kdJU iS. 'k'.d J5ortIjent i&fjobestfa Joint Fisheries Research Organisation ANNUAL REPORT No. 10 i960 Price: 7s. 6d. yitaA A v i £ 9- O 1962 PRINTED BY THE GOVERNMENT PRINTER tn.75—1185 1-02 L U S A K A luirJuy&lg, Sfzt/?/ CONTENTS St a f f a n d C o m m it t e e s , 1960 .................................................................................. iii I ntroduction ... ... ... ... ... ... ... ... ... ... 1 A c t iv it ie s o f t h e O rganisation in N o r t h e r n R h o d e s ia : A. Report for the year ended 31st December, 1960 ... ... ... ... 3 B. Research Results, Lake Tanganyika: I. Hydrology and Plankton ... ... ... ... ... ... ... 7 II. The sardine (Ndagaa) fishery on southern Lake Tanganyika, with notes on the introduction of the Chirimila net ... ... ... 9 III. The sardines Limnothrissa miodon (Blgr) and Stolothrissa tanganicae Regan ... ... ... ... ... ... ... ... ... 18 IV. Shoaling and vertical migration behaviour of the sardines, as recorded by echo-sounding ... ... ... ... ... ... ... ... 20 V. Diurnal and vertical migrations of fish, and effect of predation ... 23 VI. The gill-net fishery for the Nile perch Lates mariae ... ... ... 27 VII. Observations on the growth of juvenile Lates (Nile perch) species ... 30 C. Research on Lake Mweru ... ... ... ... ... ... ... 31 D. Research on Kariba ... ... ... ... ... ... ... ... 32 A c t iv it ie s o f t h e O rganisation in N y a s a l a n d : A. Report for the year ended 31st December, 1960 ... ... ... ... 41 B. Research Results, Lake Nyasa: I. H ydrology............................................................................................... 41 II. The long-line fishery ........................................................................ 48 III. Further notes on gill-net experiments on Labeo mesops (Gunther) ... 48 IV. Length-weight relationships of some Nyasa fishes ... ... ... 57 V. Bagrus meridionalis: variation in catch per unit effort and changes in gonad state ... ... ... ... ... ... ... ... 61 Contributions : (i) Notes on the salinity tolerations of certain Tilapia species (Pisces, Cichlidae) in Northern Rhodesia. By M. A. E. Mortimer, m .sc ., Department of Game and Fisheries, Northern Rhodesia ... ... ... ... ... ... 63 (ii) Notes on misidentifications of Serranochromis species (Pisces, Cichlidae) in recent literature. By M. A. E. Mortimer, m .s c . ... ... ... ... 64 (iii) The spoilage of dry fish products through insect infestation and damp.- By E. G. R. Pike, Department of Game and Fisheries, Northern Rhodesia ... 65 P ublications .................................................................................................................................... 67 i J o in t F is h e r i e s R e s e a r c h O rganisation , P.O. Box 48, Sa m f y a , N o r t h e r n R h o d e s ia . N o t e .—This report was edited by Mr. Jackson; he also wrote Sections 1, 2A, 2C and 5. Section 2B was written by Mr. Coulter, Section 2D by Mr. Harding, Section 3A and 3B III-V by Mr. lies, and 3B I- II by Mr. Eccles. ii STAFF AND COMMITTEES, 1960 Scientific Advisory Committee: H. J. H. Borley .............. Director, Department of Game, Fish and Tsetse Control, Blantyre, Nyasaland. F. I. Parnell, m .b .e . ... Director, Department of Game and Fisheries, Chilanga, Northern Rhodesia. P. B. N. Jackson ... ... Chief Fisheries Research Officer, Joint Fisheries Research Organisation, Samfya, Northern Rhodesia. Dr. V. D. van Someren, m .b .e . Director, East African Freshwater Fisheries Research Organisation, Jinja, Uganda. T. D. l i e s ..................................... Officer in Charge, Joint Fisheries Research Organisa­ tion, Nkata Bay, Nyasaland. Samfya Laboratory (Headquarters): Chief Fisheries Research Officer ... P. B. N. Jackson, m .s c . (Principal Scientific Officer, Her Majesty’s Overseas Research Service). Research Officer ... ... ... A. P. Bowmaker, b .sc. (Scientific Officer, Her Majesty’s Overseas Research Service). Senior Technical Assistant ... M. P. Gilbert. Clerk ..................................... Mrs. M. B. G. Sandwith. Senior Fish Guard ... ... L. Phiri. Chilanga (Kariba Substation): Research Officer ... ... ... D. Harding, b .s c . (Senior Scientific Officer, Her Majesty’s Overseas Research Service). Research Assistant ... ... F. Chibuye. Abercorn (Lake Tanganyika Substation): Research Officer ... ... ... G. W. Coulter, b .sc. (Scientific Officer, Her Majesty’s Overseas Research Service). Research Assistant ... ... J. Chela. Nchelenge (Lake Mweru Substation): Research Officer ... ... ... T. G. Carey, b .s c . (Temporary Zoologist). Fiyongole Fish Farm: Supervisor ... ... ... ... W. Gay. Nkata Bay Laboratory: Research Officer in Charge ... T. D. lies, b .sc. (Senior Scientific Officer, Her Majesty’s Overseas Research Service). Research Officer ... ... ... D. H. Eccles, b .sc. (Scientific Officer, Her Majesty’s Overseas Research Service). " Senior Research Assistant ... A. J. P. Mzumara. Joint Fisheries Research Organisation Annual Report No. io, i960 1. INTRODUCTION This year has been an extremely