Aspects of ecology of Owena reservoirs: implication on fish production

The article gives physical description of Owana reservoir, Nigeria. The reservoir was chemically and thermally stratified partial mixing of the water was observed during the rains. The concentration of major ions in the water showed distinct peculiarities. The captions (Na super(+), K super(+)Ca super(H),Ca super(Z), Mg super(++)) SO sub(4) super(2-) were relatively low. The water had high dissolved oxygen, it was acidic and also had low values of alkalinity, conductivity and total dissolved solids. About 61 plankton taxa belonging to 21 species were identified. The reservoir supports a commercial fishery of about fifteen fishermen with about fifteen species of fish caught daily with the aid of traps set and cast nets. Effective management of the lake will enhance fish production

Post harvest losses in the fisheries of Kainji Lake

An assessment is given of the post-harvest losses in the Lake Kainji fisheries of Nigeria. The study focussed on quantifiable information on post-harvest technology and post-harvest losses from fisherfolk, fish processors and fish traders operating within the Kainji Lake basin. The information was obtained from questionnaires sent to a total of 665 respondents, comprising 317 fishermen, 115 fish processors, 125 fish buyers, and 111 fish sellers in 45 fishing villages and collection centres within the lake basin. Considering the total catch from gillnets, longlines, traps and cast nets estimated at 14,000 in 1995 about 1,000 t of fish was either discarded or lost value due to spoilage during handling by fisherfolk. Assuming an average prices of 80 Naira/kg of fish, the loss to the economy amounted to 80 million Naira annually. Appropriate recommendations are made to significantly reduce post-harvest losses in the Kainji Lake fishery. (PDF contains 91 pages)

Fishing gear survey of Kainji Lake, northern Nigeria, 1996

A survey was carried out in September 1996 alongside the annual frame survey of Kainji Lake, Nigeria. As in the previous surveys, there were 6 main fishing gear types in use on the lake, which included gill nets, drift nets, beach seines, cast nets, longlines (baited and foul hooking) acid fishing traps. A total of 813 canoes were sampled. The canoe lengths were similar to the previous gear surveys. Altogether 466 gill nets were measured. They had an average length of 149 m, and were mostly bottom set. Of the gill nets measured 68% had a mesh size below 3 inches the minimum mesh size allowable according to the Niger and Kebbi State Fisheries Edict, 1996. Of concern was the large increase in the number of 1 inch meshed nets recorded on the lake. Drift nets had a mean length of 74 m. A total of 88% of all drift nets measured had a mesh size below 2.5 inches, the minimum mesh size stipulated in the State Edict. A total number of 102 beach seines were sampled with a mean length of 110 m, the mesh size in use on the lake remained as 0.1 inches under the Edict beach seines are banned from fishing in Kainji Lake. The decline in the lengths of the beach seines (and therefore catch rates) recorded since l995 was encouraging in the light of the destructive nature of these nets. A total of 30 cast nets were sampled, they had a mean diameter of 9.8 and a mean mesh size of 1.9 inches. All the nets had a hanging ratio of 0.5. Of the cast nets measured 40% had a mesh size below the minimum size of 2 inches recommended by the State Fisheries Edicts. Of concern was the continued rise in the number of gill nets with mesh sizes less than 2 inches. There were 2 types of longlines in operation on the lake. The baited and the foul hooking longlines. They were mostly bottom set and the hook size nos. 12-14 (Kirby sea hook) were predominant. Two types of fishing traps were identified, one was covered with a mesh of thin cane, one with netting material. The fishing traps had a mean height of 0.8 m and a mean width at the vase of 0.53 m. The mean mesh size used was 0.86 inches. Citharinus was reported as the most targeted of all fish species on the lake. Synodontis membranaceous was also targeted by most gears especially the smaller meshed nets. Labeo and Tilapia were low on the list of targeted species but their incidence remains high in the catches. (PDF contains 27 pages)

