout the months of the S.E. monsoon, and indeed until the beginning ofDecember. This variation between the S.E. monsoons of 1952 and 1953 was clearly visible in the amount of pelagic fish passing through Zanzibar market and in the other fish markets along the East Mrican coast. It is necessary here to take into account the effect ofthe monsoon condi tions of the coastal area on the pelagic fishery. The S.E. monsoon is of a longer duration and normally stronger than the N.B. In 1952 the S.E. monsoon was "short-lived" and variable, with long calm periods in July, August and September. In 1953, however, the S.E. monsoon was one ofthe longest and strongest on record and lasted from late May until the beginning ofDecember. Thus the variability in the pelagic catches in the months ofthe S.E. monsoons of 1952 and 1953 may be due to the difference in monsoon conditions. The N.E. monsoon appears much less variable than the S.E. but catches do still seem to be reduced in "heavy" weather. In the case of fish present throughout the year (Carangids, Aprion) the possibilities were as follows-that the fish were forced to leave normal feeding grounds in shallow water because of the disturbed state of the water, or that the fish were present and the problem was that of fishing successfully (and safely) on shallow banks in big seas. On "Research" it has been found that both possibilities are valid. On some occasions in big seas fish have been taken, on others they appeared to be completely absent. On most occasions in heavy weather it has been found impossible, for safety reasons, to get close enough to reefs or shallow banks. There is little doubt that the monsoon weather conditions have a considerable effect on the pelagic fishery. Table 8 (a-i) gives the following details for each section: (i) cruise no. (ii) hours trolled. (iii) line hours, (iv) numbers of fish caught, (v) lbs. of fish, and (vi) the catch rate in lbs./line/ hour, together with the overall totals and average catch rate for each section during the survey. The following is the list of sections in order of catch rate. Section Average catch rate lbs./line/hr. Zanzibar (Latham Is. only) 2·66 Mafia 1·82 *Malindi 1 '75 Kilwa 1'56 Pemba 0·62 Lamu 0·61 Zanzibar (excluding Latham Is.) 0'47 Lindi 0'38 Mombasa 0'06 (*High due to catch of August, 1952). DISTRIBUTION To give a general idea ofthe distribution ofthe pelagic fish the positions ofall strikes, successful and unsuccessful, have been plotted for each section-Fig. 9 (a-h). Lamu (Fig. 9 (a)). Fish and strikes in this area are mainly concentrated close to Vidal and Presgrave Banks to the north of Lamu. These banks are from 2t-IO fms., with a coral bottom, and are surrounded by water from 20-30 fins. Bottom fish are plentiful on these banks. Few pelagic fish were caught elsewhere in the section. Malindi (Fig. 9(b)). The vast majority of fish have been found near Ozi Reef and in the extreme N.E. corner of Formosa Bay. Ozi Reef (Zewoyu Archipelago) consists of two parallel 48 lines of islets and half submerged reefs. To the seaward side ofthe outer row the bottom drops steeply to more than 20 fms. The N.E. portion of Formosa Bay is shallow, 2i'-IO fins., with a sand and mud bottom. Small numbers of fish were also taken around Pamamba shoals (S.W. Formosa Bay). Surprisingly few fish were found on the extensive Malindi Bank. It is to be noted that C. sansun and Chorinemus lysan have been taken by "Research" almost exclusively in this section. Mombasa (Fig. 9(c)). Only 3 fish and 3 strikes have been recorded from this section, for the most part of which there is a narrow fringing reef beyond which the depth increases rapidly up to 100 fms. Pemba (Fig. 9(d)). Few fish recorded in this section from anywhere except the North Pemba Bank. Most ofthe fish were taken in the Ras Kiuyu area and along the seaward edge ofthe reefs to the N.W. of Ras Kiuyu, mainly inside the 20 fm. line. There is a conspicuous absence offish on the mainland side of the Pemba Channel. Zanzibar (Fig. 9(e)). At Latham Island Bank fish and strikes have been too numerous to plot on the chart (more than 200). The fish have been found at all points on the bank, but the main concentration