State of the stocks of shallow water prawns at Sofala Bank

In 1977 a preliminary assessment of the shallow water prawn (Penaeus indicus ) stocks at Sofala Bank (Mozambique) was made (Ulltang et al., 1980). Using additional data from 1977-1982, the first assessment was updated in 1980 (Ulltang, 1980) and in 1983 (Ulltang et al., 1983). The present report includes a detailed description of data and explanations of the methods used in the last assessment. Data from 1983, which were not available during the last assessment, are also included.

Results of a random stratified bottom trawl survey for scad and mackerel stocks in Mozambican waters: small pelagic fish December-January 1985

The results obtained during the third phase of Nauka are reported concerning the standing stock estimates, population length structure and gonad development of scad and mackerel stocks and the catch composition in Mozambican waters.

Problemas da gestāo dos stocks de camarāo

The worldwide shrimp landings in 1988 were reported to be 2.484.000 tons an increase of about 460.000 tons compared with 1985. The majority of shrimp fishing areas located in the tropical and sub-tropical regions with a contribution of more than 2 million tone. The most important species are the shallow water Penaeid shrimps. This quantity of about 2.5 million tons represents approximately 3% of the world marine catch. In terms of value, it represents almost 30% of the world trade in fish products. Main management objectives include: long term resources conservation; to maximize physical catches; to maximize the total income from catches or foreign exchange; to maximize economic profits; to reduce the shrimp by catch or improve its utilization; other social and economic interests. These objectives are in part interconnected and some are in conflict. Resource conservation is a basic condition for all other management objectives. Management policy definition should be in accordance with national goals and based on available scientific knowledge of the resources and of the fishing industry. The definition and selection of management objectives is an important process, to which the scientists must contribute the best way they can, mainly in providing the necessary information and options for management.

A preliminary assessment of the shallow water prawn stocks off Mocambique, North of Beira

At present, the trawl fishery for shallow water prawns is the only industrialized national fishery in Mozambique. Most of the catch is exported. Plans are laid for expansion of the fishery, and this report is an attempt to make a preliminary assessment of the potential yields from the stocks occupying the shallow water areas between Beira and Angoche.

A preliminary assessment of the scad and mackerel stocks at Sofala Bank, Mozambique

Scads (Decapterus russellii, D. macrosoma, Selar crumenophthalmus), Indian mackerel (Rastrelliger kanagurta) and horse mackerel (Trachurus trachurus) are the main pelagic species caught in a bottom trawl fishery at Sofala Bank and at Boa Paz. Information on catch and effort is presented together with available data on distribution, spawning, size at first maturity, growth, mortality and biomass of the species. As the present catch and fishing mortality are low compared to the estimates of biomass and total mortality it is concluded that the fishery may be expanded further in the future.

Allozyme and morphological variation in four hatchery stocks of Thai pangas, Pangasius hypophthalmus in Mymensingh, Bangladesh

Genetic and morphological characters of four hatchery population (Shambhuganj, Brahmaputra, Anudan and Bhai-Bhai) of Thai pangas, Pangasius hypophthalmus in Mymensingh region of Bangladesh was studied using morphological characters and allozyme markers from 29 November 2001 to 29 November 2002. A total of 14 morphometric and 6 meristic characters were verified, among which 3 morphometric (BDA, PELFL and HW) and 2 meristic characters (AFR, CFR) of Anudan hatchery population were found to be significantly higher (p>0.001) than those of the other three hatchery populations. Brahmaputra hatchery population was also significantly higher in two meristic characters (PCFR and CFR). For allozyme electrophoresis nine enzyme markers were used viz.: Esr-1*, G3pdh-2*, Gpi-1*, Gpi-2*, Ldh-1*, Ldh-2*, Mdh-1*, Mdh-2* and Pgm* where three loci (Esr-1*, Gpi-2* and Pgm*) were polymorphic (p>0.95) in Anudan and Brahmaputra hatchery populations. The mean proportion of polymorphic loci per population was higher (33.3%) in Brahmaputra and Anudan hatchery populations. Also the expected heterozygosity levels were 0.149 and 0.177 in Brahmaputra and Anudan hatchery populations, respectively. Based on Nei's (1972) genetic distances, the UPGMA dendrogram grouped the populations into two clusters. The Brahmaputra and Anudan populations are in one group; Shambhuganj, and Bhai-Bhai populations are in the second group. High genetic variation in Thai pangas was observed in the Brahmaputra and Anudan hatchery populations and less variation in the other two hatchery populations.