Frame survey of Kainji Lake, northern Nigeria, 1996

Since 1993, annual frame surveys have been conducted by the Nigerian-German Kainji Lake Fisheries Promotion Project to determine the distribution and number of fishing localities, fishing canoes and fishing gears around Kainji Lake, Nigeria. The total number of fishing localities has increased from 221 in 1993 to 286 in 1996. The fishing localities included 245 permanent fishing villages, 29 permanent fishing camps, 8 temporary fishing camps (with fishermen from Kainji Lake) and 4 temporary fishing camps (with fishermen from outside Kainji Lake area). There was an increase in the total number of fishing entrepreneurs, fishing assistants and fishing canoes over the years. A total number of 5,499 fishing entrepreneurs, 12,449 fishing assistants and 9,278 fishing canoes were recorded during the 1996 frame survey. From 1995 there was a decrease in the number of shoreline fisherfolk and a decrease in the number of transport canoes, the number of engines remained the same. During the 1996 survey, a total number of 18,655 gill nets, 1,560 drift nets, 753 beach seines, 5,548 cast nets, 7,400 longlines and 36,979 traps were recorded. The concentration of the gears (number per km shoreline) was highest in substrata 06 and 08. The total number of gill nets increased from 17,680 in 1995 to 18,655 in 1996. For the remaining 5 gear types a decrease in number was observed. Despite increasing numbers of gears on the lake, of concern is the decline recorded in all the fishing methods of the number of gears owned by individual entrepreneurs. This was most notable in the gill net and longline fisheries. These two fisheries have the lowest daily catch values and coupled with the problem of gear theft on the lake, ownership in future, may be expected to fall further. The number of larger fishing units also declined as did the number of gears new entrants enter the fishery with. The decline is particularly worrying for the beach seine fishery where diversification into other fishing methods would be beneficial in light of the present ban on seines. The group of not active fishing entrepreneurs (those who do not themselves participate in fishing activities) had the highest ownership of gears whilst the new entrants into the fishery had the lowest. There was evidence that these new entrants into the fishery were using cast nets which is worrying given the trend of using smaller mesh size of this gearSince 1993, annual frame surveys have been conducted by the Nigerian-German Kainji Lake Fisheries Promotion Project to determine the distribution and number of fishing localities, fishing canoes and fishing gears around Kainji Lake, Nigeria. The total number of fishing localities has increased from 221 in 1993 to 286 in 1996. The fishing localities included 245 permanent fishing villages, 29 permanent fishing camps, 8 temporary fishing camps (with fishermen from Kainji Lake) and 4 temporary fishing camps (with fishermen from outside Kainji Lake area). There was an increase in the total number of fishing entrepreneurs, fishing assistants and fishing canoes over the years. A total number of 5,499 fishing entrepreneurs, 12,449 fishing assistants and 9,278 fishing canoes were recorded during the 1996 frame survey. From 1995 there was a decrease in the number of shoreline fisherfolk and a decrease in the number of transport canoes, the number of engines remained the same. During the 1996 survey, a total number of 18,655 gill nets, 1,560 drift nets, 753 beach seines, 5,548 cast nets, 7,400 longlines and 36,979 traps were recorded. The concentration of the gears (number per km shoreline) was highest in substrata 06 and 08. The total number of gill nets increased from 17,680 in 1995 to 18,655 in 1996. For the remaining 5 gear types a decrease in number was observed. Despite increasing numbers of gears on the lake, of concern is the decline recorded in all the fishing methods of the number of gears owned by individual entrepreneurs. This was most notable in the gill net and longline fisheries. These two fisheries have the lowest daily catch values and coupled with the problem of gear theft on the lake, ownership in future, may be expected to fall further. The number of larger fishing units also declined as did the number of gears new entrants enter the fishery with. The decline is particularly worrying for the beach seine fishery where diversification into other fishing methods would be beneficial in light of the present ban on seines. The group of not active fishing entrepreneurs (those who do not themselves participate in fishing activities) had the highest ownership of gears whilst the new entrants into the fishery had the lowest. There was evidence that these new entrants into the fishery were using cast nets which is worrying given the trend of using smaller mesh size of this gear. (PDF contains 44 pages)

The effect of long term exploitation by the gill net fishery on the multispecies fish stocks in Kainji Lake, Nigeria, 1969-1997