would appear to be at the edges ofthe bank in 10-15 fms., and all inside the 100 fm. line. The remainder of the fish in this section are rather scattered except for the east coast of Zanzibar where fish have been found close alongside the reef. Mafia (Fig. 9(f)). The fish are mainly distributed alopg the seaward (E) edge ofthe Tutia Kibondo reef. In this area and at Forbes Bay and Ras Mkumbe to the north, there is a shelf (3-10 fms.) extending outwards from the reef. Beyond the shelf, the width of which varies considerably, the bottom drops steeply towards the 100 fm. line. It is above the shelf that the fish are normally found. In other parts of the section fish soon to be found on or alongside the many small banks and reefs in Mafia Bay. Kilwa (Fig. 9(g)). The concentration offish in this section is close to the seaward edge ofthe outer Kilwa reefs from Okuza in the north to Fanjove in the south. The depth ofwater increases rapidly outside the reefs except where frequent shallow spurs jut out from the reef. To the south end of Fanjove Reef there is a considerable shallow shelf extending out from the reef. It is on this shelf and around the shallow spurs that most fish have been taken. Lindi (Fig. 9(h)). Few fish have been found in this section. Most of those have been found close to the fringing reef which borders almost completely the coast line in this section. Some general information can be given as to the distribution of the pelagic fishes in the area under survey. It would appear that few pelagic fish are caught, at least in the surface waters, outside the 100 fm. line. The majority are caught where a shallow shelfor spur extends outwards from the fringing reef and then drops rapidly into deep water towards the 100 fm. line. Such areas are Tutia-Kibondo (f), South Fanjove (g) and N. Pemba (d). Ofthe remaining fish most are caught over shallow offshore coral banks such as Latham Island Bank (c) and Lamu Banks (a). It must be taken into consideration that owing to the size and geographical nature of the area, more trolling has been carried out in some sections than in others, but the fact does remain that the catch rate is highest when the conditions described above exist. The reasons for this distribution are not clear at present. There is little doubt, however, that the nature ofthe bottom and hydrographic conditions have an important bearing on this problem. The shelf extending outwards from the reef gives a greater area for coral growth than where the reef props steeply into deep water, although the actual coral growth may be as rich. Thus the shelf gives a greater feeding and protection area for the bottom and mid-water fishes, and other animals, on which feed many of the large pelagics such as Caranx, Aprion and Plectropoma. Detailed hydrographic work would have to be carried out in these areas before the exact nature of the water conditions and their effect on the coral growth, and hence the fish population, could be established. In the case of the shoals of tunny-like Scombrids, their appearance at certain times of the year is probably due to large concentrations ofplankton or small fish such as sardines, Atherinids and half-beaks, etc. This is also true ofthe shoals ofCaranx sansun, and Chorinemus lysan found 49 in the Ozi Reefarea. The distribution ofthe tunny-like shoals listed in Table 6is shown on Fig. 8. These shoals have been seen mainly inside the roo fin. line, although they must migrate outside this line to be seen at Latham Island. Main concentrations have been in North Mafia Bay and the Zanzibar Channel. Unlike other pelagics, these shoals are found over open water, as well as close to the reefs. Little is known as yet about the distribution ofthe plankton and small fish on which the tunny-like fishes feed. Thus to gain knowledge ofthe distribution ofthese shoals it is vitally important to know the seasonal abundance and distribution of the members of the food chain. Table 6 Log of Tunny-like shoals ( January, 1953-January, 1954) I Cruise Position and No. Date Time Section I Species I Birds Remarks 37 2/1/53 11.05 Pungume (Zanzibar) Bonito I - Small fish. 38 II/I/53 18·40 Offshore (Mafia) ? Yes Small fish 42 21/2/53 12·47 Kilifi (Mombasa) . Skipjack No One taken, others feeding. 