Study of distribution, growth and reproduction polychaetes Nereidae in intertidal zone of Bandar Abbas and effect dominant species on white Indian shrimp brood stocks (Fenneropenaeus indicus)

Distribution of polychaetes worms Nereidae in intertidal zone of Bandar Abbass indicated that distribution rate of worms from the west to east for the reason status of seabed type, habitat and feeding substrate used to worms increased. Also investigation description that last-mentioned worms are belong to Nereididae family, Perinereis genus and species of Perinereis nuntia. By viewpoint seabed soil types experiments implement indicated Nereididae worms have higher survival with sandy clay loam soil texture. Statistical analysis showed positive relation coefficient correlation of Pearson between substrate type to frequency of worms and too substrate type with soil organic matter value (P<0.05). By viewpoint feeding also experiments with different feed treatment indicated that Nereid worms is Omnivore but in natural condition more utilized algae substrate special Entermorpha and survival rate had the worms last-mentioned in dietary treatments on this algae 93/3% different significant with other treatments (P<0.05). In this project pond-reared white Indian shrimp (Fenneropenaeus indicus) were used in four maturation and spawning trials lasting 60 days. one group of shrimps was fed a formulated pelleted special of broodstock diet only, a second group was fed squid meat diet; a third group of shrimps with mollusca (Solen vagina) meat diet and fourth group was fed polychaete worms Nereidae family, collected in intertidal zone of Bandar Abbass. Four types of dietary treatments (M1, M4) were given to separate batches that were run in three duplicate. Results of experiments demonstrate that more grew rate and maturation and spawning rate and we found that shrimps fed with polychaete worms have the best condition and then shrimps fed with solen. This is demonstrate furthermore environmental circumstance, endocrine hormone, types of feed important of maturation and spawning of shrimps and in polychaete worms used HUFA help to maturation ovarian in shrimp.

Composition, biomass, distribution and population structure of the fish stocks

Until the 1970s, Lake Victoria had a multi-species fishery dominated by the tilapiine and haplochromine cichlids. There were important subsidiary fisheries for more than 20 genera of non-cichlid fishes, including catfishes (Bagrus docmak, Clarias gariepinus, Synodontis spp and Schilbe intermedius), the lungfish (Protopterus aethiopicus) and Labeo victorianus) (Kudhongania and Cordone 1974). Stocks of most of these species declined and others disappeared following the introduction of four tilapiines (Oreochromis niloticus, Oreochromis leucostictus, Tilapia rendalli and Tilapia zillit) and Nile perch (Lates niloticus) during the 1950s. Since then the commercial fishery in the Uganda portion of Lake Victoria has been dominated by the Nile perch, Nile tilapia (Oreochromis niloticus) and the native cyprinid species, Rastrineobola argentea (Mukene).

The decline of Alestes baremose Boulenger, 1901 and Hydrocynus forskahlii (Cuvier, 1819) stocks in Lake Albert: implications for sustainable management of their fisheries

The fish stocks of Lake Albert face immense exploitation pressure which has led to “fishingdown” of their fisheries, with some larger species having been driven to near-extinction, while others such as Citharinus citharus have almost disappeared. Both A. baremose (Angara) and H. forskahlii (Ngassia) historically formed the most important commercial species in Lake Albert until the early 2000s but recent Catch Assessment Surveys (2007-2013) revealed a sweeping decline in their contribution to the commercial catch from 72.7% in 1971 to less than 6% in 2013. The catch per unit effort also registered a two-fold decline from 45.6 and 36.1 kg/boat/day to 22.6 and 18.1 kg/boat/day for A. baremose and H. forskahlii respective between 1971 and 2007. Over 50% of illegal gillnets, below the legal minimum limit of four inches (101.6 mm) used on Lake Albert target the two species. Gillnet experiments found the three inch (76.2 mm) gill net mesh size suitable for sustained harvest of the two species. The study concludes that optimal utilization of the two species and probably other non target fish species is achievable through species specific management strategies, coupling species specific licensing, and controlling harvest of juvenile individuals, overall fishing effort and fish catch on Lake Albert and protecting the vulnerable fish habitats.

The fisheries and fish stocks of Lake George: their productivity, exploitation, management and conservation

The study was confined to the fisheries of Lake George. The fishery of Lake George has been exploited under controlled exploitation but the permitted number of boats was fixed in the 1950s before the human population increased to the current level. Many more people were involved in fishing and it was feared that the fish stocks might not support the human population. The assignment involved preparation of a research proposal, collection of field data and production of a report in a period of eight months.