The findings are presented of an assessment made of the gillnet fishery in Kainji Lake, Nigeria from 1969 to the present, on the basis of data sets from commercial and experimental gillnet fishing, with the purpose to detect trends in some key fishery monitoring indicators. During this period, there has been an increase in the number of small meshed nets in the fishery resulting in a shift in the mode to lower mesh sizes; consequently, the average mesh size declined gradually in the fishery. This trend is found to be directly correlated with the decline in the CPUE and mean weight of the fish species. It is argued that the observed trend in CPUE and mean weight is forcing the fishermen to switch effort to gears such as traps which have very small meshes and can indescriminately take all sizes of the fish. It is shown that the catch composition by weight of Citharinus citharus, Lates niloticus and tilapias declined in the gillnet fishery in the late 70's and early 80's. Recent data, from 1994 to 1996, however indicates that C. citharus is recovering, but with declining mean weight. This suggests that the exploitation pattern is shifting to the smaller fish through the use of small meshed nets. In general, however, there has not been drastic changes in species bio-diversity in the Lake as a result of predatory effect and ecosystem overfishing as has happened in other great African Lakes. The species composition since lake formation continued to be dominated by fewer that 20 species. The potential yield for the lake has been estimated to be 32,166 tonnes (excluding clupeids) and the required optimum fishing effort to be 1,814 fishing canoes. In view of the relative stability of the species diversity in the lake and the current fish production level, it is proposed here that this MSY be adopted for all species. This would be achieved with the current effort level in the lake assuming that the efficiency of the fishermen and their gears do not improve. It should be reviewed after 10 or more years of catch and effort data collection. (PDF contains 65 pages)

Evaluation of a new fishing pot trap (Lege) in River Rima, north western Nigeria

Based on the findings and diagnostic survey, a new fishing trap, christened Lege trap was designed and fabricated, and the performance evaluated. The 8-valve Lege trap was assessed concurrently with Malian and Ndurutu traps by the fishermen in the study area. The experiment was conducted in a randomized complete block design with one factor each replicated three times. Data collected on fish diversity number, biomass and size were subjected to descriptive statistics and analysis of variance. The results showed that 22 fish species belonging to thirteen families were caught. The prototype (Lege) trap recorded higher species diversity index (0.90) than the Malian (0.50) and Ndurutu (0.50) traps. The Lege trap also accounted for the largest number (55%) and biomass (63%) of fish caught which was significantly (P<0.05) higher than those of the Malian and Nduutu traps were. The mean length (15.03~c5.70cm), weight (60.43~c48.61g) and girth (4.77~c1.65cm) of fishes caught in the Lege trap were also significantly (P0.05) higher than those caught in the other two traps. These results demonstrated better performance of the new trap than the two conventional traps, even though the sizes of some of the fish species caught in all the traps were below those allowed by the Sokoto State Fisheries Edict where the study was conducted. Therefore, since it is desirable to develop conservation-oriented trap at a least cost, it is necessary to research further on the number of valves and mesh size of the new trap

Influence of number of valves on catch composition of a fishing pot trap (Lege) in River Rima, north western Nigeria

Three types of prototype (Lege) traps with different numbers of entrance valves were evaluated in River Rima, north western Nigeria. The traps contained 4,6 and 8 valves, tagged 4-V, 6-V and 8-V respectively. The experiment was carried out in a randomized complete block design with one factor each replicated three times. Data collected on fish diversity, number biomass and sizes were subjected to descriptive statistics and analysis of variance. The results of the catch composition showed close diversity index of 0.86 for 6-V, 0.80 for 8-V and 0.60 for 4-V Lege traps. However, the number (41%) and biomass 48%) of fish caught in the 6-V Lege trap were significantly (P0.05) higher than those caught in the other traps. There was no definite trend in the sizes (length and girth) of fish caught in the traps. On the basis of species diversity, and the number and biomass of fish caught, the 6-V Lege showed preference for adoption than the other two traps. However, further studies are recommended on the appropriate mesh size net for the trap in line with the provisions of fisheries edicts

Impact assessment of Niger State fisheries legislation on fisheries conservation in Edozhigi local government area (L.G.A.) of Niger State

A preliminary survey was conducted among the fishermen in five selected villages in Edozhigi L.G.A. of Niger State. One hundred and fifty fishermen were randomly selected and interviewed to find out the impact of Niger State fisheries legislation on fisheries conservation resources in the area. The analysis of data collected using descriptive statistics indicated that undersized mesh of gill nets, beach seines and traps are being used unabated. Also, fenced barriers across the entrance of flood plain ponds and Ex-bow lakes from the main stream are in the area. The fisheries rules and regulations implementers are rarely seen or not seen at all in the area. The decreasing nature of fish catches was detected. It is observed that government policy on fish conversation is neglected due to inadequate or lack of funding for meaningful extension and implementation of the fisheries rules and regulations