43 10/3/53 07·45 N. Mafia Bay (Mafia) Rastrelliger sp.? Yes 15/3/53 10·55- Mbudya Patches (Zanzi- Bonito, Rastrelliger Yes Many shoals. 15·00 bar) sp? Megalaspis sp.? 44 22/3/53 12.15 Mwamba Hanawi (Lamu) Bonito Yes Several shoals feeding (I fish taken). 25/3/53 08.10 Kwyhu Is. (Lamu) Bonito and/or Yes Many shoals Skipjack II.25 Rees Is. (Lamu) Bonito . Yes I shoal. 26/5/53 11.45 N. Shearwater Patches Bonito and/or Yes 5 large shoals. (Zanzibar) Skipjack 11.55 N. Shearwater Patches Bonito and/or Yes 3 large shoals. (Zanzibar) Skipjack 14.30 Mangapwani (Zanzibar). Bonito and/or Yes 3 large shoals. Skipjack 46 7/5/53 18.00 Kibondo anchorage Bonito - Several shoals seen. (Mafia) .. . 8/5/53 17·00 Kilwa Kisiwani (Kilwa) . Bonito Yes I shoal. I wahoo taken nearby. 13/5/53 13·00- Zanzibar Channel Bonito and/or Yes Many shoals Dar- 16.30 (Zanzibar) Skipjack Zanzibar. 47 27/5/53 08·55 Shearwater Patches Bonito and/or Yes 2 shoals. (Zanzibar) Skipjack 16.05 Pemba Channel (Pemba) Bonito and/or Skipjack Yes Several shoals. 48 17/6/53 16.00 N. Ras Kimbiji (Zanzibar) Bonito No 2. shoals feeding. 16·50 N. Ras Kimbiji (Zanzibar) Bonito No I shoal feeding. 21/6/53 II.OO S. Mtwara (Lindi) Bonito Yes I shoal feeding. 11.15 S. Mtwara (Lindi) Bonito Yes I shoal feeding. 16·35 } Same shoals as a.m.? 19·00 22/6/53 10.10 Lindi Bay (Lindi) . Bonito Yes I shoal feeding. 10.25 Lindi Bay (Lindi) . Bonito Yes I shoal feeding. 11.30 Lindi Bay (Lindi) . Bonito Yes I shoal feeding. 23/6/53 12.10 Zanzibar Channel Bonito Yes 2 shoals feeding. (Zanzibar) 12.15 Zanzibar Channel Bonito Yes I shoal feeding. (Zanzibar) 12·35 Zanzibar Channel Bonito Yes I shoal feeding. (Zanzibar) 51 17/7/53 13·45 N. Wasin (Pemba) Bonito? . No Large shoal-small fish. 14·10 N. Wasin (Pemba) Bonito? . Yes Several shoals- small fish. 18/7/53 10.25 Manza Bay (Pemba) Rastrelliger sp. - Shoal of small fish. 16.15 Pangani River (Pemba) Bonito . Yes Small fish. 17.00 E. of Maziwi Is. (Pemba) Bonito and/or Yes Very large number of Skipjack fish but widely scat- teredo Feeding on sardine-like fishes. 17.05 E. of Maziwi Is. (Pemba) Bonito and/or Yes Small shoal. I Skipjack 5° Table 6-continued. I Cruise I I Position and I Date Time Section I Species Birds Remarks -~I I I 5I I 18/7/53 17·2O E. of Maziwi Is. (Pemba) I Bonito and/or Yes 2 shoals. I Skipjack . 19/7/53 I 09.30 Mangapwani (Zanzibar) Bonito and/or Yes I shoal feeding. Skipjack . I Io.05 Mangapwani (Zanzibar) Bonito or Yes 2 shoals feeding. Skipjack 52 28/7/53 IO.OO Latham Is. (Zanzibar) Yellow fin tunny? Yes 2 shoals feeding. 29/7/53 08.00 Latham Is. (Zanzibar) I Bonito or Yes I shoal large fish. I I Skipjack 12.00 Latham Is. (Zanzibar) Bonito or Yes I shoal large fish. I Skipjack Same shoal? 16·40 Latham Is. (Zanzibar) Bonito or Yes I shoal. Skipjack 53 '17/8/53 17·45 Mangapwani (Zanzibar) . Bonito and/or No 2 shoals. Skipjack 19/8/53 09.70 Pamamba Shoals (Malindi) ? - Small fish, I strike. 2I/8/53 ILIO Shearwater Patches ? Yes Large shoal. (Zanzibar) 55 9/9/53 14·00 Latham Is. (Zanzibar) ? Yes I shoal feeding. 15·00 Latham Is. (Zanzibar) Rastrelliger sp. - 3 shoals. 9/9/53 15·30 Latham Is. (Zanzibar) Yellow fin tunny No Feeding, sounded on approach. App. IOO lbs. 15·50 Latham Is. (Zanzibar) Yellow fin tunny No Feeding, sounded 0n approach. App. lOO lbs. IO/9/53 I2·30 Latham Is. (Zanzibar) Yellow fin tunny No I shoal. 15·30 Latham Is. (Zanzibar) Yellow fin tunny No I shoal, I strike. 56 24/9/53 Allday N. Mafia Bay (Mafia) Rastrelliger sp. Yes Very many shoals seen Megalaspis sp. during the day. Bonito and/or I Skipjack 25/9/53 07·40 N. Mafia Bay (Mafia) Rastrelliger sp. or No 3 shoals. Bonito 27/9/53 13·50 Forbes Bay (Mafia) Yellow fin tunny No Chasing shoal of small fish. 14·IO Forbes Bay (Mafia) Yellow fin tunny No Leaping in the air. 28/9/53 I2·30 Zanzibar Channel ? Yes Small fish, I shoal. (Zanzibar) 57 2I/IO/53 ILOO Lamu. ? Yes I shoal. 22/IO/53 17·45 IO miles S80E Ras ? Yes Small fish. Ngomeni (Malindi) 24/IO/53 16.15 N. Pemba (Pemba) Bonito No I shoal. 58 II/II/53 06.50 N. Mafia Bay (Mafia) YFTorRB. Yes I shoal, no strikes. °7·15 N. Mafia Bay (Mafia) YFT or R.B. . Yes I shoal, no strikes. 