THE FISHERY OF STOLOTHRISSA TANGANICAE REGAN, 1917 IN THE TANZANIAN WATERS OF LAKE TANGANYIKA

by

K.I. Katonda
Tanzania Fisheries Research Institute
Kigoma Centre
P.O. Box 90
Kigoma
Tanzania

1. INTRODUCTION

The small pelagic fishes have been reported to be on the increase in many of African Great Lakes (Fig. 1) and some reservoirs where they support important fisheries. Typical examples include: the cyprinids Rastrineobola argentea in Lakes Victoria, Kyoga and Nabugabo; Engraulicypris sardella in Lake Malawi (Nyasa); Neobola bredoi in Lake Albert, Neobola moeruensis in Lakes Mweru and Bangweulu, the clupeids Poecilothrissa moeruensis in Lake Mweru, Stolothrissa tanganicae in Lake Tanganyika and Limnothrissa miodon in Lakes Tanganyika, Kivu and Kariba. Lake Tanganyika is also known to contain a cyprinid Chelaethiops minutus but this species is not of commercial importance. However, adults of C. minutus are commonly caught together with clupeids and they are readily distinguishable from each other by their behaviour. The clupeids tend to form dense schools a metre or so below the surface whereas C. minutus swim as individuals just below the surface and do not school (Coulter, 1991).

The pelagic fish community in Lake Tanganyika is composed of six endemic species. These include two clupeids, Stolothrissa tanganicae and Limnothrissa miodon as prey species, and four centropomids, Lates stappersii, L. mariae, L. microlepis and L. angustifrons as predators (Johannesson, 1974; Ellis, 1978; Bayona, 1988; Lindqvist and Mikkola, 1989; Coulter, 1991). Over 80% of fish production of the lake is contributed by these six species of which the two clupeids contribute on average 65% and the four Lates species on average 20% (Katonda and Kalangali, 1992). Of the clupeids, S. tanganicae, which is locally known as ‘dagaa’ in Tanzania, ‘ndagala’ in Burundi and Zaire, and ‘Kapenta’ in Zambia, is the most abundant (Van Well and Chapman, 1975) and therefore the most important commercial species in the lake. It is also a principal food source for the pelagic fishes as well as for many bathypelagic and scavenging benthic fish and invertebrates (Coulter, 1991).

Stolothrissa is a monotypic genus which has evolved in the lake probably from a common ancestor, with Limnothrissa (another monotypic genus), that originated in the ancient Zaire River System (Coulter, 1991). A proposal for future research on the clupeids is made. Suggestions on the improvement of fisheries statistics data collections are also made.

2. THE BIOLOGY OF THE CLUPEIDS

Clupeids are prominent in the pelagic zones of many large lakes (Whitehead, 1985; in Coulter, 1991). They are usually small, numerous and short-lived, highly fecund and productive, showing seasonality in abundance and also fluctuating markedly from year to year (Coulter, 1991). They are also usually key members of pelagic food chains in which they occur, linking planktonic and piscivorous tropic levels (Fig. 2). All these attributes are found in Stolothrissa tanganicae (Coulter, 1991).

2.1 Reproductive biology

Sexually mature, S. tanganicae occur throughout the year (Ellis, 1971) and spawning may take place several times in a year (Coulter, 1991). Spawning peaks, indicated by variations in the relative number of ripe gonads, have been found to be November – December and April – July in Zambia (Ellis, 1971), January – April in Kigoma, Tanzania (Chapman and Van Well, 1978) and February – May in Burundi (Roest, 1977).

Matthes (1968), who made observations at the south of the lake in Zambia, noted that the eggs increase in size two fold after fertilization, and sink slowly (4–5cm a minute). They hatch 24 h to 36 h later, at depths of 75 to 150 m, and the larvae undertake upward swimming movements to remain in oxygenated water.

As the juveniles grow, they move progressively nearer shore where they are caught in great abundance by the inshore fishery from about 35 mm length (Coulter, 1970). From about 50 mm they move offshore and start to appear in pelagic catches at 55 mm (FAO 1978). The annual mean size at which 50% reach maturity is about 75 mm in females and 64 mm in males (Ellis, 1971). Evidence that adult Stolothrissa migrate back from pelagic regions for spawning near the shore is provided by the absence of ripe-running fish in pelagic catches (Mann et al, 1973) and the occurrence of a high proportion of ripe adult Stolothrissa near the shore during main spawning period (Enderlein, 1976). Annual mortality of Stolothrissa exceeds 99% (FAO, 1978), so the life span can conveniently be regarded as a year (Coulter, 1991).