Influence of number of valves on catch composition of a fishing pot trap (Lege) in River Rima, north western Nigeria

Three types of prototype (Lege) traps with different numbers of entrance valves were evaluated in River Rima, north western Nigeria. The traps contained 4,6 and 8 valves, tagged 4-V, 6-V and 8-V respectively. The experiment was carried out in a randomized complete block design with one factor each replicated three times. Data collected on fish diversity, number, biomass and sizes were subjected to descriptive statistics and analysis of variance. The results of the catch composition showed close diversity index of 0.86 for 6-V, 0.80 for 8-V and 0.60 for 4-V Lege traps. However, the number (41%) and biomass (48%) of fish caught in the 6-V Lege trap were significantly (P<0.05) higher than those caught in the other traps. There was no definite trend in the sizes (length and girth) of fish caught in the traps. On the basis of species diversity, and the number and biomass of fish caught, the 6-V Lege showed preference for adoption than the other two traps. However, further studies are recommended on the appropriate mesh size net for the trap in line with the provisions of fisheries edicts

A GEOPASS-NERC project on diatom deposition and sediment accumulation in Lake Baikal, Siberia

This new project is multidisciplinary, with physical and chemical palaeolimnological aspects mainly the responsibility of Swiss and Russian scientists, and the biological limnology and palaeolimnology components mainly undertaken by the British and Russian groups. The overall project aim is to improve palaeoclimate reconstructions using sedimentary diatoms by promoting better understanding of diatom ecology and sediment-forming processes. The initial work plan is divided into four main parts: To understand diatom phytoplankton ecology more fully, to assess taphonomic changes associated with the transformation of phytoplankton diatom communities into sediment assemblages, to demonstrate sediment core integrity and representativity and to calibrate modern diatom assemblages against contemporary climate records. The preliminary results from the interrelated studies of phytoplankton, sediment traps and sediment cores used in GEOPASS-NERC, demonstrate the complexity of links between the living and fossil systems. Furthermore, the nature of recent sedimentation in Lake Baikal is spatially variable and incompletely known. This poses a major challenge to palaeolimnological interpretation. Turbidite deposits and differential preservation of microfossils, combined with inadequate knowledge of the modern ecology of endemic diatoms, all conspire to obfuscate the sedimentary record of environmental change.

The Windermere perch and pike project: an historical review

This paper is an attempt to set the background, provide a brief history, review some of the Windermere perch and pike project's scientific achievements, note current developments and hopes for the future, and comment on some aspects of such long-term projects. The project was originally started in 1939 in order to provide fish in freshwater lakes which might be harvested to enhance the supplies of food in a country subject to blockade. Pike traps and gill-netting were trialed as fishing methods. Catch statistics are available from 1939 which can be used to study population dynamics or for modelling purposes. The author provides an overview of changes in the population dynamics of perch and pike but covers briefly other species like arctic charr and brown trout. Also covered are several aspects of the basic biology and ecology of the principal species involved.

Trapping success and population analysis of Siren lacertina and Amphiuma means

Siren and Amphiuma are two poorly known genera of aquatic salamanders that occur in the Southeastern United States. A primarily bottom-dwelling existence makes these salamanders difficult to detect with conventional sampling methodologies. Therefore, the current status of their populations is unknown. I compared the capture success of modified crayfish traps and plastic minnow traps in capturing these salamanders. In addition, a mark-recapture study of S. lacertina (Greater siren) and A. means (Two-toed amphiuma) was conducted at Okefenokee National Wildlife Refuge (southern Georgia) and at Katharine Ordway Preserve (north-central Florida) from August 2001 until September 2002. Crayfish traps were much more successful than minnow traps in catching siren and amphiuma. Crayfish traps yielded 270 captures for an overall capture success of 16%, whereas minnow traps yielded only 13 captures for an overall success rate of 0.05%. In addition, several marking techniques were evaluated, and of these, only passive integrated transponder (PIT) tags were retained for the duration of the study. Therefore, I recommend this marking technique for long-term monitoring of S. lacertina and A. means. Several variables were found to have significant effects on capture rates of salamanders. A. means were most often captured in summer and the number of captures was positively correlated with water temperature, water level, and rainfall. S. lacertina were most often captured during winter and spring. Number of captures was negatively correlated with water temperature, while no relationship was found with water level or rainfall. Trap day and baiting had no significant effect on number of A. means or S. lacertina captured. Recapture probabilities of both species were low, 0.025-0.03 for S. lacertina and 0.08-0.11 for A. means. Monthly survival rates were high, 0.77-0.97 for A. means and 0.88-1.00 for S. lacertina. Density estimates of 1.3 salamanders/m2 (S. lacertina) and 0.28 salamanders/m2 (A. means) were obtained for Lake Suggs using Jolly-Seber models. Siren and amphiuma make up a substantial part of wetland biomass and can impact many other wetland species. Thus, more attention must be focused on evaluating and monitoring their populations.