09.30 N. Mafia Bay (Mafia) ? Yes Very small shoal sounded. I LOO- Fawn Bank (Mafia) YFTorRB.. Yes Fish IO-30 lbs. 500 II.25 scattered. IL4° Fawn Bank (Mafia) YFT or RB. . Yes Similar to above. IL45 Fawn Bank (Mafia) YFTor RB.. Yes I shoal. IL50 Fawn Bank (Mafia) YFT or RB. . Yes I shoal. 13·00 Cumulus Bank (Mafia) YFT No Jumping near ship. 14·00 Mafia Lighthouse (Mafia) Skipjack Yes I shoal. I2/II/53 06·35 Cumulus Bank (Mafia) ? No I shoal feeding. IO.20 Niororo Is. (Mafia) ? Yes I shoal. 12.15 Vulture Bank (Mafia) ? Yes I shoal. 13/II/53 IO.OO Cumulus Bank (Mafia) YFT or RB. . Yes Feeding. I,OOO+ IO·30 N. Mafia Bay (Mafia) Tunny or large Yes I shoal feeding. Bonito IO·45 N. Mafia Bay (Mafia) Tunny or large Yes I shoal feeding. Bonito IO·50 N. Mafia Bay (Mafia) Tunny or large Yes I shoal feeding. Bonito IO·55 N. Mafia Bay (Mafia) Tunny or large Yes I shoal feeding. Bonito ILOO N. Mafia Bay (Mafia) Tunny or large Yes I shoal feeding. Bonito IL20 N. Mafia Bay (Mafia) YFT No I shoal feeding. I 16.20 N. Mafia Bay (Mafia) YFT Yes I shoal feeding. 51 Table 6-continued Cruise Position and No. Date Time Section Species Birds Remarks 58 I3/II/53 I7·IO N. Mafia Bay (Mafia) YFT Yes I shoal feeding. I7·40 N. Mafia Bay (Mafia) YFT Yes I shoal feeding. I5/II/53 I5·50 Kilwa Kivinje (Kilwa) ? Yes I shoal feeding. I6.45 Kilwa Kivinje (Kilwa) ? Yes I shoal feeding. I7·05 Kilwa Kivinje (Kilwa) ? I Yes I shoal feeding and jumping. I7·30 Kilwa Kivinje (Kilwa) YFT Yes I shoal. I7·35 Kilwa Kivinje (Kilwa) YFT Yes I shoal. I7-4° Kilwa Kivinje (Kilwa) YFT Yes I shoal. 60 I7/I2/53 II.30 Lamu Bay (Lamu) ? Yes I large shoal. I8/I2/53 IO.OO Kywhu Is. (Lamu) ? YFT Yes 2 shoals feeding. I2.00 Kywhu Is. (Lamu) ? Yes Small fish. I3·I5 Kywhu Is. (Lamu) ? Yes Small fish. 6I 2I/I/54 I3·00 Mywara Approaches YFT No Small shoal of small (Lindi) YFT. I5·I5 Mtwara Approaches YFT Yes 30-40 lbs. (Lindi) I 30/I/54 I5·IO Mtwara Approaches YFT ?I shoal. (Lindi) . YFT = Yellow fin tunny. R.B. = Riippell's Bonito. Table 7 Monthly Catches of Pelagics at Trolling Speed (Rate in Ibs./line/hour) Number of Rate in Date line/hrs. Lbs. offish Ibs./line/hr. I95I November I47 87 0'59 December 339 3°7 0'92 I952 January 226 674 2'98 XI. February I05 9 0'08 March 56I 9°7 I'6I April . 290 I99 0·68 May . 8I6 686 0'84 June. 290 36 0'I2 July I53 324 2'°5 August I94 663 3'4I September. I7I 649 3'79 X2. October - - - November 290 459 I'58 December 82 287 3'57 I953 January 267 902 3'37 X3· February I45 I2 0'08 March 59I 259 0'43 April • - - - May. I86 I96 I'05 June. 258 II7 0'45 July 37I II9 0'32 August 85 26 0'3° September. 28I 68 0'24 October I08 55 0'5° November 355 I9I 0'53 December I35 75 0'55 I954 January 373 496 I'33 6822 7803 Av. rate I'I4 (At full speed 832 lbs. 10 3762 hrs., I.e. 0'22 lbs./line/hr. XI. In dry dock. X2. Breakdown gears. )[3. In dry dock. Table 8(a) Lamu Section Cruise Hours Line Number of Lbs. of Rate ~n Date No. I Trolled hours fish caught fish Ibs.{line{hr. March,1952 16 21 140 16 124 0·88 August, 1952 28 14 II6 10 145 1'25 November, 1952 33 6 54 6 67 1'24 March,1953 44 21 234 5 54 0'25 October, 1953 57 5 45 0 0 0 December, 1953 60 10 90 2 27 0'30 Totals 77 679 39 417 0'61 Table 8(b) Malindi Section Cruise Hours Line Number of Lbs. of Rate in Date No. Trolled hours fish caught fish Ibs.{line{hr. March, 1952 16 24 158 16 154 0'96 August, 1952 28 9 78 43 518 6'64 November, 1952 . 33 8 72 9 126 1'65 February, 1953 42 4 45 0 0 0 March, 1953 44 5 60 4 55 0'91 August, 1953 53 2 25 0 0 0 October, 1953 57 7 63 I 55 0'87 December, 1953 . 60 5 45 4 48 1'06 Totals 64 546 77 956 1'75 Table 8(c) Mombasa Section Cruise Hours Line Number of Lbs. of Rate in Date No. Trolled hours fish caught fish Ibs.