2.2 Schooling and vertical migration

Schooling is an outstanding behavioural attribute of Stolothrissa (Matthes, 1968; Chapman, 1976b). Information on clupeid schooling and vertical migration in Lake Tanganyika has been gathered by echo sounding. Catches in the same area as echo soundings have repeatedly confirmed that pelagic layer and school traces are mainly Stolothrissa (Chapman, 1976a).

Coulter (1961), who studied the inshore regions of the Zambian sector, found that clupeid fry form schools close to the bottom near shore, and in deeper water they form dense schools just off the bottom. Upward migration occurs at dusk. From acoustic surveys of the pelagic zones (off shore) of the lake, Chapman (1975) concluded that Stolothrissa form extensive superficial layers at night.

Coulter (1991) summarises that mass vertical migrations are undertaken daily by the clupeids both inshore and in the pelagic regions, and it appears that schooling behaviour is closely linked to these movements as well as to the depth occupied at times when the fishes are not actively migrating. Dawn and dusk migrations seem to be a more regular and unified behaviour in shallow and shelf regions than in the pelagic zone.

3. THE FISHERY

The main fishing methods for Stolothrissa tanganicae include scoopnet (locally known as Lusenga), beach - seine (Mkwabo), liftnet (Kipe) and industrial purse-seine. Thése methods have been described by Coulter (1991); Challe and Kihakwi (1992); and Katonda and Kalangali (1992).

3.1 Catch

The increase in human population with high demand for fish protein has led to the increase in exploitation of the clupeids and in particular Stolothrissa tanganicae. Other reasons which have led to the increase in exploitation of S. tanganicae include easy processing methods i.e. drying of the clupeids on the sand; and high demand of dried S. tanganicae in Tanzania and the neighbouring countries (Zambia and Zaire). S. tanganicae is also the most abundant fish species in the lake.

In general, Limnothrissa miodon occupies a more inshore habitat throughout its life than S. tanganicae, and much of its population inhabits relatively shallow shelf areas (Coulter, 1991). Hence, L. miodon is unimportant in catches where the littoral belt is narrow and steep e.g. at Kigoma, Tanzania (FAO, 1978). Since most of the Tanzania coast is of this nature, Limnothrissa is, therefore, unimportant in our catches. Because of this fact, the two clupeids (i.e. S. tanganicae and L. miodon) are grouped together as ‘dagaa’ in our fisheries Annual Statistics Reports (See Table 2 –5). This fact has also been revealed in the data collected at Kigoma from the liftnet fishery. Sampling was done on the liftnet catches at the centre from February to May, 1992. Two hauls of a liftnet were made in each fishing night sampled and the catch was pooled due to very low catches. The catch was later sorted out into separate species and weighed. Fishing was done at stations near Kigoma harbour i.e. Mtanga and Kasekela, north of Kigoma harbour; and Katonga and Ujiji, south of Kigoma harbour (Fig. 3). The results of the catch composition of the liftnet fishery are shown in Table 1. As observed earlier, Limnothrissa miodon is unimportant in liftnet catches around Kigoma area.

Tables 3 – 5, which show the weight of fish caught in metric tons and species composition in percentage of the pelagic fish species and the non-pelagic fish species from 1984 to 1989, reveal that ‘dagaa’ contributed an average of 79.1% of the total catch in Kigoma region, and only 34.7% in Rukwa region. There are stations like Kala, Kizumbi and Kirando in Rukwa Region (Fig. 3) where ‘dagaa’ is not fished at all (See Tables 3 – 5). This may be due to the lack of Kerosine and pressure lamp accessories (e.g. mantles, etc) in the remote stations. Since light attraction fishing techniques (i.e. scoopnets, liftnets and purse-seines) need these facilities, which are available in major towns like Kigoma, fishing for ‘dagaa’ will concentrate in areas near Kigoma region and near Kasanga in Rukwa region.

The processing methods employed for S. tanganicae include sun-drying on the sandy beaches on one hand (the most common drying technique) and brining and drying on racks (mainly done in Kigoma town) and smoking on the other. Smoking is not a very common technique.