Linefish resources annual report for the year 2000. Part 1: fisheries assessment

This work reflects the activities of line and trap fishing in Southern Mozambique in 2000. The catch in line fishing has been estimated at 441 mt, according to the DNAP records. The same sources indicated that 1767 days were spent at sea and the estimated catch rate was 250 Kg per boaticlay. Most of the line fishing effort shifted away from Maputo and moved to Inhambane region. The monthly analysis of fishing vessels, stricter controls over catch and effort data submission, development of long-term research programme and the continuation of the on board sampling to improve the data collection are the recommendation for line fishing. The catch of trap vessels increases from 30mt in 1997 to 172 mt in 2000, during which the total number of traps increased from 25 to 300. During this time the number of fishing days has remained relatively constant, as well the soak time. These data sets are thus not compatible with each other, reflecting an increase in daily catch from 243 Kg to 791 kg. The species composition is mainly dominated by P. coeruleopunctatus, C. puniceus, C. nufar and E. andersoni.

Étude du crabe rouge profond Geryon quinquedens en Côte d'Ivoire. 2 - Éléments de biologie et d'écologie avec références aux résultats obtenus au Congo

Geryon quinquedens is present along the West African continental slope at depths from 300 to 1000 m, on silt-clay sediments. Geryon is a cold and rather poorly oxygenated water loving species. It is easily caught by traps as it is a scavenger and predatory crustacea. In a given area its distribution does not appear to be homogeneous: for example, densities of red crabs are higher in the eastern and western region of Côte d'Ivoire than in the central zone. Similar observations can be made off Congo, Angola and United States. It can be assumed that there is a relation between the abundance of Geryon and the productivity level of the area. Geographical variations of sex ratio are suspected to be correlated with the density distribution. Males and females have not the same bathymetric distribution: females are only common in the shallower waters (300-500 m) whereas males are present in the whole biotope. Seasonal migrations occur down and up the slope in both the sexes and are certainly related to the reproductive biology. Knowledge of the reproductive biology is also necessary to understand fishing-trap catch rate: egg maturation extends over several months and ovigerous females are exceptionally caught by traps; males also are less available during the same period (March to August) when migrations are less important; in this period, mean size increases and probably this happens at the end of a moult. From September to February the catch-rates increase. Growth is slow compared with other littoral Guinean Crustacea (Peneides). Females become sexually mature at a size of 80 mm (carapace width): modification in the allometric relations of abdomen and carapace are then conspicuous.

An evaluation of the effects of blue crab (Callinectes sapidus) behavior on the efficacy of crab pots as a tool for estimating population abundance

Crab traps have been used extensively in studies on the population dynamics of blue crabs to provide estimates of catch per unit of effort; however, these estimates have been determined without adequate consideration of escape rates. We examined the ability of the blue crab (Callinectes sapidus) to escape crab pots and the possibility that intraspecific crab interactions have an effect on catch rates. Approximately 85% of crabs that entered a pot escaped, and 83% of crabs escaped from the bait chamber (kitchen). Blue crabs exhibited few aggressive behavioral interactions in and around the crab pot and were documented to move freely in and out of the pot. Both the mean number and size of crabs caught were significantly smaller at deeper depths. Results from this study show that current estimates of catch per unit of effort may be biased given the high escape rate of blue crabs documented in this study. The results of this paper provide a mechanistic view of trap efficacy, and reveal crab behavior in and around commercial crab pots.