{line{hr. November, 1951 6 8 48 I 9 0'18 June, 1952 24 19 178 0 0 0 February, 1953 42 10 100 2 12 0'12 Totals 37 326 3 21 0'06 53 Table Sed) Pemba Section Cruise Hours Line Number of Lbs. of Rate in Date No. Trolled hours fish caught fish I lbs./line/hr. November, 1951 6 6 36 2 33 0'91 January, 1952 12 18 II8 6 94 0·80 February, 1952 15 12 84 2 9 0'10 April, 1952 18 36 248 14 182 0'73 June, 1952 24 13 100 4 36 0'36 November, 1952 33 19 164 18 266 1·62 March, 1953 41 8 88 2 39 0'44 July, 1953 51 20 214 I 0 0 0 Totals 132 I 1052 I 48 659 0·62 Table See) Zanzibar Section (Excluding Latham Is.) Cruise Hours Line Number of Lbs. of Rate in Date No. Trolled hours fish caught fish lbs./line/hr. -- I November, 1951 6,7 9 63 5 45 0'71 December, 1951 8,9 14 101 4 24 0'23 January, 1952 II, 12 6 42 0 0 0 February, 1952 15 3 21 I 0 0 0 April, 1952 16 6 42 2 17 0'40 May, 1952 21,22 44 348 16 234 0·67 June, 1952 23 I 12 0 0 0 March, 1953 44 4 50 0 0 0 July, 1953 51 10 IIO 2 34 0'30 Totals 99 789 29 354 0'47 I 54 Table S(f) Zanzibar Section (Latham Is. only) Cruise Hours Line Number of, Lbs. of Rate in Date No. Trolled hours fish caught fish ---- lbs./line/hr. December, 1951 9 13 84 10 143 1-70 January, 1952 21 II 66 29 580 8·79 May, 1952 20 9 76 15 235 3-26 July, 1952 26 5 45 12 299 2-30 December, 1952 35 9 85 20 287 3-37 March, 1953 43 6 71 6 23 0-32 July, 1953 52 4 47 3 85 1-80 August, 1953 54 6 60 3 16 0-43 September, 1953 55 7 59 2 43 0-73 November, 1953 58 6 54 0 0 0 Totals 76 647 100 1721 2-66 Table B(g) Mafia Section Cruise Hours Line Number of Lbs_ of Rate in Date No. Trolled hours fish caught fish lbs./lille/hr. --- December, 1951 8 22 154 14 140 0-91 March,1952 17 22 154 31 318 2-21 May, 1952 20 5 44 8 89 1-00 July, 1952 26 12 108 3 25 0-23 September, 1952 32 10 90 27 369 4-10 January, 1953 38 II 103 38 542 5- 26 March,1953 43 9 88 8 88 1-00 May, 1953 46 8 40 4 40 1·0 September, 1953 . 56 6 54 0 0 0 November, 1953 58 19 171 6 92 0·53 January, 1954 61 12 108 21 325 3·01 Totals 136 lII4 160 2028 1·82 I I I 55 • ..... ". e e,'* ' " LAMU SECTION o FISH CAUGHT OR STR IKE o 5 10 I, , !, I I AT Fig. 9 (a). Distribution of fish caught and strikes---Lamu section • .' •• ,!,.' ' ~~'. RAS NGOMENI • " MAL1NDI • .. BANK MAUNDI SECTION " ..-.....~. .., • FISH CAUGHT OR STRIKE ., e·' o '1 I ,S 1,0 '.' NAUT. MI F.S Fig. 9 (b). Distribution of fish caught and strikes-Malindi section 59 • • ... MOMBASA SECTION • FISH CAUGHT OR STfUKE '? ,,,, ~ ',0 DA NAUT. MILES Fig. 9 (c). Distribution of fish caught and strikes-Mombasa section 60 3<1E 3 4 ~WASIN/ ~~~IS:/ ., .... ~ -. ~/ ,l ,0:' ., ~:/ c{J./ "\] PEMBA CIl Cd', TANGANYIKA "i~// CHANNEL TERRITORY ....0\ , ... o :f.' , b ~ Q 0;,· · PEMBA SECTION ·. • FISH CAUGHT OR STRIKE \ o 5 10 ...... ~ 1" I ! ! , NAUT. MILES 3 Fig 9 Cd). Distribution of fish caught and strikes-Pemba section 39"30'E 4 ~V~'_ "'\.''''' .-"ILEVE.N BK, ZANZIBAR SECTION -··....itr • FiSH CAUGHT OR STRIKE RAS OSlO NUNGWE ! I , , • NAUT. MILES ' ,A~ .' . ••• • ~ -', ..... ~~.:...... _.. ZANZIBAR CHANNEL '-, ,,' ~"... , !'.' r • ATHAM I. BK. FISH CAUCHT ,101'10 STRIKES )200 '. INSIDE IOO~MS.LINE ". .-"HOT PLOTTED ./;....~""", •• I• ',\ .. ... '\\ ... : LATHAM '. 't :\ IS, I" I. "':""t~ \ \ .. ~ 4 Fig. 9 (e). Distribution of fish caught and strikes-Zanzibar section 62 39°3dE ~r:------""""""'="iQ'i~~;;;-;-:--""''''''''~ ·I I· ·I · o ·, TANGANYIKA ~.,. ,, TERRITORY ., ,, • ,, .,, ~ • '~~ ...... (. ... -. ... , ... 0 , ,, D> , ,, K~IS. • , I 1!1 I• , • •, G 6 ,, C VULTU'Rlh ;;. elBANKe--_." 0. ~ (1\ '-,e, I I ...., '~AS .• :IMKUMBI • .... : 9 ~ DU "":" .15. ~. , Ol• •• (fI :t ", 40"E Fig. 9 (f). Distrib\'-tion of fish caught and strikes-Mafia section • •• <) c f ••.. :t)<3~ ,<.... . ~. SON: ~ .~GA o '. • TANGANYIKA FANJ~~2~' ~. ~a. : TERFlITQBY d /"'~(j .' .~ •: .... ". . t!!! KILWA MAIN PASS f:~\j. ....\ : '-J • l~ 0' !" .. KILWA SECTION •F ISH CAUGHT OR STRIKE J,, I s, '., NAUT.MILES Fig. 9 (g). Distribution of fish caught and strikes-Kilwa section :'~~KILWA IS. ~U "0 )9"~~ ,·V,, HBR. • TANGANYIKA TERRITORY BAY BAY • LlNDI SE.CTION • FISH CAUGHT ORSTRIKE 1 f " "I NA T S Fig. 9 (h). Distribution of fish caught and strikes-Lindi section FUTURE DEVELOPMENT OF THE PELAGIC FISHERY THE AVERAGE CATCH RATE for multiple trolling during this survey has been 1·I4lbs./line/ hour at trolling speed. This rate is low when compared with commercial multiple trolling in other parts of the world. In many regions of the Pacific average catch rates of 15 lbs./line/hour and over are common-the fish being mainly large tuna. It must be remembered that "Research" had often to forego a large catch in one area, to allow for investigations of other