The effects of trawling on the fish stocks of Lake Victoria

Species composition for Lake Victoria can be divided into two major groups. Haplochromis includes at least four genera, the largest consisting of 120 major species, while the remaining species together number about eighteen. The fish species of this lake have been grouped into two for obvious reasons-Haplochromis forms at least 80 per cent, by weight, of the yield of the lake. When carrying out the survey, the lake was divided into thirteen sampling areas and, although there were variations, all the species were encountered throughout most of the sampling units, except that there were definite trends as one species moved as one from shallow water towards the centre of the lake. It was noted that there was a numerical decrease of species the nearer one got to the centre of the lake, and the catch rates of the species in deeper waters also tended to decrease. The species that were found most consistently throughout the whole lake included Haplochromis complex and Bagrus, and the species found to be confined almost entirely to the shallow waters was Tilapia, in particular Tilapia nilotica.

The fish stocks in Uganda aquatic systems: opportunities and challenges for transformation

The status of fish stocks in a water body at any one time is a function of several factors affecting the production of fish in that water body. These include: total number (abundance) and biomass(weight) present, growth (size and age), recruitment (the quantity of fish entering the fishery) including reproduction, mortality which is caused by fishing or natural causes, Other indirect factors of major importance to the status of the stocks include production factors (water quality and availability of natural food for fish), the life history parameters of the different species making up the stocks (e.g. sex ratios, condition of the fish, reproductive potential (i.e. fecundity) etc), Changes in fish stocks do occur when any of the above listed factors directly influence aspects of growth, reproduction and mortality and therefore, numbers and standing stock (biomass). In the exploited fisheries, major research concerns regarding stocks relate to the listed factors especially: estimates of stock abundance/biomass, the quantity of fish being caught,where the fish are caught, which species are caught (relative abundance)when the fish are caught, how the fish are caught. The balance between stock abundance and amount of fish caught provides the basis for intervention. Due to the diverse characteristics of the physical water environment, fishes are in general, not evenly distributed throughout a water body. Shallow and vegetated areas tend to support higher abundance and diversity of fish species. In addition, seasonal variations in fish abundance are so strong that fluctuations in catch have to be expected at fish landings.

Past trends, present stocks and possible future state of the fisheries of the Tanzania part of the Lake Victoria

The Tanzania part of Lake Victoria is the most important single fishery resource for the country. Past fishing practice caused disparity between the relative abundance in the catches and in the available stocks by overfishing some species while under-fishing others. Preliminary studies of distribution pattern, biomass estimates, etc, as derived from bollom trawl exploratory data, and the trend of the commercial catch statistics from 1958 to 1970, suggest that many of the commercially preferred species may not have the biotic potential 10 sustain higher yields under present ecological and fishing regimes. Haplochromis and a few other fish might be the only hope. Geographic extension of fishing to deeper waters may not be very promising as species diversificarion and fish density decline with depth. To develop and manage the fisheries, make full use of the resource and ensure economic and biological perpetuation of thc fishery, the appropriate fishing strategy cannot be properly developcd overnight.

The role of ecological studies in the rational management of fish stocks

Studies on the ecology of freshwaters are basic to the rational development and management of their fisheries. and the relationships between different abiotic and biotic components of aquatic ecosystems are discussed in this paper. Examples are given of the ways in which such studies have been used to establish factors that may limit or increase yields from various Zambian waters.

The increased fishing pressure and the future of the fish stocks of Lake Victoria, Uganda

The Uganda sector of Lake Victoria occupies 29,580 km2 (43%). The lake used to boast of a multi-species fishery but presently relies on three major species Lates niloticus, Oreochromis niloticus and Rastrineobola argentea. During the past decade the total fish production on the Ugandan sector increased drastically from 17,000 tonnes in 1981 to about 13,000 tonnes 1991, indicating a healthy state of the fishery. This was contributed by a combination of factors including the explosive establishment of the introduced L. niloticus which contributed 60.8% in 1991 and the increase in the number of fishing canoes from 3470 in 1988 to 8000 in 1990. Isolated fishery resources studies carried out in different areas of the lake since 1971 seem, however, to indicate contrary trends in the available stocks and, therefore, the status of the fishery. In the experimental fishery, continued decline in catch rates have been recorded. Similarly, in the commercial fishery catch per unit of effort has been considerably poor (33 kg per canoe during January - March 1992) and the average size of individual fish laRded continued to decline, obviously pointing at possible over-fishing. This, therefore, calls for further urgent research on the available stocks for proper management strategies to be formulated.