Eradication of uneconomical fishes with simple gill nets at Hirakud reservoir

Experiments with simple gill nets of mesh bar 25, 30, 35, 40 and 45 mm were carried out to determine the suitable mesh size for the eradication of the uneconomical fishes of Hirakud reservoir. Results show that net with 25 mm bar is more suitable particularly for Gudusia chapra (Ham), Rohtee cotio (Day) and Eutropichthys vacha (Ham).

A note on the comparative catch efficiency of nylon over cotton gill nets in reservoir fishing

The authors conducted a series of experiments to evaluate the relative efficiency of nylon over cotton in tropical waters, particularly in reservoir fishing. The experiments were conducted in the Gobindsagar reservoir (Himachal Pradesh/Punjab). The nets made with both materials were identical in essential details like twine size, mesh size, number of floats arid sinkers and hanging coefficients.

Selectivity of gill nets for Scomberomorus commersoni

Selectivity of gill nets for S. commersoni was studied with nets made of 4 different mesh sizes fabricated with 4 different specifications of nylon twines. Fishing operations were conducted off Cochin through the fishing seasons 1968-72. The commercially significant size group of S. commersoni was found to fall in the length range of 850-950 mm. The optimum mesh size required for the capture of this group of S. commersoni was estimated as 76 mm. bar in nylon twine 210/12/3. The relationship between the twine size and mesh size was also worked out.

Chitosan for removal of mercury from water

Chitosan from prawn waste was used for the removal of mercury from solutions. Mercuric chloride solutions containing 250, 500, 1000, 10000 and 100000 ng of Hg super(+2)/ml were treated with chitosan samples of different particle size for different periods. The effect of initial concentration of mercury in the solution, particle size of chitosan and time of treatment on the adsorption of Hg super(+2) was studied. The residual mercury content after treatment for ten min. with chitosan of 40 mesh size from a solution of initial concentration 10000 ng/ml was 10 ng/ml whereas it was 50 ng/ml for chitosan of larger particle size (10-20 mesh). From solutions of lower concentrations complete removal of mercury was possible by chitosan treatment. Though the particle size and time of treatment have significant effect, the concentration of mercury in solution is more influential on the removal of mercury from solution.

Survival rates of different postlarval stages of Penaeus monodon Fabricius

The objective of this study is to determine survival rates of different postlarval stages upon stocking in the Leganes ponds. Twelve 3m x 2m x 2m suspension nets made of nylon cloth (mesh size = 0 . 1 mm) were set up in a Leganes Station pond (ave. water depth = 1 m) by means of 3-m long poles stacked at distances approximating the area of each net. The net bottom was filled with topsoil at least 15 cm thick to stimulate the pond bottom. At least 60 cm of the upper edge of each net was above the water level to prevent mixing of water inside and outside the net. P.monodon of stages P SUB-11 , P SUB-15 , P SUB-21 (from the hatchery) and P SUB-25 (from the wet lab) were stocked in the nets at 200/sq m or 1,200 fry/net. Due to lack of fry, only one P SUB-25 net was stocked. Each net had two large dried miapi branches as shelter from predation and cannibalism for the young sugpo fry. Fresh lablab was fed at the rate of one pail (approximately 5 kg) every four days per net. Harvest data show relatively higher survival rates for P SUB-15 and P SUB-18 compared to P SUB-11 and P SUB-25 with no significant difference between these two stages. The results for P SUB-25 may not be valid because the stock came from the wet lab in comparison to the other postlarval stages which were reared in the hatchery. Moreover, the P SUB-25 stock had no replicates and the net itself (no. 10) was discovered to have many holes. These preliminary results point to P SUB-15 as the best stage for harvest from the hatchery in terms of high pond recovery and lesser expense in rearing compared to older postlarvae.

Fundamental study on the behavior of milkfish fry for the evaluation of the efficiency of traditional fry collecting gears in the Philippines

The response of Chanos chanos fry to moving and stationary nets of different mesh size and colour, underwater visibility of the nets and water filtration were studied. Results indicate that milkfish fry may be driven by nets of mesh size larger than that presently used; larger mesh size decreases the net resistance in the water so that collectors may move the equipment easily. The large mesh nets should be of a dark colour, preferably black for effective driving; bowever white mosquito net is best for the core end, since the fry are more easily visible on a white background.