poorer fishing areas. Catch rates in some areas were much higher than the average-Latham Island (2·66) Mafia (1·82) and Kilwa (1'56), and could certainly have been increased but for the reason given above. The very high catch rate of 49 lbs./line/hour off Ozi Reef (Malindi section) in August 1952 was exceptional. The fish took the trolled lines easily and were still biting when the "Research" left the area after 80 minutes' fishing. At other times similar large shoals have been seen, but would not take a trolled line. Alfree (see Copley 1952, 1953) records similar high figures in the Lamu section in March 1950 and 1951. It is interesting to note that the fish were largely C. sansun. It is not believed that multiple trolling alone from a boat the size ofthe "Research" could be commercially economical in East African waters. Ommanney (Mauritius-Seychelles Fishery' Survey Part II, p. 80) concluded that the cost ofrunning such a vessel for the catching ofpelagic fishes by trolling was not practicable. In the Seychelles area the catch rate was about 4'4 and 4'1 lbs./line/hour in 1948 and 1949. This is nearly double that in the best sections in East Africa and about 4 times the average catch rate for the whole coast. Serventy (1947) carried out tests in S.E. Australian waters with three vessels trolling for tunny and found that catch rates of 3'4, 2'0, 2·4Ibs./line/hour were not commercially profitable. However the native fishery for pelagic fish by trolling could be considerably expanded. This expansion might be along the following lines. Firstly, as an adjunct to bottom and shark fishing by a small European type fishing boat like the F.B. "Forerunner" ofZanzibar. This Mrican-run boat has been developed recently by Mr. K. F. King, the Zanzibar Fisheries Officer, and has already brought in a considerable weight of pelagic fish, mainly from the Zanzibar and Pemba areas trolling with five lines. Secondly, by the use of the large type of fishing dhow fitted with light trolling poles to enable 5-6 lines to be towed. The fitting ofthese boats with small inboard engines ofa simple design would increase the radius ofoperations and reduce the time wasted on passage to and from the fishing areas. Many ofthe fishing grounds discovered on this survey are never or only rarely visited by native fishermen. Warfel (1950) during a survey in Philippine waters found that the average trolling rate was 1·6Ibs./line/hour (47% tuna). He advocated the adaptation of powered double-outrigger canoes for multiple trolling in much the same manner as suggested above. Future work of the organization must obviously include research into methods for catching the numerous shoals of"tunny-like" Scombrids (see page 47). These shoals are not exploited by the existing fishery and have not been taken by trolling. An encircling net such a purse seine would possibly be successful in capturing these fish. The weight of a suitable net and the working space required makes it impracticable on the "Research". Thus the future use of a purse seine depends on when a new and more powerful research vessel is available. Live bait fishing with the pole and line technique might also be successful. The great difficulty is that of a constant supply ofsuitable live bait and the storing ofit on the fishing boat. The use ofa deep long line for tunny in suitable areas has been started. In many parts ofthe Pacific the shoals of tunny seen at the surface are only a small percentage of those found at lower levels. The operation of deep long lines requires large' quantities of small fish such as mackerel for bait. Experiments started on the use of gill and drift nets for the capture of shoals of small Carangids and Scomberomorids may solve the bait problem for long lining, although these fish themselves are commercially valuable. 