3.2 Marketing

In the past, fish were harvested mainly for food and most of the fishermen were also subsistence farmers. This is still true for some areas far from Kigoma town where marketing of catches in excess of local needs is generally difficult because of poor communication systems along the lake. Due to the steep slopes, there are no roads linking the scattered populations along the shores. However, transportation of goods and people in large plank boats powered by outboard engines, is a useful service to these scattered populations. A weekly transport service formerly provided by MV Liemba (grounded for major repairs and renovation) and now by MV Mwongozo has also assisted fish traders to ferry their products to the markets. Apart from landing stations near towns (Kibirizi, Ujiji and Kigoma) where Lates spp. and some clupeids are sold fresh, most of the clupeids are preserved by drying in the sun on sandy beaches. However, Lates stappersii are smoked.

3.3 Collection of Fishery Statistics

Collection of fishery statistics in Tanzania is done by beach - recorders who are deployed in all major fish landing stations along the coast of Lake Tanganyika (See Fig. 3). The data recorders are supervised by the District Fisheries Officers and Officers-in-charge of Statistics in the districts. Visits to fish landing stations has revealed that the data collection is not done properly. This is due to the fact that most beach recorders are primary school leavers and have no basic training in statistics. Furthermore, the supervisors are unable to visit the beach recorders due to lack of water transport.

In order to improve the data collecting system, the following measures are suggested:

1. beach recorders should be secondary schools leavers who have undergone some training in fisheries statistics;

2. a boat should be provided for each of the three districts along the coast of Lake Tanganyika (i.e. Kigoma District in Kigoma Region, Nkasi and Sumbawanga Districts in Rukwa Region) to enable supervisors to visit the beach recorders frequently.

4. RECOMMENDATIONS

Although high growth rate, early sexual maturity, short life-span and high natural mortality leading to the rapid succession of generations are basic features of the population biology of the clupeids and which have enabled the clupeids to tolerate high levels of exploitation and provide high yields (Mannini, 1992), certain management measures on the clupeids should still be undertaken. The memory of the Peruvian anchovy (Engraulis ringens) fishery which collapsed due to heavy exploitation and lack of management measures is still with us. As Gulland (1974) points out, action to manage or conserve a fish stock is best taken early in the development of a fishery and not after it is in trouble.

As it is now evident, more information on the clupeids, that is, Stolothrissa and Limnothrissa is needed. Comprehensive research on various aspects of the clupeids should be done. As clupeids contribute nearly 80% of total fish production in the lake, the FAO/FINNIDA Regional Research Project (GCP/RAF/271/FIN) should give high priority on this group of fishes in their research programme.

Since one of the immediate objectives of the FAO/FINNIDA Regional Research Project is the establishment of uniform methods throughout the lake for the subsequent longer-term collection, analysis, and interpretation of new data by the four participating countries, the problem of fisheries statistics data collection on a regional basis will be solved. Close co-operation among the Lake Tanganyika riparian states, however, is very essential.

5. REFERENCES

Bayona, J.D.R. 1988. A review of the biological productivity and fish predation in Lake Tanganyika. CIFA Occas. Pap. 15: 1–17

Challe, N.a. and A.D.B. Kihakwi 1992. TAFIRI catalogue of fishing gears of kigoma and Rukwa Regions of Lake Tanganyika (Tanzania). Historical Data Reports, GCP/RAF/271/FIN. (In Press).

Chapman, D.W. 1975. Characteristics of layers and schools of pelagic fish in Lake Tanganyika. FAO Report FI:DP/URT/71/012/16: 1–10.

Chapman, D.W. 1976a. Acoustic estimates of pelagic ichthyomass in Lake Tanganyika with an inexpensive echo-sounder. Trans. Am. Fish. Soc. 105 (5): 581–587.

Chapman, D.W. 1976b. Calculated weights of layers and schools of pelagic fish in Lake Tanganyika. FAO Report FI: DP/URT/71/012/40: 1–4.

Chapman, D.W. and P. Van Well 1978. Growth and mortality of Stolothrissa tanganicae. Trans. Am. Fish, 107 (1): 26–35.

Coulter, G.W. 1961. Lake Tanganyika Research. Annu. Rep. Jt. Fish. Res. Organ., 10:7–30.

Coulter, G.W. 1970. Population changes within a group of fish species in Lake Tanganyika following their exploitation. J. Fish. Biol., 2: 329–353.

Coulter, G.W. 1991. Lake Tanganyika and its life. London, Oxford and New York: Natural History Museum Publications, Oxford University Press. London, Oxford and New York 354p.

Ellis, C.M.A. 1971. The size at maturity and breeding seasons of sardines in southern Lake Tanganyika. Afr. J. Trop. Hydrobiol. Fish., (1): 59–66.

