Working Papers (KMFRI)
http://hdl.handle.net/1834/92
2024-03-25T23:00:48ZThe Stock Assessment of the Kenyan Demersal Offshore Resources, Surveyed in the Period 1979-1980-1981 - Work Report no. 8. Project KEN/74/023 ”Offshore Trawling Survey”
http://hdl.handle.net/1834/8474
The Stock Assessment of the Kenyan Demersal Offshore Resources, Surveyed in the Period 1979-1980-1981 - Work Report no. 8. Project KEN/74/023 ”Offshore Trawling Survey”
From February 1979 until June 1981 the trawler R/V Ujuzl surveyed the offshore Kenyan waters. The results of this vessel, supplemented by the results of three other trawlers, have been used for this stock assessment. The method used is the swept-area method. Three-level stratification has been applied. to all data (twelve fishing-grounds, two monsoon-period, fifteen groups of species). For the total trawlable surface of 3234 m2 (see charts 3 and 2), the total standing stock amounts to approximately 33,000 ton, the maximum sustainable yield is approximately 9,000 ton (the totals of table 4 plus the ”KUSI-area” plus the MESYATSEV-area). About half of these quantities consist of small fishes without any commercial value. The densities vary from 4.5 ton/m2 (MESYATSEV-area to 25.2 ton/m2 (stratum I). The results show further that, compared with other parts of the world, the productivity of the offshore demersal resources of Kenya is very low. A simple feasibility-study for each defined sub-area is added, showing that offshore trawling in Kenya is not profitable.
1982-01-01T00:00:00ZNotes on the Macro-benthos of Kenyan mangroves.
http://hdl.handle.net/1834/7903
Notes on the Macro-benthos of Kenyan mangroves.
Vannini, M.; Cannicci, S.
The notes were made for a post-graduate course in
“Tropical coast ecology, management and
conservation”, organised by Free University of Brussels and University of Nairobi, hosted at Kenya
Marine and Fisheries Research Institute, with a support by IOC (Gazi, Mombasa, Kenya, July 1997).
1997-01-01T00:00:00ZRehabilitation of the former Northern Swamp Lake Naivasha – Kenya. On the modeling of the sediment trapping efficacy for two rehabilitation alternatives.
http://hdl.handle.net/1834/7902
Rehabilitation of the former Northern Swamp Lake Naivasha – Kenya. On the modeling of the sediment trapping efficacy for two rehabilitation alternatives.
Cornelissen, M.A.J.M.
Erosion, induced by natural processes such as wind and rainfall and enhanced by anthropogenic activities such as agribusiness and deforestation, produces sediments that are carried downstream by rivers. The deposition of the sediments in the downstream areas creates new landmass for various life forms to live. However, the downstream deposition also causes problems such as sediment accumulation in delta regions and near boat ramps hindering navigation, and altering of the species composition affecting the ecological state. Erosion and the related problems also occur in the Lake Naivasha Basin, which is situated 80 km northwest of Nairobi in Kenya. The siltation affects the turbidity of the water with indirect influences on water use for human activities, fisheries, tourism and agriculture such as the flower business. The higher erosion rates which cause increasing sedimentation of the lake also cause greater inputs of nutrients and pollutants to the lake. These nutrients and pollutants threaten the ecological state of the lake, i.e. by an increased nutrient concentration.
A possible solution to decrease the siltation of the lake is to rehabilitate the former Northern Swamp, a former wetland of about 4 km² north of Lake Naivasha to retain sediments and prevent them from ending up in the lake. In 2009, Marula Estates, a large commercialized agricultural landholding bordering the former Northern Swamp, on its own initiative performed a study on the current state of the wetland and created a plan to rehabilitate the former Northern Swamp. The first phase of this plan was implemented already in 2009 and because the results are satisfying, the second phase of the project, which consists of the construction of a dam to buffer water from the Malewa River, will be implemented. The implementation of the second phase however is currently on hold due to the high lake water level, which needs to drop sufficiently to provide access for machinery to execute the necessary works. This forced break gives the opportunity to review the design from a Water Engineering perspective, which led to the research objective of this study: “To evaluate the functioning of two alternative rehabilitation alternatives, with in particular the sediment trapping efficacy, by modeling the sediment transport processes for various Malewa River discharges using a one-dimensional modeling approach”. The first rehabilitation alternative is a wetland through which the water flows from the Malewa River via a spillway channel and wetland into Lake Naivasha, based on the design as presented by Marula Estates (2013). The second alternative consists of the same spillway channel to divert the water from the Malewa River into a meandering channel flowing into Lake Naivasha.
To achieve this research objective, a literature study and field work, in May – June 2013, are done to get insight in the former Northern Swamp and the rehabilitation plan. To model the sediment transport processes an empirical formula that relates sediment load and discharge is used together with an integrated software package for river management called SOBEK. With this model it is possible to make an estimation of the amounts of sediments entering through the inlet construction, and it is possible to get insight in the sediment transport processes within the two rehabilitation alternatives.
The Wetland alternative turns out to be the best alternative when considering sediment trapping efficacy. For the year 2010, when taking into account the maximum discharge entering the wetland of 25 m³/s to prevent flooding of the spillway channel, the sediment inflow into Lake Naivasha could have been reduced with 15%. Due to the current wetland design specifications, based on discharge data from 1960 till 2010, on average only 1.25% of the time water can be diverted from the Malewa River through the spillway channel into the wetland. For 2010 however, water could have been diverted for almost 7% of the time and therefore, the reduction in sediment inflow into Lake Naivasha is likely to be lower for other years. Also, due to the limited possibility of utilization of the wetland, rehabilitation of the former Northern Swamp is going to be difficult.
2014-01-01T00:00:00ZProject KEN/74/023 Offshore Trawling Survey, Work Report no. 6: Line fishing during the survey period 1979–1981.
http://hdl.handle.net/1834/7791
Project KEN/74/023 Offshore Trawling Survey, Work Report no. 6: Line fishing during the survey period 1979–1981.
With four hand operated snapper reels have been fished on, for R/V UJUZI, non trawlable grounds mainly on the North Kenya Bank. The catches have been analysed by region, season and depth and compared with handline oatches. Average catch rates on the North Kenya Bank ranged from 2-3-6.4 kgs/reel-hour, highest in the depth range 16-75 meters during the south-east monsoon period. In other areas the average catch rates were below 1 kg/reel-hour. In the north-east monsoon period the family Lutjanidae formed the bulk of the catches, with two species Lutjanus sanguineus and Pristipomoides (~ clearly depth restricted. In the south-east monsoon period the family Serranidae dominated with its speoies EPinephlus tauvina especially in the shallower waters.
1981-01-01T00:00:00Z