busy one for the Joint Fisheries Research Organisation, and the calls on the Organisation’s services have increased. A number of results have been obtained and some new work started. The trend, which started several years ago, of the Organisation forming itself into a series of stations on many of the important or potentially important fisheries, has become very marked. By the end of the year there were five such stations, with a scientist permanently at Mpulungu, Southern Lake Tanganyika, at Kariba, at Nchelenge, Lake Mweru, and at what is still the headquarters of J.F.R.O, Samfya on Lake Bangweulu. The fifth station is the Fish Farm at Fiyongole, near Fort Rosebery. The erection of these stations was essential in order to obtain quickly the information urgently required on these important fisheries, which are, however, so widely separated from each other; it has proved to be much more efficient than any system of frequent long tours from a central headquarters, which are prohibitively expensive, tiring and preclude any possibility of con­ tinuous effort. It has, however, often posed many administrative problems, such as the pro­ vision of housing for scientists and other staff, the provision of launches, scientific apparatus, etc., at each station, on a limited budget. Most of these have now been overcome, and in this respect we are indebted to the Development Commission of the Northern Province of Northern Rhodesia for the financial help, over the past few years, in getting the research station for the important fishery on the Lake Tanganyika established, including the provision of a twenty-nine- foot research launch. Close liaison was maintained during the year with the Joint Fisheries Research Organisa­ tion in Nyasaland, and a meeting was arranged at Nkata Bay of all scientists from both countries in October, just before the Advisory Committee meeting. This was successful and indeed such meetings, as well as frequent visits to the headquarters and its library, are essential to combat the scientific isolation which is a real factor in the life of scientists working usually alone and far from any kindred activities. During the year Mr. T. D. lies, Senior Scientific Officer and Officer in Charge, J.F.R.O., Nyasaland, gave notice of resignation, and left early in the new year to take up an appointment at the Fisheries Laboratory, Lowestoft. Mr. lies joined the J.F.R.O. in early 1954 during the Nyasa survey and remained in Nyasaland after the survey was over to form the first of the J.F.R.O. stations away from headquarters, which he did with success. Mr. Iles’s especial interest was the mathematical treatment of gill-net catches to improve catches and estimate fish populations. Some of his early work in 1954, which will appear in the J.F.R.O. Nyasa Survey Report, was indeed pioneering in this now very important field, and others of his studies have appeared in J.F.R.O. annual reports such as the present issue. The year 1960 is the last full year in which a proportion of the costs of J.F.R.O. in Northern Rhodesia will be paid by the British Government’s Colonial Development and Welfare Scheme, and from the 1st July, 1961, the Organisation will be financed from Northern Rhodesia’s territorial budget. 1 2. ACTIVITIES OF THE ORGANISATION IN NORTHERN RHODESIA A.—Report for the year ended 31st December, 1960 Staff ' The permanent establishment remained at full strength throughout the year. In pursuance of the policy of posting scientists as near as possible to the area on which they work, by the end of the year Mr. Harding was assigned to Chilanga in order to work full time on Lake Kariba, Mr. Coulter to Abercorn for work on Lake Tanganyika, while Mr. Bowmaker remained at Samfya to work on Lake Bangweulu. Mr. W. Gay, Fish Farm Supervisor, was on vacation leave for a large part of the year, being replaced by Mr. D. Pretorious, and, on the resignation of this replacement, by Mr. P. Wright. As mentioned in last year’s report, the agreement by the Development Commission to finance a Temporary Zoologist enabled an appointment to this post to be made in 1960. This was Mr. T. G. Carey, who was posted to Nchelenge, Lake Mweru. Soon after appointment, however, Mr. Carey was called up for National Service, and spent four months in the second half of the year in camp. As a result he was not able to start serious work on Lake Mweru until November, 1960, but by the end of the year a research programme on the lake was well under way. In January and February, 1960, Miss Phillida M. Grieveson, a student of zoology at the University of Cape Town, worked for the Organisation at Samfya during her long vacation. She was able to undertake long-needed work on the sorting and labelling of the Organisation’s collection of fish specimens from Northern Rhodesia and Nyasaland. Mr. R. Chisupa, a chemistry student from the University College of Rhodesia and Nyasaland, worked at Mpulungu in December, 1960, and January, 1961. He was engaged chiefly in the estimation of oxygen in water samples and the analysis of fish records.