66 The biological problems apparent from this survey are innumerable. The specific identifica tion of most ofthe fish taken by trolling has been established. In those groups believed to make localised migration (Caranx, Sphyrcena, Aprion, Plectropoma) future work must deal with the growth, feeding and spawning habits of the fish in relation to the resilience ofthe population to increased fishing. In the case of tunny-like shoals and the "Kanadi" the specific identity is still not known. The migrations ofthese and other fish such as the Rainbow Runner (E. bipinnulatus) are probably related to feeding and spawning habits. To understand these habits the fish must be caught and the distribution and seasonal abundance of the members ofthe food chain investi gated. Until a new method is established for the capture ofthe tunny-like shoals, small explosive charges could be used to obtain a "biological satpple" for examination. In conclusion it may be stated that the pelagic fishery ofthe East African coast is capable of further development. However the efficiency of this development is dependent on a thorough knowledge ofthe biology ofthe pelagic fishes. SUMMARY THE S COP E 0 F THE SUR V EY is defined. A short description is given of the hydrographic and climatic conditions of the East African coastal region. A full description is made of the gear used in multiple trolling from M.F.V. "Research". The efficiency and limitations of the gear are discussed, with suggestions for improvements in the method. Most effective trolling speed was 5-6 knots. The twenty-eight species of fish taken by trolling are fully described. The catch, seasonal abundance and distribution of the pelagic fishes are discussed. Some species-Caranx, Sphyrcena, Aprion and Plectropoma appear to be present throughout the year. They are more numerous during the N .E. monsoon when the gonads are in the spawning condition. Coryphcena hippurus makes an inshore spawning migration from January to June. Due to migrations other pelagics such as the Scombrids show a marked seasonal abundance, but little is known as yet of the reasons for the migrations. Shoals of tunny-like Scombrids have been seen in large numbers but fish were not taken from them by trolling. Monthly details of the catch offishes are tabulated for each section ofthe coast. The average catch rate for the whole of the survey was I·I4Ibs./line/hour. The monsoon conditions have a direct bearing on the productivity ofthe fishery, especially in the S.E. monsoon. Fish are entirely restricted to within the 100 fin. line. Largest numbers are taken where a shallow extends out from the fringing reef or over the shallow off-shore banks. Reasons for this bution are advanced. It is concluded that multiple trolling alone by a fishing boat the size of"Research',' would be commercially profitable. However the expansion of the native fishery for pelagic fishes advocated. Two possible methods of development by using trolling are given. Suggestions made for the capture of tunny-like shoals by means of a purse seine or the live bait techn:lqu.e, together with the use of deep long lines for tunny and gill nets for the capture of the small(~r shoaling Carangids and Scomberomorids. The future biological investigations to be carried on the pelagic fishes are discussed. REFE Africa Pilot, Pt. III (r939) roth Edition, Admiralty, London. BARNARD, K. H. (1927). Monograph of the Marine Fishes of South Mrica Pt. II. Annals of the South African Museum. Vol. XXI. BATES, D. H., Jnr. (1950). Tuna trolling in the Line Islands in the late spring of I950. U.S. Fish and Wild Life Service. Fishery leaflet 35I. Washington. BERG, L. S. (1947). Classification ofFishes both Recent and Fossil. Ann Harbor, Michigan. BLEGVAAD, H. (1944). Fishes of the Iranian Gulf. Reprint from Danish Scientific Investigations in Iran, Pt. III. Copenhagen. COPLEY, H. (r95I). Review of Kenya Fisheries, I95I.. Government Printer, Nairobi. COPLEY, H. (r952). Review of Kenya Fisheries, I952. Government Printer, Nairobi. DAY, F. (r865). The Fishes of Malabar. London. DAY, F. (I878-r888). The Fishes of India, Vol. I and II. London. DE BEAUFORT, L. F. and CHAPMAN, W. M. (I95r). The Fishes of the Indo-Australian Archipelago, Vol. XI. Leiden. East Mrican Marine Fisheries Research Organization, Zanzibar (1952). Annual Report for I952. Nairobi. East Mrican Marine Fisheries Research Organization, Zanzibar (1953). Annual Report for I953. Nairobi. FRASER BRUNNER, A. (r949). On the Fishes of the Genus Euthynnus. Annals and Mag. Nat. Hist. Series I2, ii, p. 622. FRASER