Diversity, abundance distribution and secondary production of intertidal and subtidal benthic macrofauna of Bushehr Province with emphasis on annelida groups

The present investigation was undertaken to establish a reference situation for future use, to identify temporal and spatial composition of macrofauna and estimate some ecological indices in the sub tidal waters along the Bushehr coastal waters in Persian Gulf. Six transects were selected including Genaveh, Farakeh, Shif, Bandargah, Rostami and Asalouyeh, at each transect 3 station were sampled in depths of zero, 5 and 10 metres. Sampling was seasonally carried out by a VAN VEEN grab 0.0225 m2, during summer 2008 until spring 2009. Samples were wet sieved immediately using 0.5 mm mesh size sieves and sediment retained in the sieve was preserved in 4% buffered formalin solution. Macrofauna specimen were separated from the sediments using decantation and elutriation methods, enumerated and identified up to the Genus level. Environmental factors such as temperature. pH, and salinity were recorded in field using sensitive probs and refractometer (for salinity) and also sediment samples were taken for TOM and grain size analysis in all the stations. 5611 specimens belonging to 66 genera were collected during the present study. Polychaetes were dominant both in terms of genus number (31) and relative abundance (74 % of total macrofaunal abundance). The other dominant groups were Artheropoda, (16.1%), Molusca (2.8%), Echinodermata (1.29%) and others including Nematoda, Nemertina, Echiura and Turbellaria (5.8%). Thirty one Genera belong of 27 families of polychaeta, one genus and family of Subphylum Chlicerata,19 genera belong to 14 families of Crustacea, 8 genera belong to 6 families of Molusca, were indentified in the studied region. 1 family (Polygordidae) and 3 genera (Flabeligera, Pilargis and Polygordius) of Polychaeta, 1 family (Nymphonidae) and genus (Nymphon) of Chelicerata, 1 Family (Nematoplanidae) and genus (Nematoplana) of Turbellaria, were identified for the first time in Persian Gulf area. The result indicated that macrofauna organism have strong relationship with the grain size characteristics of the sediments they inhabit. The most surface deposit feeder specimens such as Prionospio and Cossura were found in zero meters depth of Genaveh, Farakeh, Bandargah, Rostami and Asalouyeh stations with sandy substratum, however the most burrowing deposit feeder and scavenger specimens such as Capitella and Petaloproctus were collected in 5 and 10 meter depths of stations with silty–clay substratum. The annual mean abundance, Shanon- weiner diversity and evenness of macrofauna were estimated1152.73 N/ m² , 2.72 and 0.792 respectively .The annual average biomass and secondary production were computed 1.797 gDW m² and 3.594 gDW m² y-1 .The average of water temperature, salinity, pH and oxygen concentration were recorded between 16.37-36.05 °C, 38-42 g/l, 7.89-8.76 and 4.23-8.23 mg/l, respectively during this study in 6 studied region. Among of investigated stations Asalouyeh adjacent of effluent canal of Gas and petrochemical industry sewage and Farakeh regions adjacent the Helleh estuary had the lowets and the highest community indices. The average of diversity and density in 5 meters depth stations with moderate of sand, silt and clay were slightly more than 2 other depths stations, it seems that 5 meters stations are made a transition habitats between 2 sandy and clay habitats, that can be used by 2 groups of surface and borrowing deposit feeders. Based on the data provided in this survey, the temperature variation, sediment texture, TOM, type habitat and manmade factors of Gas and petrochemical industries have had the most effect on the macrofauna community structure in the studied region during sampling periods.

Distributional patterns of brachyuran larvae in Manora Channel (Karachi, Pakistan) collected during 1995

This study gives an account of distributional patterns of Brachyuran larvae in the Manora Channel from January to November 1995. The planktonic sampling was carried out during day time from surface and sub-surface waters of station I and II (certain sites) at shallow depths (15'-20') using Bongo net of 300 micron mesh size. In all 19527 larvae were obtained through fourteen sampling. These brachyuran larvae belonged to nine families and twenty four species: Ebalia sagittifera, Philyra sp., Philyra scabriuscula (Leucosiidae), Schizophyris aspera (Majidae), Charybdis annulata, Charybdis sp. (Portunidae), Xanthid sp A., B. and C. (Xanthidae), Pilumnus karachiensis, Pilumnus sp. (Pilumnidae), Menippe rumphii (Oziidae), Pinnotheres sp. A, and B. (Pinnotheridae), Nasima dotilliforme, Serenella indica, Macrophthalmus (Mareotis) depressus, Macrophthalmus sp., Dotilla blanfordi, Ocypodid sp. A., B. and C. (Ocypodidae), Metopograpsus thukuhar and Clistocoeloma lanatum (Grapsidae). This study is based on identification, occurrence, distributional patterns along Manora Channel and percentage composition of brachyuran larvae in the area, collected during 1995.