Ellis, C.M.A. 1978. Biology of Luciolates stappersii in Lake Tanganyika (Burundi). Trans. Am. Fish. Soc., 107 (4): 557–566.

Enderlein, H.O. 1976. Biological sampling survey of the traditional and artisanal fisheries, Lake Tanganyika, Burundi. FAO Report, FI: DP/BDI/70/508/8: 1–17.

FAO, 1978. Fishery biology and stock assessment. FAO Technical Report, FI: DP/URT/71/012/1: 1–37.

Gulland, J.A. 1974. Guidelines for fishery management. Indian Ocean Fishery Commission, FAO Rome. IOFC/DEV/74/36.

Johannesson, K.A. 1974. Preliminary quantitative estimate of pelagic fish stocks in Lake Tanganyika. FAO Report, FI: AP/URT/012/9: 1–16.

Katonda, K.I. and A.N.M Kalangali 1992. The artisanal and industrial fisheries of Lake Tanganyika in Kigoma and Rukwa Regions, Tanzania. Historical Data Report. GCP/RAF/271/FIN. (In Press).

Lindqvist, O.V. and H. Mikkola 1989. Lake Tanganyika: Review of Limnology, Stock Assessment, biology of fishes and fisheries. FAO Report, GCP/RAF/271/FIN: 1–51.

Mann, M.J., Bashirwa, F., Ellis, C.M., Nahabakomeye, J.B. and H.O. Enderlein 1973. A preliminary report of fish biology and stock assessment in Lake Tanganyika (Burundi). FAO Report, FI: DP/BDI/73/020/5: 1–58.

Mannini, P. 1992. Some characteristics of small pelagic species Victoria Rastrineobola Argentea. In: Mannini, P. 1992 (Ed.). The Lake Victoria Dagaa (Rastrineobola argentea). Report of the first meeting of the working group on Lake Victoria Rastrinebola argentea, 9–11 December, 1991, Kisumu, Kenya. UNDP/FAO Regional Project for Inland Fisheries Planning (IFIP), RAF/87/099 - TD/38/92 (En): 62–79.

Matthes, H. 1968. Preliminary investigations into the biology of the Lake Tanganyika Clupeidae. Fish. Res. Bull. Zambia, 4: 39–45.

Roest, F.C. 1977. Stolothrissa tanganicae, population dynamics, biomass evolution and life history in the Burundi waters of lake Tanganyika. FAO CIFA Tech. Pap., 5: 42–63.

Van Well, P. and D.W. Chapman 1975. Growth and mortality of Stolothrissa tanganicae. FAO Report, FI: DP/URT/71/012/17: 1–12.

Whitehead, P.J.P. 1985. FAO species catalogue, clupeid fishes of the world (Suborder Clupeoidei). Part 1 - Chirocentridae, Clupeidae and Pristigasteridae. FAO Fisheries Synopsis, 125, 7(1): 1–303.

Table 1. Catch composition of the liftnet fishery for the months of February-May, 1992

Table. 2 Weight of fish caught by species in metric tons and species composition by percentage (in brackets) from Lake Tanganyika artisanal Fisheries.

NOTE:     L                = Lates
Boulenger. = Boulengerochromis

SOURCE: FISHERIES DIVISION ANNUAL STATISTICS REPORTS.

Table 3. Weight of fish caught in metric tons and species composition in percentage (in brackets) by station in Tanzania territorial waters of Lake Tanganyika, 1985 and 1986

NOTE: N/R     = Not Recorded
L         = Lates
Stapp. = stappersii
Non P. = Non pelagic

SOURCE: FISHERIES DIVISION ANNUAL STATISTICS REPORTS

Table 4. Weight of fish caught in metric tons and species composition in percentage (in brackets) by station in Tanzanian waters of Lake Tanganyika, 1986 and 1987.

NOTE: N/R = Not Recorded
L = Lates
stapp. = stappersii

SOURCE: FISHERIES DIVISION ANNUAL STATISTICS REPORTS

Table 5. Weight of fish caught in metric tons and species composition in percentage (in brackets) by station in Tanzania territorial waters of Lake Tanganyika for 1988 and 1989.

NOTE: L         = Lates
stapp. = stappersii

SOURCE : FISHERIES DIVISION ANNUAL STATISTICS REPORTS.

Fig. 1 Major lakes of East Africa

Fig. 2 Food web of the pelagic fish community: heavy arrows indicate major food preferences (From Coulter, 1991)

Fig. 3 Map of Lake Tanganyika showing the location of main fish landing centres in the Kigoma and Rukwa regions.