BRUNNER, A. (r950). The Fishes of the Family Scombridae. Annals and Mag. Nat. Hist. Series I2, iii, p. 131. FIEDLER, R. H., JARVIS, N. D. and LOBELL, M. J. (r94r). The Fisheries and Fishery Industries of Peru with Recommendations for their Expansion and Development. FOWLER, H. W. (1928). Fishes of Oceania. Mems. Bernice P. Bishop Museum, Vol. X. 1928. JORDAN, D. S. and EVERMANN, B. W. (r905). The Aquatic Resources of the Hawaiian Islands. Pt. I, The Shore Fishes. Bulletin of the U.S. Fish Commission. Vol. XXIII for, I903 Pt. I. Washington. KISHINOUYE, K. (r923). Contributions to the Comparative Study of the so-called Scombrid Fishes. Journal of the College of Agriculture, Imperial University of Tokyo. Vol. III. NO.3· MUNRO, I. S. R. (r943). Revision of the Australian species of Scomberomorus. Mems. of the Queensland Museum. Vol. XII. Pt. II. NICHOLLS, J. T. (r938). Notes on Carangid Fishes III. On Caranx sex/asciatus, Quoy and Gaimard. American Museum Novitates, 998, June 7, r938. NORMAN, J. R. and FRASER, F. C. (r937). Giant Fishes, Whales and Dolphins. Putnam, London. PLAYFAIR, R. L. and GUNTHER, A. C. L. G. (r866). The Fishes ofZanzibar. London. POWELL, D. E. and HILDEBRAND, H. A. (1949). Albacore Tuna Explorations in Alaska and adjacant waters. U.S. Fish and Wild Life Service. Fishery leaflet 376. Washington. SAUVAGE (1891). Histoire naturelle des Poissons, from Histoire physique, naturelle et politique de Madagascar. Vol. XVI. A. Grandidier, Paris, 1891. SERVENTY, D. L. (1947). Report on Commercial Tuna Trolling Tests in South Eastern Australia. Report from Journal of the Council for Scientific and Industrial Research. Vol. 20. No. 1. February, 1947. Melbourne. SMITH, J. L. B. (1949). The Sea Fishes of Southern Africa. Central News Agency Ltd., South Africa. SVEDRUP, H. V., JOHNSON, H. W. and FLEMING, R. H. (1942). The Oceans, their Physics, Chemistry and General Biology. Prentice Hull Inc., New York. U.S. Fish and Wild Life Service (1948). The Japanese Tuna Fisheries. Fishery leaflet 297. Washington. WAKIYA (1924). Carangoid Fishes ofJapan. Ann. Carnegie Museum XV. 1924. WARFEL, H. E. (1950). Outlook for Development of a Tuna Industry in the Philippines. U.S. Fish and Wild Life Service. Research Report 28. Washington. WEBER, MAx and DE BEAUFORT, L. F. (1922). The Fishes ofthe Indo-Australian Archipelago, Vol. IV. Leiden. WEBER, MAx and DE,BEAUFORT, L. F. (1931). The Fishes ofthe Indo-Australian Archipelago, Vol. VI. Leiden. WEBER, MAx and DE BEAUFORT, L. F. (1936). The Fishes of the Indo-Australian Archipelago, Vol. VII. Leiden. WHEELER, J. F. G. and OMMANNEY, F. D. (1953). Report on the Mauritius-Seychelles Fisheries Survey I948-49. Colonial Office Fisheries Publications, Vol. I, NO.3, 1953. H.M. Stationery Office, London. WILLIAMS, F. (1953). Catches of Coryphaena hippurus L. in the Western Indian Ocean. Nature, Vol. 171, Printed in Great Britain 1'- .3 __ ~1_ - ••...•1•...!.-• . r _~ __ .~_I .. "'~.' "'ry Office t,P:2~1!;6'/6'962 K4 10/56 H.P.Ltd. G592 1111111111111 "" 11111111111111111111111 COLONIAL OFFICE Fishery Publications No. I. The Food and Feeding Relationships of the Fishes of Singapore Straits. By Tham Ah Kow, B.Sc. (1950).35 pp. 3s. (3 s• 3Id.) NO.2. Report on the Tilapia and other Fish and Fisheries of Lake Nyasa, 1945-47. By Rosemary H. Lowe, M.Sc. (1952). 126 pp. 40S. (40S. 7Id.) NO.3. Report on the Mauritius-Seychelles Fisheries Survey, 1948-49. By J. F. G. Wheeler, D.Sc. and F. D. Ommanney, Ph.D., A.R.C.S. (1953). 148 pp. 40s. (40s. 7id.) NO.4. A Preliminary Study of the Physical, Chemical, and Biological Characteristics of Singapore Straits. By Tham Ah Kow, B.Sc. (1953). 65 pp. lOs. (lOS. 3id.) NO.5. Fertilisers in Fishponds. A Review and Bibliography. By C. H. Mortimer, D.Sc. and C. F. Hickling, C.M.G., Sc.D. (1954). ISS pp. 25S• (25s. 7ld.) No.6. Observations on the Biology of Eels (Anguilla spp.) of Kenya Colony, East Africa. By W. E. Frost, D.Sc. (1955). 29 pp. lU. 6d. (IU. 8td.) NO.7. Recent Developments in the Flying Fish Fishery and Contributions to the Biology of the Flying Fish Hirundichthys affinis (Gunther, 1866). By D. N. F. Hall, B.Sc. In the press. 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