Dispersion, population dynamics and stock assessment of Caspian Sea prawns, genus Palaemon in Guilan Province coastal waters

Biological aspects, population dynamics and stock assessment of the Caspian Sea prawns Palaemon adspersus and Palaemon eleganse were investigated in Guilan coastal water of the Caspian Sea. Sampling was done monthly with a bottom trawl with mesh size of 3 mm in cod end in 0 - 5 m and 5 - 10 m depth in areas as Astra, Shafa Roud, Anzali, Chonchanan Chamkhaleh and Chaboksar during year 2002. Results of one year sampling showed that mean total length of Palaemon adspersus (pooled data) was 39.9±6.84 mm (X±SD) and mean wiegth was 1.133±0.67 g. The mean total length of females and males was 41.6±7.5 mm and 37.9±5.2 mm respectively and mean weight for the mentioned sexes was 1.353±0.65 g and 0.868±0.38 g respectively. There was significant differences in mean length and weight of females and males (P<0.05). The mean total annual sex ratio of males: females for this species was 1.4 and this sex ratio deviated significantly from 1:1 (X2, P<0.05) and biased towards males in the population of this species. The spawning season of Palaemon adspersus begins in April and ends in September with a peak in June . Mean fecundity of this species was 1994.5 ± 506.6 . The growth coefficients Loo and K for females were estimated as 58.5 mm and 2.3 /Year and for males as 55.9 mm and 2.6 /year respectively . The mean CPUA ( catch / Km2 ) for this species was 9.99 ± 33.2 kg / km2 and the correspondance biomass was calculated as 5067.7 kg in 0 - 10 m depth . The mean total length of Palaemon elegans (pooled data ) was 27.5 ± 5.7 mm (X±S.D) and mm and 24.01±4.18 mm respectively and mean weight for the mentioned sexes were was 0.553 ± 0.3 g and 0.237±0.15 g respectively. There was significant differences in mean length and weight of females and males (P<0.05). The mean total annual sex ratio of males:females for this species was 0.57 and in this species also sex ratio differed significantly from 1:1 (X2, P<0.05) and skewed towards females in the population of this species. The spawning season of Palaemon elegans extended from May to September with a peak in July . Mean fecundity of this species was 642.7±313.4. The growth coefficients LOO and K for females were estimated as 42.119 mm and 2.40 /Year and 33.87 mm and 2.50 /year for males respectively. The mean. CPUA ( catch/ Km2 ) for this species was 0.75±3.86 kg/km2 and the correspondance biomass was calculated as 382.1 kg in 0-10 m depth .

Impacts of fishing gears, fishing methods and fishing effort in the fisheries of Lake Victoria and proposals for management

The initial subsistence fisheries of Lake Victoria were dominated by two indigenous tilapiines, Oreochromis esculentus (Graham 1929) and Oreochromis variabilis Boulenger 1906, exploited with simple fishing crafts and gears that had little impact on the fish stocks (Jackson 1971). Commercial fisheries, targeting the tilapia fishery, started at the beginning of the 20th Centurywhen cotton flax gillnets were first introduced in 1905 into the Nyanza Gulf in Kenya. Gillnets were quickly adopted around the whole lake and consequently, the native methods of fishing soon died out (Jackson 1971). Following the introduction of gillnets, fishing boats and their propulsion methods were also improved. These improvements in fishing capacity coincided with development of urban centres and increasing human population around the lake, which increased the demand for fishery products. To satisfy the increasing demand, fishing effort increased greatly during the 20th century, despite the decline of catch per unit of effort (CPUE) (Jackson 1971; Ogutu-Ohwayo 1990). The initial catch rates of 127mm (5 inch) mesh size gill nets in the tilapia-based fishery, in 1905, was in the range of 50 to 100 fish per gillnet of approximately 50 m in length. However, twenty years later, the catch rates of gillnets of the same mesh size had declined to about six fish per net and gillnets of smaller mesh sizes, which had better catch rates, had been introduced suggesting overfishing (Worthington and Worthington, 1933).

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.

Fishing gear selectivity of Lates niloticus L. (Nile perch), Oreochromis niloticus L. (Nile tilapia) and Rastrineobola argentea Pellegrin (Mukene) in lakes Victoria, Kyoga and Nabugabo

Catch effort data on which fisheries management regulations are sometimes based are not available for most lakes in Uganda. However, failure to regulate fishing gears and methods has been a major cause of collapse of fisheries in the country. Fisheries have been damaged by destructive and non-selective fishing gears and methods such as trawling and beach seining, by use of gill nets of mesh size which crop immature fish and by introduction of mechanised fishing. Selectivity of the gears used to crop Lates niloticus 1. (Nile perch), Oreochromis niloticus 1. (Nile tilapia) and Rastrineobola argentea (Mukene) which are currently the most important commercial species in Uganda were examined in order to recommend the most suitable types, sizes and methods that should be used in exploiting these fisheries . Gill nets of less than 127 mm mainly cropped immature Nile ti1apia and Nile perch. To protect these fisheries, the minimum mesh size of gill nets should be set at 127 mm. Seine nets of 5 mm do catch high proportions of immature Mukene while those of 10 mm catch mainly mature Mukene. When operated inshore, both sizes catch immature Nile perch and Nile ti1apia as by-catch. To protect the Mukene fishery and avoid catching immature byecatch, a minimum mesh size of the Mukene net should have been 10 mm operated as Lampara type net offshore but since most fishennen have been using the 5 mm seine for over five years the minimum size should not be allowed to drop below 5 mm pending further thorough investigations. Beach seining, trawling and are destructive to fisheries and should be prohibited until data that may justify their use is available.

The impact of fishing gears and methods: with recommendations for management of the fisheries of Lakes Victoria, Kyoga and Nabugabo

Historical analysis has shown that use of destructive fishing gears and methods contributed much to the initial depletion of fish stocks from Lakes Victoria and Kyoga. From about 1930 to 1960, the fisheries of Lake Victoria were managed by controlling the mesh size of gill nets. Gill net s of less than 127 mm (5) stretched mesh had been prohibited on Lake Victoria because they cropped immature Oreochromis esculentus (Ngege) which were at that time the most important commercial species. When the mesh size restriction was repealed in the Ugandan, Tanzanian and Kenya, there was a shift to smaller meshes which cropped immature tilapia and other large species and led to a collapse in the fishery.

A study of Rastrineobola argentea in the Ugandan lakes

Increased stocks of mukene Rastrineobola argentea and the subsequent interest in its fishery on Lake Victoria has been attributed to the poor performance of the endemic fishery as a result of introductions into this lake of foreign fish species Lates niloticus and Oreochromis niloticus. R. argentea now remains the only endemic fish species of economic importance ranking second to the Nile perch in this lake. Despite this importance, biological information on the species and knowledge of its fishery is scanty. Preliminary observations on the species in the Ugandan waters indicate that R. argentea feeds mainly on zooplankton (copepods) during daylight hours. Small quantities of aquatic insect larvae/pupae (chironomids and chaoborids) are also eaten mainly at night. These fishes breed just after the rainy seasons and the young eventually mature at between 43-44 mm standard length. Growth and population parameters show a rate of growth (K) of 0.92 with L of 64.5 mm S.L. Natural mortality (M) is given at 2.371 and total mortality (2) of 3.594. Two mesh size nets 10 and 5 mm are in use in the lake. The smaller mesh size which is more preferred by the artisanal fishermen however tends to capture many immature fishes. There is therefore need for a unified lakewide data collection on the species and its fishery in order to obtain more reliable biological information necessary proper management of this fast developing fishery.

National report of the frame survey 2012 on the Uganda side of Lake Victoria

This is a report on the results of the Frame Survey conducted in the Uganda side of Lake Victoria during August 2012 by the LVFO Institutions, namely: the Department of Fisheries Resources (DFR) Uganda and the National Fisheries Resources Research Institute (NaFIRRI) in close collaboration with the District Fisheries offices of Busia, Bugiri, Namayingo, Mayuge, Jinja, Buvuma, Buikwe, Mukono, Kampala, Wakiso, Mpigi, Kalungu, Masaka, Kalangala and Rakai. In the 2012 Frame survey some indicators of fishing effort including e.g. number of fishers, fishing crafts and long line hooks increased; whereas others like the number of gillnets less than 5 inches decreased by 10.4% from that recorded in 2010. The other indicators of fishing effort, which showed decrease in 2012 included illegal beach seines and undersized gillnets (<5 inch mesh size). However, a large proportion (66%) of long line hooks recorded in the 2012 survey were in the smallest size range (hook size >10), which target small Nile perch. The number of other illegal gears, i.e. cast nets and monofilament gillnets showed modest increases (25%) between 2010 and 2012 while beach seines decrease by 15%. Recent crackdown on illegal fishing activities as part of measures for recovery of the Nile perch stocks which are faced with depletion appear to have had an impact but much more needs to be done to eradicate illegal fishing. The fisheries in the Ugandan waters have remained predominantly near shore with 61% of all fishing crafts using paddles out of which 17% were tiny three plank, flat bottomed boats locally known as parachutes. The 2012 survey shows an increase in the number of fishing crafts using sails by 65% from 682 in 2010 to 1125 in 2012. This is an encouraging trend as more fishers are able to access distant fishing grounds using free wind power. The Mukene fishery in the Ugandan waters of Lake Victoria remained underdeveloped comprising only 15.2% of all fishing crafts, of which 31% were motorised which is a great improvement from the situation recorded in 2010. The Catamarans increased to 18 with a majority in Buikwe district where there is a private investor fishing specifically for Mukene. The Catamarans in Kalangala were reported not to be working because of the high operating cost compared to ordinary